WO2019221759A1 - Method and apparatus for determining a cure state of concrete - Google Patents

Method and apparatus for determining a cure state of concrete Download PDF

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Publication number
WO2019221759A1
WO2019221759A1 PCT/US2018/033548 US2018033548W WO2019221759A1 WO 2019221759 A1 WO2019221759 A1 WO 2019221759A1 US 2018033548 W US2018033548 W US 2018033548W WO 2019221759 A1 WO2019221759 A1 WO 2019221759A1
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WO
WIPO (PCT)
Prior art keywords
humidity
enclosure
concrete structure
oven
poured concrete
Prior art date
Application number
PCT/US2018/033548
Other languages
French (fr)
Inventor
John Joseph CARNEY
Original Assignee
Carney John Joseph
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Carney John Joseph filed Critical Carney John Joseph
Priority to PCT/US2018/033548 priority Critical patent/WO2019221759A1/en
Publication of WO2019221759A1 publication Critical patent/WO2019221759A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/38—Concrete; Lime; Mortar; Gypsum; Bricks; Ceramics; Glass
    • G01N33/383—Concrete or cement

Definitions

  • the invention relates to the field of measuring the maturity or cure state, and corresponding strength, of concrete.
  • test cylinders do not accurately measure the strength of the concrete in the structure.
  • ACI literature provide as follows:
  • the traditional method to determine the early-age concrete compressive strength is testing of field-cured cylinders.
  • a drawback of this method is that the curing history and strength development of the
  • the compressive strength of the field-cured cylinders may vary significantly from that of the structure. Also, the testing of concrete cylinders becomes cumbersome mainly due to the large number of required cylinders.
  • the maturity method relies on measuring the strength of concrete samples over time, with each sample being kept at a constant temperature. Using these laboratory measurements and the measured temperatures of an actual concrete structure, poured from the same mix, over time and using calculations based on simplifying assumptions, an estimate of the equivalent age or maturity state of the poured concrete structure can be obtained.
  • confidence in the accuracy of the results of this method is modest so that larger safety factors are used. Accordingly, longer wait times are often used to ensure that the concrete is of sufficient strength to resume further work. The longer wait times add significantly to the cost of construction projects.
  • the present invention is directed to an apparatus and a method for measuring the maturity or cure state, and corresponding strength, of poured concrete structures.
  • the apparatus includes an oven having a temperature controller that is connected to at least one thermocouple embedded in the poured concrete structure of which the maturity state is to be determined.
  • the controller receives the signal from the thermocouple embedded in the poured concrete structure and controls the oven temperature such that the oven temperature is the same as the internal temperature of the poured concrete structure.
  • a plurality of test cylinders of the same mix as the poured concrete structure are placed in the oven at about the same time as the pouring is completed for the poured concrete structure.
  • test cylinders placed in the oven will cure at approximately the same temperature as the concrete itself over time.
  • a test cylinder is periodically removed from the oven and compression tested for compressive strength either on site or in a test lab. When a test cylinder shows the concrete to have reached the target strength, then a
  • testing has shown this method to be a more accurate indicator of the actual cure state and the actual strength of the poured concrete structure than any of the multiple alternative methods.
  • the accuracy of the disclosed testing method allows significant reductions in the wait time before resuming construction operations over newly poured concrete structures, and thus provides for significant savings in construction costs, construction times, and significant improvement in safety.
  • the improvement in safety is an important advantage of the measuring method of the present invention because several construction site disasters and collapses may be attributable to premature loading of the concrete structure or the premature removal of shoring or forms.
  • An embodiment of the apparatus for performing the method of the present invention includes means for measuring the temperature of the concrete in the poured concrete structure, an oven for controlling the temperature of the samples, control means for controlling the temperature of the oven, means for communicating the signals indicative of the temperature of the concrete in the poured concrete structure to the control means for the oven, and means for compression testing each of the samples.
  • At least one controller communicating with at least one of the one or more temperature probes provided for each of the one or more enclosures, the one or more ovens, or the one or more water baths, wherein each of the enclosures, ovens, or water baths has an internal temperature, and wherein the controller controls heat energy supplied to a corresponding enclosure, oven, or water bath such that the internal temperature of the corresponding enclosure, oven, or water bath is maintained within the acceptable range of temperature deviation from the measured temperature of the concrete in the poured concrete structure.
  • one or more temperature probes embedded in the concrete structure for measuring the temperature of the concrete in the poured concrete structure during the curing process; means for housing the samples selected from the group consisting of one or more enclosures, one or more ovens, and one or more water baths; and
  • At least one controller communicating with at least one of the one or more temperature probes provided for each of the one or more enclosures, the one or more ovens, or the one or more water baths, wherein each of the enclosures, ovens, or water baths has an internal temperature, and wherein the controller controls heat energy supplied to a corresponding enclosure, oven, or water bath such that the internal temperature of the corresponding enclosure, oven, or water bath is maintained within the acceptable range of temperature deviation from the measured temperature of the concrete in the poured concrete structure.
  • each of the enclosures, ovens, or water baths comprises a heat source for supplying heat energy to a corresponding one of the enclosures, ovens, or water baths, wherein a corresponding controller of each of the enclosures, ovens, or water baths controls power supplied to the heat source of the corresponding one of the enclosures, ovens, or water baths based on the measured temperature of the concrete in the poured concrete structure and the internal temperature of the corresponding one of the enclosures, ovens, or water baths.
  • the means for housing the samples are selected from the group consisting of one or more enclosures and one or more ovens
  • the apparatus further comprising
  • At least one humidity or moisture sensor provided within at least one enclosure or oven, for measuring the humidity or moisture within said enclosure or oven, and communicating with the controller;
  • one or more humidity or moisture sensors for measuring the humidity or moisture within the poured concrete structure or the ambient humidity or moisture of the poured concrete structure;
  • At least one humidifier At least one humidifier
  • a first set of valves comprising one or more valves to control flow of air from the interior of the enclosure or oven through the ducting, the blower, and the humidifier
  • the controller is configured to control the humidity of the enclosure or oven such that the interior humidity of the enclosure or oven approaches the measured ambient humidity of the poured concrete structure or the measured humidity within the poured concrete structure to within an acceptable range of humidity deviation from the measured ambient humidity or internal humidity of the poured concrete structure, wherein the ambient or internal humidity sensors for the poured concrete structure communicate with the controller
  • controller operates the blower and first set of valves to selectively circulate air from the interior of the enclosure or oven through the humidifier to control the humidity or moisture of the interior of the enclosure or oven so that the humidity or moisture of the interior of the enclosure approaches the ambient or internal humidity of the poured concrete structure to within the acceptable range of humidity deviation based on the measured difference between the humidity of the interior of the enclosure or oven and the ambient or internal humidity of the poured concrete structure.
  • controller is configured to control the humidity of the enclosure or oven such that the interior humidity of the enclosure or oven approaches the measured ambient humidity of the poured concrete structure to within an acceptable range of humidity deviation from the measured ambient humidity of the poured concrete structure, and
  • controller is configured to operate the blower and the first and second set of valves to selectively circulate air from the interior of the enclosure or oven through the humidifier or the dryer to control the humidity or moisture of the interior of the enclosure or oven so that the humidity or moisture of the interior of the enclosure approaches the ambient humidity of the poured concrete structure to within the acceptable range of humidity deviation based on the measured difference between the humidity of the interior of the enclosure or oven and the ambient humidity of the poured concrete structure.
  • At least one humidity or moisture sensor provided within at least one enclosure or oven, for measuring the humidity or moisture within said enclosure or oven, and communicating with the controller;
  • one or more humidity or moisture sensors for measuring the humidity or moisture within the poured concrete structure or the ambient humidity or moisture of the poured concrete structure;
  • At least one humidifier At least one humidifier
  • a first set of valves comprising one or more valves to control flow of air from the interior of the enclosure or oven through the ducting, the blower or fan, and the humidifier
  • controller is configured to control the humidity of the enclosure or oven such that the interior humidity of the enclosure or oven approaches the measured ambient humidity of the poured concrete structure or the measured humidity within the poured concrete structure to within an acceptable range of humidity deviation from the measured ambient humidity or internal humidity of the poured concrete structure, wherein the ambient or internal humidity sensors for the poured concrete structure communicate with the controller,
  • controller is configured to operate the blower or fan and first set of valves to selectively circulate air from the interior of the enclosure or oven through the humidifier to control the humidity or moisture of the interior of the enclosure or oven so that the humidity or moisture of the interior of the enclosure approaches the ambient or internal humidity of the poured concrete structure to within the acceptable range of humidity deviation based on the measured difference between the humidity of the interior of the enclosure or oven and the ambient or internal humidity of the poured concrete structure.
  • At least one humidity or moisture sensor provided within at least one enclosure or oven, for measuring the humidity or moisture within said enclosure or oven, and communicating with the controller;
  • one or more humidity or moisture sensors for measuring the ambient humidity or moisture of the poured concrete structure
  • At least one humidifier At least one humidifier
  • a first set of valves comprising one or more valves to control flow of air from the interior of the enclosure or oven through the ducting, the blower, and the humidifier, wherein the controller is configured to control the humidity of the enclosure or oven such that the interior humidity of the enclosure or oven approaches the measured ambient humidity of the poured concrete structure to within an acceptable range of humidity deviation from the measured ambient humidity or internal humidity of the poured concrete structure,
  • controller is configured to operate the blower and first set of valves to selectively circulate air from the interior of the enclosure or oven through the humidifier to control the humidity or moisture of the interior of the enclosure or oven so that the humidity or moisture of the interior of the enclosure approaches the ambient humidity of the poured concrete structure to within the acceptable range of humidity deviation based on the measured difference between the humidity of the interior of the enclosure or oven and the ambient humidity of the poured concrete structure.
  • closure flaps or valves provided at the air inlet and the air outlet to the enclosure to act as inlet and outlet valves, respectively;
  • controller is configured to selectively operate the blower, the inlet and outlet valves, and the cooling unit to cool the interior of the enclosure, at least when the temperature inside the enclosure is above the measured temperature of the concrete within the poured concrete structure by a difference greater than the acceptable range of temperature deviation.
  • FIGS. 1— 2 show diagrammatic views of the apparatus of the present invention for determining the strength of the concrete in a poured concrete structure over the course of curing of the concrete.
  • FIG. 3 shows a flow diagram of the method of the present invention for determining the strength of the concrete in a poured concrete structure over the course of curing of the concrete.
  • the apparatus 100 allows the determination of the strength of the concrete in a poured concrete structure 103 over the course of curing of the concrete.
  • the apparatus 100 includes at least one enclosure 102 for housing concrete samples 101 , while allowing control of the temperature inside the enclosure such that the temperature of the environment of the samples 101 can be controlled.
  • the apparatus 100 also includes one or more temperature probes or sensors 104 embedded in the concrete structure for measuring the temperature of the concrete in the poured concrete structure 103 during the curing process.
  • the enclosure 102 is an example of the means for housing the samples 101.
  • the enclosure 102 can be part of an oven.
  • a water bath is another example of means for housing the samples 101 that provides for control of the environmental temperature of the samples and that can be used with the method of the present invention.
  • more than one enclosure 102 or water bath may be employed to house the concrete samples 101 , and the enclosures 102 or water baths may number up to the number of samples 101 .
  • the enclosure 102 is an oven and all the samples 101 are housed in a single oven 102.
  • At least one controller 106 is provided for each enclosure or oven 102, or for each water bath when a water bath is being used.
  • the controller 106 is in
  • the apparatus 100 also includes one or more sample environment temperature probes or sensors 108 that measure the
  • the environmental temperature of the samples 101 i.e. the internal temperature of the enclosure or oven 102 or the internal temperature of the water if a water bath is being used.
  • the illustrative embodiment 100 will be described with reference to the enclosure 102, but it should be understood that the enclosure 102 may be the enclosure of an oven and that the remarks are equally applicable to an oven or a water bath if such devices are used.
  • the controller 106 is preferably based on a microcomputer system having all the necessary components such as a central processing unit (CPU) or processor; volatile and non-volatile memory and mass storage for programs, data, and firmware; an input device such as a key board or keypad for an operator to input programming and data such as, for example, control instructions and parameters; an output device such as a monitor or display screen to display information such as, for example, system state, data, control mode and parameter selections to the operator; a network or telecommunications interface, for example, to allow an operator to perform all the necessary tasks from a remote location or to receive temperature data from a poured concrete structure located at a remote location from a laboratory where the samples 101 are kept; and input/output or interface circuitry for communicating with and/or controlling various temperature sensors and device controllers such as switches, actuators, and power supply controllers such as, for example, the controller for the power supply to the heat source for the enclosure 102.
  • CPU central processing unit
  • volatile and non-volatile memory and mass storage for programs
  • the control system 106 may also include a remote subunit (not shown), having some or all the capabilities of the microcomputer system described above, that communicates with the temperature sensors 104 to receive signals from the sensors 104 indicative of the internal temperature of the poured concrete structure 103 and to then communicate those signals or temperature data derived from those signals to the microcomputer system of the control system 106 located at the site of the enclosure 102 and the samples 101 over a telecommunications network.
  • a remote subunit not shown, having some or all the capabilities of the microcomputer system described above, that communicates with the temperature sensors 104 to receive signals from the sensors 104 indicative of the internal temperature of the poured concrete structure 103 and to then communicate those signals or temperature data derived from those signals to the microcomputer system of the control system 106 located at the site of the enclosure 102 and the samples 101 over a telecommunications network.
  • the controller 106 controls the heat energy supplied to the enclosure 102 such that the internal temperature of the enclosure 102 is maintained within the acceptable range of temperature deviation from the measured temperature of the concrete in the poured concrete structure 103.
  • the acceptable range of temperature deviation of the internal temperature of the enclosure 102 from the measured temperature of the concrete in the poured concrete structure 103 has been found to be about 20°F (1 1 12°C). Even more preferably, the acceptable range of temperature deviation of the internal temperature of the enclosure 102 from the measured temperature of the concrete in the poured concrete structure 103 has been found to be about 15°F (8.34°C).
  • the apparatus 100 also includes at least one sample environment temperature probe or sensor 108 provided for measuring the internal temperature of the enclosure 102, as has already been stated. The sample environment temperature probe or sensor 108 communicates with the controller or control system 106 as previously explained.
  • the enclosure 102 is provided with a heat source 1 10 for supplying heat energy to the enclosure 102 in order to bring the internal temperature of the enclosure 102, and in turn the samples 101 , up to the measured temperature of the concrete in the poured concrete structure 103.
  • the controller or control system 106 controls the internal temperature of the enclosure 102 by controlling the power supplied to the heat source 1 10 based on the measured temperature of the concrete in the poured concrete structure 103 and the internal temperature of the enclosure 102.
  • the heat source 1 10 is an electrically powered resistive heating element, but any suitable heat source may be used. Electrically powered heating elements are currently preferred for their ease of control.
  • the curing process of concrete involves an exothermic reaction that generates a significant amount of heat, particularly in the relatively large poured concrete structures 103 that are involved in major or multi-level construction projects. Accordingly, the temperature of the curing concrete is well above ambient temperature during the curing period up to the time that the strength targets of interest have been reached.
  • the test sample enclosure 102 should preferably be in an ambient temperature environment similar to or cooler than the ambient temperature of the poured concrete structure 103 so that only heating will be required to bring the samples 101 to approximately the temperature of the concrete within the poured concrete structure 103.
  • the enclosure 102 can be provided with an air inlet and an air outlet provided with closure flaps or valves 138 and 140, a blower 105, ducting 136
  • the cooling coils constitute, at least in part, a cooling unit 134 for cooling the interior of the enclosure 102.
  • Thermoelectric or Peltier cooling units may be used in place of the cooling coils of the refrigeration unit.
  • the enclosure 102 may be placed in an air conditioned or temperature controlled room the temperature of which is controlled to be about the same or cooler than the ambient temperature of the poured concrete structure 103.
  • the control system 106 may control the temperature of the enclosure 102 using a simple on/off control scheme.
  • the power to the heat source 1 10 is turned on by the control system 106 whenever the internal temperature of the enclosure 102, as sensed by the sensor 108, is below the measured internal temperature of the concrete within the poured concrete structure 103.
  • the power to the heat source 1 10 is turned off by the control system 106 whenever the internal temperature of the enclosure 102, as sensed by the sensor 108, reaches the measured internal temperature of the concrete within the poured concrete structure 103.
  • the measured internal temperature of the concrete within the poured concrete structure 103 essentially provides the temperature set point for the control system 106 for controlling the internal temperature of the enclosure 102.
  • the enclosure Preferably the enclosure
  • the 102 should also be equipped with a fan or blower 105 under the control of the control system 106 that is turned on, via switch 107, by the control system 106 while the heating element 1 10 is turned on so as to circulate the air within the enclosure 102 such that the internal temperature of the enclosure 102 can adjust to the new set point as quickly as possible.
  • the concrete curing process takes place over a period of several days. Because of the 15°F (8.34°C) or 20°F (1 1 .12°C) range for the tolerable deviation of the sample environment temperature, i.e. the internal temperature of the enclosure 102, the internal temperature of the concrete within the poured concrete structure 103 need not be sampled every second or every fraction of a second.
  • the internal temperature of the concrete within the poured concrete structure 103 it will be sufficient for the internal temperature of the concrete within the poured concrete structure 103 to be measured at intervals that are long enough to allow the internal temperature of the enclosure 102 to adjust to the new set point, i.e. the latest measured internal temperature of the concrete within the poured concrete structure 103, before measuring the internal temperature of the concrete within the poured concrete structure
  • the selected time interval between measurements of the internal temperature of the concrete within the poured concrete structure 103 can vary over a wide range depending on location, the seasons, or time of day.
  • the frequency of the measurements of the internal temperature of the concrete within the poured concrete structure 103 may need to be increased during the times of the day when the ambient temperature is subject to the most rapid changes such as, for example, after sunrise or after sundown.
  • a currently preferred range for the frequency of the measurement of the internal temperature of the concrete within the poured concrete structure 103 is from about once every five minutes to about once every two hours. Yet another preferred range for the frequency of the measurement of the internal temperature of the concrete within the poured concrete structure 103 is from about once every ten minutes to about once every hour. A further preferred range for the frequency of the measurement of the internal temperature of the concrete within the poured concrete structure 103 is from about once every fifteen minutes to about once every forty five minutes. Currently, the preferred frequency of the measurement of the internal temperature of the concrete within the poured concrete structure 103 is about once every thirty minutes. Alternatively, the internal temperature of the concrete within the poured concrete structure 103 may be sampled continuously, or nearly
  • the control system 106 varies the power supplied to the heating element 1 10 in proportion to the difference between the internal temperature of the concrete within the poured concrete structure 103 and the internal temperature of the enclosure 102.
  • the control system 106 varies the power supplied to the heating element 1 10 in accordance with a weighted sum of the difference between the internal temperature of the concrete within the poured concrete structure 103 and the internal temperature of the enclosure 102, the integral over time of this difference, and the time differential of this difference.
  • More than one probe or sensor 104 may be used to measure the internal temperature of the concrete within the poured concrete structure 103 at different locations within the poured concrete structure 103.
  • the average of temperatures measured for different locations within the poured concrete structure 103 may be used as the target or set point for controlling the internal temperature of the enclosure 102.
  • the temperature that yields the lowest concrete strength which is usually the lowest temperature, may be used as the target or set point for controlling the internal temperature of the enclosure 102 as a safety measure. This approach ensures that the most parts of the poured concrete structure 103 have reached the target strength required for proceeding with further construction activity involving the poured concrete structure 103.
  • the temperature probes or sensors 104 and 108 can be selected from the group consisting of thermocouples, thermistors, and optoelectronic thermometers.
  • the apparatus 100 also includes compression testing means 1 12, which may be a hydraulic press or a screw press type that squeezes the sample between platens or pistons for example, for testing the compressive strength of the concrete samples 101 .
  • compression testing means 1 12 may be a hydraulic press or a screw press type that squeezes the sample between platens or pistons for example, for testing the compressive strength of the concrete samples 101 .
  • 9 to 15 samples 101 are used during the period of monitoring the curing process.
  • Each day, or every two days, at least one sample 101 is compression tested, which results in the sample being sacrificed, to determine its strength and thus the strength of the concrete in the corresponding poured concrete structure 103 in order to determine if, and approximately when, the strength of the concrete in the
  • the samples 101 may be cylindrical, cubic blocks, or rectangular parallelepiped blocks.
  • cylindrical samples 101 are used.
  • the cylindrical samples 101 are right circular cylinders with a diameter of about six inches and a height of about twelve inches for highway and bridge applications. Cylindrical samples 101 that are right circular cylinders with a diameter of about four inches and a height of about eight inches are preferred for multi-story building applications.
  • the preferred configuration and size for the samples 101 are right circular cylinders having a diameter in the range of from about three inches to about six inches and a height in the range of from about six inches to about twelve inches.
  • an aspect of the present invention is to provide a method for determining the strength of the concrete in a poured concrete structure 103 over the course of curing of the concrete so as to determine when the concrete in the poured concrete structure has reached a target value for the strength of the concrete in the poured concrete structure 103.
  • the method includes several steps, which are shown diagrammatically in the appended drawings.
  • One early step 1 14 in the illustrative embodiment of the method is to obtain a plurality of samples 101 of the concrete as it is delivered for pouring of the concrete structure 103.
  • Another step 1 16 is to embed one or more temperature probes 104 in the concrete structure for measuring the temperature of the concrete in the poured concrete structure during the curing process.
  • the probes or sensors 104 can be embedded in the concrete of the poured concrete structure 103 during the pouring process or after the pouring is complete but while the concrete is still fluid.
  • Another step 1 18 in the method is to measure the temperature of the concrete in the poured concrete structure 103 during the curing process. This step is repeated periodically and continually during the disclosed method. The use of the data obtained by this measuring step is described below.
  • step 120 in the present method is placing the samples 101 in a temperature controlled environment.
  • the step of placing the samples in a temperature controlled environment includes the step of providing an apparatus that includes means for housing the samples 101 , at least one controller 106, at least one temperature probe or sensor 108 for measuring the temperature inside the means for housing the samples, and at least one temperature probe or sensor 104 for measuring the temperature of the concrete within the poured concrete structure 103.
  • the means for housing the samples 101 can be selected from the group consisting of one or more enclosures, one or more ovens, and one or more water baths.
  • the means for housing the samples 101 is an enclosure 102 that has a door 109 to allow placement and removal of the samples 101 into and from the enclosure 102.
  • the enclosure 102 also has a rack or other support structure 1 1 1 for supporting the samples 101 inside the enclosure 102.
  • the enclosure 102 can be the enclosure of an oven.
  • the controller or control system 106 communicates the temperature probes 104 and 108.
  • the controller 106 controls the heat energy supplied to the enclosure 102 such that the internal temperature of the enclosure 102 is maintained within the acceptable range of temperature deviation from the measured temperature of the concrete in the poured concrete structure 103 as previously discussed.
  • the method also includes the step 122 of maintaining the samples 101 at a temperature controlled to approach the measured temperature of the concrete in the poured concrete structure 103 to within an acceptable range of temperature deviation from the measured temperature of the concrete in the poured concrete structure.
  • step 124 periodically, one of the samples 101 is tested to determine the strength of the concrete in the sample.
  • the method continues with the step 126 of proceeding with the performance of a construction activity when a sample 101 has reached or exceeded the target value for the strength of the concrete of the poured concrete structure 103.
  • the target value corresponds to about a minimum level of strength of the concrete in the poured concrete structure 103 that would safely permit performance of the corresponding construction activity such as, for example, removing the forms used for pouring the concrete structure 103, allowing light or heavy traffic on the poured concrete structure 103, or adding new structures over the poured concrete structure 103.
  • the type of test performed is compression testing the selected sample 101.
  • the ambient humidity of the poured concrete structure 103 Aside from temperature, another significant factor that impacts the curing rate or the cure state of the concrete over time is the ambient humidity of the poured concrete structure 103.
  • a water bath is used as the means for housing and controlling the temperature of the samples 101 , the humidity of the environment of the samples 101 cannot be varied as the samples are immersed in water. Therefore, using an oven or other enclosure where the samples 101 are in a gaseous atmosphere, preferably of air, is preferred at present because such means allow the humidity of the environment of the samples 101 , within the interior of the oven or other enclosure, to be controlled to at least approximately match the ambient humidity of the poured concrete structure 103.
  • the method may further include the step of controlling the humidity of each enclosure or oven such that the humidity of each enclosure or oven approaches the measured ambient humidity of the poured concrete structure 103 to within an acceptable range of ambient humidity deviation from the measured ambient humidity of the poured concrete structure 103.
  • This can be done by providing hygrometers 123, 125 at the site of the structure 103 for measuring the ambient humidity of the structure 103 and within the enclosure 102. The hygrometers would communicate with the control system 106.
  • a humidifier 1 13 and/or a dryer 1 15 will also need to be provided, as well as ducting 121 , blowers or blower 1 17, and closure flaps or valves 1 19 to allow the air in the enclosure 102 to be selectively circulated through the humidifier or dryer to control the humidity or moisture of the interior of the enclosure 102 so that it approaches the ambient humidity of the structure 103 to within acceptable tolerances.
  • the control system 106 would control the energizing and supplying of power to the various blowers, closure flap or valve actuators, heaters, and coolers by controlling corresponding switches 127, servos 129, voltage controllers, or controlled current sources, based on the measured difference between the humidity of the interior of the enclosure 102 and the ambient humidity of the structure 103. Humidity and moisture are used interchangeably herein.
  • one or more moisture or humidity sensors 130 may be embedded in the poured concrete structure to provide moisture or humidity data from inside the poured concrete structure.
  • the sensors 130 may be located in proximity to the temperature sensors 104 and correspond in number to the temperature sensors 104.
  • a temperature sensor 104 and a moisture sensor 130 may be integrated into a single sensor unit.
  • the method may include the step of controlling the humidity of each enclosure or oven such that the humidity of each enclosure or oven approaches the measured internal humidity of the poured concrete structure 103 to within an acceptable range of ambient humidity deviation from the measured internal humidity of the poured concrete structure 103. This can be done by providing hygrometers 130 within the structure 103 for measuring the internal humidity of the structure 103 and one or more hygrometers 125 within the enclosure 102.
  • the hygrometers would communicate with the control system 106.
  • a humidifier 1 13 and/or a dryer 1 15 will also need to be provided, as well as ducting 121 , blowers or blower 1 17, and closure flaps or valves 1 19 to allow the air in the enclosure 102 to be selectively circulated through the humidifier or dryer to control the humidity or moisture of the interior of the enclosure 102 so that it approaches the internal humidity of the structure 103 to within acceptable tolerances.
  • the control system 106 would control the energizing and supplying of power to the various blowers, closure flap or valve actuators, heaters, and coolers by controlling corresponding switches 127, servos 129, voltage controllers, or controlled current sources, based on the measured difference between the humidity of the interior of the enclosure 102 and the internal humidity of the structure 103.
  • an average or a weighted average of the measured values for that parameter may be used as the set point for controlling that parameter with respect to the enclosure 102 and the samples 101 within the enclosure.
  • a corresponding oven, enclosure or water bath with its own set of samples, may be employed for each of several temperature and/or humidity sensors provided at different locations within the poured concrete structure, and the lowest strength value obtained for the tested samples at each testing step or session is used for comparison with the target strength value as an added safety factor.
  • the present invention can be applied to a concrete floor slab poured in a high-rise building. It is common practice for the building designer to specify the strength the concrete should have at 28 days after curing, which referred to herein as the design time period. Longer design time periods may be used for specifying the concrete strength in other types of structures such as bridges. By the end of the design time period, the curing process of the concrete is essentially complete, although the concrete will continue strengthening slowly over time.
  • the specified strength at 28 days is the strength deemed by the building designer to be the necessary ultimate strength needed in the concrete in the finished structure when it is put into service and takes into account all the required safety factors.
  • a critical factor in the economic feasibility of the construction of the building is the ability to load a poured concrete structure that is part of the building, for example a single level or floor in a multi-level building, prior to the end of the design time period, which is referred to in the industry as early stage loading. Without early stage loading, the downtime corresponding to the design time period, which would be required after each pour, would cause the cost of construction to balloon and may even cause the project to be cost-prohibitive.
  • the present invention can be used to determine approximately when, usually within two days or less depending upon the number of samples employed, the poured concrete structure is strong enough for early stage loading activities such as removal of forms and light and heavy traffic for workers and equipment to prepare for pouring of the next level. Each of the early stage loading activities usually has its own corresponding target strength value for the concrete.
  • the floor slab of a level in a multi-level building has a specified 28- day design strength of 8000 psi.
  • the required strength for removing forms may be 2500 psi
  • the required strength may be for light traffic may be 2500 psi
  • the required strength for heavy traffic may be 4500 psi.
  • the strength values used herein refer to the maximum compressive strength of the concrete, which is the minimum pressure (compressive force per unit area) being applied to a concrete sample at which fracture of the sample occurs.
  • the floor slab may be poured using concrete delivered to the building site by a cement mixer truck. Shortly before, during, or shortly after the pouring of the slab, a plurality of samples are taken from the concrete mixture delivered by the truck and poured into cylindrical molds, for example. The samples are then placed in an oven. The temperature of the oven is controlled to be within 20°F (1 1 12°C) or less of the temperature of the floor slab as measured by one or more temperature sensors embedded in the floor slab. On a particularly cold day, the starting temperature of the concrete samples and the oven may be far apart. About five to eight hours may be needed for the difference between the oven temperature and the measured slab temperature to stabilize such that it is stably within the desired range.
  • the method and apparatus of the present invention are applicable to many types of concrete structures.
  • the method and apparatus of the present invention can be used to safely reduce the time required for delivery of a precast structure, relative to placement of the order of the structure and to the pouring of the structure.
  • Other examples of applications that should benefit from the present invention include, without limitation, roads including highway bridges, dams, smokestacks, towers, and almost anything else made with concrete.
  • the method and apparatus of the present invention have several advantages over the standard methods for determining the maturity or cure state of the concrete and its ultimate strength that have been in use prior to the present invention. For example, removing cores from the structure for testing requires the use of water as coolant for the coring cutter. The added water impacts the moisture content and in turn the compression test results of the sample. If the sample is allowed time to dry, then it will not have undergone curing under the same conditions as the concrete in the poured structure over the duration of the drying time; therefore, the sample may no longer be a sufficiently close representative of the concrete in the poured concrete structure.
  • any contamination or variation in the concrete mixture, from the concrete mixture tested and specified at the design stage, is accounted for by the testing method of the present invention such that the construction activities, such as form removal, permitting light traffic on the poured concrete structure, or permitting heavy traffic on the poured concrete structure, can take place safely reasonably early in the design time period.
  • the present invention can also be used to ensure that the changed mixture meets the required ultimate design strength. This will be the case even though the laboratory testing done during the design stage has become irrelevant because of changes to the actual concrete mixture used as compared to the concrete mixture tested during the early design stage.
  • the present invention accounts for changes in the temperature of the concrete within the poured concrete structure due to the geometry and size of the poured concrete structure because the environmental temperature of the samples is controlled to approximate the actual measured temperatures within the poured concrete structure.
  • the temperature within the poured concrete structure can vary significantly with the size or thickness of the structure during the curing process.
  • the temperature inside a large, thick structure can reach 160°F (120.89°C), while the temperature inside a small or thin structure may not exceed 95°F (84.78°C).
  • thermoelectric unit when a Peltier or other thermoelectric unit is employed in the apparatus of the present invention, then the Peltier or other thermoelectric unit can perform both the heating and cooling functions. Also, a single fan or blower can be used, in place of multiple fans or blowers, to perform all the air circulating functions in the apparatus of the present invention. In such an embodiment, the cooling unit; the heating element, if different from the cooling unit; the humidifier; and the dryer, or as many of these as desired, would be provided in parallel conduits in the ducting or conduit circuit that includes the enclosure or oven and the blower or fan.
  • Valves controlled by the controller would then selectively direct air through one or more of the parallel conduits as required to control the temperature or humidity inside the enclosure or oven responsive to measured temperature and/or humidity differences between the interior of the enclosure or oven and the corresponding parameter, as previously described, for the poured concrete structure.
  • the conduit circuit may also include a shunt, closed off or opened by one or more valves controlled by the controller, to allow the blower to operate for air circulation only.
  • One or more of the heating element and at least a portion of the cooling unit may be provided internally in the enclosure or oven.
  • “Blower” is used herein broadly to refer to suitable fluid machine for moving air such as, without limitation, axial or centrifugal compressors, positive displacement air pumps, meshed rotary vane blowers, sliding vane blowers, and fans. Also, the terms “ducting” and“conduit circuit” are used interchangeably herein, while the terms“duct” and“conduit” should be considered interchangeable.
  • “deviation” as used herein means the absolute value of the difference between two quantities.
  • “Means for turning on” and“means for controlling” as used herein can include switches, servos, actuators, voltage controllers, controlled current sources, and the like that can be used by the controller or control system of the present invention to turn on or off or control the output of various components of the present invention; such as, for example, fans, blowers, heating or cooling elements or devices or units, humidifiers, evaporators, motors, pumps, dryers, and the like.

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Abstract

A method and apparatus for determining the strength of the concrete in a poured concrete structure by obtaining a plurality of samples of the concrete delivered for pouring the concrete structure, embedding one or more temperature probes in the concrete structure, placing the samples in a temperature controlled environment, maintaining the samples at a temperature at least approximating the measured temperature of the concrete in the poured concrete structure, and periodically compression testing one of the samples to determine when a sample has reached or exceeded a target strength level for the concrete of the poured concrete structure.

Description

METHOD AND APPARATUS FOR DETERMINING A CURE STATE OF CONCRETE
FIELD OF THE INVENTION
The invention relates to the field of measuring the maturity or cure state, and corresponding strength, of concrete.
BACKGROUND
For over half a century the primary method used to determine the compressive strength of concrete has been the casting and breaking of test cylinders. Engineers, Architects and Contractors use this system in the design and construction of buildings.
It is also used in the construction of roads, dams, bridges, precast concrete, and almost anything else made with concrete. The American Concrete Institute (ACI) has developed several standards regarding the use of concrete test cylinders.
The problem with test cylinders is they do not accurately measure the strength of the concrete in the structure. With respect to the traditional method of using test cylinders, the ACI literature provide as follows:
The traditional method to determine the early-age concrete compressive strength is testing of field-cured cylinders. A drawback of this method is that the curing history and strength development of the
cylinders and the structure will not be the same simply because of the
difference in shape and the size of the actual structural members.
Depending on the curing conditions of both the actual structure and the concrete cylinders, the compressive strength of the field-cured cylinders may vary significantly from that of the structure. Also, the testing of concrete cylinders becomes cumbersome mainly due to the large number of required cylinders.
For this reason, a number of other methods to measure the strength of in place concrete have been tried in the concrete industry. These include Pullout tests, hammer tests, core boring, the ultrasonic pulse velocity method, and other methods. Each of these methods has benefits and challenges. The ultrasonic pulse velocity method, for example, will give false or inaccurate results if there are objects such as reinforcing bars or pipes embedded in the concrete. The most successful is the Maturity method. Under this method, a laboratory baseline is developed using time and temperature.
The temperature of the concrete in the field is measured and compared to the laboratory analysis. Under this system each concrete mix must be base lined in the laboratory. The results only apply to that particular concrete mix.
The maturity method relies on measuring the strength of concrete samples over time, with each sample being kept at a constant temperature. Using these laboratory measurements and the measured temperatures of an actual concrete structure, poured from the same mix, over time and using calculations based on simplifying assumptions, an estimate of the equivalent age or maturity state of the poured concrete structure can be obtained. However, in practice, due to the simplifying assumptions used and the remoteness of the conditions of the laboratory samples from the conditions within the poured concrete structure, confidence in the accuracy of the results of this method is modest so that larger safety factors are used. Accordingly, longer wait times are often used to ensure that the concrete is of sufficient strength to resume further work. The longer wait times add significantly to the cost of construction projects. SUMMARY OF THE INVENTION
The present invention is directed to an apparatus and a method for measuring the maturity or cure state, and corresponding strength, of poured concrete structures. In the presently preferred embodiment, the apparatus includes an oven having a temperature controller that is connected to at least one thermocouple embedded in the poured concrete structure of which the maturity state is to be determined. The controller receives the signal from the thermocouple embedded in the poured concrete structure and controls the oven temperature such that the oven temperature is the same as the internal temperature of the poured concrete structure. A plurality of test cylinders of the same mix as the poured concrete structure are placed in the oven at about the same time as the pouring is completed for the poured concrete structure.
The test cylinders placed in the oven will cure at approximately the same temperature as the concrete itself over time. A test cylinder is periodically removed from the oven and compression tested for compressive strength either on site or in a test lab. When a test cylinder shows the concrete to have reached the target strength, then a
corresponding operation, such as removing the forms for the poured concrete or allowing light or heavy traffic on the poured concrete structure, can be performed. Testing has shown this method to be a more accurate indicator of the actual cure state and the actual strength of the poured concrete structure than any of the multiple alternative methods. The accuracy of the disclosed testing method allows significant reductions in the wait time before resuming construction operations over newly poured concrete structures, and thus provides for significant savings in construction costs, construction times, and significant improvement in safety. The improvement in safety is an important advantage of the measuring method of the present invention because several construction site disasters and collapses may be attributable to premature loading of the concrete structure or the premature removal of shoring or forms.
An embodiment of the apparatus for performing the method of the present invention includes means for measuring the temperature of the concrete in the poured concrete structure, an oven for controlling the temperature of the samples, control means for controlling the temperature of the oven, means for communicating the signals indicative of the temperature of the concrete in the poured concrete structure to the control means for the oven, and means for compression testing each of the samples.
Accordingly, it is an aspect of the present invention to provide a method for determining the strength of the concrete in a poured concrete structure over the course of curing of the concrete so as to determine when the concrete in the poured concrete structure has reached a target value for the strength of the concrete in the poured concrete structure, the method comprising the steps of:
obtaining a plurality of samples of the concrete delivered for pouring the concrete structure;
embedding one or more temperature probes in the concrete structure for measuring the temperature of the concrete in the poured concrete structure during the curing process;
measuring the temperature of the concrete in the poured concrete structure during the curing process;
placing the samples in a temperature controlled environment having a temperature; controlling the temperature of the temperature controlled environment to approach the measured temperature of the concrete in the poured concrete structure to within an acceptable range of temperature deviation from the measured temperature of the concrete in the poured concrete structure, while maintaining the samples in the temperature controlled environment; and
periodically testing one of the samples to determine the strength of the concrete in the sample.
It is yet another aspect of the present invention to provide a method for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete, in accordance with any of the aspects of the present invention described herein, further comprising the step of proceeding with the performance of a construction activity when a sample has reached or exceeded the target value for strength of the concrete of the poured concrete structure, the target value
corresponding to about a minimum level of strength of the concrete in the poured concrete structure that would safely permit performance of the construction activity.
It is yet another aspect of the present invention to provide a method for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete, in accordance with any of the aspects of the present invention described herein, wherein the step of periodically testing one of the samples to determine the strength of the concrete in the sample comprises compression testing the one of the samples.
It is yet another aspect of the present invention to provide a method for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete, in accordance with any of the aspects of the present invention described herein, wherein the step of placing the samples in a temperature controlled environment comprises the step of providing an apparatus comprising:
means for housing the samples selected from the group consisting of one or more enclosures, one or more ovens, and one or more water baths; and
at least one controller communicating with at least one of the one or more temperature probes provided for each of the one or more enclosures, the one or more ovens, or the one or more water baths, wherein each of the enclosures, ovens, or water baths has an internal temperature, and wherein the controller controls heat energy supplied to a corresponding enclosure, oven, or water bath such that the internal temperature of the corresponding enclosure, oven, or water bath is maintained within the acceptable range of temperature deviation from the measured temperature of the concrete in the poured concrete structure.
It is yet another aspect of the present invention to provide a method for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete, in accordance with any of the aspects of the present invention described herein, wherein the acceptable range of temperature deviation from the measured temperature of the concrete in the poured concrete structure is about 20°F (1 1 12°C).
It is yet another aspect of the present invention to provide a method for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete, in accordance with any of the aspects of the present invention described herein, wherein the acceptable range of temperature deviation from the measured temperature of the concrete in the poured concrete structure is about 15°F (8.34°C). It is yet another aspect of the present invention to provide a method for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete, in accordance with any of the aspects of the present invention described herein, wherein the temperature probes are selected from the group consisting of thermocouples, thermistors, and optoelectronic thermometers.
It is yet another aspect of the present invention to provide a method for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete, in accordance with any of the aspects of the present invention described herein, wherein the temperature of the concrete in the poured concrete structure is measured at a frequency of from about once every five minutes to about once every two hours.
It is yet another aspect of the present invention to provide a method for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete, in accordance with any of the aspects of the present invention described herein, wherein the temperature of the concrete in the poured concrete structure is measured at a frequency of from about once every ten minutes to about once every hour.
It is yet another aspect of the present invention to provide a method for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete, in accordance with any of the aspects of the present invention described herein, wherein the temperature of the concrete in the poured concrete structure is measured at a frequency of from about once every fifteen minutes to about once every forty five minutes. It is yet another aspect of the present invention to provide a method for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete, in accordance with any of the aspects of the present invention described herein, wherein the temperature of the concrete in the poured concrete structure is measured at a frequency of about once every thirty minutes.
It is yet another aspect of the present invention to provide a method for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete, in accordance with any of the aspects of the present invention described herein, wherein the means for housing the samples are selected from the group consisting of one or more enclosures and one or more ovens, each enclosure or oven having an internal humidity, the method further comprising the step of measuring ambient humidity of the poured concrete structure and the step of controlling the humidity of each enclosure or oven such that the humidity of each enclosure or oven approaches the measured ambient humidity of the poured concrete structure to within an acceptable range of ambient humidity deviation from the measured ambient humidity of the poured concrete structure.
It is an aspect of the present invention to provide an apparatus for determining the strength of the concrete in a poured concrete structure over the course of curing of the concrete using samples of the concrete delivered for pouring the poured concrete structure, the apparatus comprising:
one or more temperature probes embedded in the concrete structure for measuring the temperature of the concrete in the poured concrete structure during the curing process; means for housing the samples selected from the group consisting of one or more enclosures, one or more ovens, and one or more water baths; and
at least one controller communicating with at least one of the one or more temperature probes provided for each of the one or more enclosures, the one or more ovens, or the one or more water baths, wherein each of the enclosures, ovens, or water baths has an internal temperature, and wherein the controller controls heat energy supplied to a corresponding enclosure, oven, or water bath such that the internal temperature of the corresponding enclosure, oven, or water bath is maintained within the acceptable range of temperature deviation from the measured temperature of the concrete in the poured concrete structure.
It is yet another aspect of the present invention to provide an apparatus for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete, in accordance with any of the aspects of the present invention described herein, further comprising at least one sample environment temperature probe provided for measuring the internal temperature of each of the enclosures, ovens, or water baths, the at least one sample environment temperature probe or sensor communicating with a corresponding controller.
It is yet another aspect of the present invention to provide an apparatus for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete, in accordance with any of the aspects of the present invention described herein, wherein each of the enclosures, ovens, or water baths comprises a heat source for supplying heat energy to a corresponding one of the enclosures, ovens, or water baths, wherein a corresponding controller of each of the enclosures, ovens, or water baths controls power supplied to the heat source of the corresponding one of the enclosures, ovens, or water baths based on the measured temperature of the concrete in the poured concrete structure and the internal temperature of the corresponding one of the enclosures, ovens, or water baths.
It is yet another aspect of the present invention to provide an apparatus for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete using samples of the concrete delivered for pouring the poured concrete structure, in accordance with any of the aspects of the present invention described herein, further comprising compression testing means for testing the compressive strength of the concrete samples.
It is yet another aspect of the present invention to provide an apparatus for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete using samples of the concrete delivered for pouring the poured concrete structure, in accordance with any of the aspects of the present invention described herein, wherein the means for housing the samples are selected from the group consisting of one or more enclosures and one or more ovens, the apparatus further comprising a fan or blower and means for turning on the fan or blower, wherein the fan or blower is under the control of the controller and wherein the controller is configured to turn on the fan or blower at least while the heating element is turned on so as to circulate the air within the enclosure or oven such that the internal temperature of the enclosure or oven can adjust more quickly to approximate the measured temperature of the concrete in the poured concrete structure within the acceptable range of temperature deviation as the measured temperature of the concrete in the poured concrete structure changes over time. It is yet another aspect of the present invention to provide an apparatus for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete using samples of the concrete delivered for pouring the poured concrete structure, in accordance with any of the aspects of the present invention described herein, wherein the means for housing the samples are selected from the group consisting of one or more enclosures and one or more ovens, the apparatus further comprising:
at least one humidity or moisture sensor provided within at least one enclosure or oven, for measuring the humidity or moisture within said enclosure or oven, and communicating with the controller;
one or more humidity or moisture sensors for measuring the humidity or moisture within the poured concrete structure or the ambient humidity or moisture of the poured concrete structure;
at least one humidifier;
at least one blower;
ducting connecting at least one enclosure or oven, the humidifier, and the blower; and
a first set of valves comprising one or more valves to control flow of air from the interior of the enclosure or oven through the ducting, the blower, and the humidifier, wherein the controller is configured to control the humidity of the enclosure or oven such that the interior humidity of the enclosure or oven approaches the measured ambient humidity of the poured concrete structure or the measured humidity within the poured concrete structure to within an acceptable range of humidity deviation from the measured ambient humidity or internal humidity of the poured concrete structure, wherein the ambient or internal humidity sensors for the poured concrete structure communicate with the controller,
wherein the controller operates the blower and first set of valves to selectively circulate air from the interior of the enclosure or oven through the humidifier to control the humidity or moisture of the interior of the enclosure or oven so that the humidity or moisture of the interior of the enclosure approaches the ambient or internal humidity of the poured concrete structure to within the acceptable range of humidity deviation based on the measured difference between the humidity of the interior of the enclosure or oven and the ambient or internal humidity of the poured concrete structure.
It is yet another aspect of the present invention to provide an apparatus for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete using samples of the concrete delivered for pouring the poured concrete structure, in accordance with any of the aspects of the present invention described herein, wherein the controller is configured to operate the humidifier to introduce moisture into the air stream passing through the humidifier when the internal humidity of the enclosure or oven is below the measured ambient or internal humidity of the poured concrete structure.
It is yet another aspect of the present invention to provide an apparatus for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete using samples of the concrete delivered for pouring the poured concrete structure, in accordance with any of the aspects of the present invention described herein, further comprising a dryer and a second set of valves comprising one or more valves that are controlled by the controller in cooperation with the first set of valves to control flow of air from the interior of the enclosure or oven through the ducting, the blower or fan, and the humidifier or the dryer, wherein the controller is configured to operate the blower or fan and the first and second sets of valves to selectively circulate air from the interior of the enclosure or oven through the humidifier or the dryer to control the humidity or moisture of the interior of the enclosure or oven.
It is yet another aspect of the present invention to provide an apparatus for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete using samples of the concrete delivered for pouring the poured concrete structure, in accordance with any of the aspects of the present invention described herein, wherein the one or more humidity or moisture sensors, for measuring the humidity or moisture within the poured concrete structure or the ambient humidity or moisture of the poured concrete structure, are configured to measure the ambient humidity or moisture of the poured concrete structure,
wherein the controller is configured to control the humidity of the enclosure or oven such that the interior humidity of the enclosure or oven approaches the measured ambient humidity of the poured concrete structure to within an acceptable range of humidity deviation from the measured ambient humidity of the poured concrete structure, and
wherein the controller is configured to operate the blower and the first and second set of valves to selectively circulate air from the interior of the enclosure or oven through the humidifier or the dryer to control the humidity or moisture of the interior of the enclosure or oven so that the humidity or moisture of the interior of the enclosure approaches the ambient humidity of the poured concrete structure to within the acceptable range of humidity deviation based on the measured difference between the humidity of the interior of the enclosure or oven and the ambient humidity of the poured concrete structure.
It is yet another aspect of the present invention to provide an apparatus for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete using samples of the concrete delivered for pouring the poured concrete structure, in accordance with any of the aspects of the present invention described herein, further comprising:
at least one humidity or moisture sensor provided within at least one enclosure or oven, for measuring the humidity or moisture within said enclosure or oven, and communicating with the controller;
one or more humidity or moisture sensors for measuring the humidity or moisture within the poured concrete structure or the ambient humidity or moisture of the poured concrete structure;
at least one humidifier;
ducting connecting at least one enclosure or oven, the humidifier, and the blower or fan; and
a first set of valves comprising one or more valves to control flow of air from the interior of the enclosure or oven through the ducting, the blower or fan, and the humidifier,
wherein the controller is configured to control the humidity of the enclosure or oven such that the interior humidity of the enclosure or oven approaches the measured ambient humidity of the poured concrete structure or the measured humidity within the poured concrete structure to within an acceptable range of humidity deviation from the measured ambient humidity or internal humidity of the poured concrete structure, wherein the ambient or internal humidity sensors for the poured concrete structure communicate with the controller,
wherein the controller is configured to operate the blower or fan and first set of valves to selectively circulate air from the interior of the enclosure or oven through the humidifier to control the humidity or moisture of the interior of the enclosure or oven so that the humidity or moisture of the interior of the enclosure approaches the ambient or internal humidity of the poured concrete structure to within the acceptable range of humidity deviation based on the measured difference between the humidity of the interior of the enclosure or oven and the ambient or internal humidity of the poured concrete structure.
It is yet another aspect of the present invention to provide an apparatus for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete using samples of the concrete delivered for pouring the poured concrete structure, in accordance with any of the aspects of the present invention described herein, wherein the controller is configured to operate the humidifier to introduce moisture into the air stream passing through the humidifier when the internal humidity of the enclosure or oven is below the measured ambient or internal humidity of the poured concrete structure.
It is yet another aspect of the present invention to provide an apparatus for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete using samples of the concrete delivered for pouring the poured concrete structure, in accordance with any of the aspects of the present invention described herein, wherein the means for housing the samples are selected from the group consisting of one or more enclosures and one or more ovens, the apparatus further comprising:
at least one humidity or moisture sensor provided within at least one enclosure or oven, for measuring the humidity or moisture within said enclosure or oven, and communicating with the controller;
one or more humidity or moisture sensors for measuring the ambient humidity or moisture of the poured concrete structure;
at least one humidifier;
at least one blower;
ducting connecting at least one enclosure or oven, the humidifier, and the blower; and
a first set of valves comprising one or more valves to control flow of air from the interior of the enclosure or oven through the ducting, the blower, and the humidifier, wherein the controller is configured to control the humidity of the enclosure or oven such that the interior humidity of the enclosure or oven approaches the measured ambient humidity of the poured concrete structure to within an acceptable range of humidity deviation from the measured ambient humidity or internal humidity of the poured concrete structure,
wherein the ambient humidity sensors for the poured concrete structure communicate with the controller,
wherein the controller is configured to operate the blower and first set of valves to selectively circulate air from the interior of the enclosure or oven through the humidifier to control the humidity or moisture of the interior of the enclosure or oven so that the humidity or moisture of the interior of the enclosure approaches the ambient humidity of the poured concrete structure to within the acceptable range of humidity deviation based on the measured difference between the humidity of the interior of the enclosure or oven and the ambient humidity of the poured concrete structure.
It is yet another aspect of the present invention to provide an apparatus for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete using samples of the concrete delivered for pouring the poured concrete structure, in accordance with any of the aspects of the present invention described herein, wherein the controller is configured to operate the humidifier to introduce moisture into the air stream passing through the humidifier when the internal humidity of the enclosure or oven is below the measured ambient humidity of the poured concrete structure.
It is yet another aspect of the present invention to provide an apparatus for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete using samples of the concrete delivered for pouring the poured concrete structure, in accordance with any of the aspects of the present invention described herein, further comprising a dryer and a second set of valves comprising one or more valves that are controlled by the controller in cooperation with the first set of valves to control flow of air from the interior of the enclosure or oven through the ducting, the blower, and the humidifier or the dryer, wherein the controller is configured for operating the blower and the first and second sets of valves to selectively circulate air from the interior of the enclosure or oven through the humidifier or the dryer to control the humidity or moisture of the interior of the enclosure or oven.
It is yet another aspect of the present invention to provide an apparatus for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete using samples of the concrete delivered for pouring the poured concrete structure, in accordance with any of the aspects of the present invention described herein, wherein the means for housing the samples are selected from the group consisting of one or more enclosures and one or more ovens, wherein the enclosure is provided with an air inlet and an air outlet, the apparatus further comprising:
closure flaps or valves provided at the air inlet and the air outlet to the enclosure to act as inlet and outlet valves, respectively;
a fan or blower;
a cooling unit; and
ducting connecting at least the air outlet of the enclosure, the blower, the cooling unit, and the air inlet of the enclosure,
wherein the controller is configured to selectively operate the blower, the inlet and outlet valves, and the cooling unit to cool the interior of the enclosure, at least when the temperature inside the enclosure is above the measured temperature of the concrete within the poured concrete structure by a difference greater than the acceptable range of temperature deviation.
It is yet another aspect of the present invention to provide an apparatus for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete using samples of the concrete delivered for pouring the poured concrete structure, in accordance with any of the aspects of the present invention described herein, wherein the cooling unit comprises the coils of a refrigeration system.
It is yet another aspect of the present invention to provide an apparatus for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete using samples of the concrete delivered for pouring the poured concrete structure, in accordance with any of the aspects of the present invention described herein, wherein the means for housing the samples are selected from the group consisting of one or more enclosures and one or more ovens, the apparatus further comprising a cooling unit, wherein the controller is configured to selectively operate the cooling unit to cool the interior of the enclosure, at least when the temperature inside the enclosure is above the measured temperature of the concrete within the poured concrete structure by a difference greater than the acceptable range of temperature deviation.
It is yet another aspect of the present invention to provide an apparatus for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete using samples of the concrete delivered for pouring the poured concrete structure, in accordance with any of the aspects of the present invention described herein, wherein the cooling unit and the heating element are provided by the same apparatus.
It is yet another aspect of the present invention to provide a method for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete, in accordance with any of the aspects of the present invention described herein, wherein the means for housing the samples are selected from the group consisting of one or more enclosures and one or more ovens, each enclosure or oven having an internal humidity, the method further comprising the step of measuring an internal humidity of the poured concrete structure and the step of controlling the humidity of each enclosure or oven such that the humidity of each enclosure or oven approaches the measured internal humidity of the poured concrete structure to within an acceptable range of humidity deviation from the measured internal humidity of the poured concrete structure.
It is yet another aspect of the present invention to provide a method for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete, in accordance with any of the aspects of the present invention described herein, wherein the temperature of the concrete in the poured concrete structure is measured at a frequency of from about once every two hours or higher.
It is yet another aspect of the present invention to provide a method for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete, in accordance with any of the aspects of the present invention described herein, wherein the temperature of the concrete in the poured concrete structure is measured at a frequency of from about once every hour or higher.
It is yet another aspect of the present invention to provide a method for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete, in accordance with any of the aspects of the present invention described herein, wherein the temperature of the concrete in the poured concrete structure is measured at a frequency of from about once every forty five minutes or higher.
It is yet another aspect of the present invention to provide a method for determining the strength of the concrete in a poured concrete structure, over the course of curing of the concrete, in accordance with any of the aspects of the present invention described herein, wherein the temperature of the concrete in the poured concrete structure is measured at a frequency of about once every thirty minutes or higher. These and other aspects and advantages of the present invention will be further elucidated by the following Detailed Description, drawing figures, and Claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1— 2 show diagrammatic views of the apparatus of the present invention for determining the strength of the concrete in a poured concrete structure over the course of curing of the concrete.
FIG. 3 shows a flow diagram of the method of the present invention for determining the strength of the concrete in a poured concrete structure over the course of curing of the concrete.
DETAILED DESCRIPTION
Referring to FIGS. 1— 2, an embodiment 100 of the apparatus of the present invention can be seen. The apparatus 100 allows the determination of the strength of the concrete in a poured concrete structure 103 over the course of curing of the concrete. The apparatus 100 includes at least one enclosure 102 for housing concrete samples 101 , while allowing control of the temperature inside the enclosure such that the temperature of the environment of the samples 101 can be controlled. The apparatus 100 also includes one or more temperature probes or sensors 104 embedded in the concrete structure for measuring the temperature of the concrete in the poured concrete structure 103 during the curing process.
The enclosure 102 is an example of the means for housing the samples 101. The enclosure 102 can be part of an oven. A water bath is another example of means for housing the samples 101 that provides for control of the environmental temperature of the samples and that can be used with the method of the present invention. Also, more than one enclosure 102 or water bath may be employed to house the concrete samples 101 , and the enclosures 102 or water baths may number up to the number of samples 101 . In the presently preferred embodiment, the enclosure 102 is an oven and all the samples 101 are housed in a single oven 102.
At least one controller 106 is provided for each enclosure or oven 102, or for each water bath when a water bath is being used. The controller 106 is in
communication with the temperature probe or probes 104 and receives signals from those probes 104 that are indicative of the internal temperature of the concrete within the poured concrete structure 103. The apparatus 100 also includes one or more sample environment temperature probes or sensors 108 that measure the
environmental temperature of the samples 101 , i.e. the internal temperature of the enclosure or oven 102 or the internal temperature of the water if a water bath is being used. In the description that follows, the illustrative embodiment 100 will be described with reference to the enclosure 102, but it should be understood that the enclosure 102 may be the enclosure of an oven and that the remarks are equally applicable to an oven or a water bath if such devices are used.
The controller 106 is preferably based on a microcomputer system having all the necessary components such as a central processing unit (CPU) or processor; volatile and non-volatile memory and mass storage for programs, data, and firmware; an input device such as a key board or keypad for an operator to input programming and data such as, for example, control instructions and parameters; an output device such as a monitor or display screen to display information such as, for example, system state, data, control mode and parameter selections to the operator; a network or telecommunications interface, for example, to allow an operator to perform all the necessary tasks from a remote location or to receive temperature data from a poured concrete structure located at a remote location from a laboratory where the samples 101 are kept; and input/output or interface circuitry for communicating with and/or controlling various temperature sensors and device controllers such as switches, actuators, and power supply controllers such as, for example, the controller for the power supply to the heat source for the enclosure 102. The control system 106 may also include a remote subunit (not shown), having some or all the capabilities of the microcomputer system described above, that communicates with the temperature sensors 104 to receive signals from the sensors 104 indicative of the internal temperature of the poured concrete structure 103 and to then communicate those signals or temperature data derived from those signals to the microcomputer system of the control system 106 located at the site of the enclosure 102 and the samples 101 over a telecommunications network.
The controller 106 controls the heat energy supplied to the enclosure 102 such that the internal temperature of the enclosure 102 is maintained within the acceptable range of temperature deviation from the measured temperature of the concrete in the poured concrete structure 103. Preferably, the acceptable range of temperature deviation of the internal temperature of the enclosure 102 from the measured temperature of the concrete in the poured concrete structure 103 has been found to be about 20°F (1 1 12°C). Even more preferably, the acceptable range of temperature deviation of the internal temperature of the enclosure 102 from the measured temperature of the concrete in the poured concrete structure 103 has been found to be about 15°F (8.34°C). The apparatus 100 also includes at least one sample environment temperature probe or sensor 108 provided for measuring the internal temperature of the enclosure 102, as has already been stated. The sample environment temperature probe or sensor 108 communicates with the controller or control system 106 as previously explained.
The enclosure 102 is provided with a heat source 1 10 for supplying heat energy to the enclosure 102 in order to bring the internal temperature of the enclosure 102, and in turn the samples 101 , up to the measured temperature of the concrete in the poured concrete structure 103. The controller or control system 106 controls the internal temperature of the enclosure 102 by controlling the power supplied to the heat source 1 10 based on the measured temperature of the concrete in the poured concrete structure 103 and the internal temperature of the enclosure 102. In the illustrated example, the heat source 1 10 is an electrically powered resistive heating element, but any suitable heat source may be used. Electrically powered heating elements are currently preferred for their ease of control.
The curing process of concrete involves an exothermic reaction that generates a significant amount of heat, particularly in the relatively large poured concrete structures 103 that are involved in major or multi-level construction projects. Accordingly, the temperature of the curing concrete is well above ambient temperature during the curing period up to the time that the strength targets of interest have been reached.
Therefore, heating the samples is sufficient for replicating the temperature measured in the interior of the poured concrete structure 103. The test sample enclosure 102 should preferably be in an ambient temperature environment similar to or cooler than the ambient temperature of the poured concrete structure 103 so that only heating will be required to bring the samples 101 to approximately the temperature of the concrete within the poured concrete structure 103.
It is not inconceivable that, perhaps due to the ambient environment of the enclosure 102, the samples 101 may need to be cooled to bring the samples 101 to approximately the temperature of the concrete within the poured concrete structure 103. In such event, the enclosure 102 can be provided with an air inlet and an air outlet provided with closure flaps or valves 138 and 140, a blower 105, ducting 136
connecting the blower to the air inlet of the enclosure 102, and, if necessary, the cooling coils 132 of a refrigeration system positioned in the ducting, all under the control of the controller 106, in order to cool the samples 101 to approximately the measured temperature of the concrete within the poured concrete structure 103. The cooling coils constitute, at least in part, a cooling unit 134 for cooling the interior of the enclosure 102. Thermoelectric or Peltier cooling units may be used in place of the cooling coils of the refrigeration unit. Alternatively, the enclosure 102 may be placed in an air conditioned or temperature controlled room the temperature of which is controlled to be about the same or cooler than the ambient temperature of the poured concrete structure 103.
The control system 106 may control the temperature of the enclosure 102 using a simple on/off control scheme. In this scheme, the power to the heat source 1 10 is turned on by the control system 106 whenever the internal temperature of the enclosure 102, as sensed by the sensor 108, is below the measured internal temperature of the concrete within the poured concrete structure 103. The power to the heat source 1 10 is turned off by the control system 106 whenever the internal temperature of the enclosure 102, as sensed by the sensor 108, reaches the measured internal temperature of the concrete within the poured concrete structure 103.
The measured internal temperature of the concrete within the poured concrete structure 103 essentially provides the temperature set point for the control system 106 for controlling the internal temperature of the enclosure 102. Preferably the enclosure
102 should also be equipped with a fan or blower 105 under the control of the control system 106 that is turned on, via switch 107, by the control system 106 while the heating element 1 10 is turned on so as to circulate the air within the enclosure 102 such that the internal temperature of the enclosure 102 can adjust to the new set point as quickly as possible. The concrete curing process takes place over a period of several days. Because of the 15°F (8.34°C) or 20°F (1 1 .12°C) range for the tolerable deviation of the sample environment temperature, i.e. the internal temperature of the enclosure 102, the internal temperature of the concrete within the poured concrete structure 103 need not be sampled every second or every fraction of a second. It will be sufficient for the internal temperature of the concrete within the poured concrete structure 103 to be measured at intervals that are long enough to allow the internal temperature of the enclosure 102 to adjust to the new set point, i.e. the latest measured internal temperature of the concrete within the poured concrete structure 103, before measuring the internal temperature of the concrete within the poured concrete structure
103 again. This time period is on the order of one or more minutes and, more usually, on the order of minutes. However, much longer measurement intervals may be used if the variations in the internal temperature of the concrete within the poured concrete structure 103 occur at a relatively slow rate over time. Accordingly, the selected time interval between measurements of the internal temperature of the concrete within the poured concrete structure 103 can vary over a wide range depending on location, the seasons, or time of day. For example, the frequency of the measurements of the internal temperature of the concrete within the poured concrete structure 103 may need to be increased during the times of the day when the ambient temperature is subject to the most rapid changes such as, for example, after sunrise or after sundown. A currently preferred range for the frequency of the measurement of the internal temperature of the concrete within the poured concrete structure 103 is from about once every five minutes to about once every two hours. Yet another preferred range for the frequency of the measurement of the internal temperature of the concrete within the poured concrete structure 103 is from about once every ten minutes to about once every hour. A further preferred range for the frequency of the measurement of the internal temperature of the concrete within the poured concrete structure 103 is from about once every fifteen minutes to about once every forty five minutes. Currently, the preferred frequency of the measurement of the internal temperature of the concrete within the poured concrete structure 103 is about once every thirty minutes. Alternatively, the internal temperature of the concrete within the poured concrete structure 103 may be sampled continuously, or nearly
continuously.
Alternative control schemes to the on/off control scheme, for example, the proportional control scheme or the proportional-integral-differential (PID) control scheme, may be used if it is desired to have the internal temperature of the enclosure
102 follow the internal temperature of the concrete within the poured concrete structure
103 more closely. In the proportional control scheme, the control system 106 varies the power supplied to the heating element 1 10 in proportion to the difference between the internal temperature of the concrete within the poured concrete structure 103 and the internal temperature of the enclosure 102. In the PID control scheme, the control system 106 varies the power supplied to the heating element 1 10 in accordance with a weighted sum of the difference between the internal temperature of the concrete within the poured concrete structure 103 and the internal temperature of the enclosure 102, the integral over time of this difference, and the time differential of this difference.
More than one probe or sensor 104 may be used to measure the internal temperature of the concrete within the poured concrete structure 103 at different locations within the poured concrete structure 103. In such a case, the average of temperatures measured for different locations within the poured concrete structure 103 may be used as the target or set point for controlling the internal temperature of the enclosure 102. Alternatively, of all the temperatures measured for the concrete within the poured concrete structure 103, the temperature that yields the lowest concrete strength, which is usually the lowest temperature, may be used as the target or set point for controlling the internal temperature of the enclosure 102 as a safety measure. This approach ensures that the most parts of the poured concrete structure 103 have reached the target strength required for proceeding with further construction activity involving the poured concrete structure 103. The temperature probes or sensors 104 and 108 can be selected from the group consisting of thermocouples, thermistors, and optoelectronic thermometers.
The apparatus 100 also includes compression testing means 1 12, which may be a hydraulic press or a screw press type that squeezes the sample between platens or pistons for example, for testing the compressive strength of the concrete samples 101 . Preferably, 9 to 15 samples 101 are used during the period of monitoring the curing process. Each day, or every two days, at least one sample 101 is compression tested, which results in the sample being sacrificed, to determine its strength and thus the strength of the concrete in the corresponding poured concrete structure 103 in order to determine if, and approximately when, the strength of the concrete in the
corresponding poured concrete structure 103 has reached a given target value. It may be desirable to test two or more samples 101 in each test in order to obtain an idea of the experimental error in the compression testing process. The samples 101 may be cylindrical, cubic blocks, or rectangular parallelepiped blocks. In the illustrated embodiment, cylindrical samples 101 are used. Preferably, the cylindrical samples 101 are right circular cylinders with a diameter of about six inches and a height of about twelve inches for highway and bridge applications. Cylindrical samples 101 that are right circular cylinders with a diameter of about four inches and a height of about eight inches are preferred for multi-story building applications. At present, the preferred configuration and size for the samples 101 are right circular cylinders having a diameter in the range of from about three inches to about six inches and a height in the range of from about six inches to about twelve inches.
Referring to FIG. 3, an aspect of the present invention is to provide a method for determining the strength of the concrete in a poured concrete structure 103 over the course of curing of the concrete so as to determine when the concrete in the poured concrete structure has reached a target value for the strength of the concrete in the poured concrete structure 103. The method includes several steps, which are shown diagrammatically in the appended drawings. One early step 1 14 in the illustrative embodiment of the method is to obtain a plurality of samples 101 of the concrete as it is delivered for pouring of the concrete structure 103. Another step 1 16 is to embed one or more temperature probes 104 in the concrete structure for measuring the temperature of the concrete in the poured concrete structure during the curing process. The probes or sensors 104 can be embedded in the concrete of the poured concrete structure 103 during the pouring process or after the pouring is complete but while the concrete is still fluid.
Another step 1 18 in the method is to measure the temperature of the concrete in the poured concrete structure 103 during the curing process. This step is repeated periodically and continually during the disclosed method. The use of the data obtained by this measuring step is described below.
Yet another step 120 in the present method is placing the samples 101 in a temperature controlled environment. In the illustrated embodiment, the step of placing the samples in a temperature controlled environment includes the step of providing an apparatus that includes means for housing the samples 101 , at least one controller 106, at least one temperature probe or sensor 108 for measuring the temperature inside the means for housing the samples, and at least one temperature probe or sensor 104 for measuring the temperature of the concrete within the poured concrete structure 103.
The means for housing the samples 101 can be selected from the group consisting of one or more enclosures, one or more ovens, and one or more water baths. In the illustrated embodiment, the means for housing the samples 101 is an enclosure 102 that has a door 109 to allow placement and removal of the samples 101 into and from the enclosure 102. The enclosure 102 also has a rack or other support structure 1 1 1 for supporting the samples 101 inside the enclosure 102. The enclosure 102 can be the enclosure of an oven.
The controller or control system 106 communicates the temperature probes 104 and 108. In the illustrated embodiment, the controller 106 controls the heat energy supplied to the enclosure 102 such that the internal temperature of the enclosure 102 is maintained within the acceptable range of temperature deviation from the measured temperature of the concrete in the poured concrete structure 103 as previously discussed. Accordingly, the method also includes the step 122 of maintaining the samples 101 at a temperature controlled to approach the measured temperature of the concrete in the poured concrete structure 103 to within an acceptable range of temperature deviation from the measured temperature of the concrete in the poured concrete structure.
At step 124, periodically, one of the samples 101 is tested to determine the strength of the concrete in the sample.
Depending upon the result of the test, the method continues with the step 126 of proceeding with the performance of a construction activity when a sample 101 has reached or exceeded the target value for the strength of the concrete of the poured concrete structure 103. Comparing the result of the compression test with the target value of interest is depicted as decision structure 128 in FIG. 3. The target value corresponds to about a minimum level of strength of the concrete in the poured concrete structure 103 that would safely permit performance of the corresponding construction activity such as, for example, removing the forms used for pouring the concrete structure 103, allowing light or heavy traffic on the poured concrete structure 103, or adding new structures over the poured concrete structure 103. Preferably, the type of test performed is compression testing the selected sample 101.
Aside from temperature, another significant factor that impacts the curing rate or the cure state of the concrete over time is the ambient humidity of the poured concrete structure 103. When a water bath is used as the means for housing and controlling the temperature of the samples 101 , the humidity of the environment of the samples 101 cannot be varied as the samples are immersed in water. Therefore, using an oven or other enclosure where the samples 101 are in a gaseous atmosphere, preferably of air, is preferred at present because such means allow the humidity of the environment of the samples 101 , within the interior of the oven or other enclosure, to be controlled to at least approximately match the ambient humidity of the poured concrete structure 103.
When the means for housing the samples 101 are selected from the group consisting of one or more enclosures and one or more ovens, the method may further include the step of controlling the humidity of each enclosure or oven such that the humidity of each enclosure or oven approaches the measured ambient humidity of the poured concrete structure 103 to within an acceptable range of ambient humidity deviation from the measured ambient humidity of the poured concrete structure 103. This can be done by providing hygrometers 123, 125 at the site of the structure 103 for measuring the ambient humidity of the structure 103 and within the enclosure 102. The hygrometers would communicate with the control system 106. A humidifier 1 13 and/or a dryer 1 15 will also need to be provided, as well as ducting 121 , blowers or blower 1 17, and closure flaps or valves 1 19 to allow the air in the enclosure 102 to be selectively circulated through the humidifier or dryer to control the humidity or moisture of the interior of the enclosure 102 so that it approaches the ambient humidity of the structure 103 to within acceptable tolerances. The control system 106 would control the energizing and supplying of power to the various blowers, closure flap or valve actuators, heaters, and coolers by controlling corresponding switches 127, servos 129, voltage controllers, or controlled current sources, based on the measured difference between the humidity of the interior of the enclosure 102 and the ambient humidity of the structure 103. Humidity and moisture are used interchangeably herein.
Additionally, or alternatively, one or more moisture or humidity sensors 130 may be embedded in the poured concrete structure to provide moisture or humidity data from inside the poured concrete structure. The sensors 130 may be located in proximity to the temperature sensors 104 and correspond in number to the temperature sensors 104. Also, a temperature sensor 104 and a moisture sensor 130 may be integrated into a single sensor unit. The method may include the step of controlling the humidity of each enclosure or oven such that the humidity of each enclosure or oven approaches the measured internal humidity of the poured concrete structure 103 to within an acceptable range of ambient humidity deviation from the measured internal humidity of the poured concrete structure 103. This can be done by providing hygrometers 130 within the structure 103 for measuring the internal humidity of the structure 103 and one or more hygrometers 125 within the enclosure 102. The hygrometers would communicate with the control system 106. A humidifier 1 13 and/or a dryer 1 15 will also need to be provided, as well as ducting 121 , blowers or blower 1 17, and closure flaps or valves 1 19 to allow the air in the enclosure 102 to be selectively circulated through the humidifier or dryer to control the humidity or moisture of the interior of the enclosure 102 so that it approaches the internal humidity of the structure 103 to within acceptable tolerances. The control system 106 would control the energizing and supplying of power to the various blowers, closure flap or valve actuators, heaters, and coolers by controlling corresponding switches 127, servos 129, voltage controllers, or controlled current sources, based on the measured difference between the humidity of the interior of the enclosure 102 and the internal humidity of the structure 103.
When multiple sensors are used for sensing a single parameter such as temperature or humidity, an average or a weighted average of the measured values for that parameter may be used as the set point for controlling that parameter with respect to the enclosure 102 and the samples 101 within the enclosure.
As another alternative embodiment of the present invention, a corresponding oven, enclosure or water bath, with its own set of samples, may be employed for each of several temperature and/or humidity sensors provided at different locations within the poured concrete structure, and the lowest strength value obtained for the tested samples at each testing step or session is used for comparison with the target strength value as an added safety factor.
Example
As an example, the present invention can be applied to a concrete floor slab poured in a high-rise building. It is common practice for the building designer to specify the strength the concrete should have at 28 days after curing, which referred to herein as the design time period. Longer design time periods may be used for specifying the concrete strength in other types of structures such as bridges. By the end of the design time period, the curing process of the concrete is essentially complete, although the concrete will continue strengthening slowly over time. The specified strength at 28 days is the strength deemed by the building designer to be the necessary ultimate strength needed in the concrete in the finished structure when it is put into service and takes into account all the required safety factors.
During the design process various concrete mixes are tested in the laboratory, taking into account availability of materials at the building site, to determine the mixes that will yield the specified design strength at the end of the design time period. With this information, the building designer then specifies the concrete mixes that can be used in the construction of the building.
A critical factor in the economic feasibility of the construction of the building is the ability to load a poured concrete structure that is part of the building, for example a single level or floor in a multi-level building, prior to the end of the design time period, which is referred to in the industry as early stage loading. Without early stage loading, the downtime corresponding to the design time period, which would be required after each pour, would cause the cost of construction to balloon and may even cause the project to be cost-prohibitive.
In constructing a high-rise building using the so called climbing forms technique, forms are placed around a new level and at the core of the building. The forms are supported by the structure below. The new level is then poured. To construct the next higher level, the forms must be pulled away from the poured structure and moved up to the next level. If this step is taken prematurely, before the poured concrete has strengthened sufficiently, the poured concrete structure could collapse with catastrophic results. To ensure safety and economy, the present invention can be used to determine approximately when, usually within two days or less depending upon the number of samples employed, the poured concrete structure is strong enough for early stage loading activities such as removal of forms and light and heavy traffic for workers and equipment to prepare for pouring of the next level. Each of the early stage loading activities usually has its own corresponding target strength value for the concrete.
For example, the floor slab of a level in a multi-level building has a specified 28- day design strength of 8000 psi. The required strength for removing forms may be 2500 psi, the required strength may be for light traffic may be 2500 psi, and the required strength for heavy traffic may be 4500 psi. The strength values used herein refer to the maximum compressive strength of the concrete, which is the minimum pressure (compressive force per unit area) being applied to a concrete sample at which fracture of the sample occurs.
The floor slab may be poured using concrete delivered to the building site by a cement mixer truck. Shortly before, during, or shortly after the pouring of the slab, a plurality of samples are taken from the concrete mixture delivered by the truck and poured into cylindrical molds, for example. The samples are then placed in an oven. The temperature of the oven is controlled to be within 20°F (1 1 12°C) or less of the temperature of the floor slab as measured by one or more temperature sensors embedded in the floor slab. On a particularly cold day, the starting temperature of the concrete samples and the oven may be far apart. About five to eight hours may be needed for the difference between the oven temperature and the measured slab temperature to stabilize such that it is stably within the desired range.
An example floor slab was poured on a Saturday. The following Monday, at about 8:00 AM, the first sample or samples were removed from the oven and compression tested. An average strength of 3750 psi was obtained for the samples. Accordingly, after only about two days the concrete was sufficiently strong for removal of the forms and for allowing light traffic. The remaining samples stayed in the oven while the temperature of the oven continued to be controlled to be within 20°F
(1 1 12°C) or less of the temperature of the floor slab as measured by the embedded temperature sensors. On the same day, at 2:40 PM, more samples were compression tested yielding an average strength of 4154 psi. The remaining samples were maintained in the oven in the temperature controlled environment as before.
The following Tuesday, at about 8:00 AM, the third selection of samples were removed from the oven and compression tested. An average strength of 4415 psi was obtained for the samples. The remaining samples stayed in the oven while the temperature of the oven continued to be controlled to be within 20°F (1 1.12°C) or less of the temperature of the floor slab as measured by the embedded temperature sensors. On the same day, at 12:30 PM, a fourth set of samples were compression tested yielding an average strength of 4669 psi, which meant that now heavy traffic can be permitted on the floor slab that would be required for further progress of the construction project. The remaining samples can be maintained in the oven in the temperature controlled environment as before should the builder or engineer desire to know when, within a day or two or less, the floor slab has reached its 28-day design strength. Testing in some examples has shown that the concrete structure can reach the 28-day design strength within 7 days of the concrete structure being poured.
The method and apparatus of the present invention are applicable to many types of concrete structures. For example, when fabricating precast concrete structures, the method and apparatus of the present invention can be used to safely reduce the time required for delivery of a precast structure, relative to placement of the order of the structure and to the pouring of the structure. Other examples of applications that should benefit from the present invention include, without limitation, roads including highway bridges, dams, smokestacks, towers, and almost anything else made with concrete.
The method and apparatus of the present invention have several advantages over the standard methods for determining the maturity or cure state of the concrete and its ultimate strength that have been in use prior to the present invention. For example, removing cores from the structure for testing requires the use of water as coolant for the coring cutter. The added water impacts the moisture content and in turn the compression test results of the sample. If the sample is allowed time to dry, then it will not have undergone curing under the same conditions as the concrete in the poured structure over the duration of the drying time; therefore, the sample may no longer be a sufficiently close representative of the concrete in the poured concrete structure.
With the method and apparatus of the present invention, because the samples are representative of the concrete mix as delivered to the construction site and poured to form the structure, any contamination or variation in the concrete mixture, from the concrete mixture tested and specified at the design stage, is accounted for by the testing method of the present invention such that the construction activities, such as form removal, permitting light traffic on the poured concrete structure, or permitting heavy traffic on the poured concrete structure, can take place safely reasonably early in the design time period. The present invention can also be used to ensure that the changed mixture meets the required ultimate design strength. This will be the case even though the laboratory testing done during the design stage has become irrelevant because of changes to the actual concrete mixture used as compared to the concrete mixture tested during the early design stage. There are many circumstances that may cause the actual concrete mixture delivered to the construction site to deviate from the concrete mixture tested during the early design stage. There may be errors in the ratios of cement, aggregate, and water; there may be extreme changes in humidity; there may be accidental introduction of contaminants; there may be changes in the proportion of water in the concrete mixture due to precipitation; there may be changes in the mixture due to quality of available water; and so forth. Also, the builder may need to make changes in the concrete mixture by adding accelerators or by changing brands or sources or quality of the cement, aggregate, or water due to local availability. Prior to the present invention, any such changes in the concrete mixture would have required that the 28-day testing cycle performed during the early design stage be repeated for the changed mixture, causing significant delays. The present invention gives the builder and the engineer greater flexibility in adapting to changes in the concrete mixture without paying an inordinate economic penalty.
Also, the present invention accounts for changes in the temperature of the concrete within the poured concrete structure due to the geometry and size of the poured concrete structure because the environmental temperature of the samples is controlled to approximate the actual measured temperatures within the poured concrete structure. The temperature within the poured concrete structure can vary significantly with the size or thickness of the structure during the curing process. The temperature inside a large, thick structure can reach 160°F (120.89°C), while the temperature inside a small or thin structure may not exceed 95°F (84.78°C).
It should be noted that when a Peltier or other thermoelectric unit is employed in the apparatus of the present invention, then the Peltier or other thermoelectric unit can perform both the heating and cooling functions. Also, a single fan or blower can be used, in place of multiple fans or blowers, to perform all the air circulating functions in the apparatus of the present invention. In such an embodiment, the cooling unit; the heating element, if different from the cooling unit; the humidifier; and the dryer, or as many of these as desired, would be provided in parallel conduits in the ducting or conduit circuit that includes the enclosure or oven and the blower or fan. Valves controlled by the controller would then selectively direct air through one or more of the parallel conduits as required to control the temperature or humidity inside the enclosure or oven responsive to measured temperature and/or humidity differences between the interior of the enclosure or oven and the corresponding parameter, as previously described, for the poured concrete structure.
The conduit circuit may also include a shunt, closed off or opened by one or more valves controlled by the controller, to allow the blower to operate for air circulation only. One or more of the heating element and at least a portion of the cooling unit may be provided internally in the enclosure or oven.
“Blower” is used herein broadly to refer to suitable fluid machine for moving air such as, without limitation, axial or centrifugal compressors, positive displacement air pumps, meshed rotary vane blowers, sliding vane blowers, and fans. Also, the terms “ducting” and“conduit circuit” are used interchangeably herein, while the terms“duct” and“conduit” should be considered interchangeable.
The word“deviation” as used herein means the absolute value of the difference between two quantities. “Means for turning on” and“means for controlling” as used herein can include switches, servos, actuators, voltage controllers, controlled current sources, and the like that can be used by the controller or control system of the present invention to turn on or off or control the output of various components of the present invention; such as, for example, fans, blowers, heating or cooling elements or devices or units, humidifiers, evaporators, motors, pumps, dryers, and the like.
The invention is not limited to the exemplary embodiments described above, but includes any and all embodiments within the scope of the appended claims both literally and under the doctrine of equivalents.

Claims

1. A method for determining the strength of the concrete in a poured concrete structure over the course of curing of the concrete so as to determine when the concrete in the poured concrete structure has reached a target value for the strength of the concrete in the poured concrete structure, the method comprising the steps of: obtaining a plurality of samples of the concrete as delivered for pouring the concrete structure;
embedding one or more temperature probes in the concrete structure for measuring the temperature of the concrete in the poured concrete structure during the curing process;
measuring the temperature of the concrete in the poured concrete structure during the curing process;
placing the samples in a temperature controlled environment having a temperature;
controlling the temperature of the temperature controlled environment to approach the measured temperature of the concrete in the poured concrete structure to within an acceptable range of temperature deviation from the measured temperature of the concrete in the poured concrete structure, while maintaining the samples in the temperature controlled environment; and
periodically testing one of the samples to determine the strength of the concrete in the sample.
2. The method of claim 1 , further comprising the steps of: proceeding with the performance of a construction activity when a sample has reached or exceeded the target value for strength of the concrete of the poured concrete structure, the target value corresponding to about a minimum level of strength of the concrete in the poured concrete structure that would safely permit performance of the construction activity.
3. The method of claim 1 , wherein said step of periodically testing one of the samples to determine the strength of the concrete in the sample comprises
compression testing the one of the samples.
4. The method of claim 1 , wherein said step of placing the samples in a temperature controlled environment comprises the step of providing an apparatus comprising:
means for housing the samples selected from the group consisting of one or more enclosures, one or more ovens, and one or more water baths; and
at least one controller communicating with at least one of said one or more temperature probes provided for each of the one or more enclosures, the one or more ovens, or the one or more water baths, wherein each of said enclosures, ovens, or water baths has an internal temperature, and wherein said controller controls heat energy supplied to a corresponding enclosure, oven, or water bath such that the internal temperature of the corresponding enclosure, oven, or water bath is maintained within the acceptable range of temperature deviation from the measured temperature of the concrete in the poured concrete structure.
5. The method of claim 4, wherein the acceptable range of temperature deviation from the measured temperature of the concrete in the poured concrete structure is about 20°F (1 1.12°C).
6. The method of claim 4, wherein the acceptable range of temperature deviation from the measured temperature of the concrete in the poured concrete structure is about 15°F (8.34°C).
7. The method of claim 1 , wherein the temperature probes are selected from the group consisting of thermocouples, thermistors, and optoelectronic thermometers.
8. The method of claim 1 , wherein the temperature of the concrete in the poured concrete structure is measured at a frequency of from about once every five minutes to about once every two hours.
9. The method of claim 1 , wherein the temperature of the concrete in the poured concrete structure is measured at a frequency of from about once every ten minutes to about once every hour.
10. The method of claim 1 , wherein the temperature of the concrete in the poured concrete structure is measured at a frequency of from about once every fifteen minutes to about once every forty five minutes.
1 1. The method of claim 1 , wherein the temperature of the concrete in the poured concrete structure is measured at a frequency of about once every thirty minutes.
12. The method of claim 4, wherein the means for housing the samples are selected from the group consisting of one or more enclosures and one or more ovens, each enclosure or oven having an internal humidity, the method further comprising the step of measuring ambient humidity of the poured concrete structure and the step of controlling the humidity of each enclosure or oven such that the humidity of each enclosure or oven approaches the measured ambient humidity of the poured concrete structure to within an acceptable range of ambient humidity deviation from the measured ambient humidity of the poured concrete structure.
13. The method of claim 2, wherein said step of periodically testing one of the samples to determine the strength of the concrete in the sample comprises
compression testing the one of the samples.
14. The method of claim 13, wherein said step of placing the samples in a temperature controlled environment comprises the step of providing an apparatus comprising:
means for housing the samples selected from the group consisting of one or more enclosures, one or more ovens, and one or more water baths; and
at least one controller communicating with at least one of said one or more temperature probes provided for each of the one or more enclosures, the one or more ovens, or the one or more water baths, wherein each of said enclosures, ovens, or water baths has an internal temperature, and wherein said controller controls heat energy supplied to a corresponding enclosure, oven, or water bath such that the internal temperature of the corresponding enclosure, oven, or water bath is maintained within the acceptable range of temperature deviation from the measured temperature of the concrete in the poured concrete structure.
15. The method of claim 14, wherein the temperature probes are selected from the group consisting of thermocouples, thermistors, and optoelectronic thermometers.
16. The method of claim 15, wherein the acceptable range of temperature deviation from the measured temperature of the concrete in the poured concrete structure is about 20°F (1 1 12°C).
17. The method of claim 15, wherein the acceptable range of temperature deviation from the measured temperature of the concrete in the poured concrete structure is about 15°F (8.34°C).
18. The method of claim 15, wherein the temperature of the concrete in the poured concrete structure is measured at a frequency of about once every thirty minutes.
19. The method according to any one of claims 1 through 3, 5 through 1 1 , and 13 through 18, wherein the means for housing the samples are selected from the group consisting of one or more enclosures and one or more ovens, each enclosure or oven having an internal humidity, the method further comprising the step of controlling the humidity of each enclosure or oven such that the humidity of each enclosure or oven approaches the measured ambient humidity of the poured concrete structure to within an acceptable range of ambient humidity deviation from the measured ambient humidity of the poured concrete structure.
20. Apparatus for determining the strength of the concrete in a poured concrete structure over the course of curing of the concrete using samples of the concrete delivered for pouring the poured concrete structure, the apparatus comprising:
one or more temperature probes embedded in the concrete structure for measuring the temperature of the concrete in the poured concrete structure during the curing process;
means for housing the samples selected from the group consisting of one or more enclosures, one or more ovens, and one or more water baths; and
at least one controller communicating with at least one of said one or more temperature probes provided for each of the one or more enclosures, the one or more ovens, or the one or more water baths, wherein each of said enclosures, ovens, or water baths has an internal temperature, and wherein said controller controls heat energy supplied to a corresponding enclosure, oven, or water bath such that the internal temperature of the corresponding enclosure, oven, or water bath is maintained within the acceptable range of temperature deviation from the measured temperature of the concrete in the poured concrete structure.
21 . The apparatus of claim 20, further comprising at least one sample
environment temperature probe provided for measuring the internal temperature of each of said enclosures, ovens, or water baths, said at least one sample environment temperature probe or sensor communicating with a corresponding controller.
22. The apparatus of claim 21 , wherein each of said enclosures, ovens, or water baths comprises a heat source for supplying heat energy to a corresponding one of said enclosures, ovens, or water baths, wherein a corresponding controller of each of said enclosures, ovens, or water baths controls power supplied to said heat source of the corresponding one of said enclosures, ovens, or water baths based on the measured temperature of the concrete in the poured concrete structure and the internal temperature of the corresponding one of said enclosures, ovens, or water baths.
23. The apparatus of claim 22, further comprising compression testing means for testing the compressive strength of the concrete samples.
24. The apparatus according to any one of claims 20 to 23, wherein the means for housing the samples are selected from the group consisting of one or more enclosures and one or more ovens, the apparatus further comprising a fan or blower and means for turning on the fan or blower, wherein the fan or blower is under the control of the controller and wherein the controller is configured to turn on the fan or blower at least while the heating element is turned on so as to circulate the air within the enclosure or oven such that the internal temperature of the enclosure or oven can adjust more quickly to approximate the measured temperature of the concrete in the poured concrete structure within the acceptable range of temperature deviation as the measured temperature of the concrete in the poured concrete structure changes over time.
25. The apparatus according to any one of claims 20 to 23, wherein the means for housing the samples are selected from the group consisting of one or more enclosures and one or more ovens, the apparatus further comprising:
at least one humidity or moisture sensor provided within at least one enclosure or oven, for measuring the humidity or moisture within said enclosure or oven, and communicating with the controller;
one or more humidity or moisture sensors for measuring the humidity or moisture within the poured concrete structure or the ambient humidity or moisture of the poured concrete structure;
at least one humidifier;
at least one blower;
ducting connecting at least one enclosure or oven, the humidifier, and the blower; and
a first set of valves comprising one or more valves to control flow of air from the interior of the enclosure or oven through the ducting, the blower, and the humidifier, wherein the controller is configured to control the humidity of the enclosure or oven such that the interior humidity of the enclosure or oven approaches the measured ambient humidity of the poured concrete structure or the measured humidity within the poured concrete structure to within an acceptable range of humidity deviation from the measured ambient humidity or internal humidity of the poured concrete structure, wherein the ambient or internal humidity sensors for the poured concrete structure communicate with the controller,
wherein the controller operates the blower and first set of valves to selectively circulate air from the interior of the enclosure or oven through the humidifier to control the humidity or moisture of the interior of the enclosure or oven so that the humidity or moisture of the interior of the enclosure approaches the ambient or internal humidity of the poured concrete structure to within the acceptable range of humidity deviation based on the measured difference between the humidity of the interior of the enclosure or oven and the ambient or internal humidity of the poured concrete structure.
26. The apparatus of claim 25, wherein the controller is configured to operate the humidifier to introduce moisture into the air stream passing through the humidifier when the internal humidity of the enclosure or oven is below the measured ambient or internal humidity of the poured concrete structure.
27. The apparatus of claim 25, further comprising a dryer and a second set of valves comprising one or more valves that are controlled by the controller in
cooperation with the first set of valves to control flow of air from the interior of the enclosure or oven through the ducting, the blower, and the humidifier or the dryer, wherein the controller is configured to operate the blower and the first and second sets of valves to selectively circulate air from the interior of the enclosure or oven through the humidifier or the dryer to control the humidity or moisture of the interior of the enclosure or oven.
28. The apparatus of claim 27, wherein the one or more humidity or moisture sensors, for measuring the humidity or moisture within the poured concrete structure or the ambient humidity or moisture of the poured concrete structure, are configured to measure the ambient humidity or moisture of the poured concrete structure,
wherein the controller is configured to control the humidity of the enclosure or oven such that the interior humidity of the enclosure or oven approaches the measured ambient humidity of the poured concrete structure to within an acceptable range of humidity deviation from the measured ambient humidity of the poured concrete structure, and
wherein the controller is configured to operate the blower and the first and second set of valves to selectively circulate air from the interior of the enclosure or oven through the humidifier or the dryer to control the humidity or moisture of the interior of the enclosure or oven so that the humidity or moisture of the interior of the enclosure approaches the ambient humidity of the poured concrete structure to within the acceptable range of humidity deviation based on the measured difference between the humidity of the interior of the enclosure or oven and the ambient humidity of the poured concrete structure.
29. The apparatus according to claim 24, further comprising:
at least one humidity or moisture sensor provided within at least one enclosure or oven, for measuring the humidity or moisture within said enclosure or oven, and communicating with the controller; one or more humidity or moisture sensors for measuring the humidity or moisture within the poured concrete structure or the ambient humidity or moisture of the poured concrete structure;
at least one humidifier;
ducting connecting at least one enclosure or oven, the humidifier, and the blower or fan; and
a first set of valves comprising one or more valves to control flow of air from the interior of the enclosure or oven through the ducting, the blower or fan, and the humidifier,
wherein the controller is configured to control the humidity of the enclosure or oven such that the interior humidity of the enclosure or oven approaches the measured ambient humidity of the poured concrete structure or the measured humidity within the poured concrete structure to within an acceptable range of humidity deviation from the measured ambient humidity or internal humidity of the poured concrete structure,
wherein the ambient or internal humidity sensors for the poured concrete structure communicate with the controller,
wherein the controller is configured to operate the blower or fan and first set of valves to selectively circulate air from the interior of the enclosure or oven through the humidifier to control the humidity or moisture of the interior of the enclosure or oven so that the humidity or moisture of the interior of the enclosure approaches the ambient or internal humidity of the poured concrete structure to within the acceptable range of humidity deviation based on the measured difference between the humidity of the interior of the enclosure or oven and the ambient or internal humidity of the poured concrete structure.
30. The apparatus of claim 29, wherein the controller is configured to operate the humidifier to introduce moisture into the air stream passing through the humidifier when the internal humidity of the enclosure or oven is below the measured ambient or internal humidity of the poured concrete structure.
31. The apparatus of claim 29, further comprising a dryer and a second set of valves comprising one or more valves that are controlled by the controller in
cooperation with the first set of valves to control flow of air from the interior of the enclosure or oven through the ducting, the blower or fan, and the humidifier or the dryer, wherein the controller is configured to operate the blower or fan and the first and second sets of valves to selectively circulate air from the interior of the enclosure or oven through the humidifier or the dryer to control the humidity or moisture of the interior of the enclosure or oven.
32. The apparatus of claim 31 , wherein the one or more humidity or moisture sensors, for measuring the humidity or moisture within the poured concrete structure or the ambient humidity or moisture of the poured concrete structure, measure the ambient humidity or moisture of the poured concrete structure,
wherein the controller is configured to control the humidity of the enclosure or oven such that the interior humidity of the enclosure or oven approaches the measured ambient humidity of the poured concrete structure to within an acceptable range of humidity deviation from the measured ambient humidity of the poured concrete structure, and wherein the controller is configured to operate the blower or fan and the first and second set of valves to selectively circulate air from the interior of the enclosure or oven through the humidifier or the dryer to control the humidity or moisture of the interior of the enclosure or oven so that the humidity or moisture of the interior of the enclosure approaches the ambient humidity of the poured concrete structure to within the acceptable range of humidity deviation based on the measured difference between the humidity of the interior of the enclosure or oven and the ambient humidity of the poured concrete structure.
33. The apparatus according to any one of claims 20 to 23, wherein the means for housing the samples are selected from the group consisting of one or more enclosures and one or more ovens, the apparatus further comprising:
at least one humidity or moisture sensor provided within at least one enclosure or oven, for measuring the humidity or moisture within said enclosure or oven, and communicating with the controller;
one or more humidity or moisture sensors for measuring the ambient humidity or moisture of the poured concrete structure;
at least one humidifier;
at least one blower;
ducting connecting at least one enclosure or oven, the humidifier, and the blower; and
a first set of valves comprising one or more valves to control flow of air from the interior of the enclosure or oven through the ducting, the blower, and the humidifier, wherein the controller is configured to control the humidity of the enclosure or oven such that the interior humidity of the enclosure or oven approaches the measured ambient humidity of the poured concrete structure to within an acceptable range of humidity deviation from the measured ambient humidity or internal humidity of the poured concrete structure,
wherein the ambient humidity sensors for the poured concrete structure communicate with the controller,
wherein the controller is configured to operate the blower and first set of valves to selectively circulate air from the interior of the enclosure or oven through the humidifier to control the humidity or moisture of the interior of the enclosure or oven so that the humidity or moisture of the interior of the enclosure approaches the ambient humidity of the poured concrete structure to within the acceptable range of humidity deviation based on the measured difference between the humidity of the interior of the enclosure or oven and the ambient humidity of the poured concrete structure.
34. The apparatus of claim 33, wherein the controller is configured to operate the humidifier to introduce moisture into the air stream passing through the humidifier when the internal humidity of the enclosure or oven is below the measured ambient humidity of the poured concrete structure.
35. The apparatus of claim 33, further comprising a dryer and a second set of valves comprising one or more valves that are controlled by the controller in
cooperation with the first set of valves to control flow of air from the interior of the enclosure or oven through the ducting, the blower, and the humidifier or the dryer, wherein the controller is configured for operating the blower and the first and second sets of valves to selectively circulate air from the interior of the enclosure or oven through the humidifier or the dryer to control the humidity or moisture of the interior of the enclosure or oven.
36. The apparatus according to any one of claims 20 to 35, wherein the means for housing the samples are selected from the group consisting of one or more enclosures and one or more ovens, wherein the enclosure is provided with an air inlet and an air outlet, the apparatus further comprising:
closure flaps or valves provided at the air inlet and the air outlet to the enclosure to act as inlet and outlet valves, respectively;
a fan or blower;
a cooling unit; and
ducting connecting at least the air outlet of the enclosure, the blower, the cooling unit, and the air inlet of the enclosure,
wherein the controller is configured to selectively operate the blower, the inlet and outlet valves, and the cooling unit to cool the interior of the enclosure, at least when the temperature inside the enclosure is above the measured temperature of the concrete within the poured concrete structure by a difference greater than the acceptable range of temperature deviation.
37. The apparatus of claim 36, wherein the cooling unit comprises the coils of a refrigeration system.
38. The apparatus according to any one of claims 20 to 35, wherein the means for housing the samples are selected from the group consisting of one or more enclosures and one or more ovens, the apparatus further comprising a cooling unit, wherein the controller is configured to selectively operate the cooling unit to cool the interior of the enclosure, at least when the temperature inside the enclosure is above the measured temperature of the concrete within the poured concrete structure by a difference greater than the acceptable range of temperature deviation.
39. The apparatus according to any one of claims 36 through 38, wherein the cooling unit and the heating element are provided by the same apparatus.
40. The method according to any one of claims 1 through 1 1 and 13 through 18, wherein the means for housing the samples are selected from the group consisting of one or more enclosures and one or more ovens, each enclosure or oven having an internal humidity, the method further comprising the step of measuring an internal humidity of the poured concrete structure and the step of controlling the humidity of each enclosure or oven such that the humidity of each enclosure or oven approaches the measured internal humidity of the poured concrete structure to within an acceptable range of humidity deviation from the measured internal humidity of the poured concrete structure.
41. The method of claim 1 , wherein the temperature of the concrete in the poured concrete structure is measured at a frequency of from about once every two hours or higher.
42. The method of claim 1 , wherein the temperature of the concrete in the poured concrete structure is measured at a frequency of from about once every hour or higher.
43. The method of claim 1 , wherein the temperature of the concrete in the poured concrete structure is measured at a frequency of from about once every forty five minutes or higher.
44. The method of claim 1 , wherein the temperature of the concrete in the poured concrete structure is measured at a frequency of about once every thirty minutes or higher.
PCT/US2018/033548 2018-05-18 2018-05-18 Method and apparatus for determining a cure state of concrete WO2019221759A1 (en)

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