US20230390960A1 - Device and method for producing a concrete, in particular a high early strength concrete - Google Patents

Device and method for producing a concrete, in particular a high early strength concrete Download PDF

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Publication number
US20230390960A1
US20230390960A1 US18/039,826 US202118039826A US2023390960A1 US 20230390960 A1 US20230390960 A1 US 20230390960A1 US 202118039826 A US202118039826 A US 202118039826A US 2023390960 A1 US2023390960 A1 US 2023390960A1
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Prior art keywords
cement
crystallization tank
concrete
suspension
premixer
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US18/039,826
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Inventor
Ricardo Remus
Paul Schötzigk
Max Jentzsch
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Sonocrete GmbH
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Sonocrete GmbH
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Priority claimed from DE102020132015.9A external-priority patent/DE102020132015A1/de
Priority claimed from DE102021108917.4A external-priority patent/DE102021108917A1/de
Application filed by Sonocrete GmbH filed Critical Sonocrete GmbH
Assigned to Sonocrete GmbH reassignment Sonocrete GmbH ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: Remus, Ricardo, Jentzsch, Max, Schötzigk, Paul
Publication of US20230390960A1 publication Critical patent/US20230390960A1/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28C—PREPARING CLAY; PRODUCING MIXTURES CONTAINING CLAY OR CEMENTITIOUS MATERIAL, e.g. PLASTER
    • B28C5/00—Apparatus or methods for producing mixtures of cement with other substances, e.g. slurries, mortars, porous or fibrous compositions
    • B28C5/08—Apparatus or methods for producing mixtures of cement with other substances, e.g. slurries, mortars, porous or fibrous compositions using driven mechanical means affecting the mixing
    • B28C5/0875—Mixing in separate stages involving different containers for each stage
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28C—PREPARING CLAY; PRODUCING MIXTURES CONTAINING CLAY OR CEMENTITIOUS MATERIAL, e.g. PLASTER
    • B28C5/00—Apparatus or methods for producing mixtures of cement with other substances, e.g. slurries, mortars, porous or fibrous compositions
    • B28C5/48—Apparatus or methods for producing mixtures of cement with other substances, e.g. slurries, mortars, porous or fibrous compositions wherein the mixing is effected by vibrations
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F31/00—Mixers with shaking, oscillating, or vibrating mechanisms
    • B01F31/80—Mixing by means of high-frequency vibrations above one kHz, e.g. ultrasonic vibrations
    • B01F31/85—Mixing by means of high-frequency vibrations above one kHz, e.g. ultrasonic vibrations with a vibrating element inside the receptacle
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F33/00—Other mixers; Mixing plants; Combinations of mixers
    • B01F33/80—Mixing plants; Combinations of mixers
    • B01F33/81—Combinations of similar mixers, e.g. with rotary stirring devices in two or more receptacles
    • B01F33/811—Combinations of similar mixers, e.g. with rotary stirring devices in two or more receptacles in two or more consecutive, i.e. successive, mixing receptacles or being consecutively arranged
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F33/00—Other mixers; Mixing plants; Combinations of mixers
    • B01F33/80—Mixing plants; Combinations of mixers
    • B01F33/82—Combinations of dissimilar mixers
    • B01F33/821—Combinations of dissimilar mixers with consecutive receptacles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28C—PREPARING CLAY; PRODUCING MIXTURES CONTAINING CLAY OR CEMENTITIOUS MATERIAL, e.g. PLASTER
    • B28C5/00—Apparatus or methods for producing mixtures of cement with other substances, e.g. slurries, mortars, porous or fibrous compositions
    • B28C5/08—Apparatus or methods for producing mixtures of cement with other substances, e.g. slurries, mortars, porous or fibrous compositions using driven mechanical means affecting the mixing
    • B28C5/10—Mixing in containers not actuated to effect the mixing
    • B28C5/12—Mixing in containers not actuated to effect the mixing with stirrers sweeping through the materials, e.g. with incorporated feeding or discharging means or with oscillating stirrers
    • B28C5/1223—Mixing in containers not actuated to effect the mixing with stirrers sweeping through the materials, e.g. with incorporated feeding or discharging means or with oscillating stirrers discontinuously operating mixing devices, e.g. with consecutive containers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28C—PREPARING CLAY; PRODUCING MIXTURES CONTAINING CLAY OR CEMENTITIOUS MATERIAL, e.g. PLASTER
    • B28C5/00—Apparatus or methods for producing mixtures of cement with other substances, e.g. slurries, mortars, porous or fibrous compositions
    • B28C5/08—Apparatus or methods for producing mixtures of cement with other substances, e.g. slurries, mortars, porous or fibrous compositions using driven mechanical means affecting the mixing
    • B28C5/10—Mixing in containers not actuated to effect the mixing
    • B28C5/12—Mixing in containers not actuated to effect the mixing with stirrers sweeping through the materials, e.g. with incorporated feeding or discharging means or with oscillating stirrers
    • B28C5/16—Mixing in containers not actuated to effect the mixing with stirrers sweeping through the materials, e.g. with incorporated feeding or discharging means or with oscillating stirrers the stirrers having motion about a vertical or steeply inclined axis
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28C—PREPARING CLAY; PRODUCING MIXTURES CONTAINING CLAY OR CEMENTITIOUS MATERIAL, e.g. PLASTER
    • B28C7/00—Controlling the operation of apparatus for producing mixtures of clay or cement with other substances; Supplying or proportioning the ingredients for mixing clay or cement with other substances; Discharging the mixture
    • B28C7/02—Controlling the operation of the mixing
    • B28C7/022—Controlling the operation of the mixing by measuring the consistency or composition of the mixture, e.g. with supply of a missing component
    • B28C7/024—Controlling the operation of the mixing by measuring the consistency or composition of the mixture, e.g. with supply of a missing component by measuring properties of the mixture, e.g. moisture, electrical resistivity, density
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28C—PREPARING CLAY; PRODUCING MIXTURES CONTAINING CLAY OR CEMENTITIOUS MATERIAL, e.g. PLASTER
    • B28C7/00—Controlling the operation of apparatus for producing mixtures of clay or cement with other substances; Supplying or proportioning the ingredients for mixing clay or cement with other substances; Discharging the mixture
    • B28C7/02—Controlling the operation of the mixing
    • B28C7/022—Controlling the operation of the mixing by measuring the consistency or composition of the mixture, e.g. with supply of a missing component
    • B28C7/026—Controlling the operation of the mixing by measuring the consistency or composition of the mixture, e.g. with supply of a missing component by measuring data of the driving system, e.g. rotational speed, torque, consumed power
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28C—PREPARING CLAY; PRODUCING MIXTURES CONTAINING CLAY OR CEMENTITIOUS MATERIAL, e.g. PLASTER
    • B28C7/00—Controlling the operation of apparatus for producing mixtures of clay or cement with other substances; Supplying or proportioning the ingredients for mixing clay or cement with other substances; Discharging the mixture
    • B28C7/16—Discharge means, e.g. with intermediate storage of fresh concrete
    • B28C7/161—Discharge means, e.g. with intermediate storage of fresh concrete with storage reservoirs for temporarily storing the fresh concrete; Charging or discharging devices therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28C—PREPARING CLAY; PRODUCING MIXTURES CONTAINING CLAY OR CEMENTITIOUS MATERIAL, e.g. PLASTER
    • B28C9/00—General arrangement or layout of plant
    • B28C9/002—Mixing systems, i.e. flow charts or diagrams; Making slurries; Involving methodical aspects; Involving pretreatment of ingredients; Involving packaging
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B40/00—Processes, in general, for influencing or modifying the properties of mortars, concrete or artificial stone compositions, e.g. their setting or hardening ability
    • C04B40/0003—Processes, in general, for influencing or modifying the properties of mortars, concrete or artificial stone compositions, e.g. their setting or hardening ability making use of electric or wave energy or particle radiation
    • C04B40/0021—Sonic or ultrasonic waves, e.g. to initiate sonochemical reactions

Definitions

  • Exemplary embodiments of the present invention relate to a device for producing a concrete, in particular a high early strength concrete, and to a method for producing a corresponding concrete.
  • An important parameter of a concrete composition is its early strength.
  • Options for increasing the early strength of concrete include established processes such as heat treatment, the use of accelerating concrete admixtures or concrete technology methods such as increasing the cement content beyond what is structurally necessary or lowering the w/c ratio (the ratio of water to cement).
  • these variants are often a compromise in which the time factor is bought by significantly increased production costs.
  • the early strength is improved, the changed composition may also lead to an undesirable change in the overall material properties (e.g., shrinkage cracks).
  • DE 37 16 438 A1 describes a device with a cement premixer, a concrete mixer, and a tank arranged in between.
  • cement and water are mixed to form a cement paste. This is stored temporarily and then mixed with aggregates for concrete production, as is customary.
  • two-stage mixing processes are known that improve the early strength.
  • Applications of two-stage mixing processes are described in DE15 84 305 A or DE 10 2016 003 644 B4, among others.
  • the workability and early strength of concretes is to be improved by a two-stage mixing process, by 1.) intensive premixing of the binder components with and without sand and 2.) by final mixing in the concrete mixer.
  • the water available for preparing the suspension is 106 kg/m 3 , i.e., about 2 ⁇ 3 of the initial quantity.
  • a w/c ratio of 0.30 must now be selected. In order to mix such low w/c ratios accurately, higher superplasticizer dosages are required, which may optionally increase the concrete slump beyond a necessary level and additionally delay the hardening reaction of the cement.
  • Example 2 for illustration: If a w/c ratio of 0.35 is now applied in the production process of, for example, prestressed concrete elements, the following calculation results:
  • the water available for the production of a suspension in the premixing process is now 67 kg/m 3 , resulting in a w/c ratio of the suspension of 0.19, which can no longer be accurately premixed and metered on the basis of the technologies currently available.
  • exemplary embodiments of the present invention are directed to a device and a method for the production of concrete with high early strengths while avoiding the aforementioned problem.
  • a device according to the invention for the production of a concrete comprises
  • the device according to the present invention has one or more crystallization tanks, which enables crystallization of individual constituents contained in the cement prior to their addition to the concrete.
  • a plurality of crystallization tanks can form a crystallization tank arrangement within the scope of the present invention.
  • the crystallization tanks are preferably arranged one above the other in the crystallization tank arrangement, so that the cement suspension can be transferred by gravity from an upper crystallization tank to a crystallization tank arranged below.
  • This device is based on the knowledge that a favorable water-to-cement ratio (w/c ratio) exists for a reaction-activating premixing of cement and water, especially with the use of ultrasound.
  • This w/c ratio depends on the cement type and is preferably in the range of 0.50-2.0. Lower w/c ratios lead to stronger particle interactions due to the higher solids content, which favors strong heating of the suspension and can have a negative effect under certain circumstances.
  • Pretreatment of the cement suspension, in particular with ultrasound, produces metastable crystallization nuclei, which are given additional time to grow by storage in the crystallization tank and are (later) metered into the concrete mixer as stable crystallization nuclei.
  • This crystallization tank preferably comprises an agitator with a stirrer which keeps the cement suspension moving at a slow speed during the crystallization period.
  • a preferred stirring speed is less than 50 rpm, preferably 2-25 rpm, more preferably 5-20 rpm.
  • the cement premixer has at least one ultrasonic generator, in particular an ultrasonic probe, for providing a cement suspension.
  • the disintegration is not produced by high-speed mixing tools, but by the use of ultrasound.
  • the fact that only a small portion of the cement (e.g., 20%) with a high water content (w/c>>1.0) is premixed means that the ultrasound is at the same time less attenuated and, due to the small proportion of suspension in relation to the total concrete, the concrete is less heated.
  • Such a cement premixer not only achieves a pure mixing of cement and water, but also an activation of the cement constituents and the cement suspension, so that crystallization is also promoted.
  • the cement premixer also has a stirrer that moves the cement suspension preferably at a higher stirring speed than the stirrer in the first crystallization tank.
  • Premixing in the aforementioned parameters and/or stirring speed typically results in the formation of air bubbles within the cement suspension, which can negatively affect the final strength of the concrete. These air bubbles are expelled during the continuous gentle mixing of the cement suspension in the crystallization tank. Therefore, the combination of the crystallization tank especially with an ultrasonic cement premixer is particularly preferred.
  • a crystallization tank can also be used to store the cement suspension.
  • the cement premixer, crystallization tank and concrete mixer are arranged relative to the earth's gravity field in such a way that the cement suspension can flow by gravity from the cement premixer, into the crystallization tank and from there into the concrete mixer.
  • a pump can be used to transport the suspension into the concrete mixer.
  • connection between the respective tanks and mixers can each be a flange connection with a closing device, e.g., a flat slide valve.
  • the first and each further crystallization tank has a stirring tool and may in particular have a drive for moving the stirring tool.
  • the first and each subsequent crystallization tank may have a side wall and a bottom surface, preferably a curved bottom surface.
  • the side wall may extend parallel to the longitudinal axis of the crystallization tank.
  • the agitator may have a rotatable agitator extension as the stirrer.
  • these formations may be spiral formations.
  • the formations can be designed in such a way that they can be guided over at least 50% of the bottom surface with a distance of less than 10 cm, preferably less than 5 cm, in particular between 0.5-4 cm distance. This allows a large quantity of the cement suspension, including settled constituents, to be moved and preferably re-suspended.
  • the formations in particular in the design as spiral formations, can have edge wipers in the direction of the base. While the formations can preferably be formed from metal, the edge wipers are preferably formed from a softer material than the formations. Preferably, the edge wipers can be in the form of rubber and/or PTFE lips.
  • the device can have a second, third, fourth, fifth, and further crystallization tank, preferably with a separate agitator.
  • a second tank is particularly advantageous when large volumes are required, since the second tank can be used for metering the activated (premixer) and upstream (crystallization tank I) suspension into the concrete mixer. This ensures that no suspension leaves the crystallization tank without sufficient pre-storage time.
  • the device can be designed as a pressureless-operated system.
  • An open or pressureless-operated system means that the pressure conditions in each container, i.e., the mixer and/or the crystallization tank(s), are the same or that, if pressure differences occur in the transfer of the cement suspension, pressure compensation takes place through the open valves.
  • a regulating member is arranged for draining and/or partially draining the respective crystallization tank into the concrete mixer.
  • This regulating member can preferably be designed as a valve, in particular as a pinch valve.
  • corresponding regulating members e.g., valves, in particular pinch valves, can also be arranged between the cement premixer and the first crystallization tank and/or between the crystallization tanks.
  • the device can also advantageously have an arrangement for detecting a measured variable for controlling emergency draining of the first and/or each further crystallization tank.
  • Such an arrangement can be, for example, a sensor for torque detection of the rotatable agitator and/or—in the case of a rotating crystallization tank—a sensor for torque detection of the rotatable drum of the crystallization tank. This measurement indirectly allows a statement to be made about the state of hardening of the cement suspension.
  • the device can also have a feed device, in particular a metering device, for supplying a superplasticizer, in particular as a function of the detected measured variable. This allows the composition of the cement suspension to be readjusted when a setpoint value is exceeded.
  • the device in particular at least one of the crystallization tanks, also have according to the invention a sensor for determining the temperature of the cement suspension.
  • the temperature should be between 25-45° C.
  • Corresponding setpoint values for residence times of the cement suspension during automated draining and/or partial draining of the crystallization tank can be adjusted depending on the temperature determined.
  • the first and/or second, or any further crystallization tank can be designed for a quantity of at least 2 cubic meters, preferably 0.5-4 cubic meters of a cement suspension.
  • Such quantities are atypical for cement premixers, in particular ultrasonic cement premixers, since the ultrasonic input, in particular in the case of intensive ultrasound, cannot be sufficiently homogeneous over the volume of the mixer in the case of larger volumes.
  • the intensive ultrasonic treatment enables activation of the cement constituents.
  • the ultrasonic treatment in the preferred variant of the present method has the following characteristic data, which individually or in combination with each other characterize the type of ultrasonic treatment in more detail:
  • the intensity (I) corresponds to the power, e.g., watts, that is transported per area.
  • the unit is power per area (e.g. W/cm 2 ).
  • the amplitude (u) describes the deflection of the ultrasonic wave (e.g., in ⁇ m). At constant frequency, higher amplitudes lead to an increase in intensity. The greater the amplitude, the greater the pressure differences during high-pressure and low-pressure cycles.
  • the frequency (f) describes the rate of oscillation at the tip of the ultrasonic probe. Since the formation, growth and implosion of vapor bubbles is a time-dependent process, higher frequencies result in smaller cavitation bubbles.
  • the aforementioned values can be determined electroacoustically in water using a hydrophone, for example.
  • a diverter valve can be installed after the cement weigher so that the cement can be metered into the concrete mixer as well as into the premixer.
  • a separate metering screw can also be guided to the premixer.
  • An essential measure for the development of the early strength is the residence time. This corresponds to the residence or crystallization time of the premixed suspension in the crystallization tank.
  • the residence time depends on the concrete production process (mixing time, concrete volume per hour, concrete composition) and the desired strength increase.
  • a crystallization tank (or storage/dwell/reservoir tank) is a container in which the suspension is stored for a predefined period of time (0.5-6 hours) under continuous stirring/circulation. After the residence time, the suspension is dosed into the concrete mixer.
  • the residence or dwell time corresponds to the time that the activated suspension remains in the crystallization tank under continuous stirring or circulation.
  • the first crystallization tank has an outlet that opens into an inlet of the concrete mixer or into a second (or third, fourth, . . . ) crystallization tank.
  • the device further comprises a regulating member arranged in the outlet of the first crystallization tank and/or in the inlet of the concrete mixer.
  • the device can also have a first evaluation and/or control unit, which is equipped to operate the regulating member for partial or complete draining of the first crystallization tank after a residence time of the cement suspension in the first crystallization tank of 0.5-6 hours.
  • the cement premixer may comprise a treatment vessel having a treatment chamber, wherein the at least one ultrasonic probe, at least partially, extends into the treatment chamber, and
  • the ultrasonic probe emits ultrasound
  • the emitted ultrasound or the ultrasonic signal e.g., by the evaluation and/or control unit, is adjusted such that it has an intensity of 25-250 W/cm 2 and an amplitude of 15-500 ⁇ m.
  • a first partial quantity of cement can be added to the cement premixer and a second partial quantity of cement can be added to the concrete mixer, which is particularly advantageous in terms of energy.
  • the proportion of cement pretreated in this way is preferably between 5-95%, particularly preferably between 10-25% of the total cement content.
  • control or setting of the setpoint value for the preferred residence time of the cement suspension within the crystallization tank can advantageously be carried out as a function of a predetermined time at a predetermined temperature. Since crystallization is temperature dependent, this control provides better control over the quality of the cement suspension.
  • the transfer of the cement suspension into the concrete mixer can be done in batches.
  • the stirring speed in the first and each further crystallization tank and/or inflow and/or outflow of cement suspension into the first or each further crystallization tank can be controlled by a sensor and/or sensor arrangement.
  • a sensor and/or sensor arrangement For this purpose, one or more temperature sensors, ultrasonic sensors for determining the ultrasonic transit time and/or sensors for torque detection can preferably be used to monitor the quality of the cement suspension and, in particular, its strength.
  • the temperature of the cement suspension in the first or any further crystallization tank can be adjusted to a temperature between 10-45° C.
  • the adjustability to below 20° C., especially 10-20° C., allows better storage.
  • the crystallization time or residence time, as well as the time of emergency draining, can be set depending on the temperature and/or the above-mentioned measured variable.
  • the cement suspension can preferably be added to the concrete mixer only after a residence time of between 1-8 hours.
  • the transfer of cement suspension into the concrete mixer is carried out according to a predetermined protocol.
  • the water/cement (w/c) ratio of the cement suspension can advantageously be between 0.5-2.
  • the residence time is selected depending on the reaction rate of the cement. The indicated times are optimal for the above-mentioned specification of the residence time.
  • the pre-storage time of the cement suspension before transfer to the concrete mixer can advantageously be between 1-8 hours.
  • the aforementioned w/c ratio but also the resting phase can be combined with the aforementioned ultrasonic treatment of the cement suspension.
  • the proportion of ultrasonically pretreated cement in the concrete can advantageously be between 5-95 wt. %, ideally 10-25 wt. %.
  • the stirring speed in the first and/or second crystallization tank and/or inflow and/or outflow of cement suspension into the first and/or second crystallization tank can be controlled by a sensor and/or sensor arrangement.
  • a sensor and/or sensor arrangement For this purpose, one or more temperature sensors, ultrasonic sensors for determining the ultrasonic transit time, and/or sensors for torque detection can preferably be used to monitor the quality of the cement suspension and, in particular, its strength.
  • Another advantage within the scope of the present method is the provision of an intelligent control method and/or a control device for maintaining a defined suspension quality.
  • a series of sensors in the tank permanently analyzes the properties of the suspension (especially temperature, viscosity, density, electrical conductivity, ultrasonic transit time), evaluates them and initiates measures based on the sensor measurement data, such as adding new suspension and draining old suspension.
  • This can advantageously be kept permanently in the desired range by means of a cooling and heating device, for example by forming a double-walled tank wall as part of the first and/or second crystallization tank or by means of heat exchangers on or in the crystallization tank.
  • a sensory detection of a substance-dependent physical measured variable of the cement suspension located in the first and/or second crystallization tank can be carried out.
  • the inflow and/or outflow quantity, the stirring speed and/or the temperature can then be controlled on the basis of the measured values determined by the sensory detection.
  • FIG. 1 shows a side view of an exemplary embodiment comprising a cement premixer and a first and a second crystallization tank of a device according to the invention
  • FIG. 2 shows a perspective view of the exemplary embodiment of FIG. 1 ;
  • FIG. 3 shows a sectional view along the longitudinal axis of the crystallization tanks
  • FIG. 4 shows a schematic representation of concrete production by conventional methods
  • FIG. 5 shows a schematic representation of a concrete production according to an embodiment of the present invention
  • FIG. 6 shows a diagram of heat release rate
  • FIG. 7 shows a representation of a composition of a first concrete mix
  • FIG. 8 shows a representation of a composition of a second concrete mix
  • FIG. 9 shows a representation of a mixing ratio of cement suspension and water
  • FIG. 10 shows a diagram showing the correlation between solidification onset and pre-storage time
  • FIG. 11 shows a diagram showing the pre-storage time of an ultrasonically treated cement mortar in relation to the slump flow and slump spread.
  • FIG. 12 shows a diagram of compressive strength related to concrete age.
  • FIG. 1 shows a device 1 according to the invention, comprising a cement premixer 3 and two crystallization tanks 4 and 5 .
  • An inlet opening 7 is provided above the cement premixer 3 .
  • the cement premixer 3 and the two crystallization tanks 4 and 5 are connected to each other by a machine frame 2 .
  • the cement premixer 3 has ultrasonic probes 6 extending through the wall of the cement premixer into the interior.
  • Transfer lines are provided between the cement premixer 3 and the two tanks 4 and 5 .
  • the transfer lines can have regulating members, e.g., valve devices.
  • Tank 5 has an outlet 10 .
  • Each of the crystallization tanks 4 and 5 and the cement premixer 3 has agitators 7 - 9 .
  • FIG. 2 shows a perspective view of the device of FIG. 1 .
  • the storage levels A, B and C along which the aforementioned containers are stored can be seen.
  • FIG. 3 discloses further details.
  • the crystallization tank 4 has an agitator 8 with a rod 15 and spirally wound stirring blades 13 .
  • the crystallization tank has a cylindrical jacket section 11 and a curved bottom section 12 .
  • a sensor element 17 is arranged in the upper area of the crystallization tank 4 .
  • This can be a temperature sensor, for example.
  • the crystallization tank 4 has an outlet 18 that merges into a transfer line 20 .
  • the crystallization tank 4 has an emergency drain 16 , via which the tank 4 k can be drained in an emergency, e.g., in the case of an overlaying cement suspension.
  • the crystallization tank 5 has a similar design. Both the sensor element 27 and the agitator 9 can be seen. In the bottom section 22 there are two drain nozzles 26 and 28 , each of which has flanged ends 24 . One of the two drain nozzles again serves as an emergency drain, while the other enables transfer to the concrete mixer.
  • FIG. 4 shows a conventional method 100 for producing concrete.
  • water 103 , cement 104 and 105 , additives 102 , and, optionally, binders and admixtures are mixed with gravel 106 , 107 or sand 108 in a concrete mixer 101 .
  • binders as inorganic or organic substances which can be processed in a plastic state and which harden in the course of a certain time, firmly bonding other substances, e.g., aggregates, to each other.
  • the binders used in the concrete industry are of mineral origin and, with some exceptions, are obtained from certain rocks by firing and ground to a fine powder. Mixed with water, the binder glue is formed first. Chemical reactions, and in some cases also physical surface forces, can cause the binder paste to solidify into a stone-like state, wherein any fillers can be cemented together.
  • admixtures or “concrete admixtures” for concrete. These are substances which are added to the concrete in finely divided form, e.g., in liquid, powder form or as granules or paste, in small quantities in order to influence certain properties of the fresh or hardened concrete by chemical or physical action.
  • Typical admixtures are concrete plasticizers, superplasticizers, air entraining agents, sealants, retarders, accelerators, grouting aids and/or stabilizers.
  • additives or concrete additives are finely dispersed substances used in concrete to improve or achieve certain properties. Such substances are present as volume constituents in a concrete composition in significantly larger quantities than the admixtures. They are therefore also called fillers.
  • inorganic additives are almost inactive additives such as stone dust or pigments.
  • Type II additives are pozzolanic or latent hydraulic additives such as trass, fly ash or silicate dust.
  • a concrete mix contains a significant proportion of aggregates such as gravels and sands, the grain size and proportion of which may vary depending on the type of concrete. These aggregates are also occasionally grouped together with other materials under the generic term of aggregates.
  • the core of the present invention is now to provide a method solving these technological obstacles and still ensures the high early strengths of a concrete with e.g., ultrasonic premixing stage.
  • cement 209 , water 210 and additives 211 are mixed in a cement premixer 212 and ultrasonically activated.
  • the cement suspension is then transferred to a crystallization tank 213 and from there to a concrete mixer 201 .
  • Admixtures 202 , water 203 , cement 204 and 205 as well as gravel 206 , 207 and sand 208 can also be fed into the concrete mixer 201 as part of the method 200 according to the invention.
  • the invention is based on the fact that there is an advantageous w/c ratio or w/c range for the production of a cement suspension in which the suspension can be well homogenized and activated (e.g., by ultrasound).
  • This advantageous w/c ratio depends on the type of cement and the admixtures used and lies between 0.5 and 2.
  • the invention is based on the fact that not the entire proportion of cement and water has to be premixed and activated in order to bring about a significant increase in early strengths.
  • the cement suspension provided in the cement premixer is prepared from cement, water and, optionally, admixtures as optional components. Additives, on the other hand, are not provided in the cement suspension.
  • part of the cement is dosed into the premixer for activation and part of the cement is dosed into the concrete mixer.
  • This can be carried out either by a separate metering device (silo+screw conveyor) at the premixer or at the existing concrete mixing plant by a distributor at the cement weigher and a screw conveyor from the cement weigher to the premixer.
  • part of the method according to the invention is not to dose the premixed and activated cement suspension into the concrete mixer immediately after mixing, but to convey it into a rest or crystallization tank stored downstream of the suspension mixer.
  • the crystallization tank has a volume of approximately the amount of suspension required for one hour of concrete production.
  • the production and activation of the suspension with subsequent storage in the crystallization tank has the further advantage that the suspension can be removed or dosed as quickly as desired after a sufficient crystallization time, and thus the mixing times can still be selected to be short.
  • the rest or crystallization time results in a significant increase in early strengths, even compared to the variant in which the entire calculated available quantity of cement and water is premixed and activated. Without a resting phase, this potential is not achieved. If ultrasound is used for activation in the premixing stage, the early strengths are again significantly increased. Ideally, this resting phase lasts between 1-8 hours, depending on the cement type and composition of the suspension.
  • the mixing time of the suspension mixing process in the production process should be very short to enable short overall mixing times. This is not always guaranteed, especially when the cement suspension is activated, e.g., by ultrasound. In the production of large concrete elements (e.g., bridge girders), larger quantities of concrete have to be produced in a short time in order to complete the concrete element quickly. This also poses a particular challenge for the premixing of a cement suspension in an ultrasonic premixer, since the mixing chamber is limited to a certain size for effective ultrasonic application. By producing the suspension “in stock”, these components can also be manufactured without a relevant increase in concrete mixing times.
  • the mixing times of the concrete mixing process are not extended.
  • the early strengths are significantly increased with the same concrete composition.
  • FIG. 6 shows the time-depended heat release rate in J/gh. This is a calorimetric measurement of Portland cement, which is designated as CEM I 52.5 R in the diagram, with and without ultrasonic treatment, designated as PUS in the diagram.
  • cement and superplasticizer type as well as water content
  • the w/c ratio must be selected in such a way that the rise of the curve (so-called “acceleration phase”) does not take too long (w/c ratio lower) but also in such a way that there is no solidification of the material during pre-storage (w/c ratio higher).
  • a w/c ratio well suited for this is around 1.0 ⁇ 0.25, depending on the cement type and superplasticizer type and quantity.
  • the pre-storage time then depends on the selected w/c ratio and the reactivity of the cement. In order to keep the process engineering effort associated with pre-storage low, a maximum pre-storage time of 4 hours is aimed for.
  • part of the cement is premixed with water, sonicated, and then stored for a longer period. After storage, the cement suspension is metered into the concrete mixer. As described previously, ultrasonic activation takes place as a result of sonication. It takes place at an intensity of 25-250 W/cm 2 and an amplitude of the ultrasound of 15-500 ⁇ m.
  • Hydrate nuclei are formed in the suspension, which significantly influence the early strength of concrete. This can be proven by microscopic images, among other things.
  • the water content is low but sufficient for a premixing process, since a flowable suspension can still be prepared and metered using superplasticizer.
  • FIGS. 7 and 8 each show the metering quantities of the respective components.
  • the aggregates in the case of FIG. 8 are wetter than FIG. 7 and therefore contain more water.
  • the figures show with the bar “H2O” only the amount of added water in addition to the aggregates. “H” and “H2O” are to be understood synonymously in the figures.
  • the core is the use of only a partial quantity of the available cement—see FIG. 9 .
  • the number of hydrate nuclei that can be formed is limited to the amount of cement. This led to the concept of storing or crystallizing the suspension until a sufficient amount of hydrate nuclei has formed to accelerate hydration.
  • the number of hydrate phases increases with the pre-storage time. For this purpose, a measurement of the start of solidification, i.e., the point in time at which the hardening process has progressed so far that the concrete cannot be further processed, is shown below.
  • FIG. 10 shows the onset of solidification of a cement mortar with the following parameters:
  • FIG. 10 shows that the onset of solidification (Y axis) decreases with increasing pre-storage time (X axis). This behavior is particularly pronounced for suspensions that have been sonicated (cross-hatched). Without sonication, the reduction of the solidification time is not so pronounced (dash-hatched).
  • the workability is also influenced by the pre-storage.
  • This is determined for cements by means of slump flow and slump spread.
  • FIG. 11 shows the slump flow and slump spread of the cement mortar already described in FIG. 10 with a cement suspension of different length.
  • slump flow the slump flow and slump spread of the cement mortar already described in FIG. 10 with a cement suspension of different length.
  • both the slump flow and the spreading dimension decrease with increasing pre-storage time. This means that the workability of the mortar is reduced. In the first 240 minutes, however, the reduction is only slight, which means no significant changes for the concrete. After 240 minutes, a more pronounced decrease occurs.
  • the ideal pre-storage time for the mortar under consideration is about 240 minutes.
  • the changes in workability are small with a simultaneous significant increase in early strength.
  • a concrete with Portland cement (CEM I 52.5 R) and a w/c ratio of 0.47 was produced.
  • a superplasticizer type: polycarboxylate ether
  • FIG. 12 shows the compressive strength development over the first 24 hours of a concrete produced by the method according to the invention in comparison with a conventionally produced concrete. It can be clearly seen that the concrete sample with pre-treated suspension produced by the method according to the invention exhibits significantly higher compressive strengths at all times measured.

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DE102021108917.4A DE102021108917A1 (de) 2021-04-09 2021-04-09 Vorrichtung und Verfahren zur Herstellung eines Betons, insbesondere eines Betons mit hoher Frühfestigkeit
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