GB2111399A

GB2111399A - A method of temperature control of building materials

Info

Publication number: GB2111399A
Application number: GB08233071A
Authority: GB
Inventors: W Kallinger; F Howanietz
Original assignee: HOWANIETZ FREDRICH
Current assignee: HOWANIETZ FREDRICH
Priority date: 1981-11-20
Filing date: 1982-11-19
Publication date: 1983-07-06
Also published as: ES8400047A1; ATA501081A; JPS58106063A; GB2111399B; ES517526A0; CA1194184A; AT391103B

Abstract

A method of controlling the temperature of mixed building materials wherein a mixer (1) is provided a heat detector (2) which signals a computer ( mu ) the temperature of the mix. The computer may also be fed with the amounts and temperatures of the components of the mix and calculates an amount of heat to be added or subtracted to give a desired temperature to the mix. Final control elements (6 and 7) add steam or ice water from storage devices (8) to the mix in accordance with the directions of the computer. <IMAGE>

Description

SPECIFICATION Temperature regulation method for building materials The present invention relates to a method of regulating the temperature during the production of building materials.

It has been found that the processing or starting temperature of a hydraulically or thermoplastically setting composition, that is to say that temperature at which the concrete mortar or a bituminous hot plant mix, for example, leaves the mixer and is supplied for processing, has a considerable influence on the quality of the end product.

Thus it has been found that the starting temperature of the concrete is proportional to the early removal strength, that is to say that strength which the concrete must have attained in order to be able to be stripped.

It has further been found that it is of great importance for freshly mixed or hardened concrete to adhere to a constant temperature at all points of the structure to be erected. A prerequisite for this is that the temperature of the freshly mixed concrete of each batch is the same on average. The latter is to be understood to mean that in the case of a relatively long bridge girder for example, in which the first batch has already cooled, the last batches are adjusted to be cooler according to the cooling of the initial section so that the temperature of the bridge girder is substantially equal over its length and so the risk of cracking, as a result of temperature differences in the concrete which is not yet completely hardened, is largely avoided.

In the case of bituminous hot plant mix, it has likewise been found that adhering to a specific temperature of the plant mix has an important influence on the quality of the bituminous pavement produced from such a plant mix. Thus too high a temperature of the plant mix leads to oxidation of the butumen and hence to embrittlement of the pavement and also leads to difficulties in the compression of the surfacing, whereas too low a temperature of the plant mix leads to surfacings of poorer quality with numerous cavities.

It is the object of the invention to provide a method which obviates or reduces the above difficulties and ensures the production of a plant mix which can be processed in the optimum manner.

According to the invention, there is provided a method of regulating the temperature during the production of building-material compositions, wherein the substances corresponding to a predetermined formula are mixed together and heat is supplied or removed comprising the steps of, during the whole preparation, measuring accurately and without cohtact the temperature of the mix, either at short intervals in the region of 0.5 to 30 sec or continuously, calculating therefrom the amount of heat to be added or subtracted in order to reach the required processing temperature of the composition, and supplying or removing either an amount of heat less than the calculated value, the amount approaching the calculated value asymptotically, or the whole amount of heat corresponding to the calculated value at one time.

In the above manner, the temperature of the finished mix can be brought to a very accurate value.

In particular, the method embodying the invention avoids hunting about the desired temperature, which might otherwise lead to an unequal temperature distribution in the finally mixed composition.

As a result of the very precise adherence to a predetermined temperature of the finished mixing according to the method of the invention, it is possible, in the case of concrete, to achieve a defined early removal strength, as a result of which the possibility is afforded of beginning the stripping of the article produced from the concrete after a precisely predetermined period of time.

In the case of a butuminous hot plant mix (bitumen concrete) there is the advantage according to the method of the invention that an oxidation of the bitumen is reliably avoided because the necessary temperature of the mix is never exceeded and after only a few passes a bituminous surfacing of high quality and constant cavity content can be achieved. In addition, as a result of the method according to the invention, an optimum use of energy results and because of the satisfactory processability of the mix a considerable saving in time during the compression of a bituminous surfacing also results.

As a result of the asymptotic supply of an amount of heat reduced or increased by a fraction, the amount(s) of heat necessary to achieve the required processing temperature can be supplied with an accuracy better than 1 1%. In the calculation of the amount of heat to be supplied, the uncertainties in the weighing in of the aggregates, of the water etc. are included in the total error in accordance with the error propagation law. In order to reduce to a minimum the influence of these errors which, with the necessary amounts, may amount to more than 1%, and to prevent excessively high processing temperatures (starting temperatures) from resulting because of these Gaussian errors, this reduction or increase in the amount of heat to be supplied can be selected in fractions.The same advantages can be achieved in the case of compositions in which the mixing temperature of the substances used is above the processing temperature of the finished composition. As a result, a far-reaching approximation of the temperature to the required temperature is reached quickly. The same effect is also achieved if, in the case of compositions in which the mixing temperature of the substances used is above the processing temperature of the finished composition, an amount of heat which is less by about 1 0% than is calculated on the basis of the instantaneously measured temperature of the composition is always removed, for example by the addition of ice water.

It should be assumed to be known that each mix is not absolutely like the preceding one or the following one, except in the formula. The base materials freely exposed to the weather in the course of the day, will change in composition depending on temperature, rain and air humidity and the amount, as weii as speed of use will produce different temperature conditions in the mixer. The water temperature alters, the aggregate temperature alters. The volume of the thermal energy to be supplied for the reaction must therefore be constantly adapted to these conditions.

For the starting of the hydration or of the cement crystallisation, and so for the course of hardening of the concrete, the temperature of the freshly mixed concrete is a functional criterion. It is equally decisive for the values of the early strength, the removal strength, the freezing strength depending on time for storage in the open, for the storability and ultimately for the economy of formwork, handling and utilization of space. The required values are fixed.

Since the temperature of the freshly mixed concrete and the heat of hydration are functionally dependent on electrochemical processes, it is possible to determine empirically which temperature of the freshly mixed concrete leads to the most economical starting situation in the production of cement concrete. The temperature conditions of the mix can be determined continuously and can be printed out through a recorder or signals can be given either optically/acoustically for a manually operated or automatically with direct pulse delivery to a final control element. As a result, it becomes possible not only to achieve precisely any required temperature of the freshly mixed concrete but to adhere to this precisely controlled from one mix to the next. The supply of steam does not replace the mixing water but serves to provide the starting temperature for the microprocess in the mix.Thus the method embodying the invention requires for the starting temperature of 270C of the freshly mixed concrete, starting from a water temperature of 80C instead of 50 C, a supply of energy in the form of steam of up to 6700 kcal/cubic metre of concrete, with the following concrete formula: Quality = B 550, fresh density = 2473 kg/m3 cement = 440 kg/cm3, W/Z = 0.43, water = 188 kg/m, aggregates = 1 830 kg/m3.

Once set to the temperature of the freshly mixed concrete, the installation controls this constantly for mix after mix. With this technical equipment, therefore, it is possible to draw the greatest possible use from the absolute minimum amount of cement.

The increase in and precise control of the starting temperature causes a more rapid start of the concrete hardening and avoids negative effects for the cement crystallisation which occur with other techniques.

An embodiment of the invention will now be more particularly described by way of example and with reference to the accompanying drawings, in which: Fig. 1 shows a block diagram of a device which is suitable, in particular, for the production of hardening compositions with relatively low processing temperature; and Fig. 2 shows schematically a device for producing hot plant mix.

In the form of embodiment shown in Fig. 1, the mix present in the mixer 1 is monitored by an infrared detector 2 disposed near a closable opening of the mixer 1, the infrared detector 2 being at a distance of about 1 to 2 m from the mix. In order to eliminate any influence of water vapour or CO2 during the measurement, it has proved particularly advantageous to operate the infrared detector in the 8--14 ym band. A suction device may appropriately be provided in the vicinity of the closable opening in order to avoid soiling of the infrared detector 2. The accuracy of the temperature measurement with the infrared probe should amount to about + 0.2 OC with a temperature range to be detected between 30 and 500C and a measuring time of 0.5 s.The infrared detector 2 is connected to a computer ,u, and a reference value indicator 3 is provided for adjusting purposes.

The computer y is further connected to a director 4 and a printer 5 serving as an indicating device.

Furthermore, the computer y is supplied with analogue signals which correspond to the temperatures of the individual components of the mix to be mixed and the computer predetermines the heat content of the mix in accordance with the algorithm: Q = Mj * Cj * (t0-t1) + Mzu * q + Q* in which Q= heat content lacking in the mix i = component i, for example aggregates, cement, water bitumen etc.

Mj = mass of the component Cj = specific heat of the component to = desired temperature of the mix after the end of the mixing operation tj = initial temperature of the component Mzu = mass of the aggregates q = heat of fusion of the water (in the case of frozen components) 0* = additional amount of heat in the case of a bituminous mix, which takes into consideration the fact that the temperature in the drying drum must be higher than to in the mixer.

The computer ,tt delivers a signal, which is influenced by the actual value which is detected by the detector 2, and the desired value, to the final control elements 6, 7 which either regulate automatically the supply of steam and/or ice water from storage devices 8 to the mixer 1 or permit an adjustment by hand. Particularly for the latter case, it is provided that in the event of an actual value different from the desired value beyond a certain value, signal devices S are activated by the computer.

The form of embodiment illustrated can also be modified in such a manner that disposed close to the discharge openings of the storage containers, in which are stored the individual substances to be processed to form the mix, are further temperature measuring instruments, such as infrared detectors for example, which are connected to the computer and which supply signals corresponding to the temperatures of the individual substances to the computer.

This calculates the heat content lacking in the mix, for example in a concrete mortar, in the production of which no frozen constituents are used, according to the formula: Q= M1 C, (tsoll-t1) + M2 - C2 (tsollt2) + Mn C0 (tsoll-t0).

In this M, signifies the mass, C1 the specific heat of cement and t1 that temperature at which the cement is supplied to the mixer, M2,C2 and t2 are the corresponding values for the water to be added and M,, Cn, t0 the corresponding values for the aggregates and tsoll that temperature which the finished mix should have.

In order to cover this lacking heat content Q, a mass of steam (mass of ice) Q MD heat content of the steam (ice) is necessary.

In any case, however, the whole amount of steam (ice) calculated is not supplied immediately, but a value which is less by about 10% and after an appropriate waiting time, ever smaller masses of steam (masses of ice) are supplied. The desired values of these latter masses of steam, that is to say those values A Which would be sufficient to bring the mix to the desired temperature are calculated from the formula: Q* A MD = heat content of the steam in which Q* signifies the heat content of the mix which is still lacking, for which: 0* = m c (tsoll-tgem) in which m = mass of the mix c = average specific heat of the mix tsoll = desired temperature of the mix tgem = measured temperature of the mix.

The actual values of the masses of steam thus added step by step are less by about 1 0% than the particular values A MD which are valid.

The temperature of the mix therefore approaches the required temperature tsoll of the mix from below (or, if the temperature of the substances to be mixed is above the required temperature of the mix, from above).

The particular amount of heat or masses of steam supplied can be controlled by hand or regulated by the computer which processes the detected values at appropriate intervals of time and causes the corresponding influencing of the final control elements 6, 7.

Referring now to Fig. 2, bunkers 10 are provided for various aggregates, the discharge openings 11 of which are disposed over a conveyor belt 12. From this conveyor belt 12, the aggregates, which are conveyed on the conveyor belt 12, pass via a bucket elevator 1 3 to a drier 1 5 fired by a burner 14, and through which they are moved.

The sorted aggregates pass via a further bucket elevator 1 6 into a bunker 1 7 from which they pass, according to the formula of the composition to be produced, via a further conveyor belt 1 8 to the mixer 4' in which they are mixed with hot bitumen, the bitumen being supplied from a separately heated bunker 20.

Disposed near the discharge opening or a separate opening in the mixer 4' is an infrared detector 2 which detects the temperature of the hot mix from a distance of 1 to 2 m and is connected to the computer,u. The accuracy of the temperature measurement with the infrared probe should amount to about + 1 % of the detected temperature with a temperature range to be detected of 160-1 800C and a measuring time of 0.5 s. The computer u is also connected to further temperature measuring instruments, such as infrared detectors 2', for example, detecting the temperature of the aggregates and of the bitumen, and controls the burner 14 and hence the supply of heat to the hot mix.

Because of the deficit in heat content of the aggregates, heat must be supplied to the aggregates via the burners so that QzSOII is present in the mixer. The corresponding heat content is calculated from the formula: Qzu = MZU Cz'u (tsoll--te,,) + Q*zu in which: Mzu = mass of the aggregate c' specific heat of the aggregate tgem= measured temperature of the aggregate i (with 2') tsoll = desired temperature of the hot mix Q: that amount of heat which the aggregates lose again between burner and mixer, its magnitude is specific to the installation and is determined by external influences such as weather, time of day, season of the year etc.

The computer ju calculates this additional heat content Qzu necessary, on the basis of the measured data, with the above formula and in accordance therewith regulates the burner output or burning period of the burner according to the stored burner characteristic.

Furthermore, a continuous comparison of the desired temperature of the hot mix with the actual temperature of the hot mix detected by the infrared detector 2 is effected by the computer. If the actual temperature deviates from the desired temperature or from a predetermined tolerance range, the computer delivers correction signals for a further burner regulation.

The desired temperature t601 of the mix, referred to in the above connection, can but does not have to correspond to the processing temperature tv of the mix. Particularly in the case of producing bituminous surfacings, there may be a spatial distance of up to 10 km for example between the compacting operation, that is to say the production of the bituminous surfacing and the production of the hot mix in an installation as shown in Fig. 2. During the compacting operation, however, in order to achieve optimum results, a very specific processing temperature of 125-1 450C for example should be adhered to.In order to ensure this, in a further development of the invention, the compacting machines may be equipped, for example in the region of the compaction rollers, with at least one temperature measuring instrument, for example an infrared detector for the measurement of the temperature of the hot mix. The output signal of this temperature measuring instrument is radioed to the computer y which selects from a conformity table the desired temperature tsoii corresponding to this processing temperature and uses it as a basis for the calculating operation. In Fig. 2, this additional temperature measuring instrument and the associated transmitter and receiver unit is designated by 21, 22 and 23.

Thus, through the invention, too high or too low a temperature of the hot plant mix can be avoided, too high a temperature, causing increased oxidation of the bitumen, leading to an embrittlement of the applied bituminous surfacing, which corresponds to a free exposure to the weather of about 5 years, and too low a temperature leading to difficulties in compacting the surfacing, that is to say, to an increased cavity content and hence to a lower quality of the surfacing.

As a result of adjusting the required optimum processing temperature, a bituminous surfacing of high quality and constant cavity content is achieved with the optimum use of energy and as a result of the satisfactory compactability with a few passes.

In the same way as in the example of embodiment shown in Fig. 2, it is possible with that shown in Fig. 1 to adapt the desired temperature to the actual processing temperature. The temperature measuring instrument is there designated by 24, the transmitting and receiving unit by 25 and 26. In this case, the temperature measuring instrument 24 may appropriately be mounted adjacent to the discharge opening of a transport vehicle and the measurement is measured immediately before or during the output of the steam-cured concrete at the building site. Measurement via a separate opening in the transport container is naturally possible in the same manner. As a result of this additional possibility of adapting the desired temperature to the processing temperature of the mix, there is also the possibility, particularly in the provision of structures in which the introduction of the concrete extends over a relatively long period of time, of taking into consideration the lapse of time with regard to the incipient setting, that is to say the individual batches of concrete can be introduced with appropriately graduated processing temperatures in view of the setting of the first batches introduced.

which has already begun.

Claims

1. A method of regulating the temperature during the production of building-material compositions, wherein the substances corresponding to a predetermined formula are mixed together and heat is supplied or removed comprising the steps of, during the whole preparation, measuring accurately and without contact the temperature of the mix, either at short intervals in the region of 0.5 to 30 sec or continuously, calculating therefrom the amount of heat to be added or subtracted in order to reach the required processing temperature of the composition, and supplying or removing either an amount of heat less than the calculated value, the amount approaching the calculated value asymptotically, or the whole amount of heat corresponding to the calculated value at one time.

2. A method as claimed in claim 1, wherein, in the case of a composition in which the mixing temperature of the substances used is below the required processing temperature of the finished composition, an amount of heat which is less by a fraction, for example by 1/10th, than is calculated as a result of the instantaneously measured temperature of the composition, is supplied or its supply is increased by such a fraction.

3. A method as claimed in claim 1, wherein, in the case of compositions in which the mixing temperature of the substances used is above the processing temperature of the finished composition, an amount of heat which is less by a fraction, for example by 1/10th, than is calculated as a result of the instantaneously measured temperature of the composition, is removed, for example by the addition of ice water.

4. A method of regulating the temperature of building materials substantially as herein described with reference to the accompanying drawings.

5. An apparatus for carrying out the method as claimed in any one of claims 1 to 4, comprising a mixer to mix the individual substances of the composition, to which the individual substances can be supplied from separate storage containers and which comprises a discharge opening for the finished mixed composition and a feed device for the feed of a heat-surrendering and/or heat-absorbing medium, an infrared detector disposed near a closable opening of the mixer and at a distance from the mix, a computer connected to the detector, a director acting on the computer, at least one indicating device, for example a printer connected to the computer and/or one or more signal devices connected to the computer, the devices being activatable on exceeding or dropping below certain limiting values, a device for the supply and/or removal of heat from the mix, and a temperature measuring instrument located at the processing site, and connected to the computer.

6. An apparatus as claimed in claim 5, wherein the computer is connected to control members for the control of final control elements actuating the supply of steam or ice water to the mix.

7. An apparatus as claimed in claim 6, wherein the computer is formed by a microprocessor and delivers signals, corrected according to the actual value of the temperature of the mix, to the final control elements to control the supply or removal of heat to or from the mix.

8. An apparatus for regulating the temperature of building materials substantially as herein described with reference to the accompanying drawings.