EP2637830A1

EP2637830A1 - Controlled curing of concrete

Info

Publication number: EP2637830A1
Application number: EP11817425.9A
Authority: EP
Inventors: Jos Kronemeijer
Original assignee: Van Hattum En Blankevoort BV
Current assignee: Van Hattum En Blankevoort BV
Priority date: 2010-11-08
Filing date: 2011-11-08
Publication date: 2013-09-18
Also published as: WO2012081975A1; NL2007738C2; NL2007738A

Abstract

Method for the production of a component of cement concrete with preferably reinforcement in a mould, preferably a thick walled massive structure outdoor, wherein a pipe is located into the mould and the from free concrete is poured over it such that said pipe is embedded into the concrete, preferably at least 20 centimetre below the concrete surface, and wherein through said pipe a heating or cooling liquid or gas like fluid is flown such that the concrete is from the inside and in a controlled manner heated or cooled by the fluid while the concrete cures to its final strength.

Description

Controlled curing of concrete.

The invention relates to a specific method for production of a concrete structure and such.

5 When producing a structure from concrete a mould is applied limiting a space into which first a reinforcement is located and after that the concrete slurry is poured. The mould remains in position until the concrete is sufficiently cured and rigid. Since the mould is costly, the structure needs as quickly as

10 possible be demoulded such that the mould can be used again.

The concrete is an initially form free artificial stone like material with mineral cement as binder and mineral aggregates like sand and gravel which after curing offers a high compression strength and possibly contains an internal

15 reinforcement of e.g. steel rods.

During curing of the concrete heat is generated due to the chemical reactions. Particularly with thick walled and massive structures, e.g. a tunnel wall or pillar bar, internal area's are present where, if with typical cements conform EN

20 197-1 no cooling is applied, the temperature can raise too high, e.g. can become 65 to 80 degrees Celsius. The result can be too low concrete compressive strength, delayed sulphate degradation, too high tension stresses and thus crack formation in the cured concrete .

25 With further curing the speed of the chemical reaction decreases such that the temperature lowers. At that time however the strength and consistency of the concrete are such that the curing concrete externally starts to shrink, such that internal tension stresses are generated.

30 With large temperature differences between concrete core and surface these tension stresses will rise to a high level such that shrink cracks will be easily generated. Shrink cracks and above mentioned effects degrade the functionality and durability of the structure.

35 On the other hand the form free concrete during curing may not become too cold since otherwise curing will take too much time. Reason why at cold weather concrete is poured which in the concrete factory is preheated to a temperature between 15 and 20 degrees Celsius. Some structures, such as tunnel elements, are produced in parts, e.g. the bottom first, then the upright walls and finally the roof. Thus a next part is made against an already cured and cooled part. Also this is a reason why easily shrink cracks and high internal tension stresses and thus shrink cracks develop e.g. in the area from the location of adhesion in the direction of the cured and cooled part.

NL9500383 discloses a mould provided with a heat exchanger through which a cooling liquid circulates, such that during curing the concrete is externally intermittently cooled and heated. For thick walled structures external cooling is however no solution.

For thick walled structures it is known to apply internal cooling pipes, through which cooling liquid circulates with which during curing generated heat is directly from the core transported to the outside of the structure to thus keep the temperature of the core sufficient low.

With the invention a further improvement is desired for controlled curing of a thick walled massive structure of concrete, also in situations wherein the structure is made in parts wherein the concrete for a next concrete part is poured against an earlier made and already cured concrete part. The object is both structures produced on site and/or outdoor, and also structures produced in the factory where the process conditions, among which the application conditions, can be better controlled.

The object of the invention is versatile and is, among others, one or more of the following aspects: limiting the peak temperature during curing such that delayed sulphate degradation and strength decrease will not arise; decrease the risk for crack formation and tension stresses in the cured concrete such that structures remain homogeneous and water tight; advancing of the time of initial binding of concrete slurry at cold weather such that preheated concrete slurry shall not be required; speeding curing of fresh concrete after the chemical hydration reaction is mainly finished and the curing rate due to cooling down of the structure to environmental temperatures will slow down naturally; obtaining a more durable, high quality cross section of the concrete structure.

Thus inside the mould a mutually connected system of water/liquid transporting pipes is installed which is embedded into the form free concrete, such that said pipes are embedded into the concrete slurry and through said pipes a heating or cooling liquid or gas like fluid is flown such that the concrete is heated from inside or cooled by this fluid.

In an embodiment heating and cooling fluid is sequentially flown through the same embedded pipes or separated embedded pipes, possibly with an intermediate time during which no purposeful cooling or heating fluid flows through said pipes. During and/or after pouring the form free concrete e.g. first a heating fluid is supplied to rise the temperature of the concrete from e.g. 5 to 20 degrees Celsius, after which there is some delay time and subsequently cooling fluid is supplied to lower the rising temperature of the concrete or avoid further rising of it, after which e.g. heating fluid is again supplied.

E.g. with the through the pipe flowing fluid with at least 5 or 10 degrees temperature difference with the temperature of the concrete core, one or more of the following is done: step a: during and/or immediately after pouring fresh concrete during approximately or at the most or at least 4 or 6 or 8 or 10 or 12 hours heating (fluid hotter than concrete core); step b: during approximately or at the most or at least 40 or 50 or 60 or 70 or 80 hours cooling (fluid colder than concrete core) ;

step c: during approximately or at the most or at least 80 or 90 or 100 or 120 or 140 hours heating (fluid hotter than concrete core) ;

possibly between step a and b and/or between step b and c a time without forced cooling or heating during approximately or at the most or at least 6 or 8 or 10 or 12 hours;

two or more of steps a to c follow each other in one of the different feasible successions, preferably first step a, then step b and finally step c.

E .g step a : 8 hours heating with at least 10 degrees Celsius temperature rise; step b: 60 hours cooling with at least 10 degrees Celsius cooling, step c: 120 hours heating with at least 20 degrees Celsius heating, between step a and b and between step b and c a time without forced cooling or heating during 5 8 hours .

It is preferred to apply one or more of the following (claims 7 to 12) :

- wherein the time of the initial binding is advanced at cold weather by flowing heating fluid through the pipe during or

10 after pouring concrete, preferably during at least four or ten or twenty hours ;

- wherein for virgin concrete by flowing heating fluid through the pipe after pouring concrete and after the chemical hydration reaction is mainly, substantially or for at least 80% finished

15 and the curing rate due to cooling of the structure to

environmental temperatures will slow down naturally, the curing of the virgin concrete substantially accelerates;

- wherein during or after pouring concrete the temperature of the concrete is increased from 5 to 20 degrees Celsius or with

20 15 degrees Celsius by the through the pipe flowing fluid;

- wherein the inlet temperature of the heating fluid measures between 20 and 40, such as between 25 and 35, and/or of the cooling fluid between 5 ad 15, such as approximately 10, degrees Celsius ;

25 - wherein during and/or after pouring concrete heating fluid and subsequently cooling fluid and subsequently possibly heating fluid is flown through the pipe while the concrete cures to its final strength;

- wherein the forced cooling or heating is carried out by during 30 at least 4 hours or 10 hours or two clear days (48 hours) flowing the fluid through the pipe.

On the one hand the fluid can be flown through the pipes during the time that the concrete is not sufficient cured, e.g. to activate the concrete slurry in its binding early in its 35 chemical reaction, or to avoid that the concrete becomes too hot, followed by again circulating with which the chemical reactions are stimulated again, e.g. to speed the after curing by the supply of external heat to internally of the concrete slurry, or for decreasing the risk for crack formation by decreasing the temperature difference in the mass cross section or between the already cured, cooled part and the freshly concreted against part of an in parts produced concrete structure .

In an embodiment temperature sensors are used with which the temperature of the concrete is measured, on the basis of which measured data the flowing of the fluid through the pipe and the temperature (e.g. the inlet temperature, i.e. with which the fluid enters the embedded pipe) of the fluid is controlled. The temperature and flow of the fluid are preferably computer controlled and the sensors are connected to the same control unit. Preferably one or more temperature sensors are embedded into the concrete, e.g. by locating such a sensor into the mould after which the form free concrete is poured into the mould such that the sensor is embedded into the concrete. By embedding more than one sensor a temperature gradient can be measured, by way of which the heating and cooling can be optimised.

The heating fluid has preferably a temperature between approximately 20 and 40, more preferably between approximately 25 and 35 degrees Celsius. The cooling fluid has preferably a temperature between approximately 5 and 15, such as approximately 10 degrees Celsius.

The pipe is preferably made of steel or polymer, such as polyethylene .

In an example outside the mould there are a pump, a supply bin, a cooling and heating unit and a computer controlled control unit . The computer runs a program and starts and stops on the basis of that the pump and the cooling and heating unit, wherein the program makes use of the by the temperature sensors supplied signals. The pump circulates the fluid between the supply bin and the embedded pipe. Depending from cooling or heating the concrete, the cooling or heating unit is engaged. Dependent from the with the sensors determined temperature gradient, possibly corrected by environmental temperature, through the program the flow speed and the inlet temperature of the fluid are automatically set.

The computer could be part of a network, such that logging in to the computer from a remote location can be possible to enter control data or request for measured data .

Claims

Claims 1. Method for the production of a component of cement concrete with preferably reinforcement in a mould, preferably a thick walled massive structure outdoor, wherein a pipe is located into the mould and the from free concrete is poured over it such that said pipe is embedded into the concrete, preferably at least 20 centimetre below the concrete surface, and wherein through said pipe a heating or cooling liquid or gas like fluid is flown such that the concrete is from the inside and in a controlled manner heated or cooled by the fluid while the concrete cures to its final strength.

2. Method according to claim 1 wherein temperature sensors are used with which the temperature of the concrete is measured, on the basis of which measured data the flowing of the fluid through the pipes and the temperature of the fluid within the pipe is controlled.

3. Method according to claim 2, wherein the temperature and flow of the fluid are computer controlled by the control unit and the sensors are connected to the same control unit.

4. Method according to claim 2 or 3 , wherein the one or more temperature sensors ere embedded into the concrete, e.g. by locating such sensor into the mould after with the form free concrete is poured into the mould such that the concrete is poured over the sensor.

5. Method according to claim 2, 3 or 4 , wherein more than one sensor is embedded and with said two or more sensors a temperature gradient is measured which is used by the control unit to control the flow of the fluid through the pipe and the temperature of the fluid within the pipe.

6. Method according to any of the preceding claims, with outside the mould a pump, a supply bin, a cooling and heating unit and a computer controlled control unit running a program and on the basis of that starts and stops a pump and the cooling and heating unit, wherein the program possibly makes use of the by the temperature sensors supplied signals.

7. Method according to any of the preceding claims, wherein the time of the initial binding is advanced at cold weather by flowing heating fluid through the pipe during or after pouring concrete, preferably during at least four or ten or twenty hours .

8. Method according to any of the preceding claims, wherein for virgin concrete by flowing heating fluid through the pipe after pouring concrete and after the chemical hydration reaction is mainly, substantially or for at least 80% finished and the curing rate due to cooling of the structure to environmental temperatures will slow down naturally, the curing of the virgin concrete substantially accelerates.

9. Method according to any of the preceding claims, wherein during or after pouring concrete the temperature of the concrete is increased from 5 to 20 degrees Celsius or with 15 degrees Celsius by the through the pipe flowing fluid.

10. Method according to any of the preceding claims, wherein the inlet temperature of the heating fluid measures between 20 and 40, such as between 25 and 35, and/or of the cooling fluid between 5 ad 15, such as approximately 10, degrees Celsius .

11. Method according to any of the preceding claims, wherein the following steps are applied by cooling or heating fluid, of which the temperature at least 10 degrees Celsius differs from said of the concrete core, is flown through the pipe while the concrete cures to its end strength: step a: during and immediately after pouring of fresh concrete during at least 6 and at the most B hours heating with at least 10 degrees Celsius temperature rise;

step b: during at least 50 and at the most 60 hours cooling 5 with at least 10 degrees Celsius temperature drop,- step c: during at least 100 and at the most 120 hours heating with at least 20 degrees Celsius temperature rise;

with between step a and b and between step b and c a time without forced cooling or heating during at least 6 and at the most 10 10 hours;

first step a, subsequently step b and finally step c are carried out .

12. Method according to any of the preceding claims, wherein 15 the forced cooling or heating is carried out by during at least

4 hours or 10 hours or two clear days (48 hours) flowing the fluid through the pipe.

13. Method according to any of the preceding claims, to in 20 parts produce a tunnel element of concrete by pouring fixedly to each other the parts bottom, upright walls and roof, wherein the tunnel element has a wall thickness of at least 80 centimetre and is produced in a mould, wherein for each part in the mould a dedicated pipe of steel or polymer, such as polyethylene,

25 is located which is poured over by the form free concrete, such that said pipe is embedded within the concrete and is located at a depth of at least 20 centimetre below the concrete surface and wherein the concrete is cured until said part is sufficient rigid after which the mould is removed, wherein each next part

30 is produced by the concrete slurry of it pouring against an already cured and cooled and demoulded part such that the fresh concrete slurry adheres itself to the already cured concrete such that finally an integral tunnel element is made, and wherein, after the concrete slurry for the next part is poured 35 against the prior, demoulded part, heating flowable fluid having a temperature of 30 degrees Celsius is flown through the pipe within the prior, demoulded part against which the concrete slurry for the next part is poured, to heat the prior, demoulded part from within to provide a temperature rise of approximately 20 degrees Celsius during the curing time until the concrete of the concreted against next part is sufficiently cured to be sufficient rigid, after which this next part is demoulded, while during the same curing time cooling flowable fluid with a temperature of 10 degrees Celsius is flown through the pipe within the next part to cool this next part from the inside to remove the during curing of the concrete slurry by the occurring chemical reactions released heat while also during pouring concrete temperature sensors are simultaneously poured over with concrete with which during through the pipes flowing of fluid during said curing time the temperature of the concrete is internally measured, on the basis of which measured data the flow of the fluid through the pipe and its inlet temperature are controlled by the control computer.