Temperature control method based on mass concrete multi-layer pouring and peak shifting heat release

Abstract

A temperature control method based on mass concrete multi-layer pouring and off-peak heat release utilizes the characteristic that the time that delayed coagulation type concrete starts to generate hydration heat release temperature rise is later than that of non-delayed coagulation type concrete, so that the heat productivity of the concrete is reduced and the heat dissipation area is increased within the same time, and meanwhile, the mass concrete is kept at a relatively high temperature for a relatively long time on the whole; the overall temperature is more uniform, so that the purpose of reducing the temperature gradient and the temperature stress of the mass concrete is achieved. Compared with an existing mass concrete temperature control method, the novel mass concrete temperature control technology is simple and convenient in process, low in cost and high in applicability and operability.

Description

Technical Field

[0001] The invention belongs to the field of construction, and particularly relates to a temperature control method for mass concrete. Background Art

[0002] With the progress and development of society, while concrete is developing towards high strength and high performance, the difficulty of concrete crack control technology has also greatly increased. The increase in cement consumption, the decrease in cement fineness, and the use of various admixtures and additives have increased the early heat release and shrinkage of concrete, making the crack problem of large-volume concrete more serious.

[0003] Massive concrete structures have large cross-sections and poor thermal conductivity. During the warming phase, internal hydration heat creates a temperature difference between the inside and outside of the concrete. The shrinking exterior is constrained by internal thermal expansion and placed in tension. When the tensile stress exceeds the concrete's ultimate tensile strength, cracks form on the surface. During the initial cooling and contraction phase, the concrete is constrained by the foundation or adjacent components, generating tensile stress within the concrete. When the tensile stress exceeds the concrete's ultimate tensile strength, cracks develop on the constrained surface.

[0004] Numerous engineering crack treatments and investigations have shown that 80% to 90% of cracks in concrete structures, especially large-volume concrete structures, are caused by tensile stresses generated by cooling the concrete exceeding its tensile strength. Therefore, crack control in large-volume concrete begins with temperature control, minimizing the internal and external temperature differences and reducing thermal stresses. Second, timely crack repair is crucial for crack control in large-volume concrete.

[0005] At present, the main methods used in engineering projects are to reduce the hydration exothermic temperature rise by adding a large amount of mineral admixtures, pre-buried cooling water pipes, surface covering insulation, adding retarders to delay the hydration heat release rate, using phase-change expanded clay, using temperature-inhibiting admixtures, etc., thereby reducing the thermal shrinkage cracking of large-volume concrete. However, concrete with a large amount of admixtures still has the problem of excessive hydration exothermic temperature rise; the construction cost of pre-buried cooling water pipes is relatively high; surface covering insulation, adding retarders and temperature-inhibiting admixtures all lead to extended construction period, and when simply using retarders, although the peak of the hydration exothermic temperature rise is shifted, it cannot effectively reduce the temperature rise peak in many cases; the cost of using phase-change expanded clay is also high, and there are problems such as reduced concrete strength. Therefore, it is necessary to further develop efficient temperature control technical means and measures for large-volume concrete, so as to economically and efficiently reduce the temperature gradient of large-volume concrete and prevent thermal shrinkage cracking. Summary of the Invention

[0006] In order to overcome the shortcomings of the existing technology, the present invention provides a temperature control method based on multi-layer pouring and staggered heat release of large-volume concrete. The method utilizes the characteristic that retarded concrete using zinc hydroxide as a retarder begins to generate hydration heat and temperature rise later than non-retarded concrete. Therefore, the heat generation of concrete is reduced and the heat dissipation area is increased within the same period of time. At the same time, the overall high temperature of the large-volume concrete is maintained for a longer time, and the overall temperature is more uniform, thereby achieving the purpose of reducing the temperature gradient and temperature stress of the large-volume concrete.

[0007] The technical solution adopted by the present invention to solve its technical problem is:

[0008] A temperature control method based on multi-layer pouring of large-volume concrete and staggered heat release, comprising the following steps:

[0009] Step 1: Determine the cement hydration exothermic curve through experiments, and based on this curve, use finite element simulation software to simulate the center temperature curve of large-volume concrete from the completion of pouring;

[0010] Step 2: Based on the simulated temperature curve of the mass concrete center, determine the time when its temperature drops to 15°C above the ambient temperature;

[0011] Step 3: Determine through experiments that different retarder dosages can prolong the cement hydration induction period;

[0012] Step 4: Support the formwork according to the construction drawings and formwork construction plan, mark the inside of the side formwork, and divide the formwork evenly into several parts of reasonable thickness along the vertical direction;

[0013] Step 5: Pour concrete using a pumping pipe in the same manner as pouring large-volume concrete;

[0014] Step 6: When one layer is poured, that is, when the thickness of the poured concrete reaches the position marked in step 1, stop pouring;

[0015] Step 7: Change the type of pumped concrete to slow-setting concrete and repeat step 6;

[0016] Step 8: Change the type of pumped concrete to non-slow-setting concrete and repeat step 6;

[0017] Step 9: Repeat steps 7 and 8 in turn until the large volume concrete pouring is completed.

[0018] Furthermore, the implementation method of step 4 is: determine the thickness of each layer of concrete determined by the marking on the side of the side formwork according to the construction data, the size of the large-volume concrete and the construction equipment. The thickness of each layer should generally not be less than half the length of the vibrating rod and should not be greater than 500mm.

[0019] Furthermore, the following requirements are imposed on step 7: the amount of retarder in the retarded concrete used in step 7 must satisfy the following requirement: the time when the retarded concrete begins to experience hydration temperature rise in step 7 must be later than the time when the hydration heat release of the non-retarded concrete ends, and at least after the temperature of the non-retarded concrete drops to 15° C. above the ambient temperature.

[0020] Preferably, the hydration temperature rise of the slow-setting concrete starts when the temperature of the non-slow-setting concrete layer has dropped to within 15° C. above the ambient temperature.

[0021] Furthermore, the implementation method of step 9 is as follows: the top layer of concrete of the poured large volume concrete must be non-slow-setting concrete.

[0022] The application scope of the large-volume concrete temperature control technology is: large-volume concrete with a minimum geometric dimension of a concrete structure of not less than 1m, and is applicable to concrete with a thickness of not less than 1m.

[0023] Preferably, the mass concrete temperature control technology is applicable to various mass concretes with a strength of C30 and above.

[0024] Preferably, the retarder is zinc hydroxide.

[0025] The beneficial effects of the present invention are mainly manifested in the following: 1. By alternately pouring slow-setting and non-slow-setting concrete in layers, the present invention reduces the heat generated by large-volume concrete in the same period in a relatively simple and low-cost manner, increases the heat dissipation area of large-volume concrete, and reduces the temperature gradient of large-volume concrete, thus overcoming the high cost and complex construction problems of existing technologies. 2. The present invention only requires the use of a pouring method of alternately pouring slow-setting and non-slow-setting concrete in layers to effectively reduce the temperature gradient of large-volume concrete in various situations, thus having a wide range of applications and high operability. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the process structure of the present invention;

[0027] Figure 2 This is the curve obtained by experimental simulation in step 1 of the present invention;

[0028] Figure 3 This is a schematic diagram of the operating method of step 4 of the present invention;

[0029] Figure 4 The calculation results of Example 1, where (a) is the simulation result of non-layered pouring, and (b) is the simulation result and center temperature curve of layered pouring;

[0030] Figure 5The calculation results of Example 2, where (a) is the simulation result of non-layered pouring, and (b) is the simulation result and center temperature curve of layered pouring. DETAILED DESCRIPTION

[0031] The present invention will be further described below with reference to the accompanying drawings.

[0032] Reference Figures 1 to 5 A temperature control method based on multi-layer pouring of large-volume concrete and staggered heat release includes the following steps:

[0033] Step 1: Determine the cement hydration exothermic curve through experiments, and based on this curve, use finite element simulation software to simulate the center temperature curve of large-volume concrete from the completion of pouring;

[0034] Step 2: Based on the simulated temperature curve of the mass concrete center, determine the time when its temperature drops to 15°C above the ambient temperature;

[0035] Step 3: Determine through experiments that different retarder dosages can prolong the cement hydration induction period, wherein the retarder is zinc hydroxide.

[0036] Step 4: Support the formwork according to the construction drawings and formwork construction plan, mark the inside of the side formwork, and divide the formwork evenly into several parts of reasonable thickness along the vertical direction;

[0037] The specific implementation method of this step is: determine the thickness of each layer of concrete determined by the markings on the side of the side formwork according to the construction data, large-volume concrete dimensions and construction equipment. The thickness of each layer should generally not be less than half the length of the vibrating rod and should not be greater than 500mm.

[0038] Step 5: Pour concrete using a pumping pipe according to the general method of pouring large-volume concrete;

[0039] Step 6: When one layer is poured (i.e. the thickness of the poured concrete reaches the position marked in step 1), stop pouring;

[0040] Step 7: Change the type of pumped concrete to slow-setting concrete and repeat step 6;

[0041] The following requirements apply to this step: The amount of retarder in the retarded concrete used in this step must satisfy the following requirements: the time when the hydration temperature rise of the retarded concrete begins in this step must be later than the time when the hydration heat release of the non-retarded concrete ends, and at least after the temperature of the non-retarded concrete drops to 5°C above the ambient temperature.

[0042] Step 8: Change the type of pumped concrete to non-slow-setting concrete and repeat step 6;

[0043] Step 9: Repeat steps 7 and 8 in turn until the large volume concrete pouring is completed.

[0044] The specific implementation method of this step is: the top layer of concrete of the poured large-volume concrete must be non-slow-setting concrete.

[0045] The following are two examples of this embodiment:

[0046] Example 1: There is a concrete column with a size of 0.3m*0.3m*3m. The cement consumption per cubic meter is 500kg. The bottom is in contact with the soil. The heat dissipation coefficient is 864J / h·(m 2 ·K), the top and surrounding areas are thermally insulated, and the heat dissipation coefficient is 3200J / h·(m 2 K), when using layered pouring, the heat release time of slow-setting concrete is set to 240 hours later than that of non-slow-setting concrete. The simulation results under the two construction methods and the temperature curves at the center of the component are shown in Figure 2. Figure 4 .

[0047] Example 2: There is a concrete base plate and upper wall. The base plate size is 4.8m*4.4m*3.0m. All sides are insulated. The heat dissipation coefficient is 0.549W / ·(m 2 ·K); the upper wall size is 4.8m*1.65m*3.0m, and all sides are insulated. The heat dissipation coefficient is 0.781W / ·(m2·K). The cement consumption per cubic meter of concrete is 300kg. When layered pouring is adopted, the heat release time of the slow-setting concrete is set after 240 hours of the non-slow-setting concrete. The heat release of the upper wall is not considered. The simulation results under the two construction methods and the temperature curves at the center of the component are shown in Figure 2. Figure 5 Obviously, this method is not effective when the second heat release begins without good cooling after the first heat release.

[0048] The embodiments of this specification are merely examples of implementations of the invention and are provided for illustrative purposes only. The scope of protection of the present invention should not be considered limited to the specific embodiments described in these embodiments. The scope of protection of the present invention also extends to equivalent technical means that can be conceived by a person of ordinary skill in the art based on the invention.

Claims

1. A temperature control method based on multi-layer pouring of large-volume concrete and staggered heat release, characterized in that: The method comprises the following steps: Step 1: Determine the cement hydration exothermic curve through experiments, and based on this curve, use finite element simulation software to simulate the center temperature curve of large-volume concrete from the completion of pouring; Step 2: Based on the simulated temperature curve of the mass concrete center, determine the time it takes for the temperature to drop to 5°C above the ambient temperature; Step 3: Determine through experiments that different retarder dosages can prolong the cement hydration induction period; Step 4: Support the formwork according to the construction drawings and formwork construction plan, mark the inside of the side formwork, and divide the formwork evenly into several parts of reasonable thickness along the vertical direction; Step 5: Pour concrete using a pumping pipe in the same manner as pouring large-volume concrete; Step 6: When one layer is poured, that is, when the thickness of the poured concrete reaches the position marked in step 1, stop pouring; Step 7: Change the type of pumped concrete to slow-setting concrete and repeat step 3; Step 8: Change the type of pumped concrete to non-slow-setting concrete and repeat step 3; Step 9: Repeat steps 4 and 5 in turn until the large volume concrete pouring is completed.

2. The temperature control method based on multi-layer pouring of large-volume concrete and staggered heat release according to claim 1, characterized in that: The implementation method of step 1 is: determine the thickness of each layer of concrete determined by the marking on the side of the side formwork according to the construction data, the size of the large-volume concrete and the construction equipment. The thickness of each layer is not less than half the length of the vibrator and not more than 500mm.

3. The temperature control method based on multi-layer pouring of large-volume concrete and staggered heat release according to claim 1 or 2, characterized in that: The following requirements apply to step 4: the amount of retarder used in the retarded concrete used in step 4 must satisfy the following requirement: the time when the retarded concrete begins to experience hydration temperature rise in step 4 must be later than the time when the hydration heat release of the non-retarded concrete ends, and at least after the temperature of the non-retarded concrete drops to 15°C higher than the ambient temperature.

4. The temperature control method based on multi-layer pouring of large-volume concrete and staggered heat release as claimed in claim 3, characterized in that: The end time point of the hydration temperature rise of non-retarded concrete is when the temperature of the non-retarded concrete layer has dropped to within 15°C above the ambient temperature.

5. The temperature control method based on multi-layer pouring of large-volume concrete and staggered heat release according to claim 1 or 2, characterized in that: The implementation method of step 6 is as follows: the top layer of concrete of the poured large volume concrete must be non-slow-setting concrete.

6. The temperature control method based on multi-layer pouring of large-volume concrete and staggered heat release according to claim 1 or 2, characterized in that: The application scope of the large-volume concrete temperature control technology is: large-volume concrete with a minimum geometric dimension of a concrete structure of not less than 1m, and is applicable to concrete with a thickness of not less than 1m.

7. The temperature control method based on multi-layer pouring of large-volume concrete and staggered heat release according to claim 1 or 2, characterized in that: The mass concrete temperature control technology is applicable to various mass concretes with a strength of C30 and above.

8. The temperature control method based on multi-layer pouring of large-volume concrete and staggered heat release according to claim 1 or 2, characterized in that: The retarder is zinc hydroxide.

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