Preparation method of low-hydration-heat concrete for preventing early cracks of wall

Abstract

The invention discloses a preparation method of low-hydration-heat concrete for preventing early cracks of a wall. According to the method, various measures are comprehensively adopted, and the method specifically comprises the steps that the hydration heat of a cementing material at the one-day age is limited to be not higher than 50 J / g, the hydration heat of the cementing material at the three-day age is limited to be not higher than 200 J / g, and the hydration heat of the cementing material at the seven-day age is limited to be not higher than 250 J / g; a high-quality air entraining agent is doped, and the air content is controlled within the range of 3%-5%; the retarder is doped, and the final setting time of the concrete under the same condition is controlled within the range of 12-20 hours, so that the hydration heat release rate is reduced, and the anti-cracking performance of the concrete is improved. Quantitative systematic control on key node values such as hydration heat of a cementing material, gas content of concrete and setting time of the concrete is innovatively proposed, so that early cracks of the concrete are effectively inhibited, and economical efficiency and construction convenience are taken into account at the same time. The method is suitable for a concrete wall structure with the strength grade of C30 to C40, aims to solve the problem of early cracks, and can provide reference for related preparation of concrete with higher strength grade.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of concrete, in particular to a low hydration heat concrete preparation method for preventing early cracks of wall body. BACKGROUND

[0002] The probability of early cracks in modern concrete wall body structure is relatively high, and the proportion of cracks caused by shrinkage deformation is more than 80%. The shrinkage deformation, temperature deformation and most of the drying shrinkage phenomenon all occur in the "early stage", therefore, controlling early shrinkage cracks is the key to preventing early cracks.

[0003] At present, the research results of crack control for large volume structure are quite rich, and the control methods are relatively specific and clear. However, the crack control measures for wall body structure are relatively general. The traditional crack prevention and control methods usually include adding expansion agent, fiber, or using silane-based permeable crystalline material to enhance the self-healing ability of the structure, etc. However, the implementation cost of such measures is relatively high, and the effect is not ideal.

[0004] In the concrete wall body structure, C30, C35 and C40 are the most common strength grades. Moreover, with the increase of strength grade, the probability of cracks will also increase. Therefore, how to effectively reduce the risk of early shrinkage cracks while ensuring the strength of concrete has become the focus of research.

[0005] For the characteristics of wall body structure, the present application proposes to use low hydration heat mix proportion design, mix in functional admixture and regulate setting time multi-means comprehensive method, to reduce the hydration heat release rate, improve the crack resistance and enhance the material toughness, innovatively proposes to quantitatively control the key node values such as hydration heat, air content and final setting time of cementitious materials, so as to effectively control the early cracks of concrete, and at the same time, the economy and construction convenience are considered, the present application is suitable for concrete wall body structure with strength grade between C30 and C40, to solve the problem of early cracks. SUMMARY

[0006] Technical problem: The present application aims to solve the technical problem of a low hydration heat concrete preparation method for preventing early cracks of wall body. The method is mainly suitable for concrete wall body structure with strength grade between C30 and C40, and can also provide reference for the preparation of higher strength grade concrete.

[0007] Technical scheme: The present application is a low hydration heat concrete preparation method for preventing early cracks of wall body, the hydration heat of cementitious materials is determined at constant temperature (20.0±0.1) ℃, and the concrete preparation and setting time determination are carried out under the simulated engineering site air temperature conditions, the method comprises the following steps.

[0008] Step one: According to the mix proportion design regulation JGJ55-2011, select different admixtures for 3-5 groups of candidate reference mix proportions.

[0009] Step two: uniformly mix the cementitious materials of the candidate reference mix proportions, and measure the hydration heat of each at 1 day, 3 days and 7 days of age by isothermal conduction calorimetry.

[0010] Step three: when determining the reference mix proportion, select the mix proportion with hydration heat not higher than 50 J / g at 1 day of age, hydration heat not higher than 200 J / g at 3 days of age, and hydration heat not higher than 250 J / g at 7 days of age as the reference mix proportion.

[0011] Step four: add high-quality air entraining agents to control the air content of the concrete in the range of 3%-5%, disperse the internal stress of the concrete, reduce the elastic modulus, and enhance the toughness of the concrete.

[0012] Step five: adjust the amount of retarder to control the setting time of the concrete, and measure the setting time under simulated environmental temperature conditions, control the final setting time of the concrete in the interval of 12-20 hours, so as to ensure that the shortest final setting time is not less than 8 hours during on-site construction, delay the concentrated heat release, if the final setting time is too short, it is not conducive to the control of concrete cracks, if the final setting time is too long, it will have an adverse effect on the construction progress and formwork turnover, and the economy is poor.

[0013] Step six: use cloth and straw mats for curing after form removal to avoid direct water spraying curing. DETAILED DESCRIPTION

[0014] The mix proportion design of the examples of the present application is designed according to the “Ordinary Concrete Design Regulation” (JGJ55-2011), the hydration heat of the cementitious materials is measured according to the “Cement Hydration Heat Measurement Method” (GB / T12959-2024) “isothermal conduction calorimetry”, the setting time and air content of the concrete are measured under simulated engineering site conditions according to the “Ordinary Concrete Mixture Performance Test Method” (GB / T50080-2016), and the concrete compressive strength test specimens are cured under standard conditions of temperature (20.0±2) ℃ and humidity ≥95% to the specified age, and the compressive strength test is carried out according to the “Standard for Test Methods of Physical and Mechanical Properties of Concrete” (GB / T50081-2019).

[0015] Example one

[0016] C40 strength grade concrete, P.O42.5 cement, S95 mineral powder 1, grade II fly ash, according to the "Code for Design of Ordinary Concrete" (JGJ55-2011) for mix proportion design, the cementitious material dosage of the alternative reference mix proportion, the hydration heat test results (J / g) are shown in Table 1 No. Cement Slag Fly ash 1 day 3 days 7 days PH1 244 89 111 37.2 184 239.8 PH2 230 105 84 36.1 172.7 233.2 PH3 278 60 60 132.2 203.8 267.7

[0017] PH1 is determined as the reference mix proportion, the setting time (h), air content (%) and specimen compressive strength (MPa) results of laboratory test are shown in Table 2 No. Setting time Air content 7-day strength 28-day strength PH1 14.5 4.2 39.5 49.1

[0018] Example two

[0019] The size of the engineering accident pool of a chemical plant is: 36 meters long, 8 meters wide, 1.8 meters high, the wall thickness is 0.25 meters, using C40P6 strength grade concrete to pour and form at one time, without setting post-pouring belt or expansion joint.

[0020] In the actual production process, PH1 mix proportion is used, the cementitious material dosage is shown in Table 1, and the retardation air-entraining type admixture (including white sugar retarder and triterpenoid saponin air-entraining agent) is used, the air temperature during construction is 22-28℃, and the wind speed is level 1.

[0021] In the actual production process, the detection data of concrete construction site includes setting time, air content, and the setting time (h), air content (%) and specimen compressive strength (MPa) results of concrete test piece under standard curing conditions to the specified age are shown in Table 3 Setting time Air content 7 days 28 days Observed value 10 3.8 37.6 51.4

[0022] After 60 days of tracking observation, no cracks are found in the engineering entity.

[0023] Example three

[0024] The size of the fire pool of a chemical plant is: 24 meters long, 12 meters wide, 2 meters high, the wall thickness is 0.25 meters, using C40P6 strength grade concrete to pour and form at one time, without setting post-pouring belt or expansion joint.

[0025] In the actual production process, PH1 mix proportion is used, the cementitious material dosage is shown in Table 1, and the retardation air-entraining type admixture (including white sugar retarder and triterpenoid saponin air-entraining agent) is used, the air temperature during construction is 26-33℃, and the wind speed is level 1.

[0026] In the actual production process, the detection data of concrete construction site includes setting time, air content, and the setting time (h), air content (%) and specimen compressive strength (MPa) results of concrete test piece under standard curing conditions to the specified age are shown in Table 4 Setting time Air content 7 days 28 days Observed value 8.5 4.0 40.2 53.5

[0027] After 60 days of tracking observation, no cracks are found in the engineering entity.

[0028] Example four

[0029] P.O42.5 cement, S95 mineral powder 2, grade II fly ash, and the mix ratio is designed according to the Design Regulation of Ordinary Concrete (JGJ55-2011), and the cementitious material dosage of the alternative reference mix ratio and the hydration heat determination result (J / g) are shown in Table 5 No. Cement Slag Fly ash 1 day 3 days 7 days PH4 244 89 111 104.8 172.4 230.3 PH4 230 105 84 115.8 193.1 253.1 PH6 259 17 141 11.2 152.9 203.9

[0030] The PH6 is determined as the reference mix ratio, the laboratory detection setting time (h), air content (%) and compressive strength (MPa) are shown in Table 6 No. Setting time Air content 7-day strength 28-day strength PH6 15.2 4.0 37.2 52.7

[0031] The above test results show that the concrete prepared by the method does not appear cracks in the early stage, and the operation is simple, which is verified in the entity engineering and has high practical value.

[0032] The method has the following advantages: 1. The preparation method is simple and easy to operate, the determination method is simple and efficient, the required data amount is less, only the hydration heat data at 1 day, 3 days and 7 days, and the air content of concrete, the setting time of concrete under the same conditions need to be determined, which are all the conventional detection items of the concrete laboratory. 2. The method considers economy and construction convenience, the operation method is simple and easy to implement, and does not increase the cost of concrete. 3. The method is suitable for concrete wall structure with strength grade in the range of C30 to C40, and can provide reference for the preparation of higher strength grade wall concrete.

[0033] The technical means disclosed in the present application scheme are not limited to the technical means disclosed in the above embodiments, and also cover technical solutions composed of any combination of the above technical features. For ordinary skilled persons in the art, some improvements and modifications can be made without departing from the principles of the present application, and these improvements and modifications are also considered to be within the protection scope of the present application.

Claims

1. A method for preparing low hydration heat concrete for preventing early cracks in walls, characterized in that The method adopts a comprehensive approach of multiple means such as low hydration heat mix ratio design, incorporation of functional admixtures, and regulation of setting time, and includes the following steps: Step 1: According to the mix design specification "Ordinary Concrete Mix Design Specification" (JGJ55-2011), select different admixture dosages and design 3-5 sets of alternative reference mix proportions; Step 2: The cementitious materials of the alternative benchmark mix ratio are mixed uniformly, and the hydration heat of the cementitious materials at the ages of 1 day, 3 days, and 7 days is measured by isothermal conduction calorimetry; Step 3: Select the mix ratio with a hydration heat of no more than 50 J / g at 1 day, a hydration heat of no more than 200 J / g at 3 days, and a hydration heat of no more than 250 J / g at 7 days as the selected benchmark mix ratio; Step 4: Add high-quality air-entraining agent to control the air content of concrete within the range of 3%-5%, disperse the internal stress of concrete, reduce its elastic modulus and enhance the toughness of concrete; Step 5: Control the setting time of concrete by adjusting the amount of retarder, and simulate the ambient temperature conditions when concrete is used on site to carry out setting time measurement, so that the final setting time of concrete is controlled within the range of 12-20 hours; Step 6: Felt cloth maintenance method. After removing the mold, use felt cloth, straw mats and other similar materials for maintenance to avoid direct water spraying maintenance method.

2. A method for preparing low hydration heat concrete for preventing early cracks in walls according to claim 1, characterized in that The hydration heat value of the benchmark mix cementitious material at early age is set as follows: the hydration heat at 1 day is not higher than 50 J / g, the hydration heat at 3 days is not higher than 200 J / g, and the hydration heat at 7 days is not higher than 250 J / g.

3. The method for preparing low-hydration heat concrete for preventing early cracks in walls according to claim 1, characterized in that The air content control is achieved by adding high-quality air-entraining agent, and the air content needs to be maintained in an appropriate range of 3%-5%.

4. A method for preparing low hydration heat concrete for preventing early cracks in walls according to claim 1, characterized in that The final setting time of concrete is regulated under the simulated on-site temperature environment conditions, and the final setting time is controlled within the range of 12-20 hours to ensure that the shortest final setting time during on-site construction is not less than 8 hours, delaying concentrated heat release.