Thermal insulation and maintenance functions
1, reduce the thermal diffusion on the concrete surface, reduce the temperature gradient on the concrete surface, and prevent it from generating surface cracks.
2. Extend the heat dissipation time and give full play to the potential of concrete and the relaxation characteristics of materials. Make the tensile stress generated by the average total temperature difference of concrete less than the tensile strength of concrete to prevent through cracks.
The role of moisturizing and curing
1. The freshly poured concrete is in the solidification and hardening stage, and the hydration speed is fast. Proper wetting conditions can prevent dehydration and shrinkage cracks on the concrete surface.
2. Under wet conditions, concrete can hydrate cement smoothly and improve the ultimate tensile strength of concrete.
It is necessary to monitor and control the temperature of mass concrete in order to master the changing law of temperature rise and fall and the temperature influence of various materials under various conditions.
(1) Layout of temperature measuring points. Must be representative and comparable. Along the pouring height, it should be arranged at the bottom, middle and surface, and the vertical measuring point spacing is generally 500 ~ 800mm；; The plane should be arranged at the edge and middle, and the distance between plane measuring points is generally 2.5~5m.
(2) Temperature measuring system. In the concrete heating stage, it shall be measured every 2~4h, and in the cooling stage, it shall be measured every 8h. At the same time, the atmospheric temperature should be measured. All temperature measuring holes shall be numbered to measure different depths and surface temperatures of concrete. Temperature measurement should be carried out by specialized personnel. The temperature measurement record shall be submitted to the technical director for reading and signing as the basis for controlling the concrete construction and quality.
(3) Selection of temperature measuring tools. In order to control the temperature difference between the inside and outside of concrete in time, check the difference between the calculated value and the measured value, and grasp the concrete temperature dynamics at any time, thermocouple or semiconductor liquid crystal display thermometer should be used. In the process of temperature measurement, when the temperature difference exceeds 25℃, the thermal insulation should be strengthened or the removal of thermal insulation materials should be delayed in time to prevent the concrete from producing temperature difference stress and cracks.
0 1 construction technology
Materials for preparing mass concrete shall meet the following requirements
1. Optimize the cement with stable quality to improve the crack resistance of concrete.
2. Fine aggregate adopts medium sand with good gradation, and the fineness modulus is greater than 2.3.
3. In non-pumping construction, the particle size of coarse aggregate can be appropriately increased.
4. Choose retarding superplasticizer.
The mixture ratio of mass concrete shall meet the following requirements
1, mix design should not only meet the requirements of design strength grade, durability, impermeability and volume stability, but also meet the requirements of mass concrete construction technology characteristics, and follow the principles of rational use of materials and reducing the adiabatic temperature rise of concrete.
2. The slump of concrete mixture on the pouring surface shall not be greater than 160 mm. ..
3, mixing water consumption is not more than170 kg/m/m. ..
4, the dosage of fly ash should be appropriately increased, but not more than 40% of the cement dosage; The dosage of slag powder shall not exceed 50% of the dosage of cement, and the total amount of two additives shall not exceed 50% of the weight of cement in concrete.
5, the water-binder ratio is not greater than 0.55.
The technical scheme for mass concrete construction shall include the following contents.
1, formwork and supporting system should not only check the strength, stiffness and stability according to the current national standards, but also design the thermal insulation structure in combination with the maintenance method of mass concrete.
2, template and support system in the process of installation or removal, temporary fixed measures should be set to prevent capsizing.
3. The calculation of temperature stress and shrinkage stress of mass concrete structure should be carried out according to the specifications.
4. Determination of temperature control index and technical measures in the construction stage.
5. Raw material optimization, mix design, material preparation and transportation plan.
6. Main concrete construction equipment and site general layout.
7. Temperature monitoring equipment and test arrangement.
8, concrete pouring sequence and construction progress.
9. Concrete thermal insulation and moisture curing method, in which the thickness of thermal insulation coating is calculated according to the requirements of temperature control index.
10, emergency safeguard measures.
1 1, post responsibility system and succession system, temperature measurement operation management system.
12, construction measures for special parts and special weather conditions.
We should calculate the temperature, temperature stress and shrinkage of mass concrete structure, predict the peak temperature rise, temperature difference between core and surface and the control index of cooling rate during mass concrete pouring in construction stage, and formulate corresponding temperature control technical measures. The process test of the first casting body was carried out, and the temperature of the initial construction structure was monitored.
The pouring of mass concrete shall meet the following requirements
1, and the concrete pouring temperature is not higher than 28℃. Based on the mold entry temperature, the temperature rise of concrete pouring body shall not exceed 45℃.
2. Mass concrete engineering construction adopts layered continuous casting construction or push continuous casting construction. According to the design size, evenly segment and layer by layer.
3. When pumping concrete, the thickness of concrete pouring layer shall not be greater than 500mm. When non-pumping concrete is used, the thickness of concrete pouring layer shall not be greater than 300mm.
4. In mass concrete construction, the setting of horizontal construction joints should not only meet the design requirements, but also be determined according to the requirements of temperature crack control during concrete pouring, the supply capacity of concrete, the construction of reinforcement engineering, the installation of embedded pipe fittings and other factors.
5. In the process of mass concrete pouring, measures should be taken to prevent the displacement and deformation of steel bars, positioning bars and embedded parts.
6, mass concrete pouring surface should be timely secondary plastering treatment.
After each pouring of mass concrete, in addition to conventional curing of ordinary concrete, it should also be cured in time according to the requirements of temperature control technical measures.
The formwork removal time of mass concrete should be postponed appropriately. When the formwork is used as a part of thermal insulation and maintenance measures, the formwork removal time shall be determined according to the requirements of temperature control.
When mass concrete construction encounters hot weather, winter, strong wind or rain and snow, effective technical measures must be taken to ensure the quality of concrete pouring and maintenance.
I believe that after the above introduction, everyone has a certain understanding of the key points of mass concrete maintenance construction. Welcome to Zhong Da for more information.
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