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How to Control the Quality of Concrete Construction ?

Thomas Huang posted this article in June 28, 2020

Hot weather continues in some places. In order to guarantee the construction period, pouring concrete in high temperature weather is inevitable. In order to ensure the construction quality of concrete engineering under high temperature environment, we must attach great importance and take effective measures to strengthen the control of concrete construction quality. Concrete pouring should be strictly controlled The temperature at the time, the maximum temperature of the concrete construction under the high temperature environment when pouring is not more than 32 ℃, the temperature when pouring is in accordance with the design regulations.
Specific requirements are as follows:
1) Strengthen raw material quality management
1. Strengthen the quality control of raw materials. In particular, it is necessary to strictly control the indicators such as the sand content of the sand, the amount of crushed stone powder, the water reduction rate of the water reducing agent and the slump retention value.
2. Strengthen the storage management of raw materials, and prohibit the exposure of various raw materials.
3. Sunlight the coarse aggregate pile 2h before the concrete is mixed to promote evaporative cooling to reduce the temperature of the concrete; if wetting with cold water, the cooling effect will be better.
2) Strengthen the management of coagulation and mixing
1. To reduce the temperature of the concrete mixture, the temperature of the raw materials should be lowered first, especially the temperature of the water with the highest specific heat and the aggregate with the largest amount.
2. Construction should be strictly in accordance with the construction mix ratio, and it is strictly forbidden to change the mix ratio privately, especially to increase the amount of mixing water at will; increase the self-calibration degree of the mixing station to ensure that the measurement error of the mixing station meets the requirements.
3. When mixing concrete, deep well water with low temperature can be used to effectively reduce the temperature of the mixture, and low temperature water, ice and other cooling measures can also be used. When adding ice, flake ice or ice chips can be used, and appropriate Prolong the mixing time.
4. If the transportation distance of concrete is long, retarder can be used to control the setting time, but the parameters of retarder should be correct, especially for large area concrete projects.
5. During the concrete construction process, the temperature of the raw material of the concrete and the temperature of the concrete at the mouth should be measured every 1~3h.
6. To control the slump of concrete, the testers should strengthen the side station, increase the detection strength of the concrete preparation, mixing process and aggregate measurement on site, and adjust the construction mix ratio in time according to the water content of sand and stone; shorten the pouring time to make it The slump loss is not less than 90% of the original slump.
3) Strengthen concrete transportation management
1. Shorten the concrete transportation time. The concrete transportation equipment should be able to meet the requirements of the initial setting speed and pouring speed of the concrete, and shorten the exposure time of the concrete. At the same time, the container in transit should be covered, and there should be heat insulation and shading measures to prevent sun exposure.
2. During transportation, it should be ensured that concrete does not segregate, slurry leakage, severe bleeding and excessive slump loss occur. The concrete transported to the pouring site should maintain uniform and specified slump.
3. If the concrete transported to the site occurs segregation or slump loss is large, the concrete should be re-mixed or cement slurry added again. It is strictly forbidden to add water on the site without permission.
4) Strengthen concrete pouring management
1. Strictly control the mold entry temperature of concrete, especially large-volume concrete. When designing the mix ratio, the actual environment of the construction site should be fully considered.
2. Do a good job in construction organization and try to avoid pouring concrete at the highest temperature. During the period of high temperature and drying, the pouring concrete at night is relatively less affected by wind and temperature, and can be finalized near sunrise, and the relative humidity at this time is relatively high, so the possibility of early drying and cracking is minimal. The temperature of concrete pouring should be controlled below 32℃. It is better to choose the time when the temperature is lower in a day.
3. When pouring concrete under hot conditions, the formwork, steel bars, the place to be poured and old concrete can be sprinkled with water to cool and absorb sufficient water before pouring, and measures such as blocking sunlight and preventing ventilation at the place of pouring can be taken. Ensure that the temperature difference between the temperature of the newly poured concrete and the temperature of the surface of the connected hardened concrete is not more than 15℃.
4. Equipped with sufficient manpower, equipment and machinery to prepare the emergency plan for concrete construction under high temperature environment, so as to respond to unexpected adverse conditions in time, and control the temperature difference between the concrete surface and the outside world and the influence of the temperature difference between the concrete interior and the surface at any time . When pouring concrete, someone must have a temperature measurement and make a temperature record.
5. In order to reduce the temperature of the concrete inside the pouring of large volume concrete, a cooling water pipe can be buried in the structure to pass circulating water for cooling.
6. For the construction of large-area cast-in-place beams and slabs, a concrete pouring scheme should be made, and the concrete pouring direction, pouring sequence, and pouring time should be selected as low as possible when the temperature is low.
7. To prevent the occurrence of cracks in concrete caused by high temperature construction and improve the density of concrete. Make the vibrating technology reasonable, and control the pouring height of each layer to not exceed 30cm, which not only facilitates vibrating density, but also adds heat loss to avoid temperature cracks.
5) Strengthen concrete maintenance management
1. Immediately after pouring the concrete, sprinkle water with circulating cooling water for maintenance, and require a special person to take care of the maintenance.
2. After the general concrete is poured, it must be covered as soon as possible after the slurry is collected. The surface of the concrete must not be damaged or polluted during the covering. The cover should be removed after the initial setting and covered with a soaked geotextile to avoid exposure to sunlight and keep it in a wet state at least 7 days. Keep watering in the first 7 days to keep it moist, and often maintain it continuously; and insist on regular maintenance according to the time period; do the intermittent wellness within the next 14 days.
3. When sprinkling water is applied to the concrete at an early age, if the operation is interrupted, the concrete will crack, and the concrete should be kept wet for a certain period of time. The number of watering times can keep the concrete in a wet state. The water used for mixing is the same, and water storage should be used when possible.
4. The curing specimens under the same conditions should be cured together with the main body concrete, and it is strictly forbidden to expose to the sun and affect the test results.
5. During the curing of concrete, ensure that the temperature of the concrete core should not exceed 60°C, and the maximum temperature should not exceed 65°C. The difference between the temperature of the concrete core and the surface, the difference between the surface temperature and the ambient temperature should not exceed 20°C, and the beam concrete should not exceed 15 ℃, the difference between the temperature of curing water and the surface temperature of concrete shall not be greater than 15℃.
6) Measures to prevent cracks in concrete construction
1. The quality of raw materials must be qualified. Colleagues strictly control the sand and mud content, improve the sand and gravel grading, and control the slump, unit water consumption, and hydration ratio.
2. Improve the compactness of the concrete so that the vibrating process is reasonable.
3. Improve the temperature conditions, use low temperature concrete and low hydration heat cement, colleagues control the thickness of each layer is about 30cm.
4. The curing work starts within 12~18h after the concrete is poured. The curing is done with deep well water and covered with felt, etc., to ensure the wetness of the concrete.
In the construction of concrete under high temperature environment, construction and maintenance shall be carried out in strict accordance with the construction procedures, construction technical measures and acceptance standards to ensure the construction quality of concrete.

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