When constructing concrete in hot weather, the main attention should be paid to controlling the slump loss of concrete before pouring and maintaining moisture after pouring. What concrete admixtures need to be used in summer? In summer, retarder is used. Because the temperature is high, retarder is needed to delay the setting time of concrete and avoid concrete loss too quickly.
What issues need to be paid attention to during summer construction?
(1) Pay attention to cement temperature
Cement has high temperature, high activity, and fast hydration rate. In addition, During the grinding process, part of the dihydrate gypsum is dehydrated and becomes hemihydrate gypsum, which cannot effectively control the hydration of C3A, resulting in accelerated slump loss of the concrete soil mixture, especially in high temperature weather. High-temperature weather and high-temperature cement will also worsen the retarding effect of some retarder, making it difficult to control the slump loss of the concrete mixture. During the production process, cement with all indicators meeting standards should be selected, and the cement temperature must be controlled below 70°C. If conditions permit, the cement can be left for a period of time before use to reduce the adsorption of admixtures and control the slump loss of concrete. Most concrete companies do not have such conditions and use cement readily, which brings certain difficulties to the slump loss of concrete. Generally speaking, for fresh cement with high temperature, satisfactory results can be obtained by appropriately adjusting the dosage of admixtures. However, sometimes concrete slump loss is very fast. Increasing the dosage of concrete admixtures still cannot control the slump of concrete. loss situation. At this time, the admixture company should be contacted in time to adjust the admixture. If there is no time to adjust the admixtures, the concrete mixture can be controlled in a slightly segregated state during production to ensure that the concrete has good workability during pouring, or a secondary addition of water-reducing agent can be used at the construction site (addition process) Pay attention to the control of the dosage and uniform mixing. Do not use pumping agents containing retardant components to adjust). It is strictly forbidden to add water alone to adjust the slump of concrete.
(2) Appropriately increase the content of mineral admixtures
In hot weather, the hydration rate is fast and the slump loss of concrete is faster. While ensuring the strength of the concrete, appropriately increase the amount of mineral admixtures, reduce the amount of cement, reduce the collapse loss of concrete, and improve the construction quality of concrete.
(3) Select concrete admixtures with good compatibility
Admixtures with good compatibility with concrete raw materials usually have: ① moderate dosage and easy control; ② admixtures When the dosage changes by about ±0.1%, the state of the concrete does not change significantly; ③ When the water consumption changes by about 5kg, the state of the concrete does not change significantly; ④ The slump loss of concrete over time is small, meeting transportation and construction requirements; ⑤ Before and after pumping , the concrete state changes little.
(4) Reduce the temperature of the concrete mixture
Reducing the temperature of the raw materials is a way to reduce the temperature of the concrete mixture. Lowering the aggregate temperature is a very effective way to lower the concrete temperature. When the aggregate temperature decreases by 2°C, the concrete temperature will generally decrease by 1°C. At present, the material yards of most mixing plants are closed to prevent the sun from directly irradiating the aggregates. The specific heat of water is 4 to 5 times that of cement and aggregate. Normally, a 4°C decrease in water temperature can reduce the concrete temperature by 1°C. During the concrete mixing process, underground cold water is used to mix the concrete. Some data suggest that groundwater is used to spray and cool the aggregate and to crush the ice and mix it with water to form an ice-water mixture for mixing. You should be careful when using these two methods. Use groundwater to spray aggregates, paying attention to the control of the moisture content of the aggregate and the uniformity of spraying, that is, the difference in moisture content between the surface and the inside (bottom) of the aggregate; when using a mixture of ice and water, try to control the amount of crushed ice at 25% This ensures that the crushed ice can be completely melted during mixing to avoid the presence of incompletely melted ice after mixing, causing the concrete slump to increase.
(5) Reasonable dispatch of concrete transport vehicles
Pouring concrete in hot weather can easily cause concrete slump loss to be too rapid. Production dispatchers should base their work on the pouring situation on the construction site and the traffic conditions on the transportation road. Reasonable deployment of vehicles must ensure that no vehicles are pressed, and that no long-term interruption of vehicles is required at the construction site. Generally speaking, the pumping speed of a truck pump takes 10 to 20 minutes to pour one truck (12m3) of concrete. The dispatcher can reasonably arrange the vehicles based on traffic conditions and distance. After the concrete transport vehicle arrives at the construction site, the construction unit should arrange personnel to pour in time to ensure that the concrete is poured into the project site when it has good workability and to ensure the quality of the concrete. The concrete pouring construction on the construction site should be arranged at night as much as possible. The ambient temperature at night is slightly lower than during the day, and the performance of concrete slump and other aspects can be maintained better.
(6) Regular inspection of the measurement system
High temperature has a great impact on the accuracy of various sensors. It is necessary to calibrate various measurement sensors from time to time, especially the admixture sensors, so that The weighing value is within the error range. Excessive amounts of concrete admixtures will cause the concrete to retard and form a large number of shrinkage cracks, and in severe cases, through cracks will form.
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