【正文】 ete cracks, and further intensify the moisture inside body, and further expansion crack Second, the measures to prevent cracks From the above analysis, the crack is mainly caused by temperature difference and contraction, so in order to prevent the cracks of, will maximize reduce temperature and reduce the shrinkage of concrete, specific measures as follows. 1. Optimizing raw materials (1)Cement. The cement should be chosen according to the engineering properties, construction condition, climate and other technical requirements, prehensive consideration, to meet the strength and durability of concrete design requirements. When the choice should be labeled with cement concrete design match the label. For full strength of cement, cement, cement save from the label for concrete label to 2 times as appropriate. (2) aggregate. (a) coarse aggregate. The coarse aggregate concrete rubble is closegrained, must have the enough strength, hard to expand the coarse aggregate size. To ensure the concrete pouring dao closegrained, coarse aggregate maximum diameter less than the minimum size of the structural sections 1/4, also not greater than the minimum distance between steel for thickness 3/4, in 10 centimeters and concrete, allowing adopts maximum diameter 1 1/2 of the aggregate number, but it shall not exceed 25%. (b) fine aggregate. Sand particle gradation of technical properties of concrete influence, requests the porosity and total surface area small, small need total surface on the surface of the gravel package will reduce quantity of cement slurry, can reduce the dosage of cement hydration heat, reduce to prevent cracks. On the other hand is to control the hydraulic sand, the content of 5% in concrete, the contraction deformation, the hydraulic and larger crack, fine aggregate to use clean in the sand. (3) admixtures. (a) waterreducing agent. Jianshuiji belongs to the surface active substances, is a kind of cement dispersant. Its main function of improving concrete workability, reduce the consumption of concrete mixture, reduce watercement ratio increases, and improve the liquidity of concrete strength of concrete or keep in concrete cement strength must decrease, while the watercement ratio, the dosage of cement to prevent cracking is reduced. (b) retarder. Retarder is delaying the role of concrete exothermic peak time, 2 it is to improve workability, and reduce the loss of collapsbillity. (c) airentraining agent. In the application of concrete airentraining agent for improving the concrete workability, can pump, improving the concrete durability is very favorable. In a certain extent increase anticracking performance of concrete. (4) mass concrete chooses raw materials should pay attention to the following: ① The coarse aggregate gradation, appropriate USES continuous fine aggregate ZhongSha should be adopted. ② Admixtures appropriate USES retarder, waterreducer, Admixtures appropriate USES fly ash, slag powder etc. ③ In mass concrete strength of concrete and the slump and the requirements of the premise, should improve mixing and aggregate content, in order to reduce the dosage of cement concrete alone. ④ Should try to choose cement hydration heat low, setting time is long, the cement, low thermal Portland cement slag silicate cement, cement, slag dam Portland cement, coal ash Portland cement, volcanic gray Portland cement, etc. However, the slag cement hydration heat low water cement ratio of chromatography in other large, casting lots of water surface layer. This phenomenon is not only affect lactation water, also influence the construction speed and quality of construction. Because the water gathered in separation between the two casting concrete surface layer, change, and watercement ratio in the water and took out some of the mortar, thus forming a layer of interlining content, destroyed the cohesiv