【正文】 surface often occur cracks in thin and shallow, most of them belonging to shrinkage cracks. While this is generally shallow cracks, but its strength and durability of the structure is still a certain impact. In order to ensure the quality of concrete to prevent cracking and improve the durability of concrete, the proper use of admixtures is also one of the measures to reduce cracking. Such as the use of anticracking agent and water, in practice, its major role in concluding as follows: (1) the existence of a large number of pores in the concrete that, after evaporation of water generated by capillary capillary tension, deformation of the concrete shrinkage. Pores increased capillary diameter can reduce the surface tension, but would reduce the strength of concrete. (2) the impact of watercement ratio is an important factor for concrete shrinkage, the use of anticracking agent can reduce water consumption reduced by 25% concrete. (3) the amount of cement concrete is also an important factor in shrinkage, water 第 110 頁 addition and subtraction mixed concrete cracking agent in maintaining the strength of concrete under the condition of 15 percent can reduce the amount of cement, aggregate size, by increasing the amount to supplement. (4) anticracking agent and water can improve the consistency of cement slurry to reduce the bleeding of concrete, reduce shrinkage deformation Shen. (5) to improve and cement bonded aggregate, and enhance the anticracking performance of concrete. (6) concrete bound in the contraction produced by tensile stress, when the tensile stress is greater than the tensile strength of concrete will be produced when the cracks. Waterreducing agent can be an effective anticracking of the concrete tensile strength to increase, a substantial increase in anticracking performance of concrete. (7) mixingpacting concrete admixtures can, and can effectively improve the carbonation resistance of concrete to reduce the carbonation shrinkage. (8)doped waterreducing agent after the concrete cracking retardation time due, in the effective prevention of the rapid hydration heat of cement based on cement to avoid longterm result of noncondensable increase plastic shrinkage. (9)doped workability of concrete admixtures, and easy to find flat surfaces to form a micromembrane to reduce evaporation and reduce drying shrinkage. Many have a retarding admixture to increase the workability and improve the function of plasticity, we in engineering practice in this area should be more contrast and research experiments than simply relying on external conditions to improve may be even more simple and economic. 4. early concrete conservation Practice has proved that the mon concrete cracks, the majority of surface cracks at different depths, mainly because of the temperature gradient caused by the cold temperature region is also vulnerable to a sharp fall in the formation of cracks. Insulation so that the concrete surface to prevent early cracking is particularly important. Thermal stress from the point of view, the insulation should meet the following requirements: 1) to prevent the concrete inside and outside the concrete surface temperature difference and gradient, to prevent surface cracks. 2) to prevent the concrete supercold, it should be possible to make concrete the construction period of not less than the minimum temperature of concrete used for the stability of the temperature. 第 111 頁 3) to prevent coldold concrete in order to reduce the concrete between the old and new constraints. Early concrete conservation, the main objective is to maintain the appropriate temperature and humidity conditions in order to achieve the effect of two aspects, on