高强与高性能混凝土的收缩与开裂

高强与高性能混凝土胶结料用量较多,砂率较大,粗骨料用量相对较少,因此若处理不妥易出现混凝土早期开裂现象.通过圆环法试验,研究分析高强与高性能混凝土易于开裂的原因及主要影响因素,对商品泵送混凝土配合比的优化提出了建议.同时采用不同的混凝土收缩变形公式进行计算并将计算值与试验值进行了对比,探讨了适合于高强与高性能混凝土收缩变形的实用计算公式.

Study on shrinkage and cracking of reinforced concrete

This paper is aimed at introducing the author's series of ring tests on three batches of high performance concrete to evaluate their crack-resistant property. As is known, high strength and performance concrete has been extensively used in these years for construction purposes due to its unique advantages. However, it still has some drawbacks, such as excessive use of cementitious material, higher sand ingredient rate and less coarse aggregate. To solve the problem, the author has done a series of experiments by using different sand rates, dosages of cementitious materials and environmental conditions in intended ratios. The experimental results gained indicate that such concrete tends to get crack with the larger sand rate and less dosage of cementitious material. Thus, sand rate proves to be more influential on concrete properties than the dosage of cementitious material. Compared with the conditions of stable temperature, concrete cracks earlier with the abrupt temperature change during day and night. However, the crack tendency proves the same for concrete. Therefore, it means the necessity to control the temperature if high strength and performance is needed. Based on the above experimental results, the author has brought forward corresponding methods on how to optimize the proportion of commercial pump concrete. He also introduces the calculation models of elastic modulus, the axial tensile strength and the high strength and performance concrete developing tendency. In addition, comparisons of concrete shrinkage in various formulas and experimental values are also made in the latter part of this paper. And finally valuable formula as to the calculate shrinkage of high strength and performance concrete are provided, which prove to be in agreement with the model brought forward by Wang Tiemeng. But they can be made obviously improved by adding the coefficients of modification, with the dosage of flown ash replacing the cement and slump of concrete.