Mechanism Research On The Formation Of Shrinkage Cracks Of The Commodity Concrete

The development and large-scale use of commodity concrete has become the inevitable trend of the development of the civil engineering industry, for its obvious merits: rapid progress, spared manpower, low consumption, advanced technologies, the scene of civilization and so on. However, commodity concrete has its own characteristics:the larger use of liquidity requirements, the larger ratio of cement and fine aggregate in mixing proportion and the smaller ratio of coarse aggregate as well as some small proportion of the admixture, which makes its larger incorporation contraction and easier cracking than ordinary concrete. According to statistics, non-load cracks occupy more than 70% in all concrete structure cracks, of which about 80% are caused by shrinkage. So the control problems of the shrinkage cracks has become one of the focuses of research work at home and abroad.Through measuring 12 groups, 36 lumps of commodity concrete shrinkage specimens's shrinkage strain in series 28 days, this paper trys to analysis the laws of the early contraction of commodity concrete under the different conditions of concrete mixture ratio and conservation preliminarily.It also trys to find out the different laws of concrete shrinkage between ordinary and commodity concrete and its influencing factors. Using the theory of ultimate tensile of concrete, a beam specimen tests the theoretical analysis, as well as proposing the role of creep stress relaxation on the concrete contraction.Finally, on the basis of the analysis of this test results, the contraction of concrete and the influencing factors of concrete shrinkage, a number of prevention and control measures about the early cracks of commodity concrete are proposed.