| The durability of concrete issues is an important factor to affect its performance. As the concrete itself is a multi-phase and multi-component composite materials, the factors affecting its performance are more and large random. The destruction factors of concrete are often all kinds of physical and chemical causes, and the effects of other factors mixed with each other. In actual project, The actual concrete projects are generally subject to two or more factors.This article mainly aimed at the poor durability of concrete in South Xinjiang and other regions, to explore the common concrete failure mechanism in the chloride and freeze-thaw cycle environment, sulfate and freeze-thaw cycle environment, chloride + sulfate and freeze-thaw cycle environment. Through Orthogonal comparison, we study the compressive strength of concrete, mass loss, the length of the expansion rate in water environment, chloride environment, sulfate environment, chloride + sulfate salt compound environment under freeze-thaw cycle, to analysis of the water-cement ratio, The amount of cement, size of coarse aggregate, the three factors on the durability of concrete. Based on the above analysis, through X-ray diffraction and scanning electron microscopy to study preliminarily the failure mechanism of ordinary concrete in complex environmentsThe main conclusions of this study as follows:1. The most important impact factor of concrete strength and durability is the water-cement ratio. The greater water-cement ratio, the smaller the compressive strength of concrete, the greater the mass loss, the greater the expansion rate, the worse the durability.2. Is not greater the amount of cement, its durability, the better. Water-cement ratio in certain circumstances, should there be a reasonable amount of cement to make concrete the best durability.3. Ordinary concrete in freeze-thaw cycle under different conditions, with the increase in the number of freeze-thaw cycle, its quality was reduced after the first increase.4. The co-existence of SO42-,Cl-,Mg2+ under the freeze-thaw environment, the sulfate has obvious influence on the durability of concrete.The early stage of freeze-thaw, chloride infiltration most; to a certain extent, sulfate ions is ease of chloride ion penetration. The late stage of freeze-thaw, With More content of sulfate ion of concrete pores, more and more evidence of sulfate ions' erosion, and become the main reason for the deterioration of the durability of concrete, while chloride moderates sulfate ion erosion.Under complex environment,SO42-,Cl- accelerated the response of Mg(OH)2,a small number of CaMg(CO3)2, AlSO43·H2O, Mg4(OH)2(CO3)3·3H2O;and the response of Mg(OH)2, CaMg(CO3)2, Al2(SO4)3·H2O, Mg4(OH)2(CO3)3·3H2O consumes Ca(OH)2,CaCO3,CAH and damaged the concrete structure. This impacts the response and generating of ettringite, thaumasite.5. Under complex environment, the greater water-cement ratio and the amount of cement, the more Mg(OH)2,CaMg(CO3)2,Al2(SO4)3·H2O,Mg4(OH)2(CO3)3·3H2O which are the result of reaction by Mg2+ and Ca(OH)2,CaCO3,CAH, and even grow form concrete.
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