Effect Of Mixed Sand On Concrete Performance And Its Application

Natural sand is one of the main raw materials for preparing concrete,and it significantly affects the properties of concrete.However,Natural sand is a non-renewable resource,which is limited in exploitation and in short supply in the market with the rapid development of concrete industry and increasingly severe environmental protection situation.As a substitute material for natural sand,artificial sand is widely used.However,the properties of artificial sand such as grain shape,surface state and particle size distribution are different from natural sand.Thus it is necessary to mix artificial sand with natural extra fine sand to form mixed sand,which ensures the performance of concrete.In this article,the mixture ratio of concrete was designed by the method of equal slurry volume.On this basis,the influence of mixed sand parameters on concrete performance was studied and the optimal mix ratio was obtained.Furthermore,the concrete was prepared with the best proportion of mixed sand and natural medium sand as fine aggregate.The influence of mixed sand and natural medium sand on the working performance,anti-plastic cracking ability,mechanical property and durability of concrete was discussed,the interface state of mixed sand and natural medium sand concrete was analyzed,and the economic benefit of mixed sand was calculated and evaluated.The results of the effect of mix design and mixed sand parameters on concrete performance showed that the rough surface and irregular grain shape of artificial sand had a negative impact on the working performance of concrete,and more cracks in the artificial sand would absorb the moisture in concrete.Therefore,the slump and expansion degree of mixed sand concrete was 10～20 mm lower than that of natural medium sand concrete,as well as the longitudinal loss of slump and expansion degree was 10～30 mm higher.The research on the effect of mixed sand and natural medium sand on concrete performance indicated that the rough surface and irregular grain shape of artificial sand enhanced the mechanical bite force at the interface with cement slurry,inhibited the shrinkage of cement stone,reduced the occurrence of plastic shrinkage cracks,and improved the compressive strength and elastic modulus of concrete.The compressive strength of mixed sand concrete was 1～2 MPa higher than that of natural medium sand concrete,and the elastic modulus was 0.1～0.3×10~4MPa higher.SEM analysis of the concrete microstructure found that there were more honeycombed C-S-H gels in the mixed sand concrete because the stone powder in the artificial sand could improve the precipitation probability of C-S-H gels and make the hardened paste more compact.And the stone powder can fill the paste void,improve the paste density,so as to improve the performance of concrete.The economic benefit analysis and engineering application effect of mixed sand showed that the performance of mixed sand concrete was close to or better than that of natural sand concrete,and the pass rate of standard curing specimens was up to 100%.The cost of C30 concrete per cubic meters can be reduced by 68.9 yuan when artificial sand was used instead of natural medium sand as fine aggregate.And the mixed sand concrete are better than natural medium sand concrete on the performance index and cost performance,and it has better economic benefits.