Design Of Mix Ratio Of Mechanical Sand Concrete And Experimental Study Of Early Crack Resistance

As a substitute of natural sand,mechanism sand is an inevitable trend of civil engineering construction.The popularization and application of mechanism sand can effectively solve the problem of insufficient natural sand,and it is also an important measure to respond to the construction of ecological civilization and the sustainable development of society.However,due to the large number of influencing factors on the performance of mechanical sand concrete and the great difference in the research and application degree of mechanical sand in different regions,a complete theoretical system of mechanical sand has not yet been formed,especially the research on the crack resistance of mechanical sand concrete in the early stage is relatively few.Characteristics according to the region of guangxi limestone sand mechanism and the mechanism of limestone sand concrete preparation according to certain proportion of mixed sand pebbles mechanism,considering the different mechanism of limestone sand replacement ratio,water/cement ratio,sand ratio of three factors on the mechanism of sand concrete working performance,mechanical properties,the early crack resistance,series of experiment research.The results show:(1)When orthogonal test was used to design the optimal mix ratio of C35 concrete,the influencing factors on the strength of 7d and 28d were respectively water-cement ratio,sand ratio and limestone mechanical sand substitution ratio,among which the water-cement ratio was the main factor affecting compressive strength,while the other two factors had no significant influence on strength.(2)The mechanical performance of limestone is the best when the substitution rate of limestone mechanism sand is between 40%and 60%,the water-cement ratio is 0.38,and the sand ratio is 0.38.With the gradual increase of substitution rate of limestone mechanism sand,the working performance is changeable.The increase of water-cement ratio can improve its performance.Under the same conditions,the sand rate increases gradually,the better the working performance.The influence law of age on mechanical properties of mechanical sand concrete with different limestone mechanism sand substitution rate,water-cement ratio and sand rate is basically the same,and the change shows a nonlinear growth trend,and the growth rate of early development is faster than that of later development.(3)The values of regression coefficientsα_a andα_b in the formula for calculating the water-cement ratio of mechanical sand concrete are different from those of ordinary concrete,and the fitting analysis shows thatα_a=0.51 andα_b=0.28.Mechanism of sand concrete axial compressive strength,splitting tensile strength and modulus of elasticity and has a certain correlation between cube compressive strength,according to the ordinary concrete calculation formula for conversion there is a certain deviation,referring to the calculation formula of normal concrete,puts forward the mechanism of sand concrete axial compressive strength,splitting tensile strength,elastic modulus and calculation formula between the cube compressive strength.(4)In the range of limestone mechanism sand substitution rate of 30%～60%,water-cement ratio of 0.40～0.42,sand rate of 0.36～0.38,concrete cracking area is less,crack resistance grade is higher,crack resistance performance is better.From the aspect of strength,the calculated results of compressive ratios of 3d,7d and 28d ages were used to evaluate the early cracking test results of different limestone mechanism sand substitution rates,water-gel ratios and sand rates accurately,while the calculated results of elastic strength ratios were only used to evaluate the early cracking test results of water-gel ratios accurately.