Composition Design And Performance Research Of High Performance Mechanical Sand Cement Concrete For Pavement

Traditional river sand concrete pavement not only faces the damage of freeze-thaw and shrinkage,but also faces the problem of resource shortage.At the same time,under the influence of specific climatic conditions in Lanzhou area,the durability disease of pavement concrete is becoming more and more serious.Therefore,considering the abundant resources of machine-made sand and the excellent performance of concrete,the composition design and performance research of pavement high-performance machine-made sand concrete are carried out in this paper,so as to improve the anti-freezing durability and shrinkage performance of pavement concrete.First of all,by studying the influence law of mechanical sand characteristics on the performance of ordinary pavement concrete,the best technical index value of mechanical sand characteristics for the preparation of high-performance concrete is determined.Secondly,on this basis,silica fume,fly ash and SAP were selected as the main influencing factors,and the orthogonal test of three factors and four levels was carried out to systematically study the influence law of the mixed material on the working performance,mechanical property,shrinkage property and frost resistance of concrete,so as to optimize the preliminary mix ratio of pavement high-performance mechanized sand concrete based on specific climate environment.Then,by studying the durability and shrinkage performance of pavement high-performance machine-made sand concrete,to verify the improvement of the anti-freezing durability and shrinkage performance of composite materials on pavement concrete,so as to put forward the final mix ratio of pavement high-performance machine-made sand concrete suitable for cold and dry areas.Finally,the interfacial morphology of high performance mechanized sand concrete was analyzed from the microscopic level to observe the influence of freeze-thaw and other factors on the internal structure of concrete.The conclusions are as follows:(1)The effect of mechanical sand properties on the performance of ordinary pavement concrete shows that the mechanical properties of diabase mechanical sand concrete are the best,and granite mechanical sand concrete is the worst.Sand ratio can improve slump,flexural and compressive strength of machinemade sand concrete,and the best recommended value is 42.0%.The fineness modulus has a certain effect on the flexural strength of pavement sand concrete,but has little correlation with the compressive strength.The influence of the content of machine-made sand powder on the working and mechanical properties of pavement concrete is extremely significant,and its influence on the flexural strength and compressive strength of concrete is slightly different.It is suggested that the optimal content of machine-made sand powder for pavement concrete is 5.0%.(2)The optimization design of pavement high-performance mechanized sand concrete material composition shows that SAP can reduce the mechanical properties of pavement concrete,while silica fume and fly ash can improve the mechanical properties of concrete,and the influence of silica fume is more significant.SAP can improve the dry shrinkage and freeze resistance of concrete.Silica fume significantly reduces the dry shrinkage and freeze resistance of concrete,while fly ash can improve the freeze resistance of concrete.(3)The durability and shrinkage tests of pavement high-performance mechanical sand concrete show that increasing the number of freeze-thaw cycles can significantly reduce the frost resistance of concrete,and increasing SAP content can gradually improve the frost resistance of concrete,and the optimal content is 0.18%.The wear resistance and chloride penetration resistance of pavement high-performance mechanical sand concrete have little relation with SAP content.SAP introduced into concrete can reduce its shrinkage rate and improve the resistance to shrinkage of pavement concrete.The recommended final ratio of pavement high-performance machine-made sand concrete is as follows: water-cement ratio 0.37,sand rate 42%,SAP content 0.18%,fly ash content 15% and water reducing agent content 1.2%.(4)The experimental analysis of the microstructure of high-performance mechanical sand concrete shows that: in the microstructure of concrete,freezethaw will reduce the hydration products and microstructure compactness of concrete.Under 150 cycles of freeze-thaw,concrete with 0.18%SAP content has higher microstructure compactness.