Study On Long-term Performance Of Machine-made Sand High-strength Self-compacting Concrete

As one of the aggregates of concrete,machine-made sand is widely used in the production of concrete.Compared with river sand,the mechanical properties of MS concrete are very important because of its special properties,such as mud content,needle content and lithology.In this paper,the long-term properties of machine-made sand concrete are taken as the research object,and the macroscopic and microscopic structures of machine-made sand concrete are studied by theoretical and experimental methods.The main contents and conclusions are as follows:(1)In this paper,the high-strength self-compacting concrete made of manufactured sand with optimized materials and adjusted mixture ratio has good working performance and mechanical strength.Its inverted slump emptying time is 6.19 s,the slump of J ring is 275 mm,and the expansion of J ring is 690 mm.It has good fluidity,strong passability,and excellent self-compacting performance.28 d age cube compressive strength is 79.7Mpa,flexural strength is 5.9 Mpa,elastic modulus is 43.8 Gpa,meet the requirements of high strength concrete.(2)The shrinkage of manufactured sand high strength self-compacting concrete is small and the volume stability is good.At the age of 28 d,the overall shrinkage was 64%,and the maximum shrinkage was 319 ?m/m.(3)In this paper,the cubic compressive strength prediction model is established,and the fitting degree of this prediction model is good.The fitting correlation coefficient of high strength concrete is = 0.805,and that of C30 concrete is = 0.994.(4)The strength of manufactured sand high-strength self-compacting concrete increases rapidly in the early stage,and the cube compressive strength and flexural strength at 3d age are equivalent,which are 74% and 100% of the corresponding strength at 28 d age,respectively.Mechanical sand high strength self-compacting concrete later strength growth is small,360 d age than 28 d age,cube compressive strength ratio is 106%,flexural strength ratio is 97%,axial compressive strength is 86%,elastic modulus is 110%.(5)Through the analysis of microstructure,it is found that the high-strength selfcompacting concrete with manufactured sand has sufficient hydration in the early stage,dense internal structure and few pores.It is difficult for external water molecules to penetrate into the concrete,and the free water involved in hydration is limited.At the same time,the pozzolanic reaction of active mineral admixture reduces the free water that provides cement hydration,and the strength growth space is small.