Working Performance And Mechanical Properties Of Desert Sand Self-Compacting Concrete Experimrntal Research

As a natural resource,desert sand is widely distributed in northern my country,but due to factors such as too fine particles,poor gradation,and high alkali content,it is not suitable for ordinary concrete.Self-compacting concrete(SCC)can effectively prevent aggregate segregation and bleeding,and has good working performance and compactness.It is a high-performance concrete with innovation and development prospects.Compared with ordinary concrete,self-compacting concrete uses fly ash,silica fume and other fine particles to fill the pores,so it has better compactness.Based on this,the use of the fine particles of desert sand to partially replace the fine aggregates in self-compacting concrete is not only conducive to the formation of high-fluidity self-compacting concrete,but also has important significance for reducing project costs,protecting the local environment,and rationally developing and utilizing natural resources.This paper takes the Mu Us desert sand in northern Shaanxi as the main research object,analyzes the physical properties,chemical composition,particle gradation and influencing factors of the desert sand,and studies the working performance and mechanical properties of the self-compacting concrete with different replacement rates.The main conclusions are as follows:(1)In the case of the mix ratio listed in the specification,with the increase of the replacement rate,the fluidity,filling property and gap passability of the self-compacting concrete first increase and then decrease;the replacement rate slumps at 20% The expansion degree is 530 mm,which is 3.9% higher than the benchmark group(no desert sand addition);T500 is 5.8s,which is 0.9s less than the benchmark group;the passage time of the V-shaped funnel is 11.4s,which is 2.7s shorter than the benchmark group;the J-ring passes the test The results show that there is no aggregate accumulation at the J-ring of the self-compacting concrete with a replacement rate of 20%,and the passability is good;continuing to increase the replacement rate,a small amount of aggregate accumulation and segregation occurs near the J-ring,and the passability is poor.The cubic compressive strength of desert sand self-compacting concrete increases first and then decreases with the increase of desert sand replacement rate.The self-compacting concrete with 20% desert sand replacement rate is about 5% higher than ordinary self-compacting concrete.As the replacement rate of fly ash increases,the compressive strength of self-compacting concrete cubes increases first and then decreases.When the replacement rate of fly ash is 10%,the compressive strength of the cubes is the highest.(2)As the replacement rate increases,the strength of self-compacting concrete increases first and then decreases,and the peak value is still near the 20% replacement rate.Under the C30 design strength,the 20% replacement rate cube compressive strength reaches 39.8MPa,which is 9.8MPa higher than the design strength,and 2.6% higher than the benchmark strength;the 40% and 60% replacement rate cubes compressive strength are36.8MPa and 32.4MPa,The strength is decreased by 5.4% and 16.5% respectively compared with the benchmark group;the split tensile strength of 20% replacement rate is3.35 MPa,which is 19.7% higher than that of the benchmark group;the axial compressive strength of the 20% replacement rate is 43.3MPa,Compared with the benchmark group,the axial compressive strength is increased by 16.4%.The replacement rate is negatively correlated with the flexural strength.When the replacement rate is 60%,the flexural strength is 4.16 MPa,which is 24.2% lower than the baseline group.(3)The replacement rate of fly ash increased,the early strength of self-compacting concrete decreased,and the later strength increased.The compressive strength of 30% fly ash cubes was 15% higher than that of the benchmark group;the replacement rate of fly ash increased,and the splitting tensile strength First increase and then decrease,the splitting strength is the highest at 10%,which is 0.17 MPa higher than the benchmark group;the flexural strength increases with the increase of the fly ash replacement rate,and the flexural strength of the 30% replacement rate is 6% higher than that of the benchmark group.