Effect Of Desert Sand On The Basic Properties Of Ultra-high Performance Concrete

Ultra-High Performance Concrete(UHPC)is a cement-based composite building material with excellent compactness,strength and durability.With the Development of the Western Region and the advancement of "the Belt and Road Initiatives" strategy,undeveloped transportation and scarcity of compliant sand resources in our country’s northwestern district are bound to make it tough to suit the needs of the rapid development of construction projects in this region.The Northwestern Region has serious desertification.If desert sand can be used in the construction of this area to replace the use of aggregates in Ultra-High Performance Concrete,it will inevitably benifit the proper use of desert sand and the control of desertification,and even the Northwestern Region’s long-term construction of China due to its important ecological,economic and strategic significance.However,due to its uncertain composition,finer particles and possible harmful ions contained,desert sand has not been applied to the preparation of concrete or even UHPC on a larger scale.Therefore,this article concentrates on desert sand and make sure how the replacement of desert sand for aggregate affect UHPC’s performance.First,this article studies the impact of desert sand on the performance of UHPC under standard curing after replacing UHPC dolomite aggregate with a replacement rate of 0%,20%,40%,60%,80%,100%.The experimental results show that as the replacement rate of desert sand increases,the mobility first rises and then decreases.When the replacement rate is 40%,the mobility is the highest,which is 10.5%higher than that of no desert sand;the compressive and flexural strengths are in a downward trend.It has a greater impact on the early strength,especially the flexural strength,and the strength gap of UHPCs between different desert sand replacement rate have been reduced in the later period.The permeability continues to rise,which reaches the maximum at the desert sand replacement rate of 80%,with a risen rate of 36.3%.While the desert sand is completely replaced,the permeability is slightly decreased,but it is also significantly higher than the permeability without replacement.The autogenous shrinkage first declines and then rises.When the replacement rate is 20%,there is the smallest autogenous shrinkage,1136.4 με,which reduces 14.8% compared to the UHPC free of desert sand.Mass use of desert sand makes the increasement of autogenous shrinkage caused by desert sand lower.Since UHPC is often cured by steam curing in engineering practice,this article studies the effect of replacing aggregates with desert sand on the performance of UHPC under four different systems of steam curing.The test results show that as the the replacement rate of desert sand increases,the compressive strength of the shorter steaming time(24h)shows a slight downward trend.Steaming reduces the impact of desert sand on the compressive strength of early UHPC;The flexural strength showed a relatively obvious downward trend;under a longer steaming time(3d),the compressive and flexural strengths did not change much,and the 28 d strength showed a slight downward trend.The increase in steaming time does not necessarily increase the compressive strength,and it may even have an adverse effect on the flexural strength of UHPC which is less replaced by desert sand.The increase in steaming time increases the late compression ratio of UHPC.In a short steaming time(24h),the rise of steaming temperature increases the impermeability of UHPC,and replacement rate of desert sand has little impact on permeability.