Study On Influence Of Shale Lightweight Sand On The Mechanical Properties Of Ultra-high Performance Concrete

Ultra High Performance Concrete(UHPC)is a new cement-based material with ultra high strength,high toughness and excellent durability,which has a good application prospect.Studies have shown that the inclusion of internal curing materials in ultra-high performance concrete can effectively reduce the risk of UHPC shrinkage and cracking.In this paper,the mixture proportion of ultra-high performance concrete is firstly determined.On this basis,Shale lightweight sand is used as UHPC internal curing material.The effect of shale ceramicite on the fiber-matrix interfacial bonding properties and mechanical properties of ultra-high performance concrete were studied.The main research contents include the following three aspects:(1)The effects of the types and gradations of fine aggregate,water to cementitious materials ratio and the dosage of a liquid-based SP on the fluidity,compressive strength and flexural strength of UHPC were studied.The results show that UHPC can be prepared by replacing ordinary quartz sand with quartz sand.The compressive strength can reach about 90% of the traditional UHPC,the material cost can be reduced by about 10%.The water-binder ratio increased by 0.02,and the fluidity increased by about 35 mm.When the water-binder ratio is 0.18,the UHPC compressive strength is the highest.The strength decreases when the water-binder ratio is too low or too high.The amount of superplasticizer has little effect on the compressive strength of UHPC.(2)The effect of lightweight sand content on the fiber-matrix interface bonding properties of UHPC was studied by fiber pull-out experiment.The influence mechanism was discussed by means of concrete autoshrinkage experiment,SEM and thermogravimetric analysis.The results showed that with the increase of the content of lightweight sand,the decrease of fiber pull-out curve was faster and the slippage hardening was weaker.The amount of lightweight sand has little effect on the bond strength of the fiber matrix interface,while the interface friction stress and Fiber pull-out energy dissipation are significantly reduced.This can be explained by the reduced shrinkage of concrete and the lower strength of lightweight sand,which reduce the friction between fiber and concrete matrix.(3)By measuring the fluidity,compressive strength and tensile properties of UHPC with different lightweight sand content,the influence of lightweight sand content on the basic properties of UHPC was studied.The results showed that the addition of lightweight sand increased the fluidity of UHPC in a small range,and the strength of UHPC matrix decreased significantly in the early stage,and thenegative influence gradually decreased with the curing age.With the increase of lightweight sand content,UHPC uniaxial tensile strain hardening becomes weaker,and the initial crack strength,tensile strength,peak strain and energy consumption all decrease gradually.