超细粉煤灰对超高性能混凝土流变性、力学性能及微观结构的影响

Effect of Ultra-fine Fly Ash on Rheological Properties, Mechanical Properties and Microstructure of Ultra-high Performance Concrete

为探讨超细粉煤灰(UFA)对超高性能混凝土(UHPC)性能的影响,系统研究了UFA取代粉煤灰(NFA)后UHPC的流变性、力学性能、孔结构及微观结构变化。结果表明:当UFA取代NFA的质量分数小于50%时,UHPC的流动性会随着UFA取代量的增加而显著改善,继续增加UFA的取代量(大于50%)则UHPC的流动性降低;取代量小于50%的UFA可显著降低UHPC浆体的屈服应力和粘度;随着UFA取代量的增加,UHPC的抗压强度和抗折强度增大。当UFA完全取代NFA(100%)时,UHPC的最高抗压强度和抗折强度分别可达167.2 MPa和25.2 MPa。压汞仪和X射线计算机断层扫描成像(X-CT)被用于测试UHPC硬化体的孔隙率,试验结果显示UFA可降低UHPC的孔隙率;扫描电镜结果也表明掺UFA可使UHPC的微观结构更加致密,从而使UHPC展现出优良的力学性能。

In order to investigate the effect of ultra-fine fly ash(UFA)on the impact of ultra-high performance concrete(UHPC),the rheological properties,mechanical properties,pore structure and microstructure of UHPC were systematically studied by using UFA instead of NFA.The results show that when the mass fraction of UFA substitutes for NFA is less than 50%,the fluidity of UHPC would be significantly improved with the increase of the amount of UFA,and the further increase in the substitution of UFA(more than 50%)would reduce the fluidity of UHPC.The rheological properties also show that UFA could significantly reduce the yield stress and viscosity of UHPC paste.The mechanical test results show that the compressive strength and flexural strength of UHPC increase with the increase of UFA substitution amount.When UFA completely replace NFA(100%),the maximum compressive strength and flexural strength can reach 167.2 MPa and 25.2 MPa,respectively.Mercury pressure and X-CT were used to test the porosity of the UHPC hardened body.The results show that UFA can reduce the porosity of UHPC,and the scanning electron microscope also shows that UFA can make the microstructure of UHPC more compact,thus enabling the UHPC to exhibit excellent mechanical properties.