Effect of Ultra-fine Fly Ash on Rheological Properties, Mechanical Properties and Microstructure of Ultra-high Performance Concrete
CAO Runzhuo1,2, ZHOU Mingru1,2, ZHOU Qun1,2, HE Yong1,2
1 Key Laboratory of Disaster Prevention and Mitigation in Civil Engineering of Gansu Province, Lanzhou University of Technology, Lanzhou 730050 2 Engineering Research Center for Disaster Prevention and Reduction of Civil Engineering in Western China, Lanzhou University of Technology, Lanzhou 730050
Abstract: 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.
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