In order to study the dynamic compressive performance of concrete in frozen areas,an uniaxial dynamic compressive test is carried out on concrete specimens with different admixtures after freeze-thaw cycles.The loss ra-tio of strength and strain of the three groups of concrete(PVA fiber,nano-SiO2and PVA-nano-SiO2)under differ-ent strain rates(10-5s-1,10-4s-1 and 10-3s-1)are studied to evaluate the relationship of excellence and imper-fection of their dynamic compressive performance.The microscopic mechanism of admixture to improve the perform-ance of concrete is studied by SEM scanning test.The results show that,for concrete mixed with PVA fiber or nano-SiO2 alone(Group P or Group S),the admixture has no significant effect on the dynamic compression performance of concrete after freeze-thaw cycles.When double mixed with PVA fiber and nano-SiO2(Group SP),the C-S-H gel formed by the reaction of nano-SiO2 and hydration product Ca(OH)2 fills the pores and ITZ of concrete,enhances the compactness of concrete,and provides conditions for the more complete bridging effect of PVA fibers in concrete after freezing.After 100 freeze-thaw cycles,the strength of concrete in SP group is about 10％higher than that in P group and S group at the strain rate from 10-4s-1 to 10-3s-1.The synergistic effect of PVA fiber and nano-SiO2 improves the dynamic compressive performance of concrete after freezing.
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