Experimental study on durability characteristics of composite fiber reinforced high-performance concrete incorporating nanosilica and ultra fine fly ash

This study is aimed at investigating the durability properties of Composite Fiber Reinforced High-Performance Concrete. A 15% partial replacement of cement by weight was done with ultra-fine fly ash. The addition of nanosilica was in fractions of 0%, 1.5%, 3.0% and 4.5% by weight of cement. For each of the above combinations, 1.0% steel and 0.25% polypropylene fibers, respectively, by volume of the binders were added. A constant aggregate binder ratio of 2.0 and varying water binder ratios of 0.275, 0.300, 0.325 were used in this investigation. The sorptivity test was performed to assess the rate of absorption, and the rapid chloride permeability test (RCPT) was performed to assess the permeability of concrete. Test results revealed that all the mixes attained low to very low chloride permeability. The decrease in chloride ion permeability for mixes with nanosilica and ultra-fine fly ash ranged from 53.83% to 71.45% for 28 days curing period and 55.88% to 74.27% for 56 days curing period, as against the reference mix. 'Residual Compressive Strength' and 'Percentage Weight Loss' for 28 and 56 days of immersion in 5% concentrated solutions of HCl, H2SO4, and MgSO4 were evaluated to study the effects of aggressive ions such as chlorides and sulfates on concrete. The weight loss observed ranged from 7.09% to 2.07% in the case of HCl, from 7.96% to 2.86% in the case of MgSO4, from 17.93% to 11.02% in case of H2SO4 for water binder ratio of 0.275 and 56 days of immersion. The percentage reduction in strength after 56 days of immersion for mixes with water binder ratio of 0.275 ranged from 14.39% to 8.92% in HCl, from 14.53% to 9.66% in MgSO4 and 14.81% to 10.92% in H2SO4. The outcomes of the study showed that a combination of 15% ultra-fine fly ash and 3% nanosilica is the optimum replacement level to achieve increased durability, reduced porosity and permeability due to improved macro and micrometer densities of concrete. In addition, steel and polypropylene fibers have also made a small contribution towards improving the durability of Composite Fiber Reinforced High-Performance Concrete. (C) 2020 Published by Elsevier Ltd.