Effect of Nano-SiO2/Steel fiber on the mechanical properties and sulfate resistance of High-Volume fly ash cement materials

Abstract

The flexural strength, compressive strength, water absorption, and sulfate resistance of high-volume fly ash cement mortar hybrid containing 0–2.5 wt% nano-silica dioxide (Nano-SiO2, NS) and 0–2.0 vol% steel fibers (SF) were studied in this paper. Fly ash (FA) was used to replace 50 wt% of Portland cement. The resistance to sulfate attack was tested by exposing the specimens to 5.0 wt% sodium sulfate solution, and the flexural strength, compressive strength, and mass loss after 3, 6, and 9 months of erosion were determined. Specimens cured at normal condition were tested at the same ages for comparison. Moreover, the microstructure and pore structure were also investigated. The test results show that the combined addition of NS and SF significantly enhanced the flexural and compressive strength of high-volume fly ash mortar and significantly reduced its water absorption. Compared with control mortar, the addition of 1.0 vol% SF and 2.0 wt% NS increased the flexural and compressive strength by 70.6 % and 53.7 % respectively at the age of 28 days, and the water absorption of mortar was decreased by 45.0 % at the age of 90 days. The hybrid addition of NS and SF improved the sulfate resistance of mortar, reduced the mass loss rate of sulfate attack, and enhanced the residual strength of mortar after sulfate attack. In addition, the mercury injection test showed that adding NS and SF can obviously refine the pores of high-volume fly ash mortar, and reduce the internal average pore diameter.