Influence of fly ash on the long-term performance of low water-to-binder ratio paste containing silica fume in water curing and drying curing regimes

Abstract

The integration of fly ash into silica fume-containing cement-based material with low water-to-binder ratios (w/b) aims to elevate their overall performance. Nevertheless, the evolution of properties in these materials reinforced with fly ash, and the impact of fly ash on properties, remains elusive. This study delved into the behavior of water uptake and loss, deformation patterns, and mechanical attributes of low w/b paste, subjected to curing in limewater and drying regimes. The cementitious composition of the low w/b paste consists of cement, augmented by 15 % silica fume, and further modified with varying proportions of fly ash. The study also looked into the role of fly ash in paste performance by carrying out comprehensive evaluations of hydration, the resultant hydration product, and the characteristics of cracks that developed. The findings reveal that for low w/b paste, spherical fly ash should be preferred, as under varying curing conditions, the honeycomb-structured fly ash exacerbated water migration, thereby amplifying the deformation in the paste with low w/b containing silica fume. A relatively high dosage of fly ash incorporation was necessary to significantly enhance the hydration degree of cement in low w/b pastes. The effects of fly ash on the compressive strengths of low w/b pastes containing silica fume were relatively minor under various curing conditions but reduced the flexural strengths of the low w/b pastes with silica fume under dry curing conditions.