Effects of fly ash microspheres on sulfate erosion resistance and chlorion penetration resistance in concrete

Abstract

Fly ash microsphere (FAM) is a superfine fly ash product consisting of perfectly spherical and smooth particles. In this study, FAM was added to concrete for use in saline soil areas. The replacement levels of cement by FAM were 10% and 20% with a water-to-binder (w/b) ratio of 0.42. The hydration heat, thermogravimetric (TG) analysis, rheological performance, and the flowability of pure cement (CF0) and FAM-doped cement (CF10 and CF20) were investigated. The second exothermic peak occurred earlier and was higher in the FAM-doped cement than the CF0. The results showed that the nucleation effect of the FAM accelerated the early hydration speed of the cement. The TG results indicated that the Ca(OH)2 consumption was higher at 28 days due the addition of the FAM, which improved the interfacial transition zone and blocked the connected porosity of the hardened cement paste. The ball-bearing effect of the FAM particles in the paste reduced the internal friction between the grains, thereby significantly improving the rheology and the flowability of the cement paste. In addition, the filler effect of the FAM particles significantly improved the pore structure, which increased the compressive strength and chlorion penetration of the concrete. It was also found that the FAM increased the workability while improving the resistance of the concrete to sulfate attack when exposed to multiple drying–wetting cycles.