Enhancing mechanism of the chemically etched fly ash cenosphere on concrete performance

Abstract

Fly ash cenosphere (FAC), one of the primary coal-based derivatives, has not been extensively utilized in construction fields due to its poor performance. Although chemical etching is considered as an effective method to improve the performance of FAC, the mechanism by which the etched FAC enhances the performance of concrete is still unclear. In this study, water transport properties and pozzolanic activity of the etched FAC were evaluated to provide evidence for the enhanced properties of the etched FAC. The impact of the etched FAC on the degree of hydration, microstructure morphology and mechanical properties of concrete was further assessed by comparing with the concrete containing the raw FAC. The results show that the etched FAC has good water absorption and desorption properties, thus presenting good internal curing effect. Furthermore, the release intensity of the effective elements, i.e., Si and Al, that can participate in the pozzolanic reactivity is enhanced, which indicates an increased pozzolanic activity of the etched FAC. In addition, the incorporation of the etched FAC results in an increase of 3.2%, 16.0% and 19.5% in the 28-d hydration degree and compressive and flexural strength, respectively, compared to the concrete incorporating the raw FAC. Given the internal curing effect and the increased pozzolanic activity, the interfacial transition zone between the etched FAC and the paste is strengthened and the phase composition of the hydration products is improved.