Durability Performance of Concrete with Fly Ash as Fine Aggregate Eroded by Chloride Salt

Abstract

The aim of this study is to investigate the durability of concrete with fly ash as a fine aggregate (CFA) in chloride salt environments. The natural diffusion method is used to analyze the concrete strength, chloride ion concentration, and diffusion coefficient after chloride salt erosion in a laboratory environment. In addition, scanning electron microscopy, X-ray diffraction, and Mercury intrusion porosimetry are performed to clarify the deterioration mechanism of concrete in chloride salt environments. The results indicate that owing to the chloride ion binding effect, the concrete porosity decreases and the concrete strength increases after chloride salt immersion. The decreased porosity caused by delayed hydration is primarily due to Friedel’s salt and CaCO3 produced during chloride ion erosion. CFA has a lower chloride diffusion coefficient and lower chloride concentration compared with ordinary concrete at all depths. In general, CFA exhibits excellent resistance to chloride salt erosion.

Effect of Replacing Fine Aggregate with Fly Ash on the Performance of Mortar

“…This may be because the early strength of mortar is mainly provided by the hydration products of cement, and the secondary hydration reaction of 1 d fly ash was incomplete. Fly ash plays a significantly greater role in the microaggregate effect than volcanic ash does in the early stages of cement hydration [ 22 ]. The strength of the fly ash fine aggregate mortar first increased and then decreased with increasing fly ash substitution rate; however, it was higher than that of the benchmark group.…”

“…In addition, the compressive strength, splitting strength, and flexural strength modulus of elasticity of CFA perform best when the fly ash substitution rate is 50%. Additionally, Mao et al [ 22 ] established that when the fly ash content was below 40%, the strength of fly ash fine aggregate concrete increased with an increase in fly ash content. The active components of fly ash react fully with the cement hydration product Ca(OH) 2 to generate a C-S-H gel, which can fill the internal pores of concrete.…”