Effects of flash-calcined sediment on the mechanical – microstructural development and the durability of cementitious materials against to chloride attack and leaching

Numerous studies have highlighted the beneficial effects of flash-calcined sediment (SF) substitution on the mechanical performance of materials. However, very few studies have investigated its impacts on durability, especially the leaching. This study aims to assess its potential effects on the mechanical-microstructural development as well as durability against chloride ingress and leaching. The results indicate that the high specific surface area of SF accelerates cement hydration at early ages, while its pozzolanic reactivity contributes to an enhancement of compressive strength and microstructure in SF-based mortar (MSF) in the long term compared to the reference mortar (Mref). In addition, the formation of addition C-S-H gels from the pozzolanic reaction and the reduction in the critical diameter of pores explain the improved resistance of MSF mortar to chloride penetration. The leaching reveals a significant enhancement in the durability of SF-based cement paste, demonstrated by lower quantities of leached elements and reduced degradation depth compared to the reference. These benefits are attributed to lower Ca(OH)₂ content, a reduced Ca/Si ratio in C–S–H, and a refined microstructure in the MSF paste, which strongly hinder ion diffusion. The dissolution of hydrates during leaching also leads to a decrease in the Young’s modulus of hydration products, and degradation of the microstructure. However, the SF incorporation significantly mitigates this effect compared to the reference.