Coupled effect of pozzolanic activity and internal curing induced by pre-soaked expanded clay aggregates in no-slump mortar mixtures

Roller-compacted concrete pavements (RCCP) have low water-to-cement ratios and no-slump consistency, making them susceptible to premature desiccation and incomplete hydration. Expanded clay aggregates (ECAs) can provide both internal curing and pozzolanic activity; however, their combined influence in RCCP has not been thoroughly investigated. Dry ECAs were evaluated using suspension, modified Chapelle, TGA, XRD, and FTIR tests to assess their intrinsic pozzolanic reactivity. Results confirmed moderate pozzolanic activity, with calcium hydroxide consumption satisfying NF P18-513 requirements. Surface dissolution promoted secondary C-S-H/C-A-S-H formation, silicate polymerisation, and accelerated hydration. Mortar mixtures containing 20% pre-soaked ECAs were subsequently investigated. SEM-EDS analysis revealed localized microstructural refinement within the interfacial transition zone through higher Al/Ca and Si/Ca ratios. The strength activity index exceeded 80%, confirming the positive contribution of ECAs to strength development. Conclusively, pre-soaked ECAs synergistically enhanced hydration, densified the microstructure, and improved early-age performance of RCCP.