An alternative method for performance improvement of ultra-high performance concrete by internal curing: Role of physicochemical properties of saturated lightweight fine aggregate

To prepare low-shrinkage ultra-high performance concrete (UHPC) with adequate mechanical properties and durability, the role of physicochemical properties of saturated lightweight fine aggregate (LWFA) in controlling the properties development of UHPC was explored. The test results showed that the LWFA could not only mitigate autogenous shrinkage significantly but also improve compressive strength and durability of UHPC. The internal curing of LWFA mitigated the reduction of internal relative humidity and promoted the hydration of cement and pozzolanic reaction. As a result, more C-S-H gel with higher polymerization degree was formed, contributing to improved micro-mechanical properties. Meanwhile, the pores in UHPC containing LWFA were significantly refined and a dense zone was formed around LWFA. Therefore, the increased hydration and pozzolanic reaction degrees, enhanced density and polymerization degree of C-S-H gels and refined pore structure of matrix counteracted the negative effects induced by the porous LWFA, contributing to the improved properties of UHPC.