Effect of lightweight sand and shrinkage reducing admixture on structural build-up and mechanical performance of UHPC

Abstract

Pre-saturated lightweight sand (LWS) and shrinkage reducing admixture (SRA) can be used to mitigate autogenous shrinkage of ultra-high-performance concrete (UHPC). However, their individual and synergetic effects on structural build-up that is essential for thin bonded bridge deck overlay rehabilitation and 3D printing have not been well understood. This study investigates the impact of LWS and SRA on structural build-up of UHPC with mini-slump flow of 190 ± 10 mm. Furthermore, the cement hydration, autogenous shrinkage, mechanical performance, and porosity of UHPC prepared with LWS and SRA were studied. Test results show that the structural build-up enhanced from 90 to 138 Pa/min with the increase of the LWS content from 0 to 25% given the lower surface coverage ratio of high-range water reducer onto cement particles. The incorporation of 2% SRA led to the lowest structural build-up of 64 Pa/min due to the lower bridging effect of early-age hydration products. The LWS17&SRA1 mixture exhibited higher structural build-up of 105 Pa/min, lower autogenous shrinkage of 340 με, as well as comparable compressive strength, elastic modulus, and flexural strength of 139 MPa, 48 GPa, and 19 MPa compared to the Reference mixture prepared without any LWS and SRA that had the corresponding values of 90 Pa/min, 535 με, 142 MPa, 50 GPa and 19 MPa, respectively. The comparable mechanical performance was due to the increased effect of LWS on cement hydration and pozzolanic reaction of silica fume counteracted the reduced influence of SRA.