Mechanical properties and early-age shrinkage of ultra-high performance concrete mortar with recycled fine aggregate

Abstract

This study focuses on the shrinkage behavior of ultra-high performance concrete (UHPC) incorporating recycled fine aggregates (RFA). The effects of RFA content (0, 25, 50, 75, and 100 %) and different moisture states of RFA were investigated through mechanical properties, autogenous shrinkage, drying shrinkage, and restrained shrinkage. The results showed that the incorporation of RFA generally reduced the mechanical properties of UHPC, although marginal improvements were seen with the use of oven-dried or air-dried RFA. Saturated surface-dry (SSD) RFA effectively reduced autogenous shrinkage of UHPC through internal curing. However, the autogenous shrinkage in UHPC increased with the increase of RFA content. RFA also increased the drying shrinkage. Microstructural analysis revealed that the increase in the shrinkage with increasing RFA content were due to the increase in pores smaller than 50 nm, and the decrease in micromechanical properties resulting from the incorporation of RFA. In terms of restrained shrinkage, the circumferential strain, basic tensile creep, and cracking potential of UHPC were related to autogenous shrinkage. Reducing the moisture content of RFA led to an increase in autogenous shrinkage while concurrently decreasing drying shrinkage.