Mechanical Behavior Based on Aggregates Microstructure of Ultra-high Performance Concrete

We developed ultra-high performance concrete (UHPC) incorporating mullite sand and brown corundum sand (BCS), and the quartz sand UHPC was utilized to prepare for comparison. The properties of compressive strength, elastic modulus, ultrasonic pulse velocity, flexural strength, and toughness were investigated. Scanning electron microscopy and nanoindentation were also conducted to reveal the underlying mechanisms affecting macroscopic performance. Due to the superior interface bonding properties between mullite sand and matrix, the compressive strength and flexural toughness of UHPC have been significantly improved. Mullite sand and BCS aggregates have higher stiffness than quartz sand, contributing to the excellent elastic modulus exhibited by UHPC. The stiffness and volume of aggregates have a more significant impact on the elastic modulus of UHPC than interface performance, and the latter contributes more to the strength of UHPC. This study will provide a reference for developing UHPC with superior elastic modulus for structural engineering.