On the inherent material states of ultra-high performance concrete from an acoustic perspective: Linking mechanical properties to microstructural conditions

Abstract

This study investigates the inherent material state of ultra-high performance concrete (UHPC) by employing multiple linear and nonlinear ultrasonic techniques. The research focuses on characterizing the mechanical properties and microstructural conditions of UHPC and assessing its degradation under thermal cycling. The findings reveal that UHPC exhibits superior elastic properties compared to conventional cementitious materials, particularly with a shear modulus comparable to that of aluminum. UHPC also shows weakly dispersive behavior at high frequencies up to 10 MHz, confirming a dense and homogeneous internal structure, similar to that of cement paste without any aggregates. The integration of linear parameters enables the creation of an acoustically organized material classification diagram, positioning UHPC in the transition zone between metallic materials and cementitious materials. For microstructure analysis, the nonlinear ultrasonic parameter (beta) exhibits high sensitivity to early-stage microcracking, confirming its effectiveness in monitoring microstructural change in UHPC. The crack density (rho crack), derived by plugging the measured linear parameters, shows a linear correlation with beta, suggesting rho crack as a viable alternative to beta while improving the feasibility of detecting microstructural damage in full-scale, in-service concrete structures. The findings of this study can serve as a guideline for developing effective nondestructive evaluation methods for UHPC structures to ensure their durability and safety.