Impact resistance and life prediction of UHPC-based functional gradient concrete for wet joints

This paper explores a functional gradient design for Ultra-High Performance Concrete (UHPC) wet joints in precast bridge decks, focusing on impact resistance and life prediction. The study focuses on enhancing the structural performance through functional gradient design, optimizing the fiber ratio, and determining the most effective thickness of the UHPC layer. A total of 120 specimens were divided into 20 groups, with 6 specimens in each group, to conduct drop-weight impact tests. Experimental results demonstrated that the functional gradient design significantly enhanced impact resistance, with the synergistic effect of steel-polypropylene (SF-PPF) fibers peaking at a 2:3 mixing ratio. The thickness of the UHPC layer also had a critical effect; increasing the thickness from 1/3$H_0$ to 1/2$H_0$ resulted in a 25 % increase in the number of initial crack impacts and a 53 % increase in the number of destructive impacts. Fiber behavior on the fracture surface was analyzed, confirming that the functional gradient design and optimized fiber composition enhanced toughness, ductility, and impact life. Furthermore, based on Weibull distribution modeling, a framework was proposed for predicting the impact resistance performance under specific failure probabilities. These findings provide scientific guidance for optimizing functional gradient designs, including fiber ratios and layer thickness, while balancing cost and performance for practical applications.