Cracking behavior of CA-UHPC overlay in steel-CA-UHPC composite bridge deck: Flexural tension test and restrained shrinkage effect

Coarse Aggregate Ultra-High Performance Concrete (CA-UHPC) has emerged as a promising alternative UHPC material for steel-UHPC composite decks due to its reduced autogenous shrinkage. The cracking performance of CA-UHPC overlay is of interest to ensure the composite deck stiffness. To this end, flexural-tension tests on the composite decks were conducted to explore the effects of reinforcement ratios, concrete covers, concrete types (CA-UHPC vs. normal concrete), and loading nature (monotonic vs. cyclic). Test observations indicate that the restrained shrinkage effect leads to premature cracking of the CA-UHPC overlay under external loads. Increasing reinforcement ratios or reducing concrete covers helps to control maximum crack widths. When reinforcement ratios exceed 2.1 %, maximum crack widths of CA-UHPC overlay remain below 0.2 mm. Unlike normal concrete, steel rebars embedded in CA-UHPC overlays do not yield. Limited cyclic tension has a negligible impact on the cracking response. Moreover, a theoretical analysis based on the Trost-Bazant-algebraic-equations was conducted to understand the restrained shrinkage-induced internal force redistribution. Finally, an empirical model between the proposed restrained degree and steel-CA-UHPC bending stiffness ratio was developed to predict the restrained tensile stresses and the initial cracking loads. This study provides deeper insights into the cracking behavior of CA-UHPC overlay under various conditions, contributing to the optimization of such composite decks.