Experimental study on crack performance of steel and early-age BFRC composite beams in negative moment region

The wet joint interface concrete deck in the negative moment region of steel-concrete composite beams is sus-ceptible to tensile cracking, which compromises the durability of the structure. Herein, a basalt fiber reinforced concrete (BFRC) is proposed to examine the wet joint cracking performance of concrete deck in the negative moment region of steel-concrete composite beams. To this end, four-point bending tests were conducted on seven steel-concrete composite beams to investigate failure modes, crack distribution patterns, load-deflection rela-tionship, and load-crack width relationship. Experimentally, the effects of the wet joint concrete types (BFRC and normal concrete), basalt fiber volume content (0, 0.3%, and 0.6%), and concrete age (28, 14, 7, and 3 days) on their mechanical behavior were performed and discussed. The results showed that typical flexural failure commonly occurred in all specimens under the negative moment, with initial cracks appearing at the wet joint interface. The wet joint concrete with basalt fiber volume content of 0.3% exhibited the highest crack resistance, which resulted in a higher number of cracks, less crack spacing, and more uniform crack distribution in the wet joint concrete deck. The prediction methods of the average crack spacing and crack width of the wet joint concrete were proposed based on the existing theoretical models. The crack width and concrete age influence coefficients were proposed to rationally assess the effects of basalt fiber and concrete age. The modified formulas for the average crack spacing and crack width showed a reasonably good agreement with the experimental results when considering the effects of basalt fiber and concrete age. These formulas can be effectively utilized to evaluate the main crack width at the non-interface joint in the negative moment region of steel-concrete com-posite beam decks. The proposed approaches can provide a simple and practical method to effectively predict the crack width in the negative moment region of the steel-concrete composite beam.