Experimental analysis of influence of pouring interval on fracture performance of concrete structures with cold joints

The pouring interval will cause cold joints in concrete components, which reduce the safety and reliability of structures. This study conducted a three-point-bending test on concrete members with cold joints under different pouring intervals, and analyzed the influence of different pouring intervals on the fracture performance of concrete members with cold joints from four aspects: the crack expansion width, fracture surface characteristics, P-CMOD curve, and fracture parameters of the double-K fracture model. The tests results indicate that the crack expansion width shrank as the pouring interval was extended, the expansion path gradually converged to the vicinity of the cold joint, and the roughness of the fracture surface and the value of the fractal dimension decreased with the extension of the pouring interval. The cohesion of the cold joints' interface was the main reason for the difference in the fracture width and fracture surface characteristics. The failure mode of a concrete structure with cold joints changed from the step-wise cracking mode to the brittle cracking mode as the pouring interval increased. The cohesive toughness, crack initiation toughness, and instability toughness of the components decreased as the pouring interval was extended. The maximum decrease of the ultimate bearing capacity, cohesive toughness, and instability toughness of the components occurred after the pouring interval exceeded the initial setting time. The drop rates are 78%, 80%, 80%, respectively. The crack initiation toughness decreased linearly as the pouring interval was extended.