Effects of moisture gradient of concrete on fracture process in restrained concrete rings: Experimental and numerical.

Highlights • Non-uniform shrinkage of concrete provides approximate 40% restraint. • Crack initiates at outer surface and propagates towards inner surface of a ring. • Under uniform shrinkage assumption, external restraint is overestimated. • With increasing of concrete strength, the proportion of self-restraint increases. Abstract The non-uniform shrinkage caused by moisture gradient in concrete provides self-restraint, which has a significant effect on the assessment of cracking potential of concrete through the restrained shrinkage ring test. Furthermore, moisture gradient in concrete would be also affected by concrete strength because concretes designed for different strength grades usually have different water to cement ratio. In this paper, three series of circular and elliptical concrete rings with a 37.5 mm thick wall and three distinguished concrete strength grades of C30, C50 and C80 were tested to investigate the effect of the moisture gradient on crack initiation and propagation in restrained concrete rings. An integrative model based on the nonlinear diffusion theory is introduced to calculate the moisture distributions in concrete rings, and the fictitious temperature fields are derived for the simulation of the shrinkage effect in concrete. Meanwhile, a fracture mechanics-based numerical method is proposed to analyze the crack initiation and propagation in a concrete ring in the restrained ring test. The effects of ring geometry, concrete strength and uniform/non-uniform shrinkage assumption on the cracking initiation and propagation process are elaborated. The results indicate that the non-uniform shrinkage in concrete provides driving energy for concrete cracking, which is approximately 40% of the total driving energy. Accordingly, it significantly affects the crack initiation position and propagation direction, occurring at the outer surface and propagating toward the inner surface of the concrete ring. With the increase of concrete strength, the cracking potential of restrained concrete ring increases and the proportion of the self-restraint caused by the non-uniform shrinkage in the total restraint decreases because of the reduced moisture distribution. [ABSTRACT FROM AUTHOR]