The role of specimen geometry and boundary conditions on stress development and cracking in the restrained ring test

Effects of specimen size on assessment of shrinkage cracking of concrete via elliptical rings: Thin vs. thick

“…Therefore, it is necessary to distinguish the effects from the selfrestraint caused by nonlinear humidity distribution across a thick concrete ring wall and external restraint provided by the central steel ring. According to Hossain and Weiss [7], the circumferential tensile stress in concrete in a restrained ring specimen subjected to drying shrinkage consists of two parts: (1) the circumferential tensile stress caused by self-restraint in a concrete wall and (2) the circumferential tensile stress caused by the central steel ring restraining the shrinkage of concrete in the radial direction. In the numerical analyses of thick rings, the first part of the circumferential tensile stress can be calculated through analysing a concrete ring with non-uniform free shrinkage, due to nonlinear humidity distribution across the ring wall and without any external restraint.…”

“…Sometimes a visible crack may not even be generated in concrete rings [5,6]. Although AASHTO and ASTM recommended standard dimensions of circular ring specimens, other circular ring geometries [3,4,[6][7][8][9][10] have been used in various studies. Alternatively, novel elliptical ring geometries were adopted to replace circular ring geometries [11][12][13][14].…”

“…Alternatively, a crack would initiate at the inner circumference of a thick ring and propagate towards the outer one if based on the assumption of uniform strain across the ring wall. In order to characterise stress development while considering the effect of ring geometry and drying direction, analytical models were developed to assess residual stress in restrained ring specimens [4,6,7,20,21]. However, it should be noted that those analytical models were developed for circular rings only and may not be appropriate for elliptical ones.…”

On Utilization of Elliptical Rings in Assessing Cracking Tendency of Concrete

“…It is also regarded to have a low cracking sensitivity and not efficient for large amounts of material evaluation (See et al, 2003). In addition, because the degree of restraint is largely dependent on stiffness and geometry of the central restraining steel ring, concrete in a circular ring test may not develop a visible crack if the steel ring is not thick enough (Hossain & Weiss, 2006), that is, the restraining stiffness of the steel core is not big enough. Meanwhile, due to geometry effect, there is an equal opportunity of the crack occurring along the circumference of a circular concrete ring, so that it is not possible to predict the exact position of the crack.…”

“…The circular ring test method has been used by various researchers for investigating cracking potential of concrete or other cement-based materials under restrained conditions (Bentur & Kovler, 2003). So far, these researches have been basically concentrated on three fields, namely, the effects of concrete mixture compositions (Li, Qi, Li, & Ma, 1999;Mokarem, Weyers, & Lane, 2005;Passuello, Moriconi, & Shah, 2009;See, Attiogbe, & Miltenberger, 2003;Tongaroonsri & Tangtermsirikul, 2009;Turcry, Loukili, Haidar, Pijaudier-Cabot, & Belarbi, 2006), moisture gradients, and drying conditions (Branch, Rawling, Hannant, & Mulheron, 2002;Hossain & Weiss, 2004Moon, Rajabipour, Pease, & Weiss, 2006;Weiss & Shah, 2002;Weiss, Yang, & Shah, 2000) and ring size and geometry (Hossain & Weiss, 2006; In both standards, strain gages are used to measure strain of the central restraining steel core to provide a more accurate assessment of cracking age as compared to simple visual observation of the time-tofirst-cracking, which is useful but maybe less reliable than strain monitoring. In practice, the circular ring test is also widely used to determine the effects of material variations on cracking potential of concrete mixtures as well as on induced tensile stress in restrained concrete.…”