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

Abstract

a b s t r a c tAn elliptical ring test method is proposed to replace the circular ring test recommended by ASTM and AASHTO for faster and more reliable assessment of cracking tendency of concrete. Numerical models are also established to simulate stress development and crack initiation/propagation in restrained concrete rings. Cracking age, position and propagation in various rings are obtained from numerical analyses that agree well with experimental results. Elliptical thin rings of certain geometry can shorten the ring test duration as desirable. In thin rings, crack initiation is caused by external restraint effect so that a crack occurs at the inner circumference and propagates towards the outer one. In thick rings, crack initiation is mainly due to the self-restraint effect so that a crack occurs at the outer circumference and propagates towards their inner one. Therefore, thick elliptical concrete rings do not necessarily crack earlier than circular ones as observed from experiment.

Studies on the Influence of Drying Shrinkage Test Procedure, Specimen Geometry, and Boundary Conditions on Free Shrinkage

“…In general, the higher surface-to-volume ratio resulted in the highest magnitude of shrinkage recorded due to faster drying in higher S/V ratio specimens. ese observations are consistent with those of some previous studies [17] although the specimens in the latter were moist cured for one day, and the shrinkage was monitored up to only 28 days. In fact, this was to be expected since drying is a di usion-based process and drying shrinkage depends on the internal relative humidity change and hence on the S/V ratio exposed to drying.…”

“…is is attributed to the fact that, in specimen dried from the radial direction, moisture loss is uniform along the height direction of the specimen but not along the radial direction. In fact, the relative humidity at the outer circumferential surface is slightly higher than the ambient humidity of 50% [17]. As a result, the ring specimen shrinks faster at the outer drying surface where more rapid drying occurs.…”

“…Acknowledging that drying shrinkage is dependent on the S/V ratio exposed to drying [16,17], the rst step was basically to measure free shrinkage using prismatic specimens with di erent S/V ratios. e S/V ratios are summarised in Table 2.…”

Assessment of behaviour and cracking susceptibility of cementitious systems under restrained conditions through ring tests: A critical review

“…It is worth pointing out, however, that the selection of elastic modulus and calculation of degree of restraint will not be necessarily representative of concrete's behaviour because creep effects are disregarded. Although a reference value of elastic modulus is used in the majority of the conducted studies, few authors adopted a decrease in the elastic modulus of concrete by 40% in calculations or simulations, in order to account for the effects of creep [33][34][35]82,[89][90][91][92][93][94][95][96]. It is also worth to remark that concrete E-modulus endures significant changes during the actual experiment (as well as creep behaviour), which even adds more complexity to this analysis.…”

“…which is the static elastic modulus reduced to 60% [33][34][35]82,[89][90][91][92][93][94][95][96]. In this comparison, both original and "effective" elastic moduli are considered in both equations in order to explore the differences between the calculated values of degrees of restraint.…”