Using the Double Ring Test to Assess the Effect of Type of Aggregate Used on Thermal Cracking Potential of Concrete

Abstract

Early age thermal cracking occurs when tensile stress generated from restrained deformations in young concrete reaches its tensile strength. The risk of early age cracking is especially high for elements involving large concrete placements such as bridge piers, foundations etc. and concrete with low water-to-binder (w/c) ratio. The research in literature has focused on finding ways to mitigate cracking through mix design approaches and devising test methods to determine restraint stresses in concrete. The most commonly used test methods, such as the Rigid Cracking Frame, require special equipment and calibration to function properly. There is need for a more simple but accurate test that can measure the effects of both early-age expansion and shrinkage, as well as account for the temperature changes that occur in a mass concrete element. The double ring test, which has been used to study effects of internal curing on early age cracking, has potential to measure effects of both shrinkage and expansion. To evaluate its viability as a reliable test to characterise the early age thermal cracking potential of concrete, the double ring test was used in this study to assess the effect of type of aggregate used on early age thermal cracking of concrete subjected to temperature history similar to that experienced in an actual mass concrete structural element. Three types of locally available aggregates were investigated. Preliminary results indicate that the double ring test can be used to study effects of thermal deformations on concrete subjected to a changing temperature history, and that type of aggregate used can influence the potential of cracking.