This study used a finite element model to examine how the properties of cementitious mortar are related to the rate of stress development in the dual ring test. The results of this investigation are used to explain the thermal cracking behavior of mixtures containing pre-wetted lightweight aggregates (LWA). In addition to the beneficial effects of using the LWA as an internal curing agent to reduce the autogenous shrinkage of concrete, the LWA also helps to reduce the potential for thermal cracking due to a lower elastic modulus and increased stress relaxation. It was shown that the rate of stress development, age of cracking, and the magnitude of the temperature drop necessary to induce cracking in a dual ring specimen are dependent on a variety of factors, including the coefficient of thermal expansion of both the cementitious mortar and the restraining rings, the elastic modulus of the mortar, the creep effect of the mortar, and the rate of thermal loading. It was shown that depending on the rate of cooling, cracking may or may not occur. The slowest rate of cooling (2.5 ˚C/h) recommended minimizes the effects of creep while cooling rates faster than 8 ˚C/h can produce a thermal gradient through the concrete cross section that needs to be considered.
Citation: Cement and Concrete Composites
Pub Type: Journals
Dual ring, finite element method, internal curing, lightweight aggregate, restrained cracking, thermal cracking