Parametric Assessment of Stress Development and Cracking in Internally Cured Restrained Mortars Experiencing Autogenous Deformations and Thermal Loading

Abstract

A finite element model is used to examine how the properties of cementitious mortar are related to the stress development in the dual ring test. The results of this investigation are used to explain the thermal cracking behavior of mixtures containing prewetted lightweight aggregates (LWA) by quantifying the contribution of several material properties individually. 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. The rate of stress development, age of cracking, and 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, elastic modulus of the mortar, creep effect of the mortar, and rate of thermal loading. Depending on the rate of cooling, cracking may or may not occur. The slowest rate of cooling (C/h) minimizes the effects of creep while cooling rates faster than C/h can produce a thermal gradient through the mortar cross-section that needs to be considered.

Internal curing of mortar with low water to cementitious materials ratio using a normal weight porous aggregate

“…The descend of strength of internally cured mortar or concrete at early age (7 days or earlier) usually was observed [10][11][12][13][14] due to the porosity of lightweight aggregate (LWA). However, this was the results under free condition.…”

Influence of prewetted lightweight aggregates on the behavior and cracking potential of internally cured concrete at an early age

“…Although external water curing is utilized in HPC, its cracking potential is increased because of the low penetration of concrete with low w/c ratio [9]. Therefore, internal curing (IC) technology is employed to reduce the cracking potential [10]. IC, which is defined by the American Concrete Institute as ''a process by which the hydration of cement continues because of the availability of internal water that is not part of the mixing water" was proposed by Robert Philleo as a means of avoiding self-desiccation using saturated lightweight fine aggregate in high-strength concrete in 1991 [11].…”

Increased Use of Fly Ash in Hydraulic Cement Concrete (HCC) for Pavement Layers and Transportation Structures

“…As the temperature was reduced at later ages, this compressive stress was reduced while no significant shrinkage stresses developed. This observed behavior may also be attributed to the more compliant nature of the material due to the lower stiffness obtained with lightweight aggregate (Raoufi et al, 2011). At the end of the test, when the temperature was reduced at a faster rate in attempts to induce cracking, the shrinkage stress was also lower in the internally cured mixture.…”

“…For instance, the 0.30-60%-L mixture resulted in relatively low residual stress accumulation when held at a constant temperature, an 86% reduction in residual stress over the 0.30-0% mixture and a 68% improvement upon the 0.30-60% mixture. This can be attributed to the reduced autogenous shrinkage and a low modulus of elasticity as a result of IC with fine LWA (Raoufi, Schlitter, Bentz, & Weiss, 2011). The result is a material that has the benefits of a low w/cm (e.g.…”