Mitigation of early-age cracking in concrete structures

Early-age cracking can adversely affect the behavior and durability of concrete elements. This paper will cover means to mitigate early-age cracking in concrete bridge decks and mass concrete elements. The development of in-place stresses is affected by the shrinkage, coefficient of thermal expansion, setting characteristics, restraint conditions, stress relaxation, and temperature history of the hardening concrete. The tensile strength is impacted by the cementitious materials, the water-cementitious materials ratio, the aggregate type and gradation, the curing (internal/external) provided, and the temperature history of the hardening concrete. In this study, restraint to volume change testing with rigid cracking frames (RCF) was used to directly measure and quantify the combined effects of all variables that affect the development of in-place stresses and strength in a specific application. The laboratory testing performed involved curing the concrete in the RCF under sealed, match-cured temperature conditions to simulate concrete placement in concrete bridge decks and mass concrete. Experimental results reveal that the use of low heat of hydration concretes, concretes that use fly ash and slag cement, and lightweight aggregate concretes (because of reduced modulus of elasticity and coefficient of thermal expansion), are very effective to reduce the risk of early-age cracking in these elements