Implementation of Internal Curing in Transportation Concrete

Internal curing is one method used to improve the mechanical properties and durability of concrete. Internal curing provides additional water to the hydrating cement particles that is not part of the original mixing water. The Ohio Department of Transportation (Ohio DOT) observed significant differences in early-age cracking of high-performance bridge decks in northeast Ohio and attributed it to differences in the absorption of the coarse aggregate. Ohio DOT sponsored a study to investigate the properties and cracking tendencies of several of its classes of concrete, including high-performance concrete, paving concrete, structural concrete, and bonded overlays. A large number of studies have been published documenting the benefits of internal curing; however, work is necessary to implement it. The focus of this study is on the benefits of internal curing for pavement and overlay mixtures and the use of internal curing in the field. Evaluation was done of the fresh and hardened concrete properties of the different Ohio DOT concrete classes, made with different coarse aggregates and with lightweight aggregate replacements. Restrained shrinkage ring tests were used to predict which concrete mixtures were most likely to crack. Field tests were also conducted, and shrinkage ring data from field samples showed a possible improvement in the cracking potential of mixtures that utilized internal curing. The lightweight aggregate substitution improved both early and ultimate strength, and reduced cracking tendency. Since these are key performance measures for concrete pavements and overlays, internal curing offers strong promise for the development of long-life concrete pavements and structures