In numerous laboratory and a few large scale field studies, the use of pre-wetted lightweight aggregates (LWA) in mortars and concretes has been shown to provide internal curing to the cementitious materials (see http://ciks.cbt.nist.gov/~bentz/phpct/database/ic.html for a listing of relevant papers and reports). Experimental measurements have indicated a substantial reduction (or even complete elimination) of autogenous shrinkage, the maintenance of a higher internal relative humidity throughout curing, and an increase in later age hydration and compressive strengths, particularly under sealed curing conditions. Reductions in autegenous shrinkage and maintenance of internal relative humidity should result in a substantial reduction in early-age cracking. Higher internal humidity also promotes more complete hydration of the cementitious materials thus leading to a more efficient use of these components and the potential for reduction in the cementitious content of the concrete. These improvements have been quantitatively demonstrated for mortars and concretes based both on ordinary portland cements and on blended cements (containing slag, silica fume, or fly ash). Furthermore, three-dimensional x-ray microtomography studies have conclusively indicated the movement of internal water from the LWA to the surrounding hydrating cement paste during the first hours and days of curing. In addition, there may be further benefits of utilizing internal curing using pre-wetted LWA, such as the production of a concrete with greater slump retention (workability) and a more robust air void system, the latter due to the pores in the emptied LWAs functioning as physical air voids in addition to any entrapped and entrained air normally present in or proportioned into the concrete.

1. Demonstrate the performance benefits of internal curing provided by pre-wetted lightweight aggregates to concrete used in transportation structures. 2. Investigate additional potential benefits such as slump retention and increased freeze-thaw durability. 3. Produce a Guide document that covers the characterization of lightweight aggregates for use as internal curing agents and the proportioning and production of concrete mixtures with such aggregates.

The proposed study is planned for three phases. Phases 1 and 2 are laboratory studies to identify the characteristics of lightweight aggregates that are important in assessing and engineering their use as internal curing agents. In phase 2, a set of lightweight aggregates of differing characteristics will be used in developing concrete mixtures for varied applications. Phase 3 will demonstrate the technology through its application in field construction.