While the use of internally cured concrete in construction is not new, there is now better understanding of the internal curing process and why IC using pre-wetted lightweight aggregate increases concrete durability and service life in an economical and practical way. However, there is not currently a standard for lightweight aggregates for internal curing.

ASTM International C09 on Concrete and Concrete Aggregates is now developing such a proposed standard, ASTM WK34078, Specification for Lightweight Aggregate for Internal Curing of Concrete. The proposed standard is under the jurisdiction of Subcommittee C09.21 on Lightweight Aggregates and Concrete.

“Concrete, especially high performance concrete, is designed to limit the permeability and reduce chloride ingress,” says John Ries, technical director, Expanded Shale, Clay and Slate Institute, and a C09 member. “Unfortunately, these properties also limit the ability of externally applied curing water to reach the interior of the concrete. The main objective of internal curing is to provide a source of additional water to maintain saturation of the cementitious paste and avoid its self-desiccation.”

Ries says that internal curing can significantly increase the service life of concrete by increasing cement hydration, providing more complete reaction of supplementary cementitious materials and reducing chemical and drying shrinkage.

According to Ries, the proposed new standard will be useful in a variety of civil engineering projects, including roads, driveways, bridges, parking lots, water and sewage treatment tanks, and others. Users of the proposed standard will include the U.S. Federal Highway Administration, state departments of transportation, architects, and environmental, structural and civil engineers.

Interested parties are invited to join in the standards developing activities of C09. ASTM International welcomes and encourages participation in the development of its standards.

For more information on becoming an ASTM member, visit www.astm.org/JOIN.