Evaluation of Internally Cured Concrete for Paving Applications
Internally Cured Concrete (ICC) is a concrete mixture in which a portion of the coarse, intermediate, and/or fine aggregates (for example, 30 percent of sand) is replaced with similar sized prewetted lightweight aggregate (LWA). Internal curing (IC) is a means to provide hydrating concrete adequate moisture from within the mixture to replace water lost due to chemical shrinkage. IC may also restore, at least partially, the moisture that escapes through evaporation. IC, which naturally takes place in LWA concrete, has been designed into normal weight concrete by replacing a small portion of the normal weight aggregates with an equivalent volume of prewetted LWA that continue to release moisture well after placement. The resulting ICC exhibits physical and mechanical properties favorable for the performance of concrete structures.
ICC has been used on bridge decks in recent years in several States with good success, reducing significantly the amount of plastic shrinkage cracking and other random cracking. ICC has been used only on a few concrete pavement projects in the United States to date and these projects have also shown good results. ICC demonstrated good constructability and has shown excellent performance. The objective of this report is to evaluate the use of ICC in routine concrete pavement design and construction.
The two key benefits determined for ICC in concrete pavement is structural longevity and durability. Structural longevity is improved with ICC due to its small reduction in unit weight, elastic modulus and coefficient of expansion and a small increase in strength. These small effects, when combined, amount to a significant positive impact on slab fatigue damage and associated slab cracking in jointed concrete pavements analyzed. Likewise, ICC leads to tighter crack openings and reduced punchout failures in continuously reinforced concrete pavements. Several case studies were analyzed using the AASHTOWare ME Design procedure, and the results indicate improved performance and longer lives of ICC projects. Life cycle cost analyses for these projects showed generally lower costs in ICC as compared to conventional concrete.
ICC also provides durability benefits through moisture loss control and improved hydration, including that of SCMs from extended moisture supply. ICC shows reduction in early age shrinkage and associated plastic shrinkage cracking. Reduction in permeability and improved interfacial transition zone between aggregate and cement paste may also control joint disintegration in pavements that are subjected to freeze-thaw cycles under saturated conditions. Other potential beneficial effects include reduction in upward slab curling and less detrimental effects of long term drying shrinkage.
A long term implementation plan titled “Road Map for Internally Cured Concrete Pavements” was developed. This road map aims to give industry and government recommendations on how to proceed to achieve the goal of wider use of ICC in concrete pavement design and construction.
Authors: Chetana Rao and Michael I. Darter