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The increased absorptive capacity of lightweight aggregates (LWA) has been shown to facilitate delivery of moisture to concrete for internal curing. The additional hydration supplied by prewetted LWA to support internally cured concrete (ICC) has been linked to improved concrete performance, including reduced permeability and lower cracking tendency. To assist NCDOT in evaluating the benefits of ICC produced with local materials, as well as to establish the value of using ICC in specific types of projects, laboratory and field studies were performed. A range of concrete mixtures, including ICC mixtures using locally available prewetted LWA in concrete mixtures typically used in bridge decks and pavements were batched and tested. The results of laboratory testing confirmed the benefits of ICC, including the potential for reduced cracking and, in some instances, reduced permeability. Autogenous shrinkage test results clearly demonstrated the impact of use of prewetted LWA, with significantly reduced shrinkage observed for both types of LWA. The reduction in autogenous shrinkage correlated with LWA replacement rate. Use of fly ash, in both conventional and ICC mixtures was more influential in reducing the permeability of mixtures than addition of prewetted LWA. Use of prewetted LWA provided additional workability to conventional and very high early strength (VHES) latex-modified concrete mixtures (LMC), potentially supporting an additional opportunity to achieve superior durability performance through use of lower water to cementitious material (w/cm) ratios. The internally cured VHES LMC mixture appeared to have extended work time, possibly offering construction advantages, although field trials are suggested to explore this potential benefit. A project special provisions (specification addendum) developed as part of this work was included in the construction documents for a pilot project bridge deck to evaluate ICC. The pilot project bridge deck, comprised of both ICC and conventional (control) concrete was constructed, instrumented, and monitored for a period of 31 weeks. During this observation phase the team did not observe substantial differences in the performance of the two materials in terms of moisture retention, drying shrinkage or crack formation. However, the locally available LWA used in the pilot project has a relatively low absorption, and the substitution rate was lower than that recommended by ACI (308-213)R-13. Benefits could be more pronounced at higher substitution rates, and/or later in the project’s service life. This field implementation was successful, and lessons learned from the pilot project stakeholders and construction experience were utilized to improve the specification recommendations for future use of ICC by NCDOT. Implementation of ICC in future projects should result in longer-lasting structures with reduced maintenance and preservation costs. |
