Because of its unique properties, early-opening-to-traffic (EOT) concrete is more susceptible to durability-related distress than conventional concrete. For example, the use of high cement contents and multiple admixtures can lead to increased shrinkage, altered microstructure, and unexpected interactions. Further, the ability of standard testing to detect durability-related problems is limited, and thus deficiencies may go undetected through the mixture design and construction process. NCHRP Project 18-04B was conducted to evaluate the durability characteristics of EOT concrete to develop guidelines for materials, mixtures, and construction techniques that enhance long-term durability of EOT concrete for pavement rehabilitation. The research dealt with concrete mixtures that are suited for opening to traffic within (a) 6 to 8 hours and (b) 20 to 24 hours after placement and was limited to full-depth rehabilitation, such as a full-depth repair and slab replacement. In the course of the project, a review of literature was used to design an experiment that evaluated both fieldand laboratory-prepared EOT concrete mixtures. In the experiment, 6- to 8-hour and http://gulliver.trb.org/publications/nchrp/nchrp_rpt_540.pdf20- to 24-hour EOT concrete mixtures obtained from four states (Ohio, Georgia, Texas, and New York) were evaluated to determine typical mixture properties and performance characteristics. Also, a laboratory study was undertaken to produce and test 28 different EOT concrete mixtures (two replicates or batches were made for each mixture for a total of 56 batches). The testing included assessment of the properties of the fresh concrete, volume change, freeze-thaw durability, microstructural characterization, and the absorption/porosity of the concrete. The results were analyzed to draw conclusions regarding the durability of the mixtures and to form the basis for the guidelines. It is expected that the application of these guidelines will enable SHAs to better understand mixture design, proportioning, and construction practices that affect EOT concrete durability and to achieve longer-lasting EOT concrete repairs. (Author/publisher) This report may be accessed by Internet users at
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