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CONCRETE PAVEMENT
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BY MIKE DARTER
Highway Repair With Rapid Strength Concrete? Results of a Southern California freeway surveys that set out to determine the short- and long-term performance of rapid strength concrete for the potential repair and restoration of highway infrastructure work.
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eteriorating highway and other infrastructure conditions across the U.S., combined with widespread funding shortfalls, make it clear that there is a need for cost-effective, long-term solutions for roadway preservation. Surveys of existing projects in California have addressed this need, with results documenting pavement restoration successes and offering guidance on the practice of pavement management. The use of rapid strength concrete (RSC) for roadway construction is extremely beneficial for today’s congested highways and the traveling public. Because RSC reaches opening strength in a matter of hours, slab replacement can be accomplished overnight. The California Department of Transportation (Caltrans) has used RSC for pavement repair since the 1990s and is typically able to complete slab replacement— including removal of cracked slabs, repair of the base course, placing of dowel bars and interlayer, and placing and curing of RSC—within a six-hour window. Two surveys were conducted, the first by Caltrans in 2008, the second in 2018-20 by myself. These surveys sought to confirm that in addition to offering the immediate benefit of short lane closures, RSC was providing durable, long-lasting repairs. Condition surveys conducted for “Evaluation of Rapid Strength Concrete Slab Repairs” (Bhattacharya, Zola, and Rawool, 2008) examined 15 freeway projects across six regions, looking at more than 5,000 “individual” RSC slabs and recording
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all distress. Since the slabs were only three years old at the time of the survey, the study’s goal was to document the short-term performance of RSC. Results showed that only 1.4% of the RSC slabs surveyed showed any premature distresses. By 2018, the time was right to assess longer-term performance. The evaluation focused on two California strategies for restoration of jointed plain concrete pavement (JPCP): • “Individual” slab replacement with rapid strength concrete (ISR-RSC); • “Total lane replacement” RSC (JPCPRSC), (“Long-Term Performance of Rapid Strength Concrete (RSC) Slabs on California Highways,” Darter, 2021). For the six ISR-RSC “individual” replacement projects being assessed, cracked, or badly damaged JPCP slabs had been removed and replaced with RSC slabs along a traffic lane. RSC slab thickness (typically 8-9 in.) and joint spacing (typically 12-19 ft.) remained
A total of 3,562 RSC slabs were surveyed. Image by Mitzi McIntyre, CTS | Rapid Set.
the same and existing base courses had been largely left in place. In some cases, dowels had been included in the transverse joints. Neither shrinkage nor ASR requirements were specified at the time of slab replacement. Concrete durability issues, typically seen as surface cracks and scaling, were almost non-existent. For the six JPCP-RSC “lane replacement” projects being assessed, all slabs and base courses along one or more traffic lanes had been removed and replaced with RSC. Slab thickness was typically increased during reconstruction to be 10-14 in.; perpendicular joint spacing was uniform at 14 ft.; and dowels were placed at all transverse joints. Both RSC shrinkage and ASR requirements were included in these specifications. A survey team, working with Caltrans, randomly selected six of the 15 projects previously surveyed in 2008
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11/30/21 12:50 PM
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