Roller-compacted concrete (RCC) is a relatively stiffer hydraulic cement concrete mixture than regular concrete when fresh. Similar to regular concrete, RCC is a mixture of aggregate, cementitious materials, and water, but it is placed using asphalt pavers and compacted by vibratory rollers, and it hardens into concrete. RCC contains a low amount of water, exhibits no slump, and requires asphalt paving equipment for placement rather than expensive slip-form paving equipment. It does not contain reinforcement, tie-bars, or dowels. RCC can be placed and opened to traffic in a short period of time. All of these factors combined make it a relatively low-cost material for roadways compared to asphalt or conventional concrete pavements. However, RCC may lack the smoothness required for high-speed roadways and can undergo raveling and/or cracking; an asphalt overlay may remedy the smoothness and raveling issues. Although cracks might occur in the RCC and potentially reflect through the asphalt layer, such cracks should stay tight because of the low shrinkage of RCC. A composite pavement with RCC and an asphalt overlay has the potential to be a cost-effective long-lasting pavement system.
The purpose of this study was to document the construction procedures and provide lessons learned for a RCC project recently completed by the Virginia Department of Transportation that covered about 134,000 ft2, equivalent to 2 lane-miles, at the Park & Ride lot in Stafford County, Virginia. About one-third of the RCC was used to rehabilitate the existing Staffordboro Boulevard (Route 684). The mixture used had 15% fly ash to provide improved durability and sustainability. Batches of the RCC mixture fluctuated in moisture content, and delays in placement sometimes occurred that also resulted in wet and dry mixtures. The compaction, surface smoothness, and road profile were affected by the fluctuations in moisture content. RCC cylinders prepared using a vibratory hammer usually exceeded compressive strengths of 1,600 psi and 4,000 psi at 12 hours and 28 days, respectively. Only a few early cracks were observed in the pavement. Opening to traffic at an early age for a section, i.e., within 5 to 6 hours of placement, did not result in any visual damage to the pavement; most sections were opened in less than 48 hours. RCC overlaid with 2 in of asphalt is performing well after two winters and 18 months of traffic for one section and after one winter and 8 months of traffic for the rest.
Based on the observations in this study, for successful construction of RCC, proper compaction and mixing equipment are essential. Achieving the proper level of compaction in the field is key to attaining quality RCC. To avoid early cracks, joints need to be cut deeper than one-fourth depth of the pavement and continuous curing is essential. A continuous paving operation is needed to avoid unplanned and poor-performing cold joints. The Virginia Department of Transportation should consider RCC in future field trials, particularly for applications where fast construction of rigid (concrete) or composite pavement is needed.