As described in the final report, this research demonstrated that concretes with up to 50 percent of the fine aggregates and 100 percent of the coarse aggregates replaced with RAP were suitable for concrete pavement. A statistical experimental design procedure (response surface methodology – RSM) was used to investigate proportioning RAP concrete mixtures to achieve desired performance criteria. Based on the results of the RSM investigation, two concrete mixtures were selected for further evaluation: a high RAP mix with fine and coarse aggregate replacement rates of 50 and 100 percent respectively, and a “high” strength mix with one half of the RAP used in the high RAP mix. Both mixes met MDT concrete pavement specifications for slump (1.5 inches), air content (6 percent), and 28-day compressive and tensile strengths (3,000 psi and 500 psi, respectively). These two concrete mixtures were subjected to a suite of mechanical and durability tests to evaluate their potential use in Montana roadways. Mechanical properties tested were compressive and tensile strength, elastic modulus, shrinkage, and creep. Durability tests included alkali-silica reactivity, absorption, abrasion, chloride permeability, freeze-thaw resistance, and scaling. Overall, both mixes performed adequately in these mechanical and durability tests, although it is important to note that the inclusion of RAP had an obvious negative impact on nearly every property tested relative to those of control mixes made with 100 percent conventional aggregates.
Each year, the highway construction industry in the United States produces over 100 million tons of reclaimed asphalt pavement (RAP) through standard rehabilitation and construction of our nation’s roads. Although this reusable material has been put to use in some applications (usually in the form of asphalt paving), a large portion of this material remains unused and is either stockpiled or land filled. Therefore, alternative uses for this material are needed. One possible use for this material is the replacement of conventional aggregates in Portland cement concrete pavement (PCCP). There has been limited, preliminary research to demonstrate the feasibility of using RAP in this application. However, these research efforts have focused primarily on short-term mechanical characteristics of the material and have not addressed long-term durability characteristics such as alkali silica reactivity (ASR – which is a deleterious expansive reaction between the alkalis in the Portland cement binder and silicates in the aggregate) or freeze–thaw resistance. Therefore, the proposed research will focus on the durability characteristics of using RAP in Portland cement concrete, which is a critical step in determining whether it can be effectively incorporated into pavements, sidewalks, medians, and other transportation applications. The proposed research effort will begin by developing mix designs with similar strengths, set-times, and workability to conventional concrete mixtures. Once these mix designs are developed, the resulting concretes will be evaluated with a suite of mechanical and durability tests. These results will then be analyzed and documented. Depending on the outcome of this feasibility study, recommendations will be made for a Phase II pilot project in which this material is used in place of traditional concrete in a transportation application. This overall effort is a partnership between WTI, the Montana Department of Transportation (MDT) and the Research and Innovative Technologies Administration (RITA) of USDOT. This project represents the MDT sponsored portion.
The objective of this project is to develop and characterize an environmentally friendly concrete suitable for transportation-related applications in which a portion of the conventional aggregate has been replaced with reclaimed asphalt pavement.
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