Book Description

This research was focused on evaluating the feasibility of using minimally processed reclaimed asphalt pavement (RAP) as aggregate replacement in concrete pavements. An initial phase of 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. However, the field performance of these mixes was not evaluated. Further, these initial mixes contained a significant proportion of cement in order to achieve the desired performance criteria, hindering the economic benefit of using this recycled material in concrete. Therefore, the research discussed herein focused on: (1) evaluating the field performance of RAP concrete through a field demonstration project, and (2) reducing the amount of cement required in the RAP concrete by including water-reducing admixtures. As part of the field demonstration project, two RAP-concrete slabs were cast on a roadway near Lewistown, MT, and monitored for damage, shrinkage, and curling over a two-year period. There were no logistical issues associated with the construction of the slabs, and no damage and only minor shrinkage/curling was observed. In regards to the mixture optimization, two modified mix designs with reduced cement contents were developed, and evaluated with a suite of mechanical and durability tests. Mechanical properties tested were compressive and tensile strength, elastic modulus, and shrinkage. Durability tests included abrasion, chloride permeability, freeze-thaw resistance, and scaling. These mixes performed well with respect to all tests, with the exception of the chloride permeability. Although both mixes performed well, the resulting mixes were lean and were difficult to get good consolidation. Moreover, the process for batching these mixes may be considered a hindrance, as it involved slump adjusting the mixes with the water-reducing admixture. This was required because the nature of the RAP aggregates made it difficult to adjust mixes for variations in moisture content.