The final report describes the results of the field demonstration project and the mixture optimization investigation. 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.
Each year, the US highway industry produces over 100 million tons of reclaimed asphalt pavement (RAP) through standard rehabilitation and construction of the nation’s roads. Although this product has been reused in several applications, usually in hot plant mixes, a large portion of this material remains unused. With a sizeable share of RAP wasted in stockpiles and landfills, the exploration of further uses for this construction byproduct is warranted. Using RAP as aggregate in Portland cement concrete pavement (PCCP) is one possible application for this recyclable material. Portions of virgin aggregate used to produce concrete pavement may be replaced with RAP, creating a pavement that is both efficient and environmentally friendly.
The first phase of research used a statistical experimental design procedure (response surface methodology – RSM) to investigate mix proportioning in concrete mixtures containing RAP to achieve desired performance criteria. Based on the RSM models, two concretes were ultimately selected for further evaluation: a high RAP mix (HR) and a high strength mix (HS). These mixes were then evaluated through a suite of mechanical/durability tests.
This project encompasses the second phase of research, which focused on: (1) evaluating the field application of RAP concretes, and (2) further optimizing RAP mixes in order to reduce the amount of required cement. The field application of RAP concrete was evaluated through a field demonstration project near Lewistown, MT, in which two RAP concrete test slabs (one HR slab and one HS slab) were placed on a roadway at the MSU/WTI Transcend Research Facility. In regards to the optimization, two optimized mixes were developed and evaluated through a series of mechanical and durability tests.
The objective of this research is to investigate the feasibility of using reclaimed asphalt pavement (RAP) to replace virgin aggregates in concrete pavements.
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