Sustainable Materials For Pavement Infrastructure

As the price of liquid asphalt continuously climbs, methods are being sought to decrease material costs, which will also have less impact on ecological systems without compromising material or pavement performance. The use of recycled materials is one method that can replace a percentage of their virgin counterparts, thus reducing the negative impacts on the environment. Asphalt mixture performance is affected by the level of blending that occurs between aged and virgin asphalt binders. The interaction and compatibility of recycling agents (RAs) with recycled asphalt shingles (RAS) and reclaimed asphalt pavements (RAP) have not been thoroughly evaluated since the 1970s. To characterize laboratory mixture performance through their mechanistic and volumetric properties, a suite of tests was conducted to evaluate the low, intermediate, and high temperature performance of conventional asphalt mixtures and mixtures containing RAS and/or RAP with and without RAs. Also, the asphalt binders’ molecular structure was correlated with their cracking potential through binder fractionation. With respect to the mixes without RAs, results indicate that RAS binder does not fully blend with the virgin binder. The actual availability factor was found to range from 35 to 46%. Also shown was an improvement in rutting performance, with no adverse effects to intermediate temperature or low temperature performance because the mixtures are comprised of approximately 90% virgin asphalt. For mixtures containing RAs, a modified mixture design change was developed to improve blending between the aged and virgin asphalt binders. The actual availability factor was found to range from 50 to 100%. It was determined that RAs adversely affected the intermediate and low temperature properties of the mixtures studied due to the increase in the recycled binder content utilized within the mixture. In terms of low temperature properties, the use of soft binder performed similar to mixtures containing no RAs. The concentration of the high molecular RAS species exceeds 40% in which 25% of these are highly aggregated with apparent molecular weights approaching 100K. The use of RAs did not significantly dissociate the very high molecular weight species, and thus failed to improve mixture cracking resistance. In addition, Fourier-Transform Infrared Spectroscopy (FTIR) results were inconclusive.