Aggregate packing characterisation of cold recycled mixtures

Despite its significant role in cold recycling mix design and construction process, the effect of reclaimed asphalt pavement aggregates’ gradation and physical properties are relatively less understood. The ambiguities associated with the gradation effect led to challenges in determining the best practices in gradation control and stockpile management and blending in both cold-in-place and central plant recycling operations. Therefore, the main goal of this paper is to quantify the impact of gradation changes and proportioning of reclaimed asphalt pavement aggregates on the packing characteristics and performance of cold recycled mixtures. Binary blends consisting of fine and coarse reclaimed asphalt pavement stockpiles were combined to obtain fourteen gradations using a volumetric aggregate proportioning technique. The compatibility of five of the most prominent binary aggregate packing models was evaluated in cold recycling application. The modified Toufar model was able to accurately predict the blend of fine and coarse aggregates that offers the optimum packing prediction. Complex modulus tests showed linear viscoelastic characteristics of the cold recycled mixtures as well as the sensitivity to the packing states. In essence, this research shows the effectiveness of applying volumetric packing principles and aggregate proportioning techniques to achieve improvements in cold recycled mixtures’ volumetric and mechanical performance.