Cracking Resistance of Recycled Asphalt Mixtures in Relation to Blending of RA and Virgin Binder
The degree of blending between the reclaimed asphalt (RA) binder and the virgin bitumen during the asphalt recycling mixing process is presumed to greatly influence the performance properties of recycled asphalt mixtures. Studies on the effect of different mixing methods using different quantities of RA in the laboratory, showed that tensile strength of RA mixtures and their fatigue characteristics are affected to some extent by the preheating conditions and moisture content of the RA The effects however are not very significant. These somewhat unexpected results are believed to be due to the low void content of the mixtures tested but they also might be influenced by the amount of blending that has taken place between the RA binder and the virgin binder.
This paper will report on how well the virgin binder blends with the old binder which is part of the RA. It is believed that by knowing precisely the degree of blending of RA binders, one can develop much more realistic mix designs and modify or select better mixing processes. This will result in more durable pavements.
Nano-indentation is employed to measure the mechanical properties of the binder layer and to determine the degree of blending between the hard RAbinder and the soft virgin binder. Also the characteristics of the interface zone between binder and aggregate were measured in this way. For this purpose mono sized sea sand particles and glass beads up to 4mm were mixed with a virgin soft and hard bitumen separately to produce different mixtures in order to simulate different levels of blending and interface properties. RA was simulated by mixing aggregate with hard bitumen. Nano-indentation was employed to determine the resilient modulus and hardness at each location and these results were used to determine the degree of blending.
Although current reported nanoindentation results in this paper didn’t allow to determine blending degree between two binders; further nanoindentations will be performed on differnt types of samples to analyze the degree of blending.
KeywordsResilient Modulus Indirect Tensile Strength Partial Warming Virgin Aggregate Binder Zone
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