The effect of long-term laboratory aging on asphalt concrete fracture energy

A pavement ages over time from the effects of the environment and traffic loading. This study was conducted to examine asphalt mixture laboratory aging protocols from the standpoint of both mixture and binder physical properties that are believed to relate to various forms of pavement cracking. The new protocol, aging uncompacted mix at 135°C for 24-hours appeared to give more realistic results compared to the AASHTO R30 long-term aging procedure in regards to compliance and tensile strength for the unmodified MnROAD Cell 33 mixture. The results of this study suggest that the R30 procedure may not be severe enough on the basis of mixture fracture properties (using the Disk-Shaped Compact Tension Test), but appears to be conservative with respect to the aging of the binders on the basis of testing of the recovered binder through the Double-Edge Notched Tension Test, the Direct Tension Test, and the Bending Beam Rheometer. This study also found that the proposed 24-hour, 135°C loose mix aging procedure may be slightly conservative with respect to mixture fracture behavior, but overly conservative (too much aging) on the basis of testing of the recovered binders. This study highlights the potential danger in selecting an aging procedure or conditioning parameters based upon binder or mixture testing alone. It also recommends that more polymer-modified mixtures be investigated, as it may be necessary to develop a separate aging protocol for unmodified and modified asphalt concrete mixtures.