Evaluating the Performance Properties of Sand Asphalt Stress Absorbing Membrane Interlayer

Pavement rehabilitation can be accomplished using a variety of methods among them asphalt overlay is the most common ones. Reflective cracking occurs on the overlay surface after a short period of time, which is the most important distress annually threatening the durability of new overlays. Usually, reflective cracking starts from the base layer and continues towards the overlay. Surfacial cracking also causes infiltration of water, salts and other harmful materials which increases the speed of deteriorations. Stress Absorbing Membrane Interlayers (SAMI) can be used to postpone the reflective cracking in the overlays. Nowadays, sand asphalt is a common mixture to be used as a SAMI material. In this research, the performance properties of a sand asphalt interlayer, in an unmodified condition, as well as a crumb rubber modified (CRM) sand asphalt interlayer was evaluated. Indirect tensile strength was selected as an indicator of asphalt layer resistance to cracking. Also, by using the above test, the fracture energy of sand asphalt interlayer was determined and then was compared to that of regular dense graded asphalt used as an overlay. Modified Lottman test and Texas boiling water test were conducted to evaluate the moisture susceptibility of sand asphalt mixtures. A wheel-track test was also performed on the selected samples to evaluate the rutting potential of sand asphalt interlayer mixtures. The test results showed that sand asphalt mixtures can stand higher levels of energy before reflective cracking. Sand asphalt mixture using crumb rubber modified binder was also shown to be more resistance to moisture induced distresses. The wheel-track rutting test results also showed that although the rutting potential of pavement section using an overlay over an unmodified sand asphalt mixture is much higher than the single overlay section, but this can be rectified using a CRM sand asphalt mixture as the interlayer.