Influence of Moisture Damage and Microcrack Healing on Resilient Modulus of Recycled Asphalt Concrete

Abstract

Addition of recycling agents of the same origin (polymers) as that of asphalt binder had proved to be successful in restoration of the pavement quality. In this investigation, an attempt has been made to age asphalt cement in the laboratory with the aid of thin film oven test apparatus. The aged binder was recycled by digestion with (0.5, 1.0, and 1.5) % of polyethylene and crumb rubber. The recycled binder was implemented in the preparation of Marshal specimens at 150°C with optimum binder content and additional specimens were prepared with binder of 0.5% above and below the optimum. One group of Specimens was tested under repeated indirect tensile stresses ITS in the pneumatic repeated load system PRLS. The second group was subjected to moisture damage, then tested under repeated ITS in the PRLS. The third group was tested under repeated double punching shear stresses DPS in the PRLS. Specimens were subjected to stress level of 0.138 MPa at 25°C and loading frequency of 60 cycles per minute. The loading sequence for each cycle is 0.1 second of load duration and 0.9 second of rest period. After 1200 load repetitions, the test was terminated. Specimens were stored in an oven for 120 minutes at 60°C to allow for microcrack healing by external heating. Specimens were returned to the PRLS chamber and subjected to another cycle of stresses repetition. The resilient modulus Mr was calculated for each case. It was observed that the Mr decreases after moisture damage by (52.4, 51.8 and 55.3) % (16.5, 46.2 and 50) % for recycled mixtures with (0.5, 1.0 and 1.5) % of crumb rubber and polyethylene respectively. The Mr under DPS was increased after healing by (30.1, 14.4 and 34) % for (4.8, 5.3 and 5.8) % asphalt content respectively as compared to the mixtures before healing. It was concluded that (0.5 and 1.0) % of crumb rubber or polyethylene presents suitable recycling agents from the durability point of view. While (0.5 and 1.0) % of crumb rubber and 0.5 % of polyethylene presents suitable recycling agents from the resistance to moisture damage point of view.