Enhancing the Service Life of Aged Asphalt Concrete by Micro Crack Healing and Recycling

Aging of the asphalt cement in the pavement changes the quality of asphalt concrete from flexible to stiff and the pavement will be susceptible to all types of distresses. Recycling is considered as a good alternative to enhance the pavement for additional service life. Recycling agent can provide the required flexibility and increase its micro crack healing potential. In this investigation, aged asphalt concrete was recycled with two types of additives, carbon black CB and styrene Butadiene rubber SBR. Two set of Cylindrical specimens have been prepared, the first set has 102 mm diameter and 63.5 mm height while the second set has 102 mm diameter and 102 mm height. The first set was subjected to repeated indirect tensile stresses (ITS) at 25 °C and tested under stress level of 138 kPa, while the second set practices repeated compressive stresses (CS) at 40 °C and tested under three stress levels of (69, 138, and 207) kPa. All the specimens were tested in the pneumatic repeated load system PRLS and constant loading frequency of 60 cycles per minute. The loading sequence for each cycle is 0.1 s of load duration and 0.9 s of rest period. After 1000 load repetitions which allowed for the initiation of micro cracks, the test was terminated. Specimens were stored in an oven for 120 min at 60 °C to allow for crack healing by external heating. Specimens were returned to the PRLS chamber and subjected to another cycle of stresses repetition. The impact of crack healing was measured in terms of the change in Resilient Modulus Mr under ITS and permanent deformation under CS before and after healing for each recycling agent. It was concluded that Mr under repeated ITS increases by (25, 30, and 20) % for aged, CB treated and SBR treated mixtures respectively after healing. On the other hand, the permanent deformation under repeated CS decreases by (31, 43, and 45) %, (6, 49, and 10.6), (19, 24.5, and 13.2) % for aged, CB treated and SBR treated mixtures under stress levels of (69, 138, and 207) kPa respectively after healing.