Influence of Micro Crack Healing on Flexibility of Recycled Asphalt Concrete
Saad Issa Sarsam1*, Mohammed Chaloob Saleem2
1Professor, Department of Civil Engineering, College of Engineering, University of Baghdad, Iraq.
2MSc. Student, Department of Civil Engineering, College of Engineering, University of Baghdad, Iraq.
Excessive loading and environmental impact on asphalt concrete are considered as major issues for initiation of microcracks in the pavement structure. Aging of 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 restore the pavement for additional service life. Recycling agent can provide the required flexibility and increase its crack healing potential. In this investigation, aged asphalt concrete was recycled with liquid asphalt (cutback and emulsion). Two groups of cylindrical specimens have been prepared, the first group has 102 mm diameter and 63.5 mm height while the second group has 102 mm diameter and 102 mm height. The first group was subjected to repeated indirect tensile stresses (ITS) while the second group practices repeated compressive stresses (CS). All the specimens were tested at 20°C in the pneumatic repeated load system (PRLS). The stress level of 0.138 MPa was applied with a constant loading frequency of 60 cycles per minute and loading sequence for each cycle is 0.1 sec load duration and 0.9 sec rest period. After 20 minutes of repeated load application to allow for the initiation of micro cracks, the test was stopped. Specimens were withdrawn from the testing chamber and stored in an oven for 120 minutes at 60°C to allow for crack healing by external heating. Specimens were returned to the PRLS and subjected to another cycle of stress repetitions. The impact of crack healing was measured in terms of the change in resilient modulus before and after healing. It was concluded that Resilient modulus (Mr) under repeated (ITS) and (CS) for aged and recycled mixtures (cutback and emulsion) increases by (7.5, 13, and 9) %and (5.6, 10.7, 8.3) % after healing respectively as compared with the same mixture before healing.
Key words: Healing, Recycling, Asphalt concrete, Resilient modulus.