Impact of Repeated Load on Crack Healing Cycles of Asphalt Concrete

Abstract

Asphalt concrete pavement is designed to under take repeated loading for its design life with minimal maintenane requirements. Under such loading mode, micro cracks appears in the flexible pavement structure, while it exhibit self healing ability of micro cracks. In this work, the impact of repeated tensile and shear stresses on accumulation of permanent strain of asphalt concrete and micro crack healing cycles have been investigated. Asphalt concrete specimens of 100 mm diameter and 63 mm height have been prepared with optimum asphalt requirement and with extra 0.5% asphalt above and below the optimum. Specimens exhibits permamemt strain under repeated tensile and shear stresses using three stress levels (69, 138 and 207) kPa at 25°C environment. The loading cycle consists of load repetitions application for 0.1 second followed by 0.9 seconds of rest period. Specimens were allowed to heal by external heating at 60°C for 120 minutes after each 1000 load repetitions, then subjected to another load repetition cycles. The healing cycle was repeated twice. It was concluded that as the crack healing cycles proceeds, the resilient modulus increases while the permanent strain decreases. The impact of asphalt content on resilient modulus is variable through the crack healing cycles among tensile and shear stresses. After crack healing cycles, the permanent strain was reduced by an average of (45, 36 and 23)%, for (69, 138, and 207) kPa respectively as compared to reference mix under punching shear stress (PSS), while it was reduced by an average of (5, 23 and 21)%, for (69, 138, and 207) kPa respectively as compared to reference mix under indirect tensile stress (ITS).