Evaluation of the healing performance of hot-mix asphalt containing waste steel shavings under different microwave induction healing cycles

Increasing the temperature affects the healing potential of asphalt mixtures significantly. However, it can lead to overheating in some parts of the specimens and cause damage. Thus, the healing temperature should be decreased in order to reduce the risk of overheating, which can affect the healing performance adversely. This research aims to investigate the probability of local overheating in asphalt mixtures during the induction heating of the mixtures containing different percentages of waste steel shavings (WSS). The healing procedure of the mixtures was simulated by placing the fractured hot-mix asphalt samples in a microwave so that the fractured surfaces are healed and stuck together. The healing resistance was evaluated by conducting the fracture test on the healed specimens and comparing the results to those of the intact specimens. The results showed that increasing the healing temperature to more than 70°C and the existence of WSS additives increase the probability of overheating in asphalt mixtures. The results indicated that the intermittent heating is effective to reduce the risk of overheating. As the healing procedure accelerates when the temperature increases to more than the softening point, it is recommended that, during intermittent heating, the samples should be cooled down to the temperature of the softening point during the rest period so that the temperature of the sample does not fall below the softening point of the bitumen during healing. By doing this, in addition to reducing the risk of overheating, the healing performance improves without increasing energy consumption.