Effect of Hot-Air Lance on Crack Sealant Adhesion

The hot-air lance (HAL) is widely used in crack-sealing work based on the premise that it improves sealant adhesion. The effectiveness of the HAL in promoting adhesion is uncertain, however. Our goal was to measure the adhesion strength of bituminous crack sealant to dry asphalt concrete (AC) and assess the effect of the HAL on adhesion. To this end, we monitored the use of the HAL in the field and reproduced its effect on asphalt binders and AC pavements by using an automated HAL in a series of laboratory experiments. In those experiments, we looked at the effect of heat treatment on binder oxidation and embrittlement by means of infrared spectroscopy, thin-layer chromatography, and goniometry. We also compared the adhesion strength of three sealants applied to unheated, heated, and overheated AC substrates prepared with quartz or limestone aggregates. The results show that sealant adhesion and failure mechanisms are governed by the sealant source, the type of aggregate in the AC mix, and the heat treatment on the rout prior to pouring the sealant. The HAL does not oxidize the binder, but it may cause embrittlement by raising the asphaltenes content of the binder. Normal heat treatment has little effect on sealant adhesion to dry AC, but overheating can cause a 50% reduction in adhesion strength and lead to premature sealant failure. To retain the possible benefits of the HAL in sealing damp cracks and to prevent overheating, the HAL should be operated at reduced temperatures.