IRC's research into this high failure rate led it to examine the role of the hot-air lance in sealant adhesion. In regions with severe winters, crack sealing is often preceded by routing, cleaning and heating with the hot-air lance. IRC researchers, however, have now produced concrete evidence that using the lance in areas where crack sealants are exposed to cold winter temperatures may not be advantageous and may, in fact, cause premature sealant failure. The secret lies in the fact that the sealant needs to remain flexible at sub-zero temperatures. IRC research conducted in 1995 showed that heating a sealant can cause the more volatile components, on which its flexibility depends, to break down resulting in a loss in elasticity, tensile strength and mechanical strength.
Workers use a hot-air lance to seal pavement cracks.
This discovery focused recent research on the effects of the hot-air lance on sealants. In those experiments, researchers compared the adhesion strength of three sealants applied to dry unheated, heated and overheated asphalt-concrete substrates that had been prepared with quartz or limestone aggregates. They found that if the sealant itself is correctly selected for cold-temperature conditions and remains elastic, the lance becomes unnecessary because it does not increase sealant adhesion. Furthermore, if the wrong sealant is selected, and is prone to becoming rigid at low temperatures, the use of the lance will actually accelerate debonding. While it can be useful for removing excess moisture from a wet crack surface, its disadvantages in heating dry routs mean that simply cleaning the rout with a blast of compressed air may be just as effective, if not more so, in the long term.