Assessment of the Potential for Salt Damage to Asphalt Surfacings when Chloride-Treated Unpaved Roads Are Upgraded to a Sealed Standard

Abstract

Experience gained during research into chemical dust control/fines preservation has indicated that the reduced maintenance on, and reduced gravel loss from, treated roads justifies the use of these chemical treatments as a cost-effective road maintenance and management strategy. Treatments also serve as a means of preserving layer thickness and integrity in stage construction if upgrading the road to a paved standard is planned. However, the potential for damage to primed bases and bituminous surfacings placed on chloride-treated layers as a result of salt crystallization underneath the surface during hot, dry conditions in arid and semi-arid climates has to be considered. A laboratory test method was therefore developed to gauge the potential for this type of damage. Calcium chloride, a commonly used dust palliative, was used in the experiment. The test, which simulated a worst-case scenario, followed by two field experiments that were evaluated for 36 months, indicated that salt damage to base materials, whether primed or unprimed, and to bituminous surface treatments or thin asphalt concrete layers is unlikely to occur on roads previously treated with calcium chloride. Care should be taken in the choice of surfacing if the electrical conductivity of the top 25 mm of treated material on the road exceeds 0.15 S/m prior to priming the base and placing the surfacing. This limit can be relaxed if laboratory testing, as described in this paper, indicates that salt damage is unlikely.