Five paving mixtures typical to Utah and Nevada were prepared with and without 1.0 and 1.5 percent (by weight of aggregate) of dolomitic Type S or normally hydrated high-calcium (Type N) lime. The temperature and moisture susceptibility of each of the mixtures was determined. A slight increase in mixture stiffness resulted from the addition of either type of lime. Moisture sensitivity substantially decreased for all mixtures when lime, regardless of type, was used. The magnitude of the improvement appears to be unique for each asphalt-aggregate combination.

The stripping of asphalt from aggregate surfaces is a complex physical-chemical process that can result in early pavement distress. A popular method of combating the stripping problem is to introduce chemicals into the mixture that increase the attraction between polar sites in the asphalt and aggregate surfaces. Such chemicals are known as antistripping agents, the most popular of which is lime. Lime is produced from high-calcium or dolomitic limestone. High-calcium limestone is almost pure calcium carbonate, whereas dolomitic limestone is a combination of calcium and magnesium carbonates (1). These differences in chemical composition require that each type of limestone be processed specially to obtain the final product of lime. High-calcium limestone is calcined (ie, burned) to produce calcium oxide (quicklime, CaO). The quicklime is then hydrated lo pruum: e hy< lrateu lime. Lime produced in this manner is marketed as Type N lime. Dolomitic limestone, once calcined, requires prolonged contact with water to completely hydrate the magnesium oxide and convert it into hydroxide. Because this prolonged contact is not economical, a continuous, high-pressure system is used to complete the hydration. The designation Type S indicates this type of manufacturing process. Historically, only Type N lime has been used as an antistripping additive in asphalt concrete mixtures. However, in certain instances, Type N lime can be economically prohibitive. In these cases, substituting Type Slime for the traditional Type N would be economically preferable. This substitution can be widely accepted because of the benefits obtainable from Type Slime.