Nyfors (Sweden)

Pavement durability is often linked with water damage either through raveling or loss of integrity, especially considering asphalt materials. A large number of tests exist to address the water sensitivity and affinity between aggregates and asphalt binder. In Rilem TC 237 SIB, TG1 looked at the common test methods used to evaluate the adhesion or affinity of asphalt binder to aggregate surfaces. One of the main purposes was to run a Round Robin Test to evaluate the reproducibility and repeatability of these test methods and to give recommendations for improvement. Three asphalt binders were selected, two unmodified and a polymer modified binder and four aggregate types with different mineralogy. This paper presents the first results obtained for the rolling bottle test. The influence of aggregate type is higher than that of the asphalt binder. While there are some potential trends after 24 h comparing the different combinations of aggregate and binder, there is still a lot of variability in the absolute results. The underlining reasons are not yet clearly identified.

Aggregates and bitumen together form a composite called asphalt concrete pavement. Moisture damage to asphalt concrete pavement can occur as stripping, and is a common problem that can lead to costly repairs. There is therefore a need to understand which stone aggregates adhere best to bituminous binder and result in a minimum of stripping. Lifshitz used the refractive index to estimate the dispersive non-polar van der Waal’s interaction component of adhesion, the predominant component in adhesion between minerals and bituminous binder. The impact of an intervening thin medium such as air or water on the adhesion can be estimated using Hamaker’s coefficient, which in turn can be related to stripping potential. Aggregates consist of minerals and minerals consist of different elements. The objective of this study was to investigate variation in the dispersive component of minerals via their refractive indices using data from mineral data sheets. The influence of the position of elements in the periodic table and chemical composition on refractive index of minerals was examined in order to classify mineral aggregates for asphalt road building with regard to dispersive adhesive properties and expected resistance to stripping. It is clear from this study that the elemental composition of a mineral will affect its refractive index and hence its dispersive adhesion to bitumen. Aggregates and minerals have been classified according to degree of stripping in the literature. In this study it was shown that aggregates and minerals that have a refractive index higher than approximately 1.6 are expected to be less susceptible to stripping. Also, minerals containing alkali metals are sensitive to stripping since they are partially soluble in water.