Behaviour of crushed rock aggregates used in asphalt surface layer exposed to cold climate conditions

Geological factors (mineralogy, structure, degree of weathering), processing method (crushing, sieving, washing, storing) and user technology for a specific area of use (e.g. asphalt pavements) should be the selecting criteria for crushed rocks used in the construction industry. While the last two criteria have been widely studied, the geological origin of the material has been less considered. Mechanical properties, shape, gradation of the stone material and affinity with the binder are considered the main discriminating factors in road construction. Although those properties are extremely relevant to avoid or milden difficult challenges for pavement surface layers, a deeper knowledge of the geological properties of materials exploited could lead to a general improvement of the overall resistance and durability of the road surface, especially in extreme weathering conditions. The purpose of this work is to investigate the influence of the rock materials properties (mineralogy, texture and porosity expressed by water absorption coefficient) in asphalt pavements. Different samples of aggregates and asphalt mixtures used in Norwegian and Spanish roads were tested with the Cantabro test after conditioning in sodium chloride and freeze–thaw cycles. Mineralogy, grain size, grains bonding, orientation and porosity (expressed by water absorption coefficient) could be related to the mechanical resistance of the aggregates and asphalt mixture behaviour. Even if just a qualitative analysis, the petrographic analysis of the rocks appeared to be a relevant tool to estimate the quality and the long-term durability of aggregates and asphalt mixtures already during the design phase.