The behaviour of mica-rich aggregates under the temperate climate conditions

Abstract: In regions of temperate climate the destructive influence of frost action such as frost heave in winter and thaw weakening in spring are the main contributors to severe deterioration of the pavement structure. A number of studies on construction aggregates and field observations of road failures, especially caused by seasonal fluctuations of temperature, have revealed a negative influence of unbound mica-rich rock aggregates on the service life of road construction. The aim of this thesis was to investigate the behaviour of mica-rich aggregates under the temperate climate conditions. The study focuses on measurements of volume change (frost heave), capillarity rise and interaction between water and mica-rich aggregates. The materials studied in this research are commercially available unbound road construction aggregates with varying free mica grains, and originating from different regions of Sweden. The mineral composition of the samples has been determined by polarizing microscopy using a point-count method. In Paper I, the materials were exposed to freeze-thaw cycling in order to register the volume change (in terms of frost heave). The results show that mica-rich base-course aggregates have a large potential to produce frost heave. The results from the test for determining capillary rise (Paper II) indicate a direct correlation between mica content of the aggregates and capillary rise values confirming the capability of mica-rich unbound aggregates to transport and absorb higher amounts of water. The interaction of mica-rich aggregates with water in terms fraction sizes and free mica content was studied in Paper III, measuring water storage capacity and specific water saturation values. The results reveal a strong positive correlation between mica content, grain size, water sorption and water storage capacity of the aggregates. The overall results of this research bring the mineralogy of the fines into focus when evaluating frost susceptibility of unbound aggregates and can be considered when estimating threshold values of free mica grains in crushed road materials.