Studies of the free mica properties and its influence on quality of road constructions

Abstract: The thesis presents series of laboratory studies of aggregates containing mica minerals obtained from aggregate producers located throughout Sweden. The main idea of the research was to study physical properties and behaviour of free mica particles in unbound granular products of crushed rock materials. Another objective was to highlight the detrimental properties of mica occurrence in aggregates used for road construction industry and determine the applicable methods for quantitative determination of mica minerals presence. Due to the lack of previous investigations looking at this or similar subject, the current research can have international importance, especially for countries with crystalline, mica rich bedrock and temperate, subarctic climates. Recently a number of cases involving road construction failures and decrease in service life have been observed in northern parts of Sweden. One of the major reasons for the structural deterioration was enrichment of free mica particles in aggregates and their interaction with water. Due to this reason first paper of this thesis represents a study of the behaviour of free mica grains in crushed rock aggregates of metamorphic origin and recognition of any trend of enrichment of free mica grains aggregates. As a result two general trends of enrichment of mica were obtained: Type I (isotropic source rock) and Type A (anisotropic source rock). Type I is exemplified by a general increase of free mica towards finer grain fractions, with or without a peak for "coarser" grain fractions. Type A represents an increase of free mica up to a certain grain fraction, thereafter no increase occurs towards finer grain fractions. Second part of the thesis focuses on the determination of the possible analytical methods which are susceptible to mica content and could be used as indicating technique for quantitative determination of free mica particles in unbound granular materials. Two standard methods: Sand equivalent test and Methylene blue test were assumed as the most sensitive to mica presence. Both methods showed susceptibility to mica content and gave strong correlation in terms of mica content. The third paper enhances knowledge of the behaviour of mica rich aggregates in interaction with water in terms of fraction sizes and free mica content. During the experiment several aggregates with different content of free mica and pure mica material consisting of commercial biotite were studied. Two major parameters were investigated during the research: water storage capacity and specific water saturation value. With the aid of consecutive analytical and statistical analyses a more precise mica presence threshold value for certain unbound applications was indicated, resulting in recommendations for industry, authorities and for future experiments.