The detrimental influence of mica rich aggregates on structural deterioration of road pavement has been discussed in the literature for over a half century. This negative effect is of great importance especially for regions with crystalline, mica-rich bedrock and temperate, subarctic climates. Recent investigations reveal that elevated fractions of free mica particles in unbound granular materials, used in road constructions, greatly reduce bearing capacity and influence the hydraulic behavior of the road structure. Despite the awareness of micaÕs potential harmful effect, the absence of properly adapted analytical methods is noticeable. The scope of the current study was to test two possible analytical methods which, are susceptible to mica content and could be used as an indicating technique for quantitative determination of free mica particles in unbound granular materials. Two standard methods: Sand equivalent test and methylene blue (MB) test were assumed as the most sensitive to mica presence. The rock samples used in the tests are representative for the common crushed rock aggregates for construction purposes with different contents of mica. Both methods showed susceptibility to mica content and gave strong correlation in terms of mica content. The result of the MB test can be explained by the schistose structure of mica particles and the ability of mica to absorb liquids. Another important explanation is the increased reaction surface of mica particles, which leads to an increase in the total reaction surface of the sample. The receptiveness of the sand equivalent test to mica content could be caused by the ability of mica to stay in suspension due to its flake-shaped grains.
The main petrographic variables of intrusive rocks that influence the technical test methods common used within the aggregate industry were identified and evaluated, the aim being to investigate whether petrographic description could be used as a tool for the preliminary quality evaluation of different rock groups. Evaluation of the dependence of the technical test methods on petrographic variables covered 26 intrusive rocks, including some of their altered varieties (orthogneisses), divided into two groups: 17 granitoids and 9 gabbroids. The selective designated samples were analysed to determine their petrographic characteristics and resistance to fragmentation, wear and wear by abrasion from studded tyres. In order to identify the complicated associations between the petrographic and technical properties, multivariate statistical evaluation was performed. The results of statistical evaluation highlighted that mean grain size of mica minerals, grain size distribution, content of mica minerals and mean grain size were the main variables influencing the technical properties of granitoid rocks, while for gabbroid rocks, the main influences were the frequency of microcracks, mica content, grain size distribution and mean grain size.
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