Technological properties of rock aggregates

Sammanfattning: The commission of technical geology is to apply geological knowledge to the field of constructional engineering, mining technology, environmental protection, architecture etc. The sector of infrastructure is highly dependent on the production of crushed rock materials as the main constituent of e.g. road and railway constructions. The functional properties of crushed rock materials used are of major importance concerning the durability of the construction and they are strongly connected to economic and environmental consequences. The quality of the aggregates is the crucial agent to reach the optimal performance of the infrastructural network. Due to the geological, geographic and climatologic preconditions of Northern Scandinavia, the quality of crushed rock materials is even more important. The Fennoscandian bedrock is dominated by igneous and metamorphic rocks. The access to qualitative rocks for production of aggregates displays considerable regional variation. The oblong geographical extension of the North Scandinavian countries, the fairly low population and the frequent traffic require the widespread infrastructure. The temperate climate characterized by freeze-thaw cycles combined with usage of studded tyres requires a long lasting construction of high sustainability. In spite of available international standards dealing with the aggregates’ quality, the deterioration of the road constructions is noted in Sweden; it is mostly caused by use of mica-rich, heterogeneous rocks. The utilization of these kinds of rock materials as base courses and bituminous wearing courses results in economic losses and negative environmental consequences. The aim of the present thesis was to study technological properties of aggregates in a challenge to connect them with the petrographic characteristics of rock materials. The study includes an investigation of enrichment of free mica particles in fine fractions originating from crushed rock aggregates and the development of a scientifically based method for estimation of free mica particles in aggregate fine fractions. The second part of the thesis deals with the influence of petrographic parameters on the mechanical (functional) properties of aggregates. Finally, an interlinking method of drill cuttings analysis is applied as a tool for estimation of rock aggregates’ quality and usability. The studies of mica confirmed the enrichment of free mica particles in fine fractions of the crushed rock compared with initial mica content in the rock. The primary grain size of mica in the host rock is suggested to influence the process of enrichment. The evaluation of the developed method for estimation of free mica particles confirms its certainty and repeatability. The petrographic analyses of drill cuttings indicated the compatibility between the content of free mica in fine fractions originating from crushed rock and drill cuttings respectively. The literature review concerning the correlations between petrographic and mechanical properties of rock materials indicated the necessityto intensify the research on this field. Mineralogical composition, micro-cracks, porosity, grain size, grain shape and the degree of foliation were found to be the most important petrographic parameters influencing the mechanical and technical properties of igneous, metamorphic and sedimentary rocks. The study of the petrographic characteristics of granitoid and gabbroid intrusive rocks as a tool for evaluation of mechanical properties confirmed that grain size, content of mica and frequency of micro-cracks are the main petrographic variables influencing mechanical properties of granitoids. In the case of gabbroid rock types, the mechanical properties generally respond to the mica content and frequency of micro-cracks. The results of the study of the petrographic and mechanical properties of the rock materials point to the possibility to develop a system for estimation of the mechanical properties of rock materials using their petrographic characteristics.