Karel Miskovsky

Influence of the mineralogical composition and textural properties on the quality of coarse aggregates

To evaluate the influence of the petrographic variables on the quality of coarse aggregates consisting of granitoid (granite to tonalite) rocks, 17 samples selected from the Swedish part of the Baltic shield have been studied concerning their petrographic properties, for example, mineral composition, grain size, grain boundaries, and the frequency of micro-cracks. All of the samples selected also have been studied in mechanical tests used to evaluate the quality of aggregates in Sweden. The quality has been determined by means of flakiness, impact value, abrasion value I, and abrasion value II. An analysis of the influence of the mineral composition and textural properties on the aggregate quality has been performed using statistical correlation and linear models. The results indicate that an increasing content of feldspar negatively influences the strength against impact, while an increasing content of mica (tested to 35 vol.%) combined with a diminishing grain size and more irregular grain boundries has a positive influence on the resistance of granitoids to mechanical impact. Abrasion value II seems to be mainly influenced negatively by an increasing frequency of micro-cracks. The practical implementation of the results is suggested.

Enrichment of fine mica originating from rock aggregate production and its influence on the mechanical properties of bituminous mixtures

Analyses of mica-bearing, crushed granitoid rocks revealed a significant enrichment of free mica in the fine fraction. Qualitative tests of bituminous mixtures with an increasing content of free mica in the fine fraction suggested a considerable deterioration of the mechanical properties of the asphalt mass. The negative influence of fine mica on the mechanical properties of the asphalt mixtures was most likely caused by the ability of mica to adsorb bitumen and to create zones of weakness. This phenomenon seemed to be linked to a preferred orientation (foliation) of the mica particles that was connected to the compaction of asphalt masses during the construction of the surface course. The threshold content at which the fine mica negatively influenced the quality of the bituminous mixtures was estimated to be 30–35 vol.%.

Microstructural modeling approach applied to rock material

The importance of the microstructural parameters in rock mechanical behavior has been investigated by several authors. Moreover, the Weibull statistical model has been used to characterize the heterogeneity of several materials on the basis of the concept that the microscopic defects within the material determine their mechanical strength. The modeling of different rocks is a topic that is fundamental for the prediction of rock fragmentation. In this article, the analysis of rock microstructure is performed using the microstructural modeling approach, which consists of the simplification, quantification, and modeling of the main properties of rock microstructure. The grain size, grain shape, and microcracks are modeled by means of statistical density functions, namely, Cauchy, chi-squared, exponential, extreme value, gamma, Laplace, normal, uniform, and Weibull. It is found that the Weibull distribution is the most appropriate statistical model of the grain size and grain shape, when compared with the other eight statistical models. Regarding microcracks, the results show that the gamma distribution is the most appropriate model. The Weibull and gamma distributions are then used to analyze the heterogeneity of the microstructure. This is done by comparison of the statistical models of each microstructural property evaluated in several thin sections of the same rock. It is found that with respect to grain size and grain shape, the rock is homogeneous, while the size distribution of the microcracks shows a clear trend toward less homogeneity. The microstructural modeling approach is important for modeling, characterizing, and analyzing the microstructure of rock material. Among other applications, it can be used to explain differences in the mechanical behavior obtained in testing several specimens.

Determination of the Test Methods Sensitive to Free Mica Content in Aggregate Fine Fractions

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 mica’s 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.

Estimation of Rock Aggregates Quality Using Analyses of Drill Cuttings

There is a need for an effective method to estimate the quality of crushed rock aggregates and its usability in the early stages of project planning, e.g., for road and railway constructions and quarry prospecting. The proposed method is based on mineralogical and petrographic analyses of drill cuttings and analysis of the coarse fraction to estimate the homogeneity/heterogeneity of the bedrock. The geological analyses are followed by an estimation of the rock materials’ mechanical properties and their potential technical usability. Development and practical applicability (field and laboratory) of the method have been performed and correlated to three road projects from regions of different geological and climatic zones in Sweden. The study confirms the capability of the proposed method as a surveying tool.

The resurrection of a biologically dead lake : a case study from northern Sweden

A major release of heavy metals to surface water in Sweden is derived from oxidation of sulfidic waste sand and waste rock. The Lake Horntrasket in Northern Sweden has experienced a gradual loss of ...

The Capillarity of Mica-Rich Base-Course Aggregates

In regions of temperate climate, the destructive influence of frost is the main contributor to damage of a road structure. Commonly, the frost susceptibility of base-course aggregates is often ignored in road construction. However, a number of studies on aggregates for construction purposes, and field observations of road failures, indicate a negative influence of mica-rich rock aggregates (used in unbound applications) on the service life of road construction. The scope of the current work investigates the capillary properties of unbound base-course aggregates with varying free mica grains. The materials studied in this research are commercially available road construction aggregates, and originate from different regions of Sweden. The mineral composition of the samples has been determined by polarizing microscopy using a point-count method. The parameter characterizing the capillarity was measured using the test for determining capillary rise (VVMB24). The results show that there is a direct correlation between mica content of the aggregates and water suction by capillary forces. Therefore, mica-rich materials susceptible to frost heave, thus confirming the tendency for frost damage of unbound aggregates.