The Mineralogical Composition and Mechanical Characteristics of Selected European Coal Mining Waste Samples and Their Experimental Correlation

Globally, there is a vast amount of coal mining waste (CMW) currently stored in spoil tips and tailing dams, presenting a significant source of potentially recoverable geomaterial for construction and geotechnical applications. In the literature, the heterogeneity in compositional and mechanical properties of CMW has often been mentioned, but their shared characteristics have not been much explored. A research program was carried out to collect seven CMWs from different locations across Europe to estimate their mineralogical make-ups quantitatively using powder characterization tests and to determine their mechanical parameters using triaxial tests. It was found that all the seven European CMWs collected share several compositional patterns with each other and with non-European CMWs reported the literature, including the abundance of SiO2 and Al2O3, quartz and clay minerals, and varying levels of organic carbon content. The results of triaxial compression tests on five of the seven European CMWs collected show them possessing a reasonably high triaxial-estimated friction angle when sheared to a large strain. Some authors previously reached similar conclusion, but the experimental data from this study show a much smaller spread, indicating that the tested CMW particles had not been greatly affected by in situ weathering. Moreover, the specific gravity of the collected CMWs correlates strongly with their organic carbon content. Their triaxial-estimated friction angles at large strain correlate poorly with their alumina contents but correlate positively with the ratio of quartz mineral to the sum of clay minerals and amorphous (organic) fraction in them. Implications of these test results on their possible practical applications are also examined and discussed.