An investigation into the physical-mechanical indices of igneous rocks and their aggregates

The Present investigation is a study of the physical and mechanical properties of a suite of igneous rocks and aggregates derived from them, with special emphasis on their geological nature and the post emplacement processes which affects them. The study concentrated on: i- Petrographical characteristics. ii- Weathering effects and characterisation. iii- Index properties for intact and aggregate rock strength. iv- Los Angeles Abrasion Value, methodological and geological factors affecting values. v- Correlation between index properties for intact rock and aggregate. The rock suite ranges from volcanic to plutonic, basic to acid in composition and fresh to completely weathered. This provided an opportunity for testing and evaluating various textural and weathering variables. Weathering which systematically affects the engineering properties of rocks, can be quantified by secondary mineral content or alternatively the well established micropetrographic index (Ip). It can also be quantified by physical indices such as specific gravity, porosity and water absorption or mechanical indices such as Rebound Number and Point Load Strength. Weathering and other geological variables such as grain size and texture are prominent factors affecting the strength of both intact and aggregate strength values. An investigation into the Los Angeles Abrasion Value (LAAV) and the factors which affect it established that test results are as systematic and rational as the other recognised strength tests. Aggregate Impact (AIV) and Crushing Values (ACV). In the Los Angeles Abrasion Test It was demonstrated that the mechanism of comminution is dominantly one of impact loading (80 %) with a minor component of attrition (20%). The LAAV is consistently affected by geological variables such as grain size, texture, clast shape and degree of weathering in a manner similar to that established for AIV and ACV. Intact and aggregate strength indices are related in a simple manner and provided geological and methodological variables are known and evaluated, aggregate strength indices can be predictable from intact rock properties.