Prediction of Durability Properties of Igneous Rocks as Railway Ballast by Simultaneously Considering the Petrographical, Geochemical, and Physical Characteristics

Finding stone aggregates with desirable properties in terms of durability for use in railway ballast is one of the most important concerns of railway projects. This study investigated the suitability of some types of igneous rocks (acidic to basic groups) for use as railway ballasts in Yazd Province, Iran. Los Angeles abrasion (LAA) and ${\mathrm{MgSO}}_4$ test results for the samples were compared. The results revealed that the acidic rock group, especially dacite samples, showed lower LAA and ${\mathrm{MgSO}}_4$ weight loss compared with the basic rock group. The LAA and ${\mathrm{MgSO}}_4$ weight loss values decreased with increasing ${\mathrm{SiO}}_2$ content in both acidic and basic rocks. With an increase in ${\mathrm{Al}}_2{\mathrm{O}}_3$, the ${\mathrm{MgSO}}_4$ weight loss increased for acidic rocks and decreased for basic rocks. Normative mineralogy content was meaningfully correlated ($R^2>0.93$ in multivariate regression) with the LAA and ${\mathrm{MgSO}}_4$ weight loss values. The chlorite carbonate pyrite (CCP) weathering index, which is defined based on changes in mineralogical content, showed a strong positive relationship with the LAA. Also, the Ruxton ratio index R (${\mathrm{SiO}}_2/{\mathrm{Al}}_2{\mathrm{O}}_3$) showed good to very strong correlations with ${\mathrm{MgSO}}_4$ weight loss. The porphyry ratio index (PR) did not individually succeed in predicting the durability properties. Therefore, the PR was used along with porosity and geochemical properties to estimate the LAA and ${\mathrm{MgSO}}_4$ weight loss. The use of variables of porosity, the PR and ${\mathrm{SiO}}_2$ and ${\mathrm{Al}}_2{\mathrm{O}}_3$ oxides developed very strong and reliable relationships ($R^2>0.98$) to estimate the LAA and ${\mathrm{MgSO}}_4$ weight loss.