Effect of Crushing on Stress–Strain Behavior of Fly Ash Under Monotonic Compression and Repeated Loading–Unloading Conditions

Abstract

Use of fly ash in various geotechnical structures has increased instead of using conventional geomaterials. Million tons of fly ash is produced every year and its safe disposal is an issue as it creates health hazards if exposed to air directly. Fly ash is largely used as structural fill material in highway, railway embankments and as a backfill material in Geosynthetic reinforced structures. Fly ash is a by-product generated on coal combustion. It contains spherical, hollow particles (cenospheres), and particles filled with smaller particles (plerospheres). Due to presence of air voids in cenospheres, specific gravity of fly ash is obtained to be lower as compared to soil. Due to the hollow nature of fly ash particles, they undergo crushing and deformation when subjected to external loading. The present study evaluates the effect of crushing on stress–strain behavior under monotonic compression and repeated loading–unloading UU triaxial testing conditions. A successive cycles of standard proctor tests were performed on fly ash to induce different degrees of crushing. Specimens with different degrees of crushing (50 mm diameter and 100 mm height) were prepared at maximum dry density (MDD) of uncrushed fly ash. Stress-stain response under monotonic compression loading exhibited significant decrease in peak deviatoric stress with the increase in crushing of fly ash particles. There was significant reduction in accumulated axial strain with the increase in crushing under repeated loading–unloading conditions.