Effect of crushing and strain rate on mechanical behaviour of Gandhinagar fly ash

Fly ash is a by-product of coal combustion from thermal power plant. It comprises of hollow spherical silt size particles with low specific gravity. Fly ash finds its major use as a structural fill material in highway and railway embankment, and serves as better alternative to natural borrow soil. Its utilization as a geomaterial exposes it to stress-strain conditions, which mostly concern to natural soils in the past. The increased use of fly ash in highway/railway embankment construction raises the need to study its mechanical behavior in detail. The current research is focused on crushing effect of fly ash on its macroscopic & microscopic behavior and strain rate effect on pore pressure evolution & stress-strain response of fly ash. Although it has been reported that fly ash is susceptible to breakage, the effect of crushing on its macroscopic & microscopic behavior has not been investigated. The fly ash used in the current research was obtained from Gandhinagar Thermal Power Plant, and was identified as type F fly ash due to its low calcium oxide content. Two series of tests were conducted on Gandhinagar fly ash. First series was focused on crushing of fly ash particles and its impact on microscopic & macroscopic behavior of fly ash. The five specimens of fly ash (S0 to S4) with different degree of crushing were prepared by applying different cycles of impact loading. S0 represented the uncrushed specimen of fly ash and S4 represented the specimen with maximum degree of crushing. Index properties (grain size distribution, specific gravity and liquid limit), compactability, strength, compressibility and SEM tests were performed on these specimens (S0 to S4) to evaluate the effect of crushing of fly ash particles on its macroscopic and microscopic behavior. In second series, CU triaxial tests were performed on uncrushed fly ash specimens (S0) to evaluate the effect of strain rate on its pore pressure evolution and strain rate response for strain rates varying from 0.005%/min to 9%/min. The chosen range of strain rate simulated the vehicular loading rate commonly experienced by highway/railway embankments.