Time Dependent Strength and Stiffness of PCC Bottom Ash-Bentonite Mixtures

Utilization of bottom ash from burning of pulverized coal in construction-related applications has received some attention within the last decade. Its use in geotechnical engineering applications is still very limited, however. Within the last few years several studies have been completed to evaluate strength, stiffness, and durability properties of pulverized coal combustion (PCC) bottom ash mixed with various admixtures. Studies have shown that the physical properties of bottom ash obtained from burning of pulverized coal are similar to that of natural sand with particle sizes ranging from fine gravel to fine sand and low percentages of silt and clay sized particles. However, unlike sand, chemical composition of bottom ash results in change of strength and stiffness characteristics of the bottom ash-admixture mixtures with time. In this study, change in strength and stiffness characteristics of Illinois PCC bottom ash and bentonite mixtures with time are evaluated. A series of unconfined compression tests on bottom ash-bentonite mixtures at various curing ages was performed in the laboratory. Results presented show that strength and stiffness of bottom ash-bentonite mixtures changed significantly with time.