Properties of Circulating Fluidized Bed Combustion Ash and Pulverized Coal Bottom Ash Used for Backfill

The need to address dwindling supplies of natural resources has led researchers to seek out alternative uses for industrial bi-products. In this study, we investigate the application of ash produced in coal burning power generation plants to substitute natural aggregate in concrete and backfill. Ash from circulating fluidized bed combustion (CFBC) was mixed in various proportions with the bottom ash from pulverized coal (PC). Specimens were tested in accordance with standard specifications to evaluate engineering properties. Variables included mix proportions and preloading, and all samples were subjected to compressive strength tests, soil compaction tests, direct shear tests, California bearing ratio (CBR) tests, triaxial permeability tests, and scanning electro-microscopic (SEM) observation. These tests were performed to verify the feasibility of CFBC ash mixtures for use as backfill material or controlled low strength material. Test results indicate that the optimum moisture content of the six mixtures decreased with an increase in the proportion of PC bottom ash and increased with an increase in preloading. Cohesion and internal friction angle increased with an increase in loading. The highest CBR value was attained with a ratio of CFBC ash to PC bottom of 1:1.5 by weight. The coefficient of permeability increased with the amount of PC bottom ash.