| Coal fly ash and clean coal technology by-products represent major volumes of solid wastes disposed of in landfills. Environmental concerns have led to increased adoption of the clean coal combustion technologies in power plants, substantially increasing the volumes of clean coal technology by-products. This research evaluates the by-products of the calcium spray dryer clean coal technology as a partial replacement for Portland cement in concrete. This by-product possesses higher calcium and sulfur oxide contents, and lower silicon, aluminum and iron oxide contents when compared with the conventional Class F coal fly ash, which is commonly used in concrete.; The clean coal technology by-product, when replacing 15 {dollar}sim{dollar} 30% by weight of cement in concrete, produced concrete materials with performance characteristics comparable to those obtained with conventional coal fly ash. The clean coal by-product concrete possessed better scaling resistance than fly ash conventional concrete. When compared with plain concrete, the clean coal by-product concrete had comparable (or slightly reduced) 28-day compressive strength, improved chloride permeability, and comparable scaling resistance and freeze-thaw durability. The clean coal technology by-product concrete, like fly ash concrete, responded better than plain concrete to extended moist curing periods.; Capillary pore system characteristics were found to be a fundamental property explaining the effects of the clean coal technology by-product in concrete. There was a general reduction in capillary porosity, particularly after longer moist curing periods, in the presence of the clean coal technology by-product. The pozzolanic reaction of the by-product seemed to block the pores and thus reduce their continuity, which explains the drop in permeability in the presence of the by-product. There was a marked effect of prolonged moist curing on the total capillary porosity and particularly on the volume of larger pores. This explains the highly beneficial effects of extended moist curing on the engineering properties of the clean coal technology by-product concrete. It is my general conclusion that the by-product of calcium spray dryer offers a strong potential for use as a mineral admixture with positive effects on permeability and thus durability of concrete. |
