12 - Mechanical properties of recycled aggregate concrete with bottom ash additions

Abstract

This chapter presents a literature review on the influence of using bottom ashes in the properties of recycled aggregate concrete. Three types of bottom ashes are analyzed: coal bottom ashes, municipal solid waste incinerator bottom ashes, and biomass bottom ashes. Their physical, chemical, and mineralogical properties are discussed, as well as their effect on the fresh, mechanical, and durability-related performances of concrete. Bottom ashes from incineration of municipal solid waste or biomass waste usually exhibit extensively varying chemical compositions, due to the variability of the input waste (i.e., different kinds and amounts of waste materials from households—aluminum cans, batteries, ceramic, glassware, etc.—and different species of wood and/or plants—pine, mahogany, olive husk or kernel, wheat straw, etc.). Bottom ashes can exhibit some pozzolanicity, though less than that observed in conventional coal fly ash, which can mitigate part of the decline in performance that is typically observed when using them. These industrial by-products, when used in high amounts and in conjunction with recycled aggregates, are likely to result in a combination of negative effects, leading to a significant decline in performance. However, in moderate contents, adequately processed bottom ashes from municipal solid waste can enhance the mechanical performance of concrete, as well as the resistance to chloride ion penetration. The use of coal bottom ashes was also found to significantly reduce the drying shrinkage strains of concrete.