Characterization and Effect of Using Bottom and Fly Ashes from Co-combustion of Cocoa Waste as Mineral Addition in Concrete

Abstract

Biomass ash has been produced worldwide in large quantities and has often generated high storage costs or environmental problems. A valorisation alternative, regarding this waste, has been its use in mortar or concrete; however, as biomass ashes exhibit larger variations in physico-chemical characteristics, which depend on the type of biomass fired, combustion methods used and type of ash collected, proper knowledge of its properties is required before using it as an aggregate or mineral additive. In this study, the biomass bottom ash (BBA) and biomass fly ash (BFA) generated in the cocoa industry, by the burning of wood chips and cocoa shell waste, are characterized to evaluate their potential use as partial cement replacements. In addition, nine types of concrete were produced with 0, 5 and 10% of cement (by mass) replaced by BBA and BFA, as received and ground. For these mixtures, physical and mechanical tests were performed. For all levels of cement replacement, the ash reduced water absorption, porosity and capillary indexes, which can make the concrete more durable, despite reducing mechanical strength. The mechanical strength evaluation of concrete samples subjected to compressive loading cycles after 365 days, demonstrated that the addition of ash does not have any long-term deleterious effect on the concrete.