Effects of wood waste bottom ash (WWBA) and fly ash (FA) on the properties of concrete

Abstract

Wood waste bottom ash (WWBA) is produced in thermoelectric or small industrial furnaces. Wood processing residues, a sustainable and renewable source of energy production, generate a large amount of wood waste ash. The amount of wood waste ash increases with the growing demand for bioenergy production. The main concerns related to this ash are storage, disposal, utilization and the presence of unburnt carbon. Power plants that produce heat and electricity create combustion by-products. These products include fly ash (FA), slag, carbon dioxide and other compounds. FA that is not suitable to be reused in construction products, such as concrete, is stored in landfills. With extended urbanisation and rapid growth of construction industry, the demand for cement and aggregates, especially for the production of concrete, is increasing. Therefore, this study focuses on the use of bottom ash as a substitute for aggregate and fly ash as a substitute for cement in concrete mixes. This study aims to investigate the effect of FA and WWBA on the physical and mechanical properties of cement concrete and to evaluate the possibility of replacing part of the cement and sand in the mixes with ashes. Five concrete compositions were prepared using CEM II/A-LL 42.5 N cement, 0/2 sand, 5/16 granite crushed stone, polypropylene fibre, and superplasticizer. The 0/2 fraction sand was replaced by WWBA and the cement was replaced by FA in amounts of 0%, 2.5%, 5%, 10% and 15% by mass. The following concrete properties were tested and analysed: mixture density, flowability, density of concrete samples, compressive strength and ultrasonic pulse velocity. Analysis of the test results showed that 5% was the most suitable and useful ashes content for the preparation of concrete.