Physical properties and acid neutralisation capacity of incinerator bottom ash-portland cement mixtures

Abstract

The amount of bottom ash resulting from solid waste incineration typically ranges from 30 to 35% of burnt waste. Although such a residue stream is not classified as a hazardous waste according to the European waste catalogue, disposal of bottom ash may heavily weigh on the overall incineration costs. Furthermore, the present tendency for solid waste management in industrialised countries is towards reduction of the amount of wastes to be landfilled. With a view to that, technical approaches aimed at reusing residual streams in industrial applications as secondary materials must be strongly encouraged. As far as bottom ash is concerned, a promising option is represented by blended cement formulation. Bottom ash is indeed characterised by the presence of oxides and aluminosilicates, which might be responsible for strength development during cement hydration. In some cases, depending both on the composition of the original waste and on the combustion technology adopted, bottom ash may also exhibit pozzolanic activity. It is well known that the properties of hardened cement mixtures made with impuritiesbearing materials are strongly affected by the physical-chemical characteristics of the components, as well as the waste/cement dosage. This paper presents the results of an experimental investigation on the behaviour of mixtures made with Portland cement and bottom ash coming from an Italian medical waste incinerator. In particular, the influence of waste/binder replacement levels and water/solids ratios on strength development and acid neutralisation capacity was investigated. Different samples were prepared at low and high waste/binder ratios at various amounts of added water in each mixture. Physical properties consisting of setting time, unconfined compressive strength and evaporable water content were measured at different ages. Also, the acid neutralisation capacity of the hardened material was evaluated in order to investigate the leaching behaviour under different pH conditions. In order to quantify to what extent do the above parameters affect the properties of the solidified products, a factorial design was arranged and the analysis of variance carried out.