Influence of melted incinerator ash on durability and corrosion behaviour of reinforced concrete

Abstract

This study investigates the effects of incinerator bottom ash (IBA) fineness and the cooling process of molten IBA on the durability of concrete and the corrosion of rebar. Two finenesses of an original IBA, i.e. pulverized incinerator bottom ash (PIBA) powder with maximum particle sizes of 0.6 and 0.074 mm, were used to partially replace Portland cement at 20 per cent by weight. In addition, the powder was also obtained by melting the PIBA (<0.6 mm) in an electric-furnace at 1450 °C for 1 h and chilling it by quenching in water (WIBA, water-cooled melted incinerator bottom ash) and air (AIBA, air-cooled melted incinerator bottom ash). The powder was then ground in a ball mill until the particle size reached less than 0.074 mm. This study also presents the experimental results on the compressive strength, mercury intrusion porosimetry, scanning electron microscopy (SEM), and X-ray diffraction of concrete samples containing different types of IBA. This study uses the initial surface absorption test and rapid chloride penetration test to measure the absorption and the ability of different concrete samples to resist chloride ions. Cylindrical specimens were cast and exposed to 3.5 per cent NaCl solution under a direct current density (0.5 m A/cm2) to accelerate the corrosion process. The open circuit potential and direct current polarization resistance were obtained to evaluate the rebar corrosion. Results indicate that WIBA concrete achieved a compressive strength similar to reference specimens after 28 days of curing; WIBA and AIBA exhibited an increase in unit weight and workability when used as a replacement for cement. However, IBA can be processed by melting to regain reactive pozzolanic activity, which may be used to partially replace cement. The incorporation of WIBA and AIBA decreased the total capillary pore porosity of the mortars compared to ordinary PIBA. The large particle size of PIBA produced lower hydraulic properties than finer particles. The improved properties of WIBA and AIBA resulted from the dense structure achieved by the filling effect of the pozzolanic product. Strength activity index results, SEM, X-ray analysis, and the rate of ISA observations confirm these findings. Utilizing a proper amount of WIBA and AIBA significantly improved the chloride and corrosion resistance of rebar in concrete in this study. Therefore, WIBA and AIBA can act as cementitious materials in cement-based composites.