Production of lightweight concrete using incinerator bottom ash

The medium size fraction (14–40 mm) of aged incinerator bottom ash (IBA) obtained from a major UK energy from waste (EfW) plant has been crushed to less than 5 mm (CIBA) and thermally treated at 600 °C (TCIBA6), 700 °C (TCIBA7), 800 °C (TCIBA8) and 900 °C (TCIBA9). Thermal treatment reduced the organic carbon content and increased the amount of wollastonite (CaSiO3), mayenite (Ca12Al14O33) and gehlenite (Ca2Al2SiO7). The crushed and thermally treated IBA has been mixed with Portland cement (PC) at different water/solid (w/s) ratios and with different proportions of PC and Ca(OH)2. The volume expansion during setting and bulk densities and compressive strengths were determined. Expansion occurred in all mixes contained IBA during curing. A lightweight material (density less than 1.8 g/cm3) with 28 day compressive strength of higher than 10 MPa was prepared by mixing 20 wt% PC with 80 wt% TCIBA8 at w/s ratio of 0.20. The expansion and associated lightweight properties result from gas evolution during curing due to residual metallic Al in the IBA. The main crystalline hydration products in 28 day cured samples were portlandite (Ca(OH)2), calcite (CaCO3) and calcium aluminate carbonate hydrates (Ca4Al2O6(CO3)0.5 · 12 H2O and Ca8Al4O14CO2 · 24H2O).