Novel cementitious materials produced from incinerator bottom ash

The fine fraction of incinerator bottom ash (IBA) obtained from an energy from waste plant has been milled and thermally treated at 800 °C to investigate the potential for exploiting IBA as a cementitious material. In addition to decomposition of CaCO3 to CaO, thermal treatment increases the content of gehlenite (Ca2Al2SiO7), wollastonite (CaSiO3) and mayenite (Ca12Al14O33). Monolithic samples have been formed by adding 10 wt.% Ca(OH)2 at water to solid (w/s) ratios of 0.50 and 0.20. The high w/s samples were formed by casting and the low w/s samples were formed by pressing. The setting time and physical properties of cured samples were determined including compressive strength and the extent of reaction of Ca(OH)2. Hydration products included a mixed sulphate-carbonate AFm-type phase (Ca4Al2O6(CO3)0.67(SO3)0.33·11H2O) and a low Ca/Si ratio C–S–H gel. The release of hydrogen gas from IBA due to residual Al metal did not cause macro-porosity to form in the pressed samples, and these novel materials had significant compressive strengths of 12.7 and 14.7 MPa at 7 and 28 days, respectively.