Utilization of incineration bottom ash for production of autoclaved aerated concrete
Date of Issue2018
Interdisciplinary Graduate School
Energetics Research Institute
Singapore is a city state with limited land space and nature resource. Municipal solid waste (MSW) is incinerated to reduce the volume of refuse. The ash residue after incineration is disposed of in the Semakau landfill, which is the only remaining landfill in the country. It is estimated that the Semakau landfill will reach its full capacity in 20 years. There is an urgent need to deviate incineration bottom ash (IBA) from landfill, to convert waste into resource, and to prolong the lifespan of Semakau landfill. This research utilizes IBA to synthesize high value end products. Instead of pre-treating IBA to remove metallic aluminum or to immobilize heavy metals, IBA is used directly as gas-forming agent and silicate and calcareous sources to replace raw materials used for the production of autoclaved aerated concrete (AAC). IBA-AACs with sound mechanical, physical, and environmental properties are developed in this study. IBA was classified into 11 categories to increase its utilization potential. To utilize IBA as gas-forming agent, metallic aluminum in IBA was characterized in detail. It was found non-ferrous IBA with particle size larger than 1.18 mm contains much more metallic aluminum than other categories. With an in-house designed automatic and high precision collecting gas over water apparatus, the reaction kinetics and capacity of gas generation from IBA was investigated. Based on the shrinking core model of solid-liquid system, a kinetics model was developed to predict gas generation from IBA at different temperature and solution alkalinity. It was found IBA with particle size less than 300 m contains much more calcium, which can be used as lime replacement after calcination for AAC production. The glass category in IBA is rich in silicon and hence can be used to replace coal fly ash in AAC. The resulting IBA-AACs possess enhanced mechanical strength because the silicon phases in IBA glass are highly amorphous and reactive, which leads to formation of pure tobermorite phase in AAC. All IBA-AACs show very low heavy metal leaching far below the limiting values allowed for building materials during their service life and for waste landfill at the end-of-life. This is mainly attributed to autoclave process which is essentially a hydrothermal treatment to immobilize heavy metals in IBA. Furthermore, it was found up to 70 % of IBA could be utilized as raw ingredients for AAC production, which results in 70 % material cost saving.