The microstructure of concrete made with municipal waste incinerator bottom ash as an aggregate component

The interaction of municipal solid waste incinerator bottom ash (MSWI bottom ash), when utilized as an aggregate in concrete, with the cement matrix was investigated. The most prominent reaction observed in lab and field concrete was the formation of aluminium hydroxide and the release of hydrogen gas from aluminium grains reacting in the alkaline environment. The expansive aluminium reaction was identified as a main cause of extensive spalling on the concrete surface. Due to the higher content of bottle glass as part of the ash, in all samples, reaction products of an alkali-silica reaction (ASR) could be observed as well. However, damage due to ASR were less severe than those caused by the aluminium reaction. The expansion rates were low and only a few of the lab samples showed cracking. Microstructural analysis of the samples indicated clearly that a large quantity of the alkali-silica gel which was formed was accommodated in the pores and voids without exerting any strain on the material.