Early age hydration of blended cement with different size fractions of municipal solid waste incineration bottom ash

Municipal solid waste incineration bottom ash (IBA) may be used as cement supplements. Few studies reported IBA delays the setting and hydration of Portland cement. However, fundamental causes of this retarding effect and the consequent effects on cement hydration especially at early age are still not clear. Furthermore, no previous study has discussed the effects of different size fractions of IBA on hydration and microstructure of hardened pastes. This paper presents the effects of different size fractions of IBA on hydration of IBA-blended cement at early age. Results show that chemical compositions of IBA vary significantly with its particle size. Large particles are rich in siliceous substance which can be a potential pozzolan while small particles contain much calcareous materials and anhydrite. As a result, smaller size fraction of IBA shows stronger retarding effect due to the presence of more soluble calcium-bearing substance and leachable heavy metals which prohibit dissolution of C₃S and hinder nucleation of portlandite and C-S-H. After the onset of accelerated hydration; however, different size fractions of IBA possess similar hydration heat evolution, total heat of hydration, and cementitious properties.