Characterisation of mortars using municipal solid waste incinerator bottom ash and slag

The high cement content in repair mortars necessitates the development of sustainable and durable alternatives using supplementary cementitious materials (SCMs). Municipal solid waste incinerator bottom ash (MSWI_BA), generated in substantial volumes annually, is currently being landfilled or used in low-value applications, overlooking its potential as valuable SCM. This study investigates the mechanical properties of traditional clinker-based CEM I mortars modified with fresh (type-V) or matured (type-M) MSWI_BA and ground granulated blast-furnace slag (GGBS). CEM I was partially replaced with 10% and 20% MSWI_BA, and GGBS contents of 0%, 15%, 26%, 56%, and 71% by weight of the 10% MSWI_BA. Tests at intervals up to 120 days examined fresh properties, density, and flexural and compressive strength. Results indicate that MSWI_BA reduces density, while GGBS has a minimal effect. MSWI_BA-mortars exhibited lower flexural strengths, with 10% MSWI_BA outperforming 20%, and 15% GGBS yielding the highest flexural strength among MSWI_BA-mortars. Higher GGBS levels delayed early hydration yet promoted long-term strength development. In compressive strength, 10% MSWI_BA outperformed 20%, with type-M achieving comparable results to CEM II and CEM III/A 32.5 after 120 days, and outperforming type-V. These findings highlight the possibilities of MSWI_BA-GGBS blends as sustainable secondary materials for traditional clinker-based repair mortars.