3D-Printable Mortars Incorporating Municipal Solid Waste Incineration Bottom Ash (2025-11)¶

Municipal solid waste incineration (MSWI) bottom ash, when added as a mineral additive in concrete printing, promotes sustainable construction. In this study, the impact of using this ash on the rheological behavior, mechanical strength, and hydration in printable mortar was examined. MSWI bottom ash replaces cement in corresponding specimens labelled M−10, M−20, and M−30. The hydration behavior was analyzed using isothermal calorimetry, X-ray diffraction, thermogravimetry, and Fourier transform infrared spectroscopy. Rheological properties were assessed using a rheometer, penetration tests, and flow table tests. Additionally, the mechanical response of MSWI bottom ash-based printed mortar under compressive and flexural loading was evaluated. The results showed a reduction in calcium hydroxide content and formation of additional calcium silicate hydrate phases, enhancing hydration. Structuration rates were 11, 8.8, 12.3, and 7.5 kPa/min for M−0, M−10, M−20, and M−30, with M−20 achieving a 4 % increase over the reference mix. This increment is nontrivial because it results in an absolute increase of 8 layers and a 57 % relative improvement in buildability. The initial yield stress of M−20 was 0.55 kPa, classified as moderately stiff for extrusion and layer support. At 28 days, the anisotropy coefficient for flexural strength decreased from 0.159 in M−0 to 0.110 in M−20. The findings demonstrate that incorporating 20 % MSWI bottom ash enhances rheological performance and reduces the anisotropy coefficient. These improvements are due to the physical filler effect of fine ash particles and the pozzolanic reaction, which contribute to particle cohesion and the formation of C–S–H. Therefore, 20 % MSWI bottom ash is the optimal replacement level for 3D printable mortar.