Incinerator Bottom Ash Shows Promise as Cement Filler Without Strength Loss

New research published in the International Journal of Environmental Engineering suggests that bottom ash, a residue from incinerated municipal solid waste, can be effectively utilized as a filler in cement. The study focused on micronized powder derived from this ash, investigating its chemical makeup and performance when incorporated into mortar, a common construction mixture.

Municipal waste incineration offers benefits such as reduced landfill reliance and energy generation, but it produces significant ash byproducts. In major Chinese cities alone, annual incineration generates nearly 20 million metric tons of ash. This residue, however, contains valuable cement-related minerals like silicon dioxide, calcium oxide, aluminum oxide, and iron oxide.

When milled to a particle size under 100 micrometers, this bottom ash can participate in cement hydration, the process enabling cement to harden. The research indicates that replacing up to approximately 30% of the cement with this material does not lead to a loss in material strength. However, substituting more than this threshold initially halves the 28-day compressive strength and significantly reduces flexural strength.

Encouragingly, the study also noted that extended curing periods can eventually improve both compressive and flexural strengths even at higher replacement levels. The researchers recommend lower proportions for general construction applications and suggest higher concentrations for uses like pavement bases, where bending resistance is a key requirement. These findings highlight the potential for recycling incineration residues while also identifying limitations for broader adoption.