# Mechanical and Environmental Performance of Chemical Pretreated Incineration Bottom Ash as a Supplementary Cementitious Material

## TL;DR

This study explores how chemical treatments can improve the use of incineration bottom ash as a cement substitute, finding that calcium hydroxide is the most effective and sustainable option.

## Contribution

The study introduces a systematic evaluation of chemical pretreatments for enhancing the reactivity and sustainability of incineration bottom ash in cementitious systems.

## Key findings

- Calcium hydroxide (Ca(OH)2) pretreatment significantly improves the strength and microstructure of incineration bottom ash.
- Sodium hydroxide (NaOH) and sodium carbonate (Na2CO3) treatments lead to reduced strength due to porosity and carbonation issues.
- Ca(OH)2 offers a balanced approach with strong activation and moderate carbon emissions.

## Abstract

Municipal solid waste incineration bottom ash (IBA), a major by-product of waste-to-energy plants, is typically landfilled or utilized as low-grade aggregate due to its low intrinsic reactivity and complex composition. This study systematically investigates the efficacy of chemical pretreatment in enhancing the cementitious behavior of IBA, specifically examining the effects of alkali type (Ca(OH)2, NaOH, and Na2CO3) and pretreatment duration on reactivity, microstructure, and mechanical performance. The results indicate that Ca(OH)2 activation provides the most significant enhancement; a one-day treatment yielded a 28-day strength activity index (H28) of 76% and facilitated the formation of a compact microstructure rich in ettringite (AFt) and C-S-H gels. Conversely, NaOH and Na2CO3 treatments were less effective, leading to increased porosity and reduced strength attributed to charge imbalance and excessive carbonation, respectively. Prolonged alkaline treatment yielded diminishing returns, causing premature gel densification or excessive silicate depolymerization. Life-cycle assessment (LCA) revealed that Na2CO3 pretreatment entails the highest carbon footprint due to its high molar mass and energy-intensive production, whereas NaOH offers the highest CO2 efficiency per unit of reactivity. Overall, Ca(OH)2 represents a balanced strategy, combining strong activation potential, chemical compatibility, and moderate carbon emissions, thereby supporting the sustainable valorization of IBA in low-carbon cementitious systems.