Durability-related performance of recycled aggregate concrete containing alkali-activated municipal solid waste incinerator bottom ash

Abstract

The increasing demand for sustainable construction materials has led to a growing interest in the use of recycled materials in concrete production. The main motivation for this research is to explore sustainable alternatives to conventional concrete mixes that can reduce the environmental impact of construction activities and address the growing issue of waste accumulation. For this reason, this study intends to evaluate the performance of alkali-activated concrete with different contents of fly ash (FA) and municipal solid waste incinerator bottom ash (MIBA). For this purpose, five compositions were considered, where the binder ratios were 100% cement, 100% FA, 75% FA/25% MIBA, 50% FA/50% MIBA and 25% FA/75% MIBA, all of which were produced with natural aggregates. Five additional mixes were produced by fully replacing the natural aggregate with recycled aggregate from mixed construction and demolition waste. A mix with 100% FA, fine natural aggregates and coarse recycled aggregates was also produced to understand the difference between the full use of recycled aggregates and their partial use. The conducted tests include compressive strength, water absorption by capillarity and immersion, chloride penetration, carbonation, and shrinkage (autogenous and total). The results showed that the substitution of FA with MIBA led to progressively worse durability-related performance, though manageable in given proportions. The incorporation of recycled aggregates led to an unexpectedly steep decline of ∼80% in compressive strength and overall durability performance in comparison with equivalent cement-based recycled aggregate concrete mixes. Nevertheless, the trend reverted in terms of shrinkage, wherein recycled aggregate-containing mixes presented the least dimensional variations. In the mechanical strength test, the curing of the alkali-activated concrete mixes in a CO2 chamber led to a considerable improvement (i.e. 5–15 MPa) in all tested mixes.