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Over the past decades, extensive studies on municipal solid waste incineration (MSWI) ashes have been performed to develop more effective recycling and waste management programs. Despite the large amount of research activities and the resulting improvements to MSWI ashes, the recycling programs for MSWI ashes are limited. For instance, although the U.S. generates more MSWI ashes than any other country in the world, its reuse/recycle programs are limited; bottom ash and fly ash are combined and disposed of in landfills. Reuse of MSWI ashes in the construction sectors (i.e., geomaterials, asphalt paving, and concrete products) as replacements for raw materials is one of most promising options because of the large consumption and relatively lenient environmental criteria. The main objective of this study was to comprehensively review MSWI ashes with regard to specific engineering properties and their performance as construction materials. The focus was on (1) the current practices of MSWI ash management (in particular, a comparison between European countries and the U.S.), (2) the engineering properties and performance of ashes when they are used as substitutes of construction materials and for field applications, and (3) the environmental properties and criteria for the use of MSWI ashes. Overall, the asphalt and concrete applications are the most promising, from both the mechanical and leachate viewpoints. However, cons were also observed: high absorption of MSWI ash requires a high asphalt binder content in hot-mix asphalt, and metallic elements in the ash may generate H2 gas in the high-pH environment of the concrete. These side effects can be predicted via material characterization (i.e., chemical and physical), and accordingly, proper treatment and/or modified mix proportioning can be performed prior to use.

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Aggregate type and mineralogy are critical factors that influence the engineering properties of concrete. Temperature variations result in internal volume changes could potentially cause a network of micro-cracks leading to a reduction in the concrete's compressive strength. The study specifically studied the effect of the type and mineralogy of fine and coarse aggregates in the normal strength concrete properties. As performance measures, the coefficient of thermal expansion (CTE) and compressive strength were tested with concrete specimens containing different types of fine aggregates (manufactured and natural sands) and coarse aggregates (dolomite and granite). Petrographic examinations were then performed to determine the mineralogical characteristics of the aggregate and to examine the aggregate and concrete microstructure. The test results indicate the concrete CTE increases with the silicon (Si) volume content in the aggregate. For the concrete specimens with higher CTE, the micro-crack density in the interfacial transition zone (ITZ) tended to be higher. The width of ITZ in one of the concrete specimens with a high CTE displayed the widest core ITZ (approx. 11 µm) while the concrete specimens with a low CTE showed the narrowest core ITZ (approx. 3.5 µm). This was attributed to early-age thermal cracking. Specimens with higher CTE are more susceptible to thermal stress.

In this paper, municipal solid waste incineration (MSWI) bottom ash was characterised before and after chemical treatment and the effect of ash addition on the performance of concrete as a partial replacement of fine aggregate was evaluated. The chemical treatment aimed to eliminate the side effect of MSWI ash -the creation of a network of bubbles -which can eventually lead to a significant reduction of the overall performance of concrete.Petrographic examinations, energy dispersive X-ray spectroscopy and X-ray diffraction, were carried out to chemically characterise the MSWI bottom ash. The mechanical performance of the ash-combined concrete was evaluated by measuring its compressive strength. Analysis of the measured data demonstrates that the chemical treatment successfully transformed metallic aluminium in the ash into a stable form and hence expansion of the concrete due to hydrogen gas evolution was no longer detected in the concrete containing treated ash.Consequently, compared with specimens with untreated ash, concrete specimens with treated bottom ash showed improved performance.