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.
The use of recycled concrete aggregate (RCA) as a drainage material in exfiltration trenches and base and subbase layers is becoming increasingly common. During crushing, stockpiling, transporting, and placing, however, RCA may produce fines that could recement and clog the pavement drainage system. Many previous studies indicated that not only the structural capacity but also drainage of pavement subsurface layers can be greatly affected by the properties and gradation of the aggregate used. This study evaluated the recementation reactivity of RCA fines that could eventually impair drainage performance. RCA fines passing the No. 200 sieve (less than 75 μm) were produced through the simulation of an in-place aggregate abrasion process, and cement paste cylinders were cast with complete replacement of cement with RCA fines. The hydration properties of the paste samples with RCA fines were evaluated by means of heat of hydration, pH variation, and Vicat needle penetration in their early age. Compressive strength tests and petrographic examinations such as scanning electron microscopy, energy dispersive X-ray, and X-ray diffraction were also performed to mechanically and chemically verify the recementation reactivity of the hardened paste with RCA fines. Test results demonstrated that recementation of RCA fines was modest, and therefore the compressive strength of the paste specimens with RCA fines was minimal compared with that of ordinary cement paste specimens. The microstructural and chemical composition analyses also indicated that the recementation reactivity of RCA fines was negligible.
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