Alkali-Activated Materials with Pre-Treated Municipal Solid Waste Incinerator Bottom Ash

Abstract

This study presents the results of an experimental campaign on the use of municipal solid waste incinerator bottom ash (MIBA) and fly ash (FA) as precursors for the production of alkali-activated materials. MIBA was subjected to a pre-treatment stage in response to two issues: high metallic aluminum content, which reacts in a high pH solution, releasing hydrogen; and low amorphous content of silica-, aluminum- and calcium-bearing phases, which translates into a limited formation of reaction products. The proposed pre-treatment stage oxidizes most of the metallic aluminum fraction and compensates for the low reactivity of the material via the formation of additional reactants. Different combinations of MIBA and FA were tried—mass-based ratios of 0/100, 25/75, 50/50, 75/25, and 100/0 for MIBA/FA. Two mix designs of the alkaline activator with sodium hydroxide and sodium silicate were evaluated by varying the Na2O/binder and SiO2/Na2O ratios. These mortars were tested in the fresh and hardened state. The results showed that the pre-treatment stage was effective at stabilizing the dimensional variation of MIBA. Despite the lower reactivity of MIBA, mortars with 50/50 of MIBA/FA presented a maximum 28-day compressive strength of 25.2 MPa, higher than the 5.7 MPa of mortars made with MIBA only.

Utilization of Aluminosilicate Industrial Wastes as Precursors in CO2-Cured Alkali-Activated Precast Concrete Pavement Blocks

“…Moreover, the density of MIBA mixes decreased with increasing water content; however, no values were reported for w/b 0.40 and 0.45 due to the observed volume expansion (Figure 6) caused by the release of hydrogen gas generated by the reaction of the metallic aluminium present in MIBA, with the alkaline solution. Other studies have reported similar behaviour [41,48,60].…”

“…Moreover, the density of MIBA mixes decreased with increasing water content; however, no values were reported for w/b 0.40 and 0.45 due to the observed volume expansion (Figure 6) caused by the release of hydrogen gas generated by the reaction of the metallic aluminium present in MIBA, with the alkaline solution. Other studies have reported similar behaviour [41,48,60]. The decrease in density with the increase in w/b ratio for all binders can be explained by the increased mix's water content, which has a lower density than the other components it is replacing.…”

“…MIBA was procured from the waste-to-energy plant at the periphery of Lisbon, Portugal, operated by Valorsul. Prior to its use as a precursor, MIBA went through preparatory steps, namely the elimination of impurities (such as metals, paper, and plastic), desiccating at 105 • C, and the necessary comminution based on previous experience [39][40][41] to align with the typical particle size distribution needed for binders.…”

“…Turning to the specimens with MIBA, a substantial surge in strength, ranging from 275% to 306%, was observed, with the highest recorded compressive strength reaching 28 MPa after 91 days of carbonation. Likewise, Avila et al [41] detected enhanced strength development of alkali-activated FA and MIBA following exposure to accelerated carbonation under conditions of 5% CO 2 over time. Remarkably, the most substantial improvements in both compressive and flexural strengths were observed in the carbonated mixes (exposed for 28 days) containing 100% MIBA.…”

“…Recent research has investigated novel aluminosilicate industrial wastes, exploring their chemical composition and potential as binders. Several studies have showcased the binding prowess of materials like electric arc furnace slag (EAFS) and municipal solid waste incinerator bottom ashes (MIBAs) when used as exclusive components in alkaliactivated materials (AAMs) [29,32,[34][35][36][37][38][39][40][41]. Concrete incorporating these binders typically exhibits diminished mechanical strength and durability [32,35].…”