The feasibility of a waste glass powder residue (GP) from glass recycling as partial mineral precursor to produce alkali-activated materials is investigated. GP served as powder coal fly ash (PCFA) replacement within a reference system composed of 50% PCFA and 50% ground granulated blast furnace slag (GGBS). Compared with PCFA, GP was better involved in the alkali activation process by having a higher silica and Ca dissolution. Furthermore, increasing GP replacement up to 30% prolonged the induction period, facilitated the gel formation and yielded a 35% higher 28-day compressive strength. These observations are similar to the effect of using both sodium hydroxide and sodium silicate as alkali activator in alkali-activated slag/fly ash systems. A higher polymerization of the gel network was also observed. Microstructure analysis indicated that the main reaction product is a calcium silicate hydrate type gel substituted with Al and Na (C-(N)-AS -H type gel). This work largely contributes to the understanding of the reactivity and potential of GP and promotes its practical utilization as a mineral precursor in the production of alkaline cements.
Municipal solid waste incineration bottom ash was treated with specially designed dry and wet treatment processes, obtaining high quality bottom ash granulate fractions (BGF) suitable for up to 100% replacement of natural gravel in concrete. The wet treatment (using only water for separating and washing) significantly lowers the leaching of e.g. chloride and sulfate, heavy metals (antimony, molybdenum and copper) and dissolved organic carbon (DOC). Two potential bottom ash granulate fractions, both in compliance with the standard EN 12620 (aggregates for concrete), were added into earth-moist concrete mixtures. The fresh and hardened concrete physical performances (e.g. workability, strength and freeze-thaw) of high strength concrete mixtures were maintained or improved compared with the reference mixtures, even after replacing up to 100% of the initial natural gravel. Final element leaching of monolithic and crushed granular state BGF containing concretes, showed no differences with the gravel references. Leaching of all mixtures did not exceed the limit values set by the Dutch Soil Quality Degree. In addition, multiple-life-phase emission (pH static test) for the critical elements of input bottom ash, bottom ash granulate (BGF) and crushed BGF containing concrete were assessed. Simulation pH lowering or potential carbonation processes indicated that metal (antimony, barium, chrome and copper) and sulfate element leaching behavior are mainly pH dominated and controlled, although differ in mechanism and related mineral abundance.
This paper investigates the influence of a plasticizing admixture on the pore structure refinement of alkali-activated concrete and paste mixtures and the consequently enhanced performance. Alkali-activated fly ash-slag concrete and paste are designed using a polycarboxylate-based admixture with different dosages. The pore structure and porosity are analyzed using mercury intrusion porosimetry (MIP). The workability, compressive strength, chloride migration resistance and electrical resistivity of alkali-activated fly ash-slag concrete and paste are determined. The results show that significantly improved workability and strength development are obtained at an increased admixture content. The admixture improves the gel polymerization product layer most likely around the GGBS particles, densifying the matrix. The 28-day Cl-migration coefficient of admixture (1-2 kg/m 3 ) modified concrete is equal to the reference mixture, while at the highest admixture content the Cl-ingress is increased. At the later ages (91-days), the Cl-migration coefficients of all concretes, non-and admixture-containing samples, are comparable and low (about 2.6 × 10 -12 m 2 /s). The MIP analyses show a significant decrease of the total and effective capillary porosity over time at an increased admixture content. The relationships between the porosity and other properties are discussed, at varying admixture contents.
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