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Oulun yliopiston väitöskirjat

Dissolution-precipitation reactions of amorphous multi-oxide silicates. Application of ligands in low-CO2 cementitious binders

Kieli:	englanti
Kustantaja:	Oulun yliopisto
Laitos:	Faculty of Technology
Painosvuosi:	2025
Sidosasu:	pehmeäkantinen
Sijainti:	Print Tietotalo
Sivumäärä:	194
Tekijät:	Ramaswamy, Rajeswari

25.00 €

Utilization of inorganic waste in the production of alkali-activated materials (AAMs) has shown potential to reduce CO2 emissions and energy usage compared to the production of traditional cement and concrete. Two such wastes are mineral wool and ground granulated blast furnace slag which are composed of amorphous multi-oxide silicates. Insights into the hydration mechanisms of AAMs are still being explored, which limits the utilization of these wastes. This thesis aims to develop an understanding of the factors controlling the dissolution-precipitation reactions of these wastes in alkaline conditions and to modify their reaction properties by using ligands as a new type of chemical admixture to produce low-CO2 cementitious binders. Various analytical and microscopic techniques were employed to understand the dissolution and precipitation chemistry on the solid-solution interface. The results showed that mineral wool has a homogenous median chemical composition, fiber length, and width for their respective types. The dissolution-precipitation reactions of mineral wool are affected by the pH, liquid-to-solid ratio, and chemical composition. Stone wool dissolved better than glass wool in alkaline conditions and the formation of precipitates such as Mg-Fe-Al-Ti layered double hydroxides and Ca-Na-Al-Si hydrate gel for both wools at pH 14 and the formation of phyllosilicates (Mg-Si-Al-Fe) for stone wool at pH 11 was observed. These results confirm the potential of mineral wool as a secondary raw material for AAMs. Five types of ligands were investigated as accelerators for Na2CO3-activated slag binder. The most promising was 2,3-dihydroxynaphthalene (DHNP), which showed an acceleration of the reaction kinetics of Na2CO3-activated slag, producing a strength of 40 MPa at 2 d compared to the strength of the reference sample without ligand of 2 MPa. Ligand properties like functional group and concentration affected the reaction kinetics and mechanism compared to the reference. Dissolution studies showed that DHNP increases the extent of dissolution significantly compared to the reference due to complexation reactions with Si and Ti, which accelerated the precipitation kinetics and increased the quantity of carbonate phases. Additionally, DHNP affected the morphology of the phyllosilicate phases. These results confirm the potential of ligands as new chemical admixtures to produce sustainable engineered cementitious binders.

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