Abstract
Common alkali-activated materials (AAMs) are usually manufactured with highly alkaline solutions. However, alkaline solutions are dangerous for workers who must wear gloves, masks, and glasses when handling them. This issue makes common (or two-part) AAMs not user-friendly and problematic for bulk production if no safety procedures are followed. In this paper, the possibility of manufacturing alkali-activated pastes and mortars without alkaline solution is investigated. These innovative one-part AAMs have been prepared with metakaolin as the aluminosilicate precursor, potassium-rich biomass ash as the alkaline activator, and water. AAMs have been prepared by varying the K/Al molar ratio: pastes have been studied in terms of reaction kinetics, through isothermal calorimetry, and mortars have been tested in terms of mechanical compressive strength. Results show that the K/Al molar ratio governs both the reaction kinetics and the mechanical strength of these innovative materials. The highest compressive strength is obtained when the K/Al ratio is equal to 2.5 and the water/solid ratio is equal to 0.49. If biomass ash is heated at 700 °C to decompose the calcium carbonate, its reactivity and the final compressive strength increase.
Highlights
Conventional alkali-activated materials (AAMs) can be referred to as “two-part” AAMs.If AAMs are prepared with aluminosilicates with a SiO2 + Al2 O3 content higher than 80 wt.% and a lowCaO content, such as class F fly ash and metakaolin, they belong to the sub-class of geopolymers [1].AAMs are synthesized by activation of a powdered aluminosilicate precursor and a highly alkaline activator
The aim of this paper was to produce one-part alkali-activated pastes and mortars manufactured by adding only water to metakaolin and biomass ash coming from Europe, in order to see if the results obtained by Balo et al [25] can be reproduced by using different raw materials
The possibility of manufacturing one-part alkali-activated pastes and mortars using metakaolin as the aluminosilicate precursor and potassium-rich biomass ash obtained by the combustion of wood as the powdered alkaline activator was investigated
Summary
Conventional alkali-activated materials (AAMs) can be referred to as “two-part” AAMs.If AAMs are prepared with aluminosilicates with a SiO2 + Al2 O3 content higher than 80 wt.% and a lowCaO content, such as class F fly ash and metakaolin, they belong to the sub-class of geopolymers [1].AAMs are synthesized by activation of a powdered aluminosilicate precursor (e.g., metakaolin, fly ash, and blast furnace slag) and a highly alkaline activator. Nax SiO(2+x/2) with x usually between two and four) are categorized as corrosive and must be handled with gloves, masks, and glasses. This issue, together with the formation of a sticky and thick paste, make them not user-friendly and problematic for bulk production if no safety procedures are followed. During the last 20 years, researchers have tried to obtain a novel type of AAM that can be prepared without using dangerous alkaline solutions. They started to refer to them as one-part or “just add water” AAMs (or geopolymers), to mimic the preparation of common Portland cement-based materials
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