Strength and Microstructure Characteristics of Blended Fly Ash and Ground Granulated Blast Furnace Slag Geopolymer Mortars with Na and K Silicate Solution

Abstract

Mineral geopolymer binders can be an attractive and more sustainable alternative to traditional Portland cement materials for special applications. In geopolymer technology the precursor is a source of silicon and aluminium oxides, the second component is an alkaline solution. In the synthesis of geopolymer binders the most commonly used alkaline solution is a mixture of sodium or potassium water glass with sodium or potassium hydroxide or silicate solution with a low molar ratio, which is more convenient and much safer in use. In this paper, we present the influence of sodium or potassium silicate solution on the physical and mechanical properties of fly ash and ground granulated blast furnace slag-based geopolymer mortars. Mercury intrusion porosimetry and microstructural observation allowed for comparing the structure of materials with a different type of alkaline solution. The evolution of compressive and flexural tensile strength with time determined for composites using 10%, 30% and 50% slag contents (referring to fly ash mass) was analysed. The tests were performed after 3, 7, 14 and 28 days. It was observed that, as the amount of slag used increases in the precursor, the strength of the material grows. Mortars with the sodium alkaline solution were characterised by a higher strength at a young age. However, the values of strength 28 days were higher for geopolymers with potassium alkaline solution reaching 75 MPa in compression. Geopolymer mortar microstructure observation indicates a high matrix heterogeneity with numerous microcracks. Matrix defects may be caused by the rapid kinetics of the material binding reaction or shrinkage associated with the drying of the material.

Development, characterization, and performance analysis of shape‐stabilized phase change material included‐geopolymer for passive thermal management of buildings

“…Figure 11B shows EDX‐based chemical analysis of the GPC without SSPCM. The composition indicated presence of the same elements as FA, in different content, and the phases characteristics of FA 48,49 . Otherwise, an increase in silica and sodium content can be observed because sodium silicate and sodium hydroxide were used for GP obtaining.…”

“…The composition indicated presence of the same elements as FA, in different content, and the phases characteristics of FA. 48,49 Otherwise, an increase in silica and sodium content can be observed because sodium silicate and sodium hydroxide were used for GP obtaining. The EDXS analyses of GPC-SSPCM show the existence of the principal elements Na, Al, Si, Fe and Ca, and small quantities of Mg and K, which demonstrates the development of CASH gel, core component of FA activation.…”

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“…It was noticed from the laboratory preparation of the 9 geopolymer ratios, before specimens setting the geopolymer samples paste with more KOH than NaOH is more flowable. This may be explained by the larger size and less reactivity of K + ion than Na + ion led to slow polymerization and more compact material after long time (28 days), resulting in geopolymer with higher compressive strength [12], while the smaller Na + ion leads to higher geopolymer strength at early time (7 days) [21]. After the 0.7K+0.3NaO ratio the amount of compressive strength decreased this may be due to the increasing the amount of KOH related to NaOH.…”

Modifying geopolymer wettability by plasma treatment and high-carbon fly ash

“…When compared to sodium base, using potassium base to prepare compact geopolymer samples lowered the initial contact angle and slightly increased the speed of soaking into the surface, as seen in Figure 8, while using it to prepare foamed geopolymer samples led to more significant foaming and caused the sample surface to be completely hydrophilic, as water soaked in nearly immediately, similarly to cut surface or surface treated with plasma. Geopolymers made using different activators exhibit different properties, including mechanical, thermal and dielectric properties (El Alouani et al, 2020) (Sitarz et al, 2022).…”