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This study investigates the nucleation mechanism of slag alkali activation at different solid-to-liquid ratios, focusing on kinetics, including growth rates. Heat evolution during activation was monitored, and calorimetric data were analyzed using the Johnson–Mehl–Avrami–Kolmogorov model. Compressive strength and phase evolution (via wide-angle X-ray scattering) were correlated with heat evolution to enhance understanding of reaction mechanisms in alkali-activated material formation. This is essential for producing alkali-activated slag that meets standard requirements for construction applications. Results showed that the highest heat evolved (–360.60 J/g) did not correlate with the best strength performance (22.69 MPa at 1 day and 25.83 MPa at 3 days), since the lowest cumulative heat (–226.15 J/g) at an S/L ratio of 1.4 yielded the best strength. This was supported by the highest growth rate (0.1172 min–1) at this ratio. JMAK analysis indicated instantaneous nucleation with one-dimensional rod-like growth, driven by increased nucleation site availability. From the results obtained, it can be concluded that an increment in S/L ratio significantly increased nucleation and polymerization of alkali-activated slag, thereby hindering heat flow, as evidenced by the lowest total cumulative heat evolved. In addition, the highest growth rate observed corresponded linearly with the compressive strength, further confirming densification by polymeric gels formed during alkali activation.

The combined effect of calcium hydroxide (CH) and heat treatment on mechanical and morphological performances of geopolymer remains underexplored, presenting a critical gap in heat-resistance geopolymer research. This paper investigates the effect of CH (0, 2, and 4 wt.%) and elevated temperatures (200–1000°C) on the mechanical and morphological properties of fly ash (FA) geopolymers. The addition of 2 wt.% of CH enhanced compressive strength (35.8 MPa), attributed to coexistence of N-A-S-H and C-S-H, which enhanced structural interlocking and reinforced the compactness. At 200°C, FA geopolymers developed a robust structure due to further geopolymerization; however, structural deterioration occurred at 800–1000°C due to the melting of geopolymer gels and further phase transformation. This study provides guidelines for synthesizing sustainable and thermally resistant construction binders, particularly for applications in industrial flooring and thermal insulation structural walls.

Lightweight aggregate concrete (LWAC), produced by partially or fully replacing conventional dense aggregates with lightweight alternatives, is increasingly used in structural and building applications. Lightweight Expanded Clay Aggregate, or LECA, is a common kind of lightweight aggregate. However, due to its inherent disadvantages that include high water absorption caused by its porous structure, low mechanical strength, and high brittleness, its use in structural concrete is limited. Surface treatment of LECA has emerged as a promising strategy to improve its mechanical performance and durability, in order to overcome these limitations. Coating LECA with geopolymer-based materials made from solid waste and industrial waste that is high in aluminosilicates. These geopolymer systems can penetrate and seal the surface pores of LECA when activated by alkaline solutions to create a durable protective barrier that improves the structural integrity of the aggregate. Thus, this paper reviews the key parameters influencing the geopolymerization process including the composition and nature of the raw material, alkaline activator molarity, solid-to-liquid ratio, and curing conditions. In order to formulate long-lasting, high-strength geopolymer coatings for LECA and, subsequently, expand the use of the material in load-bearing and green structures, a comprehensive understanding of these factors is essential.