Alkali-Activated Materials and Slag-Based Geopolymers: A Review on Multi-Scale Performance and Regional Optimization of El Hadjar Slag

Abstract

Ground granulated blast-furnace slag (GGBS) requires activation due to its latent hydraulicity. The scientific literature categorizes this into binary systems and pure alkali-activated slag (AAS). In binary systems, clinker hydration releases portlandite, elevating the pH to trigger slag reaction. This improves long-term durability and sulfate resistance but leads to slow early strength development. Conversely, AAS completely eliminates Portland cement by using strong alkaline activators like NaOH or sodium silicate. This process forms a dense calcium aluminosilicate hydrate (C-A-S-H) gel, yielding exceptional early-age strength, although it faces challenges such as rapid setting and high drying shrinkage. Locally, Algerian academic research focuses on optimizing El Hadjar slag. Due to its low initial reactivity, regional studies emphasize combining fine grinding (mechanical activation), precise chemical activator dosages, and thermal curing cycles to successfully valorize this industrial by-product into high-performance, eco-friendly cementitious materials.