Ambient-pressed alkali-activated blocks: Influence of production parameters

Alkali-activated materials (AAMs) have emerged as a sustainable alternative to traditional binders due to their lower carbon footprint and ability to utilize industrial by-products or wastes as precursors. While direct casting method is commonly employed, mould pressing method has gained significant interest as it enables rapid production. In this study, alkali-activated blocks were produced via the mould pressing method under ambient conditions and are referred to as ambient-pressed alkali-activated blocks (AAABs). Ground granulated blast-furnace slag (GGBS) was used as the precursor, and sodium silicate solution (SSS) as the sole alkali activator. The influence of various production parameters, including SSS concentrations (35% and 40%), liquid-to-solid ratios (0.15–0.35), and moulding pressures (10 and 20 MPa), on the properties and microstructure of AAABs was investigated. The results reveal that higher SSS concentration intensified the reaction between GGBS and SSS, resulting in a higher degree of polymerization. Consequently, this enhanced the compressive strength and bulk density of AAABs, while reducing water absorption and porosity. Additionally, AAABs prepared at a moulding pressure of 10 MPa achieved 79.2%–82.6% and 87.0%–96.7% of the 1-day and 28-day compressive strengths of those prepared at 20 MPa, indicating increasing moulding pressure beyond 10 MPa provides only marginal benefits. Moreover, excessive pressure may cause slurry overflow during moulding. Accordingly, the optimal production parameters for AAABs were identified, with the combination of 40% SSS concentration, liquid-to-solid ratio of 0.35 and moulding pressure of 10 MPa, yielding the highest compressive strength (54.7 MPa).