Résumé
Alkali-Activated Materials (AAMs), particularly Ground Granulated Blast Furnace Slag (GGBS)-basedAlkali-Activated Slag (AAS), have emerged as a promising green alternative to cement-based binders dueto their lower carbon footprint and satisfactory mechanical properties at ambient temperatures. Withgrowing global emphasis on carbon neutrality and sustainable infrastructure, the deployment of low-carbonalternatives like AAS in all climate zones is becoming increasingly critical. However, the limited reactivityof AAS at low temperatures (5 to 10°C), especially in early ages, remains a major barrier to its large-scaleapplication in colder regions. These temperature ranges, while not extreme, are very common in Europeand parts of Asia for several months of the year, making this issue particularly relevant for real-worldimplementation. Current solutions involve maintaining ambient temperatures on construction sites usingwarm sheds and electric blankets. These measures, although effective, are costly and energy-intensive,thereby negating the CO₂ reduction benefits of AAS. Recent studies have explored the possibility ofremediating the low early-age strength using calcium salts or silicate-based activators with a high silicatemodulus. These methods, while showing promise, often suffer from delayed setting times, and inadequatecompressive strength development in the 5–10°C range. As a result, they have not yet achieved satisfactoryperformance at early ages under low-temperature conditions. To achieve better results, there is a need todelve deeper into the impact of low temperatures on the fundamental mechanisms of AAS hydration—specifically, the dissolution-precipitation process. A better understanding of this stage is essential fordeveloping targeted solutions to the observed low reactivity. This study aims to investigate the role oftemperature during the dissolution phase of AAS hydration, the precursor to the precipitation reaction anda key determinant of early-age strength. Dissolution experiments (employing NaOH as an alkali activator)were conducted at 5°C, 20°C, and 40°C using a high liquid-to-solid ratio (500) to suppress precipitationand isolate the dissolution behaviour. Two complementary techniques were used to monitor dissolutionkinetics: pore solution conductivity measurements (over a 20-hour period) and continuous ICP-OESanalysis (over 120 minutes). The latter allowed real-time quantification of key ionic species such as Si, Ca,and Al. These solution-phase observations were supported by solid residue analysis using Scanning ElectronMicroscopy (SEM), Thermogravimetric Analysis (TGA), and X-Ray Diffraction (XRD) to detect anysecondary reaction products and unreacted phases. The results clearly show that dissolution is significantlyhindered at 5°C, which likely limits subsequent hydration and strength development. However, this adverseeffect can be mitigated by increasing the fineness of slag. Tests on coarse slag, fine slag (d50 = 10 μm), andultra-fine slag (d50 = 5 μm) revealed that higher specific surface area accelerates dissolution, even undercold conditions. In contrast, coarse slag achieved effective dissolution at elevated temperatures. Thesefindings suggest that optimizing slag fineness presents a practical and less energy-intensive route toimproving AAS performance in cold environments, thus unlocking its full potential in lowering the CO₂emissions of the construction industry. Building on these findings, ongoing research will explore alternativeactivation strategies to further enhance early-age AAS reactivity at low temperatures.