Abstract
Alkali-activated materials (AAMs) have gained interest as sustainable alternatives to traditional Portland cement in recent years. However, concerns still exist regarding their durability against harsh environments such as carbonation. This study presents an experimental and thermodynamic investigation into the carbonation behavior of alkali-activated slag-calcined clay (AASCC) prepared with varying activator types (sodium hydroxide, sodium silicate, sodium carbonate), slag replacement levels with calcined clay (0 %, 10 %, 20 %), and alkali concentrations represented by the solid part of activator to base material ratio (SPA/B = 0.05, 0.075, 0.1). Furthermore, Portland cement mixtures were also prepared to compare the results with AASCC mixtures. Compressive strength, capillary water absorption, and accelerated carbonation testing were conducted on paste and concrete mixtures over 28–90 days. Thermodynamic modeling accurately predicted the experimental trends, demonstrating that this is a valuable tool for simulating complex processes in AAMs. Results illustrated that AASCC paste mixtures produced with sodium hydroxide demonstrated the best carbonation resistance due to higher pore solution pH (up to 13.74), sodium and alumino-substituted calcium silicate hydrate (CNASH) gels content, and layered double hydroxide phases (Mg-Al-LDH). Increasing alkali concentration further improved durability against the carbonation process by elevating pore solution pH and CNASH content. However, replacing slag with calcined clay reduced carbonation resistance regardless of activator type, attributed to lower pore solution pH, CNASH, and Mg-Al-LDH, although higher alkali concentrations alleviated this impact. In general, the study elucidates key chemical and physical factors regarding the carbonation of these novel materials by utilizing comparative experimental investigation and thermodynamic modeling.
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