Physicochemical characterization of synthesized Calcium-Aluminium-Silicate-Hydrate phase

Similar to Calcium-Silicate-Hydrate (C-S-H) in ordinary portland cement, which has been thor-oughly studied, Calcium-Aluminium-Silicate-Hydrate, commonly referred to as C-A-S-H, consti-tutes the principal amorphous/nano crystaline phase in blended cements such as CEM II, III and IV. It features a layered structure composed of silicon tetrahydrate chains, with aluminum subti-tuting some silicon tetrahydrate units, intercalated between water-rich layers, abundant in calcium. The synthesis of pure C-S-H/C-A-S-H from pristine precursors is pivotal for studying its charac-teristics and behaviors. This study employs Mili-Q water, analytical grade calcium hydroxide, silica fume and aluminium nitrate hydrate as precursors to synthesize pure C-A-S-H phases with varied Ca:Si and Al:Si ratios, and C-S-H phase in the same manner for comparison. Kinetic tests determine reaction times, while ATR-IR, SEM/EDX, TGA, BET and ICP/OES techniques elucidate the structures and characteristic of C-S-H/C-A-S-H. Results indicate effective synthesis of C-A-S-H within 25 days, at 90oC, a more demanding process compared to C-S-H. Furthermore, incorpo-ration of calcium in the presence of aluminium proves more challenging, lead to a significantly lower Ca/(Si+Al) ratio in C-A-S-H compared to Ca/Si ratio in C-S-H synthesized from equivalent ratios of precursors. These findings provide valuable insights for investigating the degradation and sorption behavior of C-A-S-H with respect to radionuclides in subsequent studies.