Comparative study on the preparation of belite cement from nano-silicas extracted from different agricultural wastes with calcium carbide residue

Belite cement was prepared using nano-silicas extracted from three different agricultural wastes–black rice husk ash (BRHA), bagasse ash (BA), and palm oil fuel ash (POFA)–which were reacted at 1200 − 1400 °C with CaC2 residue as calcium source. The product was compared with that from CaCO3. Nano-silica extracted from BRHA was of very fine particle size (surface area 312.4 m2/g and V/S ratio 0.35 × 106 cm) and being highly reactive, forms β-C2S at lower firing temperatures; however, at higher temperatures, less-desirable γ-polymorphs are formed. Nano-silica extracted from POFA contains Na2O, Al2O3, and K2O impurities, which stabilize the β and α-forms and delay the transformation to γ-phase. This is reflected in relatively high compressive strength at firing temperature above 1200 °C, compared to other mixtures. Thus, these results indicate that the best combination of these waste materials for the preparation of belite cement phases is POFA ash and CaC2 residue.