Abstract

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 CaC<inf>2</inf> residue as calcium source. The product was compared with that from CaCO<inf>3</inf>. 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-C<inf>2</inf>S at lower firing temperatures; however, at higher temperatures, less-desirable γ-polymorphs are formed. Nano-silica extracted from POFA contains Na<inf>2</inf>O, Al<inf>2</inf>O<inf>3</inf>, and K<inf>2</inf>O 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 CaC<inf>2</inf> residue.