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

Hydration study of ordinary portland cement in the presence of zinc ions

Hydration products of Portland cement pastes, hydrated in water and in the presence of zinc ions were studied comparatively at different ages. Hydration products were studied by X ray diffractions (XRD) and infrared spectroscopy (IR). Although IR is not frequently used in cement chemistry, it evidenced a new phase Ca(Zn(OH)3)2. 2H2O formed during cement hydration in the presence of zinc. The significant retardation of early cement hydration in the presence of zinc is assessed in detail by differential calorimetry as a complement to the study carried out by IR and XRD, providing evidence that permits to evaluate the kinetic of the early hydration