Synthesis of sodium waterglass from white rice husk ash as an activator to produce metakaolin-based geopolymer cements

• Rice husk were applied for producing sodium waterglass with different molar ratios SiO2/Na2O.
• Sodium waterglass from rice husk ash were used to synthesize geopolymer cements.
• The amount of NBO contained in the sodium waterglass influence significantly the properties of geopolymers.
• The compressive strength increase with increasing the molar ratio SiO2/Na2O defined in this work.
• Sodium waterglass from rice husk ash proved to be an effective alkaline activator in geopolymers preparation.

Rice husk from source in Cameroon was leached in HCl (5 M) to remove the most of metallic ingredients and then calcined at 600 °C in order to produce white rice husk ash. This white ash were applied for producing sodium waterglass with different molar ratios SiO2/Na2O (0.31; 0.47; 0.62; 0.78; 0.93; 1.09 and 1.25) and then used to synthesize metakaolin-based geopolymer cements. The obtained white rice husk ash shows the loss of crystalline mineral and reveals high amorphous silica with quartz as impurity. Geopolymers GPi (i varying from 1 to 7) were obtained using different synthesis sodium waterglass (NWG) with a mass ratio NWG/MK=0.87. It could be observed that the 28 days compressive strength (4/5/7/9/32/34/36 MPa) increase with increasing the molar ratios SiO2/Na2O defined in this work in the course GP1/GP2/GP3/GP4/GP5/GP6/GP7. The micrographs show the formation of more geopolymer gels when the molar ratios SiO2/Na2O in alkaline activators are between 0.93 and 1.25. Sodium waterglass from white rice husk ash proved to be an effective alkaline activator in geopolymers preparation. It can be concluded that it is possible to replace quartz sand and sodium carbonate which is responsible to greenhouse gas emitted during the production of commercial sodium silicate solution by using rice husk as silica sources.