Geopolymer binders from metakaolin using sodium waterglass from waste glass and rice husk ash as alternative activators: A comparative study

• Rice husk ash and waste glass were used to prepare sodium waterglass.
• ATR method is a suitable technique to monitor the formation of condensed and uncondensed silica in alkaline solution.
• Sodium waterglass from waste glass is more reactive than that of the one of rice husk ash.
• Metakaolin-based geopolymer binder from waste glass has a higher compressive strength.
• Geopolymer G1 at 56 days and G2 show the formation of highly cross linking network.

Rice husk and waste glass from sources in Cameroon were used for producing sodium waterglass (NWG) solution denoted S1 and S2 respectively as alternative activators to prepare metakaolin-based geopolymer binder. Metakaolin-based geopolymer binders (G1, G2) were obtained using freshly prepared NWG with a mass ratio NWG/MK = 0.83. The IR spectra of S1, S2 using ATR and KBr methods show the presence of SiQ0, SiQ1, SiQ2 units, and S1 contained also SiQ3 and SiQ4 units. The mechanical testing, environmental scanning electron microscopy, mercury intrusion porosimetry, X-ray diffractometry, infrared spectroscopy, amount of binders and thermogravimetric analysis are investigated to study the properties of the geopolymer binders. The results show that the compressive strength values of geopolymer G2 (22.9, 27.6, 32.6, 36 and 39.7 MPa) are higher than that of G1 (17.7, 19.1, 21.2, 29.9 and 32.8 MPa) at 7, 14, 21, 28 and 56 days respectively. The microstructure of G2 is more compact with fewer unreacted metakaolin particles. It can be concluded that sodium waterglass from waste glass and rice husk ash are suitable alternative activators for the production of metakaolin-based geopolymers. In addition, they constitute a better ecological choice when compared to commercial sodium silicate from melting process.