METAKAOLIN-BASED GEOPOLYMER CEMENTS FROM COMMERCIAL SODIUM WATERGLASS AND SODIUM WATERGLASS FROM RICE HUSK ASH: A COMPARATIVE STUDY

摘要

Sodium waterglass (NWG) such as commercial NWG (SI), NWG from pure rice husk ash (S2) and NWG from raw rice husk ash (S3) were used for producing geopolymer cements from metakaolin (MK) as aluminosilicate source. Geopolymers (Geol, Geo2, Geo3) were prepared using each NWG with the molar ratios SiO_2/Na_2O and H_2O/Na_2O kept constant at 1.5 and 12 respectively. It could be observed that the water absorption of Geol, Geo2 and Geo3 are 7%, 9% and 13.2% and the mass loss are 15.8%, 14.7% and 12.4% respectively. The compressive strengths (43.3/40.3/33.2 MPa) decrease in the course Geol/Geo2/Geo3. It is discussed that the presence of phosphate known as corrosion inhibitors in raw rice husk ash hinders the dissolution of SiO_2. It entails the formation of NaH_2PO_4 in S3 which reduces the soluble Si atoms suggesting thus sodium waterglass from raw rice husk ash is a less depolymerized solution. Therefore, less amount of metakaolin could be dissolved leaving thus a higher amount of unreacted metakaolin particles in Geo3. The reacted volumes and compositions of the geopolymers are different in the three cases, too. A content of approximately 20%, 25% and 35% of unreacted metakaolin was proven for Geol, Geo2 and Geo3 respectively.