Effect of waste glass incorporation on the properties of geopolymers formulated with low purity metakaolin

Given the worldwide abundant resources of low purity kaolin and urban waste glass, their use to produce alkali activated cements seem to be a promising area in the search for alternative sustainable cements with environmental advantages over Portland cement. Under this perspective, the properties of silicate activated low purity metakaolin (MK) and flat soda lime silicate waste glass (WG) at MK/WG mass ratios of 100/0, 85/15 and 70/30 were investigated. The chemical composition of the pastes was varied in terms of modulus (Ms = 0.8-1.2) SiO2/Na2O of the activating solution with additions of 12 and 16 wt% Na2O. Cubic samples dry cured at 20 degrees C were used to follow the compressive strength from 1 to 90 days, which reached from 17 to 56 MPa; the highest values were attained by samples activated with Ms = 0.8-1 and 12%Na2O. The products of the reactions were evaluated by X-ray diffraction, infrared spectroscopy, scanning electronic microscopy and nuclear magnetic resonance. The microstructures included unreacted MK, WG and N-A-S-H, while the incorporation of WG favored the formation of a more complex reaction product similar to a (N,C)-A-S-H type gel.