Technical Paper #27
published January 2020: DOI: 10.13140/RG.2.2.25792.89608/2
Ferro-sialate Geopolymers (-Fe-O-Si-O-Al-O-)
Joseph Davidovits and Ralph Davidovits
The implementation in the mass production of geopolymeric cements in the world can no longer be based on coal-fly ashes for different reasons. In addition, Global Warming concerns will inevitably stop the manufacture of this ultimate waste of coal burning, fly ash. Rock-based geopolymer cements are the solution. Yet, it cannot be limited to the geological resources based only on white kaolinitic clays, or on residual eroded granite rocks, low in iron content, as promoted until now. The use of the enormous geological layers that constitute the ferralitic or lateritic rocks and soils is a need. Rock-based geopolymeric binder or cement of the type (Ca,Na,K)-poly (ferro-silico-aluminate) (Fe-O-Si-O-Al-O-) are geopolymeric compounds in which part of the Al atoms is substituted by Fe atoms, with the approximate formula
with “x” is a value higher than 0 and lower or equal to 0.5, “y” ranging between 0 and 25. This rock-based geopolymeric binder or cement is the result of the geopolymerization of geological elements rich in iron oxides and ferro-kaolinite, produced by the weathering of acidic rocks such as granite or gneiss, or of basic rocks (mafic) like basalt and gabbro. The manufacturing process of this geopolymeric binder or cement consists in treating the geological elements at a temperature of 600°C to 850°C. During this heat treatment, all iron oxides (goethite FeO(OH) + Fe3O4 magnetite) are transformed into hematite Fe2O3 and ferro-kaolinite changes into ferro-metakaolin of type Fe-MK-750. Ca-geopolymerization in alkaline milieu involves GGBS. Hardening at room temperature provides compressive strength in the range of 75-90 MPa at 28 days.
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