Synthetic calcium aluminosilicate monolith: III. The nature of binder and high-temperature behavior

Abstract

We have studied the physicochemical properites of the SCAS monolith that was manufactured from fly ash (a large-tonnage waste of coal dust combustion at power plants), lime, and sand in a three-stage process comprising the stages of filtration combustion with superadiabatic heating, fine milling, and pressing, and then hardened in natural (laboratory) settings for 7 years. From the inspection of IR spectra together with the results of energy dispersive X-ray microanalysis, we discovered that calcium serpentine (Ca,Fe,Mg)3[(Si,Al)2O5](OH,H2O)4 was formed in the SCAS monolith during 7-year natural hydration/carbonization, this serpentine acting as a binder in the dispersion-hardened polymineral body. This inference matches the results obtained by X-ray powder diffraction. Differential scanning calorimetry/thermogravimetry (DSC/TGA) with simultaneous recording of the mass spectra of the products has been used to study dehydration, dehydroxylation, decarbonization, and recrystallization occurring in the SCAS monolith between 35 and 1000°C. We have demonstrated that the calcium carbonate polymorphs contained in the monolith have a reduced thermal destruction temperature. The tetrahedral calcium serpentine layer has not been destroyed as a result of heating to 1000°C.