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

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)(2)O(5)](OH,H(2)O)(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 1000A degrees 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 1000A degrees C.