SO 3 -Rich Portland Cements: Synthesis and Strength Development
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S03-RICH PORTLAND CEMENTS: SYNTHESIS AND STRENGTH DEVELOPMENT ABDUL-MAULA, S. and ODLER, I. Technical University Clausthal, Zehntnerstraie 2A, D-3392 Clausthal-Zellerfeld, Federal Republic of Germany
ABSTRACT Up to 8 per cent of S03 may be incorporated into the crystalline lattice of CzS if burned in the presence of CaSO4. C3S may be formed only iD the presence of F-. Under these conditions up to 5 per cent of S03 may be incorporated. In the presence of CaSO4 and CaF2 in the raw meal portland clinkers may be formed that contain simultaneously the phases C3S and C4A3S. Clinkers of this kind yield cements with favorable strength properties at "optimum gypsum" additions. INTRODUCTION In recent years several new kinds of high-S03 cements were developed (1-11). In all of them the S03 content in clinker exceeds significantly the amounts common in ordinary portland cement. All of these cements contain the phase 4CaO.3A1203.S03 (abbr. C4A3S) in which the greatest part of the present S03 is bound. At the same time none of them contains tricalcium silicate (abbr. C3S). The absence of C3S in such clinkers may be explained by the low burning temperature employed, i.e. below 1250 'C, which is not sufficient for the formation of this phase. On the other hand this temperature must not be exceeded in the burning process to preserve the formed C4A3S, that becomes unstable at higher temperatures. There were published also data, indicating an incompatibility of these two phases (12). In our work we studied the possibility to produce cements that contain both C3S and C4A3S in their clinker, as we expected that such cements may resemble ordinary portland cement closer and yield better strength properties than cements lacking tricalcium silicate among their constituent. Based on our previous work on the system CaO-Si02-CaFZ (13) we chose to use raw meals with added CaF2 to extend downwards the temperature range at which C3S may be formed and to improve the stability of this phase. The present work was performed on raw meals made out of pure chemicals and thus containing - in addition to S03 and F - only the four main clinker oxides i.e. CaO, Si02, A1203 and Fe203. In addition to cement clinkers, the possibility to synthesize S03-doped dicalcium and tricalcium silicates was also studied. The aim of this latter work was to determine whether these phases may be formed in the presence of S03 (and F) at all and if yes, to find the maximum amount of S03 that may be accomodated into their crystalline lattices.
Met. Res. Soc. Symp. Proc. Vol. 245. 01992 Materials Research Society
316
RESULTS S03-doped dicalcium and tricalcium silicate To determine the amount of S03 that may be incorporated into the crystalline lattice of dicalcium silicate, raw meals with compositions corresponding to this phase, with increasing for one hour at 900 were burned first amount of added CaSO4, "C, then recompacted and burned again for another hour at temperatures between 1100 and 1250 *C. Under these conditions the loss of S03 from the system was negligable. At
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