Development of a new high-performance belite cement

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In the present research, we have obtained the following results(1) Crystallization mechanism of interstitial melts : we have found, for the first time, the occurrence of fractional crystallization in cement clinkers during cooling. This reaction, in principle, determines the chemical compositions of the crystals and melts. In the pseudobinary system Ca2SiO4(C2S)-Ca2AlFeO5, for example, C2S solid solution, Ca2A10.41Fe0.5905, and melt coexisted at temperatures between 1375 and 1635℃. At temperatures above 1375℃, the two phases of C2S(ss) and melt was stable. Accordingly, Ca2Al0.41FeO.5905 crystallize out of the melt, thus the chemical composition of the coexisting melt becomes poor in Fe2O3 component.(2) Zonal structure of calcium aluminoferrite, which records the information on the crystallization process : As the result of the fractional crystallization, the crystals of calcium aluminoferrite showed the zonal structure, the Al/(Al+Fe) values of which seadily increases from the cores toward the rims. Tricalcium aluminate solid solutions eventually crystallize out of the differentiated melt.(3) Cationic substitution of tricalcium aluminates : the chemical formula of the tricalcium aluminate doped with Na, K, Mg, Fe and Si has been developed to be (Na, K)2x(Ca, Mg)3-x-y[(Al, Fe)1-ySiy]206 (0≦x<0.158, 0≦y<0.136).(4) Effect of substituent ions on the stable phases of calcium aluminoferrite and belite : The crystal structure of calcium aluminoferrite was dependent on the Al/(Al+Fe) value (=x). with 0≦x<0.235, space group was Pcmn, while, it was Ibm2 with 0.235≦x<0.7. The starting temperature of the α' -to-βtransformation steadily decreased from 680℃ to below the ambient temperature with increasing concentration of foreign oxides.