Influence of Silicate Structure on the Low Temperature Synthesis of Belite Cement from Different Siliceous Raw Materials

Abstract

This paper studies the low temperature synthesis of β-C 2 S from mixture of lime, BaCl 2 and siliceous raw material (white sand, metakaolin and dealuminated kaolin) with the ratio (Ca + Ba)/Si = 2. The Mixtures were hydrothermally treated in stainless steel capsule at 180 ° C for 5 hours and calcined at 750°C for 3 hours. Raw materials, hydrothermally treated and calcined mixtures were analyzed by FTIR, XRD, TGA/DTA and SEM techniques. The reactivity siliceous raw materials towards lime under hydrothermal treatment increase in the following order: sand, metakaolin, dealuminated kaolin. Because sand composes of quartz crystals, metakaolin composes of amorphous metakaolin structure while dealuminated kaolin composes from enriched amorphous silicate. Calcium aluminate and aluminosilicate hydrate were observed in case of metakaolin which contains appreciable amount of Al 2 O 3 . Dicalcium silicate crystallizes into β-C 2 S in the temperature range 590 ° C - 760 ° C. Finally, β-C 2 S transforms to α’-C 2 S in the temperature range 790 ° C - 860 ° C. There is no sign for the formation of γ-C 2 S. This proves that Ba 2+ ions stabilized β-C 2 S and retards its transformation to γ-C 2 S because Ba 2+ ions replace some of calcium atoms in the structure of β-C 2 S.