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

Ma Tantawy

doi:10.4236/msce.2015.35011

Abstract

This paper studies the low temperature synthesis of β-C2S from mixture of lime, BaCl2 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 Al2O3. Dicalcium silicate crystallizes into β-C2S in the temperature range 590°C - 760°C. Finally, β-C2S transforms to α’-C2S in the temperature range 790°C - 860°C. There is no sign for the formation of γ-C2S. This proves that Ba2+ ions stabilized β-C2S and retards its transformation to γ-C2S because Ba2+ions replace some of calcium atoms in the structure of β-C2S.

Highlights

Dicalcium silicate is the major components of Portland cement as same as tricalcium silicate and determines most of the adhesive properties, strength and durability of Portland cement
The main conclusions of this investigation are: 1) XRF, X-ray diffraction (XRD) and FTIR results of white sand, metakaolin and dealuminated kaolin prove that these siliceous materials have different proportions of SiO2 with different phase composition and crystallinity
2) XRD, FTIR and SEM results of white sand, metakaolin and dealuminated kaolin hydrothermally treated with lime at 180 ̊C for 5 hours prove the formation of dicalcium silicate hydrate

Summary

Introduction

Dicalcium silicate (belite, C2S) is the major components of Portland cement as same as tricalcium silicate (alite, C3S) and determines most of the adhesive properties, strength and durability of Portland cement. (2015) Influence of Silicate Structure on the Low Temperature Synthesis of Belite Cement from Different Siliceous Raw Materials. Belite shows about the same physical and mechanical properties as alite after complete hydration [1]. Β-C2S was prepared from different siliceous raw materials such as silica fume, white sand, rice husk ash, silica, amorphous silica, oil well drilling mud and hydraulic dam sludge under various hydrothermal conditions with lime in presence in stabilizer such as BaCl2 or B2O3 followed by calcination of the product at 650 ̊C - 1000 ̊C [5]-[9]. The aim of this work is to investigate the influence of silicate structure on the preparation of belite cement from different siliceous raw materials hydrothermally treated with lime and calcined at low temperatures

Objectives

Results

Conclusion