Studies on the Reactions between CaSO<sub>3</sub>⋅1/2H<sub>2</sub>O and 3CaO⋅Al<sub>2</sub>O<sub>3</sub>, 4CaO⋅Al<sub>2</sub>O<sub>3</sub>⋅Fe<sub>2</sub>O<sub>3</sub> and

Abstract

The authors have tried to use calcium sulphite-a low price byproduct of sulphulic acid industry-as substitution of gypsum for portland cement. The substitution resulted in an increase in strength and decrease in the construction of the cement.In the present paper the investigation of the reaction mechanism between cement clinker and calcium sulphite was carried out using X-ray diffraction, differential thermal analysis and measurement of heat of formation. The results obtained may be summarized as follows:(1) In the existence of free lime tricalcium alminate hydrated rapidly to form 4CaO⋅Al2O3⋅13H2O, 3CaO⋅Al2O3⋅8-12H2O as well as 3CaO⋅Al2O3⋅6H2O and after ten weeks the formation of 3CaO⋅Al2O3⋅8-12H2O remarkably increased. When free lime was added jointly with gypsum 3CaO⋅Al2O3 hydrated to form gypsum bacillus, 3CaO⋅Al2O3⋅CaSO4⋅31H2O, and 4CaO⋅Al2O3⋅13H2O at the first stage, and then decrease of gypsum bacillus and increase of 4CaO⋅Al2O3⋅13H2O followed. The addition of CaSO3⋅1/2H2O and lime resulted in the formation of calcium sulphoaluminate bacillus, 3CaO⋅Al2O3⋅CaSO3⋅7H2O, and 4CaO⋅Al2O3⋅13H2O.(2) The calcium sulphoaluminate bacillus was formed by the reaction of 1mol CaSO3⋅1/2H2O with 1mol 3 CaO⋅Al2O3 at 110°C in the atmosphere containing saturated steam, but it decomposed at 140°C.(3) The values 45.7, 7.15 and 1.34kcal/mol were given for the heat of formation of 3CaO⋅Al2O3⋅6H2O, 3CaO⋅Al2O3⋅CaSO3⋅7H2O and gypsum bacillus respectively.(4) In the hydration of synthetic 4CaO⋅Al2O3⋅Fe2O3 we found the same hydrated compounds as the case of 3CaO⋅Al2O3.