Influence of ternesite on the properties of calcium sulfoaluminate cements blended with fly ash

Abstract

Ternesite is a phase found in some calcium sulfoaluminate (CSA) cements and it has recently been shown to have cementitious properties. In this paper, cement combinations based on CSA cement and fly ash were developed and the effect of ternesite on the hydration and properties of the systems was studied. Properties including hydration heat, setting time, mechanical strength, dimensional stability and hydration products were investigated. The results indicated that the presence of ternesite altered the heat flow curves of CSA cements, bringing the reaction peak backward. In the presence of fly ash, the incorporation of ternesite caused a reduction on the setting times. When the water to cement ratio was kept constant, the mortars showed much higher mechanical strengths than those with a fixed water/binder ratio. The mechanical strengths of CSA cement-fly ash blends were improved by the addition of ternesite and the substitution extent of fly ash could be increased. The effect of ternesite was harmless to the volume stability of CSA cement-fly ash combined mortars. The hydration of ternesite promoted the stabilization of ettringite and would not cause delayed ettringite formation.