Characteristics of cement pastes containing sulphoaluminate and belite prepared from nano-materials: Fid-Bau Portal

Characteristics of cement pastes containing sulphoaluminate and belite prepared from nano-materials

El-Didamony, H. / Heikal, Mohamed / Khalil, Kh.A.

Highlights ► Substitution of OPC with $C_{4} A_{3} \bar{S}$ or $C_{4} A \bar{S}$ + β-C2S tends to shorten the setting times. ► The fast setting of cement pastes is due to the formation of Aft and AFm. ► Substitution of OPC with $C_{4} A_{3} \bar{S}$ or $C_{4} A \bar{S}$ increases the chemically combined water. ► The addition of $C_{4} A_{3} \bar{S}$ or $C_{4} A \bar{S}$ with belite decreases the free portlandite. ► Pastes containing $C_{4} A_{3} \bar{S}$ or $C_{4} A \bar{S}$ give higher compressive strength.

Abstract The sulphoaluminate phase $C_{4} A_{3} \bar{S}$ as well as β-C2S represent an important factor for the preparation of rapid hardened sulphoaluminate–belite cement. The hydration of $C_{4} A_{3} \bar{S}$ forms ettringite and monosulphate hydrates in addition to the liberation of aluminium hydroxide. The hydration rate of belite is much slower than that of $C_{4} A_{3} \bar{S}$ , but becomes significant at later ages. Two mixes containing sulphoaluminate ( $C_{4} A_{3} \bar{S}$ ) and monosulphate mix ( $C_{4} A_{3} \bar{S}$ , with $8 C \bar{S} + 6 C$ ) in addition to belite (β-C2S) were synthesized from nano-materials after firing at 1250°C. The hydration characteristics of 10% $C_{4} A_{3} \bar{S}$ or 10% $C_{4} A \bar{S}$ in addition to 10% β-C2S on the expanse of OPC were studied. The results revealed that the substitution of OPC with sulphoaluminate mixes as well as belite shortens the setting times. The rate of hydration of OPC with sulphoaluminate–belite phases is increased from the formation of more sulphoaluminate hydrates and the consumption of protlandite. Also, these mixes give higher chemically combined water contents. The monosulphate hydrate is deposited in some of open pores in the dormant period of hydration that tends to increase the compressive strength of sulphoaluminate–belite cement pastes.