Special cement Containing C11A7CaF2 Mineral Phase

The necessity for accelerating construction works and applications such as repair of airways and highways have provided a basis for production and use of fast set and high early strength cements. Fast set and high early strength cements, belonging to the group of special inorganic binders, have gained more and more importance in recent decade and industrial production and applications of these cements have been increased in many developed countries. Different types of clinkers are known for fast set cements such as; clinkers rich in C12A7 phase, with mineral phase composition of C2S-C12A7-C3A-C4AF, clinkers containing calcium-aluminumsulfate C4A3S and β-C2S, and clinkers containing fluorinated derivatives of C12A7 with mineral composition of C3S-C11A7CaF2-C2S-C4AF. In this work Clinker of fast set and very high early strength cement containing C11A7CaF2 mineral phase was produced by burning a proportioned raw mix at 1270°C. The produced clinker was mixed with different types of calcium sulfate such as anhydrite or a combination of anhydrite and gypsum at different ratios, and then ground to a Blaine specific surface area between 5000-6000 cm2/g. The amount of additives was adjusted based on weight ratio of Al2O3/SO3 in cement between 0.6-1.8. Setting time and early mechanical behavior of the produced cement were studied. The results showed that with controlling the mineral composition of the clinker and the amount and type of calcium sulfate added, fast set cement with final setting time between 10-21 min and very high 3-day compressive strengths up to 95 MPa can be produced. The 3-day compressive strength obtained is 2.5 times greater than similar results reported in the literature for such a cementitious systems.

Keywords:

fast set , early strength , C11A7CaF2 , setting time , compressive strength