Investigation of properties of fluorogypsum-slag composite binders – Hydration, strength and microstructure

A composite binder of high strength and low water absorption has been developed using industrial by-products fluorogypsum, granulated blast furnace slag and Portland cement. The development of strength in the binder at an early age is attributed to the conversion of anhydrite into gypsum and at later age is due to the formation of ettringite and tobermorite, as a reaction of slag with lime produced during the hydration of cement. These cementitious phases fill in pores and voids of the hydrating gypsum crystals to form a dense and compact structure of low porosity and low pore volume. The reaction products formed during the hydration period were confirmed by scanning electron microscopy and X-ray diffraction. The reduction in porosity and low pore volume of binders, as studied by mercury intrusion porosimetry, are responsible for attainment of high strength and better stability towards water in composite binders than the conventional gypsum plaster.