Ceramics-Silikáty 58 (3) 227-236 (2014)

Recycling phosphorus slag as a precursor for alkali-activated binder; Impact of type and dosage of activator

The objectives of this study were to investigate the suitability of phosphorus slag as a precursor for alkali-activated binder by studying the effects of type and dosage of alkaline activators on compressive strength and efflorescence formation of the material. Different alkaline activators including; potassium hydroxide, sodium hydroxide, sodium carbonate, calcium hydroxide, and their combinations with liquid sodium silicate were used. Different levels of total alkali content (1, 3, 5 and 7 % by weight of binder) at different silica moduli (Ms = SiO₂/Na₂O) of 0.5, 1 and 1.5 were considered. The results show that combined activators of higher reactivity and pH values containing a higher number of moles of alkali cations are more effective and 28-days compressive strengths up to 120 MPa can be achieved. Efflorescence, however, is an important issue and it is necessary to compromise between achieving the highest strength and controlling the efflorescence severity. The most suitable mix design exhibiting comparatively a high 28-day compressive strength along with a relatively low efflorescence formation was then characterized by laboratory techniques, including Fourier Transform Infrared Spectroscopy, X-ray diffractometry, and Scanning electron microscopy.

Keywords: Phosphorus slag, Alkali-activation, Compressive strength, Efflorescence