Investigations on mix design of tungsten mine waste geopolymeric binder

Strength data show that the parameters, which lead to optimum strength for 7 days curing, remain the same for long curing ages. However, when calcium hydroxide percentages above 10% are used, strength decrease after 14th curing day is noticed. In order to explain this behaviour several hypotheses are discussed. The use of an activator with a sodium hydroxide concentration of 24 M leads to a compressive strength of almost 70 MPa. The strength performance is typical of a very reactive binder, being suggested that it is due to the calcium hydroxide and also to the nucleation centers provided by the iron oxide of the mine waste mud. Results allow foreseeing that even higher strength performance could be achieved if lower water/sodium molar ratios were used.