Influence of the activator concentration on the kinetics of the alkaline activation process of a blastfurnace slag

Abstract

The influence of activator solution concentration on hydration kinetics of an alkaline activated blast furnace slag has been studied. The alkaline activator used was a mix of waterglass (Na₂SiO₃∙nH₂O) and NaOH solution (of variable concentration). Final activator concentrations were 3,4 and 5 % Na₂O wt. with respect to the slag total weight. Degree of reaction (α) was determined from hydration heat values obtained through isothermal conduction calorimetry. From the results obtained it is deduced that a treshold value of 4 % Na₂O wt. exists. For those concentrations and at test temperatures (except for 25ºC and 3 % Na₂O wt.), the mechanism controlling hydration reaction for a values higher than 0.5, is a diffusion process. This process is described by .Jander equation [D₃=(1-(1-α)^1/3)²=(k/r²)t=0,0426(t/t_0,5]. The activation energy obtained for that process is of approximately 50-58 Kj/mol.