Materiales de Construcción, Vol 47, No 246 (1997)

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


https://doi.org/10.3989/mc.1997.v47.i246.505

A. Fernández-Jiménez
Instituto de Ciencias de la Construcción Eduardo Torroja (CSIC), Spain

F. Puertas
Instituto de Ciencias de la Construcción Eduardo Torroja (CSIC), Spain

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/t0,5]. The activation energy obtained for that process is of approximately 50-58 Kj/mol.

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