Alkali activation of ground granulated blast furnace slag and low calcium fly ash using "one-part" approach

Abstract

The utilization of the solid powder activator for the activation of the ground granulated blast furnace slag (GGBFS) and its mixtures with low calcium fly ash (FA) was tested. Utilizing the activator in a powder form enabled to obtain ready-to-use dry mixtures, which, after the addition of mixing water, molding, and hydration, created compact solid samples. The selected procedure known as "one-part" or "just-add water" approach is beneficial with respect to the traditional two parts approach based on the utilization of the liquid alkali activators. The experiments were subdivided into two parts. The first part was focused on the selection of the solid alkali activator for GGBFS activation. In this stage, two solid powder activators: (i) sodium metasilicate (NS) and (ii) disodium silicate pentahydrate in amounts that carry 2.5, 5, and 7 wt% of Na2O, were tested. The second part was focused on the verification of the suitability of selected solid alkali silicate for the activation of the mixtures of GGBFS with low calcium FA (80:20 and 60:40). The evolution of the compressive strength of the prepared alkali-activated materials was studied after 2, 7, 28, and 56 days of hydration. The raw materials and hydrated samples were examined by XRFS, XRD, FTIR, and SEM techniques. The positive effect of the thermal treatment at 400 degrees C on the compressive strength of the prepared samples was observed. The obtained results indicate the "one-part" method as suitable for the activation of low calcium fly ash in combination with GGBFS.