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Title: Novel Perspective to Explain the Retarding Effect of Organic Admixtures in Silicate-Activated Slag

Author(s): Vlastimil Bílek Jr., Martin Kadlec, Radoslav Novotný, Lukáš Kalina, Petr Hrubý

Publication: Symposium Paper

Volume: 354


Appears on pages(s): 49-60

Keywords: alkali-activated slag, hexylene glycol, ethanol, organic admixtures, glycol, silicates, gelation, calorimetry, rheology

DOI: 10.14359/51736061

Date: 7/1/2022

One of the issues of alkali-activated materials is their incompatibility with conventional organic admixtures, which means that they do not improve their properties as expected on the basis of their role in the Portland cement-based system or even have adverse effects. This is also true for hexylene glycol, on which the commercial shrinkage-reducing admixture is based. In previous studies, we observed that it can reduce the drying shrinkage of alkali-activated slag (AAS), but the main reason was its adverse effect on the hydration of AAS since the early ages and related coarse pore structure. In the present study, calorimetric studies showed that a great effect of hexylene glycol and some other alcohols is especially pronounced for a high silicate modulus (around two). This was confirmed by gelation experiments, in which the activating solution was mixed with calcium hydroxide, and organic additives were used. These tests revealed that the acceleration of gelation of silicates occurs for the same admixtures as the retardation of hydration and follows the same trend. A similar effect was observed for the gelation of silicate sol by NaCl solution, showing that the destabilization of silicates by organic additives is at the origin of the affected hydration of silicate-activated slag.