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    EVALUATION OF THE SURFACTANT LEACHING FROM ALKALI-ACTIVATED SLAG-BASED COMPOSITES USING SURFACE-TENSION MEASUREMENTS

    Year: 2019

    Journal: Mater. Tehnol., Volume 53, page 33–38

    Authors: Bilek, Vlastimil, Jr.; Kalina, Lukas; Bartonickova, Eva; Porizka, Jaromir

    Organizations: National Program for Sustainability I (Ministry of Education, Youth and Sports) [REG LO1211]; Czech science foundationGrant Agency of the Czech Republic [GA17-03670S]

    Keywords: Alkali-activated slag; polyethylene glycol; leaching; surface tension

    Nowadays, there are many efforts to reduce CO2 emissions in the building industry, particularly through the use of some alternative binders to those based on Portland cement. One promising group of such binders includes binders based on alkali-activated slag (AAS). However, extensive drying, autogenous shrinkage and the associated cracking prevent AAS from being widely utilized in practice. A possible solution could be the application of shrinkage-reducing admixtures, whose molecules present in the pore solution reduce its surface tension and thus mitigate the AAS shrinkage. However, if AAS comes into contact with water, shrinkage-reducing admixtures can be leached and its effectiveness reduced. This work tries to evaluate the amount of surfactant leached from the AAS-based mortars using a very simple surface-tension (ST) measuring technique. Mortars based on AAS with and without 2 % of PEG varying in molecular weight (MW) were prepared. Waterglass with a SiO2-to-Na2O ratio equal to 2.0 was used at a dose corresponding to 8 % Na2O with respect to the slag weight. Mortar specimens were prepared and sealed for 24 h. 3 d and 7 d. Then they were demolded and immersed in demineralized water, whose ST was monitored over time. During the early stages (from minutes to a few hours) the ST dropped rapidly, while it remained approximately constant after a few days, which indicates that organic molecules are leached from the AAS specimens very quickly. It was observed that a relatively small fraction of PEGs can be leached out, which indicates that organic molecules are rather bound in the matrix, unable to reduce the ST of the pore solution.
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