Influence of activator type on hydration kinetics, hydrate assemblage and microstructural development of alkali activated blast-furnace slags |
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Authors: | M Ben Haha G Le Saout F Winnefeld B Lothenbach |
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Affiliation: | aEmpa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Concrete and Construction Chemistry, Ueberlandstrasse 129, 8600 Dübendorf, Switzerland |
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Abstract: | The hydration of two slags with different Al2O3 contents activated with sodium hydroxide and hydrous sodium metasilicate (commonly named water glass) is studied using a multi-method approach. In all systems, C-S-H incorporating aluminium and a hydrotalcite-like phase with Mg/Al ratio ~ 2 are the main hydration products. The C-S-H gels present in NaOH activated pastes are more crystalline and contain less water; a calcium silicate hydrate (C-S-H) and a sodium rich C-N-S-H with a similar Ca content are observed at longer hydration times. The activation using NaOH results in high early strength, but strength at 7 days and longer is lower than for the sodium metasilicate systems. The drastic difference in C-S-H structure leads to a coarser capillary porosity and to lower compressive strength for the NaOH activated than for the sodium metasilicate activated slags at the same degree of slag reaction. |
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Keywords: | Alkali Activated Cement (D) Microstructure (B) Calcium-Silicate-Hydrate (C-S-H) (B) Image Analysis (B) Mechanical Properties (C) |
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