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Sulfate interaction with pure calcium silicate hydrates
Sulfate attacks on pure calcium silicate hydrate phases (CSH-gel) with different CaO/SiO2 ratios were investigated. Standard test methods for length change and deterioration in compressive strength of mortars exposed to sodium sulfate solution were performed using mortars composed only of sand, as aggregate, and phase pure CSH-gel with calcium/silica ratios of 1.0 and 1.5. Mortars of Portland cement as well as of tricalcium silicate (C3S) were also investigated for comparison. Mortars bars and cubes were exposed to 5 % sodium sulfate solution at constant pH (7.0 - 7.5). Failure occurs in CSH mortars, mainly as a result of the decalcification of the calcium silicate hydrate, which is controlled by CaO/SiO2 ratio of the binder phase. Mortar with high CaO/SiO2 ratio (1.5) shows expansion due to gypsum formation associated with distraction of CSH phase. Although, mortar with low CaO/SiO2 ratio (1.0) did not show any expansion, its mechanical properties were severely deteriorated and showed softening after 13 weeks of exposure to sulfate solution. This suggested that sulfate ion attacks on CSH-gel is an important factor in strength deterioration, especially in low free lime pozzolanic cements.
Sulfate interaction with pure calcium silicate hydrates
Sulfate attacks on pure calcium silicate hydrate phases (CSH-gel) with different CaO/SiO2 ratios were investigated. Standard test methods for length change and deterioration in compressive strength of mortars exposed to sodium sulfate solution were performed using mortars composed only of sand, as aggregate, and phase pure CSH-gel with calcium/silica ratios of 1.0 and 1.5. Mortars of Portland cement as well as of tricalcium silicate (C3S) were also investigated for comparison. Mortars bars and cubes were exposed to 5 % sodium sulfate solution at constant pH (7.0 - 7.5). Failure occurs in CSH mortars, mainly as a result of the decalcification of the calcium silicate hydrate, which is controlled by CaO/SiO2 ratio of the binder phase. Mortar with high CaO/SiO2 ratio (1.5) shows expansion due to gypsum formation associated with distraction of CSH phase. Although, mortar with low CaO/SiO2 ratio (1.0) did not show any expansion, its mechanical properties were severely deteriorated and showed softening after 13 weeks of exposure to sulfate solution. This suggested that sulfate ion attacks on CSH-gel is an important factor in strength deterioration, especially in low free lime pozzolanic cements.
Sulfate interaction with pure calcium silicate hydrates
Sulfatwechselwirkung mit reinem Calciumsilicathydrat
Mostafa, N.Y. (author) / Omar, H. (author) / Abo-El-Enein, S.A. (author)
Silicates Industriels ; 73 ; 117-123
2008
7 Seiten, 6 Bilder, 2 Tabellen, 35 Quellen
Article (Journal)
English
Sulfatbeständigkeit , CSH (Calciumsilicathydrat) , Beton , Betonmörtel , Meerwasser , Tricalciumsilicat , Portlandzement , Silicafeinststaub , Prüfkörper-Präparation , Natriumsulfat , wässrige Lösung , pH-Wert , Zeitdauer , Längenmessung , Druckfestigkeit , Porosität , freier Kalk , Volumenvergrößerung , Gips , Festigkeitsverlust
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