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Special binders based on Portland cement and methyl cellulose - hydration and properties
Methyl cellulose - a polysaccharide type polymer - retards the hydration of Portland cement, a high polymer content has a strong influence on the hydration. Besides the peaks of usually mineral hydrates of Portland cement, DTA curves show some exothermic peaks that are not attributable to the pure methyl cellulose; this can be the consequence of the polymer chains cross-linking via metal ions to form organomineral compounds. The special binders based on Portland cement and methyl cellulose generally exhibits higher expansions or shrinkage - more important for high MC proportions - on wetting or drying respectively in comparison with the polymer-free samples. Kinetic evaluations for the wet curing samples reveal a process controlled by diffusion. Although the flexural and the compressive strengths decrease with an increase in the methyl cellulose/cement ratio, a complex composite effect explains the flexural strength values over 35 N/mm2; the compressive strength reaches a maximum value of 76.0 N/mm2. The relative humidity exerts on the special binders two overlapping influences: a reversible one to some extent which is of physical nature - the polymer matrix softens and swells, and an irreversible chemical one - the hydration of the Portland cement goes on and the inorganic/methyl cellulose interface weakens.
Special binders based on Portland cement and methyl cellulose - hydration and properties
Methyl cellulose - a polysaccharide type polymer - retards the hydration of Portland cement, a high polymer content has a strong influence on the hydration. Besides the peaks of usually mineral hydrates of Portland cement, DTA curves show some exothermic peaks that are not attributable to the pure methyl cellulose; this can be the consequence of the polymer chains cross-linking via metal ions to form organomineral compounds. The special binders based on Portland cement and methyl cellulose generally exhibits higher expansions or shrinkage - more important for high MC proportions - on wetting or drying respectively in comparison with the polymer-free samples. Kinetic evaluations for the wet curing samples reveal a process controlled by diffusion. Although the flexural and the compressive strengths decrease with an increase in the methyl cellulose/cement ratio, a complex composite effect explains the flexural strength values over 35 N/mm2; the compressive strength reaches a maximum value of 76.0 N/mm2. The relative humidity exerts on the special binders two overlapping influences: a reversible one to some extent which is of physical nature - the polymer matrix softens and swells, and an irreversible chemical one - the hydration of the Portland cement goes on and the inorganic/methyl cellulose interface weakens.
Special binders based on Portland cement and methyl cellulose - hydration and properties
Coarna, M. (author) / Georgescu, M. (author) / Puri, A. (author)
2003
9 Seiten, 6 Bilder, 1 Tabelle, 13 Quellen
Conference paper
English
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