Eine Plattform für die Wissenschaft: Bauingenieurwesen, Architektur und Urbanistik
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Synthesis and characterisation of geopolymers - chemical stability in water
Geopolymer bulky materials are obtained by reacting sodium or potassium hydroxide and sodium silicate with thermally activated kaolinite. Under ambient conditions, materials exhibit a rapid setting and hardening which leads to interesting mechanical properties. Mechanical properties (crushing strength) are better for B(K) materials (approx. 40 MPa) than for A(Na) ones (approx. 30 MPa). But for the B(K) material, the dispersion is high which indicates that their homogeneity must be optimised. When geopolymer materials are in contact with a high quantity of water, they dissolve and the pH increases promoting further dissolution. Probably due to a very small pore size which inhibits water diffusion, geopolymer can not fully dry under ambient condition. Heating of bulky materials leads to increase the water pressure in the pores. This effect helps to fully dry the materials, but is also associated to stresses which can induce damages such as cracking. Previous drying of materials leads to the decrease their solubility in water. This is probably due to the disappearance of silanol groups and increase of more stable Si-O-Si- covalent bondings. Drying leads also to a large shrinkage which decreases the surface area and also contributes to the stabilisation by decreasing the surface in contact with water. Treatment at high temperature (above 600 deg C) leads also to a shrinkage associated to the sintering. This phenomenon also contributes to the reduction of the surface area and to the chemical stabilisation. When geopolymers are used as cementitious phase, it is necessary to take into account the chemical and physical interactions with the bonded aggregates and the structure of the composite material.
Synthesis and characterisation of geopolymers - chemical stability in water
Geopolymer bulky materials are obtained by reacting sodium or potassium hydroxide and sodium silicate with thermally activated kaolinite. Under ambient conditions, materials exhibit a rapid setting and hardening which leads to interesting mechanical properties. Mechanical properties (crushing strength) are better for B(K) materials (approx. 40 MPa) than for A(Na) ones (approx. 30 MPa). But for the B(K) material, the dispersion is high which indicates that their homogeneity must be optimised. When geopolymer materials are in contact with a high quantity of water, they dissolve and the pH increases promoting further dissolution. Probably due to a very small pore size which inhibits water diffusion, geopolymer can not fully dry under ambient condition. Heating of bulky materials leads to increase the water pressure in the pores. This effect helps to fully dry the materials, but is also associated to stresses which can induce damages such as cracking. Previous drying of materials leads to the decrease their solubility in water. This is probably due to the disappearance of silanol groups and increase of more stable Si-O-Si- covalent bondings. Drying leads also to a large shrinkage which decreases the surface area and also contributes to the stabilisation by decreasing the surface in contact with water. Treatment at high temperature (above 600 deg C) leads also to a shrinkage associated to the sintering. This phenomenon also contributes to the reduction of the surface area and to the chemical stabilisation. When geopolymers are used as cementitious phase, it is necessary to take into account the chemical and physical interactions with the bonded aggregates and the structure of the composite material.
Synthesis and characterisation of geopolymers - chemical stability in water
Synthese und Charakterisierung von Geopolymeren - chemische Stabilität in Wasser
Pilate, P. (Autor:in) / Tirlocq, J. (Autor:in) / Cambier, F. (Autor:in) / Descamps, P. (Autor:in) / Cinar, E. (Autor:in) / Lucion, C. (Autor:in)
2009
7 Seiten, 14 Bilder, 2 Tabellen, 23 Quellen
Aufsatz (Konferenz)
Datenträger
Englisch
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