Micromechanical multiscale model for alkali activation of fly ash and metakaolin |
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Authors: | Vít Šmilauer Petr Hlaváček František Škvára Rostislav Šulc Lubomír Kopecký Jiří Němeček |
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Affiliation: | 1.Faculty of Civil Engineering,Czech Technical University in Prague,Prague 6,Czech Republic;2.Department of Glass and Ceramics,Institute of Chemical Technology Prague,Prague,Czech Republic |
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Abstract: | The process of alkali activation of fly ash and metakaolin is examined in the view of micromechanics. Elasticity is predicted
via semi-analytical homogenization methods, using a combination of intrinsic elastic properties obtained from nanoindentation,
evolving volume fractions and percolation theory. A new quantitative model for volume fraction is formulated, distinguishing
the evolution of unreacted aluminosilicate material, solid gel particles of N-A-S-H gel, and open porosity, which is partially
filled with the activator. The stiffening of N-A-S-H gel is modeled by increasing the fraction of solid gel particles. Their
packing density and intrinsic elasticity differ in N-A-S-H gels synthesized from both activated materials. Percolation theory
helps to address the quasi-solid transition at early ages and explains a long setting time and the beneficial effect of thermal
curing. The low ability of N-A-S-H gel to bind water chemically explains the high porosity of Ca-deficient activated materials.
Micromechanical analysis matches well the elastic experimental data during the activation and elucidates important stages
in the formation of the microstructure. |
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