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Moisture diffusion in cementitious materials Moisture capacity and diffusivity

✍ Scribed by Yunping Xi; Zdenňek P. Bažant; Larissa Molina; Hamlin M. Jennings

Publisher
Elsevier Science
Year
1994
Tongue
English
Weight
745 KB
Volume
1
Category
Article
ISSN
1065-7355

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✦ Synopsis

Based on a model by Ba~ant and Najjar, and using a new model for adsorption isotherms, moisture capacity and diffusivity of concrete are analyzed. The moisture capacity, obtained as a derivative of the adsorption isotherm, first drops as the humidity increases from zero, then levels off as a constant, and finally again increases when the humidity approaches saturation, regardless of the age, cement type, temperature, and water:cement ratio. The well-known diffusion mechanisms, including the ordinary diffusion, Knudsen diffusion, and surface diffusion, are analyzed and the diffusion in concrete is treated as a combination of these mechanisms. An improved formula for the dependence of diffusivity on pore humidity is proposed. The improved model for moisture diffusion is found to give satisfactory diffusion profiles and long-term drying predictions. The model is suited for incorporation into finite element programs for shrinkage and creep effects in concrete structures. ADVANCED CEMENT BASED MATEmALS 1994, 1, 258--266

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