- Volume 14 Issue 6
The purpose of the present study is first to refine the mathematical material models for moisture and temperature distributions in early-age concrete and then to incorporate those models into finite element procedure. The three dimensional finite element program developed in the present study can determine the degree of hydration, temperature and moisture distribution in hardening concrete. It is assumed that temperature and humidity fields are fully uncoupled and only the degree of hydration is coupled with two state variables. Mathematical formulation of degree of hydration Is based on the combination of three rate functions of reaction. The effect of moisture condition as well as temperature on the rate of reaction is considered in the degree of hydration model. In moisture transfer, diffusion coefficient is strongly dependent on the moisture content in pore system. Many existing models describe this phenomenon according to the composition of mixture, especially water to cement ratio, but do not consider the age dependency. Microstructure is changing with the hydration and thus transport coefficients at early ages are significantly higher because the pore structure in the cement matrix is more open. The moisture capacity and sink are derived from age-dependent desorption isotherm. Prediction of a moisture sink due to the hydration process, i.e. self-desiccation, is related to autogenous shrinkage, which may cause early-age cracking in high strength and high performance concrete. The realistic models and finite element program developed in this study provide fairly good results on the temperature and moisture distribution for early-age concrete and correlate very well with actual test data.
- Nilsson, L. O., "Moisture in Marine Concrete Structures," Studies in the BMB-project 1992-1996, Contribution to Durability of Concrete in Saline Environment, 1996.
- Bazant, Z. P., "Current Status and Advances in the Theory of Creep and Interaction with Fracture," 5th International RILEM Symposiumon Creep and Shrinkage of Concrete, Edited by Bazant, Z. P. and Carol, I., Barcelona, Chapmanand Hall, pp.291-308, 1993.
- Neville, A. M., "Properties of Concrete," 4th ed., Addison Wesley Longman Ltd, 1995.
- Brunauer, S., Emmett, P. H., and Teller, E.,"Adsorption of Gases in Multimolecular Layers," Journal of American Chemical Society,Vol. 60, pp.309-319, 1938. https://doi.org/10.1021/ja01269a023
- Hedlund, H., "Stresses in High Performance Concrete Due to Temperature and Moisture Variations at Early Ages," Licentiate thesis, Division of Structural Engineering, Lulea University of Technology, Sweden, 1996.
- Xi, Y., Bazant, Z. P. and Jennings, H. M.,"Moisture Diffusion in Cementitious Materials- Adsorption Isotherms," Advanced Cement Based Materials, No. 1, pp.248-257, 1994. https://doi.org/10.1016/1065-7355(94)90033-7
- Claesson, J., "Few Remarks on Moisture Flow PotentiaIs," Report TVBH-7163, Division of Building Physics, Lund Institute of Technology, Sweden, 1993.
- Xi, Y., Bazant, Z. P., Molina, L., and Jennings, H. M., "Moisture Diffusion in Cementitious Matehals - Moisture Capacity and Diffusivity," Advanced Cement Based Materials, No. 1, pp.258-266, 1994. https://doi.org/10.1016/1065-7355(94)90034-5
- Nilsson, L. O., "Hygroscopic Moisture in Concrete- Drying, Measurements and Related MateriaI Properties," PhD dissertation, Report TVBM 1003, Lund Institute of Technology, Sweden,1980.
- Hillerborg, A., "A Modified Absorption Theory," Cement and Concrete Research, Vol. 15, pp.809-816, 1985. https://doi.org/10.1016/0008-8846(85)90147-4
- Zienkiewicz, O. C. and Taylor, R. L, "The Finite EIement Method," McGraw Hill, New York, 1989.
- Hedenblad, G., "Moisture Permeability of Mature Cconcrete, Cement Mortar and Cement Paste," Ph.D dissertation, Report TVBM-1014, LundInstitute of Technology, Sweden, 1993.
- Cha, S. W., "Modeling of Hydration Process and Analysis of Thermal and Hygral Stresses in Hardening Concrete," Ph.D Dissertation, Seoul National University, Seoul, Korea, 1999.
- Bazant, Z. P. and Najjar, L. L, "Nonlinear Water Diffusion in Nonsaturated Concrete" MateriaIs and Structures, Vol. 5, No. 25, pp.3-20, 1972. https://doi.org/10.1007/BF02479073
- Brunauer, S., Deming, L. S., Deming, W. E., and Teller, E., Journal of American Chemical Society, Vol. 62, pp.1723-1732, 1940. https://doi.org/10.1021/ja01864a025
- Brunauer, S., Skanlny, J., and Border, E. E., Journal of Colloid Interface Science, Vol. 30, pp.546-552, 1969. https://doi.org/10.1016/0021-9797(69)90423-8
- Norling Mjornell, K, "Self-desiccation in Concrete," Licentiate thesis, Chalmers University of Technology, Sweden, 1994.
- Hedenblad, G., "The Use of Mercury Intrusion Porosity or Helium Porosity to Predict the Moisture Transport Properties of Hardened Cement Paste," Advanced Cement Based Materials, No. 6, pp.123-129, 1997. https://doi.org/10.1016/S1065-7355(97)90019-5
- Norling Mjornell, K., "Moisture Conditions in High Performance Concrete," Ph.D Dissertation, Chalmers University of Technology, Sweden,1997.
- Atlassi, E., "Influence of Cement Type on the Desorption Isotherm of Mortar," Nordic Concrete Research, No. 10, pp.25-36, 1991.
- CEB-FIP Model Code 1990, CEB Bulletin d'Information No. 213/214, 1993.
- Persson, B., "Hydration, Structure and Strength of High Performance Concrete," Licentiate thesis, Report TVBM-7009, Lund University of Technology, Sweden, 1992.