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Transport and sorption phenomena in concrete and other porous media

by Johannesson, Björn, PhD

Abstract (Summary)
The work presented in this thesis is mainly focused on transport processes involved in service life predictions of concrete. Two papers and three reports deal with ion transport in pore solution of concrete. One paper and one report deals with moisture transport in concrete and the remaining papers and reports deal with absorption and physical properties related to adsorption for different materials. The fourteen contributions have the following contents: RI:1, Diffusion of a mixture of positively and negatively charged ions in pore solution of concrete is studied. Binding of dissolved ions in pore solution and leaching of ions from solid components into pore solution are included in the model. The material constants in the developed model are chosen to give the best match of simulation to experimental data. A finite element scheme is developed solving the governing coupled constituent equations. RI:2, The models established in RI:1 and P:1 are used to study the effect of different cements and pozzolans on chloride ingress into concrete. RI:3, The models established in RI:1 and P:1 are used to study the effect of curing conditions on chloride ingress in concrete. A drying period before exposure to chlorides is shown to decrease the penetration. RII:1, Capillary suction is studied using a Newtonian fluid assumption together with a momentum source term reflecting the influence of the pore walls on the capillary sucked fluid. RIII:1, The heat of adsorption of different molecule layers on dry surfaces is investigated using a calorimetric technique. Different types of BET-equations were used to predict the distribution of adsorbate among different discrete adsorbed layers. The classical way of calculating the adsorption heat and the measured values differed with about a factor of 2.5. RIII:2, The effect of different constant temperatures on the absorption isotherms and the heat of adsorption of first and second layer molecules on porous glass are investigated. P:1, Diffusion of a mixture of positively and negatively charged ions in water is studied. An electrical potential is included in the model, which makes it possible to study diffusion caused by internal electrical forces in a mixture of different types of ions. P:2, The paper presents a model for combined chloride ion diffusion and chloride ion convection caused by capillary suction. P:3, A numerical approach capable of solving diffusion-convection equations is discussed. The so-called Petrov-Galerkin weighting is shown to be a reliable method for the diffusion problem studied. P:4, Four different methods of measuring sorption isotherms are studied. P:5, The limit of the use of a quasi-static calorimetric technique measuring absorption is investigated theoretically by simulating the diffusion behavior in the instrument. Results shows that the material constant related to the sorption kinetics must exceed a certain value. P:6, Measurements of moisture storage capacity with sorption balance and pressure extractor are described in this paper. P:7, In this paper micro-structural changes caused by carbonation of cement mortar are discussed. P:8, Water vapor diffusion and transient condensation in cement mortar are treated in this paper.
Bibliographical Information:

Advisor:

School:Lunds universitet

School Location:Sweden

Source Type:Doctoral Dissertation

Keywords:TECHNOLOGY; Byggnadsteknik; Concrete; Convection; Diffusion; Capillary suction; Sorption; Durability; Mixture Theory; Building construction

ISBN:91-628-4351-6

Date of Publication:01/01/2000

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