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  • 1.
    Addassi, Mouadh
    et al.
    Technical University of Denmark, Denmark.
    Johannesson, Björn
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Wadsö, Lars
    Lund University.
    Inverse analyses of effective diffusion parameters relevant for a two-phase moisture model of cementitious materials2018In: Cement and Concrete Research, ISSN 0008-8846, E-ISSN 1873-3948, Vol. 106, p. 117-129Article in journal (Refereed)
    Abstract [en]

    Here we present an inverse analyses approach to determining the two-phase moisture transport properties re-levant to concrete durability modeling. The purposed moisture transport model was based on a continuumapproach with two truly separate equations for the liquid and gas phase being connected by the sorption ki-netics. The moisture properties of ten binder-systems containingfly ash, calcined clay, burnt shale and graymicro-filler, were investigated experimentally. The experiments used were, (i) sorption test (moisturefixation),(ii) cup test in two different relative humidity intervals, (iii) drying test, and, (iv) capillary suction test. Masschange over time, as obtained from the drying test, the two different cup test intervals and the capillary suctiontest, was used to obtain the effective diffusion parameters using the proposed inverse analyses approach. Themoisture properties obtained with the proposed inverse analyses method provide a good description of the testperiod for the ten different binder-systems.

  • 2.
    Addassi, Mouadh
    et al.
    Technical University of Denmark, Denmark.
    Schreyer, Lynn
    Washington State University, USA.
    Johannesson, Björn
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Lin, Hai
    University of Colorado Denver, USA.
    Pore-scale modeling of vapor transport in partially saturated capillary tube with variable area using chemical potential2016In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 52, no 9, p. 7023-7035Article in journal (Refereed)
    Abstract [en]

    Here we illustrate the usefulness of using the chemical potential as the primary unknown by modeling isothermal vapor transport through a partially saturated cylindrically symmetric capillary tube of variable cross-sectional area using a single equation. There are no fitting parameters and the numerical solutions to the equation are compared with experimental results with excellent agreement. We demonstrate that isothermal vapor transport can be accurately modeled without modeling the details of the contact angle, microscale temperature fluctuations, or pressure fluctuations using a modification of the Fick-Jacobs equation. We thus conclude that for a single, axisymmetric pore, the enhancement factor depends upon relative humidity boundary conditions at the liquid bridge interfaces, distance between liquid bridges, and bridge lengths.

  • 3. Fagerlund, Göran
    et al.
    Janz, Mårten
    Johannesson, Björn
    Effect of Frost Damage on Bond between Reinforcement and Concrete – A contribution to the BRITE/EURAM project BREU-CT92-0591, Internal LTH Report, TVBM 90161994Report (Other academic)
  • 4.
    Fagerlund, Göran
    et al.
    Lund University.
    Johannesson, Björn
    Lund University.
    Betong för lagring av flytande naturgas, undersökning steg II: Inverkan av mycket hög fuktnivå, Inverkan av extremt låg temperatur, -196°C2005Report (Other academic)
  • 5.
    Fagerlund, Göran
    et al.
    Lund University.
    Johannesson, Björn
    Lund University.
    Freezable Water and Frost Resistance of Concrete at Very Low Temperature2005In: XIX Symposium on Nordic Concrete Research & Development: 12-15 June, 2005, Sandefjord, Norway, Sandefjord, Norway, 2005Conference paper (Refereed)
  • 6.
    Geiker, Mette Rica
    et al.
    Norwegian Univ Sci & Technol, Norway;Tech Univ Denmark, Denmark.
    De Weerdt, Klaartje
    Norwegian Univ Sci & Technol, Norway.
    Garzon, Sergio Ferreiro
    Cementir Holding SpA, Denmark.
    Jensen, Mads Monster
    Tech Univ Denmark, Denmark.
    Johannesson, Björn
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Michel, Alexander
    Tech Univ Denmark, Denmark.
    Screening of Low Clinker Binders, Compressive Strength and Chloride Ingress2017In: Nordic Concrete Research, ISSN 0800-6377, Vol. 57, no 2, p. 23-38Article in journal (Refereed)
    Abstract [en]

    This paper reports an initial screening of potential new binders for concrete with reduced CO2-emission. Mortars cured saturated for 90 days are compared with regard to a) compressive strength of mortars with similar water-to-binder ratio, and b) chloride ingress in similar design strength mortars exposed to seawater. The reference used was a binder composition typical for a Danish ready mixed concrete for aggressive environments and strength class C35/45. Based on the present investigation and assumptions up to around 15% reduction in CO2 emission from binder production might be obtained without compromising the 90 days compressive strength and resistance to chloride ingress in marine exposure by using selected alternative binders.

  • 7. Hosokawa, Yoshifumi
    et al.
    Yamada, Kazuo
    Johannesson, Björn
    Technical University of Denmark, Denmark.
    Nilsson, L. O.
    A development of multi-Species mass transport model considering thermodynamic phase equilibrium2008In: International RILEM Symposium on Concrete Modelling - ConMod '08 / [ed] E. Schlangen and G. De Schutter, Rilem publications, 2008, p. 543-550Conference paper (Other academic)
    Abstract [en]

    In this paper, a multi-species mass transport model, which can predict time dependent variation of pore solution and solid-phase composition due to the mass transport into the hardened cement paste, has been developed. Since most of the multi-species models established previously, based on the Poisson-Nernst-Planck theory, did not involve the modeling of chemical process, it has been coupled to thermodynamic equilibrium model in this study. By the coupling of thermodynamic equilibrium model, the multi-species model could simulate many different behaviours in hardened cement paste such as: (i) variation in solid-phase composition when using different types of cement, (ii) physicochemical evaluation of steel corrosion initiation behaviour by calculating the molar ratio of chloride ion to hydroxide ion [Cl]/[OH] in pore solution, (iii) complicated changes of solid-phase composition caused by the penetration of mineral salts during marine seawater exposure conditions. Those phenomena in concrete can be predicted using the coupled multi-species mass transport model and the thermodynamic equilibrium model described in this paper.

  • 8.
    Hosokawa, Yoshifumi
    et al.
    Taiheiyo Cement Corporation, Japan.
    Yamada, Kazuo
    Taiheiyo Cement Corporation, Japan ; Taiheiyo Consultant Co, Japan.
    Johannesson, Björn
    Technical University of Denmark, Denmark.
    Nilsson, Lars-Olof
    University of Lund.
    Development of a multi-species mass transport model for concrete with account to thermodynamic phase equilibriums2011In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 44, no 9, p. 1577-1592Article in journal (Refereed)
    Abstract [en]

    In this study, a coupled multi-species transport and chemical equilibrium model has been established. The model is capable of predicting time dependent variation of pore solution and solid-phase composition in concrete. Multi-species transport approaches, based on the Poisson–Nernst–Planck (PNP) theory alone, not involving chemical processes, have no real practical interest since the chemical action is very dominant for cement based materials. Coupled mass transport and chemical equilibrium models can be used to calculate the variation in pore solution and solid-phase composition when using different types of cements. For example, the physicochemical evaluation of steel corrosion initiation can be studied by calculating the molar ratio of chloride ion to hydroxide ion in the pore solution. The model can, further, for example, calculate changes of solid-phase composition caused by the penetration of seawater into the concrete cover. The mass transport part of the model is solved using a non-linear finite element approach adopting a modified Newton–Raphson technique for minimizing the residual error at each time step of the calculation. The chemical equilibrium part of the problem is solved by using the PHREEQC program. The coupling between the transport part and chemical part of the problem is tackled by using a sequential operator splitting technique and the calculation results are verified by comparing the elemental spacial distribution in concrete measured by the electron probe microanalysis (EPMA).

  • 9. Hosokawa, Yoshifumi
    et al.
    Yamada, Kazuo
    Johannesson, Björn
    Nilsson, Lars-Olof
    Thermodynamic Modeling of Phase Changes in Neutralization Reactions Using PHREEQC2006In: International RILEM Workshop on Performance Based Evaluation and Indicators for Concrete Durability / [ed] V. Baroghel-Bouny, C. Andrade, R. Torrent, K. Scrivener, Madrid, 2006, p. 127-133Conference paper (Refereed)
    Abstract [en]

    In the simulation technique of evaluating the ionic mass transfer for the durability assessment of RC structures, the development of models for chemical reactions, such as binding of chloride ions, has recently become a significant issue. In this study, thermodynamic modeling was investigated to simulate the changes of hydrate phases caused by neutralization using PHREEQC - a computer program for aqueous geochemical calculations. The model has been applied successfully to describe the dissolution/precipitation behavior of calcium aluminate phases, especially the decomposition of Friedel's salt, and releasing chloride ion into pore solution. For the behavior of C-S-H gel, utilizing the proposed model assuming a binary non-ideal solid solution of Ca(OH)₂ and SiO₂, a continued reduction of CaO/SiO₂ can be reproduced. Accordingly, this model has allowed appropriate evaluation of chemical reactions of cementitious materials under any type of deterioration.

  • 10.
    Janz, Marten
    et al.
    Lund University.
    Johannesson, Björn
    Lund University.
    Measurement of the moisture storage capacity using sorption balance and pressure extractors2001In: Journal of Thermal Envelope and Building Science, ISSN 1097-1963, E-ISSN 1530-8073, Vol. 24, no 4, p. 316-334Article in journal (Refereed)
    Abstract [en]

    This paper presents measurements of the moisture storage capacity for several different porous building materials. The storage capacity is measured by a sorption balance in the hygroscopic range and with pressure plate and pressure membrane extractors in the superhygroscopic range. The results are presented both as retention curves and sorption isotherms and indicate, among other things, that some materials have a large hysteresis between absorption and desorption in the superhygroscopic range. This is contrary to what sometimes has been postulated.

  • 11. Janz, Mårten
    et al.
    Johannesson, Björn
    The influence of frost damage on the bound between concrete and reinforcement bars, laboratory results1994Report (Other academic)
  • 12.
    Jensen, Mads Mønster
    et al.
    Technical University of Denmark, Denmark.
    De Weerdt, K.
    Norwegian University of science and Technology, Norway.
    Johannesson, Björn
    Technical University of Denmark, Denmark.
    Geiker, M. R.
    Norwegian University of science and Technology, Norway.
    Use of a multi-species reactive transport model to simulate chloride ingress in mortar exposed to NaCl solution or sea-water2015In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 105, p. 75-82Article in journal (Refereed)
    Abstract [en]

    Simulations of ion ingress in Portland cement mortar using a multi-species reactive mass transport model are compared with experimental test results. The model is an extended version of the Poisson–Nernst–Planck equations, accounting for chemical equilibrium. Saturated mortar samples were exposed after 8 days of hydration to a NaCl-solution or natural sea-water in a laboratory controlled environment for the experimental part. The samples were analyzed for the total chloride content after 21, 90 and 180 days of exposure, at varying depths from the exposed surface. The applicability of the reactive mass transport model is shown by comparing the simulation and experimental results. The tortuosity factor used in the simulations is adjusted to obtain the best reproduction of the experimental results. The model predicts the total chloride content satisfactorily, despite assumptions in the simulation like fixed hydration degree over time. Improvements and suggestions for further development of the model are discussed, e.g. extended hydration description, improved overall chemical description and a more strict use of the tortuosity factor.

  • 13.
    Jensen, Mads Mønster
    et al.
    Technical University of Denmark, Denmark.
    Johannesson, Björn
    Technical University of Denmark, Denmark.
    Geiker, Mette Rica
    Technical University of Denmark, Denmark ; Norwegian University of Science and Technology, Norway.
    A Coupled Chemical and Mass Transport Model for Concrete Durability2012In: Proceedings of the Eighth International Confernce on Engineering Computational Technology / [ed] B.H.V. Topping, Civil-Comp Press , 2012Conference paper (Refereed)
    Abstract [en]

    In this paper a general continuum theory is used to evaluate the service life of cement based materials, in terms of mass transport processes and chemical degradation of the solid matrix. The model established is a reactive mass transport model, based on an extended version of the Poisson-Nernst-Planck equations, which is further developed to take into account sorption hysteresis. The sorption hysteresis is modelled as phase equilibrium between the liquid and vapor phase in terms of third order polynomials. A change in sorption direction (from adsorption to or from desorption) results in inner scanning curves which is established from a set of mathematical criteria. The chemical degradation is modelled with the geochemical code iphreeqc, which provides a general tool for evaluating different paste compositions. The governing system of equations is solved by the finite element method with a Newton-Raphson iteration scheme arising from the non-linearity. The overall model is a transient problem, solved using a single parameter formulation. The sorption hysteresis and chemical equilibrium is included as source or sink terms. The advantages with this formulation is that each node in the discrete system has their individual sorption hysteresis isotherm which is of great importance when describing non fully water saturated system e.g. caused by time depended boundary conditions. Chemical equilibrium is also established in each node of the discrete system, where the rate of chemical degradation is determined by the rate of mass transport only. A consequence of the source or sink term, is the assumption that equilibrium is reached instantaneously in each time step considered. Some numerical problems was found, where the residual requirements for the chemical equilibrium was not reached. Small imbalances, in e.g. charge balance, from the mass transport calculation could cause the above mentioned numerical problems. Two different test cases are studied, the sorption hysteresis in different depth of the sample, caused by time depended boundary condition and the chemical degradation of the solid matrix in a ten year simulation. The relative simple test cases show that sorption hysteresis cannot be neglected in a mass transport model for cement based materials and a description of the chemical degradation is crucial for long term simulation of service life prediction.

  • 14.
    Jensen, Mads Mønster
    et al.
    Technical University of Denmark, Denmark.
    Johannesson, Björn
    Technical University of Denmark, Denmark.
    Geiker, Mette Rica
    Norwegian University of Science and Technology, Norway.
    A Numerical Comparison of Ionic Multi-Species Diffusion with and without Sorption Hysteresis for Cement-Based Materials2015In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 107, no 1, p. 27-47Article in journal (Refereed)
    Abstract [en]

    A finite element solution for a mass transport model for porous materials accounting for sorption hysteresis is presented in this paper. The model is prepared for modeling of concrete durability, but the general presentation makes it suitable for other porous materials like soil and tissues. The model is an extended version of the Poisson–Nernst–Planck (PNP) system of equations. The PNP extension includes a two-phase vapor and liquid model coupled by a sorption hysteresis function and a chemical equilibrium term. The strong and weak solutions for the equation system are shown, and a finite element formulation is established by Galerkin’s method. A single-parameter implicit time integration scheme is used for solving the transient response, and the out-of-balance solution is minimized by using a modified Newton–Raphson scheme in which the tangential stiffness is not computed exactly. The sorption hysteresis is added to the solution procedure by a rate function. The hysteresis effect is described by scanning curves defined between two boundary sorption isotherms. A numerical example was constructed to show the applicability and compare a simple approach and a extended approach within the sorption hysteresis model. The examples illustrate the impact of changing relative humidity at the mass transport boundary on the adsorption and desorption stages of a cement-based material. Changes in the pore solution ion concentrations are a result of the changing moisture content, which are shown by the example. Comparing the two approaches showed significant deviations in the liquid content and ion concentrations, in parts of the domain considered.

  • 15.
    Jensen, Mads Mønster
    et al.
    Technical University of Denmark, Denmark.
    Johannesson, Björn
    Technical University of Denmark, Denmark.
    Geiker, Mette Rica
    Norwegian University of Science and Technology, Norway.
    Framework for reactive mass transport: phase change modeling of concrete by a coupled mass transport and chemical equilibrium model2014In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 92, p. 213-223Article in journal (Refereed)
    Abstract [en]

    Reactive transport modeling is applicable for a range of porous materials. Here the modeling framework is focused on cement-based materials, where ion diffusion and migration are described by the Poisson–Nernst–Planck equation system. A two phase vapor/liquid flow model, with a sorption hysteresis description is coupled to the system. The mass transport is solved by using the finite element method where the chemical equilibrium is solved explicitly by an operator splitting method. The iphreeqc library is used as chemical equilibrium solver. The equation system, solved by iphreeqc, is explained for aqueous, pure phase and solid solution reactions. Numerical examples, with cement-based materials, are constructed to demonstrate transient phase change modeling. A simulation of pure multi-species leaching from the material, showing deterioration of the solid phases is described and calculated. A second simulation, showing multi-species ingress with formation of new solid phases in the domain is described and calculated. It is shown that the numerical solution method is capable of solving the reactive mass transport system for the examples considered.

  • 16.
    Johannesson, Björn
    Lund Institute of Technology.
    A theoretical model describing diffusion of a mixture of different types of ions in pore solution of concrete coupled to moisture transport2003In: Cement and Concrete Research, ISSN 0008-8846, E-ISSN 1873-3948, Vol. 33, no 4, p. 481-488Article in journal (Refereed)
    Abstract [en]

    A theoretical model is established for diffusion of different types of ions in pore solution of concrete and the coupling to moisture flow and moisture content. Mass exchanges between ions in pore solution and solid hydration products in the concrete are also considered. The basic concepts behind the so-called mixture theory are used. The development of a mass balance principle for ions in pore solution is established. This principle accounts for (i) diffusion caused by concentration gradients of ions and gradients of the so-called internal electrical potential, (ii) convection, i.e. the effect on the motion of ions due to a motion of the pore solution in concrete, (iii) the effect on the concentration due to changes in the moisture content, and finally, (iv) the effect of mass exchange of ions between solid hydration products and the bore solution phase. The model is general in the sense that all different types of ions appearing in pore solution phase can-be included and computed for during quite arbitrary boundary conditions.

  • 17.
    Johannesson, Björn
    Lund University.
    Combined Effects on Concrete Exposed to Mechanical Load and Environmentally Induced Strains1996In: Durability of Building Materials and Components 7 : proceedings of the seventh International Conference on Durability of Building Materials and Components, 7DBMC, Stockholm, Sweden, 19-23 May 1996. Vol. 1, Prediction, degradation and materials, 1996, p. 431-442Conference paper (Refereed)
  • 18.
    Johannesson, Björn
    Technical University of Denmark, Denmark.
    Comparison between the Gauss' law method and the zero current method to calculate multi-species ionic diffusion in saturated uncharged porous materials2010In: Computers and geotechnics, ISSN 0266-352X, E-ISSN 1873-7633, Vol. 37, no 5, p. 667-677Article in journal (Refereed)
    Abstract [en]

    There exist, mainly, two different continuum approaches to calculate transient multi species ionic diffusion. One of them is based on explicitly assuming a zero current in the diffusing mixture together with an introduction of a streaming electrical potential in the constitutive equations for the mass density flow of ionic species. The other is based on using the Gauss’ law and assuming no polarization, in order to obtain an equation for the determination of the electrical field, together with adding the electrical field in the constitution of the ionic mass density flows. The important difference of the two types of potentials, that is, the streaming electrical potential and the electrical field is carefully examined. A novel numerical method based on the finite element approach is established for the zero current method case. The proposed numerical method uses the direct calculation of the coupled set of equation in favor of the staggering approach. A one step truly implicit time stepping scheme is adopted together with an implementation of a modified Newton-Raphson iterational scheme for search of equilibrium at each considered time step calculation. Results from the zero current case are compared with existing results from the solutions of the Gauss’ law method. For the studied case the calculated concentrations of the ionic species, using the two different methods, differed very little.

  • 19.
    Johannesson, Björn
    Lund University.
    Convection-diffusion Problems with Significant First-order Reversible Reactions1996In: Ninth Nordic Seminar on Computational Mechanics, 25-26 October, 1996, Technical University of Denmark / [ed] Damkilde, Lars, Technical University of Denmark , 1996Conference paper (Refereed)
  • 20.
    Johannesson, Björn
    Technical University of Denmark, Denmark.
    Development of a Generalized Version of the Poisson-Nernst-Planck Equations Using the Hybrid Mixture Theory: Presentation of 2D Numerical Examples2010In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 85, no 2, p. 565-592Article in journal (Refereed)
    Abstract [en]

    A numerical scheme for the transient solution of generalized version of the Poisson-Nernst-Planck equations is presented. The finite element method is used to establish the coupled non-linear matrix system of equations capable of solving the present problem iteratively. The Poisson-Nernst-Planck equations represent a set of diffusion equations for charged species, i.e. dissolved ions. These equations are coupled to the ‘internally’ induced electrical field and to the velocity field of the fluid. The Nernst-Planck equations describing the diffusion of the ionic species and the Gauss’ law in used are, however, coupled in both directions. The governed set of equations is derived from a simplified version of the so-called hybrid mixture theory (HMT). This theory is a special version of the more ‘classical’ continuum mixture theories in the sense that it works with averaged equations at macro-scale and that it includes the volume fractions of phases in its structure. The background to the Poisson-Nernst-Planck equations can by the HMT approach be described by using the postulates of mass conservation of constituents together with the Gauss’ law used together with consistent constitutive laws. The HMT theory includes the constituent forms of the quasi-static version of Maxwell’s equations making it suitable for analyzes of the kind addressed in this work. Within the framework of HTM constitutive equations has been derived using the postulate of entropy inequality together with the technique of identifying properties by Lagrange multipliers. These results will be used in obtaining a closed set of equations for the present problem.

  • 21.
    Johannesson, Björn
    Lund Institute of Technology.
    Diffusion of a mixture of cations and anions dissolved in water1999In: Cement and Concrete Research, ISSN 0008-8846, E-ISSN 1873-3948, Vol. 29, no 8, p. 1261-1270Article in journal (Refereed)
    Abstract [en]

    In service life modeling of concrete, the ion transport in the pore solution is crucial. The main deterioration phenomena associated with ions in the pore solution are (1) corrosion due to external chloride ions reaching the embedded reinforcement bars; (2) carbonation due to presence of dissolved carbon dioxide (which will form carbonic acid with water) supplied from the surrounding air. and (3) leaching of hydroxide ions from the pore solution to the surrounding environment. Models dealing with diffusion of ions are usually based on the mass balance equations for the individual diffusing ions together with constitutive relations for the mass density flows and for the mass exchange among the constituents. The important consequences of electroneutrality among the diffusing ions, however, is often omitted in models dealing with diffusion of ions in the pore solution of concrete. Here a method will be examined that allows diffusion of different ions in water, which satisfies both the electroneutrality requirement and the mass balance laws. For simplicity the effect of built-up electric double layers on the charged pore walls will not be treated.

  • 22.
    Johannesson, Björn
    Technical University of Denmark, Denmark.
    Dimensional and ice content changes of hardened concrete at different freezing and thawing temperatures2010In: Cement & Concrete Composites, ISSN 0958-9465, E-ISSN 1873-393X, Vol. 32, no 1, p. 73-83Article in journal (Refereed)
    Abstract [en]

    Samples of concrete at different water-to-cement ratios and air contents subjected to freeze/thaw cycles with the lowest temperature at about -80 degrees C are investigated. By adopting a novel technique, a scanning calorimeter is used to obtain data from which the ice contents at different freeze temperatures can be calculated. The length change caused by temperature and ice content changes during test is measured by a separate experiment using the same types of freeze-thaw cycles as in the calorimetric tests. In this way it was possible to compare the amount of formed ice at different temperatures and the corresponding measured length changes. The development of cracks in the material structure was indicated by an ultra-sonic technique by measuring on the samples before and after the freeze-thaw tests. Further the air void structure was investigated using a microscopic technique in which air'bubble' size distributions and the so-called spacing factor, indicating the mean distance between air bubbles, were measured. By analyzing the experimental result, it is concluded that damages occur in the temperature range of about -10 degrees C to -55 degrees C, when the air content is lower than about 4% of the total volume. For a totally water-saturated concrete, damages always occur independently of the use of entrained air or low water-to-cement ratios. It is, further, concluded that the length changes of these samples correspond to the Calculated ice contents at different temperatures in a linear fashion. @ 2009 Elsevier Ltd. All rights reserved.

  • 23.
    Johannesson, Björn
    Lund University.
    Durability of Concrete with Regard to Different Interacting Physical Phenomena1996In: Nordic Concrete Research Meeting, Espoo, Finland 1996, Nordic Concrete Federation , 1996, p. 265-266Conference paper (Refereed)
  • 24.
    Johannesson, Björn
    Technical University of Denmark, Denmark.
    Freeze/thaw phenomena in concrete at low temperatures2007In: Nordic Concrete Research, 2007Conference paper (Other academic)
    Abstract [en]

    Freeze/thaw damage in concrete is by general practice concluded to be a problem that can be avoided by using air-entraining agents to develop an air bubble structure in the hardened concrete together with the use of a relatively low water to cement ratio in mix. This fact is true for inner damages, however, the so-called salt-frost damage, occurring mainly at the surfaces of concrete constructions, can not totally be avoided by the above mentioned method. The performance and the mechanisms occurring in concrete, with a substantial amount of water in its micro-structure, at very low temperature are, however, in most part unknown. In this work samples of concrete at different water to cement ratios and air bubble contents subjected to freeze/thaw cycles with the lowest temperature at about -80 oC are investigated. By adopting a novel technique a scanning calorimeter is used to obtain data from which the ice contents at different freeze temperatures can be calculated. The length change caused by temperature and ice content changes during test is measured by a separate experiment using the same types of freeze-thaw cycles as in the calorimetric tests. In this way it was possible to compare the amount of formed ice at different temperatures and the corresponding measured length changes. The development of cracks in the material structure was indicated by an ultra-sonic technique by measuring on the samples before and after the freeze thaw tests. Further the air bubble structure was investigated using a microscopic technique in which air bubble size distributions and the so-called spacing factor, indicating the mean distance between air bubbles, were measured. By analyzing the experimental result it is concluded that damages occur in the temperature range of about -10 oC to 55 oC, when the air content is lower than about 4% of the total volume. For a totally water saturated (using vacuum) concrete damages always occur independently of the use of entrained air or low water to cement ratios. It is, further, concluded that the length changes of theses samples corresponds to the calculated ice contents at different temperatures in a linear fashion. Even though a quite extensive experimental investigation are performed in this work, it is concluded to be difficult to verify or reject the three most common theories for the mechanisms of inner frost damage, i.e. the closed container-, hydraulic pressure- and ice lens growth theory. The new suggested method to calculate the ice contents at different temperatures, using raw data from the adopted scanning calorimetric technique, are however ideal suited for this purpose once more directed experiments are performed.

  • 25. Johannesson, Björn
    Interaction Between Surface Change Phenomena and Multi-Species Diffusion in Cement Based Materials2008In: International Conference on Microstructure Related Durability of Cementitious Composites / [ed] W. Sun, K. van Breugel, C. Miao, G. Ye and H. Chen, Rilem publications, 2008, p. 565-574Conference paper (Other academic)
    Abstract [en]

    Measurements strongly indicate that the ‘inner’ surface of the microscopic structure of cement based materials has a fixed negative charge. This charge contributes to the formation of so-called electrical double layers. In the case of cement based materials the ionic species located in such layers are typically potassium -, sodium - and calcium ions. Due to the high specific surface area of hydrated cement, a large amount of ions can be located in theses double layers even if the surface charge is relatively low. The attraction force, caused by the fixed surface charge on ions located close to surfaces, is one possible explanation for the observed low global diffusion rates in the pore system of positively charged ions compared to the negatively charged ones. Here it is of interest to simulate the multi ionic diffusion behavior when assigning positively charged ions a comparably lower diffusion constant and also including a negatively charged ‘ion’ with an extremely low diffusion constant so as to represent a fixed negative surface charge. The theoretical results from such simulations, using a tailor made finite element technique, indicates a strong influence of surface charges on global diffusion of different ionic species in the pore system of cement based materials.

  • 26.
    Johannesson, Björn
    Technical University of Denmark, Denmark.
    Ionic Diffusion and Kinetic Homogeneous Chemical Reactions in the Pore Solution of Porous Materials with Moisture Transport2009In: Computers and geotechnics, ISSN 0266-352X, E-ISSN 1873-7633, Vol. 36, no 4, p. 577-588Article in journal (Refereed)
    Abstract [en]

    Results from a systematic continuum mixture theory will be used to establish the governing equations for ionic diffusion and chemical reactions in the pore solution of a porous material subjected to moisture transport. The theory in use is the hybrid mixture theory (HMT), which in its general form accounts for electroquasistatics. The derived macroscopic field equations (conservation of mass, linear and angular momentum, energy and Maxwell’s equations) for the multiphase, multicomponent system are combined with the entropy inequality to obtain restrictions on constitutive equations. The so called near equilibrium results obtained from this analysis (using Lagrange multipliers to identify properties) are obtained by expanding linearly about equilibrium. The approach leads to the development of the explicit expressions for the constitutive equations. In this work the derived generalized Fick’s law of diffusion and the generalized Darcy’s law will be used together with derived constitutive equations for chemical reactions within phases. The mass balance equations for the constituents and the phases together with the constitutive equations gives the coupled set of non-linear differential equations describing the theoretical behaviour of the system under consideration. A Finite element procedure is described capable of solving the coupled set of governing differential equations. A novel approach on how to arrange the stiffness matrix of the global problem to take into account for a quite general description of chemical reactions among constituents is described. The Petrov – Galerkin approach are used in favour of the standard Galerkin weighting in order to improve the solution when the convective part of the problem is dominant. A modified type of Newton – Raphson scheme is derived for the non-linear global matrix formulation. The developed model and its numerical solution procedure are checked by running test examples which results demonstrates robustness of the proposed approach.

  • 27.
    Johannesson, Björn
    Lund University.
    Kloridinträngning i samband med tösaltning av betongkonstruktioner: Numerisk simulering med hjälp av finita elementmetoden1997Report (Other academic)
  • 28.
    Johannesson, Björn
    Lund University.
    Mikrobiell påväxt på fasader2003Report (Other academic)
  • 29.
    Johannesson, Björn
    Lund University.
    Mixture Theory Applied to Chemical Reactions and Diffusion of Different Mediums in Mature Concrete: A Hypothetical Model, Part I and Part II1995In: Proceedings pro002: International RILEM Workshop on Chloride Penetration into Concrete Saint-Rémy-lès-Chevreuse, France (1995) / [ed] Nilsson, Lars-Olof and Ollivier, J.P, Rilem publications, 1995, p. 265-289Conference paper (Refereed)
  • 30.
    Johannesson, Björn
    Lund University.
    Modelling of a Viscous Fluid Percolating a Porous Material Due to Capillary Forces2000Report (Other academic)
  • 31.
    Johannesson, Björn
    Lund University.
    Modelling of Transport Processes Involved in Service Life Prediction of Concrete: Important Principles1998Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The main focus in this licentiate thesis is a description of the environmentally introduced action of diffusing and chemically reactive (e.g. carbonation and chemical-physical adsorption-desorption) matter in the pore solution and in the air-filled space in the pore system of the material. The governing equations describing the variation of concentrations of different substances and temperature within the material will then be used in a coupled description of the stress-deformation state using the so-called smeared crack approach.

  • 32.
    Johannesson, Björn
    Lund University.
    Nonlinear Transient Phenomena in Porous Media with Special Regard to Concrete and Durability1996In: Materials research society, MRS, meeting, Boston, USA, 1996Conference paper (Refereed)
  • 33.
    Johannesson, Björn
    Lund Institute of Technology.
    Nonlinear transient phenomena in porous media with special regard to concrete and durability1997In: Advanced Cement Based Materials, ISSN 1065-7355, E-ISSN 1878-5948, Vol. 6, no 3-4, p. 71-75Article in journal (Refereed)
    Abstract [en]

    Concrete deteriorates due to many different mechanisms. Among the most important mechanisms is the reinforcement corrosion induced by deleterious substances reaching the embedded reinforcement bars. The external sources of deleterious materials may, for example, be deicing salts, sea water, and carbon dioxide. Research has sought to determine threshold values, in terms of concentration of deleterious substances in concrete, at which reinforcement corrosion will be induced, that is, at which concentration the passive condition close to the reinforcement turns to an aggressive state. To predict when this threshold value is reached, the flow properties of the pollutant in concrete must be known. Some of the most important phenomena governing the movement of pollutants in concrete are diffusion of substances in the pore water, adsorption (and desorption) of pollutants onto the pore walls, and hydrodynamic dispersion and convection of substances due to flow of the pore water. Here a set of equations will be presented based on mass and energy balance. These coupled equations cope with the above-mentioned phenomena. The migration of ions due to an electric potential is not considered as only the initiation stage of corrosion is of interest. The constituents considered in the model are a solute γ (e.g., chlorides), the pore water α, and the solid phase s of the concrete, which is restricted to be nondeformable. The governed equation system is solved using the Petrov-Galerkin scheme and finite elements (compare references 1 and 2). Some examples of the performance of the proposed model are given.

  • 34.
    Johannesson, Björn
    Lund Institute of Technology.
    Prestudy on diffusion and transient condensation of water vapor in cement mortar2002In: Cement and Concrete Research, ISSN 0008-8846, E-ISSN 1873-3948, Vol. 32, no 6, p. 955-962Article in journal (Refereed)
    Abstract [en]

    The kinetics of sorption of water vapor in mature cement mortar are examined experimentally by the use of a sorption balance (DVS1000). The relative humidity in the sample chamber is obtained by mixing dry and saturated air using flow regulators with very high accuracy. A predefined change of relative humidity in the sample chamber can be obtained in about 30 s. The time needed for equilibration in terms of the mass of a finely grained mortar sample is shown to be in the order of 2500 min for a 0-96% step in relative humidity at 25 degreesC. This fact calls for a refinement of modeling of diffusion of water vapor in materials such as mortar to take into account the kinetics of sorption. The established model involves a transient mass exchange term that explicitly describes the rate of condensation at internal material surfaces. This function becomes zero when located at the equilibrium sorption isotherm. The 'global' mass diffusion velocity of water vapor in the air-filled porosity is assumed to be significantly affected by the mass concentration of liquid water in the pore space. A satisfying match between the proposed model and measurements presented by U. Daian [Transp. Porous Media 4 (1989) 1.] was obtained by using nonlinear diffusion and sorption characteristics. In order to get a satisfying match, the sorption kinetics was, however, forced to be much slower than the recorded values obtained by the sorption balance. Some speculations as to the reason of this marked difference are performed. (C) 2002 Elsevier Science Ltd. All rights reserved.

  • 35.
    Johannesson, Björn
    Lund Institute of Technology.
    Restrictions on the Rate of Absorption When Evaluating Sorption Isotherms Obtained Using a Micro-Calorimetric Technique2001In: Journal of Thermal Envelope and Building Science, ISSN 1097-1963, E-ISSN 1530-8073, Vol. 25, no 2, p. 85-100Article in journal (Refereed)
    Abstract [en]

    One interestingway of measuring sorption isotherms and heats of sorption is the newly developed micro-calorimetric method. It turns out, however, that the adsorption kinetics must be proven to be rapid enough to fulfill the assumptions behind the theory for the determination of the isotherm to be valid. Here, the lower limit of the accepted rate of adsorption will be analyzed by making calculations of the diffusion behavior in the calorimetric vessel. The evaluation of the adsorption isotherms is based on assumptions of a quasi-static nature. If the adsorption kinetics are slow the behavior in the calorimeter will turn to a more or less transient process. When the heat of adsorption is of interest and the sorption isotherm and kinetics of sorption can be determined by other methods, compensation for the transient effects can be made.

  • 36.
    Johannesson, Björn
    Lund University.
    Theoretical Permissible Spacing of Air Bubbles in Paste During Freezing According to Powers Hydraulic Pressure Method2000Report (Other academic)
  • 37.
    Johannesson, Björn
    Lund University.
    Thermodynamics of Transport, Phase Changes, Chemical Reactions and Heat Conduction Phenomena in Stressed Elastic Porous Materials2003Report (Other academic)
  • 38.
    Johannesson, Björn
    Lund University.
    Transport and Sorption Phenomena in Concrete and Other Porous Media2000Doctoral thesis, monograph (Other academic)
    Abstract [en]

    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.

  • 39.
    Johannesson, Björn
    Lund University.
    Verification of the BET-theory by Experimental Investigations on the Heat of Adsorption2000Report (Other academic)
  • 40.
    Johannesson, Björn
    et al.
    Lund University.
    Fagerlund, Göran
    Lund University.
    Betong för lagring av flytande naturgas: Frysfenomen och frostbeständighet vid frysning till -50 °C2003Report (Other academic)
  • 41. Johannesson, Björn
    et al.
    Hosokawa, Y.
    Yamada, K.
    The effect of moiture transport and sorption hystersis on ionic multispecies diffusion in concrete2008In: International RILEM Symposium on Concrete Modelling - ConMod '08 / [ed] E. Schlangen and G. De Schutter, Rilem publications, 2008, p. 527-534Conference paper (Other academic)
    Abstract [en]

    Concrete durability is very much dependent on the moisture and ionic species concentration in the pore solution. Therefore it is of interest to find physically based models for predicting the evolution and variations of these properties for different kinds of relevant boundary conditions. A porous media technique based on the general mixture theory continuum approached is used to establish a set of governing coupled equation describing the process of interest. In this model the equations are actually derived from examine the entropy inequality of the system. Lagrange multipliers are used to identify properties such as definitions of the chemical potentials of constituents. The non-equilibrium results from such evaluations is subjected to linearization in order to obtain a generalized Darcy flow equation and a set of generalized Fickian equations including for electrical fields induced by the charge character of the mixture of ionic constituents dissolved in pore solution. The hysteresis in sorption is modelled by an explicit ‘history’ dependent assumption. The key issue in this context is to divide the moisture transport into two parts, vapour and water transport, and describing the mass exchange between them with guidance from the hysteresis equilibrium model. The coupled systems of equations are rewritten in the weak form suitable for development of finite element formulations. A Taylor expansion is performed in order to reach a Newton-Raphson iteration scheme. The tangential stiffness and tangential damping of the global system is ignorer in the equilibrium iteration obtaining a more computational economic modified Newton-Raphson scheme with good convergence properties. Numerical examples of the performance of the model are presented. The effect of hystersis in the sorption is shown to affect the diffusion of ions in the pore system. Mainly this is due to the moisture content, that is, an increased diffusion resistance at low moisture contents (and the other way around) as predicted by the hysteresis model during cases with variation of the ambient relative humidity. Further, discussions of the important influence of electrical double layers at pore walls on the global model response are performed.

  • 42.
    Johannesson, Björn
    et al.
    Technical University of Denmark, Denmark.
    Hosokawa, Yoshifumi
    Taiheiyo Cement Corporation, Japan .
    Yamada, Kazuo
    Taiheiyo Cement Corporation, Japan .
    Numerical Calculations of the Effect of Moisture Content and Moisture Flow on Ionic Multi-Species Diffusion in the Pore Solution of Porous Materials2009In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 87, no 1-2, p. 39-46Article in journal (Refereed)
    Abstract [en]

    A method to analyse and calculate concentration profiles of different types of ions in the pore solution of porous materials such as concrete subjected to external wetting and drying is described. The equations in use have a solid theoretical meaning and are derived from a porous media technique, which is a special branch of the more general mixture theory. The effect of chemical action is ignored making the presented model suitable to be implemented into codes dealing solely with chemical equilibrium. The coupled set of equations for diffusion of ionic species, the internal electrical potential and the moisture content are solved simultaneously using an implicit finite element technique, in order to avoid numerical oscillations. Important verified material behaviours are included in the model, such as the convective flow of ionic species due to moisture flow, the effect of the moisture content on the ionic diffusion resistance in the pore solution of the porous material. The Gauss’ law is included in the model in order to be able to calculate the electrical potential which develops due to small deviations from total charge neutrality among the ionic species in the pore solution. The correctness of the model should be judged from the assumptions made when developing the balance laws and the constitutive equations and the assumptions made in obtaining a working numerical calculation scheme.

  • 43.
    Johannesson, Björn
    et al.
    Technical University of Denmark, Denmark.
    Janz, Mårten
    Swedish Cement and Concrete Research Institute.
    A two-phase moisture transport model accounting for sorption hysteresis in layered porous building constructions2009In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 44, no 6, p. 1285-1294Article in journal (Refereed)
    Abstract [en]

    Building constructions most commonly consists of layered porous materials such as masonry on bricks. The moisture distribution and its variations due to change in surrounding environment is of special interest in such layered construction since materials adsorb different amounts of water and exhibits different transport properties. A successful model of such a case may shred light on the performance of different constructions with regards to, for example, mould growth and freeze thaw damages. For this purpose a model has been developed which is based on a two phase flow, vapor and liquid water, with account also to sorption hysteresis. The different materials in the considered layered construction are assigned different properties, i.e. vapor and liquid water diffusivities and boundary (wetting and drying) sorption curves. Further, the scanning behavior between wetting and drying boundary curves are model by introducing appropriate material constants. Special properties have to be given for the interface between different materials in the layered construction in the model to be presented. In this case it is assumed that vapor penetrates through such interfaces easily but not the liquid water phase. The model is developed by carefully examining the mass balance postulates for the two considered constituents together with appropriate and suitable constitutive assumptions. A test example is solved by using an implemented implicit finite element code which uses a modified Newton-Raphson scheme to tackle the strong non-linearities in the present problem. The numerical method is described to make it possible for the interested reader to judge the significance of the proposed technique to solve the coupled set of non-linear equations and also in order to make implementations of the proposed model easy.

  • 44.
    Johannesson, Björn
    et al.
    Lund Institute of Technology.
    Janz, Mårten
    Swedish Cement and Concrete Research Institute.
    Test of four different experimental methods to determine sorption isotherms2002In: Journal of materials in civil engineering, ISSN 0899-1561, E-ISSN 1943-5533, Vol. 14, no 6, p. 471-477Article in journal (Refereed)
    Abstract [en]

    One important property of materials is their moisture fixation capacity, i.e., their ability to hold moisture at different relative humidities. The sorption isotherm is one of the main input data in moisture diffusion models, and it can also be used to evaluate properties of the microstructure. We have used four different methods to measure the sorption isotherm of sandstone and porous glass. The first method was to equilibrate samples over saturated salt solutions. The second was a sorption balance in which small material samples were weighed as they were exposed to different relative humidities. The third method was the pressure plate extractor, in which a totally wet sample was equilibrated at various overpressures, corresponding to certain relative humidities. The fourth method was a newly developed microcalorimetric technique to measure sorption isotherms. Despite the different natures of the methods, a satisfying agreement,was found.

  • 45.
    Johannesson, Björn
    et al.
    Lund University.
    Kazuo, Yamada
    Hosokawa, Yoshifumi
    Chloride Penetration Model Capable of Correctly Predict the Peak Shaped Chloride Profiles2006In: 2nd International Symposium on Advances in Concrete through Science and Engineering 11-13 September 2006, Quebec City, Canada / [ed] J, Marchand, B. Bissonncttc, R. Gagnd, M. Jolin and F. Parad, Rilem publications, 2006, p. 255-256Conference paper (Refereed)
  • 46.
    Johannesson, Björn
    et al.
    Technical University of Denmark, Denmark.
    Nyman, U.
    Lund Institute of Technology.
    A Numerical Approach for Non-Linear Moisture Flow in Porous Materials with Account to Sorption Hysteresis2010In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 84, no 3, p. 735-754Article in journal (Refereed)
    Abstract [en]

    A numerical approach for moisture transport in porous materials like concrete is presented. The model considers mass balance equations for the vapour phase and the water phase in the material together with constitutive equations for the mass flows and for the exchange of mass between the two phases. History-dependent sorption behaviour is introduced by considering scanning curves between the bounding desorption and absorption curves. The method, therefore, makes it possible to calculate equilibrium water contents for arbitrary relative humidity variations at every material point considered. The scanning curves for different wetting and drying conditions are constructed by using third degree polynomial expressions. The three coefficients describing the scanning curves is determined for each wetting and drying case by assuming a relation between the slope of boundary sorption curve and the scanning curve at the point where the moisture response enters the scanning domain. Furthermore, assuming that the slope of the scanning curve is the same as the boundary curve at the junction point, that is, at the point where the scanning curve hits the boundary curve once leaving the scanning domain, a complete cyclic behaviour can be considered. A finite element approach is described, which is capable of solving the non-linear coupled equation system. The numerical calculation is based on a Taylor expansion of the residual of the stated problem together with the establishment of a Newton-Raphson equilibrium iteration scheme within the time steps. Examples are presented illustrating the performance and potential of the model. Two different types of measurements on moisture content profiles in concrete are used to verify the relevance of the novel proposed model for moisture transport and sorption. It is shown that a good match between experimental results and model predictions can be obtained by fitting the included material constants and parameters.

  • 47.
    Johannesson, Björn
    et al.
    Technical University of Denmark, Denmark.
    Ottosen, Lisbeth M.
    Technical University of Denmark, Denmark.
    Modeling of electromigration salt removal methods in building materials2008In: Salt Weathering on Building and Stone Sculptures, Technical University of Denmark , 2008, p. 351-360Conference paper (Other academic)
    Abstract [en]

    A model is established for the prediction of the effect of salt removal of building materials using electromigration. Salt-induced decay of building materials, such as masonry and sandstone, is a serious threat to our cultural heritage. Electromigration of salts from building materials, sensitive for salt attack of various kinds, is one potential method to preserve old building envelopes. By establishing a model for ionic multi-species diffusion, which also accounts for external applied electrical fields, it is proposed that an important complement to the experimental tests and that verification can be obtained. One important issue is to be able to optimizing the salt removing electromagration method in the field by first studying it theoretically. Another benefit is that models can give some answers concerning the effect of the inner surfaces of the material on the diffusion mechanisms and the effect of the composition of the ionic constituents on the overall behavior of the salt removal process. The model is obtained by assigning a Fick’s law type of assumption for each ionic species considered and also assuming that all ions is effected by the applied external electrical field in accordance with its ionic mobility properties. It is, further, assumed that Gauss’s law can be used to calculate the internal electrical field induced by the diffusion it self. In this manner the external electrical field applied can be modeled, simply, by assigning proper boundary conditions for the equation calculating the electrical field. A tailor made finite element code is written capable of solving the transient non-linear coupled set of differential equations numerically. A truly implicit time integration scheme is used together with a modified Newton-Raphson method to tackle the non-linearities of the present problem. Theoretical test examples are presented showing the performance of the model.

  • 48.
    Johannesson, Björn
    et al.
    Lund Institute of Technology.
    Utgenannt, Peter
    Lund Institute of Technology.
    Microstructural changes caused by carbonation of cement mortar2001In: Cement and Concrete Research, ISSN 0008-8846, E-ISSN 1873-3948, Vol. 31, no 6, p. 925-931Article in journal (Refereed)
    Abstract [en]

    The change of specific surface area and pore size distribution due to carbonation of an ordinary Portland cement mortar is investigated. The adsorption of water vapor on noncarbonated and well-carbonated cement mortar is measured in order to evaluate the difference in specific surface area for the two samples using the BET theory. From the measured desorption the pore size distribution is calculated using the Kelvin formula. A sorption balance is used to measure the sorption characteristics for the two studied sample qualities. In this method dry and saturated air are mixed in desired proportion in a closed system. One of the benefits of the method is that the samples not are exposed to carbon dioxide during testing, i.e., undesired effects caused by carbonation on the sorption can be eliminated. The specific surface area for a noncarbonated sample was calculated, using the measured adsorption data, to be 8% higher than for the well-carbonated sample. The difference in pore size distributions was more marked than the difference in specific surface area for the two samples. The well-carbonated mortar had about twice as much volume attributed to small pores as the noncarbonated cement mortar.

  • 49.
    Johannesson, Björn
    et al.
    Taiheiyo Cement Corporation R&D Center, Japan ; Lund Institute of Technology,.
    Yamada, K.
    Taiheiyo Cement Corporation R&D Center, Japan.
    Nilsson, L-O
    Lund Institute of Technology.
    Hosokawa, Y.
    Taiheiyo Cement Corporation R&D Center, Japan.
    Multi-species Ionic Diffusion in Concrete with Account to Interaction Between Ions in the Pore Solution and the Cement Hydrates2007In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 40, no 7, p. 651-665Article in journal (Refereed)
    Abstract [en]

    The penetration and leaching of ionic species in concrete are studied by using a model based on the Nernst-Planck equations. A finite element procedure is used to solve the coupled non-linear governing equations. A numerical example is performed in which the results are compared to measured electron probe micro analysis (EPMA) data. A close agreement of the simulated results to measured data is found for the specific studied example. The model includes the ionic species Cl-, Na+, OH-, Ca2+, K+ and SO42- and solid phases with variable composition. From the EPMA measurements the total concentration profiles of Cl-, CaO, SiO2, Na2O and SO3 are evaluated on samples exposed to a 3 wt% sodium chloride solution for one year. The main task in this investigation is to quantitatively understand the underlying mechanisms and find an accurate model that gives good correlation with the experimental results concerning the multi-species action during chloride penetration. In the model the chemical interaction between ions in solids and in pore solution is assumed governed by simple ion exchange processes only. The drawback using this approach is that the chemical part is lacking important physical relevance in terms of standard solubility thermodynamics. On the other hand the presented model is capable of accurately simulate the well documented peak behavior of the chloride profiles and the measured high content of calcium ions in pore solution under conditions when also chlorides is present. In this sense the established multi-species models for concrete based on standard solubility calculations alone is still incomplete.

  • 50. Johannesson, Björn
    et al.
    Yamada, Kazuo
    Hosokawa, Yoshifumi
    An approach for the evaluation of combined process of chloride penetration and carbonation by a multi – species model, Journal of research of the Taiheiyo Cement Corporation2005Report (Refereed)
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