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  • 1.
    Chen, Yang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per Gunnar
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Johansson, Anders
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Platell, P
    A comparative study of the carbon dioxide transcritical power cycle compared with an organic rankine cycle with R123 as working fluid in waste heat recovery2006In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 26, no 17-18, p. 2142-2147Article in journal (Refereed)
    Abstract [en]

    The organic rankine cycle (ORC) as a bottoming cycle1The expression "bottoming cycle" refers to the power cycle that uses waste industrial heat for power generation by supplementing heat from any fossil fuel.1 to convert low-grade waste heat into useful work has been widely investigated for many years. The CO2 transcritical power cycle, on the other hand, is scarcely treated in the open literature. A CO2 transcritical power cycle (CO2 TPC) shows a higher potential than an ORC when taking the behavior of the heat source and the heat transfer between heat source and working fluid in the main heat exchanger into account. This is mainly due to better temperature glide matching between heat source and working fluid. The CO2 cycle also shows no pinch limitation in the heat exchanger. This study treats the performance of the CO2 transcritical power cycle utilizing energy from low-grade waste heat to produce useful work in comparison to an ORC using R123 as working fluid. Due to the temperature gradients for the heat source and heat sink the thermodynamic mean temperature has been used as a reference temperature when comparing both cycles. The thermodynamic models have been developed in EES2EES - Engineering equation solver. The thermodynamic properties for carbon dioxide in EES are calculated by the fundamental equation of state developed by R. Span and W. Wagner, A new equation of state for carbon dioxide covering the fluid region form the triple-point temperature to 1100 K at pressures up to 800 MPa, J. Phys. Chem. Ref. Data, Vol. 25, No. 6, 1996. http://www.fchart.com/ees/ees.shtml.2 The relative efficiencies have been calculated for both cycles. The results obtained show that when utilizing the low-grade waste heat with the same thermodynamic mean heat rejection temperature, a transcritical carbon dioxide power system gives a slightly higher power output than the organic rankine cycle.

  • 2.
    Johansson, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Impregnation of concrete structures: transportation and fixation of moisture in water repellent treated concrete2006Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Water repellent agents, today mainly consisting of alkylalkoxysilanes, are often used on concrete to prolong the service life of the structure. This is accomplished by protecting the reinforcement bars from chlorides or by changing the moisture content inside. When the concrete is treated with a water repellent agent the properties of the surface layer turn from hydrophilic to hydrophobic and thereby water droplets are stopped from entering, still allowing water vapour to pass through. This property change can reduce chloride ingression and stop heavy rain from penetrating through the surface layer.

    This thesis presents results concerning how the moisture transport and fixation in the surface layer of the concrete is affected by a water repellent treatment. It also presents an investigation in which the effective penetration depth and the factors that influence it are studied. The methods used covers uni-dimensional transport of moisture using the so called cup method, measurements on moisture fixation using climate boxes with saturated salt solutions, penetration depth by cracking samples and spraying water on them, and field tests in a harsh tunnel environment.

    The moisture diffusion coefficient for a water repellent treated concrete is close to constant and not nearly as dependent on the relative humidity (RH) as for untreated concrete. Unlike untreated concrete, where capillary suction plays an important role for the moisture transport at high RH, the vapour transport is the dominant transport mechanism even at high RH for water repellent treated concrete.

    The moisture fixation is affected by a water repellent treatment and the effect is clearest at high moisture levels. There is, however, a certain amount of moisture present in a concrete treated with a water repellent agent. It can also be seen that the main reason for this is that the capillary porosity is affected by the treatment to a relatively high degree while the gel porosity to a large extent remains unaffected.

    The three most important factors for the penetration of any water repellent agent into concrete is time, porosity and degree of saturation. An empirical equation is derived that gives an idea on how much these factors affect the efficient penetration depth of the water repellent agent.

    Measures prolonging the service life of a concrete structure will lead to savings of natural resources and thus both economical and environmental savings for the community. The aim with the PhD-project is to develop explanation models to the promising results that have been obtained from the empirical research during the last decade and by doing this also create a better knowledge about when and how to apply a water repellent agent in order to benefit as much as possible from the product. The results presented in this Lisenciate thesis will be used as input in these models in the planned second phase of this project.

  • 3.
    Johansson, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Moisture Transport and Moisture Fixation of Impregnated Concrete Meeting2005In: XVIII Nordic Concrete Research Meeting, 2005Conference paper (Refereed)
  • 4.
    Johansson, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Penetration Profiles of Water Repellent Agents in Concrete as a Function of Time-Determined with FTIR-Spectrometer2008In: XX NCR Meeting, 2008, p. 46-47Conference paper (Other academic)
  • 5.
    Johansson, Anders
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Janz, Mårten
    Silfwerbrand, Johan
    Trägårdh, J.
    Moisture fixation in concrete treated with a water repellent agentIn: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873Article in journal (Other academic)
  • 6.
    Johansson, Anders
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Janz, Mårten
    Silfwerbrand, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Trägårdh, Jan
    Impregnation of concrete structures - introduction to a PhD-project2005In:  Proceedings Hydrophobe IV: water repellent treatment of building materials, Freiburg, Switzerland: Aedification Publishers , 2005, p. 59-68Conference paper (Refereed)
    Abstract [en]

    Moisture is the source of most damage in concrete bridges, such as frost damage and reinforcement corrosion. Experiments and field investigations show that impregnation with silanes and siloxanes provide good protection against moisture for at least eight to ten years. But most of the research only verifies this without providing a reason for the positive results. This project analyses how common impregnation substances work in concrete. Additionally, the authors develop models in order to explain these effects. As a first step, it is important to obtain reliable data on how the moisture diffusion coefficient is affected by hydrophobic treatments. Some of the factors investigated are how the water-cement ratio and the impregnation depth will influence moisture transport. One of the goals is to create a computer model to predict the moisture and chloride content over time when the geometry, the material properties of the concrete structure and the environmental conditions are known.

  • 7. Johansson, Anders
    et al.
    Janz, Mårten
    Silfwerbrand, Johan
    Trägårdh, Jan
    Long Term Performance of Water Repellent Treatment: Water Absorption Tests of Field Objects in Stockholm2008In: International Journal on Restoration of Buildings and Monuments, ISSN 0947-4498, Vol. 14, no 1, p. 39-47Article in journal (Refereed)
  • 8.
    Johansson, Anders
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Janz, Mårten
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Silfwerbrand, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Trägårdh, Jan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Moisture Diffusion Coefficient of Impregnated Concrete2005Conference paper (Other academic)
  • 9. Johansson, Anders
    et al.
    Janz, Mårten
    Silfwerbrand, Johan
    Trägårdh, Jan
    Moisture transport in impregnated concrete: Moisture Diffusion Coefficient, Modelling, Measurements and Verification2006In: Journal on Restoration of Buildings and Monuments, ISSN 1864-7022, Vol. 12, no 1, p. 13-24Article in journal (Refereed)
    Abstract [en]

    In order to understand the mechanisms of water repellents it is important to have reliable data on how the moisture diffusion coefficient is affected by a hydrophobic treatment. The results from the experiment described below will be used as input data in a project aiming to create a computer model for simulations of moisture and material transport in impregnated concrete structures. Two types of concrete with wo /c = 0.8 and 0.45 have been investigated by means of the cup-method to determine the moisture diffusion coefficient. Half of the specimens have been completely impregnated with trietoxy(isooctyl)silane by capillary suction and the other half were left untreated. This silane is one of the most common used water repellents on the Swedish market. Four different saturated salt solutions are used to create a relative humidity (RH) between 85 % and 97 % inside the cups while the surrounding environment is kept at 50 % RH. Three cups for each situation, two cups with pure water and four cups for verification give a total of 54 cups. The weight of the cups has been monitored weekly until a constant weight loss per unit time is obtained. With the use of Kirchhoff's potential in the calculations, the cup method is an efficient way of measuring the moisture diffusion coefficient. The moisture diffusion coefficient for treated concrete is found to be close to constant and less influenced by the RH compared to untreated concrete. Further, the results have shown that the transport of water vapour is highly reduced after a water repellent treatment. The accuracy of the method is verified at conditions of low humidity and a one dimensional steady state flow.

  • 10.
    Johansson, Anders
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Janz, Mårten
    Silfwerbrand, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Trägårdh, Jan
    Penetration depth for water repellent agents on concrete as a function of humidity, porosity and time2006In: Restoration of Buildings and Monuments, ISSN 1864-7022, Vol. 12, no 1, p. 3-16Article in journal (Refereed)
    Abstract [en]

    Water repellent agents are used on concrete to change the conditions for moisture transport and fixation and thereby protect the concrete and the reinforcement bars from, e.g., chlorides, frost damage and alkali silica reactions. The most frequently discussed topic regarding water repellent treatments is the penetration depth of the agent. What is required and what is needed to achieve it? The effective penetration depth of a water repellent agent is defined as the distance from the surface to the sharp line between dry and wet concrete after it has been sprayed with water. During the past decade several papers have been published where factors having a major influence on the penetration depth for different water repellent agents have been investigated. The conclusions that can be drawn from these papers are that the three most important factors are time, porosity and degree of saturation. The time referred to is the duration of contact between the water repellent agent and the concrete surface. The porosity and degree of saturation refer to the concrete pore system and the amount of moisture inside the concrete at the time of the impregnation. There is, however, a lack of investigations quantifying the influence of these factors. This paper presents an empirical equation that gives an idea on how much these factors affect the efficient penetration depth of the water repellent agent. The equation is based on 300 new tests described and analysed in the paper. It is clear that the polymerisation rate of the water repellent agent affects the penetration depth. A fast reaction has the effect of slowing down the penetration.

  • 11. Johansson, Anders
    et al.
    Janz, Mårten
    Silfwerbrand, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.
    Trägårdh, Jan
    Sorption Isotherms of Water Repellent Treated Concrete2008In: Proceedings, Hydrophobe V, 2008, p. 261-271Conference paper (Refereed)
  • 12.
    Johansson, Anders
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Janz, Mårten
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Trägårdh, J.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Silfwerbrand, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Long-term Measurements on Chloride Ingress in Water Repellent Treated Concrete in a Road Tunnel Environment2008In: Hydrophobe V: the 5th International Conference on Water Repellent Treatment of Building Materials, 2008, p. 327-328Conference paper (Other academic)
  • 13. Johansson, Anders
    et al.
    Nyman, B.
    Silfwerbrand, Johan
    Decreasing Humidity in Concrete Facades after Water Repellent Treatment2008In: Hydrophobe V, 2008, p. 379-386Conference paper (Refereed)
  • 14. Johansson-Selander, Anders
    et al.
    Janz, Mårten
    Silfwerbrand, Johan
    Trädgårdh, Jan
    Preventing Chloride Ingress in Concrete with Water Repellent Treatments2010In: CONSEC’10, 2010Conference paper (Refereed)
  • 15. Johansson-Selander, Anders
    et al.
    Janz, Mårten
    Silfwerbrand, Johan
    Trägårdh, Jan
    Moisture Fixation in Water Repellent Treated ConcreteArticle in journal (Other academic)
  • 16. Johansson-Selander, Anders
    et al.
    Janz, Mårten
    Silfwerbrand, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Trägårdh, Jan
    Penetration profiles of Water Repellent Agents in Concrete as a function of Time: Determined with FTIR-Spectrometer2010In: Int. journal Nordic Concrete Research, Vol. 41, no 1, p. 51-60Article in journal (Other academic)
  • 17. Johansson-Selander, Anders
    et al.
    Janz, Mårten
    Silfwerbrand, Johan
    Trägårdh, Jan
    Water Repellent Treatments: The importance of reaching a sufficient penetration depth2010In: CONSEC’10, Merida, Mexico, 2010Conference paper (Refereed)
  • 18.
    Selander, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.
    Hydrophobic Impregnation of Concrete Structures: Effects on Concrete Properties2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Hydrophobic impregnations often referred to as water repellent agents, today mainly consisting of alkylalkoxysilanes, are often used on concrete to prolong the service life of the structure. This is accomplished by protecting the reinforcement bars from chlorides or by changing the moisture content inside. When the concrete is treated with a water repellent agent the properties of the surface layer becomes hydrophobic and thereby water droplets are stopped from entering, still allowing water vapour to pass through. This change can reduce chloride ingress and stop heavy rain from penetrating through the surface layer.

    This thesis presents results concerning how the properties of concrete are affected by a hydrophobic impregnation. Moisture transport and fixation in the surface layer of the concrete are studied as well as the secondary effects of more practical use such as the effect on chloride ingress, water absorption and humidity level. It also presents results on how the penetration depth and concentration of the water repellent agent (i) depend on a number of parameters, and (ii) affect the outcome of the treatment. Water repellent treatments on a number of different concrete structures in Stockholm, ranging from tunnel to high-rice building, are evaluated as well.

    The three most important factors for the penetration of any water repellent agent into concrete are time, porosity and degree of saturation. A semi-empirical equation is derived that gives an idea on how much these factors affect the efficient penetration depth of the water repellent agent. The depth and concentration have a major effect on the performance of the treatment.

    The moisture diffusion coefficient for a water repellent treated concrete is close to constant and not nearly as dependent on the relative humidity (RH) as for untreated concrete. Unlike untreated concrete, where capillary suction plays an important role for the moisture transport at high RH, the vapour transport is the dominant transport mechanism even at high RH for water repellent treated concrete.

    The moisture fixation is affected by a water repellent treatment and the effect is clearest at high moisture levels. The main reason for this is that the capillary porosity is affected by the treatment to a relatively high degree while the gel porosity to a large extent remains unaffected. A hypothesis is presented which suggests that the RH inside the concrete at the time of the treatment affects not only the depth and concentration but also in which range of pore radii the water repellent agent is present and active.

    The durability of hydrophobic impregnations can be divided into surface effects and in depth effects. The first is sensitive to the environmental and mechanical loadings and normally disappears within a year while the later can be long lasting if a sufficient depth is reached.

    Hydrophobic impregnations are not the answer to all problems in concrete related to moisture, but if correctly used it can prolong the service life of the structure which will lead to savings of natural resources and thus both economical and environmental savings for the community.

  • 19.
    Silfwerbrand, Johan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Selander, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Storsatsa på nyttiga innovationer2008In: Betong, ISSN 1101-9190, no 6 (december), p. 43-45Article in journal (Other academic)
1 - 19 of 19
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