Introduction to heat transfer

Porous Materials Water in Porous Materials Flow in Porous Materials Unsaturated Flows Unsaturated Flow in Building Physics Composite Materials Evaporation and Drying Topics in Water Transport Appendices Symbols Used Properties of Water Minerals, Salts and Solutions Other Liquids Other Data

Water Transport in Brick, Stone and Concrete

Visualization of water penetration in cementitious materials with superabsorbent polymers by means of neutron radiography

Application of neutron imaging to investigate fundamental aspects of durability of cement-based materials: A review

Service life and durability of reinforced concrete structures have become a crucial issue because of the economical and ecological implications. Service life of reinforced concrete structures is often limited by penetration of water and chemical compounds dissolved in water into the porous cement-based material. By now it is well-known that cracks in reinforced concrete are preferential paths for ingress of aggressive substances. Neutron radiography was successfully applied to study the process of water penetration into cracked steel reinforced concrete. In addition, the effectiveness of integral water repellent concrete to prevent ingress of water and salt solutions was investigated. Results are described in detail in this contribution. It will be shown that neutron radiography is a powerful method to visualize the process of water penetration into cracked and uncracked cement-based materials. On the basis of the obtained experimental data, it is possible to quantify the time-dependent water distributions in concrete with high accuracy and spatial resolution. It is of particular interest that penetration of water and salt solutions into damaged interfaces between concrete and steel can be visualized by means of neutron radiography. Deteriorating processes in cracked reinforced concrete structures can be studied in a completely new way. This advanced technology will help and find adequate ways to improve durability and service life of reinforced concrete structures. This will mean at the same time an essential contribution to improved sustainability.

Neutron imaging of water penetration into cracked steel reinforced concrete

The measurement of moisture in building materials has been of importance to building professionals for many years to aid them in diagnosing the nature and cause of building defects. Likewise building researchers have developed an extensive selection of measurement approaches to aid them in more detailed studies of the fundamental physical processes that underlie moisture transport. This paper reviews current moisture measurement practices within the UK, and examines the more sophisticated techniques being utilised, including three particular techniques: dual probe heat pulse method; time domain reflectometry; and more sophisticated electrical approaches. These three are currently the focus of a study to evaluate how advanced research techniques can be applied to the in-situ measurement of moisture contents in practice.Practical application: This paper reviews the current UK application of measurement techniques to assessing the moisture content of building materials. It discusses the differences between the techniques used by building professionals and building researchers, and highlights potential areas currently in development which may yield more advanced site measurement options in the future.

Moisture measurement in building materials: an overview of current methods and new approaches

The successful application of moisture transport models to building envelopes requires accurate values of moisture permeability Unfortunately, although a considerable amount of information is available, much of this is in a form which is of limited use to a designer This paper examines the presentation of permeability data in terms of the concept of differential permeability This allows permeability values to be predicted accurately for the humidity conditions to which materials are exposed in practice Several suggested mathematical forms of the permeability-humidity functions have been compared by applying them to experimentally determined permeabilities for four representative building materials From this comparison the functional form which would provide the most appropriate basis for a standardised system of data presentation has been identified

Moisture permeability data: Mathematical presentation:

Condensation is now one of the greatest building problems of this decade, and it is essential that the mistakes of the past are not repeated in the future. Accurate predictive techniques for interstitial condensation are now being used widely, but calculations are only as accurate as the input vapour permeability data. Although a considerable quantity of data are available, much of these are shown to be of limited use, only applying to the conditions under which the material was originally tested. The vapour permeability of plasterboard and plywood is investigated and a new approach to the presentation of vapour permeability data is suggested.

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Interstitial condensation: Applicability of conventional vapour permeability values:

The assessment and control of hot working environments is based on an appraisal of the thermal interaction between an individual and the surroundings. This paper examines in detail the processes of convection, radiation and evaporation which constitute the principal mechanisms for this interaction. The defining equations are discussed with particular attention given to the appropriate numerical values of body heat and mass transfer coefficients. The use of the heat-mass transfer analogy for the prediction of the mass transfer coefficient is introduced and verified. Finally, recommendations are given as to the most appropriate set of energy exchange equations for use in the analysis of high-temperature environments. The physiological criteria involved in hot working conditions, and the generation of a suitable assessment procedure based on the energy exchange equations, are the subject of a companion paper.

https://journals.sagepub.com/doi/pdf/10.1243/PIME_PROC_1989_203_024_01

Occupational hot exposures: a review of heat and mass transfer theory.

The avoidance of condensation problems in the future depends on designers having available accurate and reliable vapour permeability values. The emergence of free trade within the European Community requires the transferability of measurement data between countries, as well as between individual laboratories. This paper describes a recent European intercomparison carried out to assess the comparability of existing permeability measurement techniques, and to provide the information required to enable future international standards to be properly formulated. Identical samples of two materials were tested by eleven laboratories covering thirteen European countries. At the beginning of the project detailed instructions were issued on all aspects of the test procedure. Even with such an approach, many of the participants failed to comply with all of the test requirements, and the data produced exhibited unacceptably large variations between laboratories. The major contributory factors for this are discussed, a...

R.C. McLean

Papers

Moisture measurement in building materials: an overview of current methods and new approaches

Moisture permeability data: Mathematical presentation:

Interstitial condensation: Applicability of conventional vapour permeability values:

Occupational hot exposures: a review of heat and mass transfer theory.

Vapour permeability: Suitability and consistency of current test procedures