Measurement and modelling moisture transport processes within porous construction materials
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AbstractMoisture is one of the primary factors connected with the damage observed on the envelope of buildings. The moisture states are normally dominated by moisture transport processes within and between porous building materials from rain penetration, rising damp or infiltration of water vapour that is normally accompanied with heat transfer. The research into moisture transport behaviour of building materials is extremely important for the characterisation of behaviour in connection with durability, waterproofing, degradation of appearance and thermal performance ofbuilding elements. In the first stage of this research, commercial gypsum plasters were experimentally investigated with their moisture transport specifications. The hydraulic parameters including sorptivity, saturated conductivity and permeability of water vapour were determined with new findings related with the dependence of hydraulic parameters on water/plaster ratios, wetting-drying cycles and additives. The results obtained were compared with other porous building materials and recommendations for their manufacture and selection in building construction were made. Secondly, on the basis of comprehensive investigations of the dielectric properties of gypsum plasters, an integrated automatic real-time monitoring system for moisture transport processes was designed and successfully developed utilising a pin-type resistance sensor and sensor array. The data acquisition, data analysis, result display and saving are all integrated with the computer controlled interface. The polarisation effects and temperature effects for various gypsum plaster materials were compensated and realised by control options. The monitoring system developed for moisture monitoring was directly applied in 1-dimension moisture transport processes and can easily be extended to the monitoring of 2 or 3 dimension moisture transport processes by embedding an appropriate sensor array into materials. In the third part of the research, on the basis of experimental investigation of water absorption processes of uniform materials and two-layer composites, the water diffusivity as functions of moisture content were determined from experimental moisture profiles for various gypsum plaster materials. The models governing the moisture transport processes were formed based on extended Darcy's law and experimental diffusivity functions. By applying the finite element method and developed software, the non-linear partial differential equations were numerically solved under specified boundary and initial conditions in absorption processes. The simulation results achieved satisfactory agreement with experimental moisture profiles for various materials and for two-layered composites.
CitationWang, Q. (2005) 'Measurement and modelling moisture transport processes within porous construction materials'. PhD thesis. University of Luton.
PublisherUniversity of Bedfordshire
TypeThesis or dissertation
DescriptionThesis submitted for the degree of Doctor of Philosophy at the University of Luton
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