Study On The Test Methods For The Hygric Properties Of Porous Building Materials

The hygric properties of porous building materials are indispensable parameters in theanalysis of heat and moisture transfer in building envelopes. The reliable determination ofthem is important for the design of building envelopes, the analysis of indoor hygrothermalenvironment, as well as the calculation of the energy consumption of buildings.In this thesis autoclaved aerated concrete (produced in China and Belgium), calciumsilicate board and ceramic brick are chosen as target materials. The best methods for weighingand drying their samples are studied first. Theoretical and experimental results reveal that forlarge samples it is acceptable to weigh them directly, while for small samples it is better toseal them in non-hygroscopic containers during the weighing process. For most materialsoven drying at70°C is recommended.Next, referring to many international and national standards, static gravimetric tests, cuptests, capillary absorption tests, vacuum saturation tests and pressure plate tests are performedunder various conditions. The sorption isotherms, vapor permeability, water absorptioncoefficient, capillary saturation moisture content, liquid diffusivity, bulk density, openporosity, vacuum saturation moisture content and moisture retention curve of these materialsare determined. Results show that the repeatability errors of these tests are generally smallerthan the inhomogeneity errors from materials. In addition, within10-40°C, the influence oftemperature on all these properties is limited, except for the capillary absorption coefficientand liquid diffusivity (their temperature dependence can be predicted by the Lucas-Washburnequation). What’s more, different influence factors (such as sample sizes, intermediate steps,pre-conditioning methods, test time and pressure control) are studied. It is proved that testresults are generally not sensitive to these factors. Moreover, the experimental facilities forcup tests, capillary absorption tests and pressure plate tests are improved. Methods forexpressing the results from static gravimetric tests and cup tests are innovated. It is alsoproved that ordinary linear fitting is accurate enough for analyzing the first stage in thecapillary absorption test.Finally, the influence of errors from material properties on the moisture transfercalculation is studied. The one-dimensional steady-state vapor diffusion process is taken asthe example. Study shows that the constant vapor permeability will cause noticeable errors onthe vapor flow rate calculation. The influence of errors from vapor permeability on vapor flowrate is constant, while the influence of errors from moisture content and RH depends on theactual moisture content and RH.