Zbyšek Pavlík

Interlaboratory comparison of hygric properties of porous building materials

The precision of methods used for the determination of hygric properties of porous building materials was investigated. The study was performed in the framework of the EU-initiated HAMSTAD-project. Six laboratories measured the selected hygric properties of three porous building materials. While the most measured properties show acceptable agreement, yet, it was found that some of the existing standards or commonly accepted measurement methods need improvement. Most striking were large variations in the results of the vapour transmission tests performed in accordance to the existing European Standard.

A Comparison of Different Techniques to Quantify Moisture Content Profiles in Porous Building Materials

Several advanced non-destructive techniques are available to measure the evolution of content profiles with time, allowing the analysis of unsaturated flow and the determination of the moisture diffusivity of porous building materials. The reliability of six different techniques is investigated: the NMR-technique, the MRItechnique, the γ-ray attenuation technique, the capacitance method, the X-ray projection method and the TDR-technique. All of them were applied to measure the moisture content evolution during free uptake experiments on two building materials. Considering the limitations of some of the techniques, a good overall agreement is obtained. The work presented is an outcome of the EU-initiated HAMSTAD-project.

Determination of the liquid water diffusivity from transient moisture transfer experiments

The Boltzmann transformation method is used to determine the liquid water diffusivity from moisture content profiles as measured in a capillary water absorption experiment. An inter-laboratory comparison for analyzing the reliability of the determination method showed that the inaccuracy in the liquid water diffusivity is caused by scatter in the transformed data and by uncertainty in the boundary conditions at the intake surface and ahead of the steep moisture front. A methodology is proposed based on (1) the evaluation of the validity of the diffusion approach, (2) a simplified handling of the boundary conditions, (3) smoothing of the scattered data and (4) the evaluation of the quality of the determined liquid water diffusivity. For HAM (Heat-Air-Moisture transport) calculations values of the liquid water diffusivity for moisture contents higher than the capillary moisture content are disregarded. The liquid water diffusivity can be described by an exponential function limited at a lower moisture content bound. To describe the moisture diffusivity including liquid water and water vapour transports, a new parametric description of the moisture diffusivity is presented, which shows sufficient flexibility both in the hygroscopic and overhygroscopic ranges. When permeability is calculated from diffusivity, the permeability should monotonically increase with decreasing capillary pressure. In the hygroscopic region it should coincide with the measured water vapour permeabilities.

Experimental analysis of coupled water and chloride transport in cement mortar

Abstract Coupled water and chloride transport in cement mortar is analyzed experimentally in the paper. Samples with initial moisture content corresponding to 45% relative humidity are subjected to one-sided sodium chloride-in-water solution uptake, and moisture profiles and chloride concentration profiles are determined in three chosen time intervals. In the evaluation of measured moisture profiles and chloride concentration profiles, diffusion model is employed. Moisture diffusivity is determined as function of moisture content and chloride diffusion coefficient as function of chloride concentration using two methods commonly used for analysis of moisture profiles, namely the double integration method and the Matano method. The highest values of both coefficients are obtained by Matano method for the curves corresponding to 24 h exposure to the solution, the lowest values by Matano method for 168 h, the results obtained by double integration method are in between. The complementary experiments with distilled water as penetrating liquid performed for the sake of comparison do not show this feature. It is observed that water transport in the initial time period is for the chloride solution faster and in later times slower than for distilled water. Therefore, the observed differences in the calculated apparent values of moisture diffusivity and chloride concentration coefficients are attributed to the fact that Cl− and Na+ ions are adsorbed on the pore walls faster than water molecules. This effect should be included into the mathematical models using ion binding isotherms.

Water Vapor Adsorption in Porous Building Materials: Experimental Measurement and Theoretical Analysis

An experimental and theoretical analysis of the water vapor adsorption in several types of porous building materials is presented. For the measurement of adsorption isotherms, a DVS-Advantage water sorption device is used. The experimental data is analyzed using theoretical formulas based on the BET, BSB, BDDT, and FHH isotherms, assuming a mono as well as multi-layer water vapor adsorption. The BSB equation is found to provide a good approximation for the relative humidities below 0.6–0.7, whereas the FHH equation shows a sufficient accuracy for the relative humidities above 0.4–0.5. Based on a combination of BSB and FHH isotherms, a semi-empirical formula is proposed that allows one to obtain a very accurate approximation of experimental data for all analyzed materials and all values of the relative humidity.

Determination of Moisture Diffusivity using the Time Domain Reflectometry (TDR) Method

The time domain reflectometry (TDR) method is commonly used for the measurement of moisture content in soil science. In this study, the method is employed for the measurement of moisture profiles in building materials. The practical applications of the method are presented on an example of water penetration into cellular concrete (aerated autoclaved concrete) samples. The measured results are then used for the determination of moisture diffusivity as a function of moisture content.

Effective thermal conductivity of hollow bricks with cavities filled by air and expanded polystyrene

Effective thermal conductivity of hollow bricks with the cavities filled by either air or expanded polystyrene is analyzed using a hybrid experimental–computational approach. The experimental setup involves an application of a thermal insulation box and a set of temperature and heat flux probes placed at characteristic positions of the specimen-insulating box system. Using the measured heat fluxes and temperatures, the heat loss of the system is determined. A computer simulation tool based on the finite element principle is then used for modeling the temperature fields and heat losses in the studied system. Finally, the effective thermal conductivity is identified using an iterative procedure. Experimental results show that the application of expanded polystyrene as cavity filler instead of air leads to ∼30% decrease in the effective thermal conductivity of hollow brick blocks.

Properties of municipal solid waste incineration ashes with respect to their separation temperature

Fly ashes generated by power and heating plants are commonly used in the production of building materials in some countries, mainly as partial replacement of cement or aggregates in concrete. The ashes from municipal solid waste incinerators can be applied in a similar way. However, their chemical and mineralogical composition, granulometry and toxic constituents have to be taken into account. In this paper, four types of municipal solid waste incinerator (MSWI) ashes produced by the modern MSWI facility in Liberec, Czech Republic, were investigated. The relationship between the particular ash properties (morphology, chemical composition) and its separation temperature in the incinerator line is discussed. A coal fly ash (class F) is characterized as well, for a comparison because its utilization in building industry is more developed. The studied MSWI ashes exhibit high concentration of chlorides and sulfates which is an unfavourable feature for a potential concrete admixture. On the other hand, three of four ashes are found to be pozzolanic active and certain hydration reactions are indicated.

System for Testing the Hygrothermal Performance of Multi-Layered Building Envelopes

A measuring system for determination of temperature, moisture, relative humidity, capillary pressure and salinity profiles in building envelopes is presented in the paper. The system makes it possible to analyze the hygrothermal performance of either particular materials or the whole building envelopes in the conditions of difference climate. Both the spatial dimensions of the specimens and the applied exterior and interior climatic data are chosen to be as close as possible to the conditions in the particular building site, so that the system can simulate the hygrothermal processes in the envelopes in quite a realistic way. A sophisticated technology for the determination of moisture, relative humidity, capillary pressure, temperature and salinity in the analyzed specimens based on the application of timedomain reflectometry, mini-tensiometry and mini-hygrometry is employed, which guarantees obtaining reliable data for validation of sophisticated computational models.

Service Life Assessment of Historical Building Envelopes Constructed Using Different Types of Sandstone: A Computational Analysis Based on Experimental Input Data

Service life assessment of three historical building envelopes constructed using different types of sandstone is presented. At first, experimental measurements of material parameters of sandstones are performed to provide the necessary input data for a subsequent computational analysis. In the second step, the moisture and temperature fields across the studied envelopes are calculated for a representative period of time. The computations are performed using dynamic climatic data as the boundary conditions on the exterior side of building envelope. The climatic data for three characteristic localities are experimentally determined by the Czech Hydrometeorological Institute and contain hourly values of temperature, relative humidity, rainfalls, wind velocity and direction, and sun radiation. Using the measured durability properties of the analyzed sandstones and the calculated numbers of freeze/thaw cycles under different climatic conditions, the service life of the investigated building envelopes is assessed. The obtained results show that the climatic conditions can play a very significant role in the service life assessment of historical buildings, even in the conditions of such a small country as the Czech Republic. In addition, the investigations reveal the importance of the material characteristics of sandstones, in particular the hygric properties, on their service life in a structure.