Milena Pavlíková

Free Water Intake as Means of Material Characterization

Free water intake experiment is analyzed from the point of view of the applicability of its output for material characterization. Several experimental setups are presented and discussed. Characteristic examples of sorptivity plots for different materials are given and their main features have been described. The application of the experiment for characterization of material damage and for explaining the water transport mechanisms in two-layer systems is presented. It is concluded that the free water intake experiment basically can be used as a means of material characterization but its strong and weak points should always be considered if conclusions on the behavior of a particular material are to be drawn.

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.

A Boltzmann transformation method for investigation of water vapor transport in building materials

A Boltzmann transformation method that allows determination of water vapor transport properties of building materials as functions of relative humidity during a single experiment is presented. The method is tested at the laboratory measurements on autoclaved aerated concrete. Determination of diffusion coefficient by standard steady-state cup method is done as well, for the sake of comparison. The measured results are discussed with regard to the practical application of the method in materials research and building practice.

Effect of temperature on water vapor transport properties

The temperature effect on water vapor transport properties of calcium silicate is studied, together with the influence of sample thickness. For material characterization purposes, the bulk density, matrix density, and total open porosity are measured at first. Sorption and desorption isotherms are measured using dynamic vapor sorption device in order to characterize the water vapor storage in researched material. The sorption process is analyzed for original material samples as well as for finely ground samples in order to evaluate the effect of inner porous space on water vapor storage. The steady state cup method is used for determination of water vapor transport properties, whereas the measurements are performed at several temperatures and for three different sample thicknesses. The obtained data show an important effect of temperature on water vapor transport and storage in studied material. The results also indicate a substantial influence of sample thickness on the calculated water vapor transmission properties.

Classification of a-SiO2 Rich Materials

The powder materials containing active SiO2, which are used as pozzolanic active materials in cement mixtures, can be classified in consideration of their pozzolana activity, particle size or reactivity. In this paper, several types of metakaoline are studied using Frattini and modified Chapelle test for pozzolanic activity determination. The particle size analysis is measured using the laser diffraction analyser and the differences in the chemical composition are characterized by FTIR spectroscopy. The obtained data show influence of particle size and chemical composition of tested powders on their pozzolanic activity, which corresponds with the results of Frattini and modified Chapelle test.

Coagulated silica - a-SiO2 admixture in cement paste

Amorphous silica (a-SiO2) in fine-grained form possesses a high pozzolanic activity which makes it a valuable component of blended binders in concrete production. The origin of a-SiO2 applied in cement-based composites is very diverse. SiO2 in amorphous form is present in various amounts in quite a few supplementary cementing materials (SCMs) being used as partial replacement of Portland cement. In this work, the applicability of a commercially produced coagulated silica powder as a partial replacement of Portland cement in cement paste mix design is investigated. Portland cement CEM I 42.5R produced according to the EU standard EN 197-1 is used as a reference binder. Coagulated silica is applied in dosages of 5 and 10 % by mass of cement. The water/binder ratio is kept constant in all the studied pastes. For the applied silica, specific surface area, density, loss on ignition, pozzolanic activity, chemical composition, and SiO2 amorphous phase content are determined. For the developed pastes on the basis...

Application of a-SiO2 Rich Additives in Cement Paste

The effect of a-SiO2 of various origin on the properties of cement paste with incorporated different silica containing materials is experimentally studied in the paper. For the applied a-SiO2 materials, basic physical and chemical properties are accessed, together with their chemical composition. Amount of amorphous phase of SiO2 in particular siliceous materials is determined using XRD analysis. Matrix density, bulk density, total open porosity, compressive and bending strength are measured for all developed pastes with incorporated a-SiO2 containing materials, together with initial and final setting time of fresh mixtures. The obtained data give evidence on a high and fast reaction activity of tested siliceous materials which results in a significant improvement of porosity and mechanical strength of a-SiO2 modified cement pastes.

Characterization of Building Stones Involved in Historical Masonry

Basic physical properties, pore size distribution and hygric properties of several types of stones which are used in reconstructions of historical buildings on the territory of the Czech Republic, namely several types of sandstone and argillite, are investigated. Basic physical characteristics are measured using the water vacuum saturation method, pore distribution by mercury porosimetry. Values of water absorption coefficient and apparent moisture diffusivity are determined by methods utilizing the results of water sorptivity measurements. Water vapor transport properties are accessed by the cup method. The obtained data represents valuable information for the application of studied materials in reconstructions and renewal of historical buildings.

UHPFRC at high temperatures – Simultaneous thermal analysis and thermodilatometry

Simultaneous Thermal Analysis (STA) and Thermodilatometry Analysis (TDA) are done to reveal the structural and chemical changes in UHPFRC during its high-temperature load. Based on the measured results, several physical and chemical processes that studied material underwent at high-temperatures are recognized. In the temperature interval from 25 to 300 °C, the liberation of physically bound water from pores and the dehydration reaction of C-S-H take place. Additionally, AFt and AFm phases dehydrate at 110 – 156 °C. Endothermic peat at 460 °C corresponds to the portlandite decomposition. At 575 °C, the α → β transformation of quartz is found. This reaction is accompanied by a sharp endothermic heat flow peak and a volume expansion, whereas no change of mass is measured. In the temperature interval 580-800 °C, the calcite and C-S-H gels decomposition is monitored. At the temperature above 800 °C, there is one significant exothermal peak corresponding to a crystallization of wollastonite. In summary, STA and...

Thermophysical properties of hydrophobised lime plaster – Experimental analysis of moisture effect

Lime plasters are the most popular finishing materials in renewal of historical buildings and culture monuments. Because of their limited durability, new materials and design solutions are investigated in order to improve plasters performance in harmful environmental conditions. For the practical use, the plasters mechanical resistivity and the compatibility with substrate are the most decisive material parameters. However, also plasters hygric and thermal parameters affecting the overall hygrothermal function of the renovated structures are of the particular importance. On this account, the effect of moisture content on the thermophysical properties of a newly designed lime plasters containing hydrophobic admixture is analysed in the paper. For the comparative purposes, the reference lime and cement-lime plasters are tested as well. Basic characterization of the tested materials is done using bulk density, matrix density, and porosity measurements. Thermal conductivity and volumetric heat capacity in the...