Materials Science Forum Vol. 824

Abstract: The suitability of a water vapor transport parameter determined by the cup method for the description of water vapor transport in porous building material is analyzed in the paper. The relative humidity profiles are measured by a transient method with different water vapor pressure gradients. Moisture profiles calculated using a mathematical model are compared with the measured profiles. The goodness-of-fit tests are calculated for different experimental setups. The possibility of application of the analyzed water vapor transport parameter is discussed.

Abstract: The rate of transport of liquids in porous environment is crucial engineering problem. It has importance in many fields like chemical engineering, hydropedology, economic geology and also in building materials science. The intensity of a liquid transport in porous body can be analyzed be means of three concepts – sorptivity, permeability and diffusivity. The approaches applied in field of porous rocks are discussed. Water absorption coefficients of set of sedimentary rocks of wide porosity range were determined experimentally and the relationship between them and specific pore volume of rocks was found.

Abstract: In this paper, there are summarized the results of an experimental program focused on basic, mechanical and thermal properties of cement composites according to the high – temperature loading. Four different materials were studied, which differed in used kind of cement and amount of fibers. As a matrix for studied composites the aluminous cement was chosen because of its resistance in high temperature. For a comparison the Portland cement was also tested. The second main ingredient used to provide better resistance in high temperatures - the basalt aggregate, was mixed in every specimen. The basalt fibers were chosen for two of the measured samples, remaining two ones were tested without fibers. The obtained data in this presented analyses show that the application of the aluminous cement leads to increase (depending on temperature) of porosity, which is the cause of decreasing of the coefficient of thermal conductivity. It can seems, that these cement composites will have low mechanical strength in high temperatures, but because of better sintering, the aluminous cement keeps its strength in high temperatures better than Portland cement.

Abstract: Salts and water may cause serious damage to historical masonries. Therefore, numerous conservation treatments have been developed by research teams for the consolidation and protection of porous building materials affected by salt attack. Here the focus is on methods for obtaining an effective desalination of historical masonry, indicating their advantages and disadvantages. It is pointed out that cellulose is a favourite material added to poultices used in desalination.

Abstract: Carbonation is chemical process associated with CO₂ penetration into the material porous structure causing subsequent chemical changes in the structure of cement pastes. In this work, carbonation of several pastes containing varying amount of cement replacement by three waste ceramic powders is studied. Chemical composition of particular tested materials is accessed using XRF analysis. Matrix density, bulk density, total open porosity, compressive and bending strength are measured for all developed pastes with incorporated ceramic materials. Simultaneously, the effect of carbonation on these material properties is researched. The obtained results show significant improvement of materials mechanical strength due to the carbonation. Here, the measured compressive strength is typically about ~ 60% higher for materials exposed to CO₂ rich environment compared to the materials cured in laboratory conditions.

Abstract: The paper deals with self-compacting concrete (SCC) and the change of its properties after exposure to thermal loading. Two types of microfillers were used (along with appropriate amount of superplasticizer) to gain concrete which would meet the requirements for SCC – limestone powder and fly ash. Specimens were subjected to temperatures of 600 °C for 2 hours. Results proved significant worsening of all studied parameters on samples after the thermal loading. Therefore studying of material exposed to different external conditions for better simulation of real life of construction is important in future research.

Abstract: Lime and cement-lime industrially produced dry plaster mixtures are widely used building materials. These surface treatments can come into the contact with salt solutions which cause their degradation. On this account, the influence of calcium nitrate and calcium chloride water solution exposure on mechanical properties of several commercially produced mortars is researched in the paper. The prismatic specimens having dimensions of 40/40/160 mm are cured 28 days in humid environment. Then, the studied specimens are stored 112 days in both salt solutions and reference environment of distilled water. At specific time intervals, the compressive and bending strengths are measured and the obtained data are discussed.

Abstract: Present paper deals with the experimental investigation of static modulus of elasticity of hardened concrete and its relation to compressive strength of concrete. Based on the number of measurement was derived expression of dependence of modulus of elasticity on compressive strength of concrete which was determined using cubic specimens; modulus of elasticity was measured using prismatic specimens of dimensions 100x100x400 mm. Studied concrete mixtures present commonly used concrete of all established strength classes.

Abstract: This article deals with cement matrix for the textile reinforced concrete. It is necessary to know maximum of the mechanical properties of cement matrix for using textile reinforced concrete. The main topic of this article is to determine stress-strain diagrams at various age of the cement matrix. The compressive strength of the cement matrix was determined by using cube specimens (100 x 100 x 100 mm). The cement matrix, steel fibre reinforced cement matrix and ordinary concrete C 30/37 were tested at age 12 and 18 hours and 1, 7, 28 and 45 days. Cubes were tested in one-axial press. Loading of cubes was controlled by increase of deformation. Speed of loading was 0.008 mm/s. Time, load force and deformation were recorded for determination stress strain diagrams. The results of the experimental program and stress-strain diagrams were compared with each other in conclusion of this article.

Abstract: This contribution deals with interesting and progressive curing method applied to fresh concrete matrix for textile reinforced concrete production. The application of high pressure 0.3 MPa and temperature 130 °C in 100 % humidity environment for 4 hours was performed. Cement matrix and steel fibers reinforced cement matrix has been investigated. The goal of this research is to quantified compressive strength, flexure strength, bulk density and dynamic modulus of elasticity of both mixtures. These parameters were investigated after hydrothermal curing process at the ages 6, 12, 15, 18, 21 and 24 hour after first contact of water with cement. All parameters were investigated on specimens 40 x 40 x 160 mm³ and the destructive tests were controlled by increase of deformation. Special curing condition led to an increase of the compressive strength by more than 10 % in case of cement matrix, and by more than 40 % in case of fiber reinforced cement matrix.