Materials Science Forum Vol. 824

Abstract: The article describes the influence of fine natural pozzolana as supplementary cementitious material on the properties of high strength concrete. Natural pozzolana (NP) is a porous material which results in higher porosities and thus lower compressive strength when used in high replacement levels. But if only a small part of cement (up to 10% of weight) is substituted by NP it has positive consequences. The open porosity is on the contrary lowered, resulting in better strength in compression. Thermal characteristics are as usually enhanced with the growth in the content of pores which is in disagreement of mechanical properties and durability of concrete.

Abstract: Following article deals with experimental investigation of elevated temperatures influence on mechanical properties of refractory cement composite, which seems to be very progressive and interesting field of material science. Specimens 40 x 40 x 160 mm³ were exposed to 600 °C and 1000 °C for three hours. Using of aluminous cement, in this case Secar®71 with70 % of Al₂O₃, means the basic premise for refractory composites. Natural crushed basalt aggregate of two fractions 0-4 mm and 2-5 mm works as filler. Metakaolin MefistoL05 in amount 225 kg/m³ represents the fine filler, commonly used in refractory concrete production. Ceramic fibers or combination of two lengths of basalt fibers significantly improve the flexural characteristics. The goal of this research is to quantified influence of basalt fibers and ceramic fibers on flexural strength, compressive strength and bulk density of cement composite in high temperature conditions.

Abstract: In this article selected properties of a glass and polypropylene fibre reinforced cement composite materials are studied. They are determined either after preceding thermal treatment or during thermal loading. Basic physical properties (in concrete terms bulk density, matrix density and open porosity), mechanical properties (in concrete terms tensile strength and bending strength) are determined after subjecting the specimens to the pre-heating temperatures of 600°C, 800°C and 1000°C. The linear thermal expansion coefficient is measured directly as functions of temperature up to 1000°C. The critical temperature for the glass and polypropylene fibre reinforced cement composite when most properties are worsening in a significant way is found apparently 500°C.

Abstract: This contribution brings summary of refractory hydraulic binder issue. The refractory cement composites (or refractory concrete) represent very specific area of modern material engineering. We can find its use in special monolithic structures in industry, for fire-resistance brick, protection cladding, etc. The composition brings opportunity for using aluminous cement with different amount of Al₂O₃, according to temperature level. Hydration process and products together with the decomposition due high temperatures is described in this paper. Also the risk of conversion metastable hydration to stable one is described. The issue of possible bonds between filler and binder is shown (hydraulic, ceramic and chemical). Paper also describes values of fracture energy of aluminous cement pastes with various water to cement ratio after temperature loading.

Abstract: High performance fiber reinforced concrete (HPFRC) became very popular material due to its high strength, elastic modulus, corrosion and fire resistance. However, detail description of HPFRC behaviour is necessary for its application and an effective building design and development. Here, also the fire safety of buildings must be considered. Therefore, the effect of elevated temperature on HPFRC is studied in the paper. For the reference material, experimental assessment of basic physical and mechanical properties is done. Then, the HPFRC samples are exposed to the temperatures of 600 and 800 °C respectively, and the effect of a high temperature exposure on material structure is examined. It is found that the applied high temperature loading significantly increases material porosity due to the physical, chemical and combined damage of material inner structure, and negatively affects also the pore size distribution.

Abstract: This article is focused on state of knowledge about experimental testing of uniaxial tension strength of specimens from cement-based composites. We searched for various types of experimental testing of tensile strength, shapes of specimens or type of reinforcement. There is our own experimental program at the end of this article. Our aim is to find the best way to test steel fibre reinforced cement matrix for textile reinforced concrete in oneaxial tension. Textile reinforced concrete has many advantages (e.g.: no covering layer, higher ductility) and may be used instead of common steel reinforced concrete or as a method to repair old structures (e.g.: to bind columns).