Papers by Keyword: Mechanical Properties

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: Pozzolanic materials and their usage in concrete production are nowadays widely spread. Their application as additives is inherent especially for the purpose of high strength concrete. This article deals with evaluation and comparison of the influence of two different supplementary cementitious materials on the properties of high strength concrete: natural pozzolana (NP) and finely crushed brick (FCB). The studied characteristics are basic physical properties with connection to mechanical parameters, and next to this, characterization of water transport. In the scope of this study results revealed better pertinence of finely crushed brick, as the appropriate replacement of cement was found out to be up to 30%, whilst for natural pozzolana only 10% of cement substitution is favourable. The open porosity as the first indicator of both mechanical and water transport properties appeared to be lower in all studied mixtures with FCB than in the case of NP. With increasing ratio of the additive to cement there is significant worsening of mechanical and water transport parameters when NP is involved. The behaviour of mixtures with FCB is better even when high amount of cement is substituted.

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: 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: 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: Parameters of cement pastes with ceramic powder as partial Portland cement replacement up to 40 mass% are presented in the paper. Ceramic powder belongs to the pozzolanic materials. Utilization of pozzolanic materials is accompanied by lower request on energy needed for Portland clinker calcination which generally results in lower production costs of blended binder and lower CO₂ emissions. The ceramic powder is used in cement based pastes composition in amount of 8, 16, 24, 32, and 40 mass% of cement. For the studied ceramic powder, chemical composition is measured by X-Ray Fluorescence. The particle size distribution of ceramics is accessed on laser diffraction principle. Bulk density, matrix density, and total open porosity are measured for 28 days cured paste samples. The obtained results demonstrate that ceramic powder has potential to replace a part of Portland cement in composition of cement based composites.

Abstract: The sustainability principles in building sector promote a development of new building materials and products directly designated for improvement of the thermal performance of buildings related to the energy saving for the interior climate conditioning. In order to comply with this concept and improve the thermal comfort of buildings environment, incorporation of phase change materials (PCMs) into the construction elements giving ability to store and release heat looks like a beneficial material solution. On this account, the mechanical, rheological and thermal properties of cement-lime dry plaster mixture with addition of 4, 8 and 12 mass% of PCM water dispersion are experimentally investigated in the paper. The increasing amount of applied PCM admixture causes the significant improvement of the plaster heat storage capacity in dependence on temperature exposure applied in the performed DSC experiment. Contrary to this positive finding, the higher content of tested polymer microencapsulated PCM in plaster matrix leads to the lower mechanical strength. However, it is still sufficient for construction applications.

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: Hydroxyapatite (HA) is a ceramic material broadly studied due to its great similarity with the human bone. However, this material presents high stiffness and young modulus in comparison with the bone tissue. The polyhydroxybutyrate (PHB) is a themoplatic and biodegradable polymer that presents bone like young modulus and gradative degradation that results in a permanence of the mechanical properties after implantation. The aim of this study is to evaluate the effect of the infiltration of melted PHB on the mechanical properties of porose HA bodies. The composite samples were characterized by SEM, EDS and compressive strength. The samples produced with 10% paraffin and sintered at 1200 °C showed the best mechanical properties and reached an increase of the compressive strength from 29,00 ± 4,70 MPa before infiltration to 83,00 MPa ± 4,41 after infiltration with PHB for a final porosity of 5%.

Abstract: The aim of the research is to study the effects of compatibilizer on thermal and mechanical properties ofbiopolymer poly (lactic acid) (PLA) and natural rubber (NR) blends. PLA was blended with NR in the composition of 95/5 weight percentage with present of compatibilizer. The compatibilizers, PLA grafted maleic anhydride (MA) (PLA-g-MA) and NR grafted MA (NR-g-MA) were synthesized in a composition of 9 phr of MA by using internal mixer in presence of benzoyl peroxide (BPO). The formulations of PLA/NR blended with the compatibilizer were in the range of 1, 3, 5 and 10 wt.% of PLA-g-MA and NR-g-MA, respectively. Blending process was conducted using twin screw extruder then were pelletized and hot pressed before characterized. The mechanical (tensile, flexural, impact) and thermal properties of the blends was investigated and from the results, the addition of PLA-g-MA in PLA/NR blendimproved the impact strength and elongation at break of the blends as compared with neat PLA and PLA/NR blend without compatibilizer and for thermal stability, it only had a slight influence on the blends. Addition of NR-g-MA on contrary did not give improvement on mechanical properties but increasing in thermal stability.