Advanced Materials Research Vol. 897

Abstract: The article deals with the assessment of three brick powders. Their properties are evaluated on the basis of their pozzolanic activity, specific surface area and amorphous area. The brick powders were used in amounts of 20 and 40% as a substitute for binder in lime mortars. The influence of the powders on the properties of the modified plasters in a hardened state was evaluated via the determination of strength characteristics. It was found that not all brick powders are suitable for use in modified lime mortars.

Abstract: Modulus of elasticity of building materials can be determined in a static way (loading in a press) or by means of non-destructive test methods (ultrasonic pulse method and resonance method); the parameter is most frequently determined for concrete and both methods of determining elasticity modulus are codified in Standards. Elasticity characteristics of calcium silicate bricks were determined by means of resonance test method. Because the shape of calcium silicate bricks (a block with oblong foot) is different from the shape of test specimens for concrete (usually blocks with square foot), expected frequencies for verification of accuracy of measurement by resonance method were determined. Moisture content of calcium silicate bricks (water absorbing capacity is up to 12-14%) has influence on the value of resonance frequency. Difference between dynamic Young's modulus of elasticity from fundamental longitudinal and transverse resonant frequency is on average 2.8%.

Abstract: Corrosion of reinforcements is one of the most frequent causes of defects of reinforced concrete structures resulting in significantly shortened service life of constructions. By using of corrosion inhibitors the structure failures can be prevented or already started corrosions slowed down and thus to markedly prolong the service life of constructions.

Abstract: Acoustic emission is an experimental tool well suited for monitoring fracture processes. The paper presents experiment focused on analysing acoustic emission signals captured during three-point bending fracture test of specimens of concrete. Quantitative acoustic emission techniques were used to measure micro fracture properties. For three different concrete mixtures typical acoustic emission patterns were identified in the acoustic emission records to further describe the under-the-stress behaviour and failure development. If we have a better understanding of the relationships between micro structural events and macroscopic behaviour we can better formulate predictive models for large-scale structural performance and reliability. An understanding of microstructureperformance relationships is the key to true understanding of material behaviours. Three-point bending fracture tests were conducted on these specimens and load versus crack mouth opening displacement (Load-CMOD) diagrams were recorded during the testing.

Abstract: Current times emphasize utilization of new and promising building materials with no negative environmental impact, for reasonable price and with excellent end-use properties. Insulation materials based on natural fibers represent a good alternative for current standardly used insulation materials like foamed plastic materials and mineral wool. Input materials for such industrial insulation materials are particularly crude oil and non-renewable natural resources (moreover, manufacture of these insulation materials consumes high amount of energy). From this point of view, natural insulation materials are more advantageous, because their manufacture uses easily renewable materials resources, like fibers from agriculture (flax, technical hemp). However, these materials have two disadvantages higher sensitivity to humidity (higher water absorbing capacity and hygroscopic nature) and worse reaction to fire. The paper deals with selection of appropriate hydrophobic agent preventing high sensitivity to humidity of developed natural materials and monitoring of moisture content after application of hydrophobized materials within the frame of the ETICS system.

Abstract: FRP (Fiber Reinforced Plastic) materials are corrosion resistant not requiring any specific treatment. The utilization of these materials is expanding. New research works have started to focus on using these materials on self-contained formwork in composite systems. It allows decreasing the concrete cover on minimum value just to assure sufficient bonding between reinforcement and concrete (the influence of aggressive environment is minimal). Moreover, the stay-in-place formwork is self-contained. It means using this system as formwork during casting of concrete and another supporting structure is not needed. The paper is focused on experimental analysis of stay-in-place GFRP (Fiberglass Reinforced Plastic) formwork in composite system (three-functional GFRP formwork and reinforced concrete slab – RC slab) and its use on floors in building structures. The load-carrying capacity of the composite system is highly influenced by quality of cohesion between GFRP formwork and concrete. This cohesion was investigated by using “push tests”. The results from experimental push tests were compared with the numerical model and also will serve for numerical modelling of real bonding of the girders.

Abstract: Reinforced concrete is a versatile, economical and successful construction material. Usually, it is durable and resistant material, performing well throughout its service life. However, sometimes it does not perform adequately as it is expected. It is due to poor design, construction, inadequate materials selection and more severe environment than anticipated or a combination of those factors [1, . The reinforcement corrosion is the phenomenon that highly affects the reliability and durability of reinforced concrete structures. From that reason, a lot of researchers in Slovakia and in the world pay their attention to reinforcement corrosion. The paper is concerned with detection and simulation of corrosion of steel reinforcement in the reinforced concrete. The cracking response of the reinforced concrete beams due to the corrosion effect of the steel reinforcement was analyzed. The effect of corrosion was simulated by the nonlinear numerical analysis using the program ATENA.

Abstract: Sustainable building materials are based on the use of renewable materials instead of non-renewable. A large group of renewable raw materials are materials of plant origin containing cellulosic fibres which are used as filler into building material with reinforcement function of composite. This study aimed to establish the mechanical and physical properties of cement composites with organic filler, such as wood pulp. Pulp derived from wood pulping process is very interesting material as reinforcement in cement which contributes to a reduction of pollutants. In this paper, utilization of unbleached and bleached wood pulp in combination with cement matrix with emphasis on the physical and mechanical properties is studied. Varying the producing technology (wood pulp and cement ratio in mixture) it is possible to obtain composites with density from 940 to 1260 kg.m^-3 and with compressive strength from 1.02 to 5.44 MPa after 28 days of hardening. The experimental results of mechanical properties indicate that cement composites with using unbleached wood pulp reaches higher values than composites based on bleached wood pulp. The percentage of water uptake increased with increasing the volume ratio of unbleached wood pulp in composite.

Abstract: The chloride diffusion in limestone cement concrete exposed to combined chloride and sulfate solutions at low temperature was studied. For this purpose, a normal Portland cement and two Portland limestone cements (15% and 35% w/w limestone content) were used for concrete preparation. The specimens were immersed in two combined chloride-sulfate solutions of different sulfate content, and stored at 5°C. The total and free chloride contents, as well as the chloride diffusion coefficients were determined for each concrete composition. The results show that the total chloride content and free to total chloride ratio are increased with time. The sulfate content of the corrosive solutions has not a clear effect on total chloride content and chloride diffusion coefficient. It seems that the lower sulfate content results, in general, in higher free to total chloride ratio values. The use of limestone in cement results in higher chloride concentrations in concrete and free to total chloride ratio values. In general, these phenomena are intensified for higher limestone content.

Abstract: The Slovak natural raw material kaolin sand containing 36 wt.% of kaolinite from Vyšný Petrovec deposit was thermally transformed at 650 °C for 1 hour to the metakaolin sand with relevant content of metakaolinite. Behaviour of cement composites having replacement of Portland cement with metakaolin sand including 0; 5; 10 and 15 wt.% of metakaolinite and water to solids ratio of 0.5 cured in water for 28 days and 90 days was studied by thermal analysis, X-ray diffraction analysis and mercury intrusion porosimetry analysis. The study concerned calciumsilica hydrate and calcium aluminate hydrate formation, portlandite dehydroxylation and calcite decarbonation. The influence of curing time and metakaolinite content were estimated. The replacement of Portland cement by metakaolin sand led to positive effect on relevant compressive strengths. The changes in microstructure involved especially reduction in portlandite content and pore structure refinement.