Michaela Kostelecká

Experimental Investigation of Mechanical Properties of Textile Glass Reinforcement

Mechanical tests were performed at the Klokner Institute on samples of a textile glass reinforcement. These tests will be used for determining the modulus of elasticity of textile glass reinforcements and for assessing the maximal stress that the samples will withstand. Both of these quantities are required for further modeling of the structures and for designing elements made from textile reinforced concrete (TRC). The tests were carried out on a total of 10 samples made from a single piece of 2D net (produced by V. FRAAS, GmbH, Germany). The tests were carried out on AR-glass reinforcement (alkali - resistant glass) textile glass with 2400 TEX [g/km] fineness, which is often supplied with dimensions of 1 x 2 m. The first 5 samples were prepared in the direction of the warp (the direction of the load-bearing reinforcement), and the remaining 5 samples were prepared from the transverse direction (the direction of the weft). These samples were loaded by a constant force increasing up to collapse. Then the modulus of elasticity of the textile glass reinforcement and the stress at the strength limit were determined from the monitored data.

Use of Textile Reinforced Concrete – Especially for Facade Panels

In recent years, textile reinforced concrete (TRC) is at the beginning of industrial production mainly in Germany and relates especially to facade panels and concrete footbridges. The subtle panels with a minimum thickness of coverage layer can be designed due to the textile reinforcement, which is resistant to corrosion. Furthermore, a long durability is expected in case of these structures. The textile reinforcement with the fine-grained ultra-high performance concrete (UHPC) enables to produce concrete elements with a minimum thickness. Therefore, the concrete element with up to 70 % lower weight compared to element with conventional reinforcement can be produced and significant environmental savings can be achieved (reducing the consumption of non-renewable raw materials, transport energy, reduced dead load acting on the supporting structure, etc.).

The Comparison of Moisture Balance of Diffusion-Open and Diffusion-Closed Structure of a Building Envelope

This article is oriented toward the heat-moisture behaviour of the wooden construction sheeting. The behaviour of building envelope is evaluated according to the heat transfer coefficient and foremost from the view of the condensed vapour amount inside the building envelope structure. For exemplary building envelope will be elaborated model calculations and then they will be compared. The results have shown that diffusion-open structure has the best characteristics concerning the heat-humidity behaviour and ecology of wooden constructions.

Textile Concrete in Adverse Conditions

Textile concrete (TRC) is a modern material that has been the subject of many scientific studies over the past two decades. It is a material based on a fine-grained cement-based matrix, fiber reinforced, fabric of acrylic-resistant glass, basalt or carbon reinforcement. The products from this material are thin-walled elements, which can be used, for example, for facade claddings elements, lost formwork, shell structures, garden architecture or for strengthening or repair of existing structural elements. This paper presents some examples of the behavior of glass reinforced textile concrete during exposure to road salts, under load of bending moment, at long-term loading at elevated temperatures, and assessment of glass fiber resistance during exposure simulating concrete pore solution.

Improving resistance of high strength concrete (HSC) bridge beams to frost and defrosting salt attack by application of hydrophobic agent

HSC (High Strength Concrete) is increasingly used for bearing bridge structures nowadays. Bridge structures in the Czech Republic are exposed to severe conditions in winter time and durability of the concrete is therefore a crucial requirement. The high strength and low water absorption of HSC suggests that the material will have high durability. However, the situation may not be so straightforward. We carried out a study of the very poor durability of HSC concrete C70/85 used to produce prestresed beams 37.1 m in length to build a 6-span highway bridge. After the beams were cast, a production control test indicated some problems with the durability of the concrete. There was a danger that 42 of the beams would not be suitable for use. All participants in the bridge project finally decided, after extensive discussions, to attempt to improve the durability of the concrete by applying a hydrophobic agent. Paper will present the results of comparative tests of four hydrophobic agents in order to choose one for real application and describes this application on construction site.

Determination of Mechanical Properties of Non-Conventional Reinforcement

Mechanical tests of samples of basalt and textile glass reinforcement were performed within the solution of the research project GAČR 13-12676S and SGS14/171/OHK1/2T/31. These tests were carried out because of the need to establish elementary mechanical quantities that are tensile strength and modulus of elasticity of non-conventional reinforcement. Both of these quantities are required for further modeling of structures and for designing of the elements made from textile reinforced concrete (TRC) as not being provided by reinforcement manufacturers. The tests were carried out on a total of 12 samples of reinforcement where the first 6 samples were made from textile glass reinforcement (AR-G = Alkali-Resistant Glass) and the remaining 6 samples were prepared from basalt reinforcement. The filament sheaf fibers called roving was used for the production of test specimens.

To Monitoring the Degradation of UHPC Boards with Textiles Armatures

In this article the hot water test is presented on thin UHPC slabs that are reinforced by a new type of armature. It is a textile armature, which should replace the classic metal (steel) armature. Textile armature should not only reduce the cost of production, but, because it is not susceptible to corrosion as conventional steel armature, panels can be designed with significantly less cover thickness in achieving similar or longer lifetime of these elements. The combination of UHPC concrete with a minimum thickness of cover and textile armature allows design elements weighing up to 70 % lower compared to conventional concrete elements with conventional armature. This can achieve significant savings and benefits not only in economic aspects, but also in environmental aspects.

Investigation of Glass Fibre Reinforced Cement (GFRC) Material Exposed to High Temperatures

In this paper we present the tests of high temperatures resistances of glass fibre cement plates. The aim of the research was to determine the values of tensile strength in bending for samples subjected to annealing at temperatures 200, 300, 400 and 500 °C in endurance at the highest temperature level for 24 hours. The bending strength was performed according to the norm EN 1170-4. The thermal dilatometric analysis was performed in the temperatures till 540 °C.

The Monitoring of Shrinkage of the PVA Cement-Plates

This paper presents results of a series of shrinkage tests. Described tests were performed on asbestos-free plates. The shrinkage represents very important role in monitoring of length changes for different orientation of the fibers. The results showed that humidity significantly influenced dimensions change of tested fibrecement plates. Length change ratio of dried plates and saturated plates represented the most significant difference that reached 0.25 %. Influence of fibres orientation on the length change was not confirmed. The difference in both measured direction was the same because of varied humidity impact. Elimination of free shrinkage is predominantly given by matrix, influence of fibers is not significant.

Application of Laser Microscope System for Evaluation of Separation Agents

This paper demonstrates application of laser confocal scanning microscope system for fair-face concrete surface evaluation. Measure system presents a new generation optical system for identification and description of esthetical imperfections of various building materials. System enables 3D observation and high-precision 3D measurement in real time.