CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)
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Thin concrete overlays wit carbon reinforcement on deteriorated concrete pavements
Get PDFIn many countries, concrete pavements are normally built as Jointed Plain Concrete Pavements. Due to a lack of alternatives, repairing deteriorated concrete pavements usually requires the replacement of the complete pavement structure and maintaining the joints, which is labour- and resource-intensive. To increase the durability of repairs and to save resources concrete overlays with carbon reinforcement are developed. By the application of non-corrosive carbon-textile reinforcement cracks might be distributed so fine, that such an overlay can be executed jointless, unlike in previous repair methods. For a durable repair the bond behaviour between the retained concrete and the overlay as well as between the overlay-concrete and the textile reinforcement have to be considered. In this paper, the basic principles and feasibility of such a repair method are examined. On the one hand, the decisive influencing variables and parameters such as bond behaviour and cracking behaviour within the overlay are pointed out and discussed. On the other hand, the performed special lab tests will be presented. These tests include cyclic loadings on large-scale beams with integrated overlays of such types, evaluating the bond behaviour and the durability after a few millions of load cycles. Furthermore, the crack formation in the overlay is determined by means of tensile and flexural tensile strength tests
Influence of steel fibers on the fatigue behavior of high-performance concretes under cyclic loading
Get PDFDue to the advancement of high-performance concretes, the development of filigree constructions has been improved in the last decades. However, as the demand to create more filigree designs increases, the vulnerability to fatigue loads of such structures has also become a decisive factor. Various construction projects, such as wide-span bridges or wind turbines, are exposed to fatigue loads. Especially wind turbines are permanently subjected to wind and wave loads of several hundred million load cycles during their service life. At present, the fatigue behavior of high-performance concretes under cyclic loading is still unknown. In a worst-case scenario, the significantly lower ductility can lead to a sudden failure of the entire structure. In this case, the addition of steel fibers could be advantageous, as they significantly improve the ductility of concretes. However, it is still undetermined how the material fatigue is influenced by steel fibers. Hence, systematic investigations on the fatigue behavior of various high-strength concretes with steel fibers were conducted. Since the crack-bridging effect of fibers is relevant for tensile stresses, predominantly cyclic bending tests were performed on concrete beams with different steel fiber variations. To accomplish the investigations, a test setup has been developed which allows the simultaneous testing of a total of six specimens. Based on the predetermined static concrete strengths, the specimens were subjected to cyclic loads with a defined lower stress level and various upper stress levels. During these cyclic tests, the cycles-to-failure as well as the degradation within the microstructure were detected
Research focused on low carbonation of concrete under old cement-based render
Get PDFIn-situ research and laboratory study of the concrete of old bridges shows that despite the low strength classes of concrete and the long time of exposure to CO2, it is possible to moderate the depth of their carbonation. Many old bridges were found during the in-situ survey in Slovakia, which showed negligible carbonation under an old cement render (PRC) even after more than 100 years of direct exposure to CO2. At the same time, it was found that if this protective layer was significantly damaged or missing in some places, the depth of carbonation of the same concrete reached considerable depths, locally 70-80 mm. The article presents and summarizes the findings from in-situ and laboratory research with a possible explanation of this phenomenon
Heat transfer model verification for thermal monitoring system of integral bridges
Get PDFThermal actions considered on abutments of integral bridges by the European standard (Eurocode 1) might be in variety of certain situations underestimated. Based on this assumption, thermal monitoring system has been designed and installed into structure of bridge No. 27-117. Temperature profiles in five certain spots are being measured to provide sufficient basis for evaluation of real thermal actions on abutments of integral bridges. For purpose of measurement verification, elementary heat transfer models for finite element method solver were created. These models are being loaded by simplified temperature profiles reached in real time in-situ. Evaluated models provide verification data to compare with measured temperature profiles in structure and might provide information about temperature profiles probably reached during extreme weather situations
Mesh generation and mechanical tests of basic element cells of porous structures
Get PDFAdvanced porous structures are novel, emerging materials with a broad range of applicability but a rather difficult means of design and manufacturing. The advent and availability of the additive manufacturing industry in the last decade has enabled for production of these structures via 3D printing of polymers and metals. This research deals with the design, mechanical testing and preparation of FEM meshes of novel gyroid structures manufactured by PA12 SLS 3D printing. As demonstrated, conventional means of CAD generation of these structures in the *.STL format are sufficient for manufacture of specimens, but not precise enough for the purpose of mesh generation for FEM due to errors in the geometry of tesselation. Mechanical tests show that the sheet gyroid variant is the preferable geometry as it offers the greatest peak compressive stress among all variants at the same material density
Adhesion test – testing of selected adhesives on fired clay
Get PDFThe following paper deals with the comparison of adhesion of specimens made of fired clay and selected adhesives. The adhesion was tested on specimens at the age of one, two and three days in order to determine the parameters of young masonry. Nine different adhesives (adhesives intended for masonry and adhesives for others material) were tested in total.The above mentioned test is not standardized. The obtained results from the adhesion test determine the tensile strength between the adhesive and the fired clay and the adhesion of selected adhesive to the fired clay. The small specimens were made of two ceramic plates and an adhesive. Selected adhesives were applied to ceramic plates according to the usual standards. Eighty-one small specimens were produced in total – twenty-seven specimens for the adhesion test at each defined age of the specimens (one day, two days, three days). The produced specimens were cured in the climatic chamber with set laboratory conditions until the time of the test. The specimens were tested in the laboratory of the Heluz brick plant in Dolní Bukovsko. This paper deals with the procedure of preparation of the specimens, the course of the test and the comparison of gained results
Steel elements with timber fire protection - experiment and numerical analysis
Get PDFSteel structural elements are sensitive to elevated temperatures, while timber elements have good thermal insulation properties. Timber material can fulfill the role of fire protection of steel members. The effect of the protection is demonstrated on an experiment with three beams with different levels of the protection, placed into a horizontal furnace. The experimental task was also numerically analysed with standard computational approach given by the Eurocode [1, 2], which leads to an interesting comparison, as the calculation is supposed to provide higher temperatures and larger deformations compared to the experimental data
Structural reliability of existing rc beams strengthened with UHPFRC tensile layers
Get PDFA methodology for reliability analysis of reinforced concrete (RC) beams strengthened with ultra high-performance fibre reinforced concrete (UHPFRC) tensile layers is presented. The proposed methodology includes stochastic stress-block analysis of a section, assuming a perfect bond between the RC beam and the UHPFRC layer. Annual reliability analysis of the RC beam before and after the strengthening operation is conducted. Deterioration induced by chloride corrosion is incorporated into the analysis via a chloride induced corrosion model based on Fick’s law of diffusion and described stochastically to account for the epistemic uncertainty in the time to corrosion initiation and rate of corrosion. A plot for determining the required thickness of the UHPFRC tensile layer to upgrade to the required reliability level is also given, considering the time from construction to when the strengthening operation is conducted. The proposed approach is easy to apply for routine practice
A procedure to derive partial safety factors in textile-reinforced concrete members
Get PDFIn the last decades, modern technological and research developments of textile-reinforced concrete have led to extensive applications in building and civil engineering structures all over the world. Examples of textile-reinforced concrete can be found in retrofitting of existing buildings, facade slabs or bridges. Despite its potential, the widespread use of textile-reinforced concrete remains still limited. This is partly explained by the lack of a consistent design framework since conventional design methods used for other materials (e.g., steel reinforced concrete) cannot be directly applicable to textile-reinforced concrete. Thus, procedures to derive partial safety factors for textile-reinforced concrete would be a major step forward towards a regular procedure for the design of structural members made of this material.This paper offers a general procedure to determine safety factors. The approach is illustrated with a bending design example of a textile-reinforced concrete facade slab. The example is calculated in a recently developed software package for structural reliability analysis built in the statistical programming language R. For the derivation of safety factors, initial data is required, which can be obtained from experimental or numerical tests or from literature. The paper includes the basics of data evaluation as well as the statistical characterisation of data extracted from literature
Concrete lintels reinforced with steel fibres oriented by a magnetic field
Get PDFThis paper explores the possibility of applying the technique of magnetic orientation of steel fibres for manufacturing a concrete structural element of realistic dimensions, compared to small laboratory specimens. This technique could be a part of an answer to the current need for faster and automated production in the prefabrication industry. The examined specimens have dimensions of commonly used lintels in construction, 80 mm × 100 mm × 980 mm. The properties of specimens with magnetically oriented fibres are compared with same size specimens prefabricated conventionally. The orientation of fibres has been confirmed by Q-factor non-destructive testing method using a measuring coil. All specimens were tested with a four-point bending test. The specimens with oriented fibres show a significantly higher flexural strength, by 150 %, than specimens produced conventionally with the same volume of fibres