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Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020; Aachen : RWTH Aachen University 1 Online-Ressource (XX, 238 Seiten) : Illustrationen, Diagramme (2020). = Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020, Crack repair is often necessary to ensure the durability and serviceability of concrete and reinforced concrete structures. Normally, surface protection systems, repair mortar/concrete, or steel-reinforced concrete are used for the surface repair of these components. The latter are often not suitable either for static or space reasons (e.g. underground garages, roofs, cellar walls, or weir systems). The unreinforced systems, on the other hand, lack a durable sealing functionality, especially in the case of cyclically moving cracks and joints due to their limited bond strength and crack-distribution ability. For the permanent repair of water-bearing, cyclically moving cracks and joints, DURTEX layers consisting of Carbon Textile Reinforced Concrete (CTRC) in combination with a de-bonding strip can be used. Such a combination not only enables a fine crack-distribution but also offers a sealing function against water and can be used under the aspect of durability and thus cost-effectiveness. In this thesis, experimental investigations were carried out to fill the gaps in knowledge on the topics of crack-distribution and autogenous self-healing of DURTEX layers for the repair of the cyclic crack opening of concrete and reinforced concrete components. To assess the requirements for crack width limitation, durability, mechanical resistance, water tightness, and long-term stability, the crack-distribution, as well as the bond strength, is investigated in extensive laboratory tests in the context of this thesis. In the first step, a test procedure for the DURTEX layer for both single and combined loads was developed. An essential part was the realistic depiction of the temperature-related crack width changes of the substrate and the exact measurement of the individual crack widths in the CTRC layer. These were analyzed with an optical 3D-measurement system in combination with Digital Image Correlation (DIC)-software. The laboratory tests carried out include the characterization of the design parameters repair mortar/concrete, de-bonding strip, polymer impregnated carbon textile reinforcements (CTRs) as well as performance tests on the composite bodies. Based on the results of the laboratory tests, the relevant parameters are identified and the performance and limits are derived. In general, it was shown that the subsequent surface modification of the epoxy impregnated carbon textile reinforcement (EPI-CTR) consisting of an epoxy coating and sprinkled with quartz sand (EPI+S-CTR) leads to an increase in the adhesive tensile strength perpendicular to the reinforcement plane by at least 35 % compared to the EPI-CTR. At the same time, the crack spacing is reduced to the single roving axis distance of the EPI-CTR, the number of continuous cracks is increased to its maximum (referred to as ideal crack-distribution) and the average crack width is reduced by 33 % up to 50 % in the CTRC perpendicular to the direction of tensile loading. In the context of this thesis, the surface roughness of the CTR, the roving axis distance of the CTR, the reinforcement ratio, the de-bonding width, the bond strength between repair mortar/concrete and CTR as well as between de-bonding strip and repair mortar/concrete perpendicular to the reinforcement plane were identified as decisive factors influencing the crack-distribution in DURTEX layers. It was observed that cracked DURTEX layers with w_(max.) = 0.116 mm, under cyclic loading (initial Δw_op = 0.6 mm) with a 5 m pore and crack water pressure can self-heal themselves leading to water tightness after 14 days., Published by RWTH Aachen University, Aachen

The exposition of concrete members to a chloride containing environment can lead to depassivation and corrosion of the reinforcement. A special configuration is generated if the concrete structure is only partly contaminated with chloride ions, whereas the other parts of the reinforcement remain passive. The self corrosion of the active reinforcement is superposed by the effect of a galvanic element, which leads to high metal removal rates and therefore to relevant restrictions of the structure durability. The macrocell current is influenced by a considerable number of factors. One important factor is given by the ohmic resistance between active and passive reinforcement parts, which is dependent on the specific concrete conductivity and the geometrical arrangement of both electrodes. The investigations of the geometrical influence were carried out by a combined approach consisting of laboratory experiments and numerical analyses. The laboratory program covers a wide range of practical standard cases. In the course of the numerical simulations additional cases with varying boundary conditions like surface area ratios, driving voltages and concrete resisitivities were analysed. The results allow a direct comparison of different structural members and geometrical arrangements in terms of the corrosion risk and enable a quantification of the leading influencing parameters. Furthermore the resulting data base was used to show how parameters like controlling and cell factors can be derived to describe the geometrical influence. These allow an estimation of the resulting macrocell current in order to assess the remaining life time or the determination of target values, e.g. the necessary concrete resistivity, as part of maintenance strategies.

If concrete is used as a building material the tensile strength of the reinforcement is one of the most important material properties. Traditionally concrete is reinforced with steel rebars. Textile reinforced concrete (TRC) represents a new and innovative building material, in which the reinforced is made out of technical textiles. Technical textiles are made out of AR-glass or carbon. Even the glass is considered to be alkali-resistant, the AR-glass reinforcement shows a certain loss of tensile strength over the live time of a building member. This strength loss can be up to 40% during an exposure time of 50 years. This loss of strength is mainly caused by an alkaline attack of the glass network due to the high alkalinity of the pore solution of concrete. Due to the requirements of the load-bearing capacity as well as the handling during the production of TRC building members, the reinforcement structures used meanwhile are impregnated with polymers. As polymers there are two different kinds used – water-based dispersions, e.g. SBR-dispersions, or reactive coatings, e.g. epoxy resins. The polymer-impregnation cannot only increase the load-bearing capacity but can also decrease the loss of strength of AR-glass. In order to quantify the long term loss of strength of such polymer-impregnated AR-glass reinforcement structures within the presented thesis a prediction model, called the "hull-model", was developed. The model is based on intensive laboratory research, which covers investigations of the single components of TRC (concrete, AR-glass reinforcement and polymers) as well as the compound material. Based on these laboratory investigations the deterioration mechanisms, which lead to a reduction of the tensile strength, could be identified. The physical as well as chemical processes, which lead to an decrease of the tensile strength, represent the basics of the model. The parameters of the model can all be determined by (comparatively simple) laboratory investigations. One of the main parameters, which affect the long-term loss of strength, is the diffusion coefficient of the polymer used to impregnated the AR-glass. In general the polymer-impregnation with epoxy resin leads to a reduction of the long-term loss of strength by the factor of 2. The model also allows identifying the main parameters, which affect the long-term loss of strength of polymer-impregnated AR-glass. The diffusion coefficient of the polymer as well as the shape of the reinforcement both affects the long-term loss of strength dramatically. Low diffusion coefficients (such as typical for prepreg-epoxy systems) as well as compact reinforcement cross-sections minimize the strength loss.