The Baumberger Sandstone, a sandy limestone, is used since the Middle Ages as a building material not only in the surrounding Münster region of North Rhine-Westphalia (Germany), where it is quarried since to date. To prevent the ingress of water and reduce weathering processes conservation methods, mostly in form of organosilicon compounds, were used. This study deals with the performance of applied hydrophobing agents on Baumberger Sandstone samples and their influence on the weathering processes during long-term exposure. The samples were exposed at several locations in Germany to different climatic conditions for up to 24 years. Afterwards, investigations concerning the water absorption behaviour and the degree of superficial damages were carried out. With an evaluation method on basis of NMR measurements, a very low and uneven distributed effective hydrophobic zone could be detected. This caused an ingress of water in the uppermost part and a progressive weathering of investigated natural stones. Thus the hydrophobic surface treatment did not lead to a significant decrease of weathering or damaging processes. Based on these results a hydrophobic surface treatment of Baumberger Sandstone seems not to be suitable. © 2022, The Author(s).

Porosity changes in the near-surface area of sandstones due to long-term weathering can produce deterioration. Therefore, porosity analyses on weathered sandstones are significant for detecting possible influences on the pore structure. Classical methods for determining the porosity and pore size distribution in sandstones can only investigate the entire sample volume. In contrast, in this publication, the porosity was analysed in 0.2 mm steps over a depth of 5 mm by means of single-sided NMR measurements on water-saturated sandstones under vacuum. Evaluations of Obernkirchener and Schleeriether Sandstones that were weathered outdoors in Germany for over 30 years are presented. The results showed that the water content in Vol.-% strongly correlated with the normalised NMR signal. The unweathered sandstones showed a uniform distribution of micro and capillary pores throughout the stone depth. As a result of 30 years of outdoor weathering, changes in the pore structure occurred at the sandstone surface due to weathering down to depths of about 0.6 mm. The porosity of the Schleeriether Sandstone samples, mainly the microporosity, clearly increased in this region. Due to the dominance of capillary pores in the Obernkirchener Sandstone, the changes were not as pronounced, but a shift towards smaller pores in the surface area was observable. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.

In this study, selected natural stone prisms have been compared with each other to detect the effectiveness of the hydrophobic treatment on differently orientated surfaces. The samples have been examined after 2 and 17 years of weathering at two different locations in Germany. The examinations focused on certain criteria which are based on the research of the last four years. By measuring colour changes, not only the influence of different hydrophobing agents could be investigated, but also different stone deterioration patterns could be identified. It could be determined that the effectiveness of water repellents is significantly influenced by the penetration and distribution depth of the active substance. The results of non-destructive NMR measurements show that the durability of the stones is more influenced by the uniform distribution of the active ingredient and the penetration depth than by the surface orientation. Thus, for the Obernkirchener Sandstone, the efficiency of the applied agents was proven after 17 years of outdoor weathering. Despite determined effective hydrophobic zones, degradation of the natural stones could not be prevented. Measuring the damaged depth with NMR it was found out that water penetrates the stone within the first 500 to 1000 µm, even with an intact hydrophobic layer, and can cause surface changes, like biogenic growth and decomposition. In these degradation processes, the orientation of the samples again has a significant influence. Thus, the roof surfaces show stronger deterioration. © 2021 Elsevier Masson SAS

The composite material textile reinforced concrete (TRC) requires a high bond performance between the fiber strand and the concrete matrix. While the influence of the textile on bond behavior is well known, in this publication the influence of the concrete matrix is investigated by means of single-sided pull-out tests. The results of the presented study show dependence between the concrete strength and bond performance of the composite material. When a concrete of a higher-strength class is used, the bond-flow–pull-out distance curve shifts upward independent of the textile geometry and the yarn impregnation. A simplified model is presented to predict the occurrence of a crack along the fiber strand. This model serves as a basis to investigate the correlation between concrete width per fiber strand and resistance against a splitting crack. The effective concrete tensile strength decreases to about 35% when the concrete width is increased from 10 mm to 50 mm. To quantify the decrease, a mathematical relationship, which describes the test results independent of textile and concrete type, is proposed. © 2022 by the authors.

Numerous concrete monuments built in the High Modern Era (turn of the 20th century until the 1970s) must now be repaired for preservation. Traditional concrete repair according to current guidelines involves considerable material removal, changing the appearance of the existing structure. With a combination of the material properties of high-/ultra-high-performance concrete (HPC/UHPC) with its dense microstructure and corrosion-free textile reinforcement (carbon and basalt), a high-performance mortar repair system can be developed. Such a system allows for concrete repairs with minimal material loss by using very thin layers that are durable and do not change the architectural character of the repaired monument. For the investigation of the load-bearing behaviour of a structural repair system using textile-reinforced, high-performance mortar, 20 mm thick slabs were produced and mechanically characterized. In the next step, the proposed repair system was applied to 70 mm thick old concrete slabs. The results show that a high surface tensile strength of 2.9 MPa was obtained. In a further step, the system will be applied to concrete pillars of transmission tower in Berus, adapted in terms of colour and structure and installed for long-term monitoring. © 2022 by the authors.

Repairing and strengthening of existing aged steel-reinforced concrete structures is a ma-jor challenge. Today, much of the repair work completed is insufficient and brittle. A promising new solution for repair and strengthening tasks is the use of iron-based shape memory alloy (Fe-SMA). The pre-strained Fe-SMA components enable the pre-stressing of existing building components due to the heat-triggered contraction of the steel. Thus, deflections can be reduced or even recovered. In addition, the cracking process can be adapted, and an improvement in the load, under which the first crack appears, is possible. In this paper, the effects of pre-stress generated by activated Fe-SMA rebars, which were centrally embedded inside of a concrete specimen, are shown. The objective of the study is to quantify the improvement in the loads of the first crack and show the influences of the pre-stressing on the load-bearing behavior and the cracking process. For this purpose, axial tensile tests were performed on concrete bars with height, width, and length of 50 mm, 70 mm, and 900 mm, respectively. These were compared to usual construction steel rebars, pre-strained but nonactivated Fe-SMA rebars, and activated Fe-SMA steel rebars. The evaluation of crack patterns and openings was done using digital image correlation (DIC). The pre-stressing of the concrete causes an increase in the first crack loads of more than 150%, which indicates a clear improvement in the state of serviceability limit. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

Resource-saving noise protection elements made of textile reinforced concrete as an alternative for conventional precast reinforced concrete elements. This article describes the design, production and testing of a textile reinforced concrete bearing layer as an alternative for conventional reinforced concrete noise barrier elements. The use of non-metallic reinforcement structures allows a reduction of the concrete cover to a minimum required for the safe transmission of the bond forces. The resulting cross-section, which is optimized in terms of reinforcement structures and manufacturing costs, enables the concrete volume to be reduced by 2/3. For the material selection, various technical textiles are compared with each other and a textile configured specifically for the project is chosen. Small-format bending tests are used to adjust the material and cross-section properties, while the component design is carried out on the basis of large-format component tests. The result of the project is a new type of noise barrier element, which is characterized by a significantly lower overall component volume and weight and can nevertheless be manufactured economically. © 2021, Ernst und Sohn. All rights reserved.

Resource-saving noise protection elements made of textile reinforced concrete as an alternative for conventional precast reinforced concrete elements. This article describes the design, production and testing of a textile reinforced concrete bearing layer as an alternative for conventional reinforced concrete noise barrier elements. The use of non-metallic reinforcement structures allows a reduction of the concrete cover to a minimum required for the safe transmission of the bond forces. The resulting cross-section, which is optimized in terms of reinforcement structures and manufacturing costs, enables the concrete volume to be reduced by 2/3. For the material selection, various technical textiles are compared with each other and a textile configured specifically for the project is chosen. Small-format bending tests are used to adjust the material and cross-section properties, while the component design is carried out on the basis of large-format component tests. The result of the project is a new type of noise barrier element, which is characterized by a significantly lower overall component volume and weight and can nevertheless be manufactured economically. , Ernst und Sohn. All rights reserved.

Conservation methods on buildings and monuments made out of natural stone aim on preventing weathering processes, reducing their impact on site and consequently improving the long-term durability of building stones. For this purpose, nowadays particularly organosilicon compounds are used for the application on natural stones. In this study, single-sided NMR has been used to non-destructively detect the long-term efficiency of hydrophobing agents (silanes, siloxanes and silicone resins) applied on different porous natural stones (Baumberger and Obernkirchener Sandstone), which were naturally weathered for over 24 years on different sites in Germany. An evaluation system is presented, based on non-destructive NMR measurements, to assess the hydrophobic properties and the long-term stability of the treated stone surfaces. It could be shown, that the mineralogical composition as well as the type of hydrophobing agent and its active ingredient content have a significant influence on the long-term hydrophobic effect. © 2019 Elsevier Masson SAS

The durability of eleven different water repellents applied on one sandstone type was studied after a long-term weathering at seven different locations in Germany. By measuring colour changes, it could be shown that the formation of black crusts, the deposition of particles and biogenic growth caused a gradual darkening as well as significant changes in total colour over time. Additionally, the water absorption behaviour was investigated with two different methods: applying a low pressure using the pipe method and capillary water absorption measurements from a wet underlay. Afterwards, the test results were analysed with four different evaluation methods: calculation of the protection degree from pipe method and capillary water absorption, determination of the velocity of water uptake during capillary water absorption and calculation of the damaged depth of the stone surface using single-sided NMR technique. The growing damaged depth leads to an increase of the water uptake velocity and to a decrease of the protection degree of the applied hydrophobing agents. Three protective agents based on isobutyltrimethoxysilane showed already after two years of outdoor weathering a clear loss of performance, which significantly increased after 30 years of exposure. © 2020 by the authors.

Uniaxial tensile tests in textile reinforced concretes with inorganic impregnated carbon fibres. The composite material textile reinforced concrete is being increasingly used in building construction. In particular carbon textiles are used with different impregnation materials, which are bound in mortar or concrete. Numerous research and practical projects have led to individual approvals for specific cases being granted and first directives for designing and using textile reinforced concrete being developed. The development and optimization of these materials still have huge improvement potential. Until now, most textiles have been impregnated with epoxy resin, styrene-butadiene or acrylates. Beside the introduction of a polymer in the composite material, these polymers can cause load-bearing capacity losses under temperature stresses above 80 °C. Mineral impregnation materials have hardly been researched, but are particularly interesting for use in drinking water structures in order to avoid polymer-based materials. This publication shows that a very fine crack pattern can be achieved with inorganic impregnations of carbon rovings. Very small crack widths are particularly necessary in the repair sector, for example in the rehabilitation of drinking water reservoirs. In addition, mineral impregnations are less susceptible to temperature stresses. © 2020, Ernst und Sohn. All rights reserved.

The maintenance of existing concrete structures gains increasing importance. New challenges within this topic are the durability modelling of conservation measures and the timing of renewing them. One necessary step for the solution of these new challenges are needs-oriented non-destructive testing methods. For the first time, ever, a mobile nuclear magnetic resonance (NMR) sensor allows a non-destructive determination of relevant parameters directly on the building site. By positioning the NMR sensor on a lift analysing of the amplitudes and relaxation times can be done at different depths/positions inside the concrete cover. The determined parameters are: Ingress, distribution and transport of water as well as other liquids at the concrete surface (up to 25 mm depth beginning at the concrete surface) and effectiveness of concrete coatings including thickness of different coating layers. However, before this technique can be used on steel-reinforced concrete elements, the potential effect of the reinforcement on the measurement, i.e. the NMR signal, needs to be studied. This has been done in the frame of a wide test program. Firstly, influences from temperature changes and tilting of the sensor are discussed in the present paper. Afterwards results concerning the steel reinforcement influence on the investigations are named and a practical solution to consider the determined shift of the profile towards the steel is presented. © Springer International Publishing AG 2018.

Until now, there are installed 8.8 million square meters of noise protection walls in Germany. Due to the negative impact of noise pollution on our quality of life and the rising requirements on noise protection itself, the amount of noise protection walls will increase in the next decades. The commonly used steel reinforced concrete noise barrier consist out of a non-bearing noise protection layer based on lightweight concrete (LC) and a load-bearing layer based on normal steel reinforced concrete, which means an enormous usage of resources. At the "Department of Building Materials", TU Dortmund University, a study with the aim to reduce the weight of concrete noise protection wall elements up to a third has been started. In addition to transport and installation work aspects, the targeted material savings are intended to improve the carbon dioxide footprint. The material of choice for the new lightweight wall elements is textile reinforced concrete (TRC), which consists of a fine-grained concrete and a technical-textile reinforcement. In the first step of the study, two concepts for lightweight load-bearing structures out of TRC were developed and calculated. Both concepts incorporate the benefit of the corrosion resistance of carbon textiles. The first load-bearing concept uses TRC in combination with textile reinforced LC, while the second one employs TRC in a tee-beam shape additionally reinforced with glass fiber rebars. In preliminary investigations, both load-bearing concepts were tested and the tee beam shape has demonstrated a sufficient load bearing capacity. Furthermore, the results indicate that it is possible to reduce the total weight of the walls to less than a half. In the next step of the study, the dimension of the promising specimens will be up-scaled to those of common noise protection walls, while further load-bearing concepts have to be tested. © Springer International Publishing AG 2018.

A large number of infrastructural concrete buildings are protected against aggressive environments by coating systems. The functionality of these coating systems is mainly affected by the composition and thickness of the individual polymeric layers. For the first time ever, a mobile nuclear magnetic resonance (NMR) sensor allows a non-destructive determination of these important parameters on the building site. However, before this technique can be used on steel-reinforced concrete elements, the potential effect of the reinforcement on the measurement, i.e. the NMR signal, needs to be studied. The results show a shift of the NMR profile as well as an increase of the signals amplitude in the case of the reinforced samples, while calculating the thickness of concrete coating leading to identical results. © 2016 Polish Academy of Sciences.

Impact of the addition of silane and siloxane based hydrophobic powders on cement based mortar was studied. Effect of powder addition on mechanical properties and water absorption of cement based mortar is described. Impact of accelerated ageing, including UV radiation, and rain-sun cycles on hydrophobic performance was assessed, demonstrating excellent durability of silane-based hydrophobic performance. © (2013) Trans Tech Publications, Switzerland.

Even though several models exist in the literature to predict the strength durability of glass fibre (textile) reinforced concrete (GRC), a considerable gap still exists between theory and practice. No real guidelines are available for testing, model calibration and model selection. This work analyses all the uncertainties in the GRC strength durability determination process. The paper addresses the determination of the best approximating model by applying a statistical model selection method (Akaike's information criterion) on an extensive series of accelerated aging tests; a theoretical approach is presented which enables the user to check the reliability of the model selection. A method is presented for the determination of the uncertainty in the strength prediction, taking into account both the statistical distribution present on the (tensile) strength of the GRC material as well as the effect of model calibration based on a limited set of accelerated aging tests. © Institute of Materials, Minerals and Mining 2012.

A large number of infrastructural concrete buildings are protected against aggressive environments by coating systems. The functionality of these coating systems is mainly affected by the composition and thickness of the individual polymeric layers. For the first time ever, a mobile nuclear magnetic resonance (NMR) sensor allows a non-destructive determination of these important parameters on the building site. However, before this technique can be used on steel-reinforced concrete elements, the potential effect of the reinforcement on the measurement, i.e. the NMR signal, needs to be studied. The results show a shift of the NMR profile as well as an increase of the signals amplitude in the case of the reinforced samples, while calculating the thickness of concrete coating lead to identical results. © 2011 Elsevier Ltd. All rights reserved.

Scores of infrastructural concrete buildings possesses coating systems as protection against aggressive exposure. The functionality of these coating systems is mainly affected by the composition and thickness of there different polymeric layers. A mobile NMR sensor, the so called "NMR-MOUSE®"(Nuclear Magnetic Resonance Mobile Universal Surface Explorer, registered trademark of RWTH Aachen University), enables for the first time ever a nondestructive determination of these controlling parameters. The current results demonstrate the capability of the NMR sensor investigating different coating systems applied on concrete. Analyzing the NMR amplitude as a function of the measuring depth, the composition of the different coating layers gets visible while an accuracy of about 5 to 20 μm can be achieved for the thickness determination. Studying the in fluence of steel reinforcement inside the coated concrete on the NMR signal leads to a correction of the measuring field position in fluenced by concrete cover, steel diameter, amount and position of steel. © RILEM 2013.

The potential to use the NMR-MOUSE® as non-destructive analytical tool in building maintenance is demonstrated on two examples. The first one covers moisture transport through fine grained concrete matrices, whereas in the second one the NMR-MOUSE is used to determine the layer thickness of selected coating systems for concrete protection. In using this NMR technique, significant moisture profiles have been determined in fine grained concrete matrices with a maximum measuring depth of 5 mm and a depth-resolution of 250 μm. The NMR technique also allows observing the time depended progress of capillary water uptake and evaluating the effects of polymer modifications of the concrete matrix. Furthermore, the layer thickness of one model coating system and two OS 11a-coating systems were determined on the basis of depth profiles. The results show, that layer thickness between 50 and 200 μm can be determined with a standard deviation of about 5 μm. Copyright © 2011 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin.

The long term performance of textile reinforcement in a cementitious matrix is one important factor to be considered during the design process of textile-re inforced concrete (TRC) elements, since only the residual tensile strength of the reinforcement at the end of the predicted life-time can be taken into account. The reinforcement in textile-reinforced concrete is usually made from alkali-resistant glass rovings, but their durability in concrete is known to be unsatisfactory. Herein an approach is presented to improve the durability by impregnating the glass rovings with an insoluble epoxy resin which acts as a diffusion barrier against alkai ions. The results show that generally the durability can be improved by an impregnation in dependency of the material properties of the epoxy resin. Copyright © 2011 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin.