Marc-Patrick Pfleger Dipl.-Ing.  Elisabeth Radl  FH-Prof. Dipl.-Ing. Dr. Markus Vill 《Beton- und Stahlbetonbau》2023,118(8):565-574

Investigations of the CO₂ Storage Potential of Recycled Concrete Aggregates and Cement Samples under Forced Carbonation The production of concrete, in particular the cement contained as a binder, causes a high proportion of human induced climate-impacting gas emissions. Studies show that the decarbonization of limestone causes at least 8 % of global CO₂ emissions, which underlines the acute need for action and research. Due to the current building and infrastructure stock and its increasing obsolescence or replacement, the amount of available demolition material is constantly increasing. In many cases, this material consists of high-quality concrete that could be reused as recycled aggregate in the production process to conserve primary raw material sources. Most of this crushed concrete is not carbonized. This means that this potential could be used as a CO₂ sink in the course of a recycling process. The recycled and carbonized material can be used as a substitute for natural grains. Due to the admixture as aggregate in the course of the concrete production, the degree of carbonation is irrelevant for steel corrosion or related problems. The main objective of this work was to investigate the CO₂ absorption capacity of concrete waste in order to quantify its use as a potential carbon sink. The test series show that the ecological footprint of concrete can be significantly reduced by exploiting its carbonation potential by storing more than 1.3 % CO₂ of the original mass after 24 hours.  相似文献   

    

Maximilian Schmidt  Fahad Seemab  Prof. Dr.-Ing. habil. Rostislav Chudoba  Univ.-Prof. Dr.-Ing. Martin Claßen 《Beton- und Stahlbetonbau》2023,118(7):455-466

New perspectives on the load bearing behavior of RC-structures without shear reinforcement The shear behavior of structural members has been an integral part of research in concrete structures for more than 100 years. In recent years, various mechanical shear models have been developed that deliver important insights into the background of shear behavior and are able to provide physical explanations for shear failure in RC members without shear reinforcement. However, these models require further experimental validation. New measurement techniques (e.g. digital image correlation or fiber-optic strain measurement) play a decisive role in this context, allowing deeper insights into the load-bearing behavior of reinforced concrete components subjected to shear loads. Based on experimental investigations with modern measurement techniques, software has been developed that performs an automated crack detection based on the finite element method with detailed evaluation of the kinematics and the stresses transferred in the crack. In this paper an overview of different evaluation methods of experimental investigations with modern measurement techniques is given, on the basis of which an in-depth evaluation of new model approaches can be carried out.  相似文献   

    

Dr.-Ing. Michael Frenzel  Dr.-Ing. Silke Scheerer  Dr.-Ing. Angela Schmidt 《Beton- und Stahlbetonbau》2023,118(Z2):25-36

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Dr.-Ing. Tobias Schack  Dr.-Ing. Max Coenen  Prof. Dr.-Ing. Michael Haist 《Beton- und Stahlbetonbau》2023,118(8):556-564

Image-based quality control – part 2: granulometric properties The changes in concrete technology necessary to achieve the climate protection targets will lead to a significant change in the concrete mixtures typically used. The raw materials used are becoming more diverse and complex. The use of recycled raw materials will also significantly increase the fluctuations in the properties of the raw materials. An Accurate and time-efficient determination of the granulometric properties of the aggregate is of crucial importance, especially for “eco-concretes”, in order to ensure consistent quality characteristics. As a natural raw material, the aggregate is subject to certain fluctuations to which such optimized concrete compositions can react relatively sensitively. In the future, it will be necessary to determine possible quality deviations of the fresh concrete resulting from fluctuations in the raw materials in a time-efficient manner in order to be able to make appropriate adjustments in the production process as quickly as possible. This paper presents an image-based quality control for the digital evaluation of granulometric properties of the aggregate as a part oft he flow table test. Accordingly, the range of properties of the image-based method already presented in Part 1 of this paper is extended to a fully comprehensive digital quality control. This paper presents the image-based determination of the granulometric properties of the aggregate as a part oft he flow table test. The determination is based on the image-based quality control described in part 1 of this paper.  相似文献   

    

Philipp Klsch  Hartwig Künzel  Daniel Zirkelbach 《Bauphysik》2019,41(5):269-278

Convective moisture entry in lightweight assemblies – Types of leakage, moisture distribution and conclusions for practice Compared to the overall building envelope airtightness concerning energetic aspects, the condensation caused by air exfiltration through small remaining leakages is still a challenge today. Convective moisture entry in lightweight assemblies can lead to increased moisture contents and cause massive structural damages even if the leakages are negligible from the energetic point of view. For a better understanding of the processes inside lightweight constructions, hot‐ and cold‐box experiments and airflow measurements on 14 different full‐scale wall assemblies under realistic climatic conditions were performed. The influences of different mineral wool densities and leak configurations, as well as different pressure differences were analyzed to draw conclusions for the practice. The results show some interesting aspects about the influencing factors of the convective moisture entry. The distributions of the water content between sheathing and insulation samples show that the main influencing factor is the mineral wool density. Moreover, the findings indicate that the moisture distribution over the height of the sheathing is more influenced by the pressure difference level than by insulation air permeability or arrangements of the small openings. For the tested configurations, a lateral flow due to openings near the posts shows the highest air flow rates and therefore moisture content inside the assemblies. These boundary flow can lead to increased moisture contents in posts or rafters. In addition differences in the flow behavior associated with the leak arrangements could clearly are detected. However, another important finding of these experiments is that, despite good workmanship, a remarkable amount of air and moisture seams to penetrate the sealing tape joints.  相似文献   

    

《Beton- und Stahlbetonbau》2017,112(4):219-227

Durable concrete pavements using different binders in top and bottom lift It is a matter of common knowledge that ground granulated blast furnace slag and siliceous fly ash can be used to mitigate alkali‐silica‐reaction (ASR) in concrete. Nonetheless such materials are seldom used for the construction of concrete pavements in Germany, as their application can impair the deicer‐scaling resistance of the concrete. In two‐lift concrete pavements a possible approach to avoid this problem is to use cements with a higher proportion of blast furnace slag only in the thick bottom lift, thus minimizing its susceptibility to ASR. The thin top lift, which is subjected to a high level of mechanical and freeze‐thaw stress, is still produced with Ordinary Portland Cement, hence ensuring a sufficient deicer‐scaling resistance. However, this approach is currently hindered by the German technical standards for concrete pavements, which require the use of the same cement in the top and bottom lift. Furthermore the standards do not permit the application of siliceous fly ash to partly substitute cement in concrete pavements. It was therefore the aim of a research project to obtain the necessary knowledge for assessing potential benefits and risks of a more flexible use of binders in concrete pavements.  相似文献   

    

《Beton- und Stahlbetonbau》2017,112(3):133-143

About the influence of the individual carrying parts on the shear force bearing capacity of reinforced concrete slabs with integrated void formers Until now there is no generally accepted mechanically justified design concept for the shear force bearing capacity of reinforced concrete slabs without shear reinforcement. To deliver a contribution for a better understanding of the shear force resistance, first trials were carried out at the Technical University of Kaiserslautern. In these tests the individual carrying parts were switched off in intended sequence. For this purpose, experiments were carried out with a displaced compression zone and with a switched off crack's aggregate interlock and eliminated dowel action of the longitudinal reinforcement [1]. The influence of the individual carrying parts to the total capacity could be visualized and verified by the recalculation of tests with voided flat slabs and installation slabs applying an existing mechanically justified calculation model following Görtz [2, 3].  相似文献   

    

《Stahlbau》2017,86(1):65-72

Container connection for the New Indian Antarctic Research Station – A new type of connection for complex container buildings. Bharati, the New Indian Antarctic Research Station, consists of a self‐supporting structure of customized ISO shipping containers. Up to eight ISO corner fittings per node are three‐dimensionally interconnected forming a multi‐storey building, so that the structural bracing is entirely given by the containers. The therefore necessary container connections are the key to an efficient structure. It consists of simple parts: bolts, shear blocks, anchor blocks, stackers and thread bars. In combination these elements guarantee force transmission in all directions by mounting them into the openings of the ISO corner fittings. All parts can easily be installed by hand using a wrench. The efficient use of containers did not only reduce the building material, but also the carbon dioxide emission on all transport activities. Furthermore, the new container connection and the therewith good utilization of available space within the façade shell reduces operation costs during the entire life time of the building.  相似文献   

    

《Stahlbau》2017,86(10):873-879

Diaphragm effect of sandwich panels. Full scale tests were carried out within the scope of [5] to investigate the diaphragm action of sandwich panels. Shear diaphragms were constructed to assess the load carrying action of the sandwich panels bracing the structure. The bearing behaviour of the various components contributing to the shear diaphragm effect was investigated in more detail on smaller experimental set ups. These small scale tests include investigations into the screw connections between the sandwich panels and the substructure, as well as a series of tests on the load transfer through the longitudinal joint between the individual panels. The most untapped potential for improvement of the bearing capacity has been found to be the influence of the longitudinal joint. An increased force transmission in the longitudinal joint leads to higher values of stiffness and maximum bearable load of the shear diaphragm. Various methods to improve the contribution of the joints were developed. Of these, the hook‐and‐loop tape joint reinforcement has been found to yield the best results. Therefore, this reinforcing method has also been investigated in full scale tests. The use of hook‐and‐loop tape in the longitudinal joint makes the panels acting as one big plate. The impact on the screw connection has been successfully reduced by improving the load transfer in the longitudinal joints.  相似文献   

    

《Stahlbau》2017,86(8):707-715

Equivalent geometrical initial bow imperfections e₀ for flexural buckling – additional investigations. According to Eurocode 3 Part 1‐1, a member subjected to an axial compression force may be verified by two different approaches: a verification by the equivalent member method or a cross sectional verification. Concerning the second possibility bending moments according to second order theory must be calculated, where initial bow imperfections e₀ must be taken into account, which should be taken normally from EN 1993‐1‐1, table 5.1. The values e₀ used up to now should be changed, because they are partly unsafe, this was shown earlier by intensive investigations [5]. The results of additional investigations are explained here concerning test results and analytical values for high strength steel S700. Furthermore comments are given to values e₀ calculated depending on the non‐dimensional slenderness λ .  相似文献