Ingenieurwissenschaften und zugeordnete Tätigkeiten
Filtern
Dokumenttyp
Sprache
- Englisch (40)
- Deutsch (1)
- Portugiesisch (1)
Schlagworte
- Concrete (42) (entfernen)
Organisationseinheit der BAM
- 7 Bauwerkssicherheit (15)
- 7.1 Baustoffe (11)
- 8 Zerstörungsfreie Prüfung (9)
- 7.4 Baustofftechnologie (5)
- 8.0 Abteilungsleitung und andere (5)
- 4 Material und Umwelt (2)
- 4.0 Abteilungsleitung und andere (2)
- 8.2 Zerstörungsfreie Prüfmethoden für das Bauwesen (2)
- 8.5 Röntgenbildgebung (2)
- 7.3 Brandingenieurwesen (1)
Paper des Monats
- ja (1)
Eingeladener Vortrag
- nein (11)
Welcome to the first symposium on Knowledge Exchange for Young Scientists (KEYS) in Dar es Salaam, Tanzania, 9th – 11th June 2015. This symposium is part of a three phase series organised by BAM, and funded by VolkswagenStiftung. Each symposium will focus on relevant themes in the construction sector and will include adequate training as well as offer an opportunity to participate in informal discussions between key players and young scientists, which will facilitate the fundamentals of knowledge transfer.
Our world of cement and concrete faces tremendous challenges for the future. Without doubt cement-based materials will remain the most widely used construction materials in the world. Concrete can be made available everywhere in the world, and it is more sustainable than other materials. Nevertheless, in order to become even more sustainable, we need to find solutions to reduce CO2 generation for the cement production, to quickly solve problems of housing and infrastructures, and to cope with ever increasing customer needs in terms of performances.
There is no global optimum solution for concrete. Best concrete practices always has to be found locally and regionally based on raw materials, supply chains, and construction needs, but it can be inspired by other regions. In order to tackle the future challenges and build more innovative with concrete, we need to enhance interdisciplinary engineering skills and create networks between future decision makers.
Therefore, the KEYS symposia series offers a platform whereby young African scientists can get together with peers from Germany as well as with experienced academic engineers, industry specialists and scientists from across the globe for better implementation of research analysis in their respective fields of study. This primarily provides the opportunity to obtain further knowledge in the demand for the home-base innovation and growth of the education sector. It will also provide an opportunity to network with their peers and gain relevant and objective knowledge.
The theme for this first symposium is sub-Saharan African standards for cement and concrete research – raw materials, quality control and maintenance of cementitious products. The symposium is divided into 8 sections and includes presentations from 9 international keynote speakers and 22 young scientists, who were selected out of a high number of applicants based on the excellence of their scientific writing.
We would like to thank all participants for their valuable contribution to the symposium. We are blessed to receive tremendous input from the distinguished keynote speakers and we thank them for their attendance. Last but not least, we would like to acknowledge the funding body, VolkwagenStiftung, for their support. We hope you enjoy the symposium and find your engagement valuable with the entire team in sustaining your professional development in the global world of cement and concrete.
Amplitudes variation of GPR rebar reflection due to the influence of concrete aggregate scattering
(2015)
Dense GPR measurements of rebar reflection amplitudes Show relative variations, which can be in the order of more than 10% - 20%. Former investigations demonstrated that these variations are caused by the heterogeneity of concrete, i.e. due to the inclusion of aggregates in concrete. These amplitude variations make it difficult to analyse single reflection amplitudes in order to determine the rebar diameter or to estimate the concrete deterioration state. In a systematic study we have quantified the statistical variation of the rebar reflection amplitude for concrete covers of 6 cm, 9 cm, 12 cm, 15 cm and 18 cm, for two different grading curves and for the rebar diameters 12 mm and 28 mm. Also the influence of the wavelength has been investigated by using antennas with different centre frequencies in relation to the aggregate size. The results are discussed with regard to a quantitative amplitude evaluation of GPR measurements and also the potential of using these variations for a characterization of concrete material properties.
Welcome to the second symposium on Knowledge Exchange for Young Scientists (KEYS) in Accra, Ghana 7th – 9th June 2016. This symposium is part of a three phase series organised by BAM, and funded by VolkswagenStiftung. The KEYS symposia series offers a platform whereby young African scientists can get together with peers from Germany as well as with experienced academic engineers, industry specialists and scientists from across the globe for better implementation of research analysis in their respective fields of study. This primarily provides the opportunity to obtain further knowledge in the demand for the home-base innovation and growth of the education sector. It will also provide an opportunity to network with peers and gain relevant and objective knowledge. Therefore, the symposium offers adequate training to young scientists as well as gives an opportunity to network with key players in the cement and concrete industry, which will facilitate the fundamentals of knowledge transfer.
This second symposium focuses on solid waste management and importance of valorisation of suitable by-products for utilisation in the cement and concrete industry. Today, all over the world we can no longer draw on abundant resources, and more frequently, we need to develop innovative concepts for better and more sustainable construction. This change process needs international and interdisciplinary approaches. Hence, the symposium is seen as a spark for the generation of ideas and visions, how concrete construction can become more globally sustainable based on locally tailored concepts. The symposium includes keynote lectures from 9 international keynote speakers and technical papers from 22 young scientists, who were selected out of a high number of applicants based on the excellence of their scientific writing. The presentations of all participants as well as keynote lectures are represented in these proceedings.
We would like to thank all participants for their valuable contribution to the symposium. We are blessed to receive tremendous input from the distinguished keynote speakers and we thank them for their attendance. Last but not least, we would like to acknowledge the funding body, VolkswagenStiftung, for their support. We hope you enjoy the symposium and find your engagement valuable with the entire team in sustaining your professional development in the global world of cement and concrete.
Welcome to the 2nd International Conference on Advances in Cement and Concrete Technology in Africa (ACCTA 2016), January 27– 29, 2016, held at White Sands Hotel, Dar es Salaam, Tanzania.
The first ACCTA conference that took place in January 2013 in Johannesburg was a result of an African-European collaborative research project. Due to the success of this conference, it was announced that a triennial international conference is necessary, with the next conference scheduled to take place once again in Johannesburg. Within the organisation of the conference, unfortunately some unforeseeable events arose, which would lead to either a delay of the conference in Johannesburg until 2018 or a change of venue. The great response from the international scientific community supported the option to maintain the originally scheduled date. With the support of the local organisation committee from the University of Dar es Salaam and the contributions from the University of the Witwatersrand and the University of Zagreb the conference was shifted to Dar es Salaam.
Despite the new boundary framework, we are extremely happy that it was possible to arrange an outstanding and excellent scientific programme. Therefore we would like to thank in particular the keynote speakers and all members of the international scientific community, as well as other delegates that supported the conference by their contributions and attendance. This shows us how significantly important the African cement and concrete market is for the entire global community.
Africa can become a spearhead for the future of construction with cement and concrete. The continent exhibits an enormous construction potential and due to the relatively short history of building with these materials, innovations can be adopted and adapted unbiased and without influence of stakeholders, traditions, and complicated networks of regulations. This is a fertile ground for the existing promising generation of engineers and decision makers for re-inventing cement and concrete in the best possible way.
There is no global optimum solution for concrete. The best solution in Africa is not the best solution in Europe or another part of the world, and the best solution in one particular African country is diverging from the best solution in another African country depending upon resources, supply chains, infrastructure, construction needs, traditions, available manpower, skills and technologies. Nevertheless, we can globally support our objectives to build future oriented and sustainable construction solutions by mutually learning from each other. In order to tackle the future challenges and build more sustainably and innovatively with concrete, we need to enhance interdisciplinary and cross-national skills and create networks between experts and decision makers globally.
ACCTA offers this kind of platform, and we are happy to announce that the conference reaches a high impact in the world. Delegates and speakers come from more than 40 countries in the world originating from all continents. Besides the technical content there will be plenary discussions on the most relevant topics of future binder technologies and standards and product safety with outstanding expert panellists.
We want to wish all delegates a successful conference and hope that this book can be a significant contribution for a future oriented and better concrete technology; in Africa and the entire world. Welcome to Dar es Salaam, Tanzania.
The current knowledge about fatigue behavior of concrete is still incomplete. This concerns especially the progress of fatigue which precedes the fatigue failure. Therefore, the process of fatigue itself under cyclic compressive loading was investigated in a systematic and comprehensive way. The aim of this investigation was to obtain a deeper insight and to provide a better understanding of the damage process occurring within the material during fatigue loading. Concrete cylinders were tested with a number of cycles to failure between 106 and 107. To investigate macroscopic and microscopic changes in the material, various methods of non-destructive and destructive testing were used. One main result was, in contrast to other authors, that the investigated changes in macroscopic material behavior could not be explained only by a development of micro-cracks. The results indicated rather, that the related changes in the fatigue behavior are mainly a result of viscous processes in the hardened cement paste, similar to the processes of creep. Based on the experimental results a description of the possible processes was derived which take place in the material structure during fatigue loading and also leads to the observed macroscopic changes in the material behavior. In this context, the results have shown that in case of isotropic material behavior a stiffness reduction related to a scalar value could not capture the damage effect on the stress-strain-relationship caused by fatigue.
Laser-induced breakdown spectroscopy (LIBS) is a combination of laser ablation and optical emission spectroscopy. Due to the possibility of direct measurements on the sample surface with a minimum of sample preparation investigations of building materials can be conducted quite fast. In combination with a scanning technique (translation stage or scanning mirrors head) 2D element distributions of harmful species like chlorides and alkalis are evaluated with a sub-mm resolution. By scanning a surface of typically 100 mm x 100 mm the heterogeneity of the material may be considered. LIBS is capable to identify hot spots in element concentration with a resolution of 0.1 mm or even smaller. A LIBS-system for the on-site application on building materials is, in cooperation with system developers and companies which will use this technique for investigation on real structures, under test at BAM. We present an example. Further work will focus on providing guidelines to establish LIBS as a standard procedure for chemical investigations of building materials.
The current knowledge about fatigue behavior of concrete is still incomplete. This concerns especially the progress of fatigue which precedes the fatigue failure. Therefore, the process of fatigue itself under cyclic compressive loading was investigated in a systematic and comprehensive way. The aim of this investigation was to obtain a deeper insight and to provide a better understanding of the damage process occurring within the material during fatigue loading. Concrete cylinders were tested with a number of cycles to failure between 1E6 and 1E7. To investigate macroscopic and microscopic changes in the material, various methods of non-destructive and destructive testing were used. One main result was, in contrast to other authors, that the investigated changes in macroscopic material behavior could not be explained only by a development of micro-cracks. The results indicated rather, that the related changes in the fatigue behavior are mainly a result of viscous processes in the hardened cement paste, similar to the processes of creep. Based on the experimental results a description of the possible processes was derived which take place in the material structure during fatigue loading and also leads to the observed macroscopic changes in the material behavior. In this context, the results have shown that in case of isotropic material behavior a stiffness reduction related to a scalar value could not capture the damage effect on the stress-strain-relationship caused by fatigue.
Fatigue is of relevance not only for metals but also for concrete. The current knowledge about fatigue behaviour of concrete is, however, incomplete. This concerns especially the progress of fatigue which precedes the fatigue failure. Some macroscopic effects of this process are well known but the governing material changes behind them are still less studied. The focus of the present contribution lay on a systematic and comprehensive investigation of the fatigue process under cyclic compressive loading. The aim was to obtain a deeper insight and to provide a better understanding of the damage process in the material. Cylindrical specimens were tested with a number of cycles to failure between 106 and 107. Various methods of non-destructive and destructive testing were used to investigate macroscopic and microscopic changes in the material. One main result was that the changes in the macroscopic material behaviour could not be explained only by the development of micro cracks. The results indicated that the related changes in the fatigue behaviour originate rather from viscous processes in the cement stone, similar to the process of creep. A sound description of the possible processes was derived from the obtained experimental results which concerns material structure during fatigue loading. It has been shown that in case of isotropic material behaviour a stiffness reduction related to a scalar value could not capture the damage effect on the stress-strain relationship caused by fatigue.
Fatigue is of relevance not only for metals but also for concrete. The current knowledge about fatigue behaviour of concrete is, however, incomplete. This concerns especially the progress of fatigue which precedes the fatigue failure. Some macroscopic effects of this process are well known but the governing material changes behind them are still less studied. The focus of the present contribution lay on a systematic and comprehensive investigation of the fatigue process under cyclic compressive loading. The aim was to obtain a deeper insight and to provide a better understanding of the damage process in the material. Cylindrical specimens were tested with a number of cycles to failure between 106 and 107. Various methods of non-destructive and destructive testing were used to investigate macroscopic and microscopic changes in the material. One main result was that the changes in the macroscopic material behaviour could not be explained only by the development of micro cracks. The results indicated that the related changes in the fatigue behaviour originate rather from viscous processes in the cement stone, similar to the process of creep. A sound description of the possible processes was derived from the obtained experimental results which concerns material structure during fatigue loading. It has been shown that in case of isotropic material behaviour a stiffness reduction related to a scalar value could not capture the damage effect on the stress-strain relationship caused by fatigue.