Dokument-ID Dokumenttyp Autoren/innen Persönliche Herausgeber/innen Haupttitel Abstract Auflage Verlagsort Verlag Herausgeber (Institution) Erscheinungsjahr Titel des übergeordneten Werkes Jahrgang/Band ISBN Veranstaltung Veranstaltungsort Beginndatum der Veranstaltung Enddatum der Veranstaltung Ausgabe/Heft Erste Seite Letzte Seite URN DOI Lizenz Datum der Freischaltung OPUS4-36876 Beitrag zu einem Tagungsband Umeche, E. L.; Schmidt, Wolfram; Uzoegbo, H. Ch. Schmidt, Wolfram; Priebe, Nsesheye Susan A survey and analysis of locally available cements in South Africa South Africa and recently Nigeria are the only net exporter of cement in Africa, yet cements are imported into the country mainly on the basis of price competitiveness. This poses potential for scatter in the properties of the cements in the South African market as pricing seems to be the only determining factor that affects Portland cements imported. A survey of cements of grade 42.5N in the South African cement market was carried out to identify major players in the industry. The identified cements, which included four locally produced and one imported cement were then analysed for both chemical composition and physical properties in line with the Eurocode EN 196. Tests carried out include loss on ignition, chloride content, sulphate content, specific surface (Blaine), standard consistence, initial setting time, final setting time, soundness and flexural and compressive strength at 2, 7 and 28 days. The testing program was initiated as part of on-going Africa-wide cement testing competency program in partnership with BAM and PTB in Germany. The performance of the identified cements from the different local manufacturers and the imported cement were analysed and are presented in this paper. These results reveal some similarities and differences in the properties. Particularly of interest is the marked difference in the 28 days compressive strength of the cements. This paper shows that there is need for further tests across the cement industry as some of the cements failed to meet certain requirement as set by EN 196. The paper also recommends the use of proficiency testing schemes in the cement industry of the country to ensure the cement laboratories are providing results of high quality and at the same time act as a check to make sure these laboratories are not failing to meet standard requirements. Berlin Bundesanstalt für Materialforschung und -prüfung (BAM) BAM 2016 Advances in Cement and Concrete Technology in Africa 978-3-9817502-3-2 2nd International Conference on Advances in Cement and Concrete Technology in Africa Dar es Salaam, Tanzania 27.01.2016 29.01.2016 91 98 2016-07-18 OPUS4-36862 Beitrag zu einem Tagungsband Schmidt, Wolfram; Mota Gassó, Berta; Sturm, Heinz; Pauli, Jutta Greim, M.; Kusterle, W.; Teubert, O. Influence of effects on nano and micro scale on the rheological performance of cement paste, mortar and concrete Chemical admixtures like superplasticisers or stabilising agents are of ever increasing importance for modern concrete technology. They liberate the workability of concrete from its dependency on water content, and thus, open the gate towards innovative and future oriented concrete technologies such as self-compacting concrete. Today, admixture addition has become common practice in concrete technology, but the understanding of their highly complex mode of operation is extremely difficult and demands for understanding of processes within the range between nanometres and centimetres. Due to its complex time-dependent, multi-phase and multi-scale behaviour, flowable concrete systems are highly complicated and cannot be described comprehensively by simple models. It is therefore extremely challenging to identify the relevant parameters that predominantly control flow phenomena on different size scales, since these may occur on any scale between the nano scale (e.g. superplasticizer adsorption) and macro scale (e.g. grading of the aggregates). The present study discusses fundamental mechanisms at the interface between particle or hydrate surfaces and the fluid phase at a very early stage of concrete formation, and links these effects to macroscopic flow phenomena. Methods are discussed that appear promising interdisciplinary tools for enhancement of the understanding of the relevant interactions that are responsible for the macroscopic flow of flowable concrete. Hamburg tredition 2016 Rheologische Messungen an Baustoffen 978-3-7345-1313-8 25. Workshop und Kolloquium Rheologische Messsungen an Baustoffen Regensburg, Germany 02.03.2016 03.03.2016 294 307 2016-07-15 OPUS4-40974 Beitrag zu einem Tagungsband Schmidt, Wolfram Priebe, Nsesheye Susan; Schmidt, Wolfram Why Africa can spearhead innovative and sustainable cement and concrete technologies globally The perception of concrete in the society as well as in the politics is rather negative. This becomes obvious in the fact that the phrase "concrete jungle" has become synonym for hapless living with no perspectives. In politics and research funding, it is also not easy to create a broader audience, since concrete is falsely considered as old-fashioned material that is sufficiently understood today and does not need further considerations, particularly compared to allegedly newer materials. However, particularly since the last two decades the technology has completely changed. Binders of today are no more the same binders as used before, and concrete mixture compositions of today diverge quite significantly from compositions in the past. There is little understanding world-wide about that. This causes that potentials the concrete technology bears are wasted. In the broadly found opinion that concrete is old-fashioned and ugly, it is ignored that architectural sins are not inherent to the material, which actually is extremely versatile and CO2-friendly compared to all other construction materials available. It is also ignored that 98% of the outer Earth's crust are made of the elements cement and concrete are made from, and therefore it will be an illusion to believe that the complementary 2% can create materials to develop regions and infrastructures in less developed areas in the world. For betterment in Africa the infrastructural development should have highest priority, since poor connections between settlements are responsible for enormous Price increases [2], and urban traffic congestion is responsible for an incredible loss of productivity. It is not unrealistic to assume that earners that are dependent on a car get stuck in traffic about 3-4 hours per day in cities like Lagos, Nairobi or Dar es Salaam. However, the traffic congestions do not only affect the car owners negatively but the living of the entire urban population every day. Besides infrastructure, housing should be the other priority, since a large part of the African population does not live in adequate condition. This is a societal problem, since unequal Distribution of wealth is a major driving force for instability in societies. The latter has a global impact, since 8 many phenomena that can be observed all over the world such as political radicalism, xenophobia, terrorism, and migration can often be linked to instable societies. However, the importance of infrastructure has an even wider range. Most African countries go through a change process recently. In order to strengthen very positive perspectives, the focus in politics and research funding is put on issues such as agriculture, energy, and health, which are without doubt extremely important issues. However, it is typically overlooked that all enhancements in these areas can only become effective, when an infrastructure is created to support the implementation of better concepts. Mobility is the key to a prosperous future, and mobility can only be granted by infrastructural construction activities. Hence, compared to many other regions in the world, cement and concrete technologies have a significantly higher relevance in Africa. Berlin Bundesanstalt für Materialforschung und -prüfung (BAM) 2016 Proceedings of the 2nd symposium knowledge exchange for young scientists (KEYS) - Valorisation of industrial by-products for sustainable cement and concrete construction - Improvement of solid waste management 2 978-3-9817853-1-9 2nd Symposium on Knowledge Exchange for Young Scientists (KEYS) Accra, Ghana 7.6.2016 9.6.2016 7 19 2017-07-14 OPUS4-40979 Vortrag Schmidt, Wolfram Promising bio-based rheology modifying agents for concrete Today, concrete engineers can vary consistencies between very stiff and self-compacting. The possibility to tailor rheological properties of concrete eventually opened up the path to multiple new technologies, where design criteria are no longer limited to the Young's modulus and the compressive strength, but often comprise additional added value. It can therefore be concluded that the capability to control the rheology of concrete systems can be considered as the catalyst for concrete innovations such as polymer modified cementitious composites (PCC) self-compacting concrete (SCC), high-performance concrete (HPC), ultra-high performance concrete (UHPC) or strain hardening cement based composites (SHCC). In the same way rheology modifying admixtures will become key parameters in mastering the challenges of the next decades such as: - Additive manufacturing/3D-printing - Overcoming pumping height limitations - Casting at extreme temperatures - Tailored rheology at delivery In many regions in the Southern hemisphere, and particularly in Africa, the effective use of chemical admixtures for concrete could significantly contribute to solve problems induced by the challenging climatic conditions, but particularly in Africa it is difficult to use them, due to lacking local supply and supply infrastructure. For Africa, concrete admixtures are largely shipped or transported from Europe, the Arabian Peninsula, or Asia. The long distance transportation of chemicals is not very environmentally friendly and the economic consequences are dramatic: the agents are difficult to purchase, expensive, and there is not a large variety of products available in the market. However, bio-based chemicals have been used in construction for ages effectively. Due to the enormous relevance of rheology modifying admixtures it is worthwhile to recollect that nature provides an enormous variety of chemicals that can be used readily or with low processing. Today, the use of petrol based polycarboxylate ether superplasticizers has become quite common in concrete technology due to their versatility, but their uncomplicated and cost efficient availability is limited in most countries in Africa. However, alternatives are available, which can be found in many regions. Plant extracts have been used to modify the properties of concrete for long time. These plants are typically regionally abundantly available, cheap, and they are environmental friendly. They do not require special caring for seedlings, weeding or manuring to grow since they grow wildly. The talk will present an overview of various options for rheology modifying admixtures, that can be found in nature, and that may become a real alternative, once their interaction within the complex cementitious system is well understood. 2016 Rheologie komplexer Fluide: Theorie, Experiment und Anwendung, DRG/ProcessNet | Gemeinsame Diskussionstagung Berlin, Germany 13.3.2017 2017-07-14 OPUS4-38881 Beitrag zu einem Tagungsband Ramirez Caro, Alejandra; Pauli, Jutta; Schmidt, Wolfram; Resch-Genger, Ute Study of the superplasticizer-cement hydration interaction by optical spectroscopy Nowadays, superplasticizers (SPs) are widely used to increase fluidity and reduce water content in concrete; thus, allowing better workability for final applications. The present study will focus on the hydration effect using comb shape polycarboxylates (PCEs), which are known to allow a very low water/cement ratio (w/c of 0.20) or less.Optical methods have been successfully used for the analysis and monitoring of the interactions between a broad variety of nanoscale and molecular systems like nanoparticles of various chemical composition and different types of organic ligands or biomolecules.This encouraged us to assess the potential of these methods, and particularly fluorescence, for the investigation of the interactions that occur at the interface between hydrate surfaces of cement particles and PCE at a very early stage of concrete formation and to differentiate between the impact of PCE's molecular structures on such interactions. Frankfurth am Main Gesellschaft Deutscher Chemiker e.V. 2016 GDCh-Monograph 50 978-3-936028-96-6 2nd International Conference on the Chemistry of Construction Materials Munich, Germany 10.10.2016 12.10.2016 260 263 2017-01-04 OPUS4-38849 Beitrag zu einem Tagungsband Mota Gassó, Berta; Schmidt, Wolfram; Pauli, Jutta; Sturm, Heinz Influences of hydration effects on the flow phenomena of concrete with admixtures Today, chemical admixtures like superplasticisers and stabilising agents are extremely important for modern concrete technology. These agents have meanwhile become common practice in concrete technology, but the understanding within the entire system lags far behind their application. The macroscopic rheology of concrete in the presence of superplasticizers strongly depends upon effects on a much smaller scale such as the hydration of the cement, the adsorption of superplasticizers, and the pore solution chemistry. Frankfurt am Main Gesellschaft Deutscher Chemiker e.V. 2016 GDCh-Monograph 50 978-3-936028-96-6 2nd International Conference on the Chemistry of Construction Materials München, Germany 10.10.2016 12.10.2016 276 279 2017-01-04 OPUS4-36877 Beitrag zu einem Tagungsband Barthel, Maria; Schmidt, Wolfram; Kühne, Hans-Carsten; Rübner, Katrin Schmidt, Wolfram; Priebe, Nsesheye Susan Interactions between waste paper sludge ashes and superplasticizers based on polycarboxylates In many industrial nations, about two third of the paper demand is covered by recovered paper. A major process step within the treatment of waste paper is the de-inking. It is a floating process yielding paper sludge as a waste product. About 50 % of this residue is used as a fuel. In several cases it is burnt at temperature of about 850 °C and thereafter the accrued ashes are collected in the flue gas filter. During the combustion, kaolinite and calcium oxide generate gehlenite and larnite. Calcite is the main component of waste paper sludge ash (PA).The chemical and mineralogical composition of PA suggests using it as a supplementary cementitious material. In modern construction materials technology, workability aspects gain importance, since for most modern materials the rheology and compaction ability are relevant for the operation at a hardened state. It was observed that PA significantly increases the water demand of powder systems, which can cause serious problems during the casting of mineral binder systems containing PA. It is therefore obvious that binder systems containing PA might demand for the use of superplasticizers. Superplasticizers are polymers with anionic backbone that cause electrostatic and steric repulsion effects upon adsorption on surfaces of particles and hydration phases. In this paper interactions between superplasticizers and waste paper sludge ashes are discussed and analysed. Based on observations of changes in the zeta potential and the dispersion of the particle system, the influence of the charge density of superplasticizers is observed and time dependent effects are demonstrated. Berlin Bundesanstalt für Materialforschung und -prüfung (BAM) BAM 2016 Advances in Cement and Concrete Technology in Africa 978-3-9817502-3-2 2nd International Conference on Advances in Cement and Concrete Technology in Africa Dar es Salaam, Tanzania 27.01.2016 29.01.2016 181 186 2016-07-18 OPUS4-36880 Beitrag zu einem Tagungsband Akindahunsi, A. A.; Uzoegbo, H. Ch.; Schmidt, Wolfram Schmidt, Wolfram; Priebe, Nsesheye Susan Effect of Cassava Starch on Shrinkage Characteristics of Concrete The use of starch and its derivatives in concrete as an admixture to modify relevant properties of concrete is on the increase in recent times. It is known to modify the rheology, to affect the hydration kinetics of cement, and influence on initial and final setting time of cement. This paper examines the effect of cassava starch on concrete. shrinkage properties of concrete, with and without starch addition, were studied. Various percentages (0, 0.5, 1.0, 1.5 and 2 %) of starches by weight of cement were added to concrete mixes prepared in the laboratory. Shrinkage tests were conducted for duration of up to one year. The result show that concretes with starch additions exhibit lower shrinkage, which is an indication the addition of starch as admixture in concrete improves the ability of the concrete reduce shrinkage problems. Berlin Bundesanstalt für Materialforschung und -prüfung (BAM) BAM 2016 Advances in Cement and Concrete Technology in Africa 187 978-3-9817502-3-2 2nd International Conference on Advances in Cement and Concrete Technology in Africa Dar es Salaam, Tanzania 27.01.2016 29.01.2016 196 2016-07-18