TY - CONF A1 - Pirskawetz, Stephan A1 - Wolf, Julia A1 - Schmidt, Wolfram A1 - Rogge, Andreas T1 - Einsatzmöglichkeiten der Schallemissionsanalyse im Bauwesen N2 - Die Schallemissionsanalyse (SEA) ist ein passives zerstörungsfreies Prüfverfahren. mit dem Rissbildung, Risswachstum und andere Gefügeveränderungen delektiert und lokalisiert werden können. Anhand von zwei Beispielen aus der Forschung der Bundesanstalt für Materialforschung und -prüfung (BAM) wird gezeigt welche Möglichkeiten die SEA beim Bauwerksmonitoring und bei der Untersuchung von Baustoffen bietet. Im ersten Beispiel wird die Ortung von Schallemissionen zur Verfolgung des Risswachstums in Beton eingesetzt. Weiterhin wird mit Zugversuchen an Faserbeton illustriert, dass mit der SEA Versagensmechanismen identifiziert werden können. T2 - 8. Symposium Experimentelle Untersuchungen von Baukonstruktionen CY - Dresden, Germany DA - 24.09.2015 KW - Schallemission KW - SHCC PY - 2015 SN - 1613-6934 N1 - Serientitel: Schriftenreihe Konstruktiver Ingenieurbau Dresden – Series title: Schriftenreihe Konstruktiver Ingenieurbau Dresden VL - 40 SP - 61 EP - 72 PB - Technische Universität Dresden CY - Dresden AN - OPUS4-34581 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Vasilic, Ksenija A1 - Kühne, Hans-Carsten A1 - Schmidt, Wolfram A1 - Roussel, N. T1 - Numerical simulations of scc casting: parameter determination N2 - The paper addresses numerical modelling of fresh self-compacting concrete. In the previous studies, a numerical tool for casting prediction is built based on the assumption that fresh concrete behaves as a yield-stress fluid and treating zones with rebars as porous media. The present contribution discusses the determination of material parameters, which are required as an input for numerical simulations of casting processes. T2 - International RILEM Conference on Materials, Systems and Structures in Civil Engineering 2016, Segment on Fresh Concrete CY - Lyngby, Denmark DA - 22.08.2016 KW - Fresh concrete KW - Simulation KW - CFD KW - Rheology PY - 2016 SN - 978-2-35158-184-1 SP - 163 EP - 172 PB - RILEM Publications S.A.R.L. CY - Paris, France AN - OPUS4-37446 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmidt, Wolfram T1 - Peculiarities of African cement and concrete markets: challenges and opportunities N2 - Today's African concrete construction environment differs greatly from that in Europe, Japan or North America. Europe can look back on a concrete tradition of more than 150 years. Standardising documents and guidelines have existed for over 100 years, and formed the foundation of modern Standards adopted and applied in many regions of the world. Technological developments in cement production are also strongly influenced by environmental conditions of the Northern hemisphere. In contrast, with the exception of South Africa, most countries of sub-Saharan Africa started cement production in the 1950s to 1960s, followed by a period of political and economic upheaval. As a result, there have not been serious approaches towards customised Solutions for concrete construction for conditions specific to sub-Saharan Africa; in most countries overseas Standards are applied, as a matter of course. PY - 2013 SN - 1560-2710 VL - 16 IS - 4 SP - 1 PB - Hypenica AN - OPUS4-30419 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram A1 - Kühne, Hans-Carsten A1 - Meng, Birgit ED - Rogge, A. ED - Meng, B. T1 - Zum Einfluss des Mischungsentwurfs und des Fließmittels auf temperaturbedingte Veränderungen der Rheologie von SVB T2 - 52. DAfStb-Forschungskolloquium CY - Berlin, Deutschland DA - 2011-11-07 KW - Fließmittel KW - Polycarboxylatether KW - Selbstverdichtender Beton KW - Temperatureffekte KW - Rheologie PY - 2011 SN - 978-3-9814281-0-0 SP - 40 EP - 49 PB - BAM Bundesanstalt für Materialforschung und -prüfung CY - Berlin AN - OPUS4-25194 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - "Effektivität von Stabilisierern - Einfluss des Feststoffvolumenanteils und Wechselwirkung mit Fließmitteln - "Effectiveness of Stabilising Agents - Influence of the Solid Volume Fraction and Interactions with Superplasticizers" T2 - 23. Konferenz "Rheologische Messungen an Baustoffen" CY - Regensburg, Germany DA - 2014-03-12 PY - 2014 AN - OPUS4-30832 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Govin, Alexandre A1 - Schmidt, Wolfram A1 - Bartholin, M. C. A1 - Grosseau, P. ED - Amziane, Sofiane ED - Sonebi, Mohammed ED - Charlet, Karine T1 - Effect of Guar gum derivatives combined with superplasticizers on properties of Portland cement pastes N2 - Chemical admixtures allow to create a variety of fresh and hardened state properties in cementitious materials. In the case of self-compacting concrete, plasticizers or superplasticizers are introduced with the aim to decrease the yield stress and the viscosity of the materials. However, in order to prevent segregation and bleeding, and to improve the water retention of cement-based system, stabilizing agents or viscosity agents are often introduced in addition. Among these admixtures, polysaccharides are most commonly used. The aim of this study is to provide an understanding of competitive or synergetic effects induced by the combination of hydroxypropyl guar stabilizing agents (HPG) and superplasticizers on cement pastes. Two polycarboxylate superplasticizers (PCE) exhibiting different charge densities and one HPG were studied. It was found that the combination of HPG with PCE superplasticizer strongly affects the rheological behavior of cement pastes. Despite the presence of HPG, the viscosity of the pastes strongly decreased with increasing dosage of PCE until it became close to the viscosity of a cement paste with PCE only. However, the use of HPG in combination with PCE allows maintaining a significant yield stress in the cement paste compared to PCE alone. The increase in the charge density of the PCE seemed to amplify the drop of the viscosity and to reduce the gain on the yield stress induced by HPG. The results also highlight a delay in the setting-time of the cement paste by adding HPG and PCE. The delay induced by HPG is significantly lower than that generated by PCEs. However, the combination of the both kind of admixtures leads to a slightly shorter setting-time compared to the PCE alone. T2 - Second International RILEM Conference on Bio-based Building Materials, 21-23 June 2017 CY - Clermont-Ferrand, France DA - 21.06.2017 KW - Rheology KW - Cement KW - Guar Gum KW - Polysaccharide KW - Superplasticizer PY - 2017 SN - 978-2-35158-192-6 SP - 55 EP - 61 PB - RILEM Publications S.A.R.L. CY - Paris, France AN - OPUS4-43547 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmidt, Wolfram A1 - Hirya, N.N.M. A1 - Bjegovic, D. A1 - Uzoegbo, H.C. A1 - Kumaran, S.G. T1 - Cement technology in sub-Saharan Africa-practical and scientific experiences N2 - Sub-Saharan Africa is populated by more than half a billion people, and rapid urbanization is creating challenges in the areas of housing, roads, railways, power supply, dams and water pipelines — aspects of nfrastructure that are critical to the well being of the population. This situation indicates that cement and concrete will play a major role in the future construction technology in Africa, despite the fact that it does not have a long-lasting tradition over most of the continent. Although the continent is rich in natural resources for the production of mineral binder systems, many sub-Saharan African countries exhibit challenging boundary conditions, that have to be well understood in order to use cement and concrete technologies in a sustainable and reasonable way. KW - Africa KW - Cement KW - Technology transfer KW - SPIN PY - 2012 SN - 0002-7812 VL - 91 IS - 5 SP - 52 EP - 56 PB - American Ceramic Society CY - Westerville, Ohio AN - OPUS4-26075 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Marinescu, M.V.A. A1 - Schmidt, Wolfram A1 - Priebe, Nsesheye Susan A1 - Uzoegbo, H.C. A1 - Stipanovic Oslakovic, I. A1 - Kumaran, G.S. A1 - Brouwers, H.J.H. A1 - Kühne, Hans-Carsten A1 - Rogge, Andreas T1 - Recent developments and perspectives regarding the standardisation and quality surveillance of cement in the east, central and south african region N2 - The cement and concrete market in East, Central and Southern Africa is highly fragmented. The concrete industry in this area consists of multiple parties, including producers and suppliers of construction materials, formal and informal contractors, engineers and architects, unions of trades persons and workmen, governmental bodies and formal institutions of research and education. All these institutions mostly do not interact adequately, which makes building with cementitious materials susceptible to damage and failures. Completely opposed to the situation in Europe or North America, cement in Africa is often unaffordable, while manpower is cheap, which results in a questionable economisation of cement. Typically, there is not sufficient awareness of methods to sensibly reducing the cement content in concrete or replace Ordinary Portland Cement by adequate alternative materials. Research activities in this field of technology are often missing completely. Only few countries in the area, such as South Africa, are exempted from these issues. This paper presents the SPIN project, which is a joint project of a consortium of 8 African and 3 European partners within the ACP Science and Technology Programme. The project is funded by the EC and ACP Secretariat is the project body. The main objective of the current project is to strengthen the cement and concrete industry in the East and Central African regions. The project shall generate reasonable solution strategies to implement clean, safe and sustainable cement and concrete technology on the African continent, including general and specific guidelines for sensible application. Furthermore it shall be the kick-off for future projects, research activities and the world-wide expansion of a European-African network. The paper addresses special problems the cement and concrete market in Eastern, Central and Southern African countries has to face. Several options are presented in detail, which shall help overcoming the current situation. Customized solutions for the African market include rational methods for reducing the amount of cement used and the replacement of Ordinary Portland Cement with cheaper alternatives. The use of recycled concrete through a new and economically effective method, as well as the opportunity of using locally available resources is also discussed. T2 - 13th International congress on the chemistry of cement CY - Madrid, Spain DA - 03.07.2011 KW - Africa KW - Clean and safe cement production KW - Scientific network PY - 2011 SN - 978-84-7292-400-0 N1 - Geburtsname von Priebe, Nsesheye Susan: Msinjili, N. S. - Birth name of Priebe, Nsesheye Susan: Msinjili, N. S. SP - 1 EP - 6 AN - OPUS4-24041 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram ED - Priebe, Nsesheye Susan T1 - Future civil engineering challenges - Skill requirements, new professional profiles and implementation N2 - Urbanisation, habitat, environment, infrastructure and sustainability are major global challenges of the 21st century. By planning, exploiting of resources, building, and maintaining, civil engineers and relevant adjacent disciplines have been carrying a large responsibility for the existing environmental problems. Civil engineers are responsible for 70% of all material uses in the world, and civil construction has been dominating the growth of the developing world for the next decades, with enormous impact on the global climate as well as the distribution of wealth and quality of living in the world. Today a variety of sustainable construction concepts have been developed and discussed. Recently a UNEP report was published, which provides a comprehensive overview of the challenges and potentials in the future from a scientific and industrial point of view. Sustainable solutions based on abundantly available resources (pozzolana and clay) or on renewable instead of limited industrial by-products (e.g. agricultural waste ashes) and new construction echnologies do exist. By applying, promoting and developing the implementation of the existing knowledge into real life constructions, civil engineers also hold the key for the mitigation of the global challenges. Using best practice sustainable construction solutions is particularly of highest importance in the developing world, since the implementation at an early stage creates the highest leverage for positive effects. T2 - 3rd Symposium on Knowledge Exchange for Young Scientists (KEYS) CY - Johannesburg, South Africa DA - 26.6.2017 KW - Civil Engineering KW - Cement KW - Concrete KW - Global engineering KW - Nano engineered materials KW - Sustainability PY - 2017 SN - 978-3-9818270-7-1 N1 - Geburtsname von Priebe, Nsesheye Susan: Msinjili, N. S. - Birth name of Priebe, Nsesheye Susan: Msinjili, N. S. VL - 3 SP - 9 EP - 14 PB - Bundesanstalt für Materialforschung und -prüfung (BAM) CY - Berlin AN - OPUS4-40975 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ramirez Caro, Alejandra A1 - Pauli, Jutta A1 - Schmidt, Wolfram A1 - Resch-Genger, Ute T1 - Study of the superplasticizer-cement hydration interaction by optical spectroscopy N2 - 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. T2 - 2nd International Conference on the Chemistry of Construction Materials CY - Munich, Germany DA - 10.10.2016 KW - Cement KW - Dye KW - Superplasticizers KW - Fluorescence PY - 2016 SN - 978-3-936028-96-6 VL - 50 SP - 260 EP - 263 PB - Gesellschaft Deutscher Chemiker e.V. CY - Frankfurth am Main AN - OPUS4-38881 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - A simple test method to assess the influence of pces in the rheology of flowable cementitious systems T2 - 1st International RILEM Conference on Rheology and Processing of Construction Materials and 7th RILEM Conference on Self-Compacting Concrete CY - Paris, France DA - 2013-09-02 PY - 2013 AN - OPUS4-29923 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Rheological Optimisation for Flowable Mixture Compositions Specified for African Boundary Conditions T2 - International Conference on Advances in Cement and Concrete in Africa CY - Johannesburg, South Africa DA - 2013-01-28 PY - 2013 N1 - Geburtsname von Priebe, Nsesheye Susan: Msinjili, N. S. - Birth name of Priebe, Nsesheye Susan: Msinjili, N. S. AN - OPUS4-27676 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmidt, Wolfram A1 - Kühne, Hans-Carsten T1 - Kusum-Kontrollkarten mit V-Maske in der Prozesssteuerung N2 - Seit Juli 2014 liegt die EN 206:2014 als neue Betonnorm vor. Neben kleineren Änderungen ergibt sich hierdurch als einschneidende Änderung zur Vorgängerversion EN 206-1:2008 ein ergänzendes Konzept zur Konformitätsbewertung der Druckfestigkeit von Beton. An dieser Stelle werden neben dem bekannten Mittelwertkriterium alternativ sogenannte Kontrollkartenverfahren möglich. Für die Konformitätsbewertung stellt in diesem Zusammenhang insbesondere die Kusum-Methode (kumulierte Summen, aus dem Englischen cusum – cumulative sum) ein Novum dar. Weiterführende Informationen zu Kusum-Methode in der Konformitätsbewertung können der Literatur entnommen werden. Eigentlich ist die Kusum-Methode aber nicht für die Konformitätsbewertung entwickelt worden, sondern vielmehr für die Produktionskontrolle. Der Unterschied zwischen Konformitätsbewertung und Produktionskontrolle ergibt sich daraus, dass die Konformitätskontrolle eine Bedeutung für die öffentliche Sicherheit hat und dass eindeutige technische Grenzwerte vorliegen müssen, die nicht unterschritten werden dürfen, während die Produktionssteuerung ein Werkzeug mit frei wählbaren Grenzwerten für Hersteller ist. Der Handlungsbedarf ist für die Produktionskontrolle optional und ergibt sich in der Regel aus Wirtschaftlichkeitsbetrachtungen. PY - 2015 SN - 1439-7706 IS - 4 SP - 38 EP - 44 PB - ad-media-Verl. CY - Köln AN - OPUS4-33580 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmidt, Wolfram A1 - Uzoegbo, H.C. A1 - Bella, N. A1 - Rongai, G. A1 - Kühne, Hans-Carsten A1 - Diergardt, T. T1 - Cement testing in Africa - Conclusions from the first africa-wide proficiency testing scheme N2 - African cement infrastructure is quite complex. Apart from Northern Africa and South Africa in particular, cement plants are scarce resulting in highly unstable cement pricing. Clinker and cement are imported from overseas, e.g. from Portugal, Turkey, Pakistan, Indonesia, and China. Imports are typically determined by the lowest price, and as a result the countries of origin of products vary regularly yielding large scatter of properties. Quality control and a good quality infrastructure are thus of utmost importance for the safety of the populace, an issue, which is actually often neglected. With funding of the German Metrology Institute (PTB) and support of the SPIN project, a proficiency testing scheme for cement testing according to EN 196 was set up for African laboratories. Proficiency testing schemes, also called round robins, are inter-laboratory performance comparisons allowing participants to evaluate themselves against pre-established criteria. They are a powerful tool to help laboratories improve their performance as well as demonstrate their competences to accreditation bodies or customers. 26 laboratories from 20 nations, 18 of which from Africa, participated. The BAM Federal Institute for Materials Research and Testing acted as coordinator and provider of the scheme. The aim of the round robin was to interpret the submitted data further beyond the pure statistic analyses. The data provided a positive picture of the performance of the participants in general, but it also exhibited a number of technical fields that need improvement. The paper provides the general results of the scheme and analyses identified strengths and weak points based on the submitted and non submitted data as well as on discrepancies from the EN 196 procedures during measurements. The application of EN standards for material testing is critically discussed and since quality infrastructure is also always an issue between industrial and political stakeholders, suggestions for the mitigation of the identified shared problems are given. KW - Round robin KW - Quality control KW - Cement testing KW - Proficiency testing PY - 2013 SN - 2225-0514 SN - 2224-5790 VL - 4 SP - 54 EP - 58 PB - International Institute for Conservation of Historic and Artistic Works CY - New York, NY, USA AN - OPUS4-29933 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram A1 - Uzoegbo, H.C. A1 - Bella, N. A1 - Rongai, G. A1 - Kühne, Hans-Carsten A1 - Diergardt, T. ED - Diouri, A. ED - Khachani, N. ED - Alami Talbi, M. ED - Ait Brahim, L. ED - Bahi, L. T1 - Cement testing in Africa - Conclusions from the first africa-wide proficiency testing scheme N2 - African cement inffastructure is quite complex. Apart from Northern Africa and South Africa in particular, cement plants are scarce resulting in highly unstable cement pricing. Clinker and cement are imported from overseas, e.g. from Portugal, Turkey, Pakistan, Indonesia, and China. Imports are typically determined by the lowest price, and as a result the countries of origin of products vaiy regularly yielding large scatter of properties. Quality control and a good quality infrastructure are thus of utmost importance for the safety of the popuiace, an issue, which is actually often neglected. With funding of the German Metrology Institute (PTB) and Support of the SPIN project, a proficiency testing scheme for cement testing according to EN 196 was set up for African laboratories. Proficiency testing schemes, also called round robins. are interlaboratory performance comparisons allowing participants to evaluate themselves against pre-established criteria. Thev are a powerful tool to help laboratories improve their performance as well as demonstrate their competences to accreditation bodies or Customers. 26 laboratories from 20 nations, 18 of which from Africa, participated. The BAM Federal Institute for Materials Research and Testing acted as coordinator and provider of the scheme. The aim of the round robin was to interpret the submitted data further beyond the pure statistic analyses. The data provided a positive picture of the performance of the participants in general, but it also exhibited a number of technical fields that need improvement. The paper provides the general results of the scheme and analyses identified strengths and weak points based on the submitted and non submitted data as well as on discrepancies from the EN 196 procedures during measurements. The application of EN Standards for material testing is critically discussed and since quality infrastructure is also always an issue between industrial and political stakeholders, suggestions for the mitigation of the identified shared problems are given. T2 - CMSS 2013 - International congress on materials & structural stability - Building up sustainable materials & constructions CY - Rabat, Morocco DA - 27.11.2013 KW - Viscosity modifying agent KW - Metakaolin KW - Diutan gum KW - Welan gum KW - Rheology PY - 2013 SN - 978-9954-32-689-3 SP - 1 EP - 5 AN - OPUS4-30042 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram A1 - Kühne, Hans-Carsten T1 - Improvement of durability of SCC by the use of micro fly ash and limestone filler T2 - BAM-Präsentation Nanocem-Meeting CY - Copenhagen, Denmark DA - 2006-04-25 PY - 2006 AN - OPUS4-12475 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Admixtures for Innovative Concrete - Rheological Basics and Rhelogy Modifying Admixtures T2 - ACCTA 2013, Pre-Conference Workshop CY - Johannesburg, South Africa DA - 2013-01-25 PY - 2013 AN - OPUS4-27675 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmidt, Wolfram A1 - Brouwers, H.J.H. A1 - Kühne, Hans-Carsten A1 - Meng, Birgit T1 - Influence of environmental temperatures on the performance of polymeric stabilising agent in fresh cementitious materials N2 - Stabilising admixtures are commonly used additives in repair mortars and grouts. Beyond this, such type of admixture is increasingly used in concrete and other cementitious materials. In particular when fresh mortar or concrete properties have to be adjusted reliably, stabilising agents can be beneficially used to improve workability and robustness of the mixture. The mode of operation of these admixtures varies, rather affecting either the liquid phase or the solid particles in the dispersion, both causing strong interactions with the mortar or concrete system, and significant changes in their rheological behaviour. Furthermore, these are strongly affected by the environmental temperature during the casting process. In the paper the effect of temperature on the performance of stabilising agents in cementitious systems is presented and how performance changes affect fresh and hardening mortar or concrete properties. Particular attention is placed on interactions between stabilising agents and superplasticizers. Results are discussed with special focus on self-compacting concrete. KW - Biopolymers KW - Cementitious materials KW - Polycarboxylate ether KW - Rheology KW - Setting KW - Stabilising agent KW - Starch ether KW - Self-compacting concrete KW - Superplasticizer PY - 2011 DO - https://doi.org/10.4028/www.scientific.net/KEM.466.97 SN - 1013-9826 VL - 466 SP - 97 EP - 104 PB - Trans Tech Publ. CY - Aedermannsdorf AN - OPUS4-22853 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - GEN A1 - Schmidt, Wolfram A1 - Brouwers, J. A1 - Kühne, Hans-Carsten A1 - Meng, Birgit ED - Khayat, K. H. ED - Feys, D. T1 - Effects of superplasticizer and viscosity-modifying agent on fresh concrete performance of SCC at varied ambient temperatures N2 - Varying ambient temperatures in plants or on construction sites during casting of SCC can cause serious problems affecting the fresh concrete performances, such as rheological properties and setting time, with consequences for the hardened properties in the structure. By sensible choices of the components, the robustness of SCC mixtures against temperature variations can be improved. However, this aspect has not been the focus of intensive research yet. In this study the effects of varied ambient temperatures on the early performance of differently composed SCC mixtures are investigated, with emphasis on changes in rheology, early deformations, heat evolution and setting. Focus is placed on the study of the influence of the polycarboxylate ether molecule type as well as different viscositymodifying agents on the temperature robustness. Effects on the relevance for practical concrete applications are evaluated, which will provide a reliable framework of possible actions on the appropriate use of admixtures for SCC. T2 - SCC 2010 - 6th International RILEM Symposium on self-compacting concrete / 4th North American conference on the design and use of SCC - Desgin, Production and Placement of self-consolidating concrete CY - Montreal, Canada DA - 2010-09-26 KW - Polycarboxylate KW - Modified starch KW - Rheology KW - Self-compacting concrete KW - Temperature KW - Yield stress KW - Viscosity PY - 2010 SN - 978-90-481-9663-0 DO - https://doi.org/10.1007/978-90-481-9664-7_6 N1 - Serientitel: RILEM bookseries – Series title: RILEM bookseries VL - 1 IS - 2 SP - 65 EP - 77 PB - Springer AN - OPUS4-22126 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Möglichkeiten zur Steuerung der Robustheit von selbstverdichtendem Beton gegenüber veränderlichen Umgebungstemperaturen N2 - Selbstverdichtender Beton (SVB) findet kaum Anwendung als Transportbeton. Ein wesentlicher Grund hierfür ist, dass die Außentemperaturen auf der Baustelle nicht gesteuert werden können. Während des Betonierens können allerdings Schwankungen in der Umgebungstemperatur die rheologischen Eigenschaften aber auch das Erstarrungsverhalten signifikant beeinflussen, wodurch in der Folge auch Veränderungen im Festbeton auftreten können. Durch geeignete Wahl der Komponenten kann die Robustheit von SVB gegenüber Einflüssen aus den Umgebungsbedingungen deutlich verbessert werden. In der vorgestellten Arbeit werden anhand von Untersuchungen am Betonrheometer, am Setzfließmaß und am Erstarren nach Vicat die Einflüsse von veränderlichen Umgebungstemperaturen auf die frühen Eigenschaften von SVB dargestellt. Der Fokus liegt auf Effekten, die durch die Modifikation von Polycarboxylatether-Fließmitteln und durch Stabilisierer eingetragen werden. Darüber hinaus wird der Einfluss des Mischungsentwurfes gezeigt. Die Ergebnisse werden mit Relevanz für praktische Betonanwendungen analysiert und es werden die wichtigen Einflussgrößen zur Verbesserung der Robustheit von SVB gegenüber Temperaturschwankungen herausgearbeitet. T2 - DAfStb Doktorandensymposium 2010 - 51. Forschungskolloquium CY - Kaiserslautern, Deutschland DA - 2010-11-11 KW - Selbstverdichtender Beton KW - Erstarren KW - Verarbeitungseigenschaften KW - Rheologie KW - Stabilisierer KW - Fließmittel PY - 2010 VL - 2 IS - Kap. C1 SP - 527 EP - 538 AN - OPUS4-22664 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Effect of superplasticizer and stabilising agent type on fresh concrete performance of SCC at varied ambient temperatures T2 - SCC2010 6th Int. RILEM Symposium on Self-Compacting Concrete - 4th North American Conference on the Design and Use of SCC CY - Montreal, Canada DA - 2010-09-26 PY - 2010 AN - OPUS4-20855 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Temperature related Effects on Self-Consolidating Concrete due to Interactions between Superplasticizers, supplemental Admixtures and Additions T2 - 9th International Conference on Superplasticizers and Other Chemical Admixtures in Concrete CY - Seville, Spain DA - 2009-10-12 PY - 2009 AN - OPUS4-20856 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Robustness improvement for Concrete at challenging climatic conditions T2 - Vorlesung im Rahmen des Kick-Off Meetings zum SPIN Projekt "Spearhead Network for Innovative, Clean and Safe Cement and Concrete Technologies" CY - Kigali, Rwanda DA - 2011-01-18 PY - 2011 AN - OPUS4-23183 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - LightSHIP Lightweight Construction - Scientific Cooperation for Housing with Innovative Panel Technology T2 - Workshop Cement and Concrete for Africa, BAM CY - Berlin, Germany DA - 2011-08-17 PY - 2011 AN - OPUS4-24727 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Möglichkeiten zur Steuerung der Robustheit von selbstverdichtendem Beton gegenüber veränderlichen Umgebungstemperaturen T2 - DAfStb Doktorandensymposium 2010 - 51. Forschungskolloquium CY - Kaiserslautern, Germany DA - 2010-11-11 PY - 2010 AN - OPUS4-22709 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kühne, Hans-Carsten A1 - Schmidt, Wolfram T1 - Der Siebtrennversuch nach prEN 12350-11 KW - SCC KW - SVB KW - Prüfverfahren KW - Sedimentation KW - Siebtest KW - EN 12350-11 PY - 2007 SN - 0005-9846 VL - 57 IS - 10 SP - 448 EP - 454 PB - Verlag Bau + Technik CY - Erkrath AN - OPUS4-16148 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmidt, Wolfram A1 - Wend, Dirk A1 - Kühne, Hans-Carsten A1 - Meng, Birgit T1 - Einfluss der Fließmittelmdoifikation auf Prozesse während der frühen Hydratation von selbstverdichtenden Bindemitteln N2 - Selbstverdichtender Beton (SVB) unterscheidet sich wesentlich von Normalbeton in der Höhe der Fließmitteldosierung. Die Funktionsweise von Fließmitteln auf Basis der für SVB üblichen Polycarboxylatether-Fließmittel (PCE) ist heutzutage in der bauchemischen Forschung sehr gut verstanden, allerdings dringt die Kenntnis über die Zusammenhänge nicht immer gleichermaßen umfangreich in die Praxis durch. Anders als frühere Fließmittelwirkgruppen, die auch heute noch einen wesentlichen Anteil am Fließmittelmarkt haben, sind PCEs äußerst vielgestaltig. Die Polymergeometrien können individuell auf die geforderten Leistungseigenschaften für bestimmte Anwendungen abgestimmt werden. Allerdings kann die Auswahl eines Fließmittels für spezifizierte rheologische Eigenschaften gleichsam den anschließenden Hydratationsprozess sehr stark beeinflussen. Der Ladungsdichte des verwendeten PCEs kommt dabei im Zusammenhang mit der Rheologie als auch der frühen Hydratation eine Schlüsselrolle zu. KW - Rheologie KW - Frühe Zementhydratation KW - Polycarboxylatether KW - Vicat KW - Schwinden PY - 2012 SN - 1439-7706 VL - 4 SP - 66 EP - 71 PB - ad-media-Verl. CY - Köln AN - OPUS4-26356 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Priebe, Nsesheye Susan A1 - Schmidt, Wolfram A1 - Kühne, Hans-Carsten T1 - The SPIN project N2 - Globally, cement and concrete experts are at the cutting-edge to sustainable, green, healthy but nonetheless high-performance concrete. In the present age, concrete is not yet well established in Africa, which öfters the unique opportunity to build up a cement and concrete market based on the highest available state of technology. As this industry needs high level expertise, a central issue in implementation of skilled technology is cross-linking research institutions and laboratories. It should not be neglected that concrete is a product with comparably low transport ranges, which means that an improved concrete market will mainly support the local economy without exceeding financial drains to the international market, thus fostering the fight against poverty, which is an urgent need in most African countries. The SPIN project highlights recent developments in the field of cement and concrete research with impact on the local and global economy. Challenges, future developments and opportunities for the African construction industry are in the focus. The SPIN project is funded by the European Commission (EC) and supported by the African, Caribbean and Pacific (ACP) Group of States under the project body of the ACP Science and Technology Programme. SPIN is acronym for “Spearhead network for Innovative, Clean and Safe Cement and Concrete Technologies”. The project aims to cross-link experts with industry and policy making bodies, aiming to establish sustainable cement and concrete construction in Africa. T2 - Workshop cement and concrete for Africa CY - Berlin, Germany DA - 17.08.2011 PY - 2011 SN - 978-3-9814281-4-8 N1 - Geburtsname von Priebe, Nsesheye Susan: Msinjili, N. S. - Birth name of Priebe, Nsesheye Susan: Msinjili, N. S. SP - 5 EP - 9 PB - Bundesanstalt für Materialforschung und -prüfung (BAM) CY - Berlin AN - OPUS4-24778 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Priebe, Nsesheye Susan A1 - Schmidt, Wolfram A1 - Kühne, Hans-Carsten ED - Rogge, A. ED - Meng, B. T1 - Cement and concrete development in Africa: the role of the SPIN project T2 - 52. DAfStb-Forschungskolloquium CY - Berlin, Deutschland DA - 2011-11-07 PY - 2011 SN - 978-3-9814281-0-0 N1 - Geburtsname von Priebe, Nsesheye Susan: Msinjili, N. S. - Birth name of Priebe, Nsesheye Susan: Msinjili, N. S. SP - 339 EP - 344 PB - BAM Bundesanstalt für Materialforschung und -prüfung CY - Berlin AN - OPUS4-25172 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Meng, Birgit A1 - Schmidt, Wolfram A1 - Kühne, Hans-Carsten ED - Rogge, A. ED - Meng, B. T1 - Aktuelle Forschungsansätze zur Rheologie von Frischbeton T2 - 52. DAfStb-Forschungskolloquium CY - Berlin, Deutschland DA - 2011-11-07 KW - Baustoffe KW - Beton KW - Frischbeton KW - Rheologie PY - 2011 SN - 978-3-9814281-0-0 SP - 33 EP - 39 PB - BAM Bundesanstalt für Materialforschung und -prüfung CY - Berlin AN - OPUS4-25195 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - The SPIN network for knowledge-driven, sustainable and clean cement and concrete technology in Africa - Practical experiences from international research cooperation between Europe and Africa T2 - 2nd Joint Stakeholder Conference of the EDULINK and the ACP Science and Technology (ACP S&T) programmes CY - Brussels, Belgium DA - 2011-10-26 PY - 2011 AN - OPUS4-24743 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram A1 - Kühne, Hans-Carsten A1 - Meng, Birgit T1 - Zum Einfluss des Mischungsentwurfs und des Fließmittels auf temperaturbedingte Veränderungen der Rheologie von SVB T2 - 52. DAfStb-Forschungskolloquium, BAM CY - Berlin, Germany DA - 2011-11-07 PY - 2011 AN - OPUS4-25129 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram A1 - Priebe, Nsesheye Susan A1 - Kühne, Hans-Carsten ED - Alexander, M. G. ED - Beushausen, H.-D. ED - Dehn, F. ED - Moyo, P. T1 - Robustness improvement of fresh concrete and mortar performance for challenging casting environments with focus on sub-Saharan Africa N2 - For various concrete applications, the early properties are a major specification, determining the functioning, the mechanical properties, and the durability of structures. The rheological properties of cementitious systems are depending on the water-cement interaction as well as on interactions of chemical admixtures with the cement hydration. The cement hydration, however, is strongly affected by the environmental boundary conditions, such as the climate or the available equipment for the proportioning and dispersion of concrete. This paper presents strategies for the robustness improvement of fresh properties of cementitious systems for challenging and particularly warm climate conditions. After explaining the basic mechanisms affecting the workability, practical conclusions are drawn with special attention on the circumstances of sub-Saharan Africa, where the climatic conditions are difficult and the casting technology is often limited. Solutions are suggested, how despite the disadvantageous circumstances, highly elaborate engineered concrete and mortar can be applied safely and with consistent quality. T2 - 3rd International conference on concrete repair, rehabilitation and retrofitting III CY - Cape Town, South Africa DA - 03.09.2012 PY - 2012 SN - 978-0-415-89952-9 N1 - Geburtsname von Priebe, Nsesheye Susan: Msinjili, N. S. - Birth name of Priebe, Nsesheye Susan: Msinjili, N. S. IS - Theme 4 SP - 1324 EP - 1329 PB - CRC Press CY - London, UK AN - OPUS4-26503 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmidt, Wolfram A1 - Gluth, Gregor T1 - Knowledge transfer and quality assurance - key factors for the future prospects of building with cement in Africa / Wissentransfer und Qualitätssicherung - Schlüsselfaktoren für die Zukunftsperspektiven der Bauweise mit Zement in Afrika N2 - The SPIN Project included workshops for young academics and building materials laboratories of the cement and concrete sector. Within the framework of the SPIN Project, plans were discussed for the conference 'Advances in Cement and Concrete Technology in Africa' that will take place in January 2013. A lecture on application rules for shotcrete construction was given by Prof. Regina Stratmann-Albert who took part in the courses as guest speaker. A short lecture was given by Akindehinde Ayotunde on the use of starch in cement-bound systems. Renato Rajzer talked about standard regulations for quality assurance during site operation. A workshop for an interlaboratory comparison took place with participants from all regions of Africa to test cement according to the standard series EN 196. The Round Robin test comprises the determination of the tensile bending and compressive strengths according to EN 196-1, of the water demand, the initial and final set, and the soundness according to EN 196-3 as well as of the fineness according to EN 196-6. KW - Africa KW - Cement KW - Concrete KW - Proficiency testing KW - Round robin PY - 2012 SN - 0949-0205 N1 - Sprachen: Deutsch/Englisch - Languages: German/English VL - 65 IS - 9 SP - 34 EP - 38 PB - Bauverl. BV CY - Gütersloh AN - OPUS4-26535 LA - mul AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmidt, Wolfram T1 - Start of round-robin test for cement testing in Africa T1 - Start für Ringversuch zur Zementprüfung in Afrika N2 - Within the scope of the SPIN project (www.spin.bam.de), three staff members of the Federal Institute for Materials Research and Testing (BAM), Berlin, traveled to Tanzania on 30 June. There they, together with scientists from several other African countries, were to give a course of lectures for Masters and Ph.D. students as well as leading a kick-off workshop for an all-African round-robin test for cement testing. The first stop of the BAM staff was in Zanzibar, where they inspected an on-going a building reinstatement project and discussed plans for the conference “Advances in Cement and Concrete Technology in Africa” (www.accta2013.com) to be held in January 2013. At the international conference in Johannesburg, which is mainly organized by BAM and the University of the Witwatersrand, more than 300 visitors from over 40 nations will come together. KW - Africa KW - Cement KW - Concrete KW - Proficiency testing KW - Round robin PY - 2012 UR - http://www.bft-international.com/de/artikel/bft_2012-08_Start_fuer_Ringversuch_zur_Zementpruefung_in_Afrika_1468912.html SN - 0373-4331 SN - 1865-6528 N1 - Sprachen: Deutsch/Englisch - Languages: German/English VL - 08 SP - 54 EP - 55 PB - Bauverl. CY - Gütersloh AN - OPUS4-26429 LA - mul AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Robustness Improvement of Fresh Concrete and Mortar Performance for Challenging Casting Environments with Focus on Sub-Saharan Africa T2 - 3rd International Conference on Concrete Repair, Rehabilitation and Retrofitting CY - Cape Town, South Africa DA - 2012-09-03 PY - 2012 N1 - Geburtsname von Priebe, Nsesheye Susan: Msinjili, N. S. - Birth name of Priebe, Nsesheye Susan: Msinjili, N. S. AN - OPUS4-26732 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Self-Compacting Concrete - A Solution to Improve the Fresh Concrete and Mortar Performance for the Challenging Casting Environments of Sub-Saharan Africa T2 - Workshop Cement and Concrete Technology at the University of the Witwatersrand CY - Johannesburg, South Africa DA - 2012-09-07 PY - 2012 AN - OPUS4-26731 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Importance of Cement Proficiency Testing T2 - SPIN Meeting and Cement and Concrete Workshop CY - Dar Es Salaam, Tanzania DA - 2012-07-01 PY - 2012 AN - OPUS4-26399 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram A1 - Uzoegbo, H.C. A1 - Priebe, Nsesheye Susan A1 - Kühne, Hans-Carsten A1 - Rogge, Andreas ED - Uzoegbo, H.C. ED - Schmidt, Wolfram T1 - Experiences in an African-European-cooperation project: strengthening research capacity in cement and concrete in Africa N2 - This report is based on a three-year experience as coordinator of the ACP-EU funded SPIN project. The project involved eight African and three European partners. Practical and unforeseeable problems are addressed that occurred during the project implementation and ways how they were successfully solved are reported. The major problems in many African institutions were administrations that are not used to work in multi-national consortia and a lack of institutional support for the African researchers. In Europe a misjudgement of the African boundary conditions as well as inflexible administrations caused problems. Finally the funding scheme did not always allow to easily overcome the high number of unexpected practical problems. A major deficit identified during the project was a general trend in Africa to underestimate the role of research for the development of the continent. Most universities focus on teaching applied sciences, which is without doubt important to cover the market need for qualified staff in the rapidly growing African industries. However, this makes it unattractive for highly qualified performers to conduct research on the continent. Furthermore this leads to the situation that the curricula can only contain second hand knowledge. In order to attract international high level researchers, it is suggested to install multi-national regional excellence research centres that only promote PhD and post-doc research on a level that can cope with highest international excellence. High level research is often perceived as not capable of focusing on immediate actual problems that many African economies have to cope with.. However, it is considered to be very sustainable in terms of autonomy and mastering future challenges. T2 - ACCTA - International conference on advances in cement and concrete technology in Africa 2013 CY - Johannesburg, South Africa DA - 28.01.2013 PY - 2013 SN - 978-3-9815360-3-4 N1 - Geburtsname von Priebe, Nsesheye Susan: Msinjili, N. S. - Birth name of Priebe, Nsesheye Susan: Msinjili, N. S. SP - 1177 EP - 1184 AN - OPUS4-27762 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ramge, Peter A1 - Schmidt, Wolfram A1 - Kühne, Hans-Carsten ED - Uzoegbo, H.C. ED - Schmidt, Wolfram T1 - Effect of the storage of cement on early properties of cementitious systems N2 - As soon as cement is mixed with water, the hydration reaction starts to set of. The progression of the hydration process is governed by the amount and the availability of water and its possibility to access the unhydrated cement grain surfaces. For a total hydration cement theoretically requires water amounting approximately 0.38 of its own mass. Nevertheless, due to the cement’s highly hygroscopic nature, already the moisture in the ambient air can cause first hydration reactions to set in upon the cement grain surfaces. Such pre-hydration processes have an effect on the cement's properties. Dpending on the specific conditions during the storage the significance of the impact on certain properties can vary. If cement is consumed soon after production and is transported only short distances in a silo wagon to its final destination for immediate use without further stock transfer, the effects are rather negligible. However, if cement is delivered in bags, transported over long distances, shifted serval times and stored for longer time periods until it is finally consumend, these effects can be quite severe. Due to the actual logistical situation with comparably few cement plants, large delivery distances and partially less developed infrastructures, the latter scenario pictures the situation for the most cases in Africa quite well. In order to verify the relevance of the pre-hydation for practical application, a series of tests was conducted at the German Federal Institute for Materials Research and Testing (BAM). The influence of the cement storage on gresh and hardened concrete properties was investigated for different concrete and mortar types. The investigations show that the impact of the storage conditions is more pronounced for specialized concretes with high sophisticated optimized mixture compositions containing admixtures. Nevertheless, the effects also occur for ordinary concrete and should not be ignored. T2 - ACCTA - International conference on advances in cement and concrete technology in Africa 2013 CY - Johannesburg, South Africa DA - 28.01.2013 KW - Cement KW - Storage KW - Ambient conditions KW - Hydration KW - Pre-hydration KW - Atmospheric humidity PY - 2013 SN - 978-3-9815360-3-4 SP - 339 EP - 347 AN - OPUS4-27757 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Why does Africa need African Concrete? An Observation of Concrete in Europe, America and Asia - and Conclusions for Africa T2 - International Conference on Advances in Cement and Concrete in Africa CY - Johannesburg, South Africa DA - 2013-01-28 PY - 2013 AN - OPUS4-28461 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Interactions between PCE and different polysaccharides and influences on the early hydration of cement T2 - 1st International Conference on the Chemistry of Construction Materials CY - Berlin, Germany DA - 2013-10-07 PY - 2013 AN - OPUS4-29920 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Peculiarities of African Cement and Condrete Markets - Challenges and Opportunities T2 - Global Issues in Concrete Construction CY - Johannesburg, South Africa DA - 2013-09-18 PY - 2013 N1 - Geburtsname von Priebe, Nsesheye Susan: Msinjili, N. S. - Birth name of Priebe, Nsesheye Susan: Msinjili, N. S. AN - OPUS4-29922 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmidt, Wolfram A1 - Brouwers, H.J.H. A1 - Kühne, Hans-Carsten A1 - Meng, Birgit T1 - The working mechanism of starch and diutan gum in cementitious and limestone dispersions in presence of polycarboxylate ether superplasticizers N2 - Polysaccharides provide high potential to be used as rheology modifying admixtures in mineral binder systems for the construction industry such as concrete or mortar. Since superplasticizers have become state of technology, today, concrete is more and more adjusted to flowable consistencies. This often goes along with the risk of segregation, which can be effectively avoided by adding stabilising agents supplementary to superplasticizers. Stabilising agents are typically based on polysaccharides such as cellulose, sphingan gum, or starch. Starch clearly distinguishes in its effect on rheology from other polysaccharides, mainly due to the strong influence of amylopectin on the dispersion and stabilisation of particles. Based on rheometric investigations on cementitious and limestone based dispersions with different volumetric water to solid ratios, the mode of operation of modified potato starch is explained in comparison to a sphingan gum. It is shown that the stabilising effect of starch in a coarsely dispersed system is mainly depending upon the water to solid ratio and that above a certain particle volume threshold starch mainly affects the dynamic yield stress of dispersions, while plastic viscosity is affected only to a minor degree. Sphingans operate more independent of the particle volume in a coarsely dispersed system and show significantly higher effect on the plastic viscosity than on the yield stress. In systems incorporating superplasticizers, influences of both stabilising agents on yield stress retreat into the background, while both observed polysaccharides maintain their effect on the plastic viscosity. KW - Cement KW - Limestone KW - Rheology KW - Stabilising agent KW - Coarsely dispersed systems KW - Diutan gum KW - Starch ether PY - 2013 DO - https://doi.org/10.3933/ApplRheol-23-52903 SN - 1430-6395 SN - 0939-5059 VL - 23 IS - 5 SP - 52903-1 EP - 52903-12 PB - Kerschensteiner CY - Lappersdorf AN - OPUS4-29932 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Controlling rheology - The key to individual concrete performance specifications N2 - During the last three decades concrete has emerged from a rather simple mass construction material based on only the three components cement, water, and aggregates towards a high performance material, which can be adjusted for high performance applications and according to ultimate user specifications. The reason for the rapid evolvement was the increasing awareness about how the rheology of concrete can be improved without negatively affecting the mechanical properties of concrete. Hence, mineral additions and in particular Chemical admixtures have been the most influential factors for the technological boost since approximately the 1980s. The incorporation of superplasticizers into concrete mixture compositions eventually facilitated concrete engineers to improve the workability properties without need to increase the water-cement-ratio (w/c) and furthermore to significantly reduce the w/c without loss of workability. This finally resulted in concrete with higher performance and specified properties. Fillers are basically used to improve the particle packing of cementitious Systems, but they can also be used beneficially to support the rheology, since they modify the water demand and may interact with superplasticizers as well. Finally, supplementary admixtures like polysaccharides have become more populär in the field of mortar, plaster, and grout technology. They can have a variety of rheological effects on cementitious Systems, which can be used to individually adjust their performance. The possibility to control the rheology and the significantly widened ränge of consistencies that can be adjusted opened up the gates for modern concrete and any type of high performance concrete. Therefore, without doubt, it can be concluded that the capability to control the rheology of concrete Systems can be considered as the catalyst for the invention of the many recent mortar and concrete innovations such as polymer modified cementitious composites (PCC) self-compacting concrete (SCC), high-performance concrete (HPC), ultra-high performance concrete (UHPC) or engineered cementitious composites (ECC). Therefore, understanding the rheology of cementitious Systems and how to control the workability by the use of Chemical admixtures is the key to innovations in concrete technology. However, the other side of the coin of versatility is that sophisticated cementitious Systems have become more sensitive. Hence, concrete mixture composition with admixtures demands for a high level of expertise and often there is lack of awareness about the mode of Operation of rheology modifying admixtures among concrete technoiogists. The paper gives a comprehensive overview about rheology modifying constituents such as superplasticizers, stabilising agents, and mineral fillers, and how they can be used depending upon the application in the most favourable way. T2 - Facade coatings and plasters - European coatings conference CY - Düsseldorf, Germany DA - 29.10.2013 PY - 2013 SP - 93 EP - 102 PB - Vincentz AN - OPUS4-30827 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Barthel, Maria A1 - Schmidt, Wolfram A1 - Kühne, Hans-Carsten T1 - Mitigation of the urban heat island effect by self-cooling concrete pavers N2 - Worldwide an increasing migration from rural to urban regions can be observed. Hence cities are growing and as a result the building density and the land sealing rise. Concrete as commonly used building material in urban structures provides a high heat storage capacity. Therefore the microclimate in cities has become warmer than in the surrounding areas. This phenomenon is called Urban Heat Island Effect. To mitigate this situation a large scale application of self-cooling concrete pavers is an approach to reduce the urban heat island effect. Making use of evaporation enthalpy, this new type of pavements counterbalances the absorption of solar radiation and the subsequent transfer of heat to the surrounding environment. The typical double-layer structure of concrete paving stones can be maintained. The mass concrete acts as a water storage layer and is covered by a permeable face concrete. As the different requirements of these layers demand different concrete mixtures, they are developed and optimised for their respective functions. This paper presents some suitable no-slump concrete mixtures that combine a sufficient compressive strength as well as good water transportation properties for the above mentioned approach. KW - Pavement KW - Urban heat island KW - No slump concrete KW - Fibers PY - 2013 SN - 2225-0514 SN - 2224-5790 VL - 4 SP - 35 EP - 39 PB - International Institute for Conservation of Historic and Artistic Works CY - New York, NY, USA AN - OPUS4-29931 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram A1 - Brouwers, H.J.H. A1 - Kühne, Hans-Carsten A1 - Meng, Birgit T1 - Interactions between PCE and different polysaccharides and influences on the early hydration of cement N2 - ln order to observe the influence of stabilising agents (STA) based on starch and diutan gum, rheometric experiments and setting tests were conducted on cement pastes with and without PCE superpiasticizers. The results show that with regard to yield stress both STAs show differing behaviours in Systems without PCE. In presence of PCE, yield stress infiuences of the STAs retreat into the background. The Vicat results exhibit that STAs can reduce the retard ing effect of PCE. T2 - 1st International conference on the chemistry of construction materials CY - Berlin, Germany DA - 07.10.2013 PY - 2013 SN - 978-3-936028-75-1 N1 - Serientitel: GDCh-Monographien – Series title: GDCh-Monographien VL - 46 SP - 49 EP - 52 AN - OPUS4-30045 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Zum Einfluss der Fließmittelmodifikation auf die Verarbeitungseigenschaften fließfähiger Betone - Hintergründe und Optimierungspotential T2 - betonbau.aktuell 2014 CY - Apolda, Germany DA - 2014-02-13 PY - 2014 AN - OPUS4-30831 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Self-Compacting concrete-Past, Present and Futere T2 - Totally Concrete Expo Conference 2014 CY - Johannesburg, South Africa DA - 2014-05-26 PY - 2014 AN - OPUS4-30829 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Quality Control in Concrete Production T2 - Public Seminar at the School of Civil and Environmental Engineering CY - Johannesburg, South Africa DA - 2014-05-29 PY - 2014 AN - OPUS4-30833 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -