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 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 - 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 - 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 - 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 -