TY - CONF A1 - Meng, Birgit A1 - Simon, Sebastian A1 - Sigmund, Sandra A1 - Ziemann, M. A. A1 - von Werder, Julia T1 - Characterization of Alkali-Silica Reaction Products by means of Raman Spectroscopy before and after Application of Accelerated Tests N2 - Alkali silica reaction (ASR) is a major concrete durability problem resulting in significant maintenance and reconstruction costs for concrete infrastructures all over the world. To determine whether an aggregate is potentially reactive, accelerated concrete tests are used. Aim of this study is the chemical and microstructural characterization of ASR-products formed under the performance conditions of motorway pavements and during subsequent tests on the remaining ASR susceptibility. Samples were taken from concrete motorway pavements. Some of the samples already showed first indications for beginning damages whereas others showed deteriorations only after applying a performance testing procedure for the estimation of future risk of ASR damage. In a first step ASR-products were identified by polarized light microscopy in thin sections. The reaction products where then analyzed by Raman Spectroscopy and finally the chemical composition of the ASR-products was identified by SEM with EDX. The results indicate that most reaction products show an increasing Ca/Si-ratio with progressive crack length. If an ASR-product develops inside an aggregate and moves through the cement paste, it has a high (Na+K)/Si-ratio at the beginning which decreases with increasing distance from its place of origin. The Raman spectra of the ASR-products are characterized by two broad bands indicating specific Q-species of different amorphous gel networks. Within the scope of the analysis distinctions in the microstructure and the chemical composition of the ASR-gels were detected relating to various conditions of accelerated testing. T2 - 15th International Congress on Chemistry of Cement CY - Prague, Czech Republic DA - 16.09.2019 KW - Alkali-silica reaction KW - Raman microscopy KW - Microstructure KW - Concrete motorway pavements KW - Performance test PY - 2019 AN - OPUS4-49527 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Voigt, Marieke A1 - von Werder, Julia A1 - Meng, Birgit ED - Caprai, V. ED - Brouwers, H. J. H. T1 - Investigation of the zonation of thermally treated ultra high performance concrete N2 - Ultra high performance concrete (UHPC) is characterised by its high compressive strength of more than 150 MPa and its high durability. Due to thermal treatment at 90°C a strength comparable to the 28-days-strength can be achieved immediately after the treatment and in some cases can be even further increased up to 30 %. The explanations for the increase in strength are the accelerated hydration of the clinker minerals and the intensified pozzolanic reaction contributing to a denser microstructure and hence, a high performance in compressive strength. Former research shows that thermal treatment can lead to inhomogeneities in form of a visible zonation within the cross-section. The width of the margin increases with shorter pre-storage time before the thermal treatment and with omitting protective measures against desiccation during the treatment. Specimens exhibiting a zonation typically show a lower compressive strength compared to the undisturbed reference whereas changes in chemistry, mineral content and microstructure were not reported in detail. In this study the zonation of thermally treated UHPC is investigated with respect to its chemistry, mineral composition and microstructure to allow predictions on durability and strength development. Measurements show a change in pore sizes, minerals phase composition and element distribution leading to the visible zonation and weaker bending tensile strength compared to the reference. T2 - 2nd International Conference of Sustainable Building Materials CY - Eindhoven, Netherlands DA - 12.08.2019 KW - UHPC KW - Thermal treatment KW - Zonation KW - Desiccation KW - Microstructure KW - Durability PY - 2019 VL - 2 SP - 185 EP - 193 AN - OPUS4-49479 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - von Werder, Julia A1 - Fontana, P. A1 - Hoppe, Johannes A1 - Bilgin, S. A1 - Meng, Birgit ED - Serrat, C. ED - Casas, J. R. ED - Gibert, V. T1 - Composite Facade Elements with Self-Cleaning Surface made of Ultra-High-Performance Concrete (UHPC) N2 - In the framework of the European project H-House various concrete façade elements were developed with the aim to ensure a long service life by combining a very durable material with self-cleaning properties. The façade elements presented are made of a shell of UHPC filled with blocks of aerated autoclaved concrete as insulating material. Self-cleaning properties were realized amongst others by imprinting a microstructure into the surface during casting. The paper focuses on selected technological aspects of the manufacturing process of prototypes which had to be performed in two concreting sections. Furthermore the challenges faced when upscaling the self-cleaning properties are addressed and the strategy to assess the self-cleaning properties by measuring the contact and the roll-off angel is presented. The results show that a successfull upscalaing process requires detailed planning and that the best results can often be achieved with a moderate work effort or material use. T2 - XV International Conference on Durability of Building Materials and Components (DBMC 2020) CY - Online meeting DA - 20.10.2020 KW - Ultra-High-Performance Concrete KW - Facade Elements KW - Self-Cleaning Properties KW - Adhesive Pull-Strength KW - Microstructure KW - Architectural Concrete PY - 2020 SN - 978-84-121101-8-0 SP - 1289 EP - 1297 PB - International Center for Numerical Methods in Engineering (CIMNE) CY - Spain AN - OPUS4-51967 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -