TY - CONF A1 - Lehmann, C. A1 - Meng, Birgit A1 - Nemecek, J. ED - Ludwig, H.-M. T1 - Investigations on the process of autoclaving ultra-high performance concrete (UHPC) T2 - 19. Ibausil - Internationale Baustofftagung N2 - Concrete technology results more and more in the development of materiale with enhanced properties, such as high strength, higher durability and increased ecological compatibility. One exceptional example is Ultra-High Performance Concrete (UHPC). Its advantages are very high compressive strength and an improved durability, caused by their dense micro structure. Curing under water vapor Saturation pressure (autoclaving) can improve these properties by affecting the micro structure and better the mechanical properties of UHPC. Autoclaving leads to an enhanced cement hydration and accelerated reaction rate of supplementary cementitious materials (SCM) and mineral additions, Used at the production of aerated autoclaved concrete (AAC) and sand-lime bricks, the process of autoclaving is well known, especially in highly porous Systems. One well known requirement to autoclave effectively is a porosity of at least 10%. There is no sufficient heat transfer and also not enough water available if the porosity is lower, Nevertheless, autoclaving also works in the dense structure of UHPC with porosities lower than 2%, as former investigations have shown. There is only a visible difference between the outer parts of the samples compared to their core. Investigations on the chemistry, the micro structure as well as the mechanical properties where performed to find an explanation to this effect and to explain the functionality of autoclaving UHPC in spite of the low porosity. T2 - 19. Ibausil - Internationale Baustofftagung CY - Weimar, Germany DA - 16.09.2015 PY - 2015 SN - 978-3-00-050225-5 VL - 2 SP - P2.15, 2-1039 EP - 2-1044 AN - OPUS4-34872 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Nemecek, J. A1 - Lehmann, Christian A1 - Fontana, Patrick T1 - Nanoindentation on ultra high performance concrete system JF - Chemické listy N2 - In the past decade, nanoindentation has become commonly used experimental technique for obtaining quantitative data on elastic and inelastic material properties in small volumes, typically in submicron length scale. The methodology was developed mainly for homogeneous materials or, at least, the homogeneity is assumed far enough from the tested volume in evaluation procedures1. Measurement on a heterogeneous system, in which the material phases are intermixed in small volume, is still a challenging task due to several circumstances. First, the preparation of a flat surface on the heterogeneous sample with high differences in stiffness needs Special care. Second, the mechanical interaction between the material phases during surface loading is often unavoidable and therefore the extraction of intrinsic properties of individual phases from the heterogeneous system may not be possible. If differences between the stiffnesses of the interacting phases are low, finding of intrinsic properties can be successful using conventional Evaluation. In other cases, the error in estimating intrinsic properties can reach tens of percent. KW - Mechanical properties KW - nanoindentation KW - Grid indentation KW - Heterogeneous system KW - Ultra high performance concrete PY - 2011 SN - 0009-2770 VL - 105 SP - s656 EP - s659 PB - CSAV CY - Praha AN - OPUS4-25645 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -