TY - CONF A1 - Werner, Steve A1 - Kustermann, A. A1 - Thienel, K.-Ch. T1 - Analyzing the influence of Maximum aggregate size upon the concrete behavior under projectile impact by means of fracture mechanic and surface analytic methods T2 - 15th International Symposium of Interaction of the Effects of Munitions with Structures (ISIEMS) CY - Potsdam, Germany DA - 2013-09-17 PY - 2013 AN - OPUS4-29165 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Werner, Steve A1 - Schmidt, Wolfram A1 - Pirskawetz, Stephan A1 - Rogge, Andreas ED - Khayat, Kamal Henry T1 - Fire spalling of self-compacting concrete mixtures with different limestone powder contents N2 - Self-compacting concrete typically contains a higher content of powder materials than normal concrete. Furthermore it is assumed that the use of superplasticizers yields a more homogenous microstructure in the hardened paste. Both aspects generate a very dense microstructure, which can be assumed to cause material behaviour that differs from than normal concrete when it is exposed to elevated temperatures. However, the paste volumes in SCC can vary significantly based on the mixture composition. At a low paste volumes SCC can be very similar to normal concrete at hardened state while it can vary greatly at higher paste volumes. Since the high temperature behaviour of concrete is strongly affected by the different physical behaviour of the paste and the aggregates, it is likely that the high temperature behaviour is consequently strongly affected by the ratio of these mixture components. In the present study different SCC mixtures were observed with similar mechanical properties, but with significantly differing paste to aggregate ratios. Based on observations of the heat evolution at the fire exposed surface and at different depths inside the specimens as well as based on photogrammetric observations of the spalled dimensions, the results indicate that with increasing paste volumes the heat conductivity is reduced and as a result concrete with higher paste to aggregate ratios shows less spalling. T2 - 8th RILEM Symposium on Self-Compacting Concrete CY - Washington, USA DA - 15.05.2016 KW - Spalling KW - High temperature behaviour KW - Fire exposure KW - Mixture composition KW - Photogrammetry PY - 2016 SN - 978-2-35158-157-5 SP - 353 EP - 363 PB - RILEM Publications S.A.R.L. CY - Paris, France AN - OPUS4-36873 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gluth, Gregor A1 - Rickard, W.D.A. A1 - Werner, Steve A1 - Pirskawetz, Stephan T1 - Acoustic emission and microstructural changes in fly ash geopolymer concretes exposed to simulated fire N2 - Two fly ash-based geopolymer concretes with quartz aggregates or with expanded clay (lightweight) aggregates were exposed to the ISO 834-1 standard fire curve in a small-scale fire test set-up. Acoustic emission measurements during fire exposure and subsequent cooling were employed to study spalling events and cracking during the tests. Optical microscopy and additional acoustic measurements were conducted after the testing to better understand the crack propagation in the samples. The testing revealed that neither of the concretes were susceptible to spalling, which is particularly notable for the concrete with quartz aggregates, as it is a high-strength concrete. This behavior is attributed to the relatively high permeability of the concretes and their low amount of chemically bound water. Significant crack formation was detected only around the temperature of the alpha–beta quartz transition (573 °C) and on cooling. Because of aggregate deformations at the quartz transition temperature, deterioration after heating was more significant in the geopolymer concrete with quartz aggregates. Crack formation also occurred in the concrete with expanded clay aggregates, caused by shrinkage of the geopolymer paste on cooling. Acoustic emission measurements proved to be a valuable tool to investigate processes during high temperature exposure. KW - Geopolymers KW - Spalling KW - Concrete KW - Acoustic emission KW - Heat exposure PY - 2016 U6 - https://doi.org/10.1617/s11527-016-0857-x SN - 1359-5997 SN - 1871-6873 VL - 49 IS - 12 SP - 5243 EP - 5254 PB - Springer AN - OPUS4-36907 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Werner, Steve A1 - Rogge, Andreas T1 - The effect of various fire-exposed surface dimensions on the spalling of concrete specimens N2 - Concrete spalling due to fire exposure is often defined as the sudden detachment of fragments from a concrete surface. It can be quantified by various parameters of which weight loss and spalling depth are the most common ones. The risk of spalling is influenced by many factors such as concrete composition, heating rate and applied testing methods. A reduced scale testing method should be developed to analyse the spalling behaviour and to understand its effectiveness in more detail. As a subsection of this development, this study aimed to analyse the effect of different-sized, circular heated areas in semi full-scale fire tests. Therefore, vermiculite slabs with varying cut-outs in their centre were placed between a specimen made of a spalling-sensitive concrete and the combustion chamber. The combustion chamber was heated following a standard fire curve. Our experimental results show that the thermal expansion inside of equal-sized specimens is strongly dependent on the size of the heated area. In addition, this area also affects thermal stresses. They decrease as a result of lower temperature gradients for tests with smaller unheated boundary areas. Apart from this, the analysis of fragments shows no correlation between their relative volume distribution and the heated area. KW - Concrete spalling KW - High temperature tests KW - Fire exposure area KW - Fragmentation PY - 2015 U6 - https://doi.org/10.1002/fam.2256 SN - 0308-0501 SN - 1099-1018 VL - 39 IS - 5 SP - 545 EP - 556 PB - Heyden CY - London AN - OPUS4-34160 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -