Abstract: Following the recent developments in civil engineering there is a clear trend to involve more and more innovative materials like high performance concrete (HPC). HPC is often used for tunnel lining, for columns of high raise buildings and similar structures, which require high compressive strength. However, when exposed to high temperature (fire) there is a strong degradation of mechanical properties of HPC and it shows unfavorable behavior, i.e. explosive spalling of concrete cover. In the here discussed experiments the behavior of concrete specimen that were exposed to fire is monitored by acoustic emission (AE) technique. Using this technique it is possible to observe damage processes in concrete during the entire fire history. It is in particular possible to detect the initialization of explosive spalling. The article describes the proposed concept and preliminary results of fire experiments on concrete specimens made of HPC with and without addition of polypropylene fibers. To better understand the experimental results it is also important to employ a numerical model, which is able to realistically predict the behavior of concrete at high temperature including transport of moisture and the role of pore pressure in concrete exposed to elevated temperature. Therefore, a fully coupled thermo-hygro-mechanical model for concrete was implemented into a 3D finite element code [1, 6, 7]. The application of the model demonstrates that the pore pressure in combination with thermally induced stresses is the main reason for explosive spalling of concrete cover. The addition of polypropylene fibers is resulting in a drastic decrease of the risk for explosive spalling. This is proved by the simulation as well as by the experimental results including acoustic emission analysis and ultrasound [2]. It is shown that the addition of polypropylene fibers caused increase of permeability of concrete for more than two orders of magnitude, which significantly reduces risk against explosive spalling.     «

Abstract: Following the recent developments in civil engineering there is a clear trend to involve more and more innovative materials like high performance concrete (HPC). HPC is often used for tunnel lining, for columns of high raise buildings and similar structures, which require high compressive strength. However, when exposed to high temperature (fire) there is a strong degradation of mechanical properties of HPC and it shows unfavorable behavior, i.e. explosive spalling of concrete cover....     »