TY - CONF A1 - Weise, Frank A1 - Stelzner, Ludwig A1 - Weinberger, J. A1 - Oesch, Tyler T1 - Influence of the pre-treatment of PP-fibres by means of electron irradiation on the spalling behaviour of High Strength Concrete T2 - Proceedings from the 5th International Workshop on Concrete Spalling N2 - It is known that the spalling risk of dense, high-strength concretes (HSC) can be reduced by the addition of polypropylene (PP) fibres and, in particular, PP-fibres that have been pre-treated using electron irradiation. It is presumed that the enhanced reduction in spalling resulting from electron irradiation pre-treatment of the fibres can be attributed to enhanced penetration of the molten fibre material into the micro-cracks around the fibres, due to their significantly decreased viscosity. So far there has been no experimental evidence for this. Against this background, this paper gives a com-parative analysis of the mode of action of PP-fibres with and without pre-treatment using multi-scale test methodology. Initially, fire tests on small-scale building components with accompanying damage monitoring veri-fied that the amount of PP-fibres can be halved by using pre-treated PP-fibres without reducing the fire performance of HSC. Detailed investigations of PP-fibres carried out in a completed research project funded by DFG (the German Research Foundation) using digital scanning calorimetry and thermogravimetry measurements (DSC/TG) as well as viscometer measurements showed that the pre-treatment has no significant influence on the melting temperature of the PP-fibres. However, a drastic reduction of the melt viscosity due to the electron irradiation was detectable. Additional dila-tation tests showed that the expansion behaviour of both fibre types and their melts do not differ significantly [1]. Rather, both fibre types generate high pressures when their thermal expansion is hindered. Further detailed investigations by means of continuous heating tests with a low heating rate were carried out on separately produced concrete cylinders. These tests showed that the pre-treatment of the PP-fibres causes earlier dehydration in conjunction with stagnation of thermal expansion of the concrete cylinders (temperature reduction from 180 °C to 170 °C). This is accompanied by in-creased acoustic emission activity during the thermal expansion tests. This leads to the assumption that the pre-treatment of PP-fibres results in earlier micro-crack development. However, it was not possible to confirm this assumption by microscopic examination of drilling cores with a diameter of 30 mm exposed to defined temperatures in the range between 150°C and 300°C. Microscopic obser-vations and additional X-ray 3D computed tomography (3D-CT) scans on miniaturised drilling cores exposed to temperature cycles showed a similar networking of fibre beds by means of micro-cracks in HSC for both fibre types. However, energy dispersive X-ray spectroscopy and wavelength disper-sive X-ray spectroscopy revealed fundamental differences in the penetration capacity of the fibre melts of the two fibre types. The increased penetration of the pre-treated PP-fibre melt revealed in these tests, confirms the initial working hypothesis. T2 - 5th International Workshop on Concrete Spalling due to Fire Exposure CY - Boras, Sweden DA - 12.10.2017 KW - Polypropylen fibres KW - Explosive spalling KW - HSC KW - HPC KW - Fibre melt KW - Penetration KW - Micro cracking KW - NDT PY - 2017 SN - 0284-5172 SP - 345 EP - 358 AN - OPUS4-42985 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -