Open access
Date
2013-12Type
- Report
ETH Bibliography
yes
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Abstract
A sufficient resistance of concrete structures to fire was always taken for granted. The concrete’s low thermal conductivity ensures an overall good thermal protection of the concrete’s reinforcement, even during longer fire impact. In contrast to ordinary performance concrete used in most structures, the behavior of high (HPC) and ultra-high performance concrete (UHPC) at high temperatures exhibits an increased tendency to explosive spalling and must be considered as critical. Explosive spalling might occur at high temperatures, leading to a direct fire exposure onto the reinforcement steel and a reduction of the cross section. The risk of explosive spalling of HPC and UHPC can be reduced with a modified concrete mixture including polypropylene fibers (PP-fibers); however, temperature-related damage cannot be excluded in general. Another possibility is the use of fire protective concrete linings, acting as a thermal barrier or narrow spaced stirrups. However, their application is still difficult due to the lack of existing design criteria. Within the framework of a research project at the Institute of Structural Engineering (IBK) at ETH Zurich, several tests on the analysis of the risk of temperature-related explosive spalling of HPC and UHPC was carried out. In this report, the explosive spalling of unprotected concrete cylinders (ø = 150 mm, h = 300 mm) was investigated using linear heating. Chapter 2 describes these tests. In chapter 3, the behavior of HPC and UHPC containing PP-fibers was analyzed. Different amounts of PP-fibers with varying fiber geometry were tested with the same base concrete mixture. The influence of the PP-fiber’s geometry on the intensity of explosive spalling was clearly indicated. Tests on the porosity and permeability of concrete after cooling from high temperatures are described in chapters 4 and 5. Small concrete fragments (l = 4 mm) were used to determine the cumulative pore volume using mercury intrusion porosimetry. Concrete before and after explosive spalling was analyzed, as well as the influence of PP-fibers on the porosity at different temperature levels. Tests on permeability are described in chapter 5. The gas permeability was analyzed for concrete discs (ø = 150 mm, h = 40 mm) at room temperature, after cooling from high temperatures of up to T = 500°C. The influence of steel and PPfibers on the concrete’s permeability was studied in these tests. Chapter 6 deals with the use of protective linings on concrete structures. The required material properties as input material properties for modeling and dimensioning of the linings were determined experimentally and analyzed. A description of tests on UHPC slabs (l • w • h = 1100 • 900 • 150 mm3) protected either with PP-fibers or protective lining is presented in the last part of this report (chapter 7). These slabs were heated according to the standardized ISO-fire curve [1] for a period of t = 120 min. The present test report describes the test set-up for all experimental investigations and summarizes the results. Further analysis or design models will be given in a research publication. Show more
Permanent link
https://doi.org/10.3929/ethz-a-010076314Publication status
publishedJournal / series
IBK BerichtVolume
Publisher
Institut für Baustatik und Konstruktion der ETH ZürichSubject
High performance concrete (HPC); Explosive spalling; BEWEHRUNGSFASERN (BAUSTOFFE); HIGH STRENGTH CONCRETE (BUILDING MATERIALS); Mercury intrusion porosimetry; PLASTERS + RENDERS (BUILDING MATERIALS); HOCHFESTER BETON (BAUSTOFFE); PP-fibers; Permeability; Steel fibers; ISO-fire tests; Ultra-high performance concrete (UHPC); Protective lining; FIRE BEHAVIOUR AND FIRE RESISTANCE OF BUILDING ELEMENTS AND MATERIALS (FIRE FIGHTING AND PROTECTION); REINFORCEMENT FIBRES (BUILDING MATERIALS); PUTZE + PUTZMASSEN + VERPUTZE (BAUSTOFFE); BRANDVERHALTEN UND FEUERFESTIGKEIT VON BAUSTOFFEN UND BAUMATERIALIEN (BRANDBEKÄMPFUNG UND BRANDSCHUTZ)Organisational unit
08809 - Frangi, Andrea (Tit.-Prof.)
03352 - Fontana, Mario (emeritus) / Fontana, Mario (emeritus)
02605 - Institut für Baustatik u. Konstruktion / Institute of Structural Engineering
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ETH Bibliography
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