On the Mechanism of Polypropylene Fibres in Preventing Fire Spalling in Self-Compacting and High-performance Cement Paste

With the increasing application of self-compacting concrete (SCC) in construction and infrastructure, the fire spalling behavior of SCC has been attracting due attention. In high performance concrete (HPC), addition of polypropylene fibers (PPFs) is widely used as an effective method to prevent explosive spalling. Hence, it would be useful to investigate whether the PPFs are also efficient in SCC to avoid explosive spalling. However, no universal agreement exists concerning the fundamental mechanism of reducing the spalling risk by adding PPF. For SCC, the reduction of flowability should be considered when adding a significant amount of fibers. In this study, both the micro- and macro-level properties of pastes with different fiber contents were studied to investigate the role of PPFs at elevated temperature in self-compacting cement paste samples. The micro properties were studied by backscattering electron microscopy and mercury intrusion porosimetry tests. The modification of the pore structure at elevated temperature was investigated as well as the morphology of the PPFs. Some macro properties were measured, such as the gas permeability of self-compacting cement paste after heating at different temperatures. The factors influencing gas permeability were analyzed. It is shown that with the melting of PPFs, no significant increase in total pore volume is obtained. However, the connectivity of isolated pores increases, leading to an increase of gas permeability. With the increase of temperature, the addition of PPFs reduces the damage of cement pastes, as seen from the total pore volume and the threshold pore diameter changes. From this investigation, it is concluded that the connectivity of pores as well as the creation of microcracks are the major factors which determine the gas permeability after exposure to high temperatures. Furthermore, the connectivity of the pores acts as a dominant factor for temperatures below 300°C. For higher temperatures microcracks are becoming the major factor which influences the gas permeability.

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  • English

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  • Accession Number: 01099365
  • Record Type: Publication
  • Files: TRIS
  • Created Date: May 5 2008 12:14PM