The Influence of Pressure in the Pore System on Fire Spalling of Concrete

Abstract

Fire spalling of concrete is often attributed to the pressure in the pore system. Recent results from fire tests on Self Compacting Concrete (SCC) have shown that the connection between pressure in the capillary pore system and fire spalling of concrete is not obvious [Jansson (2006) Proceedings from the 4th international workshop, Aveiro, Portugal, pp 747-756]. This issue has been investigated by performing pressure measurements on SCC and a traditional vibrated concrete designed for tunnel construction. In the tests conducted on SCC data from exposure to the hydrocarbon (HC) fire curve are presented. In the tests conducted on vibrated concrete, measurements were performed in concrete exposed to the standard fire curve (EN1363-1) and the Rijkswaterstaat (RWS) curve. The highest pressures in the two test series were measured in the concretes that did not exhibit spalling during fire. One conclusion from the tests is that pressure in the capillary system is not the driving force for spalling during fire exposure. However, pressure is involved in the redistribution of moisture during fire exposure. A new theory is proposed to explain the spalling reducing function of PP-fibres based on the presence and movement of moisture.

Concrete spalling: Interaction between tensile behaviour and pore pressure during heating

“…This indicates that the measured pressure was definitely lower than the actual pressure inside the specimen. Such evidence reminds the surprising results reported in [16], in which plain concrete exhibited very low pressures and a remarkable spalling, whereas polypropylene fiber concrete showed higher pressures and no spalling at all. One possible explanation is that for very dense cementiotious matrices, water saturation is reached around the sensor, so preventing the fluid to flow towards the probe (hence, no pressure is transmitted).…”

The effect of concrete composition on laser scabbling

“…The research literature identifies pore pressure and thermal stress as two key mechanisms responsible for explosive spalling [20,21,22,23,24,25,26,27]. Pore pressure spalling is due to vaporisation of free, interlayer and/or chemically combined water causing a rapid increase in pore pressures which exceeds the tensile strength of the material.…”

An experimental investigation into the influence of specimen size, in-situ pore pressures and temperatures on the spalling of difference size concrete panels when exposed to a hydrocarbon fire

“…Therefore, the difference between the initial weights and mass of concrete spalling represents the mass of water loss. This represents a key finding as this mass loss of water is related to the built-up of pore water pressure which is a key mechanism believed to cause concrete spalling [10,[12][13][14][15][16]. Visual observations through the viewing ports and acoustic observations were also recorded as a function of time as these observations indicate the occurrence of concrete spalling.…”