Material properties related to fire spalling of concrete

Abstract: Despite almost 100 years of research, the fundamentals of fire spalling of concrete are not
yet fully understood. Many different theories exist, each trying to describe the coupling
between different phenomenon leading to fire spalling. Some of these phenomenon have
been investigated and are presented in this thesis.
The thermal properties at high temperature have been investigated using the Transient
Plane Source (TPS) technique. Measurements of temperature in the cross-section of selfcompacting
concrete with the addition of polypropylene fibres (PP-fibres) during fire
exposure are presented. A verification calculation, based on the measured values of
temperature in the cross-section of the fire exposed concrete, was compared with results
from a full-scale fire test with the same concrete. Good correlation was obtained.
Using a measurement system consisting of oil filled steel pipes, the pressure inside the
concrete during fire exposure, was measured. Results from pressure measurement tests on
self compacting concrete show relatively low internal pressure before spalling. In fact, the
pressure was highest in a specimen that did not spall during fire exposure. Conclusions
from the tests were that pore pressure only played a secondary role in the spalling process
of the concrete investigated. Thermal stresses were believed to be the primary reason for
spalling.
With a small addition of polypropylene fibres (PP) in concrete the fire spalling can be
limited or totally avoided. Comparative studies of concrete with and without PP- fibres
were performed, and the function of PP-fibres was illustrated in small and large scale fire
tests. When determining the free thermal expansion as a function of temperature a strain
plateau was found in specimens containing PP-fibres. The plateau corresponds fairly well
with the temperature where accelerated drying behaviour was shown. This is an
indication that an accelerated drying creep phenomenon might be present. Further
experimental work is needed to verify this postulate.