| dc.description.abstract | This thesis reports on an experimental research programme into
developing a new quantitative method, based on the Stiffness Damage Test
(SDT), to be used in assessing fire-damaged concrete. The SDT subjects a
concrete core to low-stress quasi-static load cycles. The energy dissipated
during the load-cycle together with other characteristics of the stress-strain
response are used as assessing tools of the fractured state of damaged
concrete.
In addition to the SDT, the extent of damage was also monitored by the
following test methods:
The Ultrasonic Pulse Velocity (UPV) technique
The dynamic modulus measurements
The crushing strength
The full stress-strain response of fire-damaged concrete to failure
The petrographic approach including:
0 Scanning Electron Microscopy (SEM)
0 X-Ray Diffraction (XRD)
The investigated concrete was heated to various temperatures in the
range (ambient - 5000C) to the point when the temperature became uniform
and was then exposed to this temperature for various durations. Cooling of the
heated concrete was either carried out in air or by means of spraying with tap
water for a short duration. Both carbonate and siliceous aggregate concrete
were investigated. Maximum aggregate sizes of 10mm and 20mm were used
in the siliceous aggregate concrete.
The SDT was shown to be a powerful method in quantifying the extent of
fire-damage. The energy dissipated in a stress cycle was found to correlate
extremely well with the % fired residual stiffness, R 2=0
. 95. Therefore, a new
method of classification of fire-damage, based on such correlation is
introduced.
The currently accepted method of UPV was shown to be unsatisfactory in
assessing fire-damaged concrete when moisture content is altered during the
fire-fighting operations. The traditional method of assessing fire-damage using
the phenomena of colour changes of heated concrete was also shown to
underestimate the extent of internal disruption and damage.
In this thesis a large body of evidence is presented to support the
supposition that the extent of damage is not a sole function of the maximum
temperature experienced. The extent of damage was found to be a complex
function of: the maximum temperature, the method of cooling, the duration of
exposure, and the type and size of aggregate used. Spraying hot concrete with
water proved to be a major determinant in the post-firing residual stiffness of
concrete. | en_US |
