to the concrete at high temperatures, i.e. depth of
microcracking, paste alteration (colour change and
strength softening) and carbonation. However, this
method is relatively expensive and time consuming.
4. Thermoluminescence Tests
Thermoluminescence is the process in which a
mineral emits light while it is being heated. The
basis of this technique in the investigation of fire-
damaged concrete is the measurement of the
residual thermoluminescence in small samples
of sand drilled from the concrete. A major loss of
thermoluminescence occurs at approximately the
same temperature that concrete begins to lose
significant strength. This test has the advantage
that only small holes are required for sampling
the drilled dust on site, from which temperature
profiles may be determined. However, it requires
specialist laboratory equipment and experienced
operators. The usefulness of this technique is
somewhat reduced by its limited availability and
relatively high cost.
and hence should be carried out in areas that have
not been affected by the fire. The method is of
limited value in fire-affected regions as, after end
preparation, core testing will indicate an average
value for the strength of the concrete and will give
little or no information on the loss of strength of
the surface region.
6. Test for Steel Reinforcement
For confirming the limit of deterioration of steel
reinforcements, samples taken from the damaged
members should be tested in the laboratory for
yield, elongation and tensile strength. They are
then compared with the relevant British Standard
for the grade of steel concerned. If a reduced
strength compared with code requirements is
observed, a re-assessment of the structure with
modified properties should be performed.
Case Study
5. Concrete Compressive Strength Test
The most direct method of estimating the strength
of in-situ concrete is by testing cores cut from the
structure. The main value of core testing is to
determine the original strength of the concrete An investigation was commissioned to determine
the extent of damage caused by a large fire to
the reinforced concrete structure of a four-storey
building. The fire started in a chemical storage
room located on the third floor and three small
explosions were reported. The fire had been
Figure 2: Crack at the exterior wall Figure 3: Spalling of the soffits of floor slabs
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