IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
Absorbance
(a)
ν 4
712
*
ν 2
876
Raman
1070
1425
ν 3
*
Reference
10 mm
20 mm
Absorbance
2ν 2 +ν 4
500 1000 1500 2000 2500 3000 3500 4000
Wavenumber (cm -1 )
convenient method to estimate
the Ca(OH) 2 content through its
characteristic decomposition.
The content of Ca(OH) 2 as
obtained from the peak area at
753 K from DTA, is plotted as a
function of depth for the
samples from one of the blocks
in Fig.1. From the figure it is
clear that the concentration is
increasing linearly up to about
40 mm depth of interacted
concrete. Thus it is clear that
DTA is a sensitive means to
obtain the Ca(OH) 2 content,
which in turn is an indicator of
the concrete damage.
Fourier transform infrared
(FTIR) studies
Alternatively, the quality of
concrete can also be
determined from their
characteristic stretching
frequencies from the mid
infrared region absorption
spectrum. Control runs have
also been carried out to
delineate the thermal effects of
sodium fire from that of the
chemical interaction effects.
Definite signatures of
3110
3240
2ν 3
10 mm
3643
20 mm
Reference
3000 3250 3500 3750
Wavenumber (cm -1 )
Fig.2a Room temperature infrared
spectra of reference sample along
with sodium exposed samples
removed from 10 and 20 mm from
the affected surface of concrete
thermochemical degradation
indicating dehydration and
structural modification of the
limestone concrete have been
obtained for the first time using
this technique.
Fig.2a shows the room
temperature mid infrared
spectrum of the limestone
aggregate reference concrete
along with the spectra of
sodium exposed samples as a
function of depth. The spectrum
revealed the broad absorption
feature centered around 3500
cm -1
attributed to stretching
mode of bound water in
concrete. In particular the
sharp feature at 3643 cm -1
riding on the broad water
background is said to arise due
to the O-H stretching of
Ca(OH) 2 - the major hydration
product of Portland Cement.
Estimating the area under this
peak at 3643 cm -1 could follow
the extent of degradation of
concrete. It is clearly evident
from the figure that the
spectrum of the sodium
exposed sample removed from
10 mm from the affected
surface shows appreciable
changes as compared to that of
the reference sample. The
stretching modes of water in the
affected sample reveals a
significant softening associated
with a dramatic increase in the
intensity of the low frequency
components as compared to
that of the reference sample
(inset in Fig. 2a). The intensity
of the 3643 cm -1 peak is also
seen to significantly decrease.
These changes indicate the loss
of both free and bound water
from the concrete on account
of sodium exposure, thus
degrading the concrete. The
appearance of a new mode at
1070 cm -1 and the splitting of
the doubly degenerate
ν 3 and ν 4 modes indicate a
structural transformation of the
limestone aggregates.
Fig.2b shows the changes in
the vibrational frequencies of
the stretching modes of water
as a function of depth from the
affected surface. It is evident
from the figure that the
conversion of bound water into
free water is confined to depths
of 30 mm from affected
surface. Thus infrared
spectroscopy helps to provide
an insight into the changes
occurring at the molecular
level.
Frequency (cm -1 )
3260
3235
3210
3185
3450
3425
3400
3375
3615
3590
3565
(b)
A
B
C
D
Ref
3540
0 25 50 100
Distance from surface (mm)
Fig.2b Variation of stretching
frequencies of water as a function of
depth from the affected surface of
concrete. Half shaded circles
correspond to the unexposed
reference samples. A, B, C and D
Correspond to various location on
the sodium interacted surface
R&D FOR FBRs 77