Page 9 - Open Access-June 2019

TECHNICAL PAPER

3. Figure 4.3 shows the variation of residual compressive 5. Figure 4.5 shows the variation of residual compressive
strength with the number of thermal cycles for the concrete strength with the number of thermal cycles for the concrete
specimens of M 30 and M 90 grade heated from ambient specimens of M 30 grade exposed to a specific temperature. At
temperature to 300°C. In the case of M 30 grade concrete, there 100°C, for M 30 grade concrete residual compressive strength
is a decrement of residual compressive strength by 4.44% at increases at first thermal cycle and reduces gradually as thermal
first cycle and further cycles of heating and cooling reduced cycle increases. This was not so in case of remaining elevated
gradually by 28.89% after 50 cycles with respect to control temperatures (i.e 200, 300 and 400°C). This may be attributed 120 120 120
120
Percentage residual compressive strength
concrete. In the case of M 90 grade concrete, a reduction of to the slow transport of water and water vapour in the concrete
26.47% in compressive strength was noted after first cycle and specimens which may lead to elevated pore pressure levels. The
100
further 21.57% reduction occurred after 50 cycles. pore pressures exceed the tensile capacity of concrete which 100 100 100
may lead to crack in concrete. M 30 grade concrete retains 80% Percentage residual compressive strength 80 M 30 Percentage residual compressive strength 80 M30 Percentage residual compressive strength 80 M 30
of its original strength even after 50 thermal cycles when heated
120
120
120
120
Percentage residual compressive strength 100 M 30 Percentage residual compressive strength 100 M 30 Percentage residual compressive strength 100 M30 and between 40 to 45% at 400°C for 50 cycles of exposure. M 30 60 0 5 10 15 No. of cycles 35 40 45 50 M 90 60 0 5 10 15 No. of cycles 35 40 45 50 M90 60 0 5 10 15 20 No. of cycles 40 45 50
80
Percentage residual compressive strength
M 30
to 100 and 200°C. Normal strength concrete (NSC) loses 20 to
M 90
M 90
30% of its original compressive strength when heated to 300°C
100
60
This may be attributed to complete evaporation of pore water
in concrete. High temperature exposures cause vaporization
80
40
80
80
80
40
40
40
of pore water in concrete. This result is in good agreement
10
40
45
25
30
20
20
30
25
30
25
15
20
35
0
5
35
30
25
50
M 90
M 90
with the findings of Phan (2008), Venkatesh (2014) and Mateusz
No. of cycles
M90
M 90
60
60
60
60
(2017). Hence, it is suggested that NSC is good enough at low
40
40
20
5
40
45
15
30
25
0
10
35
50
0 5 10 15 20 25 30 35 40 45 50 40 0 5 10 15 20 25 30 35 40 45 50 40 0 5 10 15 20 25 30 35 40 45 50 temperatures i.e. up to 300°C when subjected to thermal cycles. 120 7 7
120
No. of cycles No. of cycles No. of cycles No. of cycles 6 6
Figure 4.3: Variation of percentage residual compressive strength of 100 100 5
M 30 & M 90 specimens exposed to temperature of 300°C. Percentage residual compressive strength 80 7 6 100 C Percentage residual compressive strength 80 100 C Percentage weight loss 5 4 3 M 30 Percentage weight loss 4 3 M 30
Percentage residual compressive strength 100 100 C Percentage residual compressive strength 100 100 C specimens of M 30 and M 90 grade heated from ambient M 30 Percentage weight loss 60 5 4 3 2 0 5 10 15 20 No. of cycles 35 40 45 50 400 C M 30 60 0 5 10 15 No. of cycles 35 40 45 50 400 C 2 1 0 0 5 10 15 No. of cycles 35 40 45 50 M 90 2 1 0 0 5 10 15 20 No. of cycles 40 45 50 M 90
7
120
120
200 C
4. Figure 4.4 shows the variation of residual compressive
200 C
6
strength with the number of thermal cycles for the concrete
300 C
300 C
Percentage weight loss
5
temperature to 400°C. Reduction of strength is high at first
4
thermal cycle i.e 11.12% and 30.39% for M 30 and M 90 grade
80
80
40
40
200 C
respectively. Strength reduced gradually by 44.44% and 55.88%
200 C
3
30
20
25
25
30
30
25
35
20
30
25
300 C
after 50 thermal cycles for M 30 and M 90 grades respectively.
300 C
60
60
2
M 90
M 90
As the temperature increases, there is a loss of free moisture
400 C
400 C
Figure 4.5: Variation of percentage residual compressive strength of
1
1
M 30 specimens exposed to temperature.
of hydrated cement products causing progressive strength loss.
0
40
40
0
25
30
5
20
30
25
40
50
35
45
15
0
20
15
50
10
0
5
45
25
20
30
40
35
10
25
0 5 10 15 20 No. of cycles 35 40 45 50 120 0 5 10 15 No. of cycles 35 40 45 50 followed by absorbed water and finally chemically bound water 6. Figure 4.6 shows the variation of residual compressive 8 7 6 8 7 6 7 6
30
7
120
120
strength with the number of thermal cycles for the concrete
No. of cycles
120
Percentage residual compressive strength 100 M 30 Percentage residual compressive strength 100 M 30 Percentage residual compressive strength 100 M30 Percentage residual compressive strength 100 M 30 For high strength concrete (HSC), higher rates of strength loss, Percentage weight loss 5 4 3 2 1 M 30 Percentage weight loss 5 4 3 2 1 100 C Percentage weight loss 5 4 3 2 1 100 C
No. of cycles
6
specimens of M 90 grade exposed to a specific temperature.
Percentage weight loss
5
as much as 40% of the original strength was observed at 100°C
4
8
and 65% strength loss at 400°C after 50 thermal cycles. At high
8
7
7
200 C
200 C
3
80
80
80
80
temperature around 200°C and 300°C, the first thermal causes a
7
M 30
7
6
6
300 C
300 C
large percentage of damage. This result is in good agreement
M 90
2
Percentage weight loss
M 90
M 90
6
M 90
6
400 C
400 C
5
5
with the findings of Campbell and Desi (1967). HSC sustains
M90
M 90
60
60
60
60
1
5
5
4
4
and dense microstructure of HSC are probably the causes
0
200 C
200 C
3
35
30
25
40
20
25
40
30
25
30
30
20
25
15
10
45
20
50
20
5
0
for creating high pore pressure making concrete brittle. An
3
300 C
300 C
0 5 10 15 20 25 30 35 40 45 50 Percentage weight loss 4 3 40 0 5 10 15 20 25 30 35 40 45 50 M 30 Percentage weight loss 40 0 5 10 15 20 25 30 35 40 45 50 M 30 Percentage weight loss 4 3 40 0 5 10 15 20 25 30 35 40 45 50 100 C markedly higher strength loss than NSC. Low permeability 100 C 0 0 5 10 15 No. of cycles 35 40 45 50 0 0 5 10 15 No. of cycles 35 40 45 50 0 0 5 10 15 No. of cycles 35 40 45
M 90
2
No. of cycles
interesting feature was observed in control specimens (reference
2
No. of cycles No. of cycles M 90 2 No. of cycles 2 No. of cycles 400 C 400 C
1
1 1 1 specimens), which failed with a loud explosion indicating high
Figure 4.4: Variation of percentage residual compressive strength of dissipation of energy whereas the failure of heated specimens
0
0 0 M 30 & M 90 specimens exposed to temperature of 400°C. was gentle.
0
20
30
25
25
0 5 10 15 20 No. of cycles 40 45 50 7 6 0 5 10 15 No. of cycles 35 40 45 50 7 6 0 5 10 15 No. of cycles 35 40 45 50 0 5 The IndIan ConCreTe Journal | June 2019 13
30
20
35
30
25
10
45
20
30
50
35
15
25
40
Percentage residual compressive strength 100 100 C Percentage residual compressive strength 100 100 C Percentage weight loss 5 4 3 2 M 30 Percentage weight loss 5 4 3 2 M 30
No. of cycles
120
120
80
80
200 C
200 C
300 C
300 C
60
60
M 90
M 90
400 C
400 C
40
0 5 10 15 20 25 30 35 40 45 50 40 0 5 10 15 20 25 30 35 40 45 50 1 0 0 5 10 15 20 25 30 35 40 45 50 1 0 0 5 10 15 20 25 30 35 40 45 50
No. of cycles No. of cycles No. of cycles No. of cycles
7 8 8 7
6 5 7 6 7 6 6 5
Percentage weight loss 4 3 M 30 Percentage weight loss 5 4 3 M 30 Percentage weight loss 5 4 3 100 C Percentage weight loss 4 3 100 C
200 C
200 C
300 C
300 C
1 2 M 90 2 1 M 90 2 1 400 C 2 1 400 C
0 0 0 0
0 5 10 15 20 25 30 35 40 45 50 0 5 10 15 20 25 30 35 40 45 50 0 5 10 15 20 25 30 35 40 45 50 0 5 10 15 20 25 30 35 40 45 50
No. of cycles No. of cycles No. of cycles No. of cycles