Page 10 - Open Access-June 2019

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Percentage residual compressive strength
100
100
100
100
80
80
80
80
M 90
M 90
M90
M 90
60
60
60
60
40
40
40
40
0 5 10 15 20 25 30 35 40 45 50 M 30 Percentage residual compressive strength 120 0 5 10 15 20 25 30 35 40 45 50 M 30 Percentage residual compressive strength 120 0 5 10 15 20 25 30 35 40 45 50 M30 Percentage residual compressive strength 120 0 5 10 15 20 25 30 35 40 45 50 M 30
No. of cycles No. of cycles No. of cycles No. of cycles
TECHNICAL PAPER
with increasing hydration until full hydration is reached. The 7 6
Percentage residual compressive strength 100 100 C Percentage residual compressive strength 100 100 C Weight loss measurements monitor the moisture migration M 30 Percentage weight loss 5 4 3 2 M 30
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120
120
evaporation of capillary water and gel water in concrete at high
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temperature is monitored by recording weight loss over time.
Percentage weight loss
5
at various structural levels, from macro to micro. Weight loss
4
of concrete at high temperatures greatly depends on the
80
80
200 C
200 C
3
composition (cement type and content, water content, water/
300 C
300 C
cement ratio, aggregate type and contents), hydration degree
60
2
60
M 90
M 90
400 C
400 C
(curing temperature, humidity and age) and the initial moisture
1
heating scenarios, e.g. heating temperature, heating rate,
0
40
20
5
15
10
40
35
50
45
30
0
25
0 5 10 15 20 25 30 35 40 45 50 40 0 5 10 15 20 25 30 35 40 45 50 states (saturated, air-dried or oven-dried). It also depends on 1 0 0 5 10 15 20 25 30 35 40 45 50
exposure time etc. This result is in good agreement with the
No. of cycles
No. of cycles No. of cycles findings of Brovwers (1948; 2003; 2004) and Taylor (1986). No. of cycles
Figure 4.6: Variation of percentage residual compressive strength of
M 90 specimens exposed to temperature. Weight loss is a continuous non-reversible process to represent
moisture migration in the concrete. The structural integrity of
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7 8 the specimens deteriorates as confirmed by the increase in 7
4.2 Effect of thermal cycles on weight loss
7
7
6 5 Weight reduction takes place in the specimens at all weight reduction with increased temperature. The reduction in 6 5
weight confirms the loss of mass by the concrete material and
Percentage weight loss
Percentage weight loss 120 120 M 30 of the release of bound water from the cement paste, air M 30 loss of the concrete specimens will estimate the durability of 100 C Percentage weight loss 4 3 2 100 C
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6
Percentage weight loss
temperatures of exposure due to the release of water. Because
the increase in the proportion of air voids. The study of weight
5
5
4
voids are formed in the concrete. So water plays a major role
4
4
concrete. Higher heating temperature always led to a higher
200 C
200 C
3
in determining the nature and influencing the behaviour and
120 3
weight loss which makes the concrete less durable.
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Percentage residual compressive strength Percentage residual compressive strength 100 100 M 30 Percentage residual compressive strength Percentage residual compressive strength 100 100 1 0 80 0 5 10 15 20 No. of cycles 40 45 50 M 30 bound water. Capillary water is evaporable water and exists not loss with number of thermal cycles for the concrete specimens of 1 0 0 5 10 15 No. of cycles 35 40 45 50
120 3
Percentage residual compressive strength
120
Percentage residual compressive strength
Percentage residual compressive strength
Percentage residual compressive strength
300 C
300 C
performance of concrete. There are three different types of
M 90
2
M 90
2
2
400 C
400 C
1. Figure 4.7, 4.8, 4.9 and 4.10 show the variation of % weight
water in concrete: capillary water, gel water and chemically
100
1001
100
100 1
0
0
M 30 and M 90 grade heated from ambient temperature to 100,
only in capillary pores of cement paste but also in aggregates
25
20
20
30
40
5
15
10
25
0
40
50
45
30
50
35
5
10
20
45
35
25
30
35
15
0
25
30
and at interface. It can easily evaporate when the ambient
200, 300, 400°C respectively. In the case of M 30 grade concrete
80
80
80
80
80
80
80
M 30
M 30
M 30
No. of cycles
No. of cycles
exposed to 100°C, the % weight loss increased from 3.29% at
temperature is high. Gel water exists in the gel pores of
M30
M30
M 30
M 90
M 90
M 90
M 90
cement paste. It is generally regarded as adsorbed water or
first cycle to 5.23% after 50 cycles. In the case of M 90 grade
M90
M90
M 90
M 90
60
60
60
60
60
60
60
60
3.43% after 50 cycles. A similar trend was observed at remaining
to the restriction of van der Waals forces with the cement gel
temperatures. It can be seen that weight loss increased with
particles. Chemically bound water is the part of cement hydrate
40
40
40
40
40
40
0
3035
3540
4045
3540
3035
2530
0 0 5 510 1015 1520 2025 2530 3035 3540 4045 4550 50 40 40 0 0 5 5 10 1015 1520 2025 2530 3035 3540 4045 4550 50 physically bound water and does not evaporate easily due concrete, the % weight loss increased from 1.86% at first cycle to
4550
4045
5 10
0 5
4550
2025
1520
1015
5 10
1520
2025
2530
1015
0 5
0
50
50
increase in thermal cycles irrespective of grade of concrete. But
compounds and takes up about 23% by weight of anhydrous
No. of cycles No. of cycles No. of cycles No. of cycles
No. of cycles
No. of cycles
No. of cycles
No. of cycles
cement. Capillary water content in concrete continuously weight loss in M 90 grade concrete was low compared to M 30
decreases but gel and chemically bound water contents increase grade due to its dense structure.
Percentage residual compressive strength Percentage residual compressive strength 100 100 100 C Percentage residual compressive strength Percentage residual compressive strength 100 100 100 C Percentage weight loss Percentage weight loss 6 5 4 3 2 6 5 4 3 2 M 30 Percentage weight loss Percentage weight loss 6 5 4 3 2 6 5 4 3 2 M 30
7
7
120
7
7
120
120
120
100 C
100 C
80
80
80
80
200 C
200 C
200 C
200 C
M 30
M 30
300 C
300 C
300 C
300 C
60
60
60
M 90
M 90
60
M 90
M 90
400 C
400 C
400 C
400 C
40
40
0 0 5 5 10 1015 1520 2025 2530 3035 3540 4045 4550 50 40 40 0 0 5 5 10 1015 1520 2025 2530 3035 3540 4045 4550 50 1 0 1 0 0 0 5 5 10 10 15 15 20 20 25 25 30 30 35 35 40 40 45 45 50 50 1 0 1 0 0 0 5 5 10 10 15 15 20 20 25 25 30 30 35 35 40 40 45 45 50 50
No. of cycles
No. of cycles No. of cycles No. of cycles No. of cycles
No. of cycles
No. of cycles
No. of cycles
Figure 4.7: Variation of percentage weight loss of M 30 & M 90 Figure 4.8: Variation of percentage weight loss of M 30 & M 90
specimens exposed to a temperature of 100°C. specimens exposed to a temperature of 200°C.
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6 5 6 5 7 6 7 6 14 The IndIan ConCreTe Journal | June 2019 6 5 6 5
Percentage weight loss Percentage weight loss 4 3 4 3 M 30 Percentage weight loss Percentage weight loss 5 4 3 5 4 3 M 30 Percentage weight loss Percentage weight loss 5 4 3 5 4 3 100 C Percentage weight loss Percentage weight loss 4 3 4 3 100 C
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6
100 C
100 C
200 C
200 C
200 C
200 C
M 30
M 30
300 C
300 C
300 C
300 C
M 90
M 90
400 C
400 C
1 2 2 1 M 90 2 1 2 1 M 90 2 1 2 1 400 C 2 1 2 1 400 C
0 0 0 0 0 0 0 0
0 0 5 5 10 10 15 15 20 20 25 25 30 30 35 35 40 40 45 45 50 50 0 0 5 5 10 10 15 15 20 20 25 25 30 30 35 35 40 40 45 45 50 50 0 0 5 5 10 1015 1520 2025 2530 3035 3540 4045 4550 50 0 0 5 5 10 1015 1520 2025 2530 3035 3540 4045 4550 50
No. of cycles
No. of cycles
No. of cycles
No. of cycles No. of cycles No. of cycles No. of cycles
No. of cycles