Estimation of Fire Damage to Concrete Structure- A Case Study
When concrete is subjected to high temperature during fire accidents, it will undergo variation of in-situ moisture content, asymmetric distribution in-situ stresses, spalling leading to exposure of reinforcement and chemical changes. Temperature attained even during mild fire accidents generally exceeds 300oC above which the concrete loses its strength. In medium to extreme fire the temperatures may rise to such an extent that it may even directly affect the reinforcement. Post fire assessment of combating features in the reinforced concrete and masonry structures must be properly conducted. A number of on-site and laboratory-based techniques such as visual inspection, non-destructive testing, and removal of concrete/reinforcement samples are available to aid in the diagnosis of the reinforced concrete and masonry structures. The paper includes the detailed investigations carried out at one of the sites in New Delhi, which experienced such fire accident. The techniques adopted for the diagnostic studies include ultrasonic pulse velocity testing, testing of cores, ascertaining mineralogical changes.
Content
International Journal of Engineering Sciences, 2(4) April 2013, Pages: 130-136
TI Journals
ISSN
2306-6474
International Journal of Engineering Sciences
www.waprogramming.com
Estimation of Fire Damage to Concrete Structure: A Case Study
R.P. Pathak 1, B.K. Munzni 2, Pankaj Sharma 3, N.V. Mahure 4, Sameer Vyas 5, Murari Ratnam 6
1-6
Central Soil and Materials Research Station, New Delhi-110016, India.
AR TIC LE INF O
AB STR AC T
Keywords:
When concrete is subjected to high temperature during fire accidents, it will undergo variation of
in-situ moisture content, asymmetric distribution in-situ stresses, spalling leading to exposure of
reinforcement and chemical changes. Temperature attained even during mild fire accidents
generally exceeds 300oC above which the concrete loses its strength. In medium to extreme fire the
temperatures may rise to such an extent that it may even directly affect the reinforcement. Post fire
assessment of combating features in the reinforced concrete and masonry structures must be
properly conducted. A number of on-site and laboratory-based techniques such as visual
inspection, non-destructive testing, and removal of concrete/reinforcement samples are available to
aid in the diagnosis of the reinforced concrete and masonry structures. The paper includes the
detailed investigations carried out at one of the sites in New Delhi, which experienced such fire
accident. The techniques adopted for the diagnostic studies include ultrasonic pulse velocity
testing, testing of cores, ascertaining mineralogical changes.
Ultrasonic pulse wave
Compressive strength
X–Ray Diffraction
Differential Thermal Analysis
Thermo Gravimetric Analysis
© 2013 Int. j. eng. sci. All rights reserved for TI Journals.
1.
Introduction
In case of fire cracks develop in the concrete structures due to linear, superficial and cubical thermal expansion of various elements. The
geometry of these cracks needs to be properly established while evaluating post fire load-bearing capacity of the structural components.
There are a number of on-site techniques[1] viz. change in color of concrete, ultrasonic pulse velocity testing (UPV) etc. and laboratorybased techniques viz. differential thermal analysis test (DTA), thermo gravimetric analysis (TGA), core testing (CT), assessment of
mineralogical changes through X-ray diffraction analysis (XRD) etc. are available for diagnosis of the condition of reinforced concrete
which got exposed to fire[5,7]. Using these techniques investigations have been carried out at one of the sites in New Delhi, which
experienced such fire accident. The paper includes the outcome of these investigations.
2.
Field investigation
The building under investigation is an exhibition hall. Its ceiling is approximately 10 m above the ground level. Its floor was fully carpeted
at the time of fire. Its floor, ceiling, columns and beams were exposed to fire.
2.1.
Ultrasonic pulse velocity test (UPV)
5
PULSE VELOCITY (Km/sec)
PULSE VELOCITY (Km/sec)
To evaluate general condition of the concrete and concrete lining non-destructive tests using ultrasonic pulse velocity testing (using
PUNDIT )[10] on the top and bottom of the beams and different sections of the columns were conducted. Scanning was done at these
locations to observe the pulse velocity. The results of observed pulse velocity in various beams and that in different columns is presented in
fig. 1 and fig 2 respectively.
4
3
2
1
0
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15
CHAINAGE (M)
Beam 3
* Corresponding author.
Email address: [email protected]
5
4
3
2
1
0
0
1
2
3
4
5
6 7 8 9 10 11 12 13 14 15
CHAINAGE (M)
Beam 5
Estimation of Fire Damage to Concrete Structure: A Case Study
131
5
PULSE VELOCITY (Km/sec)
PULSE VELOCITY (Km/sec)
Internat ional Jour nal of Engineeri ng Science s, 2(4) Apri l 2013
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3
2
1
0
0
1
2
3
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5
5
4
3
2
1
0
6 7 8 9 10 11 12 13 14 15 16
CHAINAGE (M)
0
1
2
3
4
5
6
7 8 9 10 11 12 13 14 15 16 17
CHAINAGE (M)
Beam 9
5
PULSE VELOCITY (Km/sec)
PULSE VELOCITY (Km/sec)
Beam 7
4
3
2
1
0
0
1
2
3 4
5 6
7
5
4
3
2
1
0
8 9 10 11 12 13 14 15 16 17
0
1 2
3
4 5
CHAINAGE (M )
6
5
4
3
2
1
0
1
2
3
4
5
6
7
8
5
4
3
2
1
0
0
9 10 11 12 13 14 15 16 17
1
2
3
4
5
CHAINAGE (M )
6 7 8 9 10 11 12 13 14 15 16 17
CHAINAGE (M)
Beam 17
5
PULSE VELOCITY (Km/sec)
PULSE VELOCITY (Km/sec)
Beam 15
4
3
2
1
0
0
1 2
3
4
5 6
7
8
9 10 11 12 13 14 15 16 17
5
4
3
2
1
0
0
1
2 3
4
5
6 7
8
9 10 11 12 13 14 15 16 17
CHAINAGE (M)
CHAINAGE (M)
Beam 19
LEGEND:
9 10 11 12 13 14 15 16 17
Beam 13
PULSE VELOCITY (Km/sec)
PULSE VELOCITY (Km/sec)
Beam 11
0
7 8
CHAINAGE (M)
Beam 20
▲
Beam Top
●
Beam Bottom
-----
below 3 doubtful
-----
3 - 3.5 medium
-----
3.5 – 4.5 good & above 4.5 excellent
Figure 1. Results of Pulse Velocity carried out on various beams
R. P. Pathak et al.
132
Internat ional Journal of Engineeri ng Scie nc es, 2(4) Apri l 2013
5
5
4
4
3
3
2
2
1
1
0
0
0
1
2
CHAINAGE (M)
3
4
0
Column 1
1
2
CHAINAGE (M)
3
4
Column 2
5
5
4
4
3
3
2
2
1
1
0
0
0
1
2
CHAINAGE (M)
3
4
0
1
Column 13
2
CHAINAGE (M)
3
4
3
4
Column 14
5
5
4
4
3
3
2
2
1
1
0
0
0
1
2
CHAINAGE (M )
3
4
0
1
Column 15
2
CHAINAGE (M)
Column 17
5
4
3
2
1
0
0
1
2
CHAINAGE (M)
3
4
Lounge Column
LEGEND:
▲
Beam Top
-----
below 3 doubtful
●
-----
3.5 – 4.5 good & above 4.5 excellent
-----
Beam Bottom
3 - 3.5 medium
Figure 2. Results of Pulse Velocity carried out on various Columns
2.2.
Extraction of Cores
In addition to NDT cores[11] were also extracted from different locations viz. damaged roof top (Sample R1 and R2), damaged columns
(Sample Col-14, Col-2/1, Col-2/2), damaged floor surface (Sample F1, F2 and F3) and undamaged floor surface (Sample F4, F5 and F6) in
order to determine the compressive strength.
Estimation of Fire Damage to Concrete Structure: A Case Study
133
Internat ional Jour nal of Engineeri ng Science s, 2(4) Apri l 2013
3.
3.1.
Laboratory investigations
X–Ray Diffraction Studies (XRD)
X –Ray Diffraction patterns of concrete specimens from areas exposed to fire and away (2” inside the concrete specimen) from fire were
obtained on a powder XRD model GBC Emma with CuKα1 radiation (1.54 A0) having a scanning speed of 20/minute. The result of XRD
studies using ICDD data base[5,8] are presented in fig 3 and 4. The test was conducted to see the various mineralogical changes occurred
due to fire in concrete specimens.
Fire Exposed Surface
Sub Surface Sample (2” underneath surface)
Figure 3. X-ray Diffractogram of Fire exposed Roof surface and sub surface samples
Sub Surface Sample (2” underneath surface)
Fire exposed surface
Figure 4. X-ray Diffractogram of Fire exposed Floor surface and sub surface samples
3.2.
Determination of Compressive Strength (CS)
The collected concrete cores were tested for finding their compressive strength as per the procedure given in IS: 516. The cube strength
equivalent to 150mm cubes is obtained as per SP: 24-1983-explanatory handbook on Indian standard code of practice for plain and
reinforced concrete (IS: 456-1978). The result of the compressive strength of the core samples are presented in Table 1.
R. P. Pathak et al.
134
Internat ional Journal of Engineeri ng Scie nc es, 2(4) Apri l 2013
Table 1. Results of Compressive Strength of Cores Equivalent to Cube Strength of the Samples
3.3.
Sl No
Sample No
Location
1
2
3
4
5
6
7
8
9
10
11
R-1
R-3
Col- 14
Col- 2/1
Col- 2/2
F –1
F–2
F–3
F- 4
F- 5
F- 6
Fire affected roof
Fire affected roof
Fire affected coulmn
Fire affected coulmn
Fire affected coulmn
Fire affected floor
Fire affected floor
Fire affected floor
Unaffected floor
Unaffected floor
Unaffected floor
Compressive Strength, (Kg/cm2)
(after applying Correction forCylinder to cube)
127.63
99.00
126.98
115.79
123.49
119.64
107.45
94.02
167.90
171.24
161.17
Differential Thermal Analysis (DTA) - Thermo Gravimetric Analysis (TGA)
The samples collected from fire damaged floor and undamaged areas have been subjected to DT – TG analysis and weight loss
corresponding to different temperatures. The graphical representation of variation in weight loss v/s temperature indicates the maximum
temperature to which the damaged sample was exposed during fire. The results of the same are presented in fig 5 and fig 6 respectively.
Figure 5. Results of DTA and TGA Tests carried out on fire unaffected sample from floor
Estimation of Fire Damage to Concrete Structure: A Case Study
135
Internat ional Jour nal of Engineeri ng Science s, 2(4) Apri l 2013
Figure 6. Results of DTA and TGA Tests carried out on fire affected sample from floor
4.
4.1.
Discussion of results
Ultra Sonic Pulse Velocity (UPV)
The results of UPV tests conducted at various locations in beams and columns clearly describe the extent of damage caused by fire. The
UPV values obtained at 50% locations in beam 3, 75% in beam 5, 88% in beam 5, 94% in in beam 9, 82% in beam 11, 67% in beam13,
64% in beam 15 and 73% in beam 17 lie below 3 m/sec. which indicates doubtful status of concrete. In case of beam nos. 7, 9, 19 and 20
100% observed UPV values are below 3.5 m/sec.
The column nos. 13, 14, and 15, 100% UPV values are found to be below 3.0 m/sec and in column 1, 2 and lounge about 50% UPV values
are below 3.0 m/sec indicating doubtful status of concrete while other 50% values are between 3.0 to 3.5 m/sec. showing medium status.
4.2.
Compressive Strength (CS)
The CS for the samples collected from fire affected areas of roof and columns is in the range of 99 Kg/cm2 to 127.63 Kg/cm2. The CS for
the samples collected from fire affected floor areas is found to be much less than CS of the samples collected from unaffected areas.
Though the records of actual grade of concrete was not available for interpretation, the observed CS values for the samples collected from
fire affected areas are far below the specific values for M20 and M15 grade of concrete.
4.3.
X-ray diffraction (XRD)
XRD pattern of two specimens from fire affected roof as well as floor surface areas and two subsurface (2” deep from surface) concrete
specimens have been obtained. The major phases quartz an aggregate mineral having 2θ(d) peak (Q) values at 20.85 (4.257 Ao),
26.65(3.342 Ao) and 50.14(1.818 Ao ) and calcite a concrete mineral having 2θ(d) peak (C) values at 29.40(3.035 Ao), 39.40(2.285 Ao) and
43.14 (2.095 Ao) have been observed.
The 2θ(d) peaks (P) for the mineral portlandite (a common concrete mineral) were observed at 18.09 (4.9Ao), 34.09 (2.628 Ao) and 47.12
(1.927 Ao) in the sub surface samples only. These peaks have disappeared in the fire exposed surface samples. The absence of portlandite
mineral in exposed surface samples and presence of calcite in all samples, is an indication that concrete has been exposed to temperature
exceeding about 5000C up to a depth of about 2 inch from surface.
4.4.
Differential Thermal Analysis (DTA) - Thermo Gravimetric Analysis (TGA) Curve
A comparison of DTA- TGA curve for unaffected sample and damaged sample indicates that the undamaged sample shows a peak
between 454 to 471o C(a peak at 461.56o C) is associated with loss of water brought about by dehydration of the portlandite, while in the
damaged sample it is absent. Second peak at 569.76 to 577.49o C (peak at 572.79o C) is present in both the samples, showing inversion of
silica from α to β phases[2, 4].
R. P. Pathak et al.
136
Internat ional Journal of Engineeri ng Scie nc es, 2(4) Apri l 2013
5.
Estimation of the impact of fire on the status of concrete
The Ultrasonic Pulse Velocity observations, Compressive Strength as observed from the extracted core confirm the poor status of concrete
in almost at all the beams and columns which were exposed to fire.
Comparison of compositional changes in the surface and sub-surface samples both from floor as well as roof as observed in X-Ray
diffraction studies indicate that the surface concrete was subjected to a temperature of about 500oC but sub-surface strata beneath 2”
remained unaffected[3]. The observed physico-chemical changes are further confirmed by DTA-TGA studies carried out on the concrete
specimens from fire affected and unaffected areas. Overall status of the concrete in the fire affected areas is thus categorized as poor.
Acknowledgement
The authors extend their sincere thanks to all those who have helped during collection of samples as well as their testing. We also extend
our sincere gratitude to all the authors whose publications provided us directional information from time to time.
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
Colombo M, Felicetti R., New NDT Techniques for Assessment of Fire Damaged Concrete Structures. Fire Safety Journal, 42, 461-472, 2007
Handoo, SK, Agarwal S, Agarwal SK, Physiochemical, Mineralogical, and Morphological Characteristics of Concrete Exposed to Elevated
Temperatures, Cement and Concrete Research, 32, 1009-1018, 2002.
Kodur VKR, Phan L. Critical Factors Governing the Fire Performance of High Strength Concrete Systems. Fire Safety Journal, 42, 482-488, 2007.
Kucera P. Thermal – Mechanical Analysis of Concrete Structures Exposed to High Temperature . Except from the Proceedings of the COMSOL
Users Conference, Grenoble, 2007.
Mehta PK, Concrete Structures, Properties and Materials, Prentice Hall, NJ, USA, 1986
Moore Duane M. and Reynolds Robert C., “X Ray Diffraction and the Identification and Analysis of Clay Minerals”, Oxford New York (1997)
Neville, A., Properties of Concrete, Fourth Edition, Addison Wesley Longman Limited, 1996
Powder Diffraction File, ICDD PDF-4+, 2010-11
Singh Suvir, Sharma TP, Kaushik SK, High Strength Concrete at Elevated Temperatures An Overview , International Conference on Advances in
Concrete Composites and Structures, January 6-8, 2005
Stawiski B.: The Use of Nondestructive Methods in Post fire Diagnostics , KKBN, Zakopane, 2005. pp 23-28
Stawiski B. “Attempt to estimate fire damage to concrete building structure” Archives Of Civil And Mechanical Engineering Vol. VI No. 4, 2006
TI Journals
ISSN
2306-6474
International Journal of Engineering Sciences
www.waprogramming.com
Estimation of Fire Damage to Concrete Structure: A Case Study
R.P. Pathak 1, B.K. Munzni 2, Pankaj Sharma 3, N.V. Mahure 4, Sameer Vyas 5, Murari Ratnam 6
1-6
Central Soil and Materials Research Station, New Delhi-110016, India.
AR TIC LE INF O
AB STR AC T
Keywords:
When concrete is subjected to high temperature during fire accidents, it will undergo variation of
in-situ moisture content, asymmetric distribution in-situ stresses, spalling leading to exposure of
reinforcement and chemical changes. Temperature attained even during mild fire accidents
generally exceeds 300oC above which the concrete loses its strength. In medium to extreme fire the
temperatures may rise to such an extent that it may even directly affect the reinforcement. Post fire
assessment of combating features in the reinforced concrete and masonry structures must be
properly conducted. A number of on-site and laboratory-based techniques such as visual
inspection, non-destructive testing, and removal of concrete/reinforcement samples are available to
aid in the diagnosis of the reinforced concrete and masonry structures. The paper includes the
detailed investigations carried out at one of the sites in New Delhi, which experienced such fire
accident. The techniques adopted for the diagnostic studies include ultrasonic pulse velocity
testing, testing of cores, ascertaining mineralogical changes.
Ultrasonic pulse wave
Compressive strength
X–Ray Diffraction
Differential Thermal Analysis
Thermo Gravimetric Analysis
© 2013 Int. j. eng. sci. All rights reserved for TI Journals.
1.
Introduction
In case of fire cracks develop in the concrete structures due to linear, superficial and cubical thermal expansion of various elements. The
geometry of these cracks needs to be properly established while evaluating post fire load-bearing capacity of the structural components.
There are a number of on-site techniques[1] viz. change in color of concrete, ultrasonic pulse velocity testing (UPV) etc. and laboratorybased techniques viz. differential thermal analysis test (DTA), thermo gravimetric analysis (TGA), core testing (CT), assessment of
mineralogical changes through X-ray diffraction analysis (XRD) etc. are available for diagnosis of the condition of reinforced concrete
which got exposed to fire[5,7]. Using these techniques investigations have been carried out at one of the sites in New Delhi, which
experienced such fire accident. The paper includes the outcome of these investigations.
2.
Field investigation
The building under investigation is an exhibition hall. Its ceiling is approximately 10 m above the ground level. Its floor was fully carpeted
at the time of fire. Its floor, ceiling, columns and beams were exposed to fire.
2.1.
Ultrasonic pulse velocity test (UPV)
5
PULSE VELOCITY (Km/sec)
PULSE VELOCITY (Km/sec)
To evaluate general condition of the concrete and concrete lining non-destructive tests using ultrasonic pulse velocity testing (using
PUNDIT )[10] on the top and bottom of the beams and different sections of the columns were conducted. Scanning was done at these
locations to observe the pulse velocity. The results of observed pulse velocity in various beams and that in different columns is presented in
fig. 1 and fig 2 respectively.
4
3
2
1
0
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15
CHAINAGE (M)
Beam 3
* Corresponding author.
Email address: [email protected]
5
4
3
2
1
0
0
1
2
3
4
5
6 7 8 9 10 11 12 13 14 15
CHAINAGE (M)
Beam 5
Estimation of Fire Damage to Concrete Structure: A Case Study
131
5
PULSE VELOCITY (Km/sec)
PULSE VELOCITY (Km/sec)
Internat ional Jour nal of Engineeri ng Science s, 2(4) Apri l 2013
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3
2
1
0
0
1
2
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5
5
4
3
2
1
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6 7 8 9 10 11 12 13 14 15 16
CHAINAGE (M)
0
1
2
3
4
5
6
7 8 9 10 11 12 13 14 15 16 17
CHAINAGE (M)
Beam 9
5
PULSE VELOCITY (Km/sec)
PULSE VELOCITY (Km/sec)
Beam 7
4
3
2
1
0
0
1
2
3 4
5 6
7
5
4
3
2
1
0
8 9 10 11 12 13 14 15 16 17
0
1 2
3
4 5
CHAINAGE (M )
6
5
4
3
2
1
0
1
2
3
4
5
6
7
8
5
4
3
2
1
0
0
9 10 11 12 13 14 15 16 17
1
2
3
4
5
CHAINAGE (M )
6 7 8 9 10 11 12 13 14 15 16 17
CHAINAGE (M)
Beam 17
5
PULSE VELOCITY (Km/sec)
PULSE VELOCITY (Km/sec)
Beam 15
4
3
2
1
0
0
1 2
3
4
5 6
7
8
9 10 11 12 13 14 15 16 17
5
4
3
2
1
0
0
1
2 3
4
5
6 7
8
9 10 11 12 13 14 15 16 17
CHAINAGE (M)
CHAINAGE (M)
Beam 19
LEGEND:
9 10 11 12 13 14 15 16 17
Beam 13
PULSE VELOCITY (Km/sec)
PULSE VELOCITY (Km/sec)
Beam 11
0
7 8
CHAINAGE (M)
Beam 20
▲
Beam Top
●
Beam Bottom
-----
below 3 doubtful
-----
3 - 3.5 medium
-----
3.5 – 4.5 good & above 4.5 excellent
Figure 1. Results of Pulse Velocity carried out on various beams
R. P. Pathak et al.
132
Internat ional Journal of Engineeri ng Scie nc es, 2(4) Apri l 2013
5
5
4
4
3
3
2
2
1
1
0
0
0
1
2
CHAINAGE (M)
3
4
0
Column 1
1
2
CHAINAGE (M)
3
4
Column 2
5
5
4
4
3
3
2
2
1
1
0
0
0
1
2
CHAINAGE (M)
3
4
0
1
Column 13
2
CHAINAGE (M)
3
4
3
4
Column 14
5
5
4
4
3
3
2
2
1
1
0
0
0
1
2
CHAINAGE (M )
3
4
0
1
Column 15
2
CHAINAGE (M)
Column 17
5
4
3
2
1
0
0
1
2
CHAINAGE (M)
3
4
Lounge Column
LEGEND:
▲
Beam Top
-----
below 3 doubtful
●
-----
3.5 – 4.5 good & above 4.5 excellent
-----
Beam Bottom
3 - 3.5 medium
Figure 2. Results of Pulse Velocity carried out on various Columns
2.2.
Extraction of Cores
In addition to NDT cores[11] were also extracted from different locations viz. damaged roof top (Sample R1 and R2), damaged columns
(Sample Col-14, Col-2/1, Col-2/2), damaged floor surface (Sample F1, F2 and F3) and undamaged floor surface (Sample F4, F5 and F6) in
order to determine the compressive strength.
Estimation of Fire Damage to Concrete Structure: A Case Study
133
Internat ional Jour nal of Engineeri ng Science s, 2(4) Apri l 2013
3.
3.1.
Laboratory investigations
X–Ray Diffraction Studies (XRD)
X –Ray Diffraction patterns of concrete specimens from areas exposed to fire and away (2” inside the concrete specimen) from fire were
obtained on a powder XRD model GBC Emma with CuKα1 radiation (1.54 A0) having a scanning speed of 20/minute. The result of XRD
studies using ICDD data base[5,8] are presented in fig 3 and 4. The test was conducted to see the various mineralogical changes occurred
due to fire in concrete specimens.
Fire Exposed Surface
Sub Surface Sample (2” underneath surface)
Figure 3. X-ray Diffractogram of Fire exposed Roof surface and sub surface samples
Sub Surface Sample (2” underneath surface)
Fire exposed surface
Figure 4. X-ray Diffractogram of Fire exposed Floor surface and sub surface samples
3.2.
Determination of Compressive Strength (CS)
The collected concrete cores were tested for finding their compressive strength as per the procedure given in IS: 516. The cube strength
equivalent to 150mm cubes is obtained as per SP: 24-1983-explanatory handbook on Indian standard code of practice for plain and
reinforced concrete (IS: 456-1978). The result of the compressive strength of the core samples are presented in Table 1.
R. P. Pathak et al.
134
Internat ional Journal of Engineeri ng Scie nc es, 2(4) Apri l 2013
Table 1. Results of Compressive Strength of Cores Equivalent to Cube Strength of the Samples
3.3.
Sl No
Sample No
Location
1
2
3
4
5
6
7
8
9
10
11
R-1
R-3
Col- 14
Col- 2/1
Col- 2/2
F –1
F–2
F–3
F- 4
F- 5
F- 6
Fire affected roof
Fire affected roof
Fire affected coulmn
Fire affected coulmn
Fire affected coulmn
Fire affected floor
Fire affected floor
Fire affected floor
Unaffected floor
Unaffected floor
Unaffected floor
Compressive Strength, (Kg/cm2)
(after applying Correction forCylinder to cube)
127.63
99.00
126.98
115.79
123.49
119.64
107.45
94.02
167.90
171.24
161.17
Differential Thermal Analysis (DTA) - Thermo Gravimetric Analysis (TGA)
The samples collected from fire damaged floor and undamaged areas have been subjected to DT – TG analysis and weight loss
corresponding to different temperatures. The graphical representation of variation in weight loss v/s temperature indicates the maximum
temperature to which the damaged sample was exposed during fire. The results of the same are presented in fig 5 and fig 6 respectively.
Figure 5. Results of DTA and TGA Tests carried out on fire unaffected sample from floor
Estimation of Fire Damage to Concrete Structure: A Case Study
135
Internat ional Jour nal of Engineeri ng Science s, 2(4) Apri l 2013
Figure 6. Results of DTA and TGA Tests carried out on fire affected sample from floor
4.
4.1.
Discussion of results
Ultra Sonic Pulse Velocity (UPV)
The results of UPV tests conducted at various locations in beams and columns clearly describe the extent of damage caused by fire. The
UPV values obtained at 50% locations in beam 3, 75% in beam 5, 88% in beam 5, 94% in in beam 9, 82% in beam 11, 67% in beam13,
64% in beam 15 and 73% in beam 17 lie below 3 m/sec. which indicates doubtful status of concrete. In case of beam nos. 7, 9, 19 and 20
100% observed UPV values are below 3.5 m/sec.
The column nos. 13, 14, and 15, 100% UPV values are found to be below 3.0 m/sec and in column 1, 2 and lounge about 50% UPV values
are below 3.0 m/sec indicating doubtful status of concrete while other 50% values are between 3.0 to 3.5 m/sec. showing medium status.
4.2.
Compressive Strength (CS)
The CS for the samples collected from fire affected areas of roof and columns is in the range of 99 Kg/cm2 to 127.63 Kg/cm2. The CS for
the samples collected from fire affected floor areas is found to be much less than CS of the samples collected from unaffected areas.
Though the records of actual grade of concrete was not available for interpretation, the observed CS values for the samples collected from
fire affected areas are far below the specific values for M20 and M15 grade of concrete.
4.3.
X-ray diffraction (XRD)
XRD pattern of two specimens from fire affected roof as well as floor surface areas and two subsurface (2” deep from surface) concrete
specimens have been obtained. The major phases quartz an aggregate mineral having 2θ(d) peak (Q) values at 20.85 (4.257 Ao),
26.65(3.342 Ao) and 50.14(1.818 Ao ) and calcite a concrete mineral having 2θ(d) peak (C) values at 29.40(3.035 Ao), 39.40(2.285 Ao) and
43.14 (2.095 Ao) have been observed.
The 2θ(d) peaks (P) for the mineral portlandite (a common concrete mineral) were observed at 18.09 (4.9Ao), 34.09 (2.628 Ao) and 47.12
(1.927 Ao) in the sub surface samples only. These peaks have disappeared in the fire exposed surface samples. The absence of portlandite
mineral in exposed surface samples and presence of calcite in all samples, is an indication that concrete has been exposed to temperature
exceeding about 5000C up to a depth of about 2 inch from surface.
4.4.
Differential Thermal Analysis (DTA) - Thermo Gravimetric Analysis (TGA) Curve
A comparison of DTA- TGA curve for unaffected sample and damaged sample indicates that the undamaged sample shows a peak
between 454 to 471o C(a peak at 461.56o C) is associated with loss of water brought about by dehydration of the portlandite, while in the
damaged sample it is absent. Second peak at 569.76 to 577.49o C (peak at 572.79o C) is present in both the samples, showing inversion of
silica from α to β phases[2, 4].
R. P. Pathak et al.
136
Internat ional Journal of Engineeri ng Scie nc es, 2(4) Apri l 2013
5.
Estimation of the impact of fire on the status of concrete
The Ultrasonic Pulse Velocity observations, Compressive Strength as observed from the extracted core confirm the poor status of concrete
in almost at all the beams and columns which were exposed to fire.
Comparison of compositional changes in the surface and sub-surface samples both from floor as well as roof as observed in X-Ray
diffraction studies indicate that the surface concrete was subjected to a temperature of about 500oC but sub-surface strata beneath 2”
remained unaffected[3]. The observed physico-chemical changes are further confirmed by DTA-TGA studies carried out on the concrete
specimens from fire affected and unaffected areas. Overall status of the concrete in the fire affected areas is thus categorized as poor.
Acknowledgement
The authors extend their sincere thanks to all those who have helped during collection of samples as well as their testing. We also extend
our sincere gratitude to all the authors whose publications provided us directional information from time to time.
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