Upload
others
View
8
Download
0
Embed Size (px)
Citation preview
Magnel Laboratory for Concrete Research – Department of Structural Engineering
Assessment of the residual strength of concrete structures after fire exposure
Luc R. Taerwe, Emmanuel Annerel
PhD E. Annerel – 26/03/2010
Magnel Laboratory for Concrete Research
Temperature θ?
fy(θ)
fc(θ)
M = As.fy(θ).z
Assessment techniques
Physico-chemical alterations
Residual & post-cooling strength
3
Magnel Laboratory for Concrete Research 4
fy(θ)
fc(θ)
Assessment techniques
Physico-chemical alterations
M = As.fy(θ).z
Temperature θ?
Residual & post-cooling strength
Magnel Laboratory for Concrete Research
Heating of the cement matrix
Wei
ght l
oss
[%]
Tem
pera
ture
diff
eren
ce [°
C]
T e m p e r a tu r e [ ° C ]2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0
- 3 0
- 2 0
- 1 0
0
- 7
- 6
- 5
- 4
- 3
- 2
- 1
0
Evaporation free water Dissociation of ettringite
Start breakdown of CSH
Decompositon of portlandite :
Ca(OH)2 CaO + H2O
Decarbonation:
CaCO3 CaO + CO2
SCCDecompositon of CSH
Differential thermal + thermogravimetric analysis
5
Magnel Laboratory for Concrete Research
Heating of the cement matrix
A
A A
CH
CSHettrettr
CH
CSH*
CSH*
20°C 350°C 550°C
20°C
>450°C>100°C
20°C 20°C
UVFLUVFL
more pores more pores and cracksand cracks
PPTLPPTLCPLCPL
CH↓
6
Magnel Laboratory for Concrete Research
Post-cooling behaviour
•During heating:
700°C : CaCO3 CaO + CO2
450°C : Ca(OH)2 CaO + H2O
CaO + H2O Ca(OH)2
CaO + CO2 CaCO3
•Post-cooling storage:
(re)hydration CSH, CH
~> strength loss
~> corrosion steel
~> strength recovery
7
Magnel Laboratory for Concrete Research
Post-cooling behaviour
0
5
10
15
20
25
30
35
40
0 100 200 300 400 500 600 700
Temperatuur [°C]
Car
bona
tion
dept
h [m
m]
TC1-8_27 months air storage
TC2k-1_27 months air storage
If not removed coating with CO2 inhibitor
Strength loss Strength recovery
8
Magnel Laboratory for Concrete Research
Aggregates
9
Refractory aggregate
Lightweight aggregate
Dolomitic limestone
Siliceous limestone
Calcareous limestone
Quartz
200 400 600 800 1000 1200 1400 1600
Stable
Phase change
Decarbonation
Large expansion
Contraction
Temperature [°C]Aggregate type
Calcareous CaCO3
Siliceous SiO2
α-β phase transformation: 5.7% volume increase
20°C 800°C
β-quartz cristobalite
oxidation of Fe hydroxidesdisconnection disconnection
of sand particlesof sand particles
Magnel Laboratory for Concrete Research
Interfacial debonding
20°C 300°C 700°C 1160°C
overview (35x)overview (35x)transition zone (210x)transition zone (210x)matrix (210x)matrix (210x)
10
Magnel Laboratory for Concrete Research
Interfacial bonding
Interfacial transition zone = more porous = weaker cement paste
aggregate
Thermal incompatibility
Interfacial cracking
Strength lossStrength lossGraph: Kordina
11
Magnel Laboratory for Concrete Research 12
fy(θ)
fc(θ)
Assessment techniques
M = As.fy(θ).z
Temperature θ?
Physico-chemical alterations
Residual & post-cooling strength
Magnel Laboratory for Concrete Research 13
fy(θ)
fc(θ)
Assessment techniques
Physico-chemical alterations
Residual & post-cooling strength
M = As.fy(θ).z
Temperature θ?
Magnel Laboratory for Concrete Research
Schmidt Rebound Hammer
15
0
20
40
60
80
100
120
0 100 200 300 400 500 600Temperature [°C]
Rel
ativ
e R
ebou
nd In
dex
[%]
TC1-12_fccub150_0d TC1-8_0d
TC1-8_28d_water TC1-8_28d_air
TC1-8_824d_water TC1-8_824d_air
Storage in air Storage in water
Magnel Laboratory for Concrete Research
Ultrasonic Pulse Velocity
y = 8,8382e0,0009x
R2 = 0,7846
y = 7,9494e0,0008x
R2 = 0,9542
y = 11,421e0,0007x
R2 = 0,9098
0
10
20
30
40
50
60
70
0 500 1000 1500 2000 2500 3000Pulse velocity [m/s]
Com
pres
sive
str
engt
h fc
cil [
N/m
m²]
TC -- 20°C TC -- 175°CTC -- 300°CTC -- 520°CTCk -- 20°CTCk -- 520°CSCC -- 20°CSCC -- 205°CSCC -- 315°CSCC -- 530°C
Vbc eaf ⋅⋅=
16
Magnel Laboratory for Concrete Research
Image analysis
20°C 300°C 700°C 1160°C
Surface blackened; pores and cracks filled with white BaSO4 powder
Flatbed scanner: pore size ≥ 50 µm
17
Magnel Laboratory for Concrete Research
Image analysis
Interfacial cracks
18
0
5
10
15
20
25
30
35
40
45
0 200 400 600 800Temperature [°C]
Tota
l por
osity
[%]
SCCTCGuise
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
10 100 1000 10000
Pore diameter [µm]
Poro
sity
[%]
20°C
150°C
300°C
500°C
Cement matrix cracks
Onset of strength lossOnset of strength loss
voidsvoids
550°C
crackscracks
SCC: better interfacial bond and less coarse aggregates
increase in porosity: spread over all measuring classes
Interfacial and cement matrix cracks increase at same rate
Magnel Laboratory for Concrete Research 19
-14
-12
-10
-8
-6
-4
-2
00 100 200 300 400 500 600 700 800 900
[M(T
)-M(1
20°C
)]/M
(120
°C) [
%]
TC1-8 -- 0dTC1-10 -- 0dTC1-12 -- 0dTC2k-1 -- 0dTC2k-4 -- 0dTC2k-5 -- 0dSCC1-5 -- 0dHPC1-5 -- 0d
Decarbonation
4,5
5
5,5
6
6,5
7
7,5
8
8,5
0 100 200 300 400 500 600 700Temperature [°C]
100*
[M(T
,xd)
-M(R
ef)]/
M(R
ef)
TC1-10 -- waterTC1-10 -- L, ovenTC1-10 -- L, 20°CTC2k-1 -- L, ovenTC1-8 -- L, oven
Water immersion
Weight increase due to water absorption
R² = 0,93
Concrete specimen is the reference!
Weight loss during heating
Magnel Laboratory for Concrete Research
Colorimetry
950°C1150°C
250°C
20°C
250°C 450°C
700°C20°C
20°C
700°C
1150°C
>700>700°°CC
SiO2 + Al, K
SiO2 + CaCO3
CaCO3
SiO2 + Mg
SiO2
Red
YellowYellow
20
Magnel Laboratory for Concrete Research
Colorimetry
21
-0,4
-0,2
0
0,2
0,4
0,6
0,8
1
-6 -4 -2 0 2 4 6
[a(T)-a(120°C)]/a(120°C)
[b(T
)-b(1
20°C
)]/b(
120°
C)
TC1-8
TC1-12
TC2k-4
TC2k-5
SCC1-5
HPC1-5
200°C
400°C
300°C
500°C
600°C
700°C
800°C
Red
Yellow
elimination of moisture influence → transformation: shift + scaling
Magnel Laboratory for Concrete Research
Colorimetry
20°C 300°C 700°C 1160°C
400°C
350°C
300°C
600°C700°C
800°C
1000°C
500°C
150°C
200°C250°C
150°C
200°C
250°C
300°C
350°C400°C
500°C
600°C
700°C
800°C
4
5
6
7
8
9
10
0 0,5 1 1,5 2 2,5 3
a* [-]
b* [-
]
HPCSCC
300-400°C
500-600°C
700-800°C
Red
Yellow
22
Magnel Laboratory for Concrete Research
Colorimetry Influence of moisture content
600°C500°C
400°C
300°C200°C
120°C
20°C
600°C 500°C
400°C
300°C
200°C
120°C20°C
5
5,5
6
6,5
7
7,5
8
8,5
9
9,5
10
0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8
a* [-]
b* [-
]
0d_Surface 7d_Surface14d_Surface 28d_Surface56d_Surface 90d_Surface
Red
Yellow
23
Magnel Laboratory for Concrete Research 24
Visual inspection + Schmidt Rebound
Index
RIT/RI20°C> 85(90)%
40% < RIT/RI20°C < 85(90)%
Core drilling
Colour measurement
Stereomicroscope
Reinforcementdetection
Water immersion
RIT/RI20°C< 40%
Magnel Laboratory for Concrete Research 25
fy(θ)
fc(θ)
Assessment techniques
M = As.fy(θ).z
Temperature θ?
Physico-chemical alterations
Residual & post-cooling strength
Magnel Laboratory for Concrete Research
Assessment techniques
Physico-chemical alterations
fy(θ)
fc(θ)Residual & post-cooling strength
M = As.fy(θ).z
Temperature θ?
26
Magnel Laboratory for Concrete Research
Influencing parameters
DEVELOPMENT OF PORE STRUCTURE AND CONCRETE STRENGTHconcrete (aggregates, W/C, cement, porosity),H2O (rain, household moisture production) and CO2
FIRE:Heating rateTarget temperatureDuration of fireExternal load
EXTINGUISHING: water! additional strength loss
VISUAL INSPECTION & SAMPLING
HYDRATION REHYDRATION
Sealed storage
FIRST WEEKS OF ADDITIONAL STRENGTH LOSSTHEN POSSIBLE STRENGTH RECOVERYH2O (extinguishing water, sprinkler, rain) and CO2
LAB RESEARCH
Time
27
Magnel Laboratory for Concrete Research
Influencing parameters
DEVELOPMENT OF PORE STRUCTURE AND CONCRETE STRENGTHconcrete (aggregates, W/C, cement, porosity),H2O (rain, household moisture production) and CO2
FIRE:Heating rateTarget temperatureDuration of fireExternal load
EXTINGUISHING: water! additional strength loss
VISUAL INSPECTION & SAMPLING
HYDRATION REHYDRATION
Sealed storage
FIRST WEEKS OF ADDITIONAL STRENGTH LOSSTHEN POSSIBLE STRENGTH RECOVERYH2O (extinguishing water, sprinkler, rain) and CO2
LAB RESEARCH
Time
28
Magnel Laboratory for Concrete Research
Test setup - strain evolution during heating- post-cooling strength
29
Magnel Laboratory for Concrete Research
Constitutive model εtot = εth(T) + εσ(σ, T) + εcr(σ, T, t) + εtr(σ, T)
Strains during heating
εth(T)εtot
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
5
0 50 100 150 200 250 300 350 400Temperature [°C]
Stra
in [1
0¯³]
EN 1992-1-2
TC_α=0.0: 2.17E-11.T³ + 8E-06.T - 2.21E-04
TC_α=0.2: -9.65E-13.T³ + 8E-06.T - 2.38E-04
TC_α=0.3: -5.66E-12.T³ + 7E-06.T - 1.72E-04
SCC_α=0.0: 1.23E-11.T³ + 1E-05.T - 3.62E-04
SCC_α=0.2: 1.89E-13.T³ + 8E-06.T - 2.54E-04
SCC_α=0.3: -1.44E-11.T³ + 9E-06.T - 3.71E-04
Load ratio 0.0
LITSLoad ratio 0.2
Load ratio 0.3
32
Magnel Laboratory for Concrete Research
Strains during heating
Constitutive model εtot = εth(T) + εσ(σ, T) + εcr(σ, T, t) + εtr(σ, T)
0
10
20
30
40
50
60
70
80
0 0,001 0,002 0,003 0,004 0,005 0,006Strain [-]
Stre
ss [N
/mm
²]
SCC1-7_Reference 20°C_1SCC1-7_Reference 20°C_2SCC1-7_Strength0d 205°C_load0.0SCC1-7_Strength0d 315°C_load0.0SCC1-7_Strength0d 530°C_load0.0model 20°C_0d_load0.0model 205°C_0d_load0.0model 315°C_0d_load0.0model 530°C_0d_load0.0
205°C
20°C315°C
530°C
( ) ηηησ⋅−+
−⋅=
21
2
, kk
f Tcm
T
Tc ,1εεη =
εc1,T = f(T,α). εc1,20°C
fcm,T = f(T,α). fcm,20°C
k(T,α)
33
Magnel Laboratory for Concrete Research
Constitutive model εtot = εth(T) + εσ(σ, T) + εcr(σ, T, t) + εtr(σ, T)
Strains during heating
-4
-3,5
-3
-2,5
-2
-1,5
-1
-0,5
00 50 100 150 200 250 300 350 400
Time [min]
Stra
in [1
0¯3]
205°C -- Load ratio 0,3 (model) 205°C -- Load ratio 0,2 (model)315°C -- Load ratio 0,3 (model) 315°C -- Load ratio 0,2 (model)530°C -- Load ratio 0,3 (model) 530°C -- Load ratio 0,2 (model)SCC1-7_Creep205°C_load03_1 SCC1-7_Creep205°C_load02_1SCC1-7_Creep205°C_load03_2 SCC1-7_Creep205°C_load02_2SCC1-7_Creep315°C_load03_2 SCC1-7_Creep315°C_load02_1SCC1-7_Creep315°C_load03_1 SCC1-7_Creep315°C_load02_2SCC1-7_Creep530°C_load03_1 SCC1-7_Creep530°C_load02_1SCC1-7_Creep530°C_load03_2 SCC1-7_Creep530°C_load02_2
Load ratio 0.2
Load ratio 0.3
( )2000413.03.0
20, 180000615.0 −⋅
°⋅⎟
⎠⎞
⎜⎝⎛⋅⋅−= T
Cccr et
fσε
34
Constitutive model εtot = εth(T) + εσ(σ, T) + εcr(σ, T, t) + εtr(σ, T)
Strains during heating=- - -
-5
-4,5
-4
-3,5
-3
-2,5
-2
-1,5
-1
-0,5
00 50 100 150 200 250 300 350 400
Temperature [°C]
Tran
sien
t str
ain
[10¯
³]
TC_α = 0.2_testTC_α = 0.3_testSCC_α = 0.2_testSCC_α = 0.3_testTC_α = 0.2_modelTC_α = 0.3_modelSCC_α = 0.2_modelSCC_α = 0.3_model
Load ratio 0.3
Load ratio 0.2
Magnel Laboratory for Concrete Research
TCc
tr Af
c ⋅⋅=°20,
σε
⎟⎟⎠
⎞⎜⎜⎝
⎛
+⋅⋅−
⋅⋅+⋅⋅−⋅⋅−=
−
−−−
202.0103.1
1045.31082.11011.12
2537410
T
TTTAT
TC c = 1.06
SCC c = 0.94
35
Magnel Laboratory for Concrete Research
Influencing parameters
DEVELOPMENT OF PORE STRUCTURE AND CONCRETE STRENGTHconcrete (aggregates, W/C, cement, porosity),H2O (rain, household moisture production) and CO2
FIRE:Heating rateTarget temperatureDuration of fireExternal load
EXTINGUISHING: water! additional strength loss
VISUAL INSPECTION & SAMPLING
HYDRATION REHYDRATION
Sealed storage
FIRST WEEKS OF ADDITIONAL STRENGTH LOSSTHEN POSSIBLE STRENGTH RECOVERYH2O (extinguishing water, sprinkler, rain) and CO2
LAB RESEARCH
Time
36
Magnel Laboratory for Concrete Research
Influencing parameters
DEVELOPMENT OF PORE STRUCTURE AND CONCRETE STRENGTHconcrete (aggregates, W/C, cement, porosity),H2O (rain, household moisture production) and CO2
FIRE:Heating rateTarget temperatureDuration of fireExternal load
EXTINGUISHING: water! additional strength loss
VISUAL INSPECTION & SAMPLING
REHYDRATION
Sealed storage
FIRST WEEKS OF ADDITIONAL STRENGTH LOSSTHEN POSSIBLE STRENGTH RECOVERYH2O (extinguishing water, sprinkler, rain) and CO2
LAB RESEARCH
TimeHYDRATION
37
Magnel Laboratory for Concrete Research
Compressive strength (α = 0.0)
0,50
0,60
0,70
0,80
0,90
1,00
0 10 20 30 40 50 60
Time [days]
fccu
b150
(T)/f
ccub
150(
20°C
) [-]
SCC - 350°C - water storage
SCC - 350°C - air storage
TC - 350°C - water storage
TC - 350°C - air storage
0,20,30,40,50,60,70,80,9
11,11,2
300 350 400 450 500 550 600
Temperature [°C]
fc(θ
)/fc(θ0
) [-]
SCC ref SCC 20°C/minSCC 3600min SCC waterTC ref TC 10°C/minTC 3600min TC water
Small strength recoverySmall strength recovery
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
0 100 200 300 400 500 600 700 800 900
Temperature [°C]
fccu
b150
(T)/f
ccub
150(
20°C
) [-]
EC Siliceous -- 0d (hot)EC Calcareous -- 0d (hot)TC1-12 -- 0dTC2k-4 -- 0dSCC1-5 -- 0dHPC1-5 -- 0d
Storage after cooling: Storage after cooling: + 20+ 20--30% strength loss30% strength loss
Strength immediately Strength immediately after coolingafter cooling
Watercooling (fire brigade): + 30Watercooling (fire brigade): + 30--35% loss35% loss
38
Magnel Laboratory for Concrete Research
Compressive strength (α ≥ 0.0)
-100
-80
-60
-40
-20
0
20
40
60
Stre
ngth
loss
[%]
TemperatureLoadWatercoolingStorage in airStorage in water
Load : 0% 0%20% 40% 20%
350°C 550°C
Strength recovery!!
39
Magnel Laboratory for Concrete Research
Residual & post-cooling strength models
0
10
20
30
40
50
60
70
80
0 0,001 0,002 0,003 0,004 0,005 0,006Strain [-]
Stre
ss [N
/mm
²]
SCC1-6_Reference 20°C_1SCC1-6_Reference 20°C_2SCC1-7_Reference 20°C_1SCC1-7_Reference 20°C_2SCC1-6_ResStrength 205°C_load0.0SCC1-7_ResStrength 205°C_load0.0SCC1-6_ResStrength 315°C_load0.0SCC1-7_ResStrength 315°C_load0.0SCC1-6_ResStrength 530°C_load0.0SCC1-7_ResStrength 530°C_load0.0model 20°C_8we_load0.0model 205°C_8we_load0.0model 315°C_8we_load0.0model 530°C_8we_load0.0
( ) ηηησ⋅−+
−⋅=
21
2
, kk
f Tcm
T
Tc ,1εεη =
fcm,T = f(T,α). fcm,20°C
k(T,α)
εc1,T = f(T,α). εc1,20°C
40
Magnel Laboratory for Concrete Research
Assessment techniques
41
Physico-chemical alterations
fy(θ)
fc(θ)
M = As.fy(θ).z
Temperature θ?
Residual & post-cooling strength
Magnel Laboratory for Concrete Research
Assessment techniques
42
Physico-chemical alterations
fy(θ)
fc(θ)
M = As.fy(θ).z
Temperature θ?
Residual & post-cooling strength
Magnel Laboratory for Concrete Research
CONCLUSION
Assessment techniques- Techniques are available that are easy to use in situ and in the lab- Schmidt Rebound Hammer/ UPV give values that can help the visual inspection- The shape of the colour path results in different temperature zones- Water immersion is an economic method
Residual strength- Additional strength losses due to fast cooling and post-cooling storage- These losses are important for calculating the remainig bearing capacity- Superposition of the influencing parameters is possible- Strength recovery will occur during storage after water cooling- Stress-strain models as function of both temperature and load level
44