THM behaviour of the supercontainer concrete buffer during construction

1
THM behaviour of the supercontainer concrete
buffer during construction
Bart Craeye Ghent University Faculty of
Engineering Magnel Laboratory for Concrete
Research 13th Exchange Meeting The role of
cementitious materials for deep disposal of
high-level waste in Boom Clay Thursday 29 January
2009 Club House SCKCEN, Mol
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THM behaviour of the supercontainer concrete
buffer during construction

• Thermo Hydro Mechanical behaviour
• Framework
• The feasability demonstration program of the
  supercontainer concept
• ONDRAF/NIRAS
• Objectifs
• Simulation of concrete buffer during construction
  to
• Predict and prevent crack formation
• Evaluate the need of reinforcement

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THM behaviour of the supercontainer concrete
buffer during construction
Supercontainer (SC) Different types

• Vitrified waste
• Spent Fuel (UOX, MOX)

FOCUS
Functions Corrosion protection
Radiological protection
4
THM behaviour of the supercontainer concrete
buffer during construction
Methodology Early age cracking
Concrete buffer composition and
properties Results of experimental program
Simulation results Strength verification
Closure Conclusions and future work
5
Methodology
Test and characterise 2 types of concrete SCC -
TVC Effect of concrete properties and boundaries
is non-negligible Extensive laboratory program
(thermal and mechanical tests) First simulations
(2.5 D HEAT) Define / Optimise modelisation
options Verify if early age cracking will occur
during phase 1 Second simulations (2.5 D
HEAT) Verify if early age cracking will occur
during phase 2-4
hot cell
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• The principal stresses must remain smaller than
  tensile strength

sx,y,z // fct
tensile strength
early-age cracking
tensile stresses
hardening time
Shrinkage cooling down autogenous/drying
shrinkage Expansion hydration heat Loading and
creep
Young concrete is very prone to early-age cracking
sx,y,z lt fct
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THM behaviour of the supercontainer concrete
buffer during construction
Methodology Early age cracking
Concrete buffer composition and
properties Results of experimental program
Simulation results Strength verification
Closure Conclusions and future work
8

• Different compositions
• are being considered

Self-Compacting Concrete (SCC)
Traditional Vibrated Concrete (TVC)

• use of finer aggregates
• use of filler 100 kg/m³
• use of SP 12 kg/m³
• no need of vibration

• coarser aggregates 6/20
• use of filler 50 kg/m³
• use of SP 4 kg/m³
• need of vibration

Specific needs
Chemical restricions use of OPC limited
hydration heat - high pH - low SO3 and C3A
content HSR limestone aggregates favourable
chemical environment preventing ASR Sufficient
strength (tensile and compressive) Good
workability - pumpable Avoid through-going cracks

9

• Material properties database

Laboratory characterization program Material
Database of simulation tool HEAT
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• Material properties database

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• Thermal properties

Specific heat (Cp) fixed value Heat conduction
coefficient (k) fixed value Heat production By
means of adiabatic hydration test according to De
Schutter and Taerwe (1996) Coefficient of
thermal dilation (aT) Time dependent  
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Thermal properties

• Heat production
• SCC has higher temperature development 1 higher
  after 72 h

Test results
Test set-up
De Schutter and Taerwe (1996)
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• Material properties database

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• Mechanical properties
• Compressive Tensile strength
• SCC has higher strength 10 higher after 28 days

Test results
fc Compressive strength fct Tensile
strength s Standard deviation
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• Mechanical properties
• Dilatation
• SCC has higher autogenous shrinkage 20 higher
  after 144 h

Test set-up
Test results SHORT term
Craeye and De Schutter (2006)
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• Mechanical properties
• Dilatation
• SCC has higher autogenous shrinkage 20 higher
  after 1 year

Test results LONG term
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• Mechanical properties
• Creep
• SCC has higher creep strain

Test set-up
Test results


After 168 days
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• Slightly improved
• mechanical behaviour for SCC

SCC advantage TVC advantage
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THM behaviour of the supercontainer concrete
buffer during construction
Methodology Early age cracking
Concrete buffer composition and
properties Results of experimental program
Simulation results Strength verification
Closure Conclusions and future work
20

• HEAT predicts crack formation

• Finite Elements
• to predict thermal and mechanical behaviour
• State parameter approach
• Relation between state of material and material
  properties
• 2 step calculation
• 1 simulate hydration proces
• (temperature, maturity)
• 2 calculate stresses and strength

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• THM behaviour of supercontainer concrete buffer
  during construction

4 conctruction stages
hot cell
1.
2.
4.
3.
First simulations (1.) Casting the concrete
buffer Second simulations Hot cell (2.)
insertion of canister (3.) backfill (4.)
closing lid
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• THM behaviour of supercontainer concrete buffer
  during construction

4 conctruction stages
hot cell
1.
2.
4.
3.
First simulations (1.) Casting the concrete
buffer Second simulations Hot cell (2.)
insertion of canister (3.) backfill (4.)
closing lid
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• Axisymmetrical cross-section
• as 2D-model

Boundary T1 C W1 m/s a1 W/m²K
Initial temperature 20C Demolding steel
formwork after 48 h
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• No cracks expected in standardized environment
  (20C)

SCC
TVC

• 1 higher temperature rise in SCC
• 20 higher shrinkage in SCC

Tmax,41h 54,2 C
Tmax,37h 52,8 C
25

• No cracks expected in standardized environment
  (20C)

SCC
TVC

• 1 higher temperature rise in SCC
• 20 higher shrinkage in SCC
• 30 higher stresses in SCC
• 4 h earlier in TVC
• BUT
• Sxx,Syy,Szz lt 0.7 fct

Szz,max,36h 1,56 MPa
Szz,max,32h 1,12 MPa
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No cracks expected in standardized environment
(20C)
Tensile stress
Heating phase
Point 9
Cooling phase
Point 4
Compressive stress
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• Influence of temperature
• Measurements needed in case of elevated outside
  temperatures

T 30 C
Peak is earlier Strength is not sufficient ?
Measurements
Point 3
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• Influence of temperature
• More realistic environmental temperature gives no
  cracking risk

T with daily cycle
Point 9
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• Influence of creep and shrinkage

visco elastic
Point 9
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• Influence of creep and shrinkage

visco elastic
Point 9
no AS

• Lower peak (underestimation)
• More uniform
• Parallel curves

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• Influence of creep and shrinkage
• Visco elastic nature has a considerable influence

visco elastic
Point 9
no AS

• Peak occurs later and is smaller (light
  underestimation)
• Tensile stress higher after heating phase
• Comressive stress higher after cooling phase

linear elastic
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• THM behaviour of supercontainer concrete buffer
  during construction

4 conctruction stages
hot cell
1.
2.
4.
3.
First simulations (1.) Casting the concrete
buffer Second simulations Hot cell (2.)
insertion of canister (3.) backfill (4.)
closing lid
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• Fase 1 Casting the buffer and curing
• 0 h ? 240 h

Inside buffer time 0 ? 48 h T1 20 C W1 0
m/s a1 5.59 W/m²K Demolding time 48
h time 48 h ? 240 h T1 20 C W1 0
m/s a1 5.60 W/m²K
Free surface time 0 ? 241 h T1 20 C W1 1
m/s a1 9.60 W/m²K
Steel liner time 0 ? 1344 h T1 20 C W1 1
m/s a1 9.58 W/m²K
Concrete floor time 0 ? 1344 h T1 20 C W1 0
m/s a1 2.00 W/m²K
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• Fase 2 Insertion of canister
• 240 h

Free surface time 0 ? 241 h T1 20 C W1 1
m/s a1 9.60 W/m²K
Steel liner time 0 ? 1344 h T1 20 C W1 1
m/s a1 9.58 W/m²K
Concrete floor time 0 ? 1344 h T1 20 C W1 0
m/s a1 2.00 W/m²K
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• Fase 3 Backfilling
• 240 h

Free surface time 240 ? 241 h T1 20 C W1 1
m/s a1 9.60 W/m²K
IF filler-canister time 240 ? 1344
h T1 heat-emitting W1 0 m/s a1 5.59 W/m²K
Free surface time 0 ? 241 h T1 20 C W1 1
m/s a1 9.60 W/m²K
Steel liner time 0 ? 1344 h T1 20 C W1 1
m/s a1 9.58 W/m²K
Concrete floor time 0 ? 1344 h T1 20 C W1 0
m/s a1 2.00 W/m²K
Weetjens and Sillen (2006)
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• Fase 4 Closing the lid
• 241 h ? 1344 h

Free surface time 241 ? 1344 h T1 20 C W1 1
m/s a1 9.60 W/m²K
IF filler-canister time 240 ? 1344
h T1 heat-emitting W1 0 m/s a1 5.59 W/m²K
Steel liner time 0 ? 1344 h T1 20 C W1 1
m/s a1 9.58 W/m²K
Concrete floor time 0 ? 1344 h T1 20 C W1 0
m/s a1 2.00 W/m²K
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• Axisymmetrical cross-section
• as 2D-model

Ongoing study Preliminary results 3 conctruction
cases CC 1 Buffer SCC pouring SCC
plug CC 2 Buffer TVC pouring SCC
plug CC 3 Buffer SCC precast SCC
plug Filler SCC
3
2
1
y
z
x
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• Tangential stresses are most important
• In all cases

Construction case 1
Temperature
Stresses Szz
CC1 Buffer SCC pouring SCC plug
T1344h 51,3 C
Szz,1344h 1,0 MPa
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• Slightly higher final temperature
• in construction case 1 and 3

Temperature
Construction case 1
Construction case 2
Construction case 3
CC1 Buffer SCC pouring SCC plug
CC2 Buffer TVC pouring SCC plug
CC3 Buffer SCC precast SCC
lid
T1344h 51,3 C
T1344h 51,3 C
T1344h 50,6 C
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• Slightly higher tensile stresses
• in construction case 1 and 2

Stresses Szz
Construction case 1
Construction case 2
Construction case 3
CC1 Buffer SCC pouring SCC plug
CC2 Buffer TVC pouring SCC plug
CC3 Buffer SCC precast SCC
lid
Szz,1344h 1,0 MPa
Szz,1344h 1,0 MPa
Szz,1344h 0,9 MPa
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No cracks expected in concrete buffer in all cases
Construction case 1
CC1 Buffer SCC pouring SCC plug
Insertion canister
Point 12
Point 9
Point 4
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No cracks expected in concrete buffer in all cases
Construction case 1
CC1 Buffer SCC pouring SCC plug
Insertion canister
Point 12
Point 9
Point 4
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No cracks expected in filler in all cases
Construction case 1
CC1 Buffer SCC pouring SCC plug
Cooling phase (hydration)
Point 13
Heating phase (canister)
Point 8
Point 5
Heating phase (hydration)
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No cracks expected in lid in all cases
Construction case 1
CC1 Buffer SCC pouring SCC plug
Point 7
Point 13
Point 5
Higher stresses in fresh SCC
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THM behaviour of the supercontainer concrete
buffer during construction
Methodology Early age cracking
Concrete buffer composition and
properties Results of experimental program
Simulation results Strength verification
Closure Conclusions and future work
46
Conclusions
Effect of concrete properties (creep, shrinkage)
and boundaries (T) is non-negligible An
extensive lab program was performed on SCC and
TVC SCC experiences bigger creep effect and
larger shrinkage Temperature development inside
SCC is higher Higher tensile and compressive
strength for SCC No early age cracking expected
during construction Axial, tangential and
radial stresses remain smaller then tensile
strength No need for reinforcement First
imulations Heating phase higher tensile
stresses in SCC near outer border Cooling phase
higher tensile stresses in TVC in center Second
simulations Simular temperature development in
different construction cases Higher stresses in
lid with freshly casted SCC
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Future work
Planning 2009 Further investigations on SCC and
TVC characterization Influence of increased
temperature (40-100C) on mechanical
properties Influence of gamma-irradiation on
mechanical properties Testing the robustness of
the simulations Validation of the simulation
results by means of macro-scale tests Sensitivity
analysis of different parameters -
material properties - design parameters
SC - boundary conditions
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• THM behaviour of supercontainer concrete buffer
  during construction

Bart Craeye Ghent University Faculty of
Engineering Magnel Laboratory for Concrete
Research No cracking expected during
construction of concrete buffer!
Questions? Bart.Craeye_at_UGent.be Reference
Craeye B., De Schutter G., Van Humbeeck H., Van
Cotthem A. Early age behaviour of concrete
supercontainers for radioactive waste
disposal. Nuclear Engineering and Design 239
(2009) 23-35