This presentation material is concerned with research results for Ultra High Performance Concrete. The research was focused on the behavior of shrinkage in UHPC.

1. Shrinkage Behavior of Ultra High Performance
Concrete at the Manufacturing Stage
Sungwook KIM

2. CONTENT
Introduction
Mix Proportion & Material Properties
Test Results
On Going Study
Conclusion
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3. 1. Introduction (Problems)
Drying shrinkage
Edge
Autogenous shrinkage
Steel reinforcement
Typical Shrinkage Strains of UHPC
Shrinkage
cracking
“Highly vulnerable to premature shrinkage cracking”
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4. ※ What are the influencing factors for shrinkage cracking?
“Influencing factors”
Elastic stress generated
by shrinkage only
ε
(σ=EC· sh)
• Strength test
Material
strength
Stress
Creep relaxation
Residual stress
regarding stress
relaxation
• Setting test
Age of cracking
Delay in cracking
Time • Ring-test
“by J. Weiss, 1999”
Shrinkage Tensile Shrinkage Tensile
• Free shrinkage test
potential creep rate strength
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5. 2. Mix Proportions and Material Properties
* : Shrinkage reducing agent
Mix Proportions (ratio in weight) ** : Expansive admixture
Silica Fume Superplasticizer Steel
Nomenclature W/B Cement Filler Sand SRA* EA**
(SF) (SP) fiber
Mix. A - -
0.2 1.0 0.25 0.3 1.1 0.012 Vf=2%
Mix. B 0.01 0.075
Properties of Steel Fiber Relative Humidity & Temp.
Density Tensile strength Length of fiber Aspect ratio Relative Temperature
Type of fiber
(kg/cm3) (MPa) (mm) (mm/mm) Humidity (RH) (℃)
Straight type 7.8 2,500 13 65 60±5% 23±1℃
Chemical Compositions of Materials
Composition % Specific surface Density
CaO Al2O3 SiO2 Fe2O3 MgO SO3 K2O F-CaO
(mass) (cm2/g) (g/cm3)
Cement 61.33 6.40 21.01 3.12 3.02 2.30 - - 3,413 3.15
Silica fume (SF) 0.38 0.25 96.00 0.12 0.10 - - - 200,000 2.10
EA 13.55 18.66 3.80 - - 51.35 0.56 16.02 3,117 2.98
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6. 3. Test Results (Mechanical Properties)
Compressive strength Flexural tensile strength Secant elastic modulus
fc  a  f ft  a  Ec  a 
 exp   exp   exp 
f 28 bt  f 28 bt  Ec 28  bt 
Mixture a b R2 Mixture a b R2 Mixture a b R2
Mix. A 0.971 -0.271 0.9842 Mix. A 0.303 -0.058 0.9916 Mix. A 0.389 0.001 0.9948
Mix. B 1.162 -0.326 0.9862 Mix. B 0.456 -0.101 0.9732 Mix. B 0.381 0.001 0.9986
Compressive strength Flexural tensile strength Secant elastic modulus
Flow (MPa) (MPa) (GPa)
Mixture
(mm)
1day 3days 7days 28days 1day 3days 7days 28days 1day 3days 7days 28days
Mix. A 235 78.8 105.6 126.2 152.4 26.3 28.7 33.8 34.1 28.2 40.3 41.2 43.3
Mix. B 240 70.7 98.7 127.3 152.2 24.1 25.1 32.5 33.4 30.9 41.1 44.6 46.0
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7. 3. Test Results (Setting properties)
Setting properties of UHPC (ASTM C 403)
Final setting
Initial setting
● Mix.A Log ( PR)  b  a  Log (t ) (1)
◆ Mix.B
where, PR=penetration resistance (psi)
t=elapsed time (min)
※I.S.: PR=3.5MPa, F.S.: PR=28MPa
Mixture a b R2 Initial Setting (hr) Final Setting (hr)
Mix. A 5.1483 11.0284 0.99507 11.0 13.5
Mix. B 8.3353 20.6517 0.99519 7.5 11.5
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8. 3. Test Results (Autogenous Shrinkage)
Relationship between Autogenous shrinkage and Setting time
Thermocouple
Embedded
Strain
gage
Plastic
Shrinkage
Reduction
where, εauto(t) = autogenous shrinkage (με)
 auto(t )   total (t )   plastic(t ) (2) εtotal(t) = total shrinkage except drying shrinkage (με)
εtotal(t) = plastic shrinkage (με)
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9. 3. Test Results (Free Shrinkage)
Free shrinkage with different exposed surface-to-volume ratios (S/Vs)
Thermocouple
Embedded
Strain
gage
550mm
152mm 246mm
550mm 152mm
152mm 246mm 152mm
Volume 35mm
Sealing Exposed concrete Sealing
35mm
expansion
Sealing Exposed concrete Sealing
S/V=0.0286
550mm
165mm 550mm
220mm 165mm
165mm 220mm 165mm
Combined effect of SRA and EA
76mm
≈ 40~44%
Sealing Exposed concrete Sealing
76mm
Sealing Exposed concrete Sealing
S/V=0.0132
“by H. T. See, 2003”
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10. 3. Test Results (Test procedure: Ring-test (AASHTO PP34-98))
Teflon sheet
Wooden base Outer ring Wooden base Outer ring
Inner steel ring Inner steel ring
Teflon sheet Teflon sheet
Wooden base Outer ring Wooden base Outer ring
Thermocouple Thermocouple
Inner steel ring Inner steel ring
“Data Logger system”
Strain gages Strain gages
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11. 3. Test Results (Ring-test)
Strain gage
Temperature compensation of inner steel ring
Thermocouple
“Coefficient
of Thermal
Expansion
=16με/℃”
 st (t )   m (t )  C  t (3)
where, εst(t) = actual steel strain by shrinkage of concrete (με)
εm(t) = measured steel strain (με)
C = coefficient of thermal expansion of steel ring (16με/℃)
Δt = time (hours)
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12. 3. Test Results (Ring-test)
Drying direction
Average strains of inner steel ring
Silicon Steel ring
sealing
A - R1 Steel gage
Concrete 152mm
• Type of Mixture • Thickness of concrete ring 267mm
A: Mix. A R1: 35mm 305mm
B: Mix. B R2: 76mm R1=375mm or R2=457mm
“Mix. A” “Mix. B”
34%
48%
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13. 3. Test Results (Restrained Shrinkage Behaviors)
Calculated maximum pressures and tensile stresses
Maximum interface pressures Maximum residual tensile stresses
by Eq. (4) by Eq. (5)
(ros  ris )
2 2
(ros  ris ) (ric  roc )
2 2 2 2
Pi  Est  st (4)  t max  Est  st (5)
2
2ros 2ros (roc  ric )
2 2 2
40
Mix.A Mix.B
Mix. A Mix. B
35 계열7 계열8
30 Stresses generated
by shrinkage only
Stess (MPa)
25 (σ=EC·εsh)
20 Relaxed stresses
15
10
5
Residual stresses
considering stress
0
relaxation
0 4 8 12 16 20 24 28
Age (day)
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14. 3. Test Results (Restrained Shrinkage Behaviors)
Tensile creep strains of UHPC with time dependent restrained forces
Tensile creep strains of UHPC Tensile creep strains-to-free shrinkage ratio
under restrained condition of UHPC under restrained condition
≈ 39%
≈ 0.46
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15. 4. On Going Study (Tensile Test at very early Age)
Carrying out tensile test within 1 days after mixing
Strain of steel ring occurs Tensile tests are carrying in order to
before initial setting time estimate crack at very early age
“by Dao, 2009”
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16. 4. Concluding Remarks
This study investigated experimentally the shrinkage behavior
and the corresponding stresses in UHPC for the control of cracks
1 due to the restraint of forms at early age
Free shrinkage and restrained steel strains were reduced in terms of
2 the shrinkage reducing effect of EA and SRA
Ring tests also verified the possibility to compute the confining
tensile stress and strain according to the shrinkage of UHPC at
3 very early age
Further studies will investigate solutions enabling to get tensile
strength at very early age and simulate the cross-sectional
stiffness and restraint of the form, and verify these solutions
4 experimentally
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17. Thank you for
your attention
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