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Shrinkage Behavior of Ultra High Performance     Concrete at the Manufacturing Stage               Sungwook KIM
CONTENT      Introduction      Mix Proportion & Material Properties      Test Results      On Going Study      Conclusion ...
1. Introduction (Problems)                          Drying shrinkage                                                      ...
※ What are the influencing factors for shrinkage cracking?             “Influencing factors”                              ...
2. Mix Proportions and Material Properties                                                                                ...
3. Test Results (Mechanical Properties)    Compressive strength                                Flexural tensile strength  ...
3. Test Results (Setting properties)  Setting properties of UHPC (ASTM C 403)               Final setting               In...
3. Test Results (Autogenous Shrinkage)     Relationship between Autogenous shrinkage and Setting time     Thermocouple    ...
3. Test Results (Free Shrinkage)  Free shrinkage with different exposed surface-to-volume ratios (S/Vs)       Thermocouple...
3. Test Results (Test procedure: Ring-test (AASHTO PP34-98))                                                              ...
3. Test Results (Ring-test)                                                                                  Strain gage  ...
3. Test Results (Ring-test)                                                                              Drying direction ...
3. Test Results (Restrained Shrinkage Behaviors)  Calculated maximum pressures and tensile stresses    Maximum interface p...
3. Test Results (Restrained Shrinkage Behaviors)  Tensile creep strains of UHPC with time dependent restrained forces    T...
4. On Going Study (Tensile Test at very early Age)   Carrying out tensile test within 1 days after mixing      Strain of s...
4. Concluding Remarks         This study investigated experimentally the shrinkage behavior         and the corresponding ...
Thank you foryour attention             17
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Shrikage behavior of UHPC

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

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Transcript of "Shrikage behavior of UHPC"

  1. 1. Shrinkage Behavior of Ultra High Performance Concrete at the Manufacturing Stage Sungwook KIM
  2. 2. CONTENT Introduction Mix Proportion & Material Properties Test Results On Going Study Conclusion 2
  3. 3. 1. Introduction (Problems) Drying shrinkage Edge Autogenous shrinkage Steel reinforcement Typical Shrinkage Strains of UHPC Shrinkage cracking “Highly vulnerable to premature shrinkage cracking” 3
  4. 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 4
  5. 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 5
  6. 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 28daysMix. A 235 78.8 105.6 126.2 152.4 26.3 28.7 33.8 34.1 28.2 40.3 41.2 43.3Mix. 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 6
  7. 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 7
  8. 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) 8
  9. 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” 9
  10. 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 10
  11. 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) 11
  12. 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% 12
  13. 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) 13
  14. 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 14
  15. 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” 15
  16. 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 16
  17. 17. Thank you foryour attention 17
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