Shrinkage Behavior of Ultra High Performance

Concrete at the Manufacturing Stage

Sungwook KIM

2

Introduction

Mix Proportion & Material Properties

Test Results

On Going Study

CONTENT

Conclusion

3

1. Introduction (Problems)

Shrinkage cracking

Typical Shrinkage Strains of UHPC

Edge

Steel reinforcement Autogenous shrinkage

Drying shrinkage

“Highly vulnerable to premature shrinkage cracking”

4

Str

ess

Time

Elastic stress generated

by shrinkage only

(σ=EC·εsh)

Delay in cracking

Age of cracking

Creep relaxationResidual stress

regarding stress

relaxation

Material

strength

※ What are the influencing factors for shrinkage cracking?

“Influencing factors”

“by J. Weiss, 1999”

• Strength test

• Setting test

• Ring-test

• Free shrinkage test Tensile creep

Shrinkage rate

Tensile strength

Shrinkage potential

5

2. Mix Proportions and Material Properties

Nomenclature W/B Cement Silica Fume

(SF) Filler Sand

Superplasticizer

(SP) SRA* EA**

Steel

fiber

Mix. A 0.2 1.0 0.25 0.3 1.1 0.012

- - Vf=2%

Mix. B 0.01 0.075

* : Shrinkage reducing agent ** : Expansive admixture

Type of fiber Density

(kg/cm3) Tensile strength

(MPa) Length of fiber

(mm) Aspect ratio

(mm/mm)

Straight type 7.8 2,500 13 65

Composition %

(mass) CaO Al2O3 SiO2 Fe2O3 MgO SO3 K2O F-CaO

Specific surface

(cm2/g) Density

(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

Chemical Compositions of Materials

Properties of Steel Fiber

Mix Proportions (ratio in weight)

Relative Humidity & Temp.

Relative

Humidity (RH)

Temperature

(℃)

60±5% 23±1℃

6

Compressive strength Flexural tensile strength Secant elastic modulus

tb

a

f

fc exp28

Mixture Flow

(mm)

Compressive strength

(MPa)

Flexural tensile strength

(MPa)

Secant elastic modulus

(GPa)

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

tb

a

f

f ftexp

28

tb

a

E

E

c

c exp28

Mixture a b R2

Mix. A 0.971 -0.271 0.9842

Mix. B 1.162 -0.326 0.9862

Mixture a b R2

Mix. A 0.303 -0.058 0.9916

Mix. B 0.456 -0.101 0.9732

Mixture a b R2

Mix. A 0.389 0.001 0.9948

Mix. B 0.381 0.001 0.9986

3. Test Results (Mechanical Properties)

7

3. Test Results (Setting properties)

Setting properties of UHPC (ASTM C 403)

)(Log)(Log tabPR

where, PR=penetration resistance (psi)

t=elapsed time (min)

(1)

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

※I.S.: PR=3.5MPa, F.S.: PR=28MPa

Initial setting

Final setting

● Mix.A

◆ Mix.B

8

Relationship between Autogenous shrinkage and Setting time

3. Test Results (Autogenous Shrinkage)

Embedded

Strain

gage

Thermocouple

)()()( ttt plastictotalauto where, εauto(t) = autogenous shrinkage (με)

εtotal(t) = total shrinkage except drying shrinkage (με)

εtotal(t) = plastic shrinkage (με)

(2)

Plastic

Shrinkage

Reduction

9

Free shrinkage with different exposed surface-to-volume ratios (S/Vs)

3. Test Results (Free Shrinkage)

Combined effect of SRA and EA

S/V=0.0132

S/V=0.0286

550mm

152mm 152mm246mm

35

mm

Sealing SealingExposed concrete

Sealing SealingExposed concrete

550mm

165mm 220mm 165mm

76

mm

550mm

152mm 152mm246mm

35

mm

Sealing SealingExposed concrete

Sealing SealingExposed concrete

550mm

165mm 220mm 165mm

76

mm

Embedded

Strain

gage

Thermocouple

≈ 40~44%

“by H. T. See, 2003”

Volume

expansion

10

Inner steel ring

Outer ringWooden base

Inner steel ring

Outer ringWooden base

Teflon sheet

Inner steel ring

Outer ringWooden base

Teflon sheet

Strain gages

Thermocouple

Inner steel ring

Outer ringWooden base

Teflon sheet

Strain gages

Thermocouple

Inner steel ring

“Data Logger system”

3. Test Results (Test procedure: Ring-test (AASHTO PP34-98))

11

3. Test Results (Ring-test)

tCtt mst )()(

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)

“Coefficient

of Thermal

Expansion

=16με/℃”

Temperature compensation of inner steel ring

(3)

Strain gage

Thermocouple

12

Average strains of inner steel ring

3. Test Results (Ring-test)

A R1-

• Type of Mixture

A: Mix. A

B: Mix. B

• Thickness of concrete ring

R1: 35mm

R2: 76mm

“Mix. A” “Mix. B”

267mm305mm

R1=375mm or R2=457mm

Silicon

sealing

Steel gage

Concrete

Steel ring

Drying direction

152mm

34%

48%

13

0

5

10

15

20

25

30

35

40

0 4 8 12 16 20 24 28

Ste

ss (

MP

a)

Age (day)

Mix.A Mix.B

계열7 계열8Mix. A Mix. B

Relaxed stresses

stst

os

isosi E

r

rrP

2

22

2

)( stst

icoc

ocic

os

isost E

rr

rr

r

rr

)(

)(

2

)(22

22

2

22

max

Calculated maximum pressures and tensile stresses

Maximum interface pressures

by Eq. (4)

Maximum residual tensile stresses

by Eq. (5)

(4) (5)

3. Test Results (Restrained Shrinkage Behaviors)

Stresses generated

by shrinkage only

(σ=EC·εsh)

Residual stresses

considering stress

relaxation

14

3. Test Results (Restrained Shrinkage Behaviors)

Tensile creep strains of UHPC with time dependent restrained forces

Tensile creep strains of UHPC

under restrained condition

Tensile creep strains-to-free shrinkage ratio

of UHPC under restrained condition

≈ 39% ≈ 0.46

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

before initial setting time

Tensile tests are carrying in order to

estimate crack at very early age

“by Dao, 2009”

16

4. Concluding Remarks

1

2

3

4

Ring tests also verified the possibility to compute the confining

tensile stress and strain according to the shrinkage of UHPC at

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 experimentally

This study investigated experimentally the shrinkage behavior

and the corresponding stresses in UHPC for the control of cracks

due to the restraint of forms at early age

Free shrinkage and restrained steel strains were reduced in terms of the shrinkage reducing effect of EA and SRA

17

Thank you for

your attention