uhpc.pdf

1Creep of Ultra-High Performance Concrete (UHPC)

Victor Y. Garas

CEE 8813

04/13/2007

School of Civil and Environmental EngineeringGeorgia Institute of Technology

Atlanta, GA, 30332

Presentation Organization

Ultra-High Performance Concrete- Definition- Developing- Advantages- Applications

Creep of Concrete- Definitions- Mechanisms

Creep of Ultra-High Performance Concrete- Compressive

- Tensile (Motivation)- Tensile (Background)- Tensile (Test Setups)- Tensile (Key Results)

Concluding Remarks

2ACI Committee 116

A concrete meeting special combinations of performance and

uniformity requirements that cannot always be achieved routinely using

conventional constituent materials and normal mixing, placing, and

curing practices.

The Federal Highway Administration (FHWA)

HPC can be specified not only by the strength, but by also the

following: freeze-thaw durability, scaling resistance, abrasion resistance,

chloride penetration, creep, shrinkage, and modulus of elasticity.

UHPC (Definitions)

Collepardi et al. 1997

UHPC can be defined as an ultra-high strength and high ductility

concrete with advanced mechanical properties.

Shah and Weiss, 1998

Ultra-High Strength Concrete (UHSC) is defined as a mixture with

compressive strength greater than 22 ksi (150 MPa).

UHPC (Definitions)

31- Decreasing Permeability

- Reducing the water-cement ratio (typically < 0.2)

- Providing proper compaction (vibration)

- Eliminating Coarse aggregates

Image from: Mehta and Monteiro, 2005

UHPC (Developing)

2- Densification with micro-fine particles

- Filling remaining void space

- Denser material

- Stronger and more durable material

Image from: http://techalive.mtu.edu/meec/module06/Packing.htm

UHPC (Developing)

43- Macro-defect free (MDF) Materials- Cement + Water-soluble polymer @ low w/c (typically less than 0.2). - Increase in strength arises as a result of the cross-linking between cement and polymer (Poyola et al. 1990).

4- Using Fibers

5- Temperature Curing

Image from: Shah and Weiss, 1998

UHPC (Developing)

0.180.180.180.180.18W/CM

341341341341341Water

6060606060Glenium (HRWR)

1,5901,5901,5901,5901,590BB (150-600) Sand

098196295393Metakaolin - 235

320320320320320Class C Fly Ash

360270180900Grace Silica Fume

1,2001,2001,2001,2001,200P. Cement Type I

SF/MK-INFlb/yd3

SF/MK- 300lb/yd3

SF/MK- 100lb/yd3

SF/MK - 33lb/yd3

SF/MK - 0lb/yd3

Material

UHPC (Developing)

6- Example

5750 (but nothing 750 (but nothing after heat curing)after heat curing)

400 400 -- 800800Total Shrinkage @ 180 of drying Total Shrinkage @ 180 of drying (() (in/in x 10) (in/in x 10--66))

0.0390.0390.21 0.21 0.520.52Specific Total Creep in Specific Total Creep in Compression @ 180 (Compression @ 180 (//psipsi))

1818Negligible if < 100Negligible if < 100

800 800 3,0003,000Chloride Permeability Chloride Permeability (coulombs)(coulombs)

989860 60 -- 8080Freeze/thaw durability (%)Freeze/thaw durability (%)

7,350 7,350 7,8207,8204,060 4,060 7,2507,250Min. E Min. E ((ksiksi))

1,350 1,350 1,7501,750(direct tension)(direct tension)

about 10% of about 10% of ffccMin.Min. ff t t ((psipsi) )

> 22,000> 22,0006,000 6,000 14,00014,000Min. Min. ff c c ((psipsi) @ 56 days) @ 56 days

UltraUltra--High High Performance Performance

ConcreteConcrete

High High Performance Performance

ConcreteConcrete

PropertyPropertyHigh strength

Reduction in member x-sec. Dimensions.

High Durability

Low long-term maintenance

cost.

High Ductility

Data from: Goodspeed et al., 1999 & Graybeal, 2005

UHPC (Advantages)

UHPC (Advantages)

61- Increase in Girder spans

2- Increasing the spacing between girders

3- Permeability of concrete decreased (increased durability).

UHPC (Advantages)

Girders

4- Offsetting the Long term maintenance costs

5- Minimumizing depth girders

Steel Beam

UHPC (Advantages)

76- Further, it is predicted that an Ultra-HPC girder would not require web shear reinforcement except for an amount required to connect the cast-in-place deck slab to the girder.

Normal Concrete Section(Shear Rft.)

UHPC Section(No Shear Rft.)

UHPC (Advantages)

1- Sherbrooke Footbridge - (1999)

197 ftLength

2.84x10-5 ksiPrestressing

55 yd3Volume of RPC

1.18 inThickness of the slab

2175 ft2Deck area

UHPC (Applications)

82- Seonyu Footbridge Seoul South Korea (2002)

Images from: Lafarge

120 m (393 ft)

15 m (49 ft)

26.46 kipsPrestressing

NoneConventional reinforcement

4.27 ftHeight of the transverse section

48.75 ftHeight at mid-span (ft)

1.20 inThickness of the slab

393.60 ftLength

UHPC (Applications)

Images from: Lafarge

2- Seonyu Footbridge Seoul South Korea (2002) (cont.)

UHPC (Applications)

9 Creep: time-dependent increase in strain under constant load taking place

after the initial strain at loading.

Basic creep: time-dependent increase in strain under sustained constant load of a concrete sealed specimen (Independent of specimen shape and size).

Drying creep: it is the creep occurring in a specimen exposed to the environment

and allowed to dry (Depends on specimen shape and size).

Image and Definitions from ACI 209-1R-05

Creep of Concrete (Definitions)

Creep coefficient: it is the ratio of the creep strain to the initial strain (dimensionless).

Specific creep: it is

the creep strain per unit load (strain/stress).

Image and Definitions from ACI 209-1R-05

Creep of Concrete (Definitions)

10

Viscous flow of the cement matrix

Consolidation due to seepage of water in the microstructure

Permanent deformation- microcracking- formation of new physical

bonds.

Physically adsorbed

water

Capillary water

Interlayer water

C-S-H layer

Creep of Concrete (Mechanisms)

Compressive

Data from: Graybeal, 2005 (Compression creep test of UHPC)

Creep of UHPC

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Compressive

0.04400.3148515800.4624.42Delayed Steam

(90oC & 95% RH) for 48 h starting after

15 days

0.09800.6611016700.4325.65Tempered Steam(60oC & 95% RH)

for 48 h after casting

0.1460.78160020570.6716.53Air(Ambient Conditions)

0.03900.2944015000.4127.27Steam curing

(90oC & 95% RH) for 48 h after casting

Specific Creep

(/psi)Creep

CoefficientFinal Creep

Strain()

Initial ElasticStrain

()Stress/Strain

ControlStrength

(ksi)Curing regime

Data from: Graybeal, 2005 (Compression creep test of UHPC)

Creep of UHPC

There is a specific interest in using UHPC for

prestressed highway bridge girders. With the UHPC

manufacturers recommendation not to use transverse

reinforcement, the long-term tensile performance of the

material should be characterized before specifying it.

Images from: Lafarge and Nawy, 2006

Tensile (Motivation)

Creep of UHPC

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Tensile (background)

Creep of UHPC

tot = fs+ bc+ dc

Pickett effect (1942)

- Due to the nonuniformity of the moisture distribution in a drying specimen.

- drying creep component was explained by many models by the so called microcracking effect.

- Study of the microcrakingproblem in tension will be more effective.


Creep of UHPC

Total Creep

Basic Creep

Total Creep

Basic Creep

Kovler (1995)

- Nature of total creep is different than basic creep.

- At the beginning, total creep was less than basic creep.

- Drying creep component had a negative value initially, shrinkage, which decreases gradually and transforms to positive later.

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Creep of UHPC

Total Creep

Basic Creep

Total Creep

Basic Creep

Kovler (1995)

Where:cs is creep-induced shrinkage

dominating at the beginning (always ve),

sc is shrinkage-induced creep, dominating at the later stage (same as basic creep).

dc = sc+ cs


Creep of UHPC

Abnormal behavior [Kovler, 1999]

- It was found difficult to apply the previous approach to experimental data.

- Tensile loading and drying produce strains of different directions.

- These two components will change with time.

Total strain

Free shrinkage

Basic creep

Total strain

Basic creep

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Creep of UHPC


- The excess basic creep strain over total creep was attributed to swelling of the sealed specimens.

a- evaporation of water in the capillaries under 100% RH (no shrinkage).

b- evaporation continues and R reduces to r (shrinkage).

c- swelling starts with sealing as the minsucs becomes flatter.

(a)

(c)

(b)


c = tot - fs

bc,corr = bc - sw


Creep of UHPC

Basic creep

Total strain

Drying creep of concrete under tension actually represents creep strain not shrinkage

w/cm = 0.7 w/cm = 0.7

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Tensile (Background)

Creep of UHPC

Due to the significant difference in the water-to-cement

ratios between both the cases (0.7 in the case of this

study vs. < 0.2 in case of UHPC, results that could be

obtained from similar tests on UHPC might be

significantly different than what was obtained in the

previous study.

1- Kovler (1994)

Advantages:1-high resolution (512 reading/sec).2-completely automated setup.

Disadvantages:1-compensation cycles may cause premature failure if the load/strength is high.

2-limited number of specimens.

3- possible load eccentricity.

Tensile (Test Setups)

Creep of UHPC

16

2- Bissonnette and Pigeon (1995)

Advantages:1- Relatively simpler.2- Constant, centric loading is

guaranteed throughout the test.

Disadvantages:1- Top and bottom specimen connections design especially for high strength concrete applications.

2- Manual loading may cause disturbance.

3-limited number of specimens.


Creep of UHPC


Water tank (capacity of

75 L)

System of pulleys

(amplification 8: 1)

Advantages:1- Steady load application.

2-ability to test 3 replicates simultaneously.

Disadvantages:1- 50% of the applied load is lost by friction in the system of pulleys.


Creep of UHPC

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Advantages:1- Steady load application.

2-ability to test 3 replicates / frame.

Disadvantages:1- the strain gage electrical properties change with time and thus make it unsuitable for long term testing.

2- loading is not

constant allover the test


Creep of UHPC


Creep of UHPC

Detail II

Detail III

Detail I

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Test Setup Features

Loading: Axial and constant loading throughout the test. Load capacity

of 16,000 lb (1,780 psi on a 3x3 in specimens).

Strain measurements: using mechanical dial gages (accuracy of 0.0001 inch).

Specimens:6 frames will be built (total of 18 3x3x15 in specimens can be

tested at the same time).

Challenge:Designing the specimen-end plates connection


Creep of UHPC

1- Use of Silica fume as SCM

Portland cement concrete

Cement /silica fume concrete

Data from: Bissonnette and Pigeon, 1995 (tensile creep)

Tensile (Key Results)

Creep of UHPC

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Data from: Bissonnette and Pigeon, 1995 (tensile creep)

fibers

M fibers

control


Creep of UHPC

2- Use of steel fibers

Image from: Bissonnette and Pigeon, 1995 (tensile creep)

stress/strain = 0.04

stress/strain = 0.09


Creep of UHPC

3- Stress/strength ratio

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Results (Altoubat and Lange, 2001)

Effect of fibers The incorporation of fibers in the wet condition decreased the initial basic creep as they controlled microcracking.

Under drying conditions, these previously effects of using fibers are not evident likely because under these conditions, more surface microcracking occurs.

Effect of w/cm The tensile basic creep increased upon decreasing the w/cm. This may suggest that the tensile creep behavior at early age is governed by different factors than in mature concrete.


Creep of UHPC

Concluding Remarks

1. There is a need to improve the fundamental understanding of the tensile creep behavior of steel-fiber reinforced ultra-high cementitious matrices.

2. Characterizing the the long-term tensile behavior of UHPC reinforced with steel fibers and will assess the efficiency of specifying it for use in highway bridge girders without transverse bar reinforcement.

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THANK YOU

Questions ?

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Appendix

Failure patterns as a function of beam slenderness. (a) Flexural failure, (b) Diagonal tension failure (flexure shear), and (c) Shear compression failure (web shear) (a/d < 2.5) (Nawy 2006)).

a/d > 5.5 conc. Load a/d > 16 dist. load

a/d = 2.5 - 5.5 conc. Load

a/d = 5.0 16 dist. laod

1

2

3

a/d < 2.5 conc. Load a/d

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