Chapter 2. Using Silica Fume in Concrete

Enhancing Mechanical Properties Improving Durability

Enhancing Constructability Producing High-Performance Concrete

Bridges

Silica Fume is Not a Cement Replacement

Material!

Enhancing Mechanical Properties

Chapter

Outline

Enhancing Mechanical Properties

Increased Concrete Strength

High-rise columnsPrecast bridge beams

0

2

4

6

8

10

Co

mp

ress

ive

Str

eng

th, k

si

Control mixture

cement: 658 lb/yd3

w/c: 0.41

air: 5%

0%

5%

10%15%

Age, days

Silica-Fume Concrete: Typical Strengths

0 3 7 28 60

0

10

20

30

40

50

60

70

Co

mp

ress

ive

Str

eng

th, M

Pa

Control mixture

cement: 390 kg/m3

w/c: 0.41

air: 5%

0%

5%

10%

15%

Age, days SI

Silica-Fume Concrete: Typical Strengths

0 3 7 28 60

High-Strength Silica-Fume Concrete

0

5,000

10,000

15,000

20,000

25,000

0 200 400 600 800 1000 1200

Age, days

Com

pres

sive

Str

engt

h, p

si

cement: 950 lb/yd3

silica fume: 150 lb/yd3

w/cm: 0.220

air: 1.1%

0

20

40

60

80

100

120

140

160

0 200 400 600 800 1000 1200

Age, days

Com

pres

sive

Str

engt

h, M

PaHigh-Strength Silica-Fume Concrete

cement: 564 kg/m3

silica fume: 89 kg/m3

w/cm: 0.220

air: 1.1%

SI

Why Use High-Strength Concrete?

ConcreteStrength,

psi

Columnsize,

inches

Reinforcingrequired

Comments

6,000 45 x 45 44 No. 11 Base case

7,500 45 x 45 20 No. 9 Save steel

12,000 45 x 30 20 No. 8 Save spaceSave steel

12,000 36 x 36 16 No. 8 Save spaceSave steel

Column design load = 10,000 kips

Why Use High-Strength Concrete?

Column design load = 50 MN

ConcreteStrength,

MPa

Column size,meters

Reinforcingrequired

Comments

40 1.2 x 1.2 56 No. 36 Base case

55 1.2 x 1.2 24 No. 29 Save steel

85 1.2 x 0.75 24 No. 22 Save spaceSave steel

85 0.95 x 0.95 24 No. 22 Save spaceSave steel

SI

Enhancing Mechanical Properties

Increased Modulus of Elasticity

High-rise columns

Key Bank Tower

Cleveland, Ohio

High-strength (12,000 psi), high-modulus (6.8 million psi) concrete columns were specified at the corners of this structure to stiffen against wind sway.

Key Bank Tower

Cleveland, Ohio

High-strength (83 MPa), high-modulus (47 GPa) concrete columns were specified at the corners of this structure to stiffen against wind sway.

SI

Improving Durability

Chapter

Outline

Improving Durability

Decreased Permeability for Corrosion-Resisting

ConcreteParking structuresBridge decksMarine structures

Silica-Fume Concrete:Corrosion Protection

5-10% silica fume added by mass of cementMixture may include fly ash or slagw/cm < 0.40: use HRWRATotal cementitious materials < 700 lb/yd3

Permeability estimated using ASTM C 1202

SI

Silica-Fume Concrete:Corrosion Protection

5-10% silica fume added by mass of cementMixture may include fly ash or slagw/cm < 0.40: use HRWRATotal cementitious materials < 415 kg/m3

Permeability estimated using ASTM C 1202

Silica fume RCP Compressive Strength (by mass of cement)

0% > 3,000 coulombs = 5,000 psi

7-10% < 1,000 coulombs > 7,000 psi

>10% < 500 coulombs > 9,000 psi

Don’t fall into strength trap!

Silica-Fume Concrete: Typical Values

SI

Silica fume RCP Compressive Strength (by mass of cement)

0% > 3,000 coulombs = 35 MPa

7-10% < 1,000 coulombs > 50 MPa

>10% < 500 coulombs > 65 MPa

Don’t fall into strength trap!

Silica-Fume Concrete: Typical Values

What About Simply Reducing w/cm to Achieve Durability?

“The results clearly indicate that silica fume was effective in reducing the [Rapid Chloride Permeability Test] values regardless of the curing regimes applied. Moreover, silica fume enhanced chloride resistance more than reducing w/cm. This effect was confirmed by the diffusion tests.” -- Hooton et al. 1997

w/cm reduction versus adding silica fume

0.45 0 3527 10.50.45 7 719 1.90.40 0 3062 9.40.40 7 442 1.80.35 0 2530 5.90.35 7 295 1.9

w/cm % sf RCP Diffusivity (coulombs) (m2/s E-12)

0102030405060708090

100

RCPT 120-DayDiffusivity

Per

cent

of

w/c

m =

0.4

5, 0

% S

F

w/cm 0.45, 0% SF

w/cm 0.40, 0% SF

w/cm 0.35, 0% SF

w/cm 0.45, 7% SF

w/cm 0.40, 7% SF

w/cm 0.35, 7% SF

w/cm 0.35, 12% SF

w/cm reduction versus adding silica fume

Capitol South Parking Structure

Columbus, OH

5,000 parking spaces

Bridge Deck Overlay

Ohio DOT

Improving Durability

Increased Abrasion Resistance

Kinzua Dam

Western Pennsylvania

Abrasion-erosion damage to the stilling basin of Kinzua Dam

Improving Durability

Improved Chemical Resistance

0

40

80

120

160

200

LMC

SFMC

LWC

1% HCl 1% Lactic Acid 5% (NH4)2SO4

5% Acetic Acid 1% H2SO4

Days to 25% Mass Loss

Silica-Fume Concrete: Chemical Resistance

0

10

20

30

40

50

60

0% sf7.5% sf12.5 %sf15% sf25% sf30% sf

Silica-Fume Concrete: Chemical Resistance

Cycles to 25% Mass Loss

1% 5% 5% 5%

H2SO4 Acetic Formic H2SO4

Enhancing Constructability

Chapter

Outline

Enhancing Constructability

Improve Shotcrete

Silica-fume shotcrete

Benefits of Silica Fume in Shotcrete

Reduction of rebound loss up to 50% Increased one-pass thickness up to

12 in. (300 mm) Higher bond strength Improved cohesion to resist washout

in tidal rehabilitation of piles and seawalls

Enhancing Constructability

Increase Early Strength

Control Temperature

Nuclear Waste Storage Facility

Hanford, WA

These massive walls include

portland cement, fly ash, and silica fume to reduce heat and

to provide early strength for form

removal.

Enhancing Constructability

Fast-Track Finishing

Producing High-Performance Concrete

Bridges

Chapter

Outline

Why Use High-Performance Concrete

in Bridges?

High strength -- girders and beams

High durability -- decks, sidewalks, parapets, piles, piers, pier caps,

and splash zones

Why High-Strength HPC?

Longer spans Increased beam spacings

Shallower sections for same span

“The use of high-strength concrete in the fabrication and construction of

pretensioned concrete girder bridges can result in lighter bridge designs, with corresponding economic advantages, by allowing longer span lengths and

increased girder spacings for standard shapes.”

-- B. W. Russell PCI Journal

Ohio HPC Bridge

New Hampshire HPC Bridge

Colorado HPC Bridge

For High-Strength Bridges, You Must Consider:

Design issues:Larger diameter strandTake advantage of strength of high-durability concretes

Concrete materials and proportioning issues:Random approach to trial mixtures may not be best approach

Conduct full-scale testing of selected mixture

For High-Strength Bridges, You Must Consider:

Construction issues:Bed capacitiesCuring temperaturesTransportation and erection limitations

For High-Strength Bridges, You Must Consider:

Why High-Durability HPC?

Reduced maintenance costs Longer life

“Life-cycle costing”

“The results of this study indicate that there are no fundamental reasons why

use of silica fume concrete in bridge deck applications should not continue

to grow as ‘high-performance concretes’ become an increasingly

important part of bridge construction.”

-- Whiting and Detwiler NCHRP Report 410

One approach to improving the durability of concrete bridge

decks exposed to chlorides in service is to reduce the rate at which chlorides can enter the

concrete.

Silica-Fume Concrete: Long-Term Performance

Illinois State Route 4, bridge over I-55Constructed 1973October, 1986: southbound lane repaired

with dense concrete, w/cm = 0.32March, 1987: northbound lane repaired

with silica-fume concrete, w/cm = 0.31, sf = 11%

Silica-fumeconcrete

Dense concrete

Depth 10 mm(0.4 in.)

25 mm(1.0 in.)

10 mm(0.4 in.)

25 mm(1.0 in.)

0.152 0.042 0.253 0.0840.074 0.014 0.263 0.061

0.087 0.014 0.077 0.021

0.066 0.018 0.370 0.114

Percent chloride by mass of concrete

Illinois State Route 4, Bridge over I-55

What About Cracking of HPC Silica-Fume

Concrete Bridge Decks?

NCHRP Project 18-3

Silica-fume concretes tend to crack only when they are insufficiently moist-cured.

If silica-fume concrete mixtures are given 7 days of continuous moist curing, there is then no association between silica fume content and cracking.

New York State DOT Review

Since April, 1996, NYSDOT has used HPC concrete in its bridge decks to reduce cracking and permeability.

Class HP concrete:

Portland cement 500 lb/yd3

Fly ash 135 lb/yd3

Silica fume 40 lb/yd3

w/cm 0.40

New York State DOT Review

Since April, 1996, NYSDOT has used HPC concrete in its bridge decks to reduce cracking and permeability.

Class HP concrete:

Portland cement 300 kg/m3

Fly ash 80 kg/m3

Silica fume 25 kg/m3

W/CM 0.40

SI

84 HPC bridge decks were inspected -- 49% showed no cracking

“Results indicated that Class HP decks performed better than previously specified concrete in resisting both longitudinal and transverse cracking.”

New York State DOT Review

Interstate 15 rebuilding

project in Salt Lake City

144 bridges, all with silica-fume concrete decks!

Need more information on

HPC for Bridges?

PCA’s new

HPC Bridge Booklet

Can HPC Reduce the Life-Cycle Cost of a

Bridge?

High-strength HPC -- Possibly High-durability HPC -- Probably

End of Chapter 2

Main

Outline