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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.

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chapter 2 using silica fume in concrete
Chapter 2. Using Silica Fume in Concrete
  • Enhancing Mechanical Properties
  • Improving Durability
  • Enhancing Constructability
  • Producing High-Performance Concrete Bridges
increased concrete strength
Increased Concrete Strength

Enhancing Mechanical Properties

  • High-rise columns
  • Precast bridge beams
silica fume concrete typical strengths
Silica-Fume Concrete: Typical Strengths

15%

10%

5%

0%

Control mixture

cement: 658 lb/yd3

w/c: 0.41

air: 5%

0 3 7 28 60

Age, days

silica fume concrete typical strengths6

SI

Silica-Fume Concrete: Typical Strengths

15%

10%

5%

0%

Control mixture

cement: 390 kg/m3

w/c: 0.41

air: 5%

0 3 7 28 60

Age, days

high strength silica fume concrete
High-Strength Silica-Fume Concrete

cement: 950 lb/yd3

silica fume: 150 lb/yd3

w/cm: 0.220

air: 1.1%

high strength silica fume concrete8

SI

High-Strength Silica-Fume Concrete

cement: 564 kg/m3

silica fume: 89 kg/m3

w/cm: 0.220

air: 1.1%

why use high strength concrete
Why Use High-Strength Concrete?

Column design load = 10,000 kips

slide11

SI

Why Use High-Strength Concrete?

Column design load = 50 MN

increased modulus of elasticity
Increased Modulus of Elasticity

Enhancing Mechanical Properties

  • High-rise columns
slide13

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.

slide14

SI

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.

improving durability
Improving Durability

Chapter

Outline

decreased permeability for corrosion resisting concrete
Decreased Permeability for Corrosion-Resisting Concrete

Improving Durability

  • Parking structures
  • Bridge decks
  • Marine structures
silica fume concrete corrosion protection
Silica-Fume Concrete:Corrosion Protection
  • 5-10% silica fume added by mass of cement
  • Mixture may include fly ash or slag
  • w/cm < 0.40: use HRWRA
  • Total cementitious materials < 700 lb/yd3
  • Permeability estimated using ASTM C 1202
silica fume concrete corrosion protection22

SI

Silica-Fume Concrete:Corrosion Protection
  • 5-10% silica fume added by mass of cement
  • Mixture may include fly ash or slag
  • w/cm < 0.40: use HRWRA
  • Total cementitious materials < 415 kg/m3
  • Permeability estimated using ASTM C 1202
silica fume concrete typical values
Silica-Fume Concrete: Typical Values

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 values25

SI

Silica-Fume Concrete: Typical Values

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!

what about simply reducing w cm to achieve durability
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
w/cm reduction versus adding silica fume

w/cm % sf RCP Diffusivity

(coulombs) (m2/s E-12)

slide29

Capitol South Parking Structure

Columbus, OH

5,000 parking spaces

increased abrasion resistance
Increased Abrasion Resistance

Improving Durability

slide32

Kinzua Dam

Western Pennsylvania

improved chemical resistance
Improved Chemical Resistance

Improving Durability

silica fume concrete chemical resistance
Silica-Fume Concrete: Chemical Resistance

Days to 25% Mass Loss

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

5% Acetic Acid 1% H2SO4

silica fume concrete chemical resistance37
Silica-Fume Concrete: Chemical Resistance

Cycles to 25% Mass Loss

1% 5% 5% 5%

H2SO4 Acetic Formic H2SO4

improve shotcrete
Improve Shotcrete

Enhancing Constructability

benefits of silica fume in 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
slide46

These massive walls include portland cement, fly ash, and silica fume to reduce heat and to provide early strength for form removal.

fast track finishing
Fast-Track Finishing

Enhancing Constructability

why use high performance concrete in bridges
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
Why High-Strength HPC?
  • Longer spans
  • Increased beam spacings
  • Shallower sections for same span
slide52

“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

for high strength bridges you must consider
For High-Strength Bridges, You Must Consider:
  • Design issues:
    • Larger diameter strand
    • Take advantage of strength of high-durability concretes
for high strength bridges you must consider57
For High-Strength Bridges, You Must Consider:
  • 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 consider58
For High-Strength Bridges, You Must Consider:
  • Construction issues:
    • Bed capacities
    • Curing temperatures
    • Transportation and erection limitations
why high durability hpc
Why High-Durability HPC?
  • Reduced maintenance costs
  • Longer life
  • “Life-cycle costing”
slide60

“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

slide61

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
Silica-Fume Concrete: Long-Term Performance
  • Illinois State Route 4, bridge over I-55
  • Constructed 1973
  • October, 1986: southbound lane repaired with dense concrete, w/cm = 0.32
  • March, 1987: northbound lane repaired with silica-fume concrete, w/cm = 0.31, sf = 11%
illinois state route 4 bridge over i 55
Illinois State Route 4, Bridge over I-55

Percent chloride by mass of concrete

nchrp project 18 3
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
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 review67

SI

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

new york state dot review68
New York State DOT Review
  • 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.”
slide69

Interstate 15 rebuilding project in Salt Lake City

144 bridges, all with silica-fume concrete decks!

slide71

PCA’s new

HPC Bridge Booklet

can hpc reduce the life cycle cost of a bridge
Can HPC Reduce the Life-Cycle Cost of a Bridge?
  • High-strength HPC -- Possibly
  • High-durability HPC -- Probably
end of chapter 2
End of Chapter 2

Main

Outline