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 columns Precast bridge beams

Control mixture cement: 658 lb/yd 3 w/c: 0.41 air: 5% 0% 5% 10% 15% Age, days Silica-Fume Concrete: Typical Strengths

Control mixture cement: 390 kg/m 3 w/c: 0.41 air: 5% 0% 5% 10% 15% Age, days SI Silica-Fume Concrete: Typical Strengths

High-Strength Silica-Fume Concrete cement: 950 lb/yd 3 silica fume: 150 lb/yd 3 w/cm: air: 1.1%

High-Strength Silica-Fume Concrete cement: 564 kg/m 3 silica fume: 89 kg/m 3 w/cm: air: 1.1% SI

Why Use High-Strength Concrete? Column design load = 10,000 kips

Why Use High-Strength Concrete? Column design load = 50 MN 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 Concrete Parking structures Bridge decks Marine structures

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/yd 3 Permeability estimated using ASTM C 1202

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/m 3 Permeability estimated using ASTM C 1202

Silica fume RCP Compressive Strength (by mass of cement) 0% > 3,000 coulombs= 5,000 psi 7-10% 7,000 psi >10% 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% 50 MPa >10% 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 w/cm % sf RCP Diffusivity (coulombs) (m 2 /s E-12)

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

1% HCl 1% Lactic Acid 5% (NH 4 ) 2 SO 4 5% Acetic Acid 1% H 2 SO 4 Days to 25% Mass Loss Silica-Fume Concrete: Chemical Resistance

Cycles to 25% Mass Loss 1% 5% 5% 5% H 2 SO 4 Acetic Formic H 2 SO 4

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 strand  Take 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 capacities  Curing temperatures  Transportation 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-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%

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 cement500 lb/yd 3 Fly ash135 lb/yd 3 Silica fume40 lb/yd 3 w/cm0.40

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 cement300 kg/m 3 Fly ash80 kg/m 3 Silica fume25 kg/m 3 W/CM0.40 SI

 84 HPC bridge decks were inspected % 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