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Transcript of Chapter 2. Using Silica Fume in Concrete Enhancing Mechanical Properties Improving Durability ...
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