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Chapter 3. Obtaining Silica-Fume Concrete. Specifying Silica Fume and SFC Proportioning SFC Producing SFC. Specifying Silica Fume and Silica-Fume Concrete. Chapter Outline. Specifying Silica Fume. ASTM C 1240 AASHTO M 307 CSA A 23.5. Key Provisions: ASTM C 1240.

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chapter 3 obtaining silica fume concrete
Chapter 3. Obtaining Silica-Fume Concrete
  • Specifying Silica Fume and SFC
  • Proportioning SFC
  • Producing SFC
specifying silica fume
Specifying Silica Fume
  • ASTM C 1240
  • AASHTO M 307
  • CSA A 23.5
key provisions astm c 1240
Key Provisions: ASTM C 1240
  • SiO2 content, 85% min
  • Loss on ignition, 6% max
  • Retained, 45-µm sieve, 10% max
  • Specific Surface, BET, 15 m2/g min
minimum specification elements
Minimum Specification Elements
  • Required concrete performance
  • Test placement requirements
  • Type of finish desired
  • Protection requirements
  • Curing requirements
general rules for proportioning silica fume concrete
General Rules for Proportioning Silica-Fume Concrete
  • There is no empirical method
  • Local materials, local proportions
  • Follow the step-by-step procedure
  • Test, test, test
proportioning step 1 determine project requirements
Proportioning Step 1: Determine project requirements

Compressive strength

Chloride exposure

Freezing and thawing exposure

Chemical exposure

Abrasion resistance

Other requirements

proportioning step 2 coordinate with contractor
Proportioning Step 2: Coordinate with contractor

Special constructability requirements?

Maximum size aggregate

Placement method

Maximum slump -- Concrete will be cohesive and won’t segregate -- increase slump by about 2 in. (50 mm)

proportioning step 3 select starting mixture
Proportioning Step 3: Select starting mixture

Use SFA table to find a mixture with approximately your project requirements

proportioning step 4 determine volume of entrained air
Proportioning Step 4: Determine volume of entrained air

Air is absolutely required if silica-fume concrete will be exposed to freezing and thawing while saturated

Use an industry standard document (ACI 211.1, ACI 318, or ASTM C 94) for recommended air content

Air may be reduced 1% if compressive strength is over 5,000 psi (35 MPa)

proportioning step 5 add your local aggregates
Proportioning Step 5: Add your local aggregates

Calculate total aggregate volume to achieve desired yield

Use ratio of fine to coarse aggregate that works works your materials

proportioning step 6 prepare laboratory trial mixtures 1 of 2
Proportioning Step 6: Prepare laboratory trial mixtures, 1 of 2

Ensure that densified silica fume is adequately dispersed

Don’t worry about water slump -- there may not be any!

Batch at maximum allowed water content -- use WRA and HRWRA to develop workability

proportioning step 6 prepare laboratory trial mixtures 2 of 2
Proportioning Step 6: Prepare laboratory trial mixtures, 2 of 2
  • Does concrete meet fresh and hardened requirements?
  • Adjust mixture proportions as necessary
proportioning step 7 conduct full scale testing
Proportioning Step 7: Conduct full-scale testing

Use same plant and trucks, if possible

Batch enough concrete, at least 2 yd3 (1.5 m3) -- bad time to save $$$

Does concrete meet all requirements?

Adjust mixture as necessary

Work with the contractor

slide18
Low chloride permeability

Compressive strength of 5,000 psi (35 MPa) at 28 days

Reduced heat and shrinkage

Reduced rate of strength gain

Protection against freezing and thawing

Proportioning Example 1, Step 1: Project Requirements

proportioning example 1 step 2 contractor requirements
Proportioning Example 1, Step 2: Contractor Requirements
  • Use 1 in. (25 mm) maximum aggregate
  • 4 to 6 in. (100 to 150 mm) slump
  • Pump placement
proportioning example 1 step 3 starting mixture from sfa table
Proportioning Example 1, Step 3: Starting Mixture from SFA Table
  • Cement: 500 lb yd3 (300 kg/m3)
  • Fly ash: 135 lb/yd3 (80 kg/m3)
  • Silica fume: 40 lb/yd3 (25 kg/m3)
  • Maximum w/cm: 0.40
  • Entrained air: required
proportioning example 1 step 4 entrained air requirements
Proportioning Example 1, Step 4: Entrained Air Requirements
  • ACI 211.1 recommends 6.0% total air for severe exposure
  • Compressive strength > 5,000 psi (35 MPa) allows for reduction to 5.0%
proportioning example 1 step 5 add local aggregates 2 of 2
Proportioning Example 1, Step 5: Add Local Aggregates, (2 of 2)
  • Coarse aggregate density: 2.68
  • Fine aggregate density: 2.64
  • Fine aggregate: 40% of total aggregate volume
  • Aggregate vol = 27.00 - 9.38 = 17.62 ft3
  • Fine aggregate: 7.05 ft3, 1,160 lb/yd3
  • Coarse aggregate: 10.57 ft3, 1,770 lb/yd3
slide24

SI

Proportioning Example 1, Step 5: Add Local Aggregates, (1 of 2)

Total Paste Volume: 0.350 m3

proportioning example 1 step 5 add local aggregates 2 of 21

SI

Proportioning Example 1, Step 5: Add Local Aggregates, (2 of 2)
  • Coarse aggregate density: 2.68
  • Fine aggregate density: 2.64
  • Fine aggregate: 40% of total aggregate volume
  • Aggregate vol = 1.000 - 0.350 = 0.650 m3
  • Fine aggregate: 0.260 m3, 686 kg/m3
  • Coarse aggregate: 0.390 m3, 1045 kg/m3
proportioning example 1 step 6 prepare lab mixtures
Proportioning Example 1, Step 6: Prepare Lab Mixtures
  • You are now ready to go into a laboratory and begin making trial mixtures.
  • Control silica fume dispersion
  • Mix thoroughly
  • Conduct necessary testing on fresh and hardened concrete
slide27

Proportioning Example 1, Step 7: Prepare Lab Mixtures

  • Adjust from lab mixes as necessary
  • Use large enough batches
  • Work with contractor to conduct placing and finishing trials as required
slide28

Proportioning Example 2

High-Strength Columns

slide29
Design compressive strength of 14,000 psi (98 MPa) at 28 days

Proportion for 15,400 psi (108 MPa) in laboratory mixes

No exposure to freezing and thawing

Proportioning Example 2, Step 1: Project Requirements

proportioning example 2 step 2 contractor requirements
Proportioning Example 2, Step 2: Contractor Requirements
  • Use 1/2 in. (13 mm) maximum aggregate
  • 8 to 10 in. (200 to 250 mm) slump
  • Pump placement
proportioning example 2 step 3 starting mixture from sfa table
Proportioning Example 2, Step 3: Starting Mixture from SFA Table
  • Cement: 800 lb yd3 (475 kg/m3)
  • Fly ash: 175 lb/yd3 (104 kg/m3)
  • Silica fume: 125 lb/yd3 (74 kg/m3)
  • Maximum w/cm: 0.231
  • Entrained air: none
proportioning example 2 step 5 add local aggregates 2 of 2
Proportioning Example 2, Step 5: Add Local Aggregates, (2 of 2)
  • Coarse aggregate density: 2.68
  • Fine aggregate density: 2.60
  • Fine aggregate: 38% of total aggregate volume
  • Aggregate vol = 27.00 - 10.58 = 16.42 ft3
  • Fine aggregate: 6.24 ft3, 1,000 lb/yd3
  • Coarse aggregate: 10.18 ft3, 1,700 lb/yd3
slide35

SI

Proportioning Example 2, Step 5: Add Local Aggregates, (1 of 2)

Total Paste Volume: 0.393 m3

proportioning example 2 step 5 add local aggregates 2 of 21

SI

Proportioning Example 2, Step 5: Add Local Aggregates, (2 of 2)
  • Coarse aggregate density: 2.68
  • Fine aggregate density: 2.64
  • Fine aggregate: 38% of total aggregate volume
  • Aggregate vol = 1.000 - 0.393 = 0.607 m3
  • Fine aggregate: 0.231 m3, 600 kg/m3
  • Coarse aggregate: 0.376 m3, 1010 kg/m3
proportioning example 2 step 6 prepare lab mixtures
Proportioning Example 2, Step 6: Prepare Lab Mixtures
  • You are now ready to go into a laboratory and begin making trial mixtures.
  • Control silica fume dispersion
  • Mix thoroughly
  • Conduct necessary testing on fresh and hardened concrete
slide38

Proportioning Example 2, Step 7: Prepare Lab Mixtures

  • Adjust from lab mixes as necessary
  • Use large enough batches
  • Work with contractor to conduct placing trials as required
statistical approach to determining proportions
Statistical Approach to Determining Proportions

If you have a very complex project with a number of requirements, simply making trial batches may not be the most efficient approach. Help is available to optimize concrete performance and cost.

producing silica fume concrete1
Producing Silica-Fume Concrete
  • Measuring and batching
producing silica fume concrete2
Producing Silica-Fume Concrete
  • Measuring and batching
  • Adding HRWRA
producing silica fume concrete3
Producing Silica-Fume Concrete
  • Measuring and batching
  • Adding HRWRA
  • Mixing
slide55

Truck Mixer Rating Plate -- Don’t exceed rated mixing capacity when producing silica-fume concrete.

producing silica fume concrete4
Producing Silica-Fume Concrete
  • Measuring and batching
  • Adding HRWRA
  • Mixing
  • Controlling temperature
end of chapter 3
End of Chapter 3

Main

Outline