Chapter%203.%20Obtaining%20Silica-Fume%20Concrete

1
Chapter 3. Obtaining Silica-Fume Concrete

• Specifying Silica Fume and SFC
• Proportioning SFC
• Producing SFC

2
Specifying Silica Fumeand Silica-Fume Concrete
Chapter Outline
3
Specifying Silica Fume

• ASTM C 1240
• AASHTO M 307
• CSA A 23.5

4
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

5
Specifying Silica-Fume ConcreteFollow the
practices of your organization
6
Minimum Specification Elements

• Required concrete performance
• Test placement requirements
• Type of finish desired
• Protection requirements
• Curing requirements

7
Proportioning Silica-Fume Concrete
Chapter Outline
8
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

9
Proportioning Step 1 Determine project
requirements

• Compressive strength
• Chloride exposure
• Freezing and thawing exposure
• Chemical exposure
• Abrasion resistance
• Other requirements

10
Proportioning Step 2 Coordinate with contractor

• Special constructability requirements?
• Maximum size aggregate
• Placement method
• Maximum slump -- Concrete will be cohesive and
  wont segregate -- increase slump by about 2 in.
  (50 mm)

11
Proportioning Step 3 Select starting mixture

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

12
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)

13
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

14
Proportioning Step 6 Prepare laboratory trial
mixtures, 1 of 2

• Ensure that densified silica fume is adequately
  dispersed
• Dont worry about water slump -- there may not be
  any!
• Batch at maximum allowed water content -- use WRA
  and HRWRA to develop workability

15
Proportioning Step 6 Prepare laboratory trial
mixtures, 2 of 2

• Does concrete meet fresh and hardened
  requirements?
• Adjust mixture proportions as necessary

16
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

17
Proportioning Example 1 Parking Structure
18
Proportioning Example 1, Step 1 Project
Requirements

• 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

19
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

20
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

21
Proportioning Example 1, Step 4 Entrained Air
Requirements

• ACI 211.1 recommends 6.0 total air for severe
  exposure
• Compressive strength gt 5,000 psi (35 MPa) allows
  for reduction to 5.0

22
Proportioning Example 1, Step 5 Add Local
Aggregates, (1 of 2)
Total Paste Volume 9.38 ft3
23
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

24
Proportioning Example 1, Step 5 Add Local
Aggregates, (1 of 2)
Total Paste Volume 0.350 m3
25
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

26
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

27
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

28
Proportioning Example 2 High-Strength Columns
29
Proportioning Example 2, Step 1 Project
Requirements

• 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

30
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

31
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

32
Proportioning Example 2, Step 4 Entrained Air
Requirements

• Entrained air not required

33
Proportioning Example 2, Step 5 Add Local
Aggregates, (1 of 2)
Total Paste Volume 10.58 ft3
34
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

35
Proportioning Example 2, Step 5 Add Local
Aggregates, (1 of 2)
Total Paste Volume 0.393 m3
36
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

37
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

38
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

39
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.

40
Producing Silica-Fume Concrete
Chapter Outline
41
Producing Silica-Fume Concrete

• Measuring and batching

42
(No Transcript)
43
(No Transcript)
44
(No Transcript)
45
Tank for storage of slurried silica fume
46
(No Transcript)
47
(No Transcript)
48
Emptying bagged silica fume into truck mixer
49
Adding repulpable bags directly to truck mixer
50
Producing Silica-Fume Concrete

• Measuring and batching
• Adding HRWRA

51
(No Transcript)
52
(No Transcript)
53
(No Transcript)
54
Producing Silica-Fume Concrete

• Measuring and batching
• Adding HRWRA
• Mixing

55
Truck Mixer Rating Plate -- Dont exceed rated
mixing capacity when producing silica-fume
concrete.
56
(No Transcript)
57
Producing Silica-Fume Concrete

• Measuring and batching
• Adding HRWRA
• Mixing
• Controlling temperature

58
(No Transcript)
59
Liquid nitrogen being used to cool silica-fume
concrete
60
Producing Silica-Fume Concrete Follow
established and documented procedures
61
End of Chapter 3
Main Outline