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.
Freezing and thawing exposure
Special constructability requirements?
Maximum size aggregate
Maximum slump -- Concrete will be cohesive and won’t segregate -- increase slump by about 2 in. (50 mm)
Use SFA table to find a mixture with approximately your project requirements
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)
Calculate total aggregate volume to achieve desired yield
Use ratio of fine to coarse aggregate that works works your materials
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
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
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
Total Paste Volume: 9.38 ft3
Proportioning Example 1, Step 5: Add Local Aggregates, (1 of 2)
Total Paste Volume: 0.350 m3
Proportion for 15,400 psi (108 MPa) in laboratory mixes
No exposure to freezing and thawing
Proportioning Example 2, Step 1: Project Requirements
Total Paste Volume: 10.58 ft3
Proportioning Example 2, Step 5: Add Local Aggregates, (1 of 2)
Total Paste Volume: 0.393 m3
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.
Truck Mixer Rating Plate -- Don’t exceed rated mixing capacity when producing silica-fume concrete.