Silica Fume
Silica Fume
(OP)
Anyone have good or bad experiences with using silica fume?
Dik
Dik
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RE: Silica Fume
RE: Silica Fume
I'm thinking of including it in my General Notes... adding a max of 5%. I used it about 20 years back for some high strength concrete columns and it worked well. Just looking for some feedback...
Dik
RE: Silica Fume
You will have more reliable reduction in your water requirements by using a high range water-reducing admix.
High early strength is also a function of the rest of the mix design, and increasing strength excessively can result in increased cracking/crack width of flexural members (the stronger concrete may crack farther apart, which often results in wider cracks).
RE: Silica Fume
Dik
RE: Silica Fume
Silica fume is advantageous if you want to make your concrete more impermeable. The particle size is much smaller than a concrete particle, so it fills the voids nicely.
RE: Silica Fume
Dik
RE: Silica Fume
"1.1-Historical background
Although high-strength concrete is often considered a
relatively new material, its development has been gradual
over many years. As the development has continued, the
definition of high-strength concrete has changed. In the
1950s, concrete with a compressive strength of 5000 psi
(34 MPa) was considered high strength. In the 1960s,
concrete with 6000 and 7500 psi (41 and 52 MPa) compressive
strengths were used commercially. In the early
1970s, 9000 psi (62 MPa) concrete was being produced.
More recently, compressive strengths approaching 20,000
psi (138 MPa) have been used in cast-in-place buildings.
For many years, concrete with compressive strength in
excess of 6000 psi (41 MPa) was available at only a few
locations. However, in recent years, the applications of
high-strength concrete have increased, and high-strength
concrete has now been used in many parts of the world.
The growth has been possible as a result of recent developments in material technology and a demand for
higher-strength concrete. The construction of Chicago's
Water Tower Place and 311 South Wacker Drive concrete
buildings would not have been possible without the
development of high-strength concrete. The use of concrete
superstructures in long span cable-stayed bridges
such as East Huntington, W.V., bridge over the Ohio
River would not have taken place without the availability
of high-strength concrete."
They imply that 20 ksi is not uncommon for buildings. I used half that strength in the late 70's and that was very high strength at the time... and I understand that there is research/work being done with ultra high strength concretes.
Dik
RE: Silica Fume
The US's current tallest structure, Chicago's Trump Tower used silica fume in the 12 ksi and above mixes. The specification was 56 day strength (some elements were reported as 16 ksi / 90 day in magazine articles.)
This is a good example of where properties other than strength (low shrink/creep, ease of consolidation, etc.) were important early and strength development could lag.
RE: Silica Fume
This is also my understanding and what I've mainly used it for in the past.
RE: Silica Fume
Brad