Fly Ash in Theoretical Concrete Mix Design
Fly Ash in Theoretical Concrete Mix Design
(OP)
I generally apply the ACI volumetric mix design approach when calculating theoretical porportions. Fly ash, being a pozzolan, is commonly substituted for a portion of Portland cement in the mix. Accepting that the fly ash composition meets all ACI/ASTM/CSA criteria, can the fly ash be substituted at a 1:1 ratio with Portland cement (up to a limit of course) or should I be using a reduced equivalency ratio of say 1.0 lb fly ash : 0.75 lb Portland cement.
Thank you.
Thank you.





RE: Fly Ash in Theoretical Concrete Mix Design
I believe it's conservative, but fly ash is pretty cheap.
RE: Fly Ash in Theoretical Concrete Mix Design
RE: Fly Ash in Theoretical Concrete Mix Design
The only sure way of working up a concrete value is do some testing and establish a set of book ends of ash variability.
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RE: Fly Ash in Theoretical Concrete Mix Design
FA does lower heat of hydration--making a more durable concrete--but it also reduces water demand, increases workability and provides sacrificial silica for ASR.
Richard
RE: Fly Ash in Theoretical Concrete Mix Design
RE: Fly Ash in Theoretical Concrete Mix Design
Portland Cement Type 1 311kg/m3 (525 lb/yd3)
Fly Ash, Class F: 31kg/m3 (53 lb/yd3)
silica flume (dry): 16kg/m3 (27)
Ground granulated blast furnace slag: 47kg/m3 (79)
fine agg 676 (1140)
coarse agg 1068 (1800)
water 150.8 (254)
water Reducer Type A: 1.6litre/m3 (41 oz/yd3)
HRWR Type F: 2.1 litre/m3 (55oz/yd3)
AE - enough to get 7% air
Peformance - 28d min = 41.4MPa (6000psi)
28d max = 65.5MPa (9500 psi)
For a double deck road (Wacker Drive in Chicago)
RE: Fly Ash in Theoretical Concrete Mix Design
RE: Fly Ash in Theoretical Concrete Mix Design
RE: Fly Ash in Theoretical Concrete Mix Design
RE: Fly Ash in Theoretical Concrete Mix Design
Type F fly ash is low in free calcium (alkalinity) and must depend solely on the cement hydration to hydrate.
Type C fly ash is often replaced 1:1 or 1.1:1 with cement by weight. Up to 25% replacement is allowed.
Type F fly ash is often replaced 1.2:1 with cement by weight. Up to 25% replacement is allowed.
specific gravity of cement is 3.15, of fly ash is about 2.2 to 2.5. Keep this in mind when proportioning mixes.
In the last 5 years concrete with up to 60 and 70% fly ash has been successfully used.