Longer Term Strength Gain Using Fly Ash (Class F)

[BigH]

G'day all. I have had experience with using fly ash - up to 50% as replacement to OPC. Usually found that the strength gain from 28 days to 90 days was about 30% (50% fly ash) and a little less when using 30%. I am running into a situation now where the strength gains (albeit only two tests) show 35 abd 70% increases (and in less than 90 days).

Does anyone have typical strength gains in their experience that they might share? Anything over 30% I find to be doubtful. Would appreciate any experience you might have.

 

[Ron]

Big H... my experience is similar to yours. A 70% gain is unusual. Probably need to check the mix with petrography to see if it got overdosed with flyash. If you don't have petrography capability nearby, slice a section and hand polish as best you can with wet sandpaper up to 600 grit. With a small amount of magnification you should be able to see the flyash particles. Compare the two.

If you don't have the time or the inclination to do that, send it to me and I'll take a look!