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i'm using the equation E= 33 * Wc^1.5 * fc^0.5 Which i don't know if it applies to fc>6000 psi

I performed some MOE tests on 4"X8" cylinders of high strength concrete (12,000 psi). When i calculate MOE theoretically i get approx. 6,000,000 psi, but the actual test value is approx. 12,000,000 psi. Could this be correct?? I'm following ASTM C469 step by step.

2 sets, each set had 8 cylinder. the difference was in the 7-day results. & now the 28-day results today were basicly the same.

Ron, the comparisson was cylinders to cylinders. I was suprised to see 1000 psi difference between 2 sets of cylinders taken from the same wheelbarrow.End treatment the same, size of sample the same and age @ test the same.The only difference was tank vs moist room.

I have read in the silica fume's mfg. data sheet that Silica fumes react with free lime to form calcium silicate hydrates, which is responsible for the strength of concrete. Could this be an explanation to why i'm getting higher compressive strength reults on cylinders cured in tanks (which...