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I assume your mix design is 90 MPa concrete (@28 days). I don't know what the concrete object that has the cracking is. For that strength gain, there is likely a very small portion of fly-ash, so there is likely a lot of cement powder. What is the size of your aggregate; you could have a lot of shrinkage. 1.5% air is not unusual. You can have that amount with normal mixing. This is normally less than 1%. In our environs exterior concrete usually has about 6% or 7% for frost resistance. A lot of our concrete has fly-ash for economy. I've not used self compacting concrete, but have often spec'd superplasticisers. I always spec mechanical vibration, even for piles and caissons. Dik