I have a weird concrete problem that I have never seen before; any advice or thoughts would be appreciated. It is a prestressed, large (2'-6"deep, 6'-0"wide, 20' long) concrete beam, simple span (so PS strands towards bottom), longitudinal mild reinforcing towards top, #5 full circumference stirrups, 7 ksi concrete, 1.5" min. cover (which was special inspected, so not likely to be shortchanged on cover). The contractor used steam curing. When the steaming tarps were removed, it was noted that a "waffle" pattern had developed in the top face of the beam, with low points occurring directly over reinforcing (especially the stirrups). Any ideas why? Or similar problems experienced? My first intuition was that they should not have used steam curing for mass concrete, but I do not have any theory handy that would explain such a phenomenom. Thank you...
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