Most concrete strengths are designed stronger than working strength, this allows for just such an occasion. First, the engineer who designed the structure should do a recalculation to determine the actual strength needed for the structure. If the 28 day strengths still fall short it may be...
Use the slump cone in the normal position and do not tamp. Simply fill and record the average diameter of the spread. I believe you should have specs on this but you should be reading somewhere around 26-30 inches.
shm I believe when testing this type of concrete they use a method whereupon you use a slump cone, only instead of measuring the slump you would measure the diameter of the spread. This would be for a self compacting type of mix.
I am a Q.C. Lab manager for a precast concrete company. Needless to say we have our own in-house batch plant. The percentage of moisture in the fine aggregate is critical to preparing a proper batch of concrete per mix design. We have a moisture meter installed in our F.A. bin near the jog...