huangyhg

continous concrete placement
what is the maximun time that we can have between concrete trucks if we want have a continous concrete placement? i was pouring concrete a week ago and i had a gap between two of the truck of about 45 min. is there anywhere a definition of continous concrete placement?
it depends on several variables....the weather conditions at the time, the mix design, the construction techniques...
if the weather was warm and dry, you might have a cold joint in the concrete. 45 minutes isn't all that long, but depending on the water-cement ratio and the weather conditions, it could happen.
for efficiency of placement, you always want to have trucks staging and ready to discharge, but the queue should not be so long as to have the concrete sitting in the trucks for more than about an hour from time of batching to time of placement. astm c94 sets a 90 minute time limit, but as a practical matter, that can be too long.
concrete pour started at around 8:00 am, temp that morning was around the 70's and water-cement ratio was 0.45. we were pouring a concrete pier for job under the army corps of engineers job and the were trying to say that we had a cold joint, however, when we stripped the forms we could not see any cold joints.
get the mill certificate on the cement that was used in the mix. check the time of initial set. if your time delay was under that time, you should be ok.
when the new concrete came, was the old concrete still in a plastic state? could it be vibrated? if yes to both of those, then you likely do not have a cold joint.
the form face can be misleading for cold joints, though with a 0.45 w-c ratio, you probably don't have much excess bleed water or runny paste.
if they have rejected the concrete pier, then do ultrasonic testing to check the continuity and integrity of the concrete before you accept their rejection.

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