Why does Concrete gain air and slump on the way to a jobsite?
Answer:
the time to the site and weather conditions should be factored by the supplier for the mix
air entrainment is not bad
the slump gain seems to mean they havent added enough water for the travel conditions, perhaps the combination of admixtures needs to be looked at...
talk with the supplier, just because a certain mix is spec'd, doesnt mean its the right one for your conditions.
did you get a revolution count on the drum?
they may have had the drum revolving too fast for the travel conditions also
whatever you do, dont add water at the site
if it is too firm when it gets to you, just reject the load
also make sure the person doing the tests is doing them correctly
I had this problem on a job site and it can several things. First, if inside the mixer is too hot, water will evaporate too quickly and come to the surface of the wet mixture. At that point bubbles will start to form and get trapped in the concrete. So that means either more water needs to be added or somehow cool down the mixture.
Another problem I have heard is that sometiems it is mixing wait too quickly and the batch becomes air entranced. Its sort of like a blender, faster the blender goes more likely everything is gonna be thrown around and higher than chances it will become "fluffier".
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