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# Concrete Batch Problem from Construction Depth Ref. Manual

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When I calculated the total weight of water that should be added I subtracted the fines free moisture from 250lbs and added the absorption from the coarse aggregate. The solution subtracted both the free moisture and the absorption from the water needed. Can anyone shed some light on this?

Thanks!

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When I calculated the total weight of water that should be added I subtracted the fines free moisture from 250lbs and added the absorption from the coarse aggregate. The solution subtracted both the free moisture and the absorption from the water needed. Can anyone shed some light on this?

Thanks!

HP Junkee,

Looking at the question, we assume the fine and coarse aggregates already absorbed their respective water amounts prior to mixing. (A way of imagining this is the aggregate was stored outside, was rained on, and/or processed recently through a wash plant, etc.) The problem also states the maximum water content is 250 lb/yds3. That includes the absorbed water. Therefore we calculate what to add above the amount of water already absorbed. But total we can have no more than 250 lb/yds3. Make sense?

-Jason

Edited by Jayman_10x