02-23-2008, 05:11 PM
First of all concrete isn’t weighed like a dump truck picking up aggregate. The loading of the mixer is fully computerized at Yamada. Therefore, cement, sand, aggregate and water are mixed automatically for what ever mix design you request.
I always and 10% to my calculations for slabs, just to take in account for the uneven base material.
Now if you order 10 CY and they sent you 8 CY I could see that you might have a problem.
Considering the calculations could be in error (but Mark knows his stuff) there is another factor that many contractors don’t take in to consideration. That is the subgrade material and how compact it is? Was the native material under the base material compacted? The most important process you can under take is compacting the base material with at least 12% water added to it. Using the right equipment to compress the base material. Then have it TESTED for compressive strength because the weight of the concrete (150lbs/cf) will put pressure on the subgrade causing it to compress and this will add to a larger area then calculated. All the quarries have the proctor numbers needed to do on site testing. It only takes a ¼-1/2 inch in come areas of the slab to cause a major overrun.
These are some of the rules when building roads, ya' just might want to use them in the biggest investment of your life.
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