Date: January 1, 2010

News - Avoiding Discrepancies in Yield

Apparent concrete shortages are sometimes caused by the following:
  • Miscalculation of form volume or slab thickness by even a fraction of an inch, making the assumed dimensions smaller than the actual volume.
  • Deflection or distortion of the forms resulting from pressure exerted by the concrete.
  • Irregular subgrade, placement over granular fill, and settlement of subgrade prior to placement.  
On the other hand, an over-yield may indicate a problem if the excess concrete is caused by too much air or aggregate in the concrete, or if the forms have not been filled properly.
How to prevent yield discrepancies:
  • Measure formwork accurately.  
  • Near the end of large pours, carefully measure the remaining volume so that the order for the last 2 or 3 trucks can be adjusted to provide the required quantity of concrete. This can prevent waiting for an extra ½ cubic yard, after the plant has closed or the mixers have been scheduled for other jobs.  
  • When placing your order, plan for 4 to 10 percent over plan dimensions for waste, over-excavation, and other causes.  
  • Repetitive operations and slip form operations permit more accurate estimates of the amount of concrete that will be needed, while sporadic operations involving a combination of concrete uses such as slabs, footings, walls, and incidental fill around pipes, etc., will require a bigger allowance for contingencies.  
  • Brace forms to minimize distortion or deflection.

Other news articles from January 2010