Yield is a term used to describe the actual volume of concrete produced when a truck is batched at a ready-mix plant. Occasionally, some contractors or producers might worry that the amount of concrete batched and delivered to a jobsite might be greater or less than the amount actually ordered. In this case, a yield calculation, based on unit weight, can be performed to discover whether shortages, or overages, are occurring.
How to Calculate Concrete Weight and Yield
When customers estimate the amount of concrete needed for a job, they calculate the volume required. Orders for concrete are then placed based on the volume in cubic yards or cubic meters. Ready-mix producers, however, must batch concrete by weight. Each material is weighed on a scale before it is loaded into either a central mixing drum or a truck where it is mixed before transport to the jobsite. Many producers retain a copy of these weights (called batch tickets) for each truck that leaves their yard.
Unit Weight and Yield
The unit weight calculation is:
Example: A concrete producer knows the weight of the materials that she has batched into a truck for a standard 4,000 psi air-entrained mix design. How can she find the volume of concrete that these materials will yield?
As we know, volume and weight relationships are based on unit weight calculations. Therefore, the first step is to perform a unit weight test on the jobsite according to the procedures outlined in ASTM C 138. A container of known volume is filled with concrete that has been properly sampled from the truck according to ASTM C 172. The proper procedures for filling and consolidating this container are followed and the container is then weighed. The weight of the container is subtracted from the total weight to give the weight of the concrete sample. The volume of the container is known to be 0.25 cubic feet. If the weight of the sample was found to be 36.25 pounds, the unit weight is then:
Converting to cubic yards:
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