How can you tell if you're getting the amount of concrete you're paying for?
The real indicator is the yield, or the actual volume produced based on the actual batch quantities of cement, water and aggregates. The unit weight test can be used to determine the yield of a sample of the ready mixed concrete as delivered. It's a simple calculation that requires the unit weight of all materials batched. The total weight information may be shown on the delivery ticket or it can be provided by the producer. Many concrete producers actually over yield by about 1/2 percent to make sure they aren't short-changing their customers. But other producers may not even realize that a mix designed for one cubic yard might only produce 26.5 cubic feet or 98 percent of what they designed.
Question and answer courtesy of Portland Cement Association (PCA). More information is available at: http://www.cement.org/tech/cct_faqs.asp.