Concrete yield is defined as the volume of freshly mixed concrete from a known quantity of ingredients. Ready mixed concrete is sold on the basis of the volume of fresh, unhardened concrete-in cubic yards (yd3) or cubic meters (m3) as discharged from a truck mixer.
The basis for calculating the volume is described in the ASTM C94 – Specification for Ready Mixed Concrete. The volume of freshly mixed and unhardened concrete in a given batch is determined by dividing the total weight of the materials by the average unit weight or density of the concrete determined in accordance with ASTM C138. Three unit weight tests must be made, each from a different truck.
ASTM C94 notes: It should be understood that the volume of hardened concrete may be, or appears to be, less than expected due to waste and spillage, over-excavation, spreading forms, some loss of entrained air, or settlement of wet mixtures, none of which are the responsibility of the producer.
Further, the volume of hardened concrete in place may be about 2 percent less than its volume in a freshly mixed state due to reduction in air content, settlement and bleeding, decrease in volume of cement and water, and drying shrinkage.
Most yield complaints concern a perceived or real deficiency of concrete volume. Concerns about yield should be evaluated using unit weight measurements to calculate the yield. Apparent under-yield occurs when insufficient concrete is ordered to fill the forms and to account for contingencies discussed below. If unit weight and yield calculations indicate an actual under-yield, it should be corrected.
Apparent concrete shortages are sometimes caused for the following reasons:
An over-yield can be an indication of a problem if the excess concrete is caused by too much air or aggregate, or if the forms have not been properly filled.
Differences in batched weights of ingredients and air content in concrete, within the permitted tolerances, can result in discrepancies in yield.
To prevent or minimize concrete yield problems:
