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Concrete Batch Yield

Also known as yield of concrete · batch yield · volume of concrete produced · unit weight yield · concrete yield check · did the batch yield · short load concrete · relative yield · how much concrete did I actually get

Y=∑mρfreshY = \dfrac{\sum m}{\rho_{fresh}}

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See also
Gravimetric Air Content — The same density measurement, read the other way — the air is what makes a batch yield more than its solids.Absolute Volume of a Mix Component — The paper prediction this measurement checks: solid volumes plus air should equal the yield.Concrete Volume with Waste Allowance — The ordering side — how much to buy once yield and waste are both accounted for.Concrete Bags from Volume and Bag Yield — The same question for a job small enough to be done out of bags.

Learning zone

Yield is the check that the paper exercise worked. Weigh everything that went into the mixer, measure the density of what came out, divide, and you have the volume the batch actually produced. It is the one measurement that closes the loop on a mix design, and because it depends on nothing but a scale and a container of known volume, it is available on any site with a technician on it.

The measurement is the difficult half, not the arithmetic. The fresh density comes from a rigid measure of accurately known volume, filled and consolidated the way the standard specifies and struck off flat, weighed full and weighed empty. The volume of the measure itself is determined by weighing it full of water — which is why the density of water turns up in concrete testing far more often than a newcomer expects. Get the consolidation wrong and everything downstream is wrong: under-consolidate and the density reads low, the yield reads high, and a batch that is actually short looks generous.

What a yield number is for. Divide the measured yield by the volume the batch was designed to make and you have the relative yield. Above 1.00 the batch made more than it should; below 1.00 it made less, and somebody at the far end of a pour is going to be standing at an open form waiting for concrete that is not coming. A relative yield that runs consistently low has a cause and the cause is usually findable — air content below target, aggregate specific gravities on the mix design that no longer match the stockpile, scales out of calibration, or a moisture correction that is quietly batching stone where it thinks it is batching water. A yield running high is nearly always air: either more entrained air than intended, or entrapped air the vibrator never removed.

Yield is also the honest way to settle an argument about a short load, and the argument comes up on nearly every large pour. Concrete is sold by volume and made by mass, and the conversion between them is exactly this equation. A load that is genuinely short and a form that was bigger than the drawing said produce identical symptoms, and only a yield measurement plus a re-measured form tells them apart.

One thing yield cannot do is tell you about strength. A batch can yield perfectly and be weak, and a batch can yield short and be strong. They are separate questions with separate causes, and the reason to run the yield check anyway is that it is fast, it is cheap, and it detects a batching error days before a cylinder break could say anything at all.

Concrete Batch Yield
Y=∑mρfreshY = \dfrac{\sum m}{\rho_{fresh}}
ΣmYρ
Where
  • YY= Yield (volume produced) (m³)
  • ∑m\sum m= Total batch mass (kg)
  • ρfresh\rho_{fresh}= Fresh concrete density (kg/m³)
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