Slump and Air Content Test Report Generator

Heading to the field? Install this site from your browser menu and this tool works with no signal. See how

How to use this tool

Set the specification bands first. Anything you leave blank is still recorded on the report but not enforced, which is what you want when the specification is silent on ambient temperature or does not name a slump range.

Then add a row per sample. Slump, meter reading and concrete temperature are the three most specifications ask for. The aggregate correction factor column is the one to get right, because a pressure meter reading is not an air content until that factor comes off it.

The last three columns are optional. Fill in the measure volume and the air free density from the mix design at the top, then the empty and full masses of your unit weight measure per sample, and the tool works out density and a second air content by a completely different route.

What the tool is calculating

Corrected air content is the meter reading minus the aggregate correction factor. Density is the net mass of concrete in the measure divided by the measure volume. Gravimetric air content is the difference between the air free density from your mix design and the density you actually measured, as a percentage of the air free density.

Every band check is inclusive, so a value sitting exactly on a limit passes. A sample fails if any enforced check fails, and the row tells you which one.

Why the aggregate correction factor is not optional

A pressure air meter does not measure air. It measures how much the sample compresses under pressure, and it assumes everything that compresses is entrapped or entrained air. That assumption is not quite true, because the aggregate itself has pores, and those pores compress too.

The aggregate correction factor is how much of the meter reading came from the stone rather than from air. It is determined once for the aggregate in use, and on typical material it lands somewhere between about 0.1 and 1.0 percent. On a porous or lightweight aggregate it can be considerably more.

That range is exactly the width of a specification band. A load reading 5.2 percent on the meter against a five to eight percent requirement looks like it passes. Apply a correction factor of 0.4 and the actual air content is 4.8 percent, which fails. The tool demonstrates that on the worked example below, because it is the single most common way an air entrained mix gets accepted when it should not have been.

What makes this worth catching is that air content failures are invisible later. A low slump gets noticed on site. A low strength shows up in a cylinder break. Low air shows up in about fifteen winters, as scaling and surface loss on the one bridge deck nobody understands, long after everybody involved has moved on.

Two routes to the same number

If you are taking unit weight measurements anyway, and on most structural work you are, you get air content a second way for free. It is a genuinely independent measurement: the pressure meter works by compressing the sample, the gravimetric method works by weighing it against what the mix should weigh with no air in it at all.

When they agree, you have real confidence in the number. When they disagree by more than about a point, one of the two is wrong, and the useful thing is that the likely causes are different for each. A meter reading too high usually means a leaking seal or a bad calibration. A gravimetric figure too high usually means the measure was not rodded properly and there are voids in it that are not air entrainment at all. The tool flags the disagreement rather than picking a winner, because which one is wrong is a judgement you make standing there.

A worked check you can repeat on paper

Press Load example set. It uses a 7 litre measure, an air free density of 2450 kg per cubic metre from the mix design, and bands of 60 to 100 mm slump, 5 to 8 percent air and 10 to 30 degrees.

Sample 1 reads 6.8 percent on the meter with a correction factor of 0.4, so the reported air content is 6.4 percent, comfortably inside the band. The measure weighs 3.2 kg empty and 19.2 kg full, so 16.0 kg of concrete occupies 7 litres, giving 2285.7 kg per cubic metre. Against an air free density of 2450 that is a gravimetric air content of 6.7 percent. The two methods sit 0.3 apart, well within the one point tolerance, so the number is trustworthy and the sample passes on every check.

Sample 2 fails on slump at 110 against a maximum of 100. Sample 3 is the instructive one: the meter reads 4.2, the correction takes it to 3.8, and that is below the five percent minimum. Across the three the mean slump is 86.7 mm, mean air 5.3 percent and mean temperature 22 degrees.

Every figure above was checked against an independent implementation before publishing, including the inclusive band behaviour at the exact limits and the case where the correction factor alone decides pass or fail.

Mistakes that catch people out

Reporting the meter reading as the air content. The correction factor is a required step, not a refinement. If nobody on the job knows what it is for the aggregate in use, that is the thing to sort out before the next pour.

Testing from the first concrete out of the chute. The sample should come from the middle of the load, not the leading edge, because the first material out is not representative of what is going into the forms.

Letting the sample sit before testing. Slump falls with time and air can migrate. A slump measured twenty minutes after sampling is a measurement of the twenty minutes, not of the concrete.

Treating a disagreement between methods as a rounding problem. A gap of two or three points between the pressure meter and the unit weight is not scatter. It means an apparatus problem, and the report is worth very little until you know which apparatus.

Recording concrete temperature but not ambient. On a hot or cold day the difference between the two is what explains a result later. It is one extra column and it costs nothing.

Related Calculators and Reference

• Slump Test method reference, for how the slump values on this report are actually measured.
• Concrete Pour Record and Delivery Ticket Log, which ties each of these samples back to the truck it came from and the elapsed time on that load.
• Concrete Cylinder Break Report Generator, for the strength results from the cylinders cast alongside these tests.
• Concrete Yield reference, for the relationship between density, batch mass and the volume you actually receive.
• Unit Weight of Concrete, for typical densities to sanity check the measured figure against.
• Daily Work Report Generator, to record the testing alongside the crew and quantities for the day.
• ASTM International, publisher of C143 for slump, C231 for air by the pressure method and C138 for unit weight.