20 Air Content: Volumetric Method (ASTM C173) Practice Questions & Answers

Every Air Content: Volumetric Method (ASTM C173) practice question from the ACI Concrete Field Testing Technician Grade I Practice Test, with the correct answer and a short explanation.

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1. Why does the volumetric method not require an aggregate correction factor of the kind used with the pressure method?
- A.The isopropyl alcohol dissolves the air held in aggregate pores, so that air is removed before reading
- B.The bowl is calibrated with the project's own aggregate, so aggregate air is built into the neck scale
- C.Agitation in water frees the air in the paste and mortar but not the air sealed inside aggregate particles✓ Answer
- D.The calibrated cups of water added at the end make up automatically for the air held in the aggregate
The test works by washing the concrete out of its own volume with water; only the air in the paste and mortar is displaced and rises into the neck, while air inside aggregate particles is not released. Because aggregate air never enters the reading, nothing has to be subtracted for it, unlike the pressure method, which compresses that air too.
Ref QB-KFJQNXSource: ASTM C173/C173M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method — Significance and use: measures air in the mortar fraction, unaffected by air in porous aggregate; no aggregate correction factorReport a problem with this question
2. In the volumetric method, what physically produces the change in liquid level seen in the graduated neck?
- A.Water takes the place of the air as the concrete is agitated, and the freed air rises so the level drops✓ Answer
- B.Air compressed by shaking the sealed meter pushes the water up the neck in proportion to its volume
- C.The concrete settles under its own weight during rolling, and the settlement is read on the neck scale
- D.The alcohol reacts with the cement paste, and the gas it gives off is read directly on the neck scale
Agitating the sealed meter breaks the concrete apart in water, so water fills the spaces the air bubbles occupied. The freed air collects at the top, and the liquid in the neck falls by an amount equal to the air volume, which the scale reports directly as a percentage of the bowl volume. No compression or chemical reaction is involved.
Ref QB-3YCJ3XSource: ASTM C173/C173M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method — Summary of test method: displacement of air by water read directly on the graduated neckReport a problem with this question
3. A volumetric test on fresh concrete gives 6.0% air. How should that result be understood with respect to the hardened concrete?
- A.It equals the air in the hardened concrete, because entrained bubbles stay fixed once the mix is placed
- B.It describes the fresh concrete only, and air in the hardened concrete may be higher or lower than 6.0%✓ Answer
- C.It must first be adjusted with an aggregate correction factor before it can describe hardened concrete
- D.It always runs about 1% above hardened air, because bubbles escape during consolidation and finishing
The standard notes that air content of hardened concrete may be higher or lower than that measured on the fresh sample, because handling, placing, consolidation and finishing in the structure differ from the test. The result is a fresh-concrete value; there is no fixed offset and no aggregate correction in this method.
Ref QB-MFW2UYSource: ASTM C173/C173M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method — Significance and use: air content of hardened concrete may differ from the fresh-concrete resultReport a problem with this question
4. What is the purpose of adding isopropyl alcohol during the initial filling of the volumetric air meter?
- A.To dissolve air trapped in aggregate pores so that it is counted as part of the air content
- B.To lower the freezing point of the water so the test can be run in cold-weather conditions
- C.To dispel the foam that would otherwise hide the true liquid level in the graduated neck✓ Answer
- D.To speed setting of the cement paste so the concrete breaks free of the bowl more easily
Agitating air-entrained concrete in water generates foam, and foam floating in the neck masks the meniscus so the true level cannot be read. Isopropyl alcohol breaks down that foam. It has nothing to do with freezing, setting or aggregate air.
Ref QB-4YQV8YSource: ASTM C173/C173M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method — Apparatus and procedure: isopropyl alcohol used to dispel foam in the neckReport a problem with this question
5. During a volumetric test on a heavily air-entrained mix, the liquid level drops below the lowest graduation on the neck. What should the technician do?
- A.Add more isopropyl alcohol through the neck until the level returns to the scale, then record that volume
- B.Discard the test and repeat it with a smaller sample so the displaced air will fit within the scale
- C.Add calibrated cups of water until the level is on the scale, record the count, and add it to the result✓ Answer
- D.Report the air content as the top value of the scale, noting that the true value lies beyond the scale
When air exceeds the range of the neck scale, the technician adds water with the calibrated cup until the level is back within the graduations. Each cup equals a known fraction of the bowl volume, so the number of cups is recorded and added to the meter reading. Alcohol may not be added after the initial filling, and the bowl must always be filled completely.
Ref QB-NF9DZZSource: ASTM C173/C173M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method — Procedure for readings beyond the graduated range: calibrated cup additions recorded and added in the calculationReport a problem with this question
6. A volumetric air meter's bowl was dropped on the job site and now looks slightly dented. What is the correct response before it is used again?
- A.Deduct a fixed amount from each reading, since a dented bowl always holds less concrete than its rating
- B.Recheck only the neck graduations, since the bowl volume has no influence on the percentage readings
- C.Keep using it until the next scheduled check, since only the periodic calibration makes a meter valid
- D.Recalibrate the bowl volume and related items, since suspected deformation calls for a new calibration✓ Answer
The neck graduations are percentages of the bowl volume, so a deformed bowl makes every reading wrong. The standard requires calibration of the bowl, the neck scale and the calibrated cup at first use, periodically, and whenever damage or deformation is suspected; a guessed deduction is not a substitute.
Ref QB-5Y38EZSource: ASTM C173/C173M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method — Calibration: bowl volume, neck scale and calibrated cup recalibrated whenever damage or deformation is suspectedReport a problem with this question
7. Assume the method requires that, when concrete contains coarse aggregate that would be retained on a 1-1/2 in. (37.5 mm) sieve, enough material is wet-sieved over a 1 in. (25 mm) sieve for the test. A mix has 2 in. (50 mm) maximum size aggregate. How should the test portion be prepared?
- A.Test the full sample and apply an oversize correction factor to the final meter reading
- B.Wet-sieve the sample over the 1 in. sieve and test the material that passes in the bowl✓ Answer
- C.Wet-sieve the sample over the 1-1/2 in. sieve, because that size triggers the requirement
- D.Test the full sample and pick out by hand any particles that touch the rim of the bowl
Under the rule given in the stem, 2 in. aggregate would be retained on the 1-1/2 in. sieve, so the trigger is met and the material must be wet-sieved over the 1 in. sieve; only the passing concrete goes into the bowl. The trigger size is not the sieve used, and the method has no oversize correction factor.
Ref QB-PFMQ63Source: ASTM C173/C173M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method — Sampling: wet-sieving of concrete containing aggregate larger than the permitted maximum sizeReport a problem with this question
8. After rodding each layer in the measuring bowl, the technician taps the outside of the bowl with the mallet. What is the purpose of this step?
- A.To work additional entrained air into the paste so the reading represents the full mix
- B.To level the surface of the layer so that the next layer can be placed at an even depth
- C.To confirm the bowl is seated firmly on its base before the next layer is placed in it
- D.To close the holes left by the rod and release large air bubbles trapped in the layer✓ Answer
Tapping the sides after rodding closes the voids left by the tamping rod and lets large entrapped bubbles escape, so the bowl holds consolidated concrete whose air reflects the mix rather than consolidation defects. It does not add air or level the surface; strike-off does the leveling at the end.
Ref QB-6YEJK2Source: ASTM C173/C173M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method — Procedure, placement and consolidation: tapping the bowl after rodding each layerReport a problem with this question
9. After striking off the concrete level with the rim, why must the technician wipe the bowl's flange clean before clamping on the top section?
- A.So the top section seats tightly and the assembled meter stays watertight during agitation✓ Answer
- B.So the technician can measure the overfill above the rim before rodding the final layer
- C.So no paste reacts with the alcohol and gives off gas that would raise the final reading
- D.So the wiped paste can be weighed and subtracted from the mass of concrete in the bowl
Grit or paste on the flange keeps the gasket from sealing, and any leak during inversion or rolling lets liquid escape and invalidates the test. The bowl is not weighed in this method, overfill is handled before strike-off, and paste does not react with alcohol.
Ref QB-BTCZYFSource: ASTM C173/C173M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method — Procedure: strike-off, cleaning the flange and attaching the top section watertightReport a problem with this question
10. With the top section clamped on and the funnel inserted, which sequence of additions is correct?
- A.The selected alcohol first, then water to the zero mark, then more alcohol later if any foam forms
- B.Water first, then the selected alcohol, then more water until it shows in the neck and is set to zero✓ Answer
- C.Water to the zero mark first, then the selected alcohol, then removal of the excess with the syringe
- D.Alcohol and water premixed in a single pour, then alcohol alone to bring the level to the zero mark
The funnel first receives water, then the measured quantity of alcohol (which is recorded), then more water until liquid appears in the neck; the funnel is removed and the syringe brings the bottom of the meniscus to zero. Alcohol is introduced only during this initial filling, never later to fight foam.
Ref QB-UAJ6KGSource: ASTM C173/C173M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method — Procedure: initial addition of water and alcohol, adjusting to the zero markReport a problem with this question
11. Why must the technician record the volume of isopropyl alcohol added during the initial filling?
- A.The alcohol volume sets how many calibrated cups of water may be added later in the test
- B.The same alcohol volume must be reused on the next test regardless of foam conditions
- C.The alcohol volume must be added to the final reading to account for its displacement
- D.Larger alcohol volumes call for a correction that is subtracted from the final reading✓ Answer
Alcohol mixed with water occupies slightly less volume than the two separately, so large amounts of alcohol make the reading too high. The standard provides a correction based on the alcohol volume, which is subtracted from the final reading, and the alcohol volume is also reported. That is impossible unless the amount was recorded.
Ref QB-CTQB6HSource: ASTM C173/C173M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method — Calculation: alcohol correction factor subtracted from the final meter reading; alcohol volume recorded and reportedReport a problem with this question
12. Assume the method allows no more than 2 full percent divisions of foam on the liquid in the neck. After agitation, foam covers 3 divisions. What should the technician do?
- A.Add more alcohol through the neck right away to break the foam, then read the cleared level
- B.Read the level at the top of the foam layer, since the foam is part of the displaced air volume
- C.Wait for the foam to collapse on its own, then take the reading and report the result as usual
- D.Discard the test and run a new one on a fresh sample, using more alcohol in the initial filling✓ Answer
Foam beyond the allowed limit means too little alcohol was used, and the remedy is a new test on a fresh sample with more alcohol in the initial filling. Adding alcohol after the initial filling to dispel foam is not permitted, because it changes the liquid volume after the zero was set.
Ref QB-VAWGRHSource: ASTM C173/C173M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method — Procedure, readings: excessive foam requires a new test with more alcohol; adding alcohol later is not permittedReport a problem with this question
13. What condition must be met before the technician moves from inverting and shaking the meter to rolling it on its side?
- A.The liquid level in the neck has gone back to zero so the meter is balanced for rolling
- B.The concrete has broken free of the bowl so the whole mass can move about in the water✓ Answer
- C.The meter has been warmed by handling so the water matches the concrete's temperature
- D.The foam in the neck has vanished entirely so the rolling starts from a clear liquid level
Inverting and shaking continues for a minimum time and until the concrete has broken free of the bowl; the technician can hear and feel the mass shift. Only when the concrete is loose can the water reach all of it and displace its air during rolling. The level is expected to drop, not return to zero.
Ref QB-DT3PBJSource: ASTM C173/C173M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method — Procedure: inverting and shaking until the concrete breaks free, then rollingReport a problem with this question
14. While rolling the tilted meter back and forth with quick starts and stops, the technician listens to the contents. What is the technician listening for?
- A.A hiss at the cap, a sign that pressure is building and the meter needs venting right away
- B.A ringing tone from the bowl, a sign the concrete has set hard against the bowl's walls
- C.Liquid sloshing in the neck, a sign the level is already stable and can be read at once
- D.Aggregate sliding inside, a sign the concrete is loose and its trapped air can still be freed✓ Answer
Rolling with quick starts and stops keeps the concrete and aggregate moving so remaining air is released. Hearing the aggregate slide confirms the mass is loose and being worked; if it is not heard, the concrete may still be packed in the bowl. The meter is not pressurized, and stability is judged visually after the meter is set upright.
Ref QB-WA9UWJSource: ASTM C173/C173M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method — Procedure: rolling the meter and listening for aggregate slidingReport a problem with this question
15. During rolling, the technician notices liquid escaping at the joint between the bowl and the top section. What should be done?
- A.Finish the test and report the result with a note that a minor leak was observed
- B.Tighten the clamps, top up with water to the zero mark, and continue rolling to the end
- C.Treat the test as invalid and repeat it on a new sample with the meter properly sealed✓ Answer
- D.Finish the test and subtract an estimate of the leaked volume from the final reading
The reading depends on a closed, constant volume of liquid; any escaping liquid lowers the level and reads as extra air. The standard treats a leak during inversion or rolling as invalidating the test, so it must be repeated on a new sample. Topping up or estimating cannot restore the lost volume reliably.
Ref QB-ETEZGKSource: ASTM C173/C173M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method — Procedure: a leak during inversion or rolling invalidates the testReport a problem with this question
16. Assume consecutive readings must agree within 0.25% air. The initial reading is 5.25%. After another minute of rolling, the second reading is 5.75%. What should the technician do next?
- A.Average the two readings to 5.50% and report that value as the final meter reading
- B.Use 5.75% as the new initial reading, roll again, and compare a third reading against it✓ Answer
- C.Accept 5.75% as the final reading, because the later reading always reflects more freed air
- D.Discard the test at once and repeat it with more alcohol on a new sample of concrete
The two readings differ by 0.50%, more than the 0.25% allowed, so more air may still be trapped. The second reading becomes the new initial reading and the meter is rolled again; if the third reading agrees with it within the limit, that reading is final. Only if it still does not agree is the test discarded and repeated with more alcohol. Averaging is never permitted.
Ref QB-FTSBPMSource: ASTM C173/C173M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method — Procedure, readings: initial and final readings must agree within the stated limit; otherwise roll againReport a problem with this question
17. Along with the air content itself, what else should the report of a volumetric air test include?
- A.The volume of alcohol used and the number of calibrated cups of water that were added✓ Answer
- B.The slump of the batch tested and the temperature of the water poured into the meter
- C.The aggregate correction factor applied and the gauge pressure reached during the test
- D.The mass of concrete held in the bowl and the density calculated from that same mass
Both items enter the calculation: the alcohol volume determines the correction subtracted from the reading, and each calibrated cup adds to it. Reporting them lets anyone check how the air content was obtained. Aggregate correction factors and gauge pressure belong to the pressure method, and density and slump are reported under their own methods.
Ref QB-YAYG9NSource: ASTM C173/C173M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method — Report: air content with the amount of alcohol used and the number of calibrated cups of water addedReport a problem with this question
18. When taking a reading of the liquid level in the graduated neck, where should the technician read it?
- A.At the bottom of the meniscus, where the curved liquid surface sits at its lowest point✓ Answer
- B.At the top of any foam layer, where the bubbles meet the air space at the top of the neck
- C.At the upper edge of the meniscus, where the liquid clings to the inside of the neck wall
- D.At the midpoint between the top of the foam and the bottom of the curved liquid surface
The scale was set to zero at the bottom of the meniscus during the initial filling, so every later reading must be taken at the same point to measure the true change in level. Foam is not liquid and must not be read; excessive foam calls for a new test with more alcohol.
Ref QB-MZCGJTSource: ASTM C173/C173M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method — Procedure, readings: read the bottom of the meniscusReport a problem with this question
19. After the final reading, the technician removes the top section, drains the liquid and dumps the bowl. A tightly packed, undisturbed slug of concrete is found at the bottom. What does this mean?
- A.The test is valid, because some concrete always sticks to the bowl and that part holds no air
- B.The test is invalid because not all of the air was displaced, so it is repeated on a new sample✓ Answer
- C.The test is invalid only when the slug fills more than about a quarter of the bowl's volume
- D.The test is valid, but the air content is raised by one calibrated cup to make up for the slug
Air in concrete that never broke free was not displaced by water, so the reading understates the air content. The standard requires examining the bowl contents and, if any undisturbed, tightly packed concrete remains, declaring the test invalid and repeating it on a new sample. Loose sand settled in the bowl does not by itself invalidate the test.
Ref QB-4H7BYSSource: ASTM C173/C173M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method — Procedure: examination of the bowl contents after disassembly; undisturbed concrete invalidates the testReport a problem with this question
20. A volumetric test gives a final meter reading of 4.75%. The technician added 2 calibrated cups of water to bring the level onto the scale, and the alcohol used calls for a correction of 0.50%. Each cup represents 1.00% air. What air content should be calculated?
- A.6.25%✓ Answer
- B.2.25%
- C.7.25%
- D.4.25%
Air content equals the final reading minus the alcohol correction plus the calibrated cups: 4.75 - 0.50 + 2.00 = 6.25%. The correction is subtracted because the alcohol-water mixture shrinks and inflates the reading; the cups are added because they represent air the scale could not show. Adding the correction gives 7.25%, subtracting the cups gives 2.25%, and ignoring the cups gives 4.25%.
Ref QB-NZQTQUSource: ASTM C173/C173M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method — Calculation: air content = final meter reading - alcohol correction + number of calibrated cupsReport a problem with this question

1. Why does the volumetric method not require an aggregate correction factor of the kind used with the pressure method?

2. In the volumetric method, what physically produces the change in liquid level seen in the graduated neck?

3. A volumetric test on fresh concrete gives 6.0% air. How should that result be understood with respect to the hardened concrete?

4. What is the purpose of adding isopropyl alcohol during the initial filling of the volumetric air meter?

5. During a volumetric test on a heavily air-entrained mix, the liquid level drops below the lowest graduation on the neck. What should the technician do?

6. A volumetric air meter's bowl was dropped on the job site and now looks slightly dented. What is the correct response before it is used again?

7. Assume the method requires that, when concrete contains coarse aggregate that would be retained on a 1-1/2 in. (37.5 mm) sieve, enough material is wet-sieved over a 1 in. (25 mm) sieve for the test. A mix has 2 in. (50 mm) maximum size aggregate. How should the test portion be prepared?

8. After rodding each layer in the measuring bowl, the technician taps the outside of the bowl with the mallet. What is the purpose of this step?

9. After striking off the concrete level with the rim, why must the technician wipe the bowl's flange clean before clamping on the top section?

10. With the top section clamped on and the funnel inserted, which sequence of additions is correct?

11. Why must the technician record the volume of isopropyl alcohol added during the initial filling?

12. Assume the method allows no more than 2 full percent divisions of foam on the liquid in the neck. After agitation, foam covers 3 divisions. What should the technician do?

13. What condition must be met before the technician moves from inverting and shaking the meter to rolling it on its side?

14. While rolling the tilted meter back and forth with quick starts and stops, the technician listens to the contents. What is the technician listening for?

15. During rolling, the technician notices liquid escaping at the joint between the bowl and the top section. What should be done?

16. Assume consecutive readings must agree within 0.25% air. The initial reading is 5.25%. After another minute of rolling, the second reading is 5.75%. What should the technician do next?

17. Along with the air content itself, what else should the report of a volumetric air test include?

18. When taking a reading of the liquid level in the graduated neck, where should the technician read it?

19. After the final reading, the technician removes the top section, drains the liquid and dumps the bowl. A tightly packed, undisturbed slug of concrete is found at the bottom. What does this mean?

20. A volumetric test gives a final meter reading of 4.75%. The technician added 2 calibrated cups of water to bring the level onto the scale, and the alcohol used calls for a correction of 0.50%. Each cup represents 1.00% air. What air content should be calculated?

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