🏗️ Air content of fresh concrete — pressure methods
In short
Two pressure methods (the water column method and the pressure gauge method) for determining the air content of compacted fresh concrete, based on Boyle-Mariotte's law. The test is performed according to PN-EN 12350-7:2019-08; Range of application: Normal-weight or relatively dense aggregate, Dmax ≤ 63 mm, slump ≥ 10 mm. The procedure comprises 7 steps; it is used for: Control of the air entrainment of fresh concrete for freeze-resistant concretes (the exposure classes XF), Testing of the mix for pavements of cement concrete (design of the composition, approval of the mix proportions, trial batch, control of the works), Factory production control of ready-mixed concrete.
At a glance
- Standard: PN-EN 12350-7:2019-08
- Category: Construction
- Procedure steps: 7
- Range of application: Normal-weight or relatively dense aggregate, Dmax ≤ 63 mm, slump ≥ 10 mm
- Measuring container (water column method): Capacity ≥ 5 l, ratio of diameter to height 0.75–1.25, working pressure about 0.1 MPa
- Scale of the tube (water column method): From 0 % to at least 8 % (preferably 10 %), graduations every 0.1 %
Overview
The standard PN-EN 12350-7 describes two methods of determining the air content of compacted fresh concrete made with normal-weight or relatively dense aggregate with a declared maximum aggregate size Dmax of not more than 63 mm. Both use apparatus working on the principle of Boyle-Mariotte's law: the water column method (apparatus with a water column) and the pressure gauge method (apparatus with a pressure gauge, commonly called an air meter). The test is not suitable for concretes with a slump below 10 mm according to PN-EN 12350-2.
Neither method is used for concretes with lightweight aggregate, with air-cooled blast-furnace slag or with aggregate of high porosity, because the aggregate correction factor would be too large in relation to the entrained air content. The determination of the aggregate correction factor for both methods is set out in the normative Annexes A and B, and the calibration of both types of apparatus in Annexes C and D. The apparatus has to be calibrated at the time of the test; after it has been moved to an altitude differing by more than 200 m it requires recalibration.
The air content is measured above all for air-entrained concretes (the exposure classes XF). The interlaboratory comparison cited in the standard showed no significant difference between the two methods, but the compaction of an air-entrained mix with an internal vibrator has to be carried out with care, so that the entrained air is not lost. In pavements of cement concrete GDDKiA requires the air content to be determined according to PN-EN 12350-7 at the stage of design, of the approval of the mix proportions, of the trial batch and of the control of the works.
Method principle
The water column method: above a specimen of compacted concrete of known volume, in an airtight container, water is introduced to a prescribed height and a prescribed air pressure is applied above it. The reduction of the volume of air in the specimen is measured by the fall of the water level in a tube graduated in percentage of air. The pressure gauge method: a known volume of air at a known pressure is combined in an airtight container with the unknown volume of air in the specimen; the dial of the pressure gauge is graduated in percentage of air for the resulting pressure. The air content of the concrete Ac = A1 − G, where A1 is the reading for the concrete and G the aggregate correction factor determined for the container filled only with aggregate and water.
Applications
- Control of the air entrainment of fresh concrete for freeze-resistant concretes (the exposure classes XF)
- Testing of the mix for pavements of cement concrete (design of the composition, approval of the mix proportions, trial batch, control of the works)
- Factory production control of ready-mixed concrete
- Proficiency testing of construction laboratories (the pressure gauge method of clause 6 of the standard)
- Studies of the effect of air-entraining admixtures and of cements on the air content
Key parameters
| Parameter | Value |
|---|---|
| Range of application | Normal-weight or relatively dense aggregate, Dmax ≤ 63 mm, slump ≥ 10 mm |
| Measuring container (water column method) | Capacity ≥ 5 l, ratio of diameter to height 0.75–1.25, working pressure about 0.1 MPa |
| Scale of the tube (water column method) | From 0 % to at least 8 % (preferably 10 %), graduations every 0.1 % |
| Pressure gauge (water column method) | Graduations every 0.005 MPa, full range 0.2 MPa |
| Pressure expansion constant e | ≤ 0.1 % of air content |
| Calibration | The apparatus calibrated at the time of the test; recalibration after a change of altitude of more than 200 m |
Standard
- Standard number
- PN-EN 12350-7:2019-08
- Title (PL)
- Badania mieszanki betonowej — Część 7: Zawartość powietrza — Metody ciśnieniowe
- Title (EN)
- Testing fresh concrete — Part 7: Air content — Pressure methods
Step-by-step procedure
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Sampling
Take the sample of the mix in accordance with PN-EN 12350-1. If the concrete is sampled and tested at different places, the way of filling and compacting in the measuring container must be the same whichever method is used.
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Filling of the container and compaction
Fill the measuring container and compact the concrete with an internal vibrator, on a vibrating table or by hand with a rod or a tamper. With air-entrained concrete use the internal vibrator with care, so that the entrained air is not lost.
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Closing of the apparatus
Clean the flange of the container and fix the lid so as to obtain an airtight joint with no air trapped between the flanges.
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Water column method
Introduce water above the concrete to the prescribed height (through the dispersing plate or the spray tube, so as not to disturb the concrete), apply the prescribed pressure P with the pump and read the level h1; after the pressure has been released read h2. The difference h1 − h2 = A1.
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Pressure gauge method
Combine a known volume of air at a known pressure with the air contained in the specimen and read the air content from the dial of the pressure gauge, graduated in per cent.
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Aggregate correction factor
Determine the correction factor G for the container filled only with aggregate and water in accordance with Annex A (water column) or B (pressure gauge).
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Calculation and test report
The air content of the concrete Ac = A1 − G. Give the method, the result and the identification of the sample in the test report; in proficiency testing the results are recorded immediately after the test.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Water column apparatus | A cylindrical container of hard metal of ≥ 5 l, a conical lid with a tube graduated in % of air, air-release and drain valves, a pressure gauge, a dispersing plate or spray tube, a pump | — |
| Pressure gauge apparatus (air meter) | An apparatus with a pressure chamber and a dial graduated in % of air | — |
| Compaction equipment | An internal vibrator, a vibrating table, a rod or a tamper for compaction | — |
| Scoop, trowel or float, container or tray for remixing the sample | The common apparatus according to PN-EN 12350-1 | — |
| Calibration cylinder | For the calibration of the apparatus according to Annexes C and D | — |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Water | — | For filling the space above the concrete in the water column method and for determining the aggregate correction factor |
Health and safety (OHS)
- The apparatus works at a pressure of about 0.1 MPa — use only sound, calibrated containers and valves and do not exceed the working pressure
- Fresh concrete is alkaline — gloves and eye protection
- Operate the internal vibrator in accordance with the manufacturer's instructions; with air-entrained concrete limit the time of vibration
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN 12350-7:2019-08 — “Testing fresh concrete — Part 7: Air content — Pressure methods”.
How does this method work?
The water column method: above a specimen of compacted concrete of known volume, in an airtight container, water is introduced to a prescribed height and a prescribed air pressure is applied above it. The reduction of the volume of air in the specimen is measured by the fall of the water level in a tube graduated in percentage of air.
What is the measuring range and accuracy?
Range of application: Normal-weight or relatively dense aggregate, Dmax ≤ 63 mm, slump ≥ 10 mm; Measuring container (water column method): Capacity ≥ 5 l, ratio of diameter to height 0.75–1.25, working pressure about 0.1 MPa; Scale of the tube (water column method): From 0 % to at least 8 % (preferably 10 %), graduations every 0.1 %; Pressure gauge (water column method): Graduations every 0.005 MPa, full range 0.2 MPa.
How long does the test take?
The procedure comprises 7 steps. The standard does not give a duration for every stage — the laboratory's own procedure decides.
What equipment is required?
Water column apparatus, Pressure gauge apparatus (air meter), Compaction equipment, Scoop, trowel or float, container or tray for remixing the sample, Calibration cylinder.
Where is this test used?
Control of the air entrainment of fresh concrete for freeze-resistant concretes (the exposure classes XF); Testing of the mix for pavements of cement concrete (design of the composition, approval of the mix proportions, trial batch, control of the works); Factory production control of ready-mixed concrete; Proficiency testing of construction laboratories (the pressure gauge method of clause 6 of the standard); Studies of the effect of air-entraining admixtures and of cements on the air content.
What safety precautions apply?
The apparatus works at a pressure of about 0.1 MPa — use only sound, calibrated containers and valves and do not exceed the working pressure; Fresh concrete is alkaline — gloves and eye protection; Operate the internal vibrator in accordance with the manufacturer's instructions; with air-entrained concrete limit the time of vibration.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN 12350-7.