Study guide
7.4 Inversion, Shaking, Rolling, and Air Release
ACI Concrete Field Testing Technician Grade I Study Guide Exam
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1 Orientation: Certification Requirements, Written Exam, Performance Exam, and Study Sources
1.1 Credential Purpose and Official Definition 1.2 Eligibility and the Two-Part Certification Path 1.3 Written Exam Format and Dual Passing Rule 1.4 Performance Exam Format and Grading 1.5 Current Study Sources and CP-1 41st Edition 1.6 Validity, Recertification, and Myth Control
2 JTA, Performance Checklists, Common Fail Points, and Field Mindset
2.1 JTA as the Exam Blueprint 2.2 Written Knowledge Versus Performance Skill 2.3 Performance Checklists and the Six Demonstrations 2.4 Timing, Sequence, and Verbal Description Discipline 2.5 Common Fail Points and Result Recording 2.6 Field Mindset, Exam Habits, and Second Trials
3 ASTM C172: Sampling Fresh Concrete and Field Sample Control
3.1 Representative Sampling Purpose and Exam Role 3.2 Sampling Locations and Middle-Discharge Control 3.3 Composite Sample Timing, Remixing, and Protection 3.4 Sample Size, Large Aggregate, and Wet Sieving 3.5 Sequence With Slump, Temperature, Air, Density, and Specimens 3.6 Performance Exam Verbal Description and Field Habits
4 ASTM C1064 Temperature and ASTM C143 Slump
4.1 ASTM C1064 Purpose, Equipment, and Timing 4.2 Sensor Placement, Stabilization, and Reporting 4.3 Temperature Field Errors and Performance Habits 4.4 ASTM C143 Scope, Equipment, and Setup 4.5 Filling, Rodding, Lifting, and Measuring Slump 4.6 Invalid Slump Results, Reporting, and Integrated Habits
5 ASTM C138: Density, Unit Weight, Yield, and Gravimetric Air
5.1 Purpose, Equipment, and the Calibrated Measure 5.2 Sampling, Filling, and Consolidation Choice 5.3 Strike-Off, Cleaning, Mass, and Density 5.4 Yield, Relative Yield, and Batch Comparison 5.5 Gravimetric Air and Theoretical Density 5.6 Reporting, Validity, and Calculation Traps
6 ASTM C231: Pressure Air Method, Type B Meter, and Aggregate Correction
6.1 Scope, Principle, and When Pressure Air Fits 6.2 Type B Meter Equipment, Calibration, and Setup 6.3 Sampling, Bowl Filling, Consolidation, and Strike-Off 6.4 Type B Sequence: Water, Petcocks, Pressure, and Reading 6.5 Aggregate Correction Factor and Final Air Content 6.6 Reporting, Validity, and Invalid-Result Traps
7 ASTM C173: Volumetric Air Method, Rollameter, Alcohol Correction, and Validity
7.1 Scope, Equipment, and When the Volumetric Method Fits 7.2 Sample, Bowl Filling, Consolidation, and Strike-Off 7.3 Water, Alcohol, Initial Liquid Level, and Sealing 7.4 Inversion, Shaking, Rolling, and Air Release 7.5 Reading Agreement, Out-of-Range Steps, and Invalid Results 7.6 Alcohol Correction, Calculation, Reporting, and Performance Habits
8 ASTM C31: Making and Curing Cylinders and Beams, Initial Curing, and Transport
8.1 Purpose, Sample, Equipment, and Specimen Plan 8.2 Cylinder Molding, Consolidation, Finishing, and Identification 8.3 Beam Molding, Flexural Specimens, and Finishing 8.4 Initial Curing, Protection, Temperature, and Moisture 8.5 Standard Curing, Field Curing, Final Curing, and Interpretation 8.6 Transport, Lab Handoff, Reporting, and Common Failures
9 Integrated Field Workflow: Test Order, Documentation, and Quality Control
9.1 Field Sample to Report Workflow 9.2 Test Order and Parallel Timing 9.3 Documentation and Report Accuracy 9.4 Invalid Results and Retest Decisions 9.5 QA/QC Communication and Acceptance Context 9.6 Contamination, Delays, and Handoff Control
10 Written Exam Strategy: Numerical Values, Calculations, and Category Scoring
10.1 One-Hour Written Exam Pacing 10.2 Category Scoring and the No-Compensation Rule 10.3 High-Yield Numerical Values and Units 10.4 Density, Yield, and Gravimetric Air Calculations 10.5 Air Content Corrections and Validity Checks 10.6 Method-by-Method Practice Plan
11 Performance Exam Strategy: Equipment Setup, Examiner Communication, and Remediation
11.1 Performance Exam Map and Mindset 11.2 Equipment Setup, Station Control, and Safety 11.3 Examiner Communication and Speaking the Work 11.4 One-Step Errors, Timing, and Method Control 11.5 C172 Verbal Description Under Pressure 11.6 Remediation, Retest Planning, and Field Confidence
12 Final Review: Recertification, Career Paths, and Next ACI Credentials
12.1 Two-to-Six Week Final Review Plan 12.2 Final Week and Test-Day Checklist 12.3 CP-1, JTA, and Source Control 12.4 Recertification, Five-Year Cycle, and Re-Exam Requirement 12.5 Career Paths After Field Testing Grade I 12.6 Next ACI Credentials and Growth Map
7.4 Inversion, Shaking, Rolling, and Air Release
Key Takeaways Explain This Topic AI
The sealed meter is inverted and shaken — using roughly 5-second inversion intervals for at least 45 seconds total — to loosen concrete from the bowl base.
It is then rolled on its side at about a 45° tilt for roughly 1 minute, rocking back and forth a quarter to half turn to wash air out of the concrete.
Rolling and agitation are repeated as needed until the liquid level stops changing — the air is fully released.
If material leaks or the cap loosens during rolling, the test is invalid and must be restarted.
Last updated: June 2026
Why C173 Is Called the Rollameter Test
After the meter is sealed, filled with water, and dosed with alcohol, the agitation sequence physically separates air from the concrete. This is the defining step of the method — the apparatus is literally rolled, which is why the meter is nicknamed the rollameter . The goal is to free every air bubble from the concrete mass and let it rise into the neck, while simultaneously breaking the concrete apart so no air stays trapped in clumps.
The Inversion and Shaking Sequence
The operator first inverts and shakes the sealed meter to loosen the concrete that has settled against the bowl base. A representative sequence:
- Action Detail
- Invert Turn the meter upside down, then upright, in ~5-second intervals
- Shake Agitate while inverted to dislodge concrete from the base
- Total Continue inverting/shaking at least 45 seconds total
Inversion alone does not finish the job — it loosens the mass so the subsequent rolling can wash air out. The candidate must keep a firm grip and keep the cap secured; a meter that comes apart mid-inversion spills concrete and invalidates the test.
The full agitation sequence in order:
Invert and shake in ~5-second cycles, at least 45 seconds total, to free concrete from the base.
Roll on the side at ~45°, rocking a quarter to half turn, for about 1 minute.
Stand upright and let settle (~2 minutes) so foam clears.
Read the neck, then repeat rolling and reading until the level stops changing.
Rolling at 45 Degrees
With the concrete loosened, the meter is laid on its side and rolled at about a 45° tilt for roughly 1 minute , rocking it back and forth a quarter to a half turn vigorously. Rolling tumbles the concrete through the water so trapped air is scrubbed loose and floats to the neck. The operator then stands the meter upright and lets the foam settle (about 2 minutes) before reading.
The sequence is iterative, not one-and-done :
Roll for ~1 minute, let settle, read the level.
Roll again and read again. If the level dropped, air is still being released.
Repeat rolling until the liquid level stops changing — i.e., two successive readings agree (within 0.25 %). Only then is all the air out.
A reading taken after a single roll, before the concrete has fully released its air, is not a valid final result; it will read low because air remains trapped.
Controlled Agitation and Common Faults
Movement must be purposeful and controlled . A short fault list the exam likes:
Cap loosens / leaks during rolling → liquid lost → invalid; restart with fresh sample.
Rolling too gently → air not fully released → false low reading; keep rolling until stable.
Concrete sticks in a wad → some air stays trapped; inversion/shaking must break the mass first.
Foam not settled before reading → unreadable meniscus; add a little alcohol next cycle and let it settle.
The takeaway: inversion frees the concrete from the base, rolling washes the air out, and the level keeps dropping until — and only until — the concrete has given up all its air.
Timing discipline matters because air release is time-dependent. If the liquid level fails to stabilize within about 6 minutes of total settling, the test is discarded — the concrete is either stiffening or foam is not clearing, and continued rolling will not produce a trustworthy number. Conversely, a technician who reads after one quick roll and reports it has almost certainly under-measured the air, because trapped pockets had no chance to wash free. The rule of thumb: roll, settle, read, repeat — and trust only the reading that two cycles confirm.
What the Liquid Level Is Telling You
It helps to picture the physics. Inside the sealed meter sit three things: the concrete solids, the water, and the air that was in the concrete. Before rolling, that air is still locked in bubbles inside the paste, so the liquid sits at zero. As rolling tumbles the mix, each freed bubble rises and occupies space in the neck that liquid used to fill , so the liquid level drops . The total drop, in percent, is the air content. When no more bubbles are being freed, the level stops dropping — which is exactly why the agreement of two successive readings signals completion.
A short troubleshooting list ties the mechanics to field symptoms:
Level not dropping at all → seal failed or no air to release; check the seal and that admixture was actually used.
Level still dropping after several rolls → keep rolling; air is not fully out.
Level dropped below the neck → off scale; add measured water back (covered in 7.5).
Foam capping the column → add a little alcohol, settle longer.
Reading the level correctly therefore is not a clerical step — it is the entire measurement, and every part of the inversion-and-rolling routine exists to make that one number trustworthy.