7.1 Scope, Equipment, and When the Volumetric Method Fits

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

7.1 Scope, Equipment, and When the Volumetric Method Fits

Key Takeaways Explain This Topic AI

ASTM C173/C173M measures the air content of freshly mixed concrete by displacing air with water and reading the displaced volume directly on a calibrated neck.

C173 is the air test that works on ANY aggregate — normal-weight, lightweight, cellular, porous, and slag — because it requires no aggregate correction factor.

The pressure method (ASTM C231) is invalid for lightweight or highly porous aggregate, so C173 becomes the required method for those mixes.

A complete rollameter (volumetric air meter) set includes a calibrated bowl and graduated top section, a 5/8 in. tamping rod, a 1.25 ± 0.50 lb mallet, a strike-off bar, a funnel, water, and isopropyl alcohol.

Last updated: September 2026

What ASTM C173 Measures

ASTM C173/C173M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method, determines how much air — entrained plus entrapped — is present in a freshly mixed sample. The principle is mechanical, not pneumatic: a measured volume of concrete is mixed with water inside a sealed rollameter (volumetric air meter), and the apparatus is rolled and agitated until the air is physically washed out of the concrete and rises into a graduated neck . The drop in liquid level equals the volume of air, which is read directly as a percent of the concrete volume on the calibrated neck.

Because the air is separated physically rather than compressed under pressure, the result is independent of the aggregate's own air voids . This is the single most important fact about C173 on the exam: no aggregate correction factor is required . Air content is reported to the nearest 0.25 % .

When You Must Use C173 Instead of C231

The pressure method, ASTM C231 , relies on Boyle's Law — applying a known pressure and reading how much the air volume compresses. That logic only holds when the aggregate itself contains essentially no compressible air voids. With lightweight aggregate, highly porous or cellular aggregate, or air-cooled blast-furnace slag , the aggregate pores compress under pressure and corrupt the reading, so C231 is invalid for those mixes.

Mix Condition Use C231 (Pressure) Use C173 (Volumetric)
Normal-weight dense aggregate Yes (preferred, faster) Yes (also valid)
Lightweight aggregate No — invalid Yes — required
Highly porous / cellular aggregate No — invalid Yes — required
Air-cooled blast-furnace slag / highly porous aggregate No — not applicable Yes

C173 is slower and more physical, but it works on every aggregate, which is why it is the universal fallback.

The reason air content is worth all this effort is durability. Entrained air provides the microscopic pressure-relief chambers that let saturated concrete survive freeze-thaw cycling and deicer scaling . The required air content and acceptance tolerance depend on the project specification, exposure, mixture, and applicable standard; there is no single target for every concrete placement. Excess air can reduce strength, while insufficient entrained air can impair freeze-thaw resistance. Report the measured result and compare it with the specified limits using the project’s acceptance procedure. For lightweight or highly porous aggregate, use the appropriate volumetric method rather than applying a pressure-method aggregate correction.

The Rollameter Apparatus

The volumetric air meter comes in two mating parts that clamp together into a watertight assembly:

Measuring bowl (base): A rigid metal bowl of known, calibrated volume that holds the concrete sample. Bowl capacity is at least 0.075 ft³ (2 L).

Top section: A funnel-shaped upper unit with a clear, graduated neck marked in percent air. It seats on the bowl with a gasket and is secured by clamps to form a leak-proof seal. The neck is the scale you read.

Supporting equipment the candidate must be able to identify and check:

Item Specification / Purpose
Tamping rod 5/8 in. (16 mm) diameter, rounded tip, used to consolidate each layer
Mallet 1.25 ± 0.50 lb (0.57 ± 0.23 kg) rubber/rawhide, to tap the bowl
Strike-off bar Flat steel or plastic bar to level concrete flush with the rim
Funnel + measuring cup To add water and isopropyl alcohol in measured amounts
Syringe / bulb To make small water additions and read the meniscus precisely
Equipment Condition Checks Before Testing

Exam scenarios often hinge on spotting a defective meter before the test starts. Confirm the gasket is intact and the clamps seat squarely — a leak invalidates the test. Verify the neck scale is legible and undamaged , the bowl rim is clean and not dented (a dent changes the calibrated volume), and that you have isopropyl alcohol on hand. The meter must have been calibrated for its specific bowl-and-top combination; the two halves are a matched set and are not interchangeable between meters. Recognizing these conditions — not memorizing a serial number — is what the Grade I exam tests.

C173 in the Field-Test Family

Grade I candidates run seven core ASTM field tests, and C173 has to be placed correctly among them. Sampling follows C172 ; consistency is C143 (slump) ; density and yield are C138 (unit weight) ; specimens are molded under C31 ; temperature is C1064 . Air content is measured by either C231 (pressure) or C173 (volumetric) — they are alternatives, not partners, and you choose based on the aggregate. A useful mental model: C231 is the everyday meter for normal-weight concrete, and C173 is the rollameter you reach for when the aggregate would lie to a pressure gauge.

Two facts anchor every C173 exam question. First, the result is a direct volumetric reading — air is read off the neck as a percent, not back-calculated from a pressure dial. Second, no aggregate correction factor exists for this method, so any answer choice that adds one is wrong. Keep those two ideas front of mind and most scope-level questions answer themselves.