Study guide
7.5 Reading Agreement, Out-of-Range Steps, and Invalid Results
ACI Concrete Field Testing Technician Grade I Study Guide Exam
Track your progress as you read
Finished sections get a check mark.
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
7.5 Reading Agreement, Out-of-Range Steps, and Invalid Results
Key Takeaways Explain This Topic AI
A valid C173 result requires two successive readings that agree within 0.25%; if they differ more, roll a third time for 1 minute and re-read.
If the liquid level drops below the bottom of the scale, add a measured amount of water and add that water back to the reading to stay on scale.
If the level fails to stabilize within about 6 minutes, or readings keep disagreeing after a third roll, discard the test and restart with more alcohol.
Excess foam, leakage, an unreadable meniscus, lost material, or concrete left stuck in the bowl all invalidate the result.
Last updated: June 2026
Reading Agreement: The 0.25 % Rule
A single rolling cycle rarely releases all the air, so C173 builds in a stability check . After the first roll and settle, the level is read; the meter is rolled again, settled, and re-read. The two readings must agree within 0.25 % . If they do, the test is essentially complete; the second reading governs. If they differ by more than 0.25 % , air is still coming out, so a third 1-minute roll is performed and a third reading taken.
- Comparison Outcome
- 2nd reading within 0.25 % of 1st Stable — accept the result
- 2nd differs > 0.25 % from 1st Roll a 3rd time, re-read
- 3rd differs > 0.25 % from 2nd Discard test; restart with more alcohol
- Level not stable within ~6 min Discard test
All readings and the reported air content are taken to the nearest 0.25 % . The exam often gives two numbers and asks whether they "agree" — apply the 0.25 % window.
Work an example. First reading 5.50 %, second 5.75 % → they differ by exactly 0.25 %, which is within the window, so the result is stable and 5.75 % governs. Change the second to 6.25 % → a 0.75 % difference, so a third roll is required; if the third reading lands at 6.25 % (within 0.25 % of the second), it is accepted. If the third still drifts more than 0.25 %, the test is discarded and rerun with more alcohol. This iterative agreement check, not the completion of any single roll, is what makes a C173 result final.
Off-Scale (Out-of-Range) Readings
If the air content is high, the liquid level can drop below the bottom of the graduated neck , leaving no meniscus to read. The procedure is not to estimate beyond the scale. , full units of the scale) to bring the meniscus back onto the scale , then add that known amount of water back to the meter reading to get the true air content. For example, if you add water equal to 5 % of scale to return the meniscus to a readable point, the actual air is the on-scale reading plus 5 %. This keeps high-air mixes measurable without guessing past the end of the neck.
The water is added in known scale units so the bookkeeping is exact, and the addition is recorded so the final calculation can add it back. Lightweight mixes, which often carry high design air, are the usual reason a level runs off scale, which is one more way C173 and lightweight concrete go together.
Conditions That Invalidate the Test
The Grade I exam expects the candidate to recite the validity failures while performing the test. A test is invalid when:
Persistent foam obscures the neck and will not clear even with added alcohol — restart with more alcohol from the beginning.
Leakage from the seal or cap during inversion/rolling — any lost liquid voids the result.
The liquid level never stabilizes (no agreement within 0.25 %) after the third roll, or fails to stabilize within about 6 minutes .
Material was lost at any point — spilled concrete or water changes the closed-system balance.
Concrete remains stuck/caked in the bowl when the meter is opened at the end; trapped concrete means trapped air that never reached the neck, so the reading is low and the test is invalid.
The final-bowl examination is a real exam scenario: even a textbook-looking reading is invalid if, on opening the meter, a wad of concrete is found clinging to the base.
A Decision Flow for the Reading Phase
Candidates do best when they carry a single decision flow for what to do with each reading:
Foam in the neck? If it will not clear with alcohol, the test is invalid — restart with more alcohol.
Level off the bottom of the scale? Add measured water back, record it, and add it to the result.
Two readings within 0.25 %? Yes → accept. No → roll a third minute and re-read.
Third reading still off by >0.25 %, or no stability within ~6 min? Discard and rerun.
Open the bowl: any concrete caked on the base? If yes → invalid, regardless of how clean the number looked.
Why These Checks Exist
Each validity rule maps to a physical failure that would otherwise hide in a plausible-looking number. Leakage removes liquid the calculation assumes is present. 25 % precision is meaningless. Instability past 6 minutes usually means the concrete is stiffening or air is still escaping — the moving target cannot be reported. Concrete stuck in the bowl means some air never reached the neck, so the reading understates the true value. The Grade I exam rewards the technician who can name the failure behind each rule, not merely memorize the rule, because the field throws combinations these checks are designed to catch.
Reading-agreement quick recap
Successive readings must agree within 0.25 % air before the result is accepted.
If they do not agree, roll the meter again ; discard the test if it will not stabilize within about 6 minutes.
Foam, leaks, lost material, or caked aggregate in the bowl invalidate the test and require a fresh sample.