Study guide
7.2 Sample, Bowl Filling, Consolidation, and Strike-Off
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
7.2 Sample, Bowl Filling, Consolidation, and Strike-Off
Key Takeaways Explain This Topic AI
The C173 bowl is filled in TWO equal layers, with each layer rodded 25 times using a 5/8 in. tamping rod.
After rodding each layer, the bowl sides are tapped 10 to 15 times with the 1.25 ± 0.50 lb mallet to close rod holes and release entrapped air.
The second layer's rod strokes should just penetrate about 1 in. into the first layer.
Strike-off must leave the concrete flush and flat with the bowl rim so the measured concrete volume is exact.
Last updated: June 2026
Obtaining and Placing the Sample
The air sample must come from a representative composite sample obtained per ASTM C172 — not from the first or last of the discharge, and remixed in the wheelbarrow before any test specimen is taken. The same composite that feeds slump (C143) and unit weight (C138) feeds the air test. If the concrete has visibly segregated , it is remixed; testing partially consolidated or segregated material gives an air result that describes nothing on the project.
The rollameter bowl is filled with concrete in two equal layers . "Equal" means roughly half the bowl depth per layer, eyeballed at placement — not weighed. Concrete is placed with a scoop moved around the perimeter so the bowl loads evenly and the sample does not heap to one side. Filling in two layers (rather than one) is what makes the 25-stroke rodding reach the full depth without leaving a poorly consolidated bottom.
Consolidation: Rodding and Tapping
Each layer is consolidated by rodding 25 times with the standard 5/8 in. (16 mm) rounded-tip tamping rod , distributing the strokes uniformly over the surface:
- Layer Rod Strokes Rod Penetration Mallet Taps
- 1 (bottom) 25 Through the full depth of the layer, without forcibly striking the bottom 10–15
- 2 (top) 25 About 1 in. (25 mm) into the first layer 10–15
After rodding each layer, tap the sides of the bowl 10 to 15 times with the 1.25 ± 0.50 lb mallet , distributing the blows around the perimeter. Tapping closes the holes left by the rod and releases large entrapped air pockets trapped against the wall. The candidate must say and do both actions per layer; skipping the taps leaves voids that read as false air. A common performance-exam deduction is rodding the first layer all the way through and striking the bottom of the bowl — the rod should reach the full depth of the layer but not forcibly hammer the base, which can dent the calibrated bowl.
Why Consolidation Must Be Controlled
The number one conceptual trap on the exam is the difference between entrapped and entrained air. Rodding and tapping are designed to drive out the large, irregular entrapped voids — the accidental pockets from placement — while leaving the small, deliberate, uniformly distributed entrained air bubbles that the admixture created and that the test is meant to measure. Over-vibrating or over-rodding would expel entrained air and report an artificially low result; under-consolidating leaves entrapped voids and reports an artificially high result.
C173 specifies rodding (not internal vibration) so the operator does not accidentally drive out entrained air. Internal vibration is generally not used in the C173 fill — the controlled 25-stroke rodding plus mallet tapping is the prescribed consolidation for this bowl size.
Entrained vs. entrapped air, side by side:
- Property Entrained Air (wanted) Entrapped Air (unwanted)
- Origin Air-entraining admixture Accidental, from placement
- Bubble size ~10–1000 microns, tiny Large, irregular
- Distribution Uniform, closely spaced Random pockets
- Effect Freeze-thaw durability None beneficial; weakens concrete
- Removed by consolidation? No (preserved) Yes (rodding/tapping expels it)
- Strike-Off and Cleaning the Rim
After the second layer is rodded and tapped, the surface is struck off flush and flat with the top rim of the bowl using the strike-off bar in a sawing, then a leveling, motion. A short list governs a clean strike-off:
Remove any excess concrete heaped above the rim.
Fill any low spots, then re-level so the surface is planar with the rim — not crowned, not dished.
Wipe the flange/rim completely clean of all concrete, grout, and grit before the top section is set on.
Why this matters: the calibrated bowl volume is the basis of the air percentage . If the concrete is struck off high, the true concrete volume is unknown and the air reads low; if struck off low, air reads high. A dirty rim prevents a watertight seal, which causes leakage and an invalid test. Strike-off, not the later rolling, defines the measured volume — the rolling step can never recover a bad fill.
Sequencing the Fill Within the Field Tests
Timing matters. Air, slump, and temperature are all time-sensitive because fresh concrete is changing from the moment it leaves the mixer. ASTM limits how long you may wait: air testing should begin promptly after sampling, generally completing the measurement within the window allowed after obtaining the composite sample, because air content can drift as the concrete stiffens and as entrained bubbles coalesce or escape. A technician who lets the wheelbarrow sit for twenty minutes and then fills the bowl is testing a different concrete than the one being placed.
A disciplined fill sequence the candidate should be able to recite in order:
Remix the composite sample in the wheelbarrow.
Place the first equal layer with a scoop moved around the perimeter.
Rod 25 times , then tap the sides 10–15 times with the mallet.
Place the second equal layer to slightly overfill the bowl.
Rod 25 times (penetrating ~1 in. into layer one), then tap 10–15 times .
Strike off flush , fill low spots, re-level, and wipe the rim clean .
Doing these steps out of order — for example, striking off before tapping the second layer — leaves the surface voids open and changes the measured volume, so the candidate must keep the sequence intact.