5.4 Yield, Relative Yield, and Batch Comparison

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

5.4 Yield, Relative Yield, and Batch Comparison

Key Takeaways Explain This Topic AI

Yield Y = total batch mass / density (D); in ft³, divide by 27 to convert to yd³.

Relative yield Ry = Y / Vd, where Vd is the design volume; Ry = 1.00 means exactly as designed.

Relative yield above 1.00 means more concrete was produced than designed (overyield); below 1.00 means less (underyield, a shortfall).

Cement content = total mass of cement in the batch / yield, giving actual cement per cubic yard.

Because density is the divisor, a high density always produces a low yield, and vice versa.

Last updated: June 2026

Yield: How Much Concrete the Batch Made

Yield (Y) is the volume of concrete produced from a batch of known total mass. C138 computes it directly from density:

Y = (total batch mass) / D

The total batch mass is the sum of all ingredient masses actually weighed into the batch — cement, supplementary cementitious materials, all aggregates, water, and admixtures (in pounds). Dividing by density (lb/ft³) yields a volume in cubic feet . To express it in cubic yards , divide by 27 (since 1 yd³ = 27 ft³).

Worked yield example

A batch contains the following masses:

Ingredient Mass (lb)
Cement 564
Coarse aggregate 1,800
Fine aggregate 1,240
Water 282
Total batch mass 3,886

Measured density D = 145.0 lb/ft³ . Yield Y = 3,886 / 145.0 = 26.80 ft³ = 26.80 / 27 = 0.993 yd³ .

Relative Yield: Did the Batch Deliver What Was Designed?

Relative yield (Ry) compares the actual yield to the design volume (Vd) the mix was proportioned to make:

Ry = Y / Vd

Ry = 1.00 → the batch produced exactly the designed volume.

Ry > 1.00 → overyield : more concrete than designed (you'll have extra; the mix is slightly 'light').

Ry < 1.00 → underyield/shortfall : less concrete than designed — a paving or slab order could come up short.

Worked relative-yield example

Using the batch above, the mix was designed to make Vd = 27.00 ft³ (1.000 yd³). Ry = 26.80 / 27.00 = 0.993 . Because 0.993 < 1.00, the batch underyielded by about 0.7% — it produced slightly less concrete than ordered. If the same batch had measured a density of only 143.0 lb/ft³ , yield would be 3,886 / 143.0 = 27.18 ft³ and Ry = 27.18 / 27.00 = 1.007 , an overyield. Higher density → lower yield → lower relative yield , and vice versa.

Cement Content From Yield

C138 also lets you back out the actual cement content (C) delivered per unit volume:

C = (total mass of cement in the batch) / Y

Using the example: 564 lb cement ÷ 0.993 yd³ = 568 lb/yd³ . If a specification calls for 564 lb/yd³ (a six-bag mix), the slightly low yield means each cubic yard actually carries a hair more cement than designed — an underyield concentrates the cement. Conversely, overyield dilutes cement content below the target. This is why owners care about relative yield: it ties directly to whether the hardened concrete will meet its strength-driving cement factor.

Why These Numbers Matter on the Job

Yield and relative yield are the producer's quality-control link between the batch ticket and the truck:

A consistent Ry near 1.00 confirms the plant's batch weights and the assumed aggregate specific gravities are accurate.

A persistent underyield (Ry < 1.00) means trucks deliver less concrete than billed — costly and a contractual problem.

A persistent overyield (Ry > 1.00) often signals higher-than-assumed air content or lighter materials, which can compromise strength.

Because all of this rests on the density number, sloppy C138 technique doesn't just mis-state density — it mis-states yield, relative yield, and cement content together.

Units and Conversions to Keep Straight

Yield problems trip candidates up on units more than on the formula. Keep these straight:

Quantity Inch-pound unit Conversion
Density (D) lb/ft³ —
Batch mass lb —
Yield (raw) ft³ ÷ 27 → yd³
Yield (reported) yd³ report to 0.01 yd³
Relative yield dimensionless report to 0.01
Cement content lb/yd³ report to 1 lb/yd³

A disciplined approach: compute yield in ft³ first (batch mass ÷ density), then divide by 27 only when you need cubic yards. Many wrong answers come from dividing by 27 too early or forgetting it entirely. Likewise, relative yield is unitless — both yield and design volume must be in the same unit (both ft³ or both yd³) before you divide, or the ratio is meaningless.

A Fully Worked Batch

Put it all together with one clean example. A batch of total mass 3,950 lb is designed to produce 27.0 ft³ (1.00 yd³) and contains 611 lb of cement. The measured density is 148.0 lb/ft³ .

Yield: 3,950 / 148.0 = 26.69 ft³ = 26.69 / 27 = 0.99 yd³ .

Relative yield: 26.69 / 27.0 = 0.988 → rounds to 0.99 . Below 1.00, so a slight underyield.

Cement content: 611 / 0.99 yd³ = 617 lb/yd³ , slightly above the 611 lb/yd³ target because the underyield concentrates the cement.

Every one of these answers traces back to the single measured density of 148.0 lb/ft³ — which is exactly why the procedure sections (5.1–5.3) matter so much.

One more nuance: the total batch mass must include the water and admixtures actually added, not just the dry materials on the mix-design sheet. If a truck received extra tempering water at the site, that water is part of the batch mass for yield purposes. Using the design batch mass while testing a tempered batch mismatches the numerator and denominator and produces a misleading yield — so always pair the measured density with the as-delivered batch weights when one is computing yield in the field.