7.3 ACI Performance Examination Mastery & Practical Lab Checklists

The ACI Performance Examination is the practical proving ground of the Aggregate Testing Technician Level 1 certification. Unlike the written examination—which is an open-book evaluation of technical calculations, standard specifications, and testing theory—the performance examination is strictly closed-book. Candidates are prohibited from bringing notes, standards, CP-44 workbooks, mobile devices, or scratch calculation aids into the examination room.

During the performance exam, you will stand before an authorized ACI Certification Examiner and physically execute or verbally describe the standardized testing procedures across eight distinct laboratory stations. The examiner evaluates your actions against a standardized rubric of checklist items published by the American Concrete Institute. To earn your certification, you must achieve a passing evaluation on every single one of the eight standards.

1. Structure, Logistics & Practical Examination Rules

The Closed-Book Testing Environment

• Station Setup: Testing facilities typically arrange eight independent testing stations corresponding to the eight core standards (ASTM D75, C702, C117, C136, C127, C128, C566, and C40).
• Examiner Proctors: Examiners are seasoned materials engineers, laboratory managers, or senior certified technicians appointed by the Local Sponsoring Group (LSG). Their role is to observe, take notes against the official checklist rubric, and ensure testing integrity without coaching or prompting.
• Pass/Fail Scoring Standard: Every checklist step is scored on a binary basis: Satisfactory (Pass) or Unsatisfactory (Fail). Skipping a mandatory procedural step (such as failing to sweep conveyor belt fines or overfilling a splitter hopper) constitutes an immediate step failure.

The Essential Art of Examiner Verbalization

In an actual commercial laboratory, soaking an aggregate specimen takes 24 hours, drying an aggregate in an oven takes several hours, and running a mechanical shaker takes several minutes. During a performance exam, candidates obviously cannot wait 24 hours for soaking or 4 hours for oven drying.

To accommodate real-world constraints, ACI establishes a protocol combining hands-on physical demonstration with clear verbal articulation:

• Physical Demonstration: You must physically manipulate the tools—inserting templates, adjusting splitter chutes, tamping sand cones, manipulating pycnometers, nesting sieves, and operating balances.
• Verbal Articulation: When a step represents a prolonged or simulated condition, you must explicitly state the standard parameters out loud to the examiner. For example: "I am placing the sample in the oven at 110 ± 5°C and drying it to constant mass, which means less than 0.1% mass change between successive weighings."

[!TIP] The "Talk-Through" Golden Rule: Never assume the examiner knows what you are thinking. If you silently check that a balance is level or visually inspect a wash water decant, the examiner cannot verify that you evaluated the standard criterion. Always say what you are doing as you do it: "I am checking the spirit bubble to verify the balance is level," or "I am verifying that the wash water running through the No. 200 sieve is crystal clear."

2. Master Performance Checklists: Standards 1 through 4

The following master checklists present the mandatory procedural criteria evaluated by examiners for each standard:

Station 1: ASTM D75 / AASHTO R 90 — Sampling Aggregates

1. Conveyor Belt Sampling (Primary Method):
   • Ensure the conveyor belt is stopped and locked/tagged out.
   • Insert two parallel templates shaped to match the exact cross-sectional contour of the belt.
   • Scoop out all aggregate material situated between the two templates into a sample container.
   • Critical Examiner Step: Using a soft-bristle brush and dustpan, meticulously sweep ALL fine material and dust from the belt surface between the templates into the sample container. (Missing fines results in an immediate failure!).
2. Stockpile Sampling:
   • Loader Pad Method (coarse and mixed aggregate): Use power equipment to develop a separate small sampling pile composed of material drawn from the main pile, then back-drag the small pile to create a flat surface. Take at least three increments — the manual equivalents are drawn from the top third, midpoint, and bottom third of the pile — by inserting a flat-nosed shovel vertically into the pad and avoiding the outer perimeter.
   • Manual Stockpile Board Method: If power equipment is not available, shove a board vertically into the pile just above the sampling point to prevent sloughing of non-representative surface stones, and excavate the increment from beneath it. When sampling fine stockpiles, remove the outer layer and sample the material beneath; a 30-mm (1-1/4 in.) diameter sampling tube may optionally be inserted at random locations to extract a minimum of five increments of fine material.
3. Sampling from Stream Discharge (Bins/Chutes): Select the units to be sampled by an approved random method, then pass a pan large enough to intercept the entire cross-section of the discharging stream through it, without allowing the pan to overflow. Combine at least three equal increments into the field sample.

Station 2: ASTM C702 / AASHTO R 76 — Reducing Field Samples to Testing Size

1. Method A — Mechanical Riffle Splitter:
   • Chute Verification: Verify that the splitter has an even number of equal-width chutes discharging alternately to each side, not fewer than eight for coarse aggregate or twelve for fine aggregate.
   • Chute Width Check: For coarse aggregate, chute width must be at least 1.5 times the NMAS (e.g., ≥1-1/8 in. for 3/4-in. stone). For dry fine aggregate passing the 9.5-mm (3/8-in.) sieve, chute width must be 12.5 to 20 mm (1/2 to 3/4 in.).
   • Leveling: Verify that the splitter frame is level on a stable work surface.
   • Operation: Pour the sample into the hopper pan, distribute it evenly across the full length of the hopper, and introduce it into the chutes at a controlled rate from edge to edge.
2. Method B — Quartering:
   • Place sample on a clean, level, hard surface or clean quartering canvas.
   • Mix thoroughly by turning the entire sample over three times, shovelling it into a conical pile on the last turning by depositing each shovelful on top of the preceding one.
   • Flatten the cone into a uniform circular disc with a diameter approximately 4 to 8 times its thickness.
   • Divide the disc into four equal quarters using a straightedge, trowel, or shovel.
   • Discard two diagonally opposite quarters (including all swept fines); retain the remaining opposite pair.
3. Method C — Miniature Stockpile Sampling (Damp Fine Aggregate Only):
   • Applicable only to fine aggregate possessing surface moisture (coarse or dry fine aggregate is strictly prohibited!).
   • Place on a hard, clean, level surface, turn the entire sample over three times, and form a conical mound by depositing each shovelful on top of the preceding one. Flattening the cone is optional under Section 12.1.
   • Take at least five increments at random locations from the miniature stockpile using a sampling thief, small scoop, or spoon.

Station 3: ASTM C117 / AASHTO T 11 — Materials Finer than 75-µm (No. 200) Sieve by Washing

1. Initial Preparation & Mass: Dry the test sample to constant mass at 110 ± 5°C and determine the mass to the nearest 0.1% of the mass of the test sample (ASTM C117 Section 8.1). The balance itself must be readable and accurate to 0.1 g or 0.1% of the test load, whichever is greater.
2. Washing Vessel & Nesting Sieves: Place the sample in the container and add sufficient water to cover it. In Procedure A, no detergent, dispersing agent, or other substance may be added; Procedure B is the variant that adds a wetting agent, and only on the first charge.
3. Sieve Assembly: Nest the 1.18-mm (No. 16) protective sieve directly on top of the delicate 75-µm (No. 200) sieve (ASTM C117 specifies this exact two-sieve nest).
4. Agitation & Decantation: Agitate sample vigorously with hands or a stirring rod to disperse micro-fines into suspension. Immediately pour the wash water over the nested sieves, taking care not to pour coarse rock particles out of the container.
5. Repeat Wash Cycles: Add fresh water, agitate, and decant repeatedly until the decanted wash water is visually clear.
6. Backwashing Retained Material: Wash all material retained on the nested sieves back into the original sample container using a gentle stream from a wash bottle.
7. Final Drying: Dry washed aggregate to constant mass at 110 ± 5°C; determine final dry mass.

Station 4: ASTM C136 / AASHTO T 27 — Sieve Analysis of Fine and Coarse Aggregates

1. Sieve Nesting: Nest sieves in descending order of opening size from top to bottom, with the pan at the base.
2. Mechanical Agitation: Pour the dry sample onto the top sieve, secure the lid, and agitate for a period established by trial to satisfy the Section 8.4 sufficiency criterion. ASTM C136 Note 2 cautions that taking more than approximately 10 min to achieve adequate sieving may degrade the sample.
3. Sieve Overloading Prevention: Ensure that the mass retained on each sieve does not exceed the ASTM C136 Table 1 limit. For openings smaller than 4.75 mm the limit is 7 kg/m² (200 g on a 203-mm sieve); for openings of 4.75 mm and larger it is $M_{\max} = 2.5 \times d \times A$, where $d$ is the sieve opening in mm and $A$ is the effective sieving area in m².
4. Hand-Sieving Completeness Test (Endpoint Verification):
   • Hold the individual sieve, provided with a snug-fitting pan and cover, in a slightly inclined position in one hand. (ASTM C136 says "slightly inclined" and fixes no angle — do not quote a number.)
   • Strike the side of the sieve sharply and with an upward motion against the heel of the other hand at a rate of about 150 times per minute.
   • Turn the sieve about one sixth of a revolution at intervals of about 25 strokes.
   • Continue for 1 minute. Under ASTM C136 Section 8.4, sieving is sufficient when not more than 1% by mass of the material retained on that individual sieve passes it during that minute; under AASHTO T 27 the same endpoint is stated as not more than 0.5% by mass of the total sample.
   • When checking sizes larger than the 4.75-mm (No. 4) sieve, limit the material on the sieve to a single layer of particles. If the mounted sieve size makes this motion impractical, use 203-mm (8-in.) sieves to verify sufficiency.
5. The 0.3% Mass Check Rule:
   • Sum the masses retained on all individual sieves plus the material in the pan.
   • ASTM C136 Section 8.7: the total mass after sieving should check closely with the original mass; if the amounts differ by more than 0.3%, based on the original dry sample mass, the results should not be used for acceptance purposes: $|M_{\text{initial}} - \sum M_{\text{retained}}| / M_{\text{initial}} \le 0.003$.

3. Master Performance Checklists: Standards 5 through 8

Station 5: ASTM C127 / AASHTO T 85 — Specific Gravity & Absorption of Coarse Aggregate

1. Pre-Test Separation: Sieve field sample over the 4.75-mm (No. 4) sieve; discard all material passing the No. 4 sieve.
2. Washing & Initial Soaking: Wash retained coarse aggregate to remove surface dust; dry to constant mass; submerge in potable water at room temperature for 24 ± 4 hours.
3. Achieving SSD Condition:
   • Remove aggregate from water and place on a large, clean, absorbent terrycloth towel.
   • Roll particles in the towel until all visible surface water films disappear. Larger particles may be individually wiped.
   • Stop rolling the instant surface films vanish to avoid evaporating water from internal pore capillaries.
4. Mass B (SSD Mass in Air): Immediately weigh SSD sample in air; record mass as Mass B to nearest 0.5 g or 0.05%.
5. Mass C (Submerged Buoyant Mass):
   • Immediately place SSD aggregate into wire basket suspended from a center-load balance hook.
   • Lower the 3.35-mm (No. 6) or finer mesh basket into water at 23 ± 2.0°C (ASTM C127; AASHTO T 85 states 23.0 ± 1.7°C / 73.4 ± 3°F).
   • Critical Examiner Step: Shake the submerged basket vigorously while underwater to dislodge all entrapped air bubbles.
   • Record buoyant submerged mass as Mass C.
6. Mass A (Oven-Dry Mass): Empty basket into pan, dry to constant mass in oven at 110 ± 5°C, cool, and record as Mass A.

Station 6: ASTM C128 / AASHTO T 84 — Specific Gravity & Absorption of Fine Aggregate

1. Sample Soaking: Obtain approximately 1 kg of fine aggregate per ASTM C702; dry to constant mass at 110 ± 5°C; cool to a comfortable handling temperature (about 50°C); then cover with water either by immersion or by the addition of at least 6% moisture, and let stand 24 ± 4 h.
2. Gentle Warm Air Drying: Decant excess water; spread sand on flat non-absorbent pan; blow gentle warm air while stirring continuously.
3. The Cone and Tamper Test for SSD:
   • Place standard conical metal mold (40 mm top ID, 90 mm bottom ID, 75 mm height) firmly on smooth, non-absorbent surface.
   • Fill mold to overflowing in one single layer without pre-compacting.
   • Tamp sand lightly 25 times with standard 340 ± 15 g tamper dropping freely from 5 mm (0.2 in.) above sand surface. Distribute drops uniformly across surface.
   • Remove loose sand from the base and lift the mold vertically. (Levelling the material even with the top of the mold belongs to the Note 2 Provisional Cone Test, not to the standard Section 8.3 test.)
   • Slump Evaluation:
     • Retains cone shape perfectly: Sand has surface moisture (too wet) -> Continue warm air drying.
     • Slumps slightly on all sides (first slump): SSD condition reached! Immediately weigh out 500.0 ± 10.0 g (Mass S).
     • Collapses completely on the first trial: the sand was dried past SSD -> thoroughly mix a few millilitres of water with the fine aggregate, let the specimen stand in a covered container for 30 min, then resume drying and testing.
     • Angular or high-fines sand that will not slump at all: drop a handful from 100 to 150 mm and watch for airborne fines. If fines go airborne, take SSD as the point where one side slumps slightly, or use the Note 2 Provisional Cone Test (10, 10, 3 and 2 tamper drops over four layers, levelled off, then lift).
4. Pycnometer Method & Agitation:
   • Transfer 500.0 g SSD sand (Mass S) into calibrated 500-mL pycnometer flask; add water to ~90% full.
   • Agitation for De-Airing: Partially fill the pycnometer with water first, introduce the 500 ± 10 g of SSD sand, then fill to about 90% of capacity. Manually roll, invert or agitate to eliminate visible air bubbles — ASTM C128 Note 3 says about 15 to 20 min are normally required. For foam, dip the tip of a paper towel into the pycnometer, or optionally use a small amount of isopropyl alcohol.
   • Adjust the pycnometer and its contents to 23.0 ± 2.0°C (ASTM C128; AASHTO T 84 states 23.0 ± 1.7°C), bring the water to the calibration mark, and weigh to the nearest 0.1 g (Mass C).
5. Mass A Recovery: Empty pycnometer into pan, rinse all clinging grains from neck/flask, dry to constant mass at 110 ± 5°C (Mass A).

Station 7: ASTM C566 / AASHTO T 255 — Total Evaporable Moisture Content by Drying

1. Sample Mass Compliance: Select sample meeting Table 1 minimum mass by NMAS (e.g., 500 g for sand, 3.0 kg for 3/4-in. coarse stone).
2. Moisture Protection: Weigh sample immediately in a sealed container to avoid evaporation loss; record net wet mass $W$.
3. Drying Procedure: Place in ventilated oven at 110 ± 5°C or on hot plate. If using hot plate, stir continuously to prevent localized overheating and particle popping.
4. Constant Mass Check: Verify that successive weighings after additional heating show less than 0.1% mass change.
5. Computation & Precision: Calculate $p = 100 \times (W - D) / D$; report result to nearest 0.1%.

Station 8: ASTM C40 / AASHTO T 21 — Organic Impurities in Fine Aggregate for Concrete

1. Glass Bottle: Select a clean, colorless graduated glass bottle of approximately 240 to 470 mL (8 to 16 oz) capacity, with a watertight stopper or cap not soluble in the reagents. Measured along the line of sight used for the comparison, the bottle's maximum outside thickness must be not more than 63.5 mm (2.5 in.) and not less than 38.1 mm (1.5 in.).
2. Sand Addition: Add fine aggregate to bottle until the settled sand volume reaches approximately 130 mL (4-1/2 fluid oz).
3. Reagent Addition: Add a 3% sodium hydroxide (NaOH) solution (prepared by dissolving 3 parts by mass of reagent-grade NaOH in 97 parts of distilled water) until the total combined volume of sand and liquid reaches 200 mL (7 fluid oz).
4. Agitation: Stopper the bottle securely and shake vigorously. ASTM C40 Section 8.3 prescribes no shaking duration; do not state one.
5. Standing Time: Allow bottle to stand undisturbed for 24 hours at room temperature.
6. Color Evaluation: Two approved comparisons, and the candidate should be able to describe both.
   • Standard Color Solution Procedure (Section 9.1): fill a second bottle to the approximately 75-mL (2-1/2 fluid oz) level with standard color solution prepared not longer than 2 h previously, hold the two bottles side by side, compare the light transmitted through each, and record whether the supernatant liquid is lighter, darker, or equal to the standard.
   • Glass Color Standard Procedure (Section 9.2): compare against the five mounted glass standards — Gardner Color Standard Nos. 5, 8, 11, 14 and 16, corresponding to Organic Plate Nos. 1 through 5 — and report the organic plate number nearest the color of the supernatant liquid. No standard color solution needs to be prepared for this route. The reference standard is Organic Plate No. 3, which is Gardner Color Standard No. 11.
   • Pass/Fail Criteria:
     • Lighter than or equal to Organic Plate No. 3: Fine aggregate is acceptable (free of harmful organic compounds).
     • Darker than Organic Plate No. 3: Aggregate contains potentially injurious organic matter (decaying vegetation, humic acid). Aggregate fails ASTM C40 and cannot be used unless approved by ASTM C87 mortar strength testing.

4. Ten Recurring Ways Candidates Lose Performance-Exam Steps

ACI does not publish failure statistics for this program, so treat the list below as a study checklist drawn from the procedural requirements of the eight standards themselves — each item is a step that a standard states explicitly and that is easy to omit under exam pressure — rather than as a ranked frequency table:

1. Over-Drying Sand Past SSD (ASTM C128): Drying sand too aggressively so it completely collapses on the very first cone test. The candidate must detect the initial slight slump.
2. Leaving Fines on Conveyor Belt (ASTM D75): Removing coarse stones between templates but failing to sweep the microscopic dust and fines off the rubber belt with a brush and dustpan.
3. Sieve Overloading (ASTM C136): Dumping an entire 4-kg coarse sample into a small 8-in. sieve nest, burying the mesh in 3 inches of rock and blinding the openings.
4. Incomplete Backwashing (ASTM C117): Rinsing the nested No. 200 sieve carelessly and leaving sand grains trapped in the corners of the sieve frame rather than backwashing 100% of material into the drying pan.
5. Rushing Pycnometer De-Airing (ASTM C128): Inverting the flask only once or twice instead of sustaining 15 to 20 minutes of active rolling and agitating to expel entrapped air bubbles.
6. Exceeding the 0.3% Mass Check (ASTM C136): Spilling rock fragments while transferring sieves to the scale, causing the final sum to differ from the initial dry mass by more than 0.3%.
7. Improper Tamper Drop Height (ASTM C128): Holding the tamper 2 inches above the sand and pounding downward, instead of releasing the 340-g weight from exactly 5 mm (0.2 in.) above the sand surface.
8. Neglecting Underwater Basket Shaking (ASTM C127): Lowering the wire basket into the water tank and immediately reading Mass C without shaking the basket underwater to dislodge air bubbles trapped beneath coarse rock faces.
9. Splitter Mismanagement (ASTM C702): Using a chute width less than approximately 50% larger than the largest particle in the sample (the standard keys chute width to the largest particle, not to nominal maximum size), or dumping the sample into one corner of the hopper instead of distributing it uniformly from edge to edge.
10. The Denominator Inversion (ASTM C566): Dividing evaporated water by wet mass $W$ instead of oven-dry mass $D$ when asked by the examiner to calculate the moisture percentage.