ACI Concrete Finisher Certification — Questions and Answers

Question 1: According to ACI mix design principles, what is the purpose of the 'trial batch' step?

To measure aggregate moisture content
To determine cement type required
To verify calculated proportions produce desired fresh and hardened properties (Correct answer)
To establish the mixing time

Correct answer: To verify calculated proportions produce desired fresh and hardened properties

Trial batches confirm that calculated mix proportions achieve the target slump, air content, and compressive strength before full-scale production.

Question 2: During cold weather concreting, the concrete temperature at the point of placement should be maintained at a minimum of:

50°F (10°C) (Correct answer)
40°F (5°C)
55°F (13°C)
25°F (-4°C)

Correct answer: 50°F (10°C)

ACI 306 requires concrete to be placed and maintained at a minimum of 50°F (10°C) to ensure adequate hydration in cold weather.

Question 3: Which test method measures the resistance of hardened concrete to chloride ion penetration, relevant to durability in coastal or de-iced environments?

ASTM C78 flexural strength test
ASTM C231 air content test
ASTM C1202 rapid chloride permeability test (RCPT) (Correct answer)
ASTM C39 compressive strength test

Correct answer: ASTM C1202 rapid chloride permeability test (RCPT)

ASTM C1202 (RCPT) measures electrical charge passed through a concrete disc to assess its resistance to chloride ion penetration.

Question 4: What is the purpose of a 'release agent' when stamping concrete?

To accelerate the set of the concrete surface
To increase the depth of the stamped pattern
To prevent the stamp from bonding to the concrete and add a secondary color accent (Correct answer)
To seal the concrete after stamping is complete

Correct answer: To prevent the stamp from bonding to the concrete and add a secondary color accent

Release agents serve a dual purpose: they prevent stamps from sticking to the surface and add a contrasting antiquing color that highlights pattern details.

Question 5: Which repair method is most appropriate for filling wide, dormant horizontal cracks in a concrete floor slab?

Routing and sealing with a flexible sealant
Epoxy injection under pressure
Shotcrete overlay
Dry-pack mortar rodded into the crack (Correct answer)

Correct answer: Dry-pack mortar rodded into the crack

Wide dormant cracks in horizontal slabs are best repaired by routing to a uniform shape and filling with dry-pack mortar or rigid filler.

Question 6: When using dry-pack mortar for repair, the water-to-cement ratio should be:

Just enough to ball in your hand without crumbling or releasing water (Correct answer)
As high as possible to aid workability
Equal to that used for standard ready-mix concrete
At least 0.60 to ensure full hydration

Correct answer: Just enough to ball in your hand without crumbling or releasing water

Dry-pack mortar uses a very low w/c ratio; the mix should barely hold together when squeezed, minimizing shrinkage.

Question 7: Under EPA's National Pollutant Discharge Elimination System (NPDES), construction sites disturbing one or more acres must have which document in place?

A Waste Management Manifest
A RCRA Part B permit
An Environmental Impact Statement (EIS)
A Stormwater Pollution Prevention Plan (SWPPP) (Correct answer)

Correct answer: A Stormwater Pollution Prevention Plan (SWPPP)

NPDES Construction General Permits require a SWPPP that identifies pollutant sources (like concrete washout) and best management practices to control stormwater runoff.

Question 8: When sampling fresh concrete for quality control testing, ASTM C172 requires the composite sample to be obtained over what time period?

Within 2 minutes
No more than 15 minutes (Correct answer)
Within 5 minutes
No more than 30 minutes

Correct answer: No more than 15 minutes

ASTM C172 requires that the composite sample be collected over a period of no more than 15 minutes to represent a single batch or load.

Question 9: How should ACI professionals measure success in concrete repair & restoration?

Using defined metrics, benchmarks, and regular evaluation against established goals (Correct answer)
Success measurement is not applicable
By comparing only to minimum requirements
Through subjective self-assessment only

Correct answer: Using defined metrics, benchmarks, and regular evaluation against established goals

Success in concrete repair & restoration is measured through defined metrics and benchmarks, with regular evaluation against established professional goals.

Question 10: According to ACI 117, what is the standard flatness tolerance for a conventional concrete slab (not a defined-traffic floor) unless otherwise specified?

±1 inch in 10 feet
±3/8 inch in 10 feet
±1/2 inch in 10 feet (Correct answer)
±1/4 inch in 10 feet

Correct answer: ±1/2 inch in 10 feet

ACI 117 specifies a standard tolerance of ±1/2 inch measured under a 10-foot straightedge for conventional flatwork unless more restrictive tolerances are specified.

Question 11: Concrete scaling in cold climates is most effectively prevented by:

Ensuring adequate air entrainment (4–7%) and proper curing (Correct answer)
Increasing the w/cm ratio above 0.50
Using Type IV low-heat cement
Applying deicers immediately after finishing

Correct answer: Ensuring adequate air entrainment (4–7%) and proper curing

Adequate air entrainment provides freeze-thaw resistance, and proper curing achieves the strength and density needed to resist scaling.

Question 12: During screeding, what does a 'wet' area (low spot filled with paste) in an otherwise consistent surface most likely indicate?

The screed guides are set too high at that location
The mix has too little water and is over-vibrated
A soft spot or void in the subgrade beneath that area (Correct answer)
Excessive cement content in the batch

Correct answer: A soft spot or void in the subgrade beneath that area

Paste-filled low spots often indicate soft subgrade areas where concrete has settled slightly, a warning sign of inadequate or non-uniform subgrade support.

Question 13: When finishing concrete in hot weather, which measure helps prevent rapid surface drying?

Troweling more aggressively
Adding extra water to the mix at the jobsite
Placing concrete in thicker lifts
Using evaporation retarder (aliphatic alcohol spray) on the surface (Correct answer)

Correct answer: Using evaporation retarder (aliphatic alcohol spray) on the surface

Aliphatic alcohol-based evaporation retarders form a temporary film that slows moisture loss from the concrete surface during finishing.

Question 14: What defect results from troweling concrete before bleed water has evaporated?

Scaling
Delamination (Correct answer)
Crazing
Pop-outs

Correct answer: Delamination

Troweling too early traps bleed water under the surface, causing delamination where the top layer separates from the base.

Question 15: Which of the following best describes 'plastic shrinkage cracking' in flatwork?

Cracking that occurs within the first few hours after placement as moisture evaporates rapidly from the surface (Correct answer)
Cracking that occurs months after placement due to drying
Cracking due to inadequate subbase compaction
Cracking caused by thermal expansion in summer heat

Correct answer: Cracking that occurs within the first few hours after placement as moisture evaporates rapidly from the surface

Plastic shrinkage cracks form within hours of placement when the evaporation rate exceeds the bleed water rate, causing surface tension-induced cracking before the concrete sets.

Question 16: What is the primary binder in concrete?

Fly ash
Portland cement (Correct answer)
Gravel
Sand

Correct answer: Portland cement

Portland cement is the primary binder in concrete. When mixed with water, it undergoes a chemical reaction called hydration, forming a paste that coats the aggregates (sand and gravel). This paste then hardens and binds the aggregates together, creating the solid, durable material known as concrete.

Question 17: What instrument is most commonly used to measure floor flatness F-numbers per ASTM E1155?

Digital micrometer
Laser level
Steel straightedge
Dipstick profiler (Correct answer)

Correct answer: Dipstick profiler

The dipstick profiler is the standard instrument used to measure floor elevation differences for calculating F-numbers per ASTM E1155.

Question 18: When frozen ground or ice is present at a subgrade before cold-weather concrete placement, the finisher should ensure:

The concrete is placed directly on the frozen surface for natural thawing
A thicker slab is poured to compensate for the cold base
The subgrade is thawed and free of ice before concrete is placed (Correct answer)
Ice is broken up and mixed into the subgrade for drainage

Correct answer: The subgrade is thawed and free of ice before concrete is placed

Frozen subgrade will thaw after placement, causing settlement and potential cracking; the subgrade must be thawed to a minimum depth before concreting.

Question 19: Why is curing important for concrete?

To prevent color changes
To dry the surface quickly
To ensure strength development (Correct answer)
To remove air bubbles

Correct answer: To ensure strength development

Curing is a critical process for concrete that involves maintaining adequate moisture and temperature conditions after placement. This allows the cement to fully hydrate, which is the chemical reaction responsible for concrete gaining strength and durability. Proper curing prevents the concrete from drying out too quickly, ensuring it reaches its designed strength, reduces shrinkage, and improves its resistance to wear and environmental factors.

Question 20: What is 'efflorescence' and why is it a concern on decorative concrete?

A type of surface scaling caused by freeze-thaw cycles only
Excess release agent residue trapped under the sealer
White mineral deposits that migrate to the surface and mar the decorative appearance (Correct answer)
A chemical reaction that darkens the concrete permanently

Correct answer: White mineral deposits that migrate to the surface and mar the decorative appearance

Efflorescence is soluble salt deposits carried to the surface by moisture that, when dry, leave white hazy stains that diminish the look of decorative work.

Question 21: When placing concrete in hot weather (above 90°F), which practice best prevents rapid moisture loss during flatwork placement?

Use sunshades, windbreaks, and mist the subgrade before placement (Correct answer)
Increase the water-cement ratio
Pour concrete thicker than specified
Add extra cement to the mix

Correct answer: Use sunshades, windbreaks, and mist the subgrade before placement

Sunshades, windbreaks, and pre-moistened subgrade reduce evaporation rate and prevent premature surface drying during hot-weather placement.

Question 22: Which type of screed is best suited for large flatwork areas requiring high flatness tolerances (high FF numbers)?

Laser-guided or GPS-controlled vibratory screed (Correct answer)
Manual rod screed
Hand-held jitterbug tamper
Rubber float

Correct answer: Laser-guided or GPS-controlled vibratory screed

Laser-guided or GPS-controlled vibratory screeds provide the precision and consistency needed to achieve high FF/FL tolerances on large slab areas.

Question 23: What is the primary purpose of using a highway straightedge (10-foot screed) during flatwork leveling?

To apply curing compound evenly
To compact the concrete surface
To detect and remove high and low spots across the slab (Correct answer)
To create control joints

Correct answer: To detect and remove high and low spots across the slab

A highway straightedge spans across the slab to identify and correct high and low spots, ensuring a flat, even surface.

Question 24: Which factor most significantly affects the color uniformity of a large integrally colored concrete placement?

Consistent mix design and water-cement ratio maintained across all loads (Correct answer)
The ambient temperature on the day of placement
The type of curing compound applied
The brand of stamps used for texturing

Correct answer: Consistent mix design and water-cement ratio maintained across all loads

Color uniformity across a large pour depends on maintaining the exact same mix proportions, pigment dosage, and water content in every truck load.

Question 25: According to ACI, what finishing action most frequently leads to delamination in flatwork?

Applying the curing compound before final troweling
Finishing the surface before bleed water has evaporated (Correct answer)
Placing concrete directly on a dry subgrade
Using a bull float before screeding

Correct answer: Finishing the surface before bleed water has evaporated

ACI states that prematurely closing the surface traps bleed water and air beneath the mortar-rich layer, causing delamination.

Question 26: Who is credited with developing the F-number floor flatness and levelness system?

Joseph Phelan
Robert Ytterberg
Allen Face (Correct answer)
James Warner

Correct answer: Allen Face

Allen Face developed the F-number system in the 1980s, which was subsequently adopted by ACI and ASTM as the standard method for measuring floor flatness and levelness.

Question 27: When should white-pigmented curing compound NOT be used?

On flatwork in hot weather
On slabs with a broom finish
On surfaces that will receive a bonded overlay or coating (Correct answer)
On slabs exposed to direct sunlight

Correct answer: On surfaces that will receive a bonded overlay or coating

Curing compounds form a membrane that prevents bond between concrete and subsequent overlays, adhesives, or coatings.

Question 28: When screedng concrete between forms, the screed should be moved with what motion?

Circular motion to distribute aggregate
Straight push only, no side-to-side motion
Pulling only, never pushing
A sawing side-to-side motion while advancing forward (Correct answer)

Correct answer: A sawing side-to-side motion while advancing forward

A sawing back-and-forth lateral motion while advancing forward fills voids and levels the surface without leaving ridges.

Question 29: What does the term 'protected curing period' refer to in cold weather concreting per ACI 306?

The period during which curing compound must remain intact on the surface
The duration calcium chloride remains active in the mix
The time concrete must be kept above 50°F (10°C) to achieve adequate strength before exposure to freezing (Correct answer)
The time between placement and form removal

Correct answer: The time concrete must be kept above 50°F (10°C) to achieve adequate strength before exposure to freezing

ACI 306 defines the protected curing period as the time concrete must be maintained above 50°F to develop sufficient strength to resist freezing damage.

Question 30: Which test is performed in the field to determine the air content of fresh concrete?

Proctor compaction test
Vebe consistometer test
Pressure meter (Type B) test (Correct answer)
Kelly ball test

Correct answer: Pressure meter (Type B) test

The pressure meter (ASTM C231) is the most common field method for measuring air content in fresh concrete.

Question 31: Which type of float is used to bring moisture and fine particles to the surface during the first finishing pass?

Bull float (Correct answer)
Fresno trowel
Steel trowel
Edger

Correct answer: Bull float

A bull float is used immediately after screeding to embed aggregate and bring a thin layer of cement paste to the surface.

Question 32: What is the function of a 'jitterbug' (grate tamper) during flatwork placement, and when should its use be limited?

It vibrates the forms; avoid use near walls
It forces coarse aggregate below the surface; limit use on slabs that will receive a hard trowel finish (Correct answer)
It compacts the subgrade; use only before concrete is placed
It smooths the surface; use freely on all slabs

Correct answer: It forces coarse aggregate below the surface; limit use on slabs that will receive a hard trowel finish

A jitterbug forces coarse aggregate below the surface to create a mortar-rich layer, but overuse can produce a weak surface layer prone to scaling on hard-troweled slabs.

Question 33: What spacing is typically recommended for hand-jointing (grooving) a 4-inch thick concrete slab to control cracking?

Every 1 foot
Equal to the slab thickness in feet
10 times the slab thickness in inches (approximately) (Correct answer)
Every 50 feet

Correct answer: 10 times the slab thickness in inches (approximately)

Control joints are typically spaced at intervals of 24–36 times the slab thickness, or roughly 8–12 feet for a 4-inch slab.

Question 34: When must a concrete finisher wear chemical-resistant gloves and boots?

When using a bull float only
Only during hot weather pours
Only when mixing concrete by hand
Whenever in prolonged contact with fresh concrete (Correct answer)

Correct answer: Whenever in prolonged contact with fresh concrete

Fresh concrete is highly alkaline and prolonged skin contact causes chemical burns; protective gloves and boots are required.

Question 35: When placing concrete in freezing weather, which measure helps protect the concrete from freeze-thaw damage before adequate strength is gained?

Delaying curing compound application by 24 hours
Adding extra water to keep the mix fluid
Using Type III high-early-strength cement and enclosures with heat (Correct answer)
Placing thinner sections to speed up cooling

Correct answer: Using Type III high-early-strength cement and enclosures with heat

Type III cement accelerates early strength gain and heated enclosures maintain temperature, both protecting concrete before it reaches freeze-thaw resistance.

Question 36: Which of the following is NOT a recommended practice for reducing concrete temperature during hot weather production?

Adding extra cement to increase heat of hydration (Correct answer)
Using liquid nitrogen injection into the mixer
Replacing mixing water with crushed ice
Shading aggregate stockpiles

Correct answer: Adding extra cement to increase heat of hydration

Adding extra cement increases heat of hydration, raising concrete temperature — the opposite of what is needed in hot weather.

Question 37: Which ACI document includes F-number tolerances for floor flatness and levelness?

ACI 318
ACI 301
ACI 117 (Correct answer)
ACI 360R

Correct answer: ACI 117

ACI 117, 'Specification for Tolerances for Concrete Construction and Materials,' includes F-number tolerances for floor flatness and levelness.

Question 38: In hot weather concrete work, which action best reduces the risk of plastic shrinkage cracking before finishing is complete?

Applying a curing compound immediately after screeding
Increasing the water-cement ratio of the mix
Using an evaporation retarder on the concrete surface (Correct answer)
Finishing the surface more aggressively to close pores

Correct answer: Using an evaporation retarder on the concrete surface

Evaporation retarders form a thin monomolecular film on the concrete surface that slows moisture loss during the finishing window.

Question 39: What condition indicates that concrete is too stiff to finish properly?

The concrete temperature is above 70°F
The surface has a sheen of bleed water
Trowel pressure does not embed the blade and the surface tears or shows drag marks (Correct answer)
Trowel marks disappear immediately

Correct answer: Trowel pressure does not embed the blade and the surface tears or shows drag marks

When the concrete is too stiff, trowel blades skip or tear the surface rather than smoothing it, indicating the finishing window has closed.

Question 40: Spalling along the soffit of a concrete bridge deck is most commonly caused by:

Freeze-thaw damage to the cement paste
Corrosion of reinforcing steel expanding and fracturing the cover concrete (Correct answer)
Improper air entrainment during original placement
Alkali-silica reaction in the coarse aggregate

Correct answer: Corrosion of reinforcing steel expanding and fracturing the cover concrete

Corrosion products occupy up to 6 times the volume of the original steel, creating expansive forces that spall the concrete cover.

Question 41: When polishing concrete to achieve a decorative finish, which sequence of diamond tooling grits is correct?

Fine grits first, then progressively coarser grits
Grit selection is irrelevant as long as the surface is wet
Coarse grits first, then progressively finer grits (Correct answer)
Alternating coarse and fine grits to prevent surface cracking

Correct answer: Coarse grits first, then progressively finer grits

Concrete polishing always begins with coarse diamond grits to remove surface imperfections and progressively advances through finer grits to achieve the desired sheen level.

Question 42: What construction condition is most likely to produce low FF numbers (poor flatness) in freshly placed concrete?

Allowing adequate bleed water evaporation before finishing
Using a low water-to-cement ratio mix
Curing with wet burlap immediately after finishing
Inconsistent screed strikes causing ridges and low spots during placement (Correct answer)

Correct answer: Inconsistent screed strikes causing ridges and low spots during placement

Inconsistent screed strikes that leave ridges, valleys, or uneven surfaces during placement directly result in low FF numbers, as these local deviations are captured by the profiler.

Question 43: A power trowel blade set at a high positive pitch angle will produce what effect?

Increased bleed water extraction
More aggressive compaction and flatness
Deeper cutting action
A burnished, hard surface finish (Correct answer)

Correct answer: A burnished, hard surface finish

Increasing the blade pitch angle on a power trowel creates more friction and pressure, resulting in a denser, burnished surface.

Question 44: When implementing concrete strength & testing methods practices, what should ACI professionals prioritize?

Speed of implementation above all else
Cost reduction as the sole objective
Alignment with professional standards, stakeholder needs, and organizational goals (Correct answer)
Personal preferences and comfort level

Correct answer: Alignment with professional standards, stakeholder needs, and organizational goals

Effective implementation of concrete strength & testing methods requires balancing professional standards, stakeholder needs, and organizational objectives for optimal results.

Question 45: What challenge is most commonly encountered in flatwork placement & leveling within American Concrete Institute Concrete Finisher practice?

Lack of available training materials
Unlimited budget allocation
Excessive regulatory support
Resistance to change and difficulty maintaining consistency across stakeholders (Correct answer)

Correct answer: Resistance to change and difficulty maintaining consistency across stakeholders

The most common challenge in flatwork placement & leveling is overcoming resistance to change while maintaining consistent implementation across diverse stakeholders.

Question 46: What is the maximum noise exposure level (dBA) permitted by OSHA for an 8-hour workday without hearing protection?

90 dBA (Correct answer)
100 dBA
80 dBA
85 dBA

Correct answer: 90 dBA

OSHA's permissible exposure limit for noise is 90 dBA as an 8-hour TWA under 29 CFR 1910.95/1926.52, above which engineering controls or hearing protection are mandatory.

Question 47: ACI 302.1R recommends that subgrade fill be compacted to a minimum of what percentage of maximum dry density?

95% (Correct answer)
70%
90%
80%

Correct answer: 95%

ACI 302.1R specifies 95% of maximum dry density (per ASTM D698) to ensure adequate bearing capacity and limit future settlement.

Question 48: When placing concrete for a sloped flatwork slab (e.g., a driveway approach), where should placement begin?

At the bottom (low end) of the slope (Correct answer)
In the center and work outward
At the top (high end) of the slope
At any point since slope doesn't matter

Correct answer: At the bottom (low end) of the slope

Placement begins at the low end of a slope so that fresh concrete is placed against already-placed concrete, preventing runoff and ensuring proper consolidation.

Question 49: When electrochemical chloride extraction (ECE) is used on reinforced concrete, the process:

Injects corrosion inhibitors through drilled holes
Drives chloride ions out of the concrete toward an external anode in an electrolyte (Correct answer)
Applies cathodic protection current permanently
Coats rebar with a sacrificial zinc anode

Correct answer: Drives chloride ions out of the concrete toward an external anode in an electrolyte

ECE uses an impressed electrical current to migrate chloride ions from the steel reinforcement toward a temporary external anode.

Question 50: Which chemical compound is primarily responsible for the color produced by integral iron oxide pigments in concrete?

Titanium dioxide
Iron oxide (Fe2O3 or Fe3O4) (Correct answer)
Carbon black
Calcium silicate hydrate

Correct answer: Iron oxide (Fe2O3 or Fe3O4)

Iron oxide pigments in red, yellow, brown, and black shades are the most common and stable colorants used in integrally colored concrete.

Question 51: What is the primary purpose of a release agent applied before stamping concrete?

To prevent stamps from sticking to the concrete surface (Correct answer)
To increase the compressive strength of the mix
To add air entrainment to the concrete
To accelerate curing of the slab

Correct answer: To prevent stamps from sticking to the concrete surface

Release agents create a barrier between the stamp tool and fresh concrete so the tool lifts cleanly without tearing the surface texture.

Question 52: When taking a concrete sample for cylinder fabrication from a truck, at what point in the discharge should the sample be taken?

After the entire load has been discharged
From the chute after adding water on site
From the very first portion discharged
After the first 10% and before the last 10% of the load is discharged (Correct answer)

Correct answer: After the first 10% and before the last 10% of the load is discharged

ASTM C172 requires sampling after discarding the first and last 10% of the load to obtain a representative sample.

ACI Concrete Finisher Certification

The ACI Concrete Finisher certification program validates the knowledge and skills of concrete finishers.

Questions

60 min

Time Limit

70%

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