Mixed Deck — All ACI Certification Topics Flashcards

What does the fineness modulus (FM) of fine aggregate indicate?

Answer: An index of the overall coarseness or fineness of the aggregate

FM is computed by summing cumulative percentages retained on a specified series of sieves and dividing by 100; higher values denote coarser material.

Which ASTM standard is the practice for making and curing concrete test specimens in the field?

Answer: ASTM C31

ASTM C31 is the standard practice for making and curing concrete test specimens in the field; C192 covers laboratory fabrication.

Per ASTM C172, composite concrete samples shall NOT be taken from the first or last:

Answer: 10% of the load

ASTM C172 requires that the first and last 10% of each load be excluded from sampling because these portions may not represent the bulk of the concrete.

When striking off excess concrete from the top of a unit weight measure per ASTM C138, the preferred instrument is:

Answer: A flat plate or piece of plate glass

A flat plate or piece of plate glass is used in a sawing and rolling motion to create a smooth, level surface on the unit weight container.

An ACI Certified Field Testing Technician is performing a slump test (ASTM C143) on a sample of fresh concrete. The concrete slumps and falls away to one side. What is the correct action for the technician to take?

Answer: Disregard the test and immediately perform a retest on another portion of the same sample.

According to ASTM C143/C143M, if the concrete shears off or slips sideways, the test is considered invalid. The technician must disregard the result and conduct a new test on a different portion of the composite sample. If a similar result occurs on the retest, the concrete is likely not cohesive enough for the slump test to be applicable, and this should be noted in the report.

According to ACI 302.1R, what is the required F-number flatness rating for a 'superflat' floor used with guided vehicles in defined traffic lanes?

Answer: FF 100 / FL 50 (defined traffic area)

ACI 302.1R classifies superflat floors as requiring FF 100 / FL 50 in defined traffic areas; these floors are used in high-bay warehouses with wire-guided or rail-guided forklifts operating at speed.

What is the primary difference between ACI 301 'Specifications for Structural Concrete' and ACI 318 'Building Code Requirements for Structural Concrete'?

Answer: ACI 318 is a design code specifying structural requirements enforced through building codes; ACI 301 is a project specification document used to specify materials, proportioning, and construction quality requirements

ACI 318 is the design code (typically adopted by jurisdictions into law) governing structural concrete design; ACI 301 is a reference specification that project owners and engineers incorporate into contract documents to govern construction quality.

How does the addition of a polycarboxylate-based superplasticizer affect the air content of a mix that already contains an air-entraining admixture?

Answer: Some superplasticizers can significantly reduce entrained air content; the effect depends on the superplasticizer chemistry and requires air content to be checked after both admixtures are added

Certain polycarboxylate-based superplasticizers can destabilize the air void system, reducing measured air content or changing void size distribution, so air must be tested after adding all admixtures.

A technician is preparing to cast 6x12-inch concrete cylinders. The concrete has a slump of 3 inches. Which of the following consolidation procedures is correct?

Answer: Fill the mold in three equal layers, rodding each layer 25 times.

For 6x12-inch cylinders, ASTM C31/C31M requires the mold to be filled in three approximately equal layers. Each layer must be rodded 25 times, penetrating the underlying layer by about 1 inch.

Which ACI certification is specifically designed for concrete field testing technicians at the entry level?

Answer: ACI Concrete Field Testing Technician – Grade I

ACI Concrete Field Testing Technician – Grade I is the entry-level certification for technicians who perform standard field tests on fresh concrete, making it the first step for many concrete professionals.

What is the purpose of using neoprene pad systems (ASTM C1231) as an alternative to sulfur mortar capping for concrete cylinder testing?

Answer: To provide a reusable, faster, and safer method of end preparation that eliminates fumes and reduces lab preparation time, acceptable for concrete strengths up to 12,000 psi

Neoprene pad systems are reusable, eliminate the hazards of molten sulfur, and provide acceptable accuracy for concrete with f'c up to approximately 12,000 psi (83 MPa), per ASTM C1231.

Unbonded neoprene pad caps used as an alternative to sulfur mortar for compressive strength testing must conform to which ASTM standard?

Answer: ASTM C1231

ASTM C1231 governs the use of unbonded neoprene pads in retaining rings as an alternative to sulfur mortar caps for testing concrete cylinders.

What is the primary purpose of consolidating concrete using internal vibration during placement?

Answer: To remove entrapped air and ensure the concrete completely fills the form without voids

Internal vibration consolidates fresh concrete by reducing entrapped air voids and ensuring the concrete flows around reinforcement and form edges, resulting in denser, stronger hardened concrete.

Which of the following is the correct tamping procedure for filling a 0.5 ft³ unit weight measure when performing the test for Density (Unit Weight) of Concrete (ASTM C138)?

Answer: Fill in 3 equal layers, rodding each layer 50 times.

For a measure with a volume of 0.5 ft³, ASTM C138 requires the concrete to be placed in three approximately equal layers. Each layer must be rodded 50 times with the tamping rod, distributing the strokes evenly over the cross-section.

How does ACI certification typically affect compensation for concrete technicians?

Answer: Certified technicians generally earn higher wages due to demonstrated specialized knowledge

Industry surveys consistently show that ACI-certified technicians earn more than non-certified peers, as certification validates specialized skills that employers value and are willing to pay a premium for.

What is the recommended contraction joint spacing formula provided by ACI 302.1R for plain (unreinforced) slabs-on-grade?

Answer: Joint spacing in feet should not exceed 2 to 3 times the slab thickness in inches (e.g., a 4-inch slab: 8–12 ft spacing)

ACI 302.1R recommends joint spacing of 2–3 times the slab thickness in inches, expressed in feet; for a 4-inch slab this yields 8–12-foot joint panels.

According to ACI 305R, what is the maximum concrete temperature at point of discharge permitted without special hot-weather precautions?

Answer: 95°F (35°C)

ACI 305R recommends that concrete temperature at point of discharge not exceed 95°F (35°C); higher temperatures accelerate hydration, reduce workability, and can lead to strength loss.

What is the purpose of placing a vapor retarder directly beneath an interior concrete slab-on-grade?

Answer: To prevent moisture transmission from the subgrade through the slab into the building interior, protecting floor coverings and occupant comfort

A vapor retarder (e.g., 10-mil polyethylene film) limits moisture vapor transmission from soil beneath the slab, preventing moisture-related failures of adhesive-bonded flooring, hardwood, and carpet.

Per ASTM C1064, the minimum immersion depth for a concrete temperature-measuring device is:

Answer: 3 inches (75 mm)

ASTM C1064 requires the temperature device to be inserted to a minimum depth of 3 inches (75 mm) to ensure an accurate reading.

Supplementary cementitious materials (SCMs) such as fly ash are used in concrete mix design primarily to:

Answer: Replace a portion of portland cement while maintaining or improving properties

SCMs like fly ash partially replace portland cement, often improving workability and long-term durability while reducing heat of hydration and material cost.