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Concrete Strength Testing Procedures Flashcards

6 cards from real ACI Certification practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 6 Concrete Strength Testing Procedures flashcards as text

  1. 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.

  2. What does the coefficient of variation (COV) of compressive strength test results indicate about a concrete testing program?

    Answer: It measures the variability of test results relative to the mean; a lower COV indicates better mix consistency, materials control, and testing quality

    COV (standard deviation ÷ mean × 100%) quantifies relative variability; ACI 214R classifies COV below 10% as excellent control and above 20% as poor control for laboratory-mixed concrete.

  3. What is the standard curing condition and test age for compressive strength cylinders used to verify mix design acceptance?

    Answer: Standard moist curing at 73°F ± 3°F, tested at 28 days

    ACI 318 specifies acceptance testing at 28 days under standard moist curing (ASTM C31) as the standard reference for evaluating whether a concrete mix meets the specified f'c.

  4. When testing 4×8-inch cylinders instead of 6×12-inch cylinders, what does ACI 318 Section 26.12.2 require for defining a 'strength test'?

    Answer: A strength test must be the average of at least three 4×8-inch cylinders rather than the two required for 6×12-inch cylinders

    ACI 318 requires averaging at least three 4×8-inch cylinders per test to account for their higher inherent variability compared to 6×12-inch cylinders that require only two.

  5. What does it mean when a compressive strength test cylinder exhibits a 'columnar' fracture pattern (Type E per ASTM C39)?

    Answer: Vertical splitting through the full height of the cylinder, often indicating improper end preparation or very high-strength brittle concrete

    Columnar (Type E) fracture is characterized by vertical cracking from top to bottom, often associated with rough, non-planar ends that concentrate stress in columns, or with very high-strength, brittle mixes.

  6. How often must the calibration of a concrete compression testing machine be verified per ASTM E4?

    Answer: At least annually, or whenever the machine is relocated, repaired, or results appear erratic

    ASTM E4 requires compression machine calibration verification at least every 12 months, plus any time the machine is moved, repaired, or results deviate unexpectedly.