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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.

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  1. According to ASTM C39, what is the required rate of load application during compressive strength testing of a concrete cylinder?

    Answer: 20 to 50 psi/s (0.14 to 0.34 MPa/s)

    ASTM C39 specifies a loading rate of 20 to 50 psi/s (0.14 to 0.34 MPa/s) during the final phase of loading; rates outside this range can produce inaccurate results.

  2. What is the maximum permissible departure from perpendicularity of the end surface of a concrete test cylinder when measured with a square?

    Answer: 0.5°

    ASTM C39 and C617 require that the ends of cylinders be perpendicular to the cylinder axis within 0.5°; non-perpendicular ends introduce eccentric loading and reduce measured strength.

  3. What is a Type B fracture pattern in a compressive strength test per ASTM C39, and is it considered acceptable?

    Answer: A well-formed cone with slight cracking through one base; it is an acceptable fracture pattern

    ASTM C39 Figure 2 defines Type B as a well-formed cone on one end with some vertical cracking toward the other end; it is a normal, acceptable fracture pattern indicating good end conditions.

  4. If a compressive strength test result falls below f'c by more than 500 psi, what condition must be checked first according to ACI 318?

    Answer: Whether the strength test is the average of at least two cylinders (or three for 4×8-inch cylinders) from the same sample

    ACI 318 defines a strength test as the average of cylinders from one sample; if averaging was not done correctly, that is the first thing to verify before escalating the investigation.

  5. Why must concrete test cylinders be stored in a standardized moist curing environment (73 ± 3°F / 23 ± 2°C) after the initial 24-hour field period?

    Answer: To simulate ideal hydration conditions and produce strength results that reflect the concrete's potential strength, not the field curing quality

    Standard laboratory curing conditions eliminate variability from field temperature and moisture, so all cylinders are tested under the same reference conditions, making results comparable and representative of the mix's potential.

  6. What is the maximum permitted length-to-diameter ratio (L/D) for a concrete test cylinder per ASTM C39?

    Answer: Between 1.8D and 2.2D (where D is diameter), with 2.0D being the standard

    ASTM C39 requires cylinders with a length-to-diameter ratio between 1.8 and 2.2; cylinders outside this range require strength correction factors.