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Question 1. Which organization publishes the standard ASTM C39 for compressive strength testing of concrete cylinders? A) ISO B) AASHTO C) ASTM International D) EN Answer: C Explanation: ASTM International is the body that develops and publishes ASTM C39, the standard test method for compressive strength of cylindrical concrete specimens. Question 2. The primary responsibility of a Strength Testing Technician includes which of the following? A) Designing concrete mixes B) Performing compressive strength tests and documenting results C) Operating concrete batching plants D) Inspecting structural foundations Answer: B Explanation: A Strength Testing Technician is tasked with preparing specimens, conducting strength tests, and accurately recording the data. Question 3. When wearing personal protective equipment (PPE) for concrete testing, which item is essential to protect against cement dust inhalation? A) Safety glasses B) Ear plugs C) Respirator or dust mask D) Steel-toe boots Answer: C
Explanation: Cement dust can cause respiratory irritation; a respirator or dust mask is required to protect the lungs. Question 4. In the SI system, compressive strength is most commonly expressed in which unit? A) psi B) MPa C) kN D) lb/ft² Answer: B Explanation: The International System of Units (SI) uses megapascals (MPa) for stress, including concrete compressive strength. Question 5. According to ASTM C192, what is the recommended temperature range for standard laboratory curing of concrete cylinders? A) 15 ± 2 °C B) 23 ± 2 °C C) 30 ± 5 °C D) 40 ± 3 °C Answer: B Explanation: ASTM C192 specifies a curing temperature of 23 °C ± 2 °C (73.5 °F ± 3.5 °F) for standard laboratory conditions. Question 6. Which material is NOT acceptable for making a concrete cylinder mold? A) Steel B) Plastic C) Waxed cardboard
D) When specimen ends are perfectly smooth Answer: B Explanation: Unbonded pads allow immediate testing because they do not require curing time like bonded caps. Question 10. The ASTM E4 standard applies to: A) Calibration of load cells in compression testing machines B) Sampling procedures for concrete batches C) Procedures for curing concrete in the field D) Determining flexural strength of beams Answer: A Explanation: ASTM E4 outlines the verification and calibration procedures for testing machines, including load cells. Question 11. During specimen molding per ASTM C192, the concrete should be placed in the mold in how many layers? A) One continuous pour B) Two layers, each compacted C) Three layers, each compacted D) Four layers, each compacted Answer: C Explanation: ASTM C192 specifies filling the mold in three equal layers, each compacted by rodding or vibration. Question 12. The purpose of “striking off” the top surface of a concrete cylinder after molding is to: A) Increase the specimen’s length
B) Ensure a smooth, level surface for capping C) Remove excess water from the surface D) Embed steel reinforcement Answer: B Explanation: Striking off creates a flat, even top surface that facilitates accurate capping and load application. Question 13. In field specimen preparation (ASTM C31), why is it important to protect freshly molded cylinders from direct sunlight? A) Sunlight can cause rapid cooling, leading to cracks B) Sunlight raises temperature, potentially affecting strength development C) Sunlight causes carbonation of concrete surface D) Sunlight dehydrates the specimen causing mass loss Answer: B Explanation: Direct sunlight can increase the specimen temperature, accelerating curing and potentially leading to non‑representative strength values. Question 14. Which of the following moisture conditions is required for standard laboratory curing? A) 50 % relative humidity B) 75 % relative humidity C) 100 % relative humidity (continuous moisture) D) Dry environment with periodic watering Answer: C Explanation: ASTM C31/C192 require continuous moisture, typically achieved by storing specimens in a water bath or moist room with 100 % relative humidity.
Explanation: ASTM C39 specifies a loading rate of 0.1 MPa per second (approximately 1.45 psi/s) to ensure uniform stress distribution. Question 18. In compression testing, the “maximum load” recorded is: A) The load at which the specimen first shows any cracking B) The load at which the machine reaches its capacity C) The highest load sustained before a sudden drop in load D) The average load over the entire test duration Answer: C Explanation: The maximum load is the peak load the specimen carries before failure, indicated by a sudden load drop. Question 19. A conical fracture pattern in a concrete cylinder indicates: A) Improper alignment of the specimen B) Correct testing conditions and valid results C) Excessive loading rate D) Inadequate capping thickness Answer: B Explanation: A conical fracture is typical for a properly tested concrete cylinder, confirming valid test conditions. Question 20. To calculate compressive strength (f'c), which formula is used? A) f'c = P × A B) f'c = P ÷ A C) f'c = A ÷ P D) f'c = √(P × A) Answer: B
Explanation: Compressive strength equals the maximum load (P) divided by the cross‑sectional area (A). Question 21. When reporting compressive strength, values are rounded to the nearest: A) 1 psi (0.01 MPa) B) 5 psi (0.03 MPa) C) 10 psi (0.1 MPa) D) 100 psi (1 MPa) Answer: C Explanation: ASTM C39 requires rounding the reported strength to the nearest 10 psi (0.1 MPa). Question 22. Which of the following is NOT a required item in the final test report for a concrete cylinder? A) Specimen identification number B) Ambient temperature during testing C) Maximum load recorded D) Type of fracture observed Answer: B Explanation: While ambient temperature may be noted, it is not a mandatory item in the ASTM C39 report; the other items are required. Question 23. The purpose of a lower bearing block in a compression testing machine is to: A) Apply the load to the specimen B) Support the specimen and allow uniform load distribution C) Measure the specimen’s mass D) Record the fracture pattern Answer: B
Answer: B Explanation: ASTM C617 requires a minimum of 2 hours for sulfur mortar to cure before the specimen can be tested. Question 27. Which of the following statements about gypsum (neat cement paste) caps is correct? A) They can be used for specimens with strength > 8,000 psi B) They require a minimum thickness of 0.75 in (19 mm) C) They must be allowed to cure for at least 4 hours before testing D) They are reusable on multiple specimens without re‑mixing Answer: C Explanation: Gypsum caps need at least 4 hours of curing before the test to achieve sufficient strength. Question 28. The ASTM C1231 standard covers which testing method? A) Compression testing of concrete cylinders with bonded caps B) Use of unbonded elastomeric pads for compression testing C) Flexural testing of concrete beams D) Determination of tensile strength by splitting test Answer: B Explanation: ASTM C1231 describes the use of unbonded elastomeric pads (unbonded caps) for compressive strength testing. Question 29. Which condition would make the use of unbonded caps (ASTM C1231) inappropriate? A) Specimen strength less than 5,000 psi B) Specimen strength greater than 8,000 psi
C) Testing at 7 days age D) Curing in a moist room Answer: B Explanation: Unbonded caps are limited to specimens with compressive strength up to about 8,000 psi; beyond that, bonded caps are required. Question 30. When performing a flexural strength test (ASTM C78), the load is applied at which points on the beam? A) Center point only B) Two points, one-third from each support (third‑point loading) C) Four equally spaced points D) At the supports only Answer: B Explanation: ASTM C78 uses third‑point loading, where the load is applied at points one‑third the span length from each support. Question 31. In a flexural test, the Modulus of Rupture (MOR) is calculated using which of the following parameters? A) Maximum load, beam span, and cross‑sectional dimensions B) Maximum load and specimen mass only C) Load rate and specimen temperature D) Curing time and humidity Answer: A Explanation: MOR is derived from the maximum load, the span length between supports, and the beam’s cross‑sectional dimensions. Question 32. Which of the following is a recommended practice for ensuring the specimen is centered on the lower bearing block?
Question 35. Which of the following is a primary advantage of using a moist room for curing over a water bath? A) Faster strength gain B) Reduced risk of specimen surface scaling C) Lower energy consumption D) Ability to cure larger specimens simultaneously Answer: D Explanation: A moist room can accommodate many specimens at once, whereas a water bath is limited by tank size. Question 36. In a compression test, “stress rate” refers to: A) The rate at which the specimen’s temperature changes B) The rate of increase of load per unit time C) The rate of change of specimen length during loading D) The rate of moisture loss from the specimen Answer: B Explanation: Stress rate (or loading rate) is the speed at which load is applied, expressed as load per unit time. Question 37. Which of the following is NOT a typical defect to be noted on a concrete cylinder test report? A) Hairline surface cracks before testing B) Misalignment on the bearing block C) Slight deviation in cylinder length after testing D) Color of the concrete mix Answer: D
Explanation: The color of the concrete mix is not a defect affecting test validity; the other items are relevant observations. Question 38. The term “moist cure” in concrete testing means: A) Curing specimens in a dry oven at 60 °C B) Maintaining 100 % relative humidity around the specimen C) Spraying the specimen with water every hour D) Covering specimens with plastic film only for 24 hours Answer: B Explanation: Moist cure requires continuous exposure to saturated humidity, typically 100 % RH. Question 39. Which of the following best describes the purpose of “retaining rings” in the ASTM C1231 unbonded cap system? A) To hold the elastomeric pad in place during testing B) To increase the load capacity of the testing machine C) To measure the specimen’s diameter accurately D) To act as a secondary bearing surface Answer: A Explanation: Retaining rings secure the elastomeric pad to the cylinder ends, preventing movement during compression. Question 40. The hardness of elastomeric pads used in unbonded caps is typically measured in: A) Shore A durometer B) Rockwell B scale C) Brinell hardness number D) Vickers hardness
A) Reduce friction between the block and specimen B) Allow for minor misalignment without inducing eccentric loading C) Increase the load capacity of the machine D) Provide a visual indicator of load application Answer: B Explanation: The spherical seat accommodates slight angular misalignments, ensuring the load remains centered. Question 44. In the context of concrete strength testing, “age” of a specimen refers to: A) The time since the concrete was mixed until the moment of testing B) The number of days the specimen has been stored in the lab after molding C) The calendar date on which the specimen was cast D) The time the specimen spent in the curing tank Answer: A Explanation: “Age” is defined as the elapsed time from mixing (or casting) to the point of testing, commonly expressed in days (e.g., 7‑day, 28‑day). Question 45. Which of the following is a permissible method for initial curing of concrete cylinders in the laboratory? A) Placing them in a refrigerator at 5 °C B) Covering them with a plastic sheet and storing at 23 °C ± 2 °C C) Leaving them exposed on the bench for 24 hours D) Immersing them in a saline solution Answer: B Explanation: Covering with a plastic sheet maintains moisture while the controlled temperature provides standard curing conditions.
Question 46. When measuring the length of a concrete cylinder for reporting, the measurement should be taken: A) From the top of the cap to the bottom of the cap after testing B) From the face of the cylinder to the opposite face, excluding caps C) Including the cap thickness in the total length D) Using a laser scanner for precise geometry Answer: B Explanation: ASTM C39 requires measuring the specimen length excluding any caps, from the exposed concrete faces. Question 47. The term “dead‑weight” in machine verification refers to: A) The weight of the testing machine itself B) Calibrated masses used to apply known loads to the load cell C) The weight of the specimen during testing D) A safety device that stops the machine if overload occurs Answer: B Explanation: Dead‑weight sets consist of known masses that generate precise loads for calibrating the load cell. Question 48. Which of the following is a common cause of “splitting” failure in concrete cylinders during compression testing? A) Incorrect bearing block material B) Excessive loading rate C) Misalignment causing eccentric loading D) Using too thin a cap Answer: C
D) Moist curing is only used for high‑strength concrete. Answer: A Explanation: Moist curing maintains hydration, leading to higher early‑age strength compared to dry curing. Question 52. The ASTM C192 standard specifies the minimum number of specimens that should be cast for a typical 28‑day strength test batch. A) 1 B) 3 C) 5 D) 10 Answer: C Explanation: ASTM C192 recommends casting at least five specimens for a given batch to provide a reliable average strength. Question 53. When preparing a concrete mix for laboratory testing, the water‑to‑cement ratio is most directly related to: A) The workability of the mix only B) The ultimate compressive strength of the hardened concrete C) The color of the concrete D) The size of aggregates that can be used Answer: B Explanation: The water‑to‑cement ratio strongly influences the final compressive strength; lower ratios generally yield higher strength. Question 54. A specimen that shows a “columnar” fracture pattern after compression testing likely indicates: A) Over‑capped specimen
B) Improper loading rate (too fast) C) Correct testing procedure and valid result D) Inadequate curing temperature Answer: C Explanation: A columnar fracture is typical for a correctly tested cylinder and signifies a valid result. Question 55. Which of the following is a recommended practice for extending the life of elastomeric pads used in unbonded caps? A) Re‑use the same pad on multiple specimens without inspection B) Replace pads after each test regardless of condition C) Inspect pads for cuts or wear and replace only when damaged D) Soak pads in water before each use Answer: C Explanation: Pads should be inspected for damage; only damaged pads need replacement, extending their service life. Question 56. The term “cross‑sectional area” for a cylindrical specimen is calculated using which geometric formula? A) π × (diameter)² B) π × (diameter ÷ 2)² C) (π ÷ 4) × (diameter)² D) (π ÷ 2) × (diameter)² Answer: C Explanation: The area of a circle is (π ÷ 4) × (diameter)², which is used for cylinder cross‑section.
