Free ACI Field Testing Technician Questions and Answers 1 — Questions and Answers
Question 1: The concrete sample that will be used for the slump test needs to be obtained in compliance with ASTM Standard _____.
- 0.75 in. [19 mm], 1.50 in. [38 mm]
- C172, Standard Practice for Sampling Freshly Mixed Concrete (Correct answer)
- Removed by wet sieving the sample over 1.5 in. [37.5 mm] sieve
- 2 5/8 in. [70 mm], 6 1/8 in. [160 mm]
Correct answer: C172, Standard Practice for Sampling Freshly Mixed Concrete
The concrete sample for a slump test must be obtained in compliance with ASTM Standard C172, Standard Practice for Sampling Freshly Mixed Concrete. Adhering to this standard ensures that the sample is representative of the concrete batch, which is critical for accurate and reliable test results. Proper sampling prevents misleading data that could lead to incorrect assessments of concrete quality.
Question 2: Before starting any tests on a composite sample, certain portions of the sample must be fully blended. Is it True or False?
- TRUE (Correct answer)
- FALSE
Correct answer: TRUE
TRUE. Before starting any tests on a composite concrete sample, certain portions of the sample must be fully blended. This ensures that the sample is homogeneous and representative of the entire batch of concrete, providing accurate and consistent test results. Proper blending prevents segregation of aggregates and ensures uniformity.
Question 3: Use one stroke for every _____ of top surface area when rodding a flexural strength test specimen.
- 1 in. [25 mm]
- 1/8 in. [3 mm]
- 6 in. [150 mm]
- 2 in.^2 [14 cm^2] (Correct answer)
Correct answer: 2 in.^2 [14 cm^2]
When rodding a flexural strength test specimen, you should use one stroke for every 2 in.^2 [14 cm^2] of top surface area. This specific rodding frequency, as outlined in ASTM standards, ensures uniform compaction of the concrete within the mold. Proper compaction is essential for producing a consistent and representative specimen, which is critical for accurate flexural strength testing.
Question 4: Every layer ought to occupy around _____ of the mold's volume.
- One-fourth
- One-third (Correct answer)
- One-half
- 3 Equal
Correct answer: One-third
Every layer of concrete ought to occupy approximately one-third of the mold's volume when preparing test specimens. This standardized layering technique, combined with proper rodding or vibration, ensures uniform compaction throughout the specimen. Filling the mold in equal layers helps eliminate voids and segregation, leading to consistent and reliable test results for concrete properties.
Question 5: Which consolidation technique needs to be applied when the slump is less than one inch? (25 mm)?
- Vibration (Correct answer)
- 9000 Vibrations Per Minute [150 Hz]
- Rodding
- Rapid Evaporation
Correct answer: Vibration
When the concrete slump is less than one inch (25 mm), indicating a very stiff mix, vibration is the necessary consolidation technique. Rodding alone is insufficient to remove entrapped air and achieve proper density in such low-slump concrete. Vibration effectively mobilizes the stiff concrete, allowing it to settle and fill the mold completely, ensuring a dense and void-free specimen.
Question 6: How far into each layer should the tamping rod be inserted?
- Flat, straight steel bar at least 1/8 by 3/4 by 12 in. [3 by 20 by 300 mm] or a 4.4 flat, straight high-density polyethylene bar, or other plastic of equal or greater abrasion resistance, at least 1/4 by 3/4 by 23 in [6 by 30 by 300 mm].
- Round, straight steel rod, with a 16 mm [5/8 in.] +- 2 mm [1/16 in.] diameter, length at least 100 mm [4 in.] greater than the depth of the measuring bowl, but not greater than 600 mm [24 in.] in overall length, with the tamping end rounded to a hemispherical tip of the same diameter as the rod.
- No more than five seconds at a time, but must be repeated for a minimum of 45 seconds to free concrete from the base
- Rod each layer throughout its depth; on the second and final layers, the rod should penetrate into the previous layer approximately 1 in. [25 mm] (Correct answer)
Correct answer: Rod each layer throughout its depth; on the second and final layers, the rod should penetrate into the previous layer approximately 1 in. [25 mm]
When consolidating concrete specimens with a tamping rod, each layer must be rodded throughout its entire depth. For the second and subsequent layers, the rod should penetrate approximately 1 inch (25 mm) into the previous layer. This overlap ensures proper intermixing and bonding between layers, eliminating potential planes of weakness and achieving uniform consolidation throughout the specimen.
Question 7: Should vibration be used to solidify the concrete, a typical 4 by 8 in. It is necessary to fill the [100 mm by 200 mm] cylinder mold in _____ equal layers.
- C172
- Wet sieved over a 1 1/2 in. (37.5 mm) sieve
- 2 (Correct answer)
- Wet sieved over a 1-in. (25-mm) sieve
Correct answer: 2
When consolidating a 4 by 8 inch (100 mm by 200 mm) concrete cylinder mold using vibration, it should be filled in two equal layers. Vibration is a more efficient method of consolidation compared to rodding, allowing for larger layer thicknesses to be properly compacted. This ensures that the concrete is adequately consolidated to remove entrapped air and achieve the required density for strength testing.
Question 8: Field-cured cylinders are kept __________ and safeguarded __________.
- False, if the air content is more than 9%, the number of calibrated cups of water introduced into the meter to bring the liquid level within the graduated range must be added
- Rod each layer throughout its depth; on the second and final layers, the rod should penetrate into the previous layer approximately 1 in. [25 mm]
- Acceptance testing for specified strength, checking the adequacy of mixture proportions for strength, quality control
- In or on the structure as near to the point of deposit of the concrete represented as possible; In as near as possible the same way as the formed work (Correct answer)
Correct answer: In or on the structure as near to the point of deposit of the concrete represented as possible; In as near as possible the same way as the formed work
Field-cured cylinders are designed to represent the strength development of concrete under actual job-site conditions. Therefore, they must be stored in or on the structure as close as possible to where the concrete was placed. This ensures the cylinders experience similar temperature and moisture conditions as the in-place concrete, providing a realistic assessment of its strength in the structure.
Question 9: After the last layer has been firmed up, what should be done if there is an excessive amount of concrete in the measurement?
- C172, Standard Practice for Sampling Freshly Mixed Concrete
- Add additional concrete to keep an excess of concrete above the top of the mold at all times
- Remove a representative quantity of concrete with the scoop or trowel before the strike off (Correct answer)
- Lightweight, air-cooled blast furnace slag, or aggregates of high porosity
Correct answer: Remove a representative quantity of concrete with the scoop or trowel before the strike off
If there is an excessive amount of concrete in the mold after the last layer has been consolidated, a representative quantity should be removed with a scoop or trowel before striking off the top surface. This ensures that the mold contains the correct volume of concrete for accurate density measurements and allows for a clean, level strike-off. Adding more concrete would only be necessary if there was insufficient concrete after consolidation.
Question 10: What is the measuring bowl's minimum permitted volume that this test procedure uses?
- 28 l (1ft^3)
- 50 Mm (2 in.)
- 1/2 In. [12 mm]
- 6 L (0.20 ft^3) (Correct answer)
Correct answer: 6 L (0.20 ft^3)
The minimum permitted volume for the measuring bowl used in this test procedure (likely referring to ASTM C138 for density, yield, and air content) is 6 L (0.20 ft^3). This specific volume is required to ensure a representative sample size for accurate determination of the concrete's properties. Using a smaller volume might lead to less reliable test results.
Question 11: What form does the rod's tamping end need to take?
- A pointed tip
- A flat plane
- Rounded to a hemispherical tip (Correct answer)
- The frustum of a cone
Correct answer: Rounded to a hemispherical tip
The tamping end of the rod used for consolidating concrete specimens must be rounded to a hemispherical tip. This specific shape ensures uniform consolidation without puncturing or excessively disturbing the concrete. A hemispherical tip helps to evenly distribute the tamping force, effectively removing entrapped air and preventing localized stress concentrations that could affect the specimen's integrity.
Free ACI Field Testing Technician Questions and Answers 1
The concrete sample that will be used for the slump test needs to be obtained in compliance with ASTM Standard _____.