Free General Contractor License Site Work and Concrete Questions and Answers — Questions and Answers
Question 1: A competent person inspects an excavation and classifies the soil as Type C. According to OSHA standards for excavations 20 feet or less in depth, what is the maximum allowable simple slope?
- 3/4 horizontal to 1 vertical (3/4:1)
- 1 horizontal to 1 vertical (1:1)
- 1 ½ horizontal to 1 vertical (1½:1) (Correct answer)
- Vertical (90 degrees)
Correct answer: 1 ½ horizontal to 1 vertical (1½:1)
OSHA's Subpart P specifies the maximum allowable slopes for excavations less than 20 feet deep. For Type C soil, which is the least stable classification (includes granular soils, submerged soil, or soil with freely seeping water), the required slope is 1½ horizontal to 1 vertical (1½:1), which corresponds to a 34-degree angle.
Question 2: During a concrete slump test (ASTM C143), the fresh concrete is placed into the cone in three equal layers by volume. How many times should each layer be rodded?
- 10 times
- 25 times (Correct answer)
- 30 times
- 15 times
Correct answer: 25 times
The standard procedure for the ASTM C143 slump test requires that each of the three layers of concrete placed in the slump cone be rodded exactly 25 times. This ensures uniform compaction of the sample to get an accurate measure of the concrete's consistency and workability.
Question 3: A contractor is preparing to place a 6-inch thick concrete slab on grade. To ensure the rebar provides the intended tensile strength and is protected from corrosion, it must be positioned correctly within the slab. What is the primary purpose of using rebar chairs or bolsters during this process?
- To electrically ground the rebar grid.
- To help the concrete cure more evenly.
- To tie intersecting rebar pieces together.
- To maintain the proper concrete cover over the reinforcement. (Correct answer)
Correct answer: To maintain the proper concrete cover over the reinforcement.
Rebar chairs, bolsters, or other supports are used to hold the reinforcing steel at the correct height within the formwork before and during the concrete pour. This ensures that the specified amount of concrete cover (the distance from the steel to the surface) is maintained, which is critical for protecting the rebar from corrosion and for the structural integrity of the slab.
Question 4: Which of the following best describes the primary goal of concrete curing?
- To accelerate the drying of the concrete surface.
- To maintain satisfactory moisture and temperature conditions. (Correct answer)
- To remove excess water from the concrete mix.
- To increase the surface hardness for better wear resistance.
Correct answer: To maintain satisfactory moisture and temperature conditions.
Curing is the process of maintaining adequate moisture and temperature in freshly placed concrete for a period of time to allow for proper cement hydration. This process is critical for the concrete to achieve its designed strength, durability, and other potential properties. It is not about drying the concrete, but rather controlling the rate of moisture loss.
Question 5: A laboratory soil analysis, known as a Proctor test (ASTM D698), is performed on a soil sample from a job site. What is the primary purpose of this test?
- To determine the soil's permeability and water drainage characteristics.
- To identify the unconfined compressive strength for excavation sloping.
- To establish the optimal moisture content for maximum compaction. (Correct answer)
- To classify the soil's organic and mineral content.
Correct answer: To establish the optimal moisture content for maximum compaction.
The Proctor compaction test is a laboratory method used to determine the optimal moisture content at which a specific soil type will achieve its maximum dry density (compaction). This information is crucial for site work to ensure that fills and subgrades are properly compacted for stability.
Question 6: During a slump test, the concrete subsides, but one side shears off and falls away from the main mass of the concrete. According to ASTM C143, what should be done?
- Measure the slump at the highest remaining point.
- Average the height of the sheared portion and the main portion.
- Record the result as a 'shear slump' and accept the concrete.
- Disregard the test and perform another test on a new sample. (Correct answer)
Correct answer: Disregard the test and perform another test on a new sample.
If a concrete sample exhibits a 'shear slump,' where a portion of the concrete shears away, the test result is not considered valid. The ASTM C143 standard requires that the test be disregarded and a new test must be performed on a different portion of the concrete sample. If a second test also results in a shear slump, the concrete may lack the necessary cohesion for the test to be applicable.
Free General Contractor License Site Work and Concrete Questions and Answers
A competent person inspects an excavation and classifies the soil as Type C.
According to OSHA standards for excavations 20 feet or less in depth, what is the maximum allowable simple slope?