Description
Sample Questions
Question 1. A contractor is ordering ready-mix concrete for a 30-foot by 48-foot garage slab that will be placed 4 inches thick. The subgrade is slightly irregular, so the estimator adds 10 percent to cover spillage and thickness variation. Concrete is sold by the cubic yard. How much concrete should the contractor order?
A. 17.8 cubic yards
B. 18.7 cubic yards
C. 19.6 cubic yards
D. 21.3 cubic yards
Correct Answer: C. 19.6 cubic yards
Answer Explanation:
Start by converting every dimension to feet: 30 × 48 × (4 ÷ 12) equals 480 cubic feet. Concrete is purchased by the cubic yard, and one cubic yard contains 27 cubic feet, so 480 ÷ 27 equals about 17.78 cubic yards. The stated 10 percent allowance covers subgrade variation, spillage, and chute or pump losses: 17.78 × 1.10 equals 19.56, which rounds to 19.6 cubic yards. Ordering only the theoretical volume leaves no margin, and a short load can force a cold joint or a second delivery from a different batch. The waste factor should reflect site conditions, so a rough or over-excavated subgrade may justify an even larger allowance.
Why the Other Options Are Incorrect:
A. 17.8 cubic yards — Incorrect. This is the theoretical volume with no waste allowance, so the pour would likely run short.
B. 18.7 cubic yards — Incorrect. This applies only a 5 percent allowance, which does not match the 10 percent stated in the problem.
D. 21.3 cubic yards — Incorrect. This applies a 20 percent allowance, which overstates the order and wastes material and money.
Quick Study Guide:
Concrete volume starts with consistent units. Convert thickness from inches to feet, multiply length, width, and depth for cubic feet, then divide by 27 for cubic yards. Apply the waste allowance last. Order slightly more rather than less, because a short load forces a cold joint or a second delivery. Recheck thickness at edges and thickened areas.
Question 2. A ready-mix truck arrives at a commercial slab placement with a specified slump of 4 inches. The jobsite test measures 2 inches, and the finishing crew asks the driver to add water until the concrete reaches about 7 inches. The approved mix design lists a maximum water-cementitious materials ratio. What is the correct response?
A. Add water until the slump reaches 7 inches, since extra water only improves workability.
B. Add cement at the chute to offset the extra water and keep the strength the same.
C. Reject the load automatically because any slump below the specified value is unacceptable.
D. Use an approved water-reducing admixture or any water adjustment the mix design allows, mix thoroughly, and retest the slump.
Correct Answer: D. Use an approved water-reducing admixture or any water adjustment the mix design allows, mix thoroughly, and retest the slump.
Answer Explanation:
Slump measures workability, but the water-cementitious materials ratio controls strength, permeability, and shrinkage. Adding water without limit raises that ratio, lowering compressive strength and durability and increasing shrinkage cracking. When extra workability is needed, a water-reducing or high-range water-reducing admixture can raise slump without changing the ratio, provided the dosage fits the approved submittal. Limited water may be added at the site only if the mix design and delivery ticket allow it, and the drum must then be mixed for the required revolutions before a retest. Any adjustment should be documented. Placing out-of-spec concrete and hoping for acceptable results is a quality-control failure.
Why the Other Options Are Incorrect:
A. Add water until the slump reaches 7 inches — Incorrect. Extra water beyond the approved maximum weakens the concrete and increases shrinkage, even though it feels easier to place.
B. Add cement at the chute — Incorrect. Jobsite cement additions change the approved mix without batching control and do not reliably restore the ratio.
C. Reject the load automatically — Incorrect. A low slump can often be corrected within the mix design limits, so rejection is not automatic.
Quick Study Guide:
Water added at the jobsite raises the water-cementitious materials ratio, which lowers strength and durability and increases shrinkage. When workability is needed, use an approved water-reducing admixture or an adjustment the mix design allows. Retest slump after mixing, document any changes on the delivery ticket, and never exceed the approved maximum water for the mix.
Question 3. A crew is placing an exterior slab in Phoenix in July. Air temperature is 105°F, relative humidity is 15 percent, wind is blowing at 15 miles per hour, and the concrete temperature is 95°F. The finishers report that the surface is drying faster than bleed water can rise. Which action best reduces the risk of plastic shrinkage cracking?
A. Sprinkle water on the surface during finishing to keep the paste workable.
B. Install windbreaks and sunshades, apply an evaporation retarder after screeding, and begin curing as soon as finishing allows.
C. Delay all curing for 24 hours so the slab can reach initial set on its own.
D. Finish the surface while bleed water is still present to seal in moisture.
Correct Answer: B. Install windbreaks and sunshades, apply an evaporation retarder after screeding, and begin curing as soon as finishing allows.
Answer Explanation:
Plastic shrinkage cracks form when moisture leaves the surface faster than bleed water replaces it. Heat, low humidity, wind, and warm concrete all raise the evaporation rate, and the conditions described are well past the level where precautions are needed. Windbreaks and sunshades cut wind speed and surface temperature at the source. A film-forming evaporation retarder applied after screeding slows moisture loss between finishing passes, and prompt curing with wet coverings or a curing compound keeps the surface from drying out. The crew should also monitor air and concrete temperature, humidity, and wind speed during the pour, and plan the placement for cooler hours when possible. Preventing the problem is far cheaper than repairing cracked slabs.
Why the Other Options Are Incorrect:
A. Sprinkle water on the surface during finishing — Incorrect. Adding water to the surface raises the local water ratio and can cause a weak, dusty, or scaling surface.
C. Delay all curing for 24 hours — Incorrect. Waiting leaves the slab exposed during the highest-risk period, which invites cracking.
D. Finish while bleed water is still present — Incorrect. Troweling bleed water into the surface creates a weak layer that can scale or craze.
Quick Study Guide:
Hot, dry, windy weather can evaporate surface moisture faster than bleed water rises, producing plastic shrinkage cracks. Reduce evaporation with windbreaks, sunshades, evaporation retarder, and prompt curing. Never sprinkle water into the surface or finish over bleed water. Monitor concrete and air temperature, humidity, and wind speed before and during the placement.
Question 4. On a commercial footing job, vertical reinforcing dowels extend 18 inches above the concrete along a path where workers will carry forms and walk during the next phase. The foreman proposes to paint the bar tips bright orange and make sure everyone wears steel-toe boots. What should the contractor do?
A. Guard the exposed bars with caps, troughs, or similar protection, or bend them to remove the impalement hazard.
B. Accept the plan because high-visibility paint adequately warns workers of the hazard.
C. Accept the plan because steel-toe boots protect against reinforcing steel injuries.
D. Provide protection only if the bars extend more than 6 feet above the work surface.
Correct Answer: A. Guard the exposed bars with caps, troughs, or similar protection, or bend them to remove the impalement hazard.
Answer Explanation:
Federal construction standards for concrete work require protruding reinforcing steel to be guarded wherever workers could fall onto it, so the impalement hazard is eliminated. The requirement does not depend on a height threshold, so short dowels at ground level still qualify because a trip, stumble, or fall onto the bars can cause serious injury. Acceptable methods include rebar caps, troughs, guard systems, or bending the bars where the design allows. Paint increases visibility but provides no physical protection, and footwear cannot stop a bar from penetrating the body. Arizona enforces comparable requirements through its state occupational safety program. The contractor should inspect protection throughout the shift, because caps that get knocked off or removed defeat the purpose.
Why the Other Options Are Incorrect:
B. Accept the plan because high-visibility paint adequately warns workers — Incorrect. Paint is only a warning and does not physically prevent impalement.
C. Accept the plan because steel-toe boots protect against reinforcing steel injuries — Incorrect. Boots protect the feet from crushing and do not guard against a fall onto vertical bars.
D. Provide protection only if the bars extend more than 6 feet above the work surface — Incorrect. The hazard applies wherever workers could fall onto the bars, regardless of height.
Quick Study Guide:
Exposed reinforcing steel is an impalement hazard wherever workers could fall onto it, regardless of height. Use rebar caps, troughs, guards, or bend the bars to remove the hazard. Colored paint and boots do not count as protection. Inspect protection during the shift, because bumped or removed caps defeat it.
Question 5. A contractor is building a spread footing in an excavated trench. The footing will be cast directly against undisturbed soil, with no side forms and no mud slab, and it is reinforced with No. 6 bars. Under ACI 318, what minimum concrete cover is required for the reinforcement?
A. 1-1/2 inches
B. 2 inches
C. 3 inches
D. 4 inches
Correct Answer: C. 3 inches
Answer Explanation:
Concrete cast directly against soil and permanently in contact with it requires 3 inches of cover, regardless of bar size. The rough excavated surface, moisture, and soil chemicals expose the steel to corrosion, and the section may include irregular overbreak. Cover is measured from the concrete surface to the nearest surface of the reinforcement. Footings formed on all sides and exposed to ground or weather use smaller values: 2 inches for No. 6 bars and larger, and 1-1/2 inches for No. 5 and smaller. Because this footing is cast against earth with no forms, the larger 3-inch value governs. The crew should use proper bar supports to hold the cage off the soil, and the contractor should confirm the code edition adopted for the project.
Why the Other Options Are Incorrect:
A. 1-1/2 inches — Incorrect. This applies to No. 5 and smaller bars that are formed and exposed to ground or weather, not to concrete cast against earth.
B. 2 inches — Incorrect. This is the formed value for No. 6 and larger bars, which does not apply when concrete is placed directly against soil.
D. 4 inches — Incorrect. This is not a code value for this condition and would waste concrete and reduce effective depth.
Quick Study Guide:
Cover protects reinforcing steel from corrosion and fire and keeps it bonded to the concrete. Memorize the ground-contact values: 3 inches when cast against earth, and 2 inches or 1-1/2 inches when formed, depending on bar size. Use chairs and bolsters to hold the steel in position, and check cover before the pour.
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