CSLB C-8 Concrete (Trade Exam) — All Questions
17 questions
Concrete must drop 12 ft into a column form on a Caltrans-type job. What is needed?
- a.Nothing; 12 ft is allowed
- b.A drop chute✓
- c.A wetter mix so it flows
- d.A bucket dumped all at once
Caltrans limits free fall to 8 ft and says to minimize it; drop chutes control the height of fall and reduce segregation. A wetter mix weakens the concrete.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
Where should placement begin on a large slab-on-ground?
- a.Wherever the truck parks
- b.At several spots at once
- c.Perimeter, at one end✓
- d.In the center, working out
Caltrans describes starting along the perimeter at one end, with each batch discharged against previously placed concrete, which avoids pushing stone ahead of the mortar.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
How thick should lifts be for mass concrete, per Caltrans guidance?
- a.About 3 to 5 inches
- b.About 3 to 4 feet
- c.About 15 to 20 inches✓
- d.The full height at once
Caltrans suggests lifts of about 15 to 20 inches for mass concrete and 6 to 20 inches for reinforced members, each consolidated before the next.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
When should an internal vibrator be withdrawn from the concrete?
- a.When paste nears the head's top✓
- b.When bubbles stop entirely
- c.After exactly one minute
- d.As soon as it touches the bottom
Caltrans says paste accumulates around the vibrator, usually in 5 to 15 seconds, and when it appears near the top of the head the vibrator is withdrawn at about the rate it descended.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
Compared with a high-slump mix, how much vibration does a low-slump mix need?
- a.More vibration✓
- b.No vibration
- c.Only external vibration
- d.Less vibration
Caltrans states that to get the same consolidation, low-slump concrete requires more vibration than concrete with a higher slump.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
Concrete is placed around epoxy-coated reinforcement. What kind of vibrator head is required?
- a.A rubber- or plastic-coated one✓
- b.A bare steel head only
- c.No vibrator may be used
- d.An oversized steel head
Where epoxy-coated rebar is used, vibrators must be coated with plastic or hard rubber to avoid damaging the coating.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
Before new concrete is placed against a hardened construction joint, what must be removed?
- a.The reinforcing steel
- b.Laitance and loose material✓
- c.Every trace of moisture
- d.All surface texture
Caltrans requires construction joint surfaces to be abrasive-blast cleaned to remove laitance and other materials that hinder bond; a roughened surface improves it.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
Ice replaces part of the mixing water on a hot day. What must be true before the truck discharges?
- a.All the ice has melted and mixed.✓
- b.The ice was added at the site.
- c.Half the ice has melted.
- d.The ice is still visible.
Caltrans requires any ice to be completely melted and mixed before the mixer discharges; unmelted ice leaves water pockets.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
Hot water is used in cold weather. Why should it not hit the cement directly?
- a.It lowers the air content.
- b.It stops the cement hydrating.
- c.Flash set or cement balls✓
- d.It cools the aggregate.
Direct contact of hot water and cement may cause premature (flash) set or cement balls, so water and most of the aggregate go in before the cement.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
What does bull floating do right after screeding?
- a.Cuts the contraction joints
- b.Seals the surface for curing
- c.Smooths large areas✓
- d.Adds the broom texture
Bull floats are larger floating devices used to finish large and hard-to-reach areas right after strike-off; texture, jointing and curing come later.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
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What does an edging tool produce on a slab?
- a.A nonslip grit surface
- b.Contraction joint grooves
- c.Rounded or beveled edges✓
- d.A stamped pattern
Caltrans defines edging as shaping concrete edges with an edging hand tool to produce smooth rounded or beveled edges; grooving tools make contraction joints.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
When is steel troweling done in the finishing sequence?
- a.Immediately after strike-off
- b.After the concrete has partly hardened✓
- c.While bleed water is on the surface
- d.Before bull floating
Troweling brings a thin layer of mortar to the surface using a metal float or trowel after the concrete has partially hardened; working bleed water in weakens the surface.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
A second coat of curing compound is needed for full coverage. How should it be sprayed?
- a.Diluted with water
- b.In the same direction as the first
- c.At right angles to the first coat✓
- d.Only along the edges
Caltrans says a needed second coat should be applied perpendicular to the first coat for effective coverage; curing compound must not be diluted.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
Why is white-pigmented curing compound often preferred on hidden surfaces?
- a.It dries clear on colored concrete.
- b.It bonds tile better.
- c.It shows coverage and reflects sun.✓
- d.It makes the concrete stronger.
The white pigment makes it easy to see complete coverage and reduces temperature rise by reflecting sunlight. It is not used where appearance or bonding matter.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
A 24-inch-thick footing is cured with its forms left in place, Caltrans method. How long must the forms stay?
- a.At least 14 days
- b.At least 5 days✓
- c.At least 3 days
- d.At least 7 days
The forms-in-place method requires at least 5 days for structures over 20 in in least dimension and 7 days for smaller ones; a 24-in footing qualifies for 5.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
Which ASTM standard does the federal guide specification cite for sampling freshly mixed concrete?
- a.ASTM C143
- b.ASTM C172✓
- c.ASTM C1074
- d.ASTM C39
The specification collects samples of fresh concrete per ASTM C172. C39 is the compression test of cylinders, C143 the slump test, and C1074 the maturity method.UFGS 03 30 00 Cast-in-Place Concrete (Chg 10, Aug 2025)
In hot weather, where should concrete temperature be tested under the federal guide specification?
- a.Delivered and in the forms✓
- b.Only at the batch plant
- c.Only in the cylinders
- d.Only after curing starts
The specification says to test the concrete delivered and the concrete in the forms, and in hot or cold conditions for each batch or every 20 cu yd until the specified temperature is obtained.UFGS 03 30 00 Cast-in-Place Concrete (Chg 10, Aug 2025)