CSLB C-8 Concrete (Trade Exam) — All Questions
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43 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When should an internal vibrator be withdrawn from the concrete?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around the vibrator, usually in 5 to 15 seconds, and when it appears near the top of the head the vibrator is withdrawn at about the rate it descended.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5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)
Which is more likely to leave unsatisfactory concrete: under-consolidation or over-consolidation?
- a.Too little vibration, which leaves voids and honeycomb✓
- b.Too much vibration, since it separates the aggregate from paste
- c.Both are about equally likely to cause trouble
- d.Neither one, since vibration changes only the color
Caltrans notes that unsatisfactory concrete is much more likely from too little vibration, which leaves honeycomb, rock pockets and cold joints. Overvibration can separate the mix but is the lesser risk, the two are not equally likely, and vibration affects consolidation, not color.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
Why should an internal vibrator not touch the subgrade when a slab on grade is being consolidated?
- a.It would stir subgrade soil into the concrete✓
- b.It would draw the water out of the fresh concrete
- c.It would short out the motor in the vibrator head
- d.It would wear out the head of the vibrator quickly
Contact with the subgrade disturbs it and incorporates soil into the concrete. Head wear, motor shorting, and water loss are not the stated reason.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
How can bleeding be reduced during placement?
- a.Vibrate a good deal longer at each insertion point
- b.Spray extra water over the surface as it goes in
- c.Place it faster, using a wetter and looser mix
- d.Place slowly with a stiffer mix low down✓
Bleeding can be reduced by slower placement and stiffer concrete, particularly in the lower part of the forms. A wetter mix and more surface water add bleed water, and extra vibration does not cure it.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
What is a cold joint?
- a.A break caused by a delay between lifts✓
- b.A crack caused by freezing weather
- c.A contraction joint sawed after hardening
- d.A construction joint formed with a keyway
A cold joint results from a delay between lifts so that the earlier concrete has begun to set. A sawed joint is a contraction joint, a keyway is a construction-joint detail, and a freeze crack is a different defect.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
A finisher wants to add water to concrete in a chute, or use a vibrator, to keep it flowing. What does Caltrans allow?
- a.A vibrator is allowed but water is not
- b.Water is allowed but a vibrator is not
- c.Neither is allowed✓
- d.Water is allowed if the load has slump to spare
The contractor must not add water to concrete in a chute or use a vibrator to promote its free flow. Spare slump does not permit adding water, and allowing either one alone gets the rule wrong.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
How must placing of a Caltrans element proceed once it has started?
- a.For as long as the finishers keep pace
- b.Stopping and restarting whenever it suits the crew
- c.In stages, with a rest between each truck
- d.Continuously, until the cure is applied✓
Once started, placement must continue without interruption until curing is applied. Planned rests, matching the finishers' pace, and stop-and-go placing invite cold joints.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
What should the inspector keep checking throughout a pour?
- a.Rebar clearances, fixing displaced bars and dobies✓
- b.A running count of cylinders made for the pour
- c.The amount of form oil used on the forms
- d.The slump of the first truck delivered to the site
Clearances of the reinforcing steel are checked throughout the pour, and displaced bars and broken dobies are fixed. A first-truck slump, form oil, and cylinder counts do not cover steel moving during placement.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
In hot weather, what is the easiest and most effective way to lower the temperature of the mix?
- a.Chill the mixing water✓
- b.Add extra cement to the batch
- c.Warm the aggregate stockpile
- d.Paint the truck drums black
Cooling the mixing water, including by using ice, is the easiest and most effective way to cool the mix. Warming aggregate raises the temperature, extra cement adds heat, and black drums absorb heat (white drums absorb less).Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
In cold weather, what is the highest temperature to which water or aggregate may be heated under Caltrans specifications?
- a.90 °F
- b.150 °F✓
- c.212 °F
- d.120 °F
Neither water nor aggregate may be heated above 150 °F. 90 °F is the upper limit for the concrete as placed, 120 °F is not the stated limit, and 212 °F is boiling water, far too hot.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
Why must frozen aggregate be thawed before it goes into the mixer?
- a.It would harden the cement in the drum
- b.It would cut the air content of the mix
- c.It would make the concrete set too slowly
- d.Thawing in the mixer adds too much water✓
Frozen aggregate thawing inside the mixer adds excessive water to the mix. Slow set, lower air content, and hardened cement are not the stated consequence.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
What is the main advantage of a drop chute, also called an elephant trunk?
- a.It lets the concrete free-fall a longer distance
- b.It speeds up the placing rate of the pour
- c.It helps limit segregation✓
- d.It removes the need for vibrating the concrete
A drop chute directs the flow and helps limit segregation. It does not speed placing, vibration is still required, and its purpose is to reduce free fall, not extend it.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
Bleedwater is on a slab surface before floating. What does the federal guide specification say about using dry cement to soak it up?
- a.Sprinkle a light dusting of dry cement to soak it up
- b.No; drag the excess off or absorb it with porous material✓
- c.Cover the wet surface with a thin layer of sand
- d.Work the bleedwater into the surface with the float
Dry cement must not be used to absorb bleedwater, because it makes a weak, uneven surface; the water is dragged off or absorbed by porous material. Dusting dry cement, floating it in, and covering with sand all leave a weak layer.UFGS 03 30 00 Cast-in-Place Concrete (Chg 10, Aug 2025)
What radius does the federal guide specification call for on an edger used to round slab edges and joints?
- a.3/4 inch
- b.1 inch
- c.1/2 inch
- d.1/8 inch✓
Edges and joints are rounded with an edger having a radius of 1/8 inch. 1/2, 3/4 and 1 inch are larger than the stated radius.UFGS 03 30 00 Cast-in-Place Concrete (Chg 10, Aug 2025)
What is laitance?
- a.A web of fine map cracks across the slab surface
- b.A thin film of curing compound on top of the slab
- c.A soupy mix of cement, fine sand and water on top✓
- d.A hard, glassy skin left behind by steel troweling
Laitance is the soupy cement, fine sand and water layer that collects when bleed water accumulates on an excessively wet mix. Steel-troweling gloss, map cracking, and curing film are different things.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
A finished slab surface is soft and powdery. Which cause fits Caltrans's description of dusting?
- a.Far too little water added at the batch plant
- b.Contraction joints that were sawed far too early
- c.Poor curing, over-finishing, or high heat or wind✓
- d.Far too much entrained air in a thick slab
Dusting may come from inadequate curing, over-finishing, or exposure to high temperatures or strong winds. Low batch water, early sawing and heavy air entrainment are not the causes given.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
Under the federal guide specification, how deep are contraction joints cut in a 4-in-thick walk with a jointing tool?
- a.2 inches
- b.1/2 inch
- c.3/4 inch
- d.1 inch✓
Joints are cut 1 inch deep or one-fourth of the slab thickness, whichever is deeper; one-fourth of 4 in is 1 in, so 1 inch governs. 1/2 and 3/4 inch are too shallow, and 2 inches is half the thickness.UFGS 03 30 00 Cast-in-Place Concrete (Chg 10, Aug 2025)
Unless otherwise indicated, how far apart does the federal guide specification space contraction joints in a concrete walk?
- a.Every 5 feet✓
- b.Every 10 feet
- c.Every 2 feet
- d.Every 50 feet
Walks get contraction joints every 5 linear feet. 10 feet is the maximum for curbs, 50 feet is the maximum spacing for walk expansion joints, and 2 feet is not specified.UFGS 03 30 00 Cast-in-Place Concrete (Chg 10, Aug 2025)
For specified textures, what does the referenced specification require the contractor to build?
- a.A photograph that the owner approves
- b.A mock-up only after a complaint
- c.A lab sample sent to the inspector
- d.A test panel for each type of texture✓
The specification requires test panels for each type of specified texture so the finish can be approved before the work proceeds. Lab samples, complaint-driven mock-ups, and photographs do not show the actual finish.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
When is the most critical time of the curing period?
- a.Only after the forms come off
- b.When the cylinders are broken
- c.The last day of the period
- d.Immediately after placement✓
Caltrans says the most critical time is right after placement, when moisture loss does the most damage. The last day, post-stripping, and cylinder breaks come after the critical window.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
Cracks appear on a newly cast surface before curing compound has been applied. What does Caltrans advise?
- a.Broom the surface lightly to close the cracks up
- b.Wait for the bleed water to return to the surface
- c.Spray a double coat of compound over the cracks
- d.Apply atomized water at once until compound goes on✓
The contractor should apply atomized water at once and keep it up until curing compound is applied. Compound over a drying surface is not the fix, waiting lets more cracks form, and brooming does not close them.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
What is the purpose of a fugitive dye in a clear curing compound?
- a.To match the color of the slab permanently
- b.To show coverage with a fading red tint✓
- c.To make the compound dry out much faster than usual
- d.To harden the top layer of the concrete surface
A fugitive dye tints the compound red while it is applied so coverage can be seen, and fades as it dries. It does not change drying speed, harden the surface, or leave a lasting color.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
If curing compound is left in place, what does it do between successive layers of concrete?
- a.It greatly improves the bond
- b.It fills the surface voids
- c.It speeds up the initial set
- d.It acts as a bond breaker✓
Left in place, curing compound acts as a bond breaker, which is why it is removed before the next pour. It does not improve bond, fill voids, or accelerate set.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
Which four factors determine the rate of evaporation from fresh concrete?
- a.Slump, cement type, aggregate size and slab thickness
- b.Form material, bar spacing, truck speed and crew size
- c.Concrete temperature, air temperature, wind velocity and humidity✓
- d.Water-cement ratio, air content, sand fineness and the admixture type used
Evaporation depends on concrete temperature, air temperature, wind velocity and humidity, which together drive plastic shrinkage cracking. Mix properties, form and steel details, and truck or crew factors do not set the evaporation rate.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5
What must be done to strength-test cylinders after they are made?
- a.Strip the molds and weigh them within the hour
- b.Protect them from evaporation✓
- c.Leave them uncovered so they can air-dry
- d.Warm them up to speed their strength gain
Precautions must be taken to prevent evaporation and water loss from the specimens. Air drying and heating change the result, and stripping within the hour would damage fresh specimens.UFGS 03 30 00 Cast-in-Place Concrete (Chg 10, Aug 2025)
Which ASTM test method does the federal guide specification cite for slump?
- a.ASTM C39
- b.ASTM C172
- c.ASTM C231
- d.ASTM C143✓
Slump tests follow ASTM C143. C172 covers sampling fresh concrete, C39 is the compressive strength test for cylinders, and C231 is the pressure method for air content.UFGS 03 30 00 Cast-in-Place Concrete (Chg 10, Aug 2025)
Which ASTM method does the federal guide specification cite for the maturity method of assessing in-place strength?
- a.ASTM C873
- b.ASTM C138
- c.ASTM C1074✓
- d.ASTM C1107
The maturity method is ASTM C1074. C873 is the test for cast-in-place cylinders, C138 measures unit weight, yield and gravimetric air content, and C1107 is the nonshrink grout standard.UFGS 03 30 00 Cast-in-Place Concrete (Chg 10, Aug 2025)