CSLB C-8 Concrete (Trade Exam) — All Questions

A shed slab is 16 ft by 20 ft and 4 in thick. How much concrete does it contain?

• a.About 3.5 cubic yards
• b.About 4.0 cubic yards✓
• c.About 47.4 cubic yards
• d.About 11.9 cubic yards

16 × 20 = 320 sq ft; 4 in = 0.333 ft; 320 × 0.333 = 106.7 cu ft; ÷ 27 = 4.0 cu yd. Dividing by 9 gives 11.9, and multiplying by 4 without converting inches gives 47.4.NIST Handbook 44 (2026), Appendix C

A sidewalk is 5 ft wide, 120 ft long and 4 in thick. How much concrete does it need?

• a.About 6.2 cubic yards
• b.About 22.2 cubic yards
• c.About 88.9 cubic yards
• d.About 7.4 cubic yards✓

5 × 120 = 600 sq ft × 0.333 ft = 200 cu ft ÷ 27 = 7.4 cu yd. 22.2 comes from dividing by 9 instead of 27, and 88.9 from treating 4 in as 4 ft.NIST Handbook 44 (2026), Appendix C

About how many square feet does one cubic yard of concrete cover at 4 inches thick?

• a.81 square feet✓
• b.324 square feet
• c.27 square feet
• d.108 square feet

One cubic yard is 27 cu ft; 27 ÷ 0.333 ft = 81 sq ft. 27 is the cubic feet in a yard, not the area it covers, and 324 comes from multiplying by 12 instead of dividing by the thickness in feet.NIST Handbook 44 (2026), Appendix C

About how many square feet does one cubic yard of concrete cover at 6 inches thick?

• a.54 square feet✓
• b.162 square feet
• c.81 square feet
• d.36 square feet

27 cu ft ÷ 0.5 ft = 54 sq ft. 81 sq ft is the coverage at 4 in; a thicker slab covers less area per yard, not more.NIST Handbook 44 (2026), Appendix C

Twelve piers are 12 in in diameter and 6 ft deep. About how much concrete do they take?

• a.About 6.3 cubic yards
• b.About 8.4 cubic yards
• c.About 2.1 cubic yards✓
• d.About 2.7 cubic yards

Area = 0.785 × 1² = 0.785 sq ft; one pier = 0.785 × 6 = 4.71 cu ft; twelve = 56.5 cu ft ÷ 27 = 2.1 cu yd. Treating each pier as a 1-ft square gives 2.7, and using the diameter as the radius gives 8.4.NIST Handbook 44 (2026), Appendix C

A continuous footing is 24 in wide and 12 in deep with a centerline length of 150 ft. How much concrete does it hold?

• a.About 11.1 cubic yards✓
• b.About 33.3 cubic yards
• c.About 5.6 cubic yards
• d.About 13.3 cubic yards

150 × 2 × 1 = 300 cu ft ÷ 27 = 11.1 cu yd. Dividing by 9 gives 33.3, and using a 12-in width by mistake gives 5.6.NIST Handbook 44 (2026), Appendix C

Bars will be spaced 18 in on center across a 30-ft-wide slab. How many bars run the other way?

• a.22
• b.18
• c.21✓
• d.20

30 ft = 360 in; 360 ÷ 18 = 20 spaces; bars = spaces + 1 = 21. Answering 20 counts the spaces rather than the bars.NIST Handbook 44 (2026), Appendix C

What is the nominal diameter of a #7 reinforcing bar?

• a.7 millimeters
• b.7/16 inch
• c.7/8 inch✓
• d.3/4 inch

U.S. bar sizes are identified in eighths of an inch, so #7 is 7/8 in. 3/4 in is a #6, and reading the number as sixteenths or millimeters is a common error.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 4

A takeoff totals 1,350 cubic feet of concrete. How many cubic yards is that?

• a.150 cubic yards
• b.112.5 cubic yards
• c.45 cubic yards
• d.50 cubic yards✓

1,350 ÷ 27 = 50 cu yd. Dividing by 9 gives 150, and dividing by 12 gives 112.5, neither of which converts cubic feet to cubic yards.NIST Handbook 44 (2026), Appendix C

A square column is 12 in by 12 in and 10 ft tall. How much form contact area do its four sides need?

• a.10 square feet
• b.40 square feet✓
• c.120 square feet
• d.20 square feet

Each side is 1 ft × 10 ft = 10 sq ft, and four sides give 40 sq ft. 10 sq ft is one side, and 120 comes from using inches for the side width.Estimating practice (form contact area)

A 23-cubic-yard pour will come in trucks carrying 10 cubic yards each. How many loads must be ordered?

• a.4
• b.2
• c.1
• d.3✓

23 ÷ 10 = 2.3, and a partial load is still a truck, so 3 loads. Two loads bring only 20 cu yd.NIST Handbook 44 (2026), Appendix C

A single, stand-alone project will disturb 30,000 square feet of soil and is not part of a larger plan. Does it need state Construction Stormwater General Permit coverage?

• a.No, it is under one acre.✓
• b.Yes, over 10,000 square feet needs it.
• c.Only if it is a public project.
• d.Yes, all grading needs coverage.

One acre is 43,560 sq ft; the State Water Board's permit applies to projects disturbing one or more acres, or less if part of a larger common plan that disturbs an acre. Local stormwater rules still apply.State Water Resources Control Board, Order 2022-0057-DWQ

On public concrete work, what does a "rebar factor" describe?

• a.Average pounds of rebar per cubic yard✓
• b.The ratio of bar length to lap length
• c.The yield strength of the steel
• d.The number of bars per square foot

Caltrans describes establishing the average pounds of rebar per cubic yard of a concrete item, the "rebar factor," to pay for reinforcement in step with concrete quantities. Yield strength is shown by the grade mark.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 2

A winter pour needs faster setting. Which ASTM C494 admixture type accelerates?

• a.Type C✓
• b.Type D
• c.Type B
• d.Type F

Type C is accelerating. Type B and Type D retard setting, which is the opposite of what a cold pour needs, and Type F is a high-range water reducer.IMCP Manual for Concrete Pavement, 2nd ed. (FHWA/CP Tech Center, 2019)

Which portland cement type offers moderate sulfate resistance?

• a.Type IV
• b.Type III
• c.Type I
• d.Type II✓

Type II is moderate sulfate resistance (Type V is high). Type III is high early strength and Type IV is low heat of hydration.IMCP Manual for Concrete Pavement, 2nd ed. (FHWA/CP Tech Center, 2019)

Why is an air-entraining admixture specified for exterior concrete in freezing areas?

• a.To reduce the need for curing
• b.To speed up the set
• c.To raise the compressive strength
• d.For freeze-thaw and scaling resistance✓

Air-entraining admixtures stabilize microscopic bubbles that provide freeze-thaw resistance and improve resistance to deicer salt scaling. They do not raise strength, speed setting or replace curing.IMCP Manual for Concrete Pavement, 2nd ed. (FHWA/CP Tech Center, 2019)

A load has stiffened in the truck. The driver offers to add water and remix it. What is the rule?

• a.It may be re-tempered if the slump is low.
• b.It may be re-tempered below 90 °F.
• c.It may be re-tempered once.
• d.Re-tempering it with water is prohibited.✓

Caltrans states that re-tempering partially hardened concrete with additional water is expressly prohibited, because it can markedly reduce strength. Low slump from stiffening is the symptom, not a reason to add water.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5

A load without a retarder is 95 minutes from batching and has turned 200 drum revolutions. Under the Caltrans limits, may it be placed?

• a.No, it is past 90 minutes.✓
• b.Yes, it is under 250 revolutions.
• c.Yes, if it is placed quickly.
• d.Yes, the limit is 120 minutes.

Without a retarder the limit is 250 revolutions or 90 minutes, whichever occurs first; 95 minutes exceeds the time limit even though the revolutions are under 250. The 120-minute limit applies only with a retarder.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5

Water held back at the plant is added to a truck on site within the mix design. What must happen before discharge continues?

• a.Add an equal amount of cement
• b.Mix at least 30 drum revolutions✓
• c.Wait 30 minutes for it to absorb
• d.Mix for at least 5 revolutions

Caltrans requires added water to be introduced only once and mixed for at least 30 drum revolutions before more than a quarter cubic yard of the load has been discharged. Waiting without mixing does not blend it.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5

Which item belongs on the equipment list for a large wall pour, in case of breakdown?

• a.Extra form oil
• b.A spare slump cone
• c.A second finishing crew only
• d.A standby vibrator and generator✓

Caltrans calls it best practice to always have a standby vibrator and generator on hand, and lists backup equipment among pre-pour items. A breakdown with no spare leaves unconsolidated concrete and cold joints.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5

Why might a pump be chosen over a crane and bucket under a low roof or canopy?

• a.Pumps allow water to be added.
• b.Pumps need less overhead clearance.✓
• c.Pumps place concrete more slowly.
• d.Pumps need no setup inspection.

Caltrans notes that pumps normally require less headroom than a crane and bucket. Pumps also place faster, and they still require inspection and follow the water limits.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5

What is the main placing drawback of a belt conveyor?

• a.It cannot reach more than 20 feet
• b.It requires aluminum pipe
• c.Segregation where it transfers✓
• d.It only works with low slump

Caltrans identifies a tendency for concrete to segregate at intermediate transfer points and at the discharge point as a major disadvantage of belts; hoppers or baffles at discharge help.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5

Heavy rain begins on a slab being placed. What is the concern for the surface?

• a.Rain speeds up the set.
• b.Rain only matters after finishing.
• c.Rain improves surface strength.
• d.Diluted paste, higher w/c ratio✓

Rain dilutes the mortar at the surface and may increase the water-cement ratio enough to decrease strength and durability there, so placement should be protected or suspended.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5

A plan sheet references a standard detail from a Standard Plans book. How binding is that detail?

• a.It is part of the contract.✓
• b.It is only a suggestion.
• c.It is binding only on public work.
• d.It applies only if drawn on the sheet.

Caltrans states that Standard Plans are contractual supplements to the project plans; a referenced detail is as binding as the sheet. On any job, referenced details are part of the documents you build to.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 2

Workers will enter a 4-ft-deep footing trench. Does the trench need a Cal/OSHA excavation permit?

• a.Yes, if it is longer than 50 ft.
• b.Only if the soil is Type C.
• c.Yes, every entered trench needs one.
• d.No; that permit starts at 5 ft.✓

Title 8 §341 requires a permit for trenches or excavations 5 feet or deeper into which any person must descend. A 4-ft trench still needs a competent person's check for cave-in signs, but no permit.Cal. Code Regs. tit. 8, §341

An excavator's 811 ticket expires while trenching is still going on. What must happen?

• a.Keep going if marks are visible.
• b.Finish that day, then renew.
• c.Call the operator directly instead.
• d.Stop and get a new ticket.✓

If a ticket expires while work is ongoing, the excavator must immediately cease excavation, contact the regional notification center and get a new ticket before resuming.Cal. Gov. Code §§4216–4216.9

An applicant has 2 years at an accredited construction program and 3 years as a journey-level concrete finisher. How much of the program can count toward the 4-year requirement?

• a.Only 6 months per year attended
• b.None, school never counts
• c.All of it, plus up to 4 years
• d.Up to 2 years; never over 3✓

Under 16 CCR §825, accredited training or apprenticeship can count as experience, but never for more than 3 years; here the 2 years can count, giving 5 years total.Cal. Code Regs. tit. 16, §825

Which field change lowers concrete strength the most directly?

• a.Consolidating with a vibrator
• b.Curing for the full specified time
• c.Using a water-reducing admixture
• d.Water beyond the mix design✓

Strength increases as the water-cementitious ratio decreases, so water beyond the mix design raises the ratio and lowers strength. Water reducers, curing and vibration all help strength.IMCP Manual for Concrete Pavement, 2nd ed. (FHWA/CP Tech Center, 2019)

Proof-rolling reveals a soft, rutting area in a slab subgrade. What should be done?

• a.Replace it with compacted fill.✓
• b.Pour thicker concrete over it.
• c.Leave it; the slab will bridge it.
• d.Cover it with plastic sheeting.

A uniform foundation matters more than a strong one, and there should be no hard or soft spots. A soft area left in place becomes a crack line; it is removed or reworked and recompacted.IMCP Manual for Concrete Pavement, 2nd ed. (FHWA/CP Tech Center, 2019)

Expansive clay under a planned slab has dried out badly during a delay. Why is that a concern?

• a.Dry clay makes the slab cure faster.
• b.Dry clay is always Type A soil.
• c.Later swelling can lift the slab.✓
• d.Dry clay has no effect on slabs.

The IMCP manual notes expansive soils cause trouble when compacted too dry or allowed to dry out before paving; later wetting makes them swell unevenly. Moisture conditioning per the soils report addresses it.IMCP Manual for Concrete Pavement, 2nd ed. (FHWA/CP Tech Center, 2019)

A dry, semi-porous subgrade will receive a footing. What does the federal guide specification say to do?

• a.Flood it to 2 inches deep.
• b.Cover it with dry cement.
• c.Leave it dry for better bond.
• d.Sprinkle it to eliminate suction.✓

The specification says to sprinkle a semi-porous, dry subgrade to eliminate suction when concrete is deposited, or seal it with the specified vapor retarder. Flooding leaves standing water, which must be removed.UFGS 03 30 00 Cast-in-Place Concrete (Chg 10, Aug 2025)

Under the 811 law, how wide is the tolerance zone around an operator's field marking?

• a.5 feet on each side
• b.12 inches on each side
• c.24 inches on each side✓
• d.36 inches total

Government Code §4216 defines the tolerance zone as 24 inches on each side of the operator's field marking; inside it, the excavator uses hand tools to find the exact location first.Cal. Gov. Code §§4216–4216.9

A footing will be dug 6 ft from a high-priority gas transmission line. What must happen first?

• a.Nothing extra; hand dig only
• b.An onsite meeting✓
• c.A Cal/OSHA permit for the line
• d.A second 811 ticket

When excavation is proposed within 10 feet of a high-priority installation, the operator sets up an onsite meeting, and the excavator may not begin until it is completed.Cal. Gov. Code §§4216–4216.9

For the 811 notice period, which of these counts as a working day?

• a.A non-holiday Wednesday✓
• b.A state holiday
• c.A Sunday afternoon
• d.A Saturday morning

A working day is a weekday, Monday through Friday, 7:00 a.m. to 5:00 p.m., excluding federal and state holidays. Weekends and holidays do not count toward the two working days.Cal. Gov. Code §§4216–4216.9

What must every operator on the ticket provide before the legal excavation start time?

• a.A copy of its insurance
• b.A crew to dig by hand
• c.A written excavation permit
• d.An electronic positive response✓

Every operator must supply an electronic positive response through the regional notification center before the legal start date and time, and the excavator may not begin until all listed operators have done so.Cal. Gov. Code §§4216–4216.9

When may an excavation have vertical sides with no protective system, whatever its depth?

• a.When it is entirely in stable rock✓
• b.When it is dug in dry clay
• c.When workers wear hard hats
• d.When it will be open one day

Title 8 §1541.1 exempts excavations made entirely in stable rock. Dry clay can still cave, and short duration or PPE does not replace a protective system.Cal. Code Regs. tit. 8, §1541.1

An 8-ft-deep excavation in Type A soil will be sloped. How far back must each side lay back from the bottom edge?

• a.8 feet
• b.12 feet
• c.6 feet✓
• d.4 feet

Type A soil is sloped no steeper than 3/4 horizontal to 1 vertical for excavations under 20 ft: 0.75 × 8 = 6 ft. Eight feet is a 1:1 Type B slope and 12 ft is the 1½:1 Type C slope.Cal. Code Regs. tit. 8, §1541.1, App. B

A 6-ft excavation is near an old landfill where hazardous gases could be present. What is required before entry?

• a.Only post a warning sign.
• b.Only limit entry to 15 minutes.
• c.Only open the trench wider.
• d.Test the atmosphere first.✓

Where oxygen deficiency (under 19.5%) or a hazardous atmosphere could reasonably exist, the atmosphere must be tested before employees enter excavations greater than 4 ft deep.Cal. Code Regs. tit. 8, §1541

A worker must enter a deep bell-bottom pier hole. What does Title 8 require?

• a.Only a hard hat and gloves
• b.A harness with an attended lifeline✓
• c.A second worker in the hole
• d.A ladder within 50 feet

Employees entering bell-bottom pier holes must wear a harness with a lifeline, separate from any material line, individually attended at all times.Cal. Code Regs. tit. 8, §1541

Why are layout lines often carried on batter boards set back from the corners?

• a.To mark the property line.
• b.To hold the forms plumb.
• c.To make the corners square.
• d.So the lines survive excavation.✓

Stakes on the exact corners are dug out with the footing; batter boards set outside the work hold the string lines so they can be removed for digging and restored to the same marks.Field layout practice; Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 2 (control stakes)