A driver adds water to a ready-mix load at the site beyond what the mix design allows. What is the main effect on the hardened concrete?
- Higher strength and less surface dusting
- Faster set and higher early strength
- Better freeze-thaw resistance once fully cured
- Lower strength and more shrinkage cracking
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D. Lower strength and more shrinkage cracking
Extra water raises the water-cement ratio, which lowers strength and durability and increases drying shrinkage. It makes placing easier, but it does not speed the set or add strength.
Reference: ACI 318 durability and mix provisions; ASTM C94 (ready-mixed concrete)
A straight wall 24 ft long is framed with studs at 16 in. on centre. Counting one stud at each end and no extras for corners or openings, how many studs are needed?
Answer in studs.
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19 studs
Spaces = (24 x 12) / 16 = 288 / 16 = 18. Studs = spaces + 1 = 19.
Reference: Wood framing takeoff: studs
A reinforced block foundation wall must resist soil pressure from backfill. Which of these mortar types is the usual choice?
- Type N
- Type O
- Type S
- Type K
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C. Type S
Type S has high bond and compressive strength and is the usual pick for below-grade walls and walls with lateral load. Type N is intended for general above-grade work, and O and K are low-strength mortars for non-loadbearing or restoration work.
Reference: ASTM C270 (mortar for unit masonry), guide for selection
On a floor plan drawn at 1/4 in. = 1 ft 0 in., a wall measures 3-1/2 in. long. How long is the actual wall?
Answer in ft.
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14 ft
Each 1/4 in. is 1 ft, so there are 4 ft to the inch. Length = 3.5 x 4 = 14 ft.
Reference: Plan reading: architect's scale
A roof surface measures 2,400 sq ft. Shingles come three bundles to the square. Allowing 10% for waste, how many bundles must be ordered? Round up to whole bundles.
Answer in bundles.
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80 bundles
Area with waste = 2,400 x 1.10 = 2,640 sq ft = 26.4 squares. Bundles = 26.4 x 3 = 79.2, so 80 bundles.
Reference: Roofing estimating: squares and bundles