Concrete materials, mixes, placing, finishing, curing, testing, reinforcement, formwork and masonry units and mortar for contractor and field technician exams.
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What is a snap tie designed to do after the forms are stripped?
Pull out of the wall in one whole piece
Stay sticking out of the wall to hold insulation
Break off a short distance inside the wall face
Be cut off flush with the wall surface
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C. Break off a short distance inside the wall face
Snap ties have a weakened point so the ends break back inside the concrete surface, leaving a small hole to patch. Ties that pull out whole are tapered or she-bolt ties.
Reference: ACI 347R, form ties
Which mortar type has the highest compressive strength and is suited to heavily loaded masonry and work below grade?
Type N
Type O
Type K
Type M
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D. Type M
Type M is the strongest, about 2500 psi under the property specification, and is used for foundations, retaining walls and heavy loads. Type N is a medium-strength mortar for above-grade work.
Reference: ASTM C270, mortar types
Concrete for a footing will be in contact with soil that has a very high sulfate content. Which portland cement type gives the highest sulfate resistance?
Type I
Type V
Type II
Type III
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B. Type V
Type V is the high-sulfate-resistance cement. Type II is the tempting choice, but it only gives moderate sulfate resistance and is meant for moderate exposure.
Reference: ASTM C150, portland cement types
How many cubic yards of concrete are needed for a slab 20 ft by 30 ft and 4 in. thick? Do not add waste.
Answer in cu yd.
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7.41 cu yd
Thickness = 4/12 = 0.333 ft. Volume = 20 x 30 x 0.333 = 200 cu ft. 200 / 27 = 7.41 cu yd.
Reference: Concrete estimating: volume in cubic yards
Which practice is best when placing concrete in a slab?
Dump it in one pile and drag it out with rakes
Dump it in one pile and move it along with a vibrator
Start at the middle and push it to the edges
Deposit it as close as possible to its final position
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D. Deposit it as close as possible to its final position
Concrete should be placed as near as possible to where it will stay. Dragging it or flowing it with a vibrator makes the mortar run ahead of the stone and causes segregation.