COSC 253 EXAM II

who invented concrete

The ancient Romans

what are the three main ingredients in concrete

1. Portland cement 2. Aggregates (sand and gravel/crushed stone, coarse and fine) 3. Water

what are 3 benefits of air entraining

1. Improves resistance to freezing and thawing 2. Improves workability 3. Reduces segregation and bleeding

what are the three effects of lowering the water content of concrete

1. Increases strength 2. Increases density 3. Reduces shrinkage during curing

what is the main cause of segregation in concrete placements

Excessive vibration, moving concrete too far horizontally, or dropping it through obstructed spaces. This causes coarse aggregates to separate from the cement paste

list four ways concrete and rebar complement one another

1. Concrete resists compression; steel resists tension 2. Concrete protects steel from fire 3. Concrete protects steel from corrosion 4. Both have similar rates of thermal expansion

what are three methods used to splice rebar (combining rebar together)

1. Lap splicing (overlapping bars) 2. Welding 3. Mechanical splicing (couplers/sleeves)

how are chairs and bolsters different

Chairs support one or two reinforcing bars at specific points individuals to keep rebar off ground. Bolsters are long supports that hold multiple bars across slabs or wide beams to keep rebar off the ground

what is concrete creep

The gradual, permanent shortening of concrete under sustained stress from its own weight, weight of other building components, or force of prestressing

what are two differences between prestressing and posttensioning

1. Pretensioning tensions steel BEFORE concrete is poured; posttensioning tensions steel AFTER concrete has hardened 2. Pretensioning is generally done in precast plants; posttensioning is generally done on-site

what are seven steps in creating a slab-on-grade, in order?

1. Prepare and compact the subgrade 2. Place compacted crushed stone (capillary break) 3. Install edge forms and vapor retarder 4. Place reinforcing steel or welded wire mesh 5. Pour and consolidate concrete 6. Screed, float, and finish the surface 7. Cure the concrete

what is the different between control joints and expansion joints

Control joints create weakened sections to control where shrinkage cracks occur in visually acceptable patterns. Expansion joints completely separate concrete sections from adjacent elements to allow larger movement from temperature changes, settlement, or loading.

what do form ties do

Form ties hold opposite sides of wall formwork together, maintain proper wall thickness, and resist the pressure of wet concrete

when would a two-way slab be chosen as opposed to a one-way slab

When column bays are square or nearly square, allowing loads to be carried in both directions. Two-way slabs can be thinner, use less steel, and cost less

name three methods used to reduce traditional framework

1. Tilt-up construction 2. Shotcrete 3. Insulating concrete forms (ICFs) that remain permanently in place

name 4 advantages of precast concrete as opposed to site cast

Faster construction and installation 2. Better quality control in factories 3. Less on-site formwork 4. Construction can continue during unfavorable weather

what are two ways to cure concrete

1. Moist curing (keeping concrete wet using water or damp coverings) 2. Membrane curing (using plastic sheets or liquid curing compounds to retain moisture)

what are bull floats and darbies used for

To flatten, smooth, and consolidate the surface of freshly placed concrete during initial finishing

what are three benefits of a concrete topping over precast elements

1. Creates a smooth and level surface 2. Connects precast elements into a unified structure 3. Improves structural performance by providing composite action

what are two benefits of insulated concrete forms

1. Provide permanent thermal insulation and improve energy efficiency 2. Reduce the need for removing traditional formwork because the forms remain in place

21. will give you a rebar number and you give the diameter (formula)

Rebar diameter (inches) = Rebar number / 8

22. what are three benefits of using fly ash in concrete mixture

1. Increases concrete strength 2. Reduces permeability 3. Improves workability. It also reduces cement consumption and environmental impact

what are 5 ways to improve the environmental impact of concrete

1. Replace some Portland cement with fly ash or slag 2. Use recycled aggregates 3. Use recycled steel reinforcement 4. Reduce cement consumption through efficient concrete design 5. Improve cement manufacturing efficiency to reduce energy use and emissions

describe what each part of the welded wire reinforcement designation means: 8x12 D12xW7

8 = longitudinal wire spacing of 8 inches; 12 = transverse wire spacing of 12 inches; D12 = deformed wire with an area of 0.12 square inches; W7 = smooth wire with an area of 0.07 square inches

what is an organized system of joints in a slab that allow cracking to occur in a neat and visually acceptable pattern

Contraction joints, also called control joints

what is laid over crushed stone to protect a slab from moisture from the ground

A vapor retarder, usually a heavy plastic sheet.

i will give you a concrete slab plan and section and you will give the total amount of concrete needed

Concrete volume = Length × Width × Thickness. Convert all dimensions to feet. For cubic yards: Volume (yd³) = Length (ft) × Width (ft) × Thickness (ft) ÷ 27. Add the volumes of thickened edges, grade beams, or footings separately without double-counting overlapping concrete.

how many days until concrete reaches full strength after placement

28 days. Reaches its full design strength after 28 days, but strength can continue increasing afterward

what are the methods used to imprint decorative finishes on concrete

Stamping patterns into fresh concrete and using textured form liners or boards to transfer patterns onto concrete surfaces

30. what is the time a concrete truck should be in transit, ideally?

Approximately 90 minutes maximum from the introduction of mixing water to completion of placement, according to the provided foundation plans.