COSC 253 Exam 2

A collection of Q&A flashcards covering key concepts related to concrete, its components, properties, and applications.

Who invented concrete?

The Ancient Romans; modern version by Joseph Aspdin (invented Portland cement in 1824).

What are the three main ingredients in concrete?

Cement, water, aggregates (sand and gravel/crushed stone).

What are three benefits of air entraining?

Increases freeze-thaw resistance, improves workability, reduces bleeding and segregation.

What are three effects of lowering the water content of concrete?

Higher strength, less shrinkage and cracking, lower workability.

What is the main cause of segregation in concrete placement?

Excessive vibration or dropping from too great a height.

List four ways concrete and rebar complement one another.

Concrete resists compression, rebar resists tension, similar thermal expansion, rebar adds ductility.

What are three methods used to splice rebar?

Lap splice, mechanical coupler, welding.

How are chairs and bolsters different?

Chairs support rebar in slabs; bolsters support long runs in beams/slabs.

What is concrete creep?

Long-term deformation under sustained load.

What are two differences between prestressing and post-tensioning?

Prestressing = tension before pouring; post-tensioning = after hardening.

What are seven steps in creating a slab-on-grade?

Prepare subgrade, install vapor barrier, place reinforcement, set forms, pour, finish, cure.

What is the difference between control joints and expansion joints?

Control joints manage cracks; expansion joints allow slab movement.

What do form ties do?

Hold formwork together under concrete pressure.

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

Used when loads act in both directions (square spans).

Name three methods used to reduce traditional formwork.

Reusable panels, slipforming, modular forms.

What are four advantages of precast concrete as opposed to sitecast?

Better quality control, faster installation, less weather dependency, reusable molds.

What are two ways to cure concrete?

Moist curing and membrane curing.

What are bull floats and darbies used for?

Leveling and smoothing fresh concrete before troweling.

What are three benefits of a concrete topping over precast elements?

Smooth finish, increased strength, composite action.

What are two benefits of insulated concrete forms (ICFs)?

High energy efficiency, good sound insulation.

What is the diameter of a #6 rebar?

¾ inch (0.75 in).

What are three benefits of using fly ash in concrete mixtures?

Increases strength, reduces permeability, lowers cost and emissions.

What are five ways to improve the environmental impact of concrete?

Use SCMs, optimize mix design, recycle aggregates, use local materials, extend lifespan.

Describe welded wire reinforcement 8x12–D12xW7.

8x12 = wire spacing; D12 = deformed longitudinal wire; W7 = plain transverse wire.

What is an organized system of joints in a slab?

Control joint layout system.

What is laid over crushed stone to protect a slab from moisture?

Vapor barrier or vapor retarder.