Formwork & Reinforcement

Question 1

What is concrete formwork, and how does it aid the curing process? (2)

Answer 1

• temporary support to hold freshly-poured concrete in the desired shape until the concrete gains sufficient strength to support itself
• formwork also helps to cure concrete by preventing evaporation of water

Question 2

How strong does formwork need to be, and how much does it cost? What is it made of? (3)

Answer 2

• formwork must be strong enough to support the weight and fluid pressure of wet concrete
• formwork can account for half or more of total cost of concrete construction
• typically made of wood, metal, plastic, earth, or flexible material such as masonite

Question 3

How do you keep concrete from adhering to the forms?

Answer 3

form release compounds are oils, waxes, or plastic coatings applied to formwork surfaces to prevent adhesion of the formwork to the concrete and ease formwork removal

Question 4

Why should concrete be reinforced?

Answer 4

concrete is strong in compression but weak in tension

Question 5

Why do concrete and steel work so well together? (4)

Answer 5

• concrete is strong in compression and steel is strong in tension
• the two materials have similar rates of expansion/contraction
• the alkaline chemistry of concrete protects steel from corrosion
• concrete mechanically bonds well to rebar, allowing them to work as a single unit

Question 6

What are the basic concepts behind reinforced concrete? (3)

Answer 6

• place reinforcing steel in concrete where there are tensile forces
• allow the concrete to resist the compression forces
• steel can also be used to help resist cracking

Question 7

How are simple concrete beams reinforced? (2)

Answer 7

• in a simply supported beam, the greatest tension forces occur at the bottom middle of the beam
• the location of reinforcing in a concrete beam approximates the lines of tension, where the concrete needs help

Question 8

What materials are used to reinforce concrete?

Answer 8

bars or wires, usually steel, placed in concrete along lines of tension to provide resistance to the tensile stress

Question 9

What is rebar?

Answer 9

rebar is hot-rolled steel, deformed with surface ridges so it will mechanically bond with the concrete

Question 10

How is rebar measured? (2)

Answer 10

• rebar size numbers correspond to the diameter in 1/8 of an inch
• each size number increases in .125 inch increments

Question 11

How is rebar made? (3)

Answer 11

• rebar is made with steel grades of varying strength
• higher strength steel allows for rebar smaller in diameter or with greater spacing
• markings on the rebar provide information on producing mill, bar size, steel type, and grade

Question 12

What sort of IRC requirements must rebar meet? (2)

Answer 12

• rebar grade allowed by the IRC varies by seismic design category
• minimum allowed is 40,000 psi

Question 13

What is corrosion-resistant rebar, and where is it used? (2)

Answer 13

• includes epoxy coated, galvanized, and stainless steel rebar
• typically used in marine structures, highway construction, and parking garages

Question 14

What is welded wire reinforcing, and where is it used? (2)

Answer 14

• prefabricated welded grids of reinforcing bars or wires

- especially common for concrete slab reinforcing

Question 15

How are reinforcements fabricated and erected?

Answer 15

reinforcing can be cut to length, bent, and partially assembled by the fabricator before transportation to the construction site