CONCRETE

Question 1

Components of concrete

Answer 1

Cement (portland cement), aggregates and water

Question 2

Difference between prestressed, pre-tensioned, and post-tensioned?

Answer 2

Prestressted: squeezing concrete together; category

It can be pretensioned or posttensioned

Pre-tension: precast

Post-tensione: cast in place; pull draped cable with hydraulic

Question 3

Components of concrete

Answer 3

Cement (portland cement), aggregates and water

Question 4

Difference between prestressed, pre-tensioned, and post-tensioned?

Answer 4

Prestressted: squeezing concrete together; category

It can be pretensioned or posttensioned

Pre-tension: precast; cable or wire is draped then concrete poured, then cable is cut so that the resulting compressive force is teansferred to the concrete

Post-tensione: cast in place; pull draped cable with hydraulic

Question 5

Types of Portland Cement

Answer 5

Type I: normal concrete
Type IA: air entrained
Type II: concrete with moderate resistance to sulfates and used  when the groundwater or aggregate contains sulfates
Type IIA
Type III: high early strenght (precast)
Type III A
Type IV: low heat of hydration (massive structures)
Type V: high resistance to sulfates

Question 6

size of aggregates

Answer 6

less than 3/4 space between rebar and less than 1/3 depth of slab

Question 7

why use lightweight aggregates

Answer 7

lighter weight or higher therman resistance (better insulation)

Question 8

range of concrete strength

Answer 8

2,000 psi to 20,000 psi

Question 9

concrete strength test

Answer 9

slump test: measures consistency of concrete
concrete cylinders (lab testing): measures compressive strength

Question 10

how are reinforcing bars measured

Answer 10

in 1/8 in

Question 11

what do chairs do

Answer 11

they keep the rebar at the right height when the concrete slab is poured

Question 12

what is shrinkage-temperature steel

Answer 12

steel wire reinforcing in concrete slabs that runs perpedicular to the lenght of the slab

Question 13

what do vertical bars do

Answer 13

take up vertical compression loads and tensile loads on the column

Question 14

what do column ties do

Answer 14

prevent outward buckling

Question 15

what does fibrous reinforcing in concrete do and what are the types

Answer 15

types: microfiber and macrofiber

the fibers act as tension members during curing

Question 16

prestressing

Answer 16

squeeze the concrete to increase its strength

Question 17

slab on grade steps

Answer 17

1. scrape top soil
2. add crushed stone
3. roll out plastic sheeting
4. place formwork leveled top
5. place welded wire or rebar on chairs
6. pour slab
7. screed the slab
8. give slab floating
9. trowel the surface for smooth
10. cover surface to keep damp
11. create control joints

Question 18

how to minimize need for control joints

Answer 18

use stronger concrete, fly ash concrete, admixtures (less shrinkage), post tension, or microfibers

Question 19

control vs isolation joint

Answer 19

control joint extends partway down the depth of the slab to limit cracking

isolation joint extends all the way through the slab to resist expansion and contraction, seismic forces, for noise or vibration, or to break up irregular shapes

Question 20

ICF (insulated concrete forms)

Answer 20

serve as concrete formwork and provide insulation - polysterene foam forms that remain in place after the concrete cures

Question 21

shores

Answer 21

adjustable height columns used to support the beams of a slab that is not poured on grade

Question 22

distribution ribs

Answer 22

added at the midspan of the joist in a one-way joist system to provide more rigidity and distribute the loads more efficiently

Question 23

drop panels

Answer 23

in a two way flat slab their job is to resist the shear forces near the top of each column, especially if there is a seismic or wind load that imparts a lateral force

Question 24

heads in waffle slab

Answer 24

resist the shear forces near the top of each column, especially if there is a seismic or wind load that imparts a lateral force

Question 25

lift slab system

Answer 25

cast all floor and roof slabs in a stack at the ground on the columns, lift them to the proper heights with a hydraulic jack and weld them into place - no formwork

Question 26

flying formwork

Answer 26

it uses large sections of reusable formwork (typ supported on metal trusses) which a crane lifts into place where the slab is poured. Then the formwork can be raised to the next level

Question 27

double tee

Answer 27

precast structure containing high strength pressure cables

Question 28

welded wire fabric

Answer 28

cold drawn steel wires set at right angles with each other and welded at the intersections

Question 29

concrete admixtures

Answer 29

• air-entraining agent: increase workability and improves its resistance to freezing and thawing cycles
• accelerator
• plasticizer:reduces amount of water needed
• retarder
• waterproofing agent

Question 30

fly ash

Answer 30

waste material obtained from coal fired power plants - imporves workability, reduces temperature rise, minimizes bleeding, reduces permeability, enhances sulfate resistance

Question 31

architectural concrete finishes

Answer 31

form lines. scrubbed, acid wash, water jet

Question 32

tooled and sandblasted finishes

Answer 32

bush hammering, grinding, applied, applied, sandblasted finishes

Question 33

rubbed finishes

Answer 33

smooth and grout cleaned

Question 34

concrete slab finishes

Answer 34

float finish, light steel troweled finish, hard steel troweled finish, broom finish

Question 35

expansion joint

Answer 35

allows entire sections of a concrete structure to move independently