CONCRETE Flashcards
Components of concrete
Cement (portland cement), aggregates and water
Difference between prestressed, pre-tensioned, and post-tensioned?
Prestressted: squeezing concrete together; category
It can be pretensioned or posttensioned
Pre-tension: precast
Post-tensione: cast in place; pull draped cable with hydraulic
Components of concrete
Cement (portland cement), aggregates and water
Difference between prestressed, pre-tensioned, and post-tensioned?
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
Types of Portland Cement
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
size of aggregates
less than 3/4 space between rebar and less than 1/3 depth of slab
why use lightweight aggregates
lighter weight or higher therman resistance (better insulation)
range of concrete strength
2,000 psi to 20,000 psi
concrete strength test
slump test: measures consistency of concrete concrete cylinders (lab testing): measures compressive strength
how are reinforcing bars measured
in 1/8 in
what do chairs do
they keep the rebar at the right height when the concrete slab is poured
what is shrinkage-temperature steel
steel wire reinforcing in concrete slabs that runs perpedicular to the lenght of the slab
what do vertical bars do
take up vertical compression loads and tensile loads on the column
what do column ties do
prevent outward buckling
what does fibrous reinforcing in concrete do and what are the types
types: microfiber and macrofiber
the fibers act as tension members during curing
prestressing
squeeze the concrete to increase its strength
slab on grade steps
- scrape top soil
- add crushed stone
- roll out plastic sheeting
- place formwork leveled top
- place welded wire or rebar on chairs
- pour slab
- screed the slab
- give slab floating
- trowel the surface for smooth
- cover surface to keep damp
- create control joints
how to minimize need for control joints
use stronger concrete, fly ash concrete, admixtures (less shrinkage), post tension, or microfibers
control vs isolation joint
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
ICF (insulated concrete forms)
serve as concrete formwork and provide insulation - polysterene foam forms that remain in place after the concrete cures
shores
adjustable height columns used to support the beams of a slab that is not poured on grade
distribution ribs
added at the midspan of the joist in a one-way joist system to provide more rigidity and distribute the loads more efficiently
drop panels
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
heads in waffle slab
resist the shear forces near the top of each column, especially if there is a seismic or wind load that imparts a lateral force
lift slab system
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
flying formwork
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
double tee
precast structure containing high strength pressure cables
welded wire fabric
cold drawn steel wires set at right angles with each other and welded at the intersections
concrete admixtures
- air-entraining agent: increase workability and improves its resistance to freezing and thawing cycles
- accelerator
- plasticizer:reduces amount of water needed
- retarder
- waterproofing agent
fly ash
waste material obtained from coal fired power plants - imporves workability, reduces temperature rise, minimizes bleeding, reduces permeability, enhances sulfate resistance
architectural concrete finishes
form lines. scrubbed, acid wash, water jet
tooled and sandblasted finishes
bush hammering, grinding, applied, applied, sandblasted finishes
rubbed finishes
smooth and grout cleaned
concrete slab finishes
float finish, light steel troweled finish, hard steel troweled finish, broom finish
expansion joint
allows entire sections of a concrete structure to move independently
