Concrete Flashcards
Framework
oil/glue/plastic on plywood + wood framing, steel/prefab, FRP, plastic, foam
slip forming: not waiting for complete cure, wait 6-12”/hour, usu for v big jobs
flying forms: reused on floor after floor
insulating (ICEs), polystyrene, remain in place, waterproofing on earth side, gyp on inside, v low acoustical and air flow
costs the most for concrete constr, bc of labor
tolerance: usu .25” out of plumb in 10’
Reinforcement
for req added tensile strength, bars or wire fabric
bar number increases w bar size in 1/8” increments
is deformed to increase bonding
markings indicate grade, source mill, size, type
grades 40/50/60/75 are yeild strengths in kips/in2
types: axle, rail, billet
min distance to surface, min dist to each other specified by SE, needs to allow aggregate to pass through
can be reg steel, galv steel, SS, epoxy coated
GFRP: glass fiber reinforced polymer, where no metal can be used, can be used for primary structure
Cement
all is pretty much Portland now = lime (CaOH, CaOx, CaCOx), silica, FeOx, AlOx
type I: normal, type II: modest sulfate resistance, heat controlled (dams), type III: high early strength, type IV: not used, low heat, type V: sulface resisting for high alkaline exposure
excess water creates pores that decrease compressive strength, should be 0.35-0.40 per 1, can create laitance, low strength, chalky pools, must be removed
Aggregates
fines: less than no.4 sieve (4 openings/inch), coarse: 3/4-1”, good to have a variety to air pockets not too large
should be 65-70% of volume
can use clay/shale/slag for lt.wt. concrete, pumice/cinders for insulating concrete
Curing
design strength = compression at 28 days
12,000 psi is high strength, 2000-4000 psi is normal
give it ideal temp/hydration for 7 days-2 weeks (longer if in critical/weird places)
slump test: consistency and water ratio
cylinder test: 7 and 28 day compression test
core cylinder test: taken from structure directly
kelly ball test: ball dropped, measure how much it sinks
impact hammer test: nondestructive hardness test
k-slump: floating scale measures liquidity
CaCl moisture dome test, weighed after 60-72 hrs
hygrometer test/relative humidity
polyethylene sheet test, tape it down, does it bubble?
mat test, same but w pc of impermeable flooring
electrical impedence test: conductance tested
litmus or titration to test for pH, alkalinity is bad for conc, because is dissolves cement, emulsifies adhesives, can avoid by using better aggregates/SCMs
Admixtures
air entraining agent: more workability, more durability bc resists freeze/thaw better, keeps things mixed
accelerator: speeds up hydration reaction, good for cold weather
retarder: slows hydration, lessens heat, good for big pours
waterproofing: reduces water perm
corrosion or shrinkage resistance
superplasticizer: increases workability wo adding water, makes higher strength conc.
SCMs
supplementary cemetitious materials
fly ash: improves workability, from coal furnaces
GGBFs: ground granulated blast furnace slag, is stronger in long run, better to work, durable
silica fume: from silica/metal furnace, reduces permeability
pozzolan: volcanic ash, might be deposited, reduces permeability, increases strength
Special concrete types
autoclave aerated concrete/AAC: precast with Al added, steam cooked, v lightweight, v airtight, but needs waterproofing, not strong
self consolidating concrete/SCC: no vibration needed, superplasticizer used, less labor, and earlier high strength
carbon fiber concrete: expoxy coated carbon fiber mesh instead of steel mesh reinf., thinner, lighter precast panels, less buffer to surface, so stronger despite thinness
ultra high performance/UHPC: high strength, low perm, v durable, 17-25000 psi, cement and silica fume and plasticizer plus alkali resistant glass or steel fibers, usually factory made, often cladding, can be very thin
poured gypsum deck
Finishes
rough: plywood face shows, smooth: from hardboard, metal, smoother wood
form liner: smooth wood, metal, harboard, thin brick
sandblasted, scrubbed, acid wash, water jet: exposes aggregate
brush hammered: looks like meat tenderized
grinding: looks like terrazo
applied: stucco or plaster
smooth rubbed: carborundum abrasive used
grout cleaned: skim coat of grout to even out
strike off: use straight edge to cut
float: bring cement to top w vibration
light steel trowel: done after floating, compacts, smooths
hard steel trowel: even more smooth
superfloat: where wheels need to be fast
broom finish: swept over top to increase grip
stamped: embossed
Concrete joints
control jts: 1/4” depth, saw cut or forms
construction jts: between pours, need waterstops
expansion jts: allows for thermal movement
isolation: prevents vibration conduction
Prestressed concrete
pretensioning: mostly only for precast conc., where tendons are stressed, conc is poured, tension released as hardens, cambers, then load on makes it flat again
post tensioning: pour, stress as it hardens, keep under stress, load
