Concrete Materials Flashcards
concrete is combination of
cement,
fine+coarse aggregate,
water
concrete admixtures contribute:
particular qualities
concrete strength depends on
materials/proportions
most critical factor in determining strength of concrete
water to cement ratio
Portland cement materials:
lime
+silica
+iron oxide
+alumina
Portland cement supplied in:
bulk or, 94lb bags (1cuft)
Portland Cement
Type I
general application.
“standard cement”,
“normal cement”,
Portland Cement
Type II
“modified cement”
minor sulfate resistance.
hydration heat controlled,
ex. dams/massive structures.
Portland Cement
Type III
quick set.
(+ cold-weather concreting)
“high-early-strength cement”
Portland Cement
Type IV
very slow setting.
massive structures,
to min cracking.
“low-heat”
Portland Cement
Type V
“sulfate-resisting cement”
if exposed to water or soil w/ high alkaline content
excess water not in chemical process forms
pores
typ req water
up to 25% weight of cement
extra ___% more water req’d to make a workable mix
10-15
Water type req’d for cement
potable
typ. min w/c ratio
0.35 - 0.40 by weight
4-4.5 gal per 94lb sack
laitance:
chalky surface deposit of low-strength concrete
laitance may be caused by
excess water
if addt’l conc will be poured, laitance must be:
removed in order to bond
fine aggregates pass through:
no.4 sieve
no.4 sieve has what density openings?
(4 openings per linear inch)
because cement = most $ of concrete, best mix uses
combination of aggregate sizes
that fill most volume while still delivering desired strength.
concrete mix is typ __% aggregate
70-75%
aggregate used for general concrete
sand+gravel (typ. 150 lb/ft3)
aggregate used for lightweight structural concrete
expanded clays/slags/shales (typ. 120 lb/ft3)
aggregate used for insulating concrete
pumice/cinders (typ. 50 lb/ft3)
coarse aggregate size determined by
size of forms/spacing between reinforcing
coarse aggregate size typ. not larger than:
¾ smallest dist. between rebars,
or ⅕ smallest dimension of forms,
or ⅓ depth of slab
Proportioning of Concrete Mix:
Method 1
define ratio cement/sand/gravel by weight
ex. 1:2:4
also amount of water must be specified
Proportioning of Concrete Mix:
Method 2
specify weight of materials, including water, per 94 lb cement
Proportioning of Concrete Mix:
Method 3
for large batches, define weight to make up 1 cubic yard
strength of mix specified by compressive strength of concrete, after cured and hardened
28 days.
concrete design strength:
most typical
3000 psi
also 2000, 4000
concrete design strength:
max
up to 12,000 for special applications ($)
Admixtures:
chemicals/other materials added to give certain qualities.
ex. speed hydration/retard hardening/improve workability
/add color/improve durability/etc.
Admixtures: form tiny bubbles in concrete. add workability/durability, improves resistance to freeze/thaw, reduce segregation of components during pour.
Air-entraining agents
Admixtures:
speed hydration, strengthens faster,
faster construction/reduces protection time in cold weather.
Accelerators
Admixtures:
reduce amount of water needed,
so higher strength.
Plasticizers
Admixtures:
reduce heat of hydration by slowing set time.
Retarders
Admixtures:
decrease permeability
Waterproofing agents
Admixtures: waste from coal power plants increase strength reduce temp rise decrease permeability increase sulfate resistance improve workability
Fly ash:
