Concrete Materials

Question 1

concrete is combination of

Answer 1

cement,
fine+coarse aggregate,
water

Question 2

concrete admixtures contribute:

Answer 2

particular qualities

Question 3

concrete strength depends on

Answer 3

materials/proportions

Question 4

most critical factor in determining strength of concrete

Answer 4

water to cement ratio

Question 5

Portland cement materials:

Answer 5

lime
+silica
+iron oxide
+alumina

Question 6

Portland cement supplied in:

Answer 6

bulk or,
94lb bags (1cuft)

Question 7

Portland Cement

Type I

Answer 7

general application.
“standard cement”,
“normal cement”,

Question 8

Portland Cement

Type II

Answer 8

“modified cement”
minor sulfate resistance.
hydration heat controlled,
ex. dams/massive structures.

Question 9

Portland Cement

Type III

Answer 9

quick set.
(+ cold-weather concreting)
“high-early-strength cement”

Question 10

Portland Cement

Type IV

Answer 10

very slow setting.

massive structures,
to min cracking.
“low-heat”

Question 11

Portland Cement

Type V

Answer 11

“sulfate-resisting cement”

if exposed to water or soil w/ high alkaline content

Question 12

excess water not in chemical process forms

Answer 12

pores

Question 13

typ req water

Answer 13

up to 25% weight of cement

Question 14

extra ___% more water req’d to make a workable mix

Answer 14

10-15

Question 15

Water type req’d for cement

Answer 15

potable

Question 16

typ. min w/c ratio

Answer 16

0.35 - 0.40 by weight

4-4.5 gal per 94lb sack

Question 17

laitance:

Answer 17

chalky surface deposit of low-strength concrete

Question 18

laitance may be caused by

Answer 18

excess water

Question 19

if addt’l conc will be poured, laitance must be:

Answer 19

removed in order to bond

Question 20

fine aggregates pass through:

Answer 20

no.4 sieve

Question 21

no.4 sieve has what density openings?

Answer 21

(4 openings per linear inch)

Question 22

because cement = most $ of concrete, best mix uses

Answer 22

combination of aggregate sizes

that fill most volume while still delivering desired strength.

Question 23

concrete mix is typ __% aggregate

Answer 23

70-75%

Question 24

aggregate used for general concrete

Answer 24

sand+gravel (typ. 150 lb/ft3)

Question 25

aggregate used for lightweight structural concrete

Answer 25

expanded clays/slags/shales (typ. 120 lb/ft3)

Question 26

aggregate used for insulating concrete

Answer 26

pumice/cinders (typ. 50 lb/ft3)

Question 27

coarse aggregate size determined by

Answer 27

size of forms/spacing between reinforcing

Question 28

coarse aggregate size typ. not larger than:

Answer 28

¾ smallest dist. between rebars,
or ⅕ smallest dimension of forms,
or ⅓ depth of slab

Question 29

Proportioning of Concrete Mix:

Method 1

Answer 29

define ratio cement/sand/gravel by weight
ex. 1:2:4
also amount of water must be specified

Question 30

Proportioning of Concrete Mix:

Method 2

Answer 30

specify weight of materials, including water, per 94 lb cement

Question 31

Proportioning of Concrete Mix:

Method 3

Answer 31

for large batches, define weight to make up 1 cubic yard

Question 32

strength of mix specified by compressive strength of concrete, after cured and hardened

Answer 32

28 days.

Question 33

concrete design strength:

most typical

Answer 33

3000 psi

also 2000, 4000

Question 34

concrete design strength:

max

Answer 34

up to 12,000 for special applications ($)

Question 35

Admixtures:

Answer 35

chemicals/other materials added to give certain qualities.

ex. speed hydration/retard hardening/improve workability
/add color/improve durability/etc.

Question 36

Admixtures:
form tiny bubbles in concrete.
add workability/durability,
improves resistance to freeze/thaw,
reduce segregation of components during pour.

Answer 36

Air-entraining agents

Question 37

Admixtures:
speed hydration, strengthens faster,
faster construction/reduces protection time in cold weather.

Answer 37

Accelerators

Question 38

Admixtures:
reduce amount of water needed,
so higher strength.

Answer 38

Plasticizers

Question 39

Admixtures:

reduce heat of hydration by slowing set time.

Answer 39

Retarders

Question 40

Admixtures:

decrease permeability

Answer 40

Waterproofing agents

Question 41

Admixtures:
waste from coal power plants
increase strength
reduce temp rise
decrease permeability
increase sulfate resistance
improve workability

Answer 41

Fly ash: