Concrete

Question 1

What is the Fuller equation trying to minimize?

Answer 1

Void content

Question 2

What is the Fuller equation trying to maximize?

Answer 2

Packing efficiency

Question 3

Fuller Equation

Answer 3

To identify agg. sample of strength related to mechanical properties

Question 4

What is/are the benefits of spherical agg.?

Answer 4

Better workability b/c less inter particles frictions, which makes it easier to move the material. However we can not achieve maximum inter particle strengths.

Question 5

About agg. gradation curves

Answer 5

• a semi-log graph, not a logarithmic graph b/c size distribution is smaller for grain size.
• plotting is the percentage (proportion, not mass) of material passing, not retained, which means passed material is smaller than sieve size

Question 6

MSA (maximum size agg.)

Answer 6

smallest sieve size where all material passed through. Or the last sieve size of 100% passing

Question 7

agg. properties concerned for long-term conc. strength

Answer 7

alkali reactivity: void creates cracking

Clay coating: reduce the ability to bond agg. to cement paste

Question 8

Alkali reactivity

Answer 8

Alkali-silica reaction creates void and cracking

It takes time to react so long term conc. strength

Question 9

Will short term conc. strength affect long term?

Answer 9

Y

Question 10

Basic ingredients of making Conc.

Answer 10

water, cement, course agg., fine agg., supplementary cementing materials

Question 11

Is super-platicizer supplementary or chemical mixture

Answer 11

chemical mixture b/c intervene chemically on changing properties of conc.

Question 12

Supplementary materials

Answer 12

mineral admixtures to produce benefits btw water and cement (fly ash, silica fume, supplementary particle has high surface area)

Question 13

Chemical mixtures

Answer 13

do not take part in hydration

Question 14

Limestone

Answer 14

durability and environmentally beneficial b/c use co2 to harden

Question 15

Concrete mixing steps

Answer 15

blending dry materials

add(slowly) water

Question 16

water

Answer 16

• more water more work-ability but less strength

- hydrate process

Question 17

vibration in cement and water mixtures

Answer 17

agitation -> more liquid and air bubbles coming out(minimize voids),
loose viscosity,
uniform distribution

Question 18

non Newtonian fluid of concrete

Answer 18

fresh fluid state is dependent on the rate of deformation
Static -> more solid
Agitation -> loose viscosity , liquid

Question 19

loosing viscosity in cement and water mixtures

Answer 19

breaking electronically charged inter particle attractions (+,-) of powder supplementary particle which has high surface area

Question 20

too much vibration

Answer 20

heavy agg. on the bottom and cement paste on the top -> segregation

Question 21

work-ability

Answer 21

ease and homogeneity with which it can be mixed, placed, consolidated, and finished ( make different shapes of structure material)

Question 22

factors of increasing work-ability

Answer 22

• temperature (summer more evaporation)
• agg. size (small size)
• time / power of agitation
• type of mixing blades
• chemical admixtures(super plasticizes, water reducing mixtures)
• particles’ shapes(round)

Question 23

curing (combinations of three)

Answer 23

• vital stage of reaction btw water and cement
• moisture + temperature + time
• exothermic (giving off heat)

Question 24

moisture in curing

Answer 24

after loosing moisture

• less hydrate
• quick evaporation -> less reaction(hydration) efficiency
• makes voids
• plastic shrinkage

Question 25

shrinkage

Answer 25

deformation (ex. volume contraction) due to the water movement

Question 26

plastic shrinkage

Answer 26

early evaporation of water and less reaction. as a result, tensile strength is weak

Question 27

start casting / curing @ lower temperature (25 celcius)

Answer 27

early strength weak

final strong

Question 28

start casting / curing @ higher temperature

Answer 28

• early strength strong
  final weak
• lower reaction(hydration) efficiency
• lower quality of micro structure

Question 29

maturity concept

Answer 29

• to predict strength gain during the hardening phase in field
• take moisture out of formula
• temperature surrounding environment

Question 30

composite material

Answer 30

agg. + cement paste + microscopic material

Question 31

cement made out of ?

Answer 31

calcium silicate hydrate (limestone)

Question 32

1 ton of cement produce 1 tone of co2

Answer 32

very high temperature process

Question 33

gypsum

Answer 33

control reactions

Question 34

Alumina and Ferric oxide

Answer 34

fluxing agents that lower fusion temperature (help manufacturing process)
but lower strength and durability

Question 35

Clinker

Answer 35

grayish-black pellets when raw materials are burnt at high temperature

Question 36

73% of OPC (ordinary Portland cement compound)

Answer 36

calcium silicate

Question 37

cement vs agg.

Answer 37

cement is active ingredient in concrete

agg are inert

Question 38

Hydraulic cement

Answer 38

needs water for hydration to gain strength. Gains strength under water and concrete(final product) is resistant to water

Question 39

stoichiometry on compound of cement

Answer 39

each compound of cement undergoes different reactions
determine properties of hydration
reactions occur at different rates

Question 40

changing proportions of compounds of cement

Answer 40

modify final properties of hardening time and hydrating cement paste b/c of stoichometry side of compounds of cement