Civl 320 Final (Concrete)

Front 1

What is durability? (In terms of material life)

Back 1

ability to last for the servce life without unacceptable performance related to materials

Front 2

Durability of materials contributes to the environment by:

Back 2

conserving natural resources, reducing green house gases

Front 3

What is the number one cause of concrete deterioration?

Back 3

Corrosion of rebar in concrete

Front 4

What is carbonation induced corrosion?

Back 4

Atmospheric CO2 diffuses the concrete, reacting with Ca(OH)2, lowering the pH

Front 5

Why does entrained air limit freeze-thaw damage?

Back 5

lets water expand into entrained air voids and/or eliminating saturation with water

Front 6

What is acid attack of concrete?

Back 6

corrosion through H2SO4 bacteria in sewage. H2S emission

Front 7

What is sulphate attack of concrete?

Back 7

sulphur from groundwater reacts with aluminate phases- creates softening, expansion and cracking

Front 8

What is Akali Aggregate Reaction (AAR)?

Back 8

Akali aggregates exposed to atmosphere reacts to create spalling and cracks

Front 9

What are general solutions to improve durability in concrete?

Back 9

low w/c by using super-P

SCM

Admixtures

proper placement and curing practices

Front 10

Name five types of targeted solutions to a specific problem:

Back 10

Air entrainment (freeze thaw)

cement/aggregate selection (AAR)

Shrinkage reduction (crack reduction)

absorption reduction (surface properties)

coatings, cathodic protection (steel corrosion)

Front 11

What are the design criteria for proportioning concrete mixtures?

Back 11

strength, durability, workability, sustainability, economy, appearance

Front 12

What are the exposure classes of CSA A23.1

Back 12

C1- strucural concrete with or without freeze thaw conditons; exposed to chlorides

C2- non-structural, freeze thaw, exposed to chloride

F1- freeze thaw, saturated, no chloride

F2- freeze thaw, unsaturated, no chloride

Front 13

What are the three phases of concrete?

Back 13

aggregate, cement paste, ITZ

Front 14

Why is concrete weaker than the aggregate and cement paste separately?

Back 14

ITZ is in concrete. creates weak points for cracks to propogate

Front 15

Why is load control testing less effective than displacement control?

Back 15

load control only gets a portion of a displacement curve (stops at failure), as displacement control goes past failure load.

Front 16

What are main differences between ITZ and bulk paste?

Back 16

ITZ

- less hydrated cement

- higher porosity

- less CSH

- more ettringite

Front 17

Explain the weakness of the ITZ.

Back 17

the mortar and aggregate have different responses

Front 18

Describe the relationship between strength and W/C

Back 18

as w/c increases, strength decreases

Front 19

Describe the relationship between permeability and W/C

Back 19

as w/c increases, coefficient of permeability exponentially increases

Front 20

What is mortar volume fraction?

Back 20

(Volume of cement, water, fine aggregate, and sometimes air)/ Total volume (1m3)

Front 21

What are the main primary strength producing minerals of clinker?

Back 21

C3S and C2S

Front 22

What are the hydration reactions of C3S and C2S?

Back 22

Hydrates with water to create CSH

Front 23

What are the elements in cement?

Back 23

Oxygen, Si, Ca, Al, Fe

Front 24

What is the nature of CSH?

Back 24

"glue" that provides strength (from VDW forces)

- poorly crystallized, porous

Front 25

What does Calcium Hydroxide provide to concrete

Back 25

- large crystal structure, however has a low strength

- forms around ITZ

reacts with pozzolanic SCM to form more CSH

Front 26

Why is gypsum added to cement?

Back 26

to avoid flash set (stiffening and loss of workability)

Front 27

Why is limestone added to cement?

Back 27

reduce greenhouse gases

Front 28

What does fineness of cement mean in regards to creating concrete?

Back 28

increasing fineness, increase rate of reaction

give off more heat earlier in hydration

Front 29

How is HE concrete achieved?

Back 29

increasing fineness

increasing C3S

Front 30

How is HS cement achieved?

Back 30

reduced C3A content

blend SCM

Front 31

What is blended cement?

Back 31

mixture of portland cement and:

fly ash

slag

silica

natural pozzolan

limestone

Front 32

What are pozzolans?

Back 32

Common name for several SCMs containing amorphous silica

Front 33

What is slag?

Back 33

waste slag from iron ore

- increases durability

-decreases permeability

-slow reaction

Front 34

What is fly ash?

Back 34

waste ash from burning of coal

(reacts with Ca(OH)2 to produce additional CSH

- increases durability

-decreases permeability-slow reaction

** used to reduce heat of hydration in large structures such as dams, raft foundations, and bridges

Front 35

What does air entrainer do?

Back 35

- Improves workability

- Lowers comp. strength

- Provide durability in terms of freeze thaw

Front 36

Whatis a water reducer? How does it work?

Back 36

- Absorbs on surface of cement particle (negativecharge)

- Lets particles slide easier

- To get to a certain slump

Front 37

Whatis superplasticizer?

Back 37

- High range water reducer

- Can create flowing concrete without segregation

Front 38

What is retarder?

Back 38

- Delay setting or hardening rate

- For long delivery times

Front 39

Whatis accelerator?

Back 39

- Early hydration (setting)

- Early strength gain

Front 40

What is corrosion inhibitor? How does it work?

Back 40

- Delays time to corrode steel reinforcement- Increases chloride threshold of steel surface

Front 41

How does shrinkage-reducing admixtures work?

Back 41

- Reducing the surface tension of the watermeniscus, reducing internal attractive forces with the pores

Front 42

Howdoes waterproofing admixtures work?

Back 42

- Reduces permeability

- Reduces absorption

Front 43

How does central plant mixing work?

Back 43

- Ingredients mixed in central mixer and wetconcrete added into truck

Front 44

Howdoes transit plant mixing work?

Back 44

Ingredientsadded separately in truck and mixed with truck’s drum

Front 45

What are three different types of curing methods?

Back 45

- Early protection (misting, evaporation retarder,wind screens

- Continuous moist curing (wet burlap andsprinkler, white fabric for reflection of sun)

- Curing compounds (polymer film on surface,reflects sunlight)

Front 46

List 5 factors that affect workability?

Back 46

- Water content

- Aggregate characteristics

- Air temp

- Concrete temp

- Fineness of cementing materials

Front 47

What are advantages of reducing water content?

Back 47

- Increase strength

- Lower permeability

- Increased durability

- Better bond between concrete and rebar - - Reduced cracking

Front 48

What are the three different models to predict elastic modulus in concrete?

Back 48

Counto

Parallel model - predicts high upper bound solution

Series model - predicts lower bound solution

Front 49

Describe the stress strain curves of aggregate, cement paste, and concrete

Back 49

Aggregate curve very steep (high stress, low strain)

Cement paste has much higher strain for a given stress (depends on porosity)

Concrete curve is in between (much more non-linear)

Front 50

Typical E values for aggregate, concrete, and paste?

Back 50

45-85 GPa for Aggregate

30-50 GPa for concrete

10GPa for paste

Front 51

What are capillary pores?

Back 51

a residue of originally filled water spaces in fresh concrete (significantly reduce strength)

Front 52

concrete permeability comes from what factors?

Back 52

capillary pores, transition zone porosity (high influence from SCM), and microcracks

Front 53

Three types of tests to type permeability:

Back 53

thru-put water permeability

absorption tests

gas permeability

chloride diffusion

resistivity

strength

Front 54

strength of concrete is a function of:

Back 54

strength of the paste, nature of the paste aggregate interface, nature of the microcracks, aggregate and cement characteristics, CM content, rate of loading, porosity

Front 55

What does rate of loading have on concrete strength?

Back 55

High rate of loading yields an overestimate of the concrete strength. Normal and slow rates of loading allow microcracks to develop and rearrange the matrix

Front 56

What increases the amount of creep in concrete?

Back 56

- high loads combined with drying

- lower cement paste content

**relative humidity also affects creep

Front 57

What are 5 different crack types in concrete?

Back 57

Plastic

Autogenous and chemical

Drying

Thermal

Load induced

Front 58

When does chemical shrinkage occur? How about Autogenous shrinkage?

Back 58

chemical shrinkage happens when the volume of products is less than the volume of reactants

Autogenous shrinkage is a component of chemical shrinkage; results in external volume change (results in cracking, particularly for high cement content mixes)

Front 59

What is plastic shrinkage?

Back 59

evaporative loss when concrete is in plastic state

water goes into tension creating tensile stress in concrete (at surface)

Front 60

When does plastic shrinkage occur?

Back 60

hot, dry, or windy conditions

works with autogenous shrinkage to make cracking worse

Front 61

What can plastic and autogenous shrinkage result in?

Back 61

reduced durability of structure

aesthetic problems

Front 62

How is plastic and autogenous shrinkage mitigated?

Back 62

early moist curing

slowing rate of reaction

less cement in mix

Front 63

What is drying shrinkage?

Back 63

time dependent strain due to loss or gain of water

Front 64

How are thermal cracks made?

Back 64

heat generated during cement hydration

differential thermal expansion between interior and exterior of element

Front 65

Name three different types of concrete cracks?

Back 65

surface cracks, shallow v-shaped (plastic) , deep (drying, thermal, load)

Front 66

What are the benefits of silica fume?

Back 66

high strength

low water permeability

improved cohesion or stickiness

high chemical resistance

Front 67

What are the main steps to the cement making process?

Back 67

Pre heating, dewatering, calcination (Ca(OH)2 converted to CaO)

Sintering in kiln to produce clinker

Grinding to fine powder, and adding gypsum, limestone, and possible SCM

Front 68

Which elements lower kiln temperature?

Back 68

Al and Fe