Midterm (Concrete And Asphalt Mix Design)

Question 1

True Or False. The Fineness Modulus (FM) is an index of the fineness of an aggregate - the higher the FM, the coarser the aggregate.

Answer 1

True

Question 2

An alkali-aggregate reaction (AAR) occurs when?

Answer 2

Aggregates containing certain constituents react with the alkali hydroxides in concrete.

Question 3

True or False. ASR is more concerning than ACR because the occurrence of aggregates containing reactive silica minerals is more common than aggregates containing carbonate minerals.

Answer 3

True

Question 4

Fill in the blank. Aggregates containing ASR reactive substances may cause deterioration of concrete when the reactive component is present in amounts as small as ___.

Answer 4

1%

Question 5

What is the expected timeline for observing cracking and deterioration post-construction for an ASR containing aggregates and a high Akali content?

Answer 5

Within 10 years

Question 6

What is the expected timeline for observing cracking and deterioration post-construction for Aggregates containing microcrystalline quartz?

Answer 6

May not show up until 20 years have passed

Question 7

What is the expected timeline for observing cracking and deterioration post-construction for concrete exposed to deicing salts?

Answer 7

5 years or less

Question 8

What are the two forms of alkali-aggregate reactivity (AAR) ?

Answer 8

1. Alkali-Silica reactions
2. Alkali-Carbonate reactions

Question 9

The two test methods for identifying ASR susceptible aggregates are?

Answer 9

1. Concrete Prism
2. Accelerated Motar Bar Test

Question 10

What is the chemical reaction between portland cement and water called?

Answer 10

Hydration

Question 11

During manufacturing of portland cement, raw material is fed into a kiln with high temperatures. These temperatures cause a chemical change resulting in material called?

Answer 11

Clinker

Question 12

Why is gypsum added to pulverized clinker?

Answer 12

Gypsum is added to pulverized clinker to regulate the setting time and improve the shrinkage and strength of the cement

Question 13

Provide an example of when you would use each type of Portland limestone cement
1. GUL
2. HE(L)
3. MS(L)
4.HS(L)

Answer 13

1. Used when the special properties of other types of cement are not required (eg. floor slabs)
2. Used when there is a race against time (eg. Forms need to be removed quickly)
3. Used for moderate sulfate resistance (eg. soil conditions where sulfate is higher than normal)
4. Used for extreme sulfate resistance (eg. Soil contains high measures of sulfate content)

Question 14

The sulphate resistance of cement is attributed to low contents of what?

Answer 14

Tricalcium Aluminate

Question 15

Which of the following is evidenced by a rapid heat and early loss of workability with the evolution of considerable heat.

Answer 15

Flash Set

Question 16

Why are supplementary cementitious materials (SCMs) used in concrete mix design?

Answer 16

To improve particular concrete properties

Question 17

Fly ash, the most widely used SCM in concrete, is a powder resembling cement that results from the combustion of what in electric power generating plant?

Answer 17

Pulverized coal

Question 18

The addition of fly ash can improve concrete durability by doing what?

Answer 18

Mitigating the alkali-silica reaction and improving resistance to sulphate attack.

Question 19

Which of the following are ingredients in concrete other than portland cement, water and aggregates that are added to the mixture immediately before or during mixing?

Answer 19

Admixtures

Question 20

Fill in the blank. Concrete properties such as workability, finishability, strong, durable, watertight and wear resistant should be achieved through _________ rather than using admixtures.

Answer 20

proper mix design

Question 21

Provide a couple reasons for using admixtures

Answer 21

1. To reduce the cost of concrete construction.
2. To create concrete that has desirable properties.
3. To maintain concrete quality throughout mixing, transportation, placement and curing.

Question 22

True or False. Trial mixtures should be made with the admixtures and the job materials at temperatures and humidity that reflect on site conditions.

Answer 22

True

Question 23

Air-entraining admixtures are used to purposely entrain microscopic air bubbles in the concrete. This results in the significant increase in resistance to what cycles?

Answer 23

Freeze-thaw cycles and chemical de-icers

Question 24

True or False. Entrained air bubbles are usually 1mm or larger and are a result of mixing, handling and placement.

Answer 24

False

Question 25

True or False. If a water reducer is used and the water-cement ratio is held constant an increase in strength may result.

Answer 25

False, if water reducer is used and the amount of water being added is remains the same, a decrease in strength may result

Question 26

Fill in the blank. A concrete having a slump greater than ________, yet maintaining cohesive properties is considered "Flowing Concrete".

Answer 26

190mm

Question 27

What type of admixture can be used to delay the rate of set which may have been accelerated due to hot weather?

Answer 27

Retarding admixtures

Question 28

True or false. Accelerating admixtures may be used to increase the rate of hydration and the rate of strength gain.

Answer 28

True

Question 29

Fill in the blank. A(n) ________ stops the hydration process and a(n) ________ restarts the hydration proces.

Answer 29

stabilizer, activator

Question 30

Hydration can be suspended for up to 72 hours which means returned concrete can be reused and this would also be beneficial for what?

Answer 30

Long haul jobs

Question 31

What would the blended supplementary cementitious material naming convention be for an: 80% low calcium fly ash 20% silica fume

Answer 31

BMb-50F-20SF

Question 32

What are the predominant, secondary, and tertiary SCM classes of the following: BMb-50F-30S-CH

Answer 32

Predominant: 50% Low calcium flyash Secondary: 30% Slah Tertiary: 20% High Calcium Content

Question 33

Provide a positive and a negative for using Natural Pozzolans in Canada

Answer 33

Positive - Use of natural pozzolans can improve resistance to sulphate attack Negative: Source issue in Canada

Question 34

What is silica fume, and what is the acronym used for naming?

Answer 34

A byproduct of the reduction of high-purity quartz in the manufacturing of silicon, essentially silicon dioxide. Acronym: SF

Question 35

What is slag, and what is the acronym used for naming?

Answer 35

Glassy, granular material is created when iron blast furnace slag is rapidly cooled. Acronym: S

Question 36

What is fly ash?

Answer 36

A residue resulted from the combination of pulverized coal in electric power generating stations

Question 37

What are the three classes of fly ash and how much calcium content is in each?

Answer 37

1. Class F = Low calcium content (<15%) 2. Class CI = Intermediate calcium content (15-20%) 3. Class CH = High calcium content (>20%)

Question 38

What is class F fly ash?

Answer 38

Low calcium content fly ash. Approx less than 15%

Question 39

What is class CI fly ash?

Answer 39

Intermediate calcium content. Approx 15-20%

Question 40

What is class CH fly ash?

Answer 40

High calcium content. More than 20%

Question 41

What are the three grading techniques used for asphalt cement?

Answer 41

1. Standard Penetration Grading (Marshall Mix Design) 2. Performance Grading (Superpave) 3. Viscosity Grading

Question 42

In performance grading binder, what does the following naming convention mean: PG-65-37

Answer 42

PG: "performance graded" 64: Avg 7 day max pavement design temp (Rutting resistance) -37: One day minimum pavement design temperature (Brittle cracking resistance)

Question 43

What are the temperature increments for Performance Graded Binder (superpave)

Answer 43

6 degree increments

Question 44

Name 4 binder tests?

Answer 44

1. Float Test 2. Rate of curing 3. Direct Tension Test 4. Ductility Test

Question 45

What are the 4 aggregates that make up standard penetration graded (marshall mix design asphalt)?

Answer 45

1. Coarse Crush 2. Medium Crush 3. Manufactured Fines 4. Natural Sand

Question 46

What is the range for design air voids in a marshall mix design?

Answer 46

3.5-4%

Question 47

True or false You should start a marshall mix design with a design air void of 4%

Answer 47

False, you should always start at 3.5% and increase if needed.

Question 48

In the formula %MF, -5000 = (AP) + (BQ) + (CR) / T . What does (AP) stand for?

Answer 48

A = Coarse Crush Design Blend % P = % Passing Coarse crush on 5mm sieve

Question 49

In the formula %MF, -5000 = (AP) + (BQ) + (CR) / T . What does (BQ) stand for?

Answer 49

B = Medium Crush Design blend % Q = % Passing medium crush on 5mm sieve

Question 50

In the formula %MF, -5000 = (AP) + (BQ) + (CR) / T . What does (CR) stand for?

Answer 50

C = Manufactured Fines Design Blend % R = % Passing manufactured fines on 5mm sieve

Question 51

In the formula %MF, -5000 = (AP) + (BQ) + (CR) / T . What does (T) stand for?

Answer 51

T = % Passing 5mm sieve in the total combined aggregate

Question 52

True or False. As the water to cementitious materials ratio (w/c) increases the strength decreases

Answer 52

True

Question 53

True or False. The strength of concrete increases as the air content increases

Answer 53

False, Strength decreases as air content increases

Question 54

To increase the air content in a concrete mix, do you add or remove water?

Answer 54

you need to decrease the amount of water

Question 55

True or False. To decrease slump you have to decrease the amount of water in the mix

Answer 55

False. You need to increase the water content in the mix to increase the slump

Question 56

When SMC's are added into a mix, what is removed from the from the batch to maintain a 1m^3 volume

Answer 56

Fine aggregate

Question 57

How do you calculate mass of aggregate per m^3 (Ms)

Answer 57

ms = m/(1+(AC/100)

Question 58

How do you calculate volume of aggregate per m^3 (Vs)

Answer 58

Vs = ms/(Rd x Pw) =Mass of solids / (Relative Density of Agg x Density of water)

Question 59

How do you calculate voids in mineral aggregate per m^3 (VMA)

Answer 59

VMA = 1m^3 - Vs VMA = 1m^3 - Volume of solids

Question 60

How do you calculate mass of asphalt content (AC) per m^3 (mb)

Answer 60

Mb = M-Ms Mass of Binder = Total Mass - Mass of Solids

Question 61

How do you calculate volume of asphalt content (AC) per m^3 (Vb)

Answer 61

Vac = Mb / (Rd x PW) Volume of asphalt content = Mass of binder / (Relative density asphalt cement x Density of water)

Question 62

How do you calculate the mass of absorbed binder (AC) per m^3 (Mac)

Answer 62

Mac = (%absorption/100) x (Ms) Mass of absorbed AC = (%absorption/100) x (Mass of solids)

Question 63

How do you calculate the effective mass of Asphalt binder (AC) per m^3 (Mbe)

Answer 63

Mbe = Mb-Mac Mass of effective binder = Mass of binder - Mass of absorbed binder

Question 64

How do you calculate the effective volume of asphalt binder (AC) per m^4 (Vbe)

Answer 64

Vbe = Mbe / Rd x Pw Volume of effective binder = Mass of effective binder / (Relative density of asphalt cement x density of water)

Question 65

How do you calculate the volume of air per m^3 in a marshall mix design (Vair)

Answer 65

Vair = Vma - Vbe Volume of air = Volume of voids in mineral agg - Volume of effective binder

Question 66

How do you calculate voids filled with asphalt per m^3 (VFA)

Answer 66

VFA = Vbe/Vma x 100 Voids filled with agg = Volume of effective binder / Volume of voids in mineral agg x 100

Question 67

How do you calculate Marshall Stability?

Answer 67

Observed Stability x Stability Correction Ratio

Question 68

A coarse aggregate has an absorption of 1.1%. If the mass of dry aggregate in a concrete batch is 1100kg, what is the mass of absorbed water?

Answer 68

Coarse Agg = (1100kg) (1.1%/100) = 12.1kg

Question 69

If the standard deviation is smaller than 3.5MPa in a concrete mix design, which formula do you use to calculate the required average strength f'cr = f'c + 1.4S or f'cr = f'c + (2.4S-3.5MPa)

Answer 69

f'cr = f'c + 1.4S

Question 70

If the standard deviation is larger than 3.5MPa in a concrete mix design, which formula do you use to calculate the required average strength f'cr = f'c + 1.4S or f'cr = f'c + (2.4S-3.5MPa)

Answer 70

f'cr = f'c + (2.4s - 3.5MPa)

Question 71

The desired compressive strength of a concrete at 28 days is 35MPa. If the standard deviation is 1.5MPa, what is the required average strength f'cr? (Hint: Use formula f'cr = f'c + 1.4S)

Answer 71

f'cr = 35Mpa + (1.4 x 1.5) = 37.1 MPa