Midterm (Concrete And Asphalt Mix Design) Flashcards
True Or False. The Fineness Modulus (FM) is an index of the fineness of an aggregate - the higher the FM, the coarser the aggregate.
True
An alkali-aggregate reaction (AAR) occurs when?
Aggregates containing certain constituents react with the alkali hydroxides in concrete.
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.
True
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 ___.
1%
What is the expected timeline for observing cracking and deterioration post-construction for an ASR containing aggregates and a high Akali content?
Within 10 years
What is the expected timeline for observing cracking and deterioration post-construction for Aggregates containing microcrystalline quartz?
May not show up until 20 years have passed
What is the expected timeline for observing cracking and deterioration post-construction for concrete exposed to deicing salts?
5 years or less
What are the two forms of alkali-aggregate reactivity (AAR) ?
- Alkali-Silica reactions
- Alkali-Carbonate reactions
The two test methods for identifying ASR susceptible aggregates are?
- Concrete Prism
- Accelerated Motar Bar Test
What is the chemical reaction between portland cement and water called?
Hydration
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?
Clinker
Why is gypsum added to pulverized clinker?
Gypsum is added to pulverized clinker to regulate the setting time and improve the shrinkage and strength of the cement
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)
- Used when the special properties of other types of cement are not required (eg. floor slabs)
- Used when there is a race against time (eg. Forms need to be removed quickly)
- Used for moderate sulfate resistance (eg. soil conditions where sulfate is higher than normal)
- Used for extreme sulfate resistance (eg. Soil contains high measures of sulfate content)
The sulphate resistance of cement is attributed to low contents of what?
Tricalcium Aluminate
Which of the following is evidenced by a rapid heat and early loss of workability with the evolution of considerable heat.
Flash Set
Why are supplementary cementitious materials (SCMs) used in concrete mix design?
To improve particular concrete properties
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?
Pulverized coal
The addition of fly ash can improve concrete durability by doing what?
Mitigating the alkali-silica reaction and improving resistance to sulphate attack.
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?
Admixtures
Fill in the blank. Concrete properties such as workability, finishability, strong, durable, watertight and wear resistant should be achieved through _________ rather than using admixtures.
proper mix design
Provide a couple reasons for using admixtures
- To reduce the cost of concrete construction.
- To create concrete that has desirable properties.
- To maintain concrete quality throughout mixing, transportation, placement and curing.
True or False. Trial mixtures should be made with the admixtures and the job materials at temperatures and humidity that reflect on site conditions.
True
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?
Freeze-thaw cycles and chemical de-icers
True or False. Entrained air bubbles are usually 1mm or larger and are a result of mixing, handling and placement.
False
True or False. If a water reducer is used and the water-cement ratio is held constant an increase in strength may result.
False, if water reducer is used and the amount of water being added is remains the same, a decrease in strength may result
Fill in the blank. A concrete having a slump greater than ________, yet maintaining cohesive properties is considered “Flowing Concrete”.
190mm
What type of admixture can be used to delay the rate of set which may have been accelerated due to hot weather?
Retarding admixtures
True or false. Accelerating admixtures may be used to increase the rate of hydration and the rate of strength gain.
True
Fill in the blank. A(n) ________ stops the hydration process and a(n) ________ restarts the hydration proces.
stabilizer, activator
Hydration can be suspended for up to 72 hours which means returned concrete can be reused and this would also be beneficial for what?
Long haul jobs
What would the blended supplementary cementitious material naming convention be for an:
80% low calcium fly ash
20% silica fume
BMb-50F-20SF
What are the predominant, secondary, and tertiary SCM classes of the following:
BMb-50F-30S-CH
Predominant: 50% Low calcium flyash
Secondary: 30% Slah
Tertiary: 20% High Calcium Content
Provide a positive and a negative for using Natural Pozzolans in Canada
Positive - Use of natural pozzolans can improve resistance to sulphate attack
Negative: Source issue in Canada
What is silica fume, and what is the acronym used for naming?
A byproduct of the reduction of high-purity quartz in the manufacturing of silicon, essentially silicon dioxide. Acronym: SF
What is slag, and what is the acronym used for naming?
Glassy, granular material is created when iron blast furnace slag is rapidly cooled. Acronym: S
What is fly ash?
A residue resulted from the combination of pulverized coal in electric power generating stations
What are the three classes of fly ash and how much calcium content is in each?
- Class F = Low calcium content (<15%)
- Class CI = Intermediate calcium content (15-20%)
- Class CH = High calcium content (>20%)
What is class F fly ash?
Low calcium content fly ash. Approx less than 15%
What is class CI fly ash?
Intermediate calcium content. Approx 15-20%
What is class CH fly ash?
High calcium content. More than 20%
What are the three grading techniques used for asphalt cement?
- Standard Penetration Grading (Marshall Mix Design)
- Performance Grading (Superpave)
- Viscosity Grading
In performance grading binder, what does the following naming convention mean:
PG-65-37
PG: “performance graded”
64: Avg 7 day max pavement design temp (Rutting resistance)
-37: One day minimum pavement design temperature (Brittle cracking resistance)
What are the temperature increments for Performance Graded Binder (superpave)
6 degree increments
Name 4 binder tests?
- Float Test
- Rate of curing
- Direct Tension Test
- Ductility Test
What are the 4 aggregates that make up standard penetration graded (marshall mix design asphalt)?
- Coarse Crush
- Medium Crush
- Manufactured Fines
- Natural Sand
What is the range for design air voids in a marshall mix design?
3.5-4%
True or false You should start a marshall mix design with a design air void of 4%
False, you should always start at 3.5% and increase if needed.
In the formula %MF, -5000 = (AP) + (BQ) + (CR) / T . What does (AP) stand for?
A = Coarse Crush Design Blend %
P = % Passing Coarse crush on 5mm sieve
In the formula %MF, -5000 = (AP) + (BQ) + (CR) / T . What does (BQ) stand for?
B = Medium Crush Design blend %
Q = % Passing medium crush on 5mm sieve
In the formula %MF, -5000 = (AP) + (BQ) + (CR) / T . What does (CR) stand for?
C = Manufactured Fines Design Blend %
R = % Passing manufactured fines on 5mm sieve
In the formula %MF, -5000 = (AP) + (BQ) + (CR) / T . What does (T) stand for?
T = % Passing 5mm sieve in the total combined aggregate
True or False. As the water to cementitious materials ratio (w/c) increases the strength decreases
True
True or False. The strength of concrete increases as the air content increases
False, Strength decreases as air content increases
To increase the air content in a concrete mix, do you add or remove water?
you need to decrease the amount of water
True or False. To decrease slump you have to decrease the amount of water in the mix
False. You need to increase the water content in the mix to increase the slump
When SMC’s are added into a mix, what is removed from the from the batch to maintain a 1m^3 volume
Fine aggregate
How do you calculate mass of aggregate per m^3 (Ms)
ms = m/(1+(AC/100)
How do you calculate volume of aggregate per m^3 (Vs)
Vs = ms/(Rd x Pw)
=Mass of solids / (Relative Density of Agg x Density of water)
How do you calculate voids in mineral aggregate per m^3 (VMA)
VMA = 1m^3 - Vs
VMA = 1m^3 - Volume of solids
How do you calculate mass of asphalt content (AC) per m^3 (mb)
Mb = M-Ms
Mass of Binder = Total Mass - Mass of Solids
How do you calculate volume of asphalt content (AC) per m^3 (Vb)
Vac = Mb / (Rd x PW)
Volume of asphalt content = Mass of binder / (Relative density asphalt cement x Density of water)
How do you calculate the mass of absorbed binder (AC) per m^3 (Mac)
Mac = (%absorption/100) x (Ms)
Mass of absorbed AC = (%absorption/100) x (Mass of solids)
How do you calculate the effective mass of Asphalt binder (AC) per m^3 (Mbe)
Mbe = Mb-Mac
Mass of effective binder = Mass of binder - Mass of absorbed binder
How do you calculate the effective volume of asphalt binder (AC) per m^4 (Vbe)
Vbe = Mbe / Rd x Pw
Volume of effective binder = Mass of effective binder / (Relative density of asphalt cement x density of water)
How do you calculate the volume of air per m^3 in a marshall mix design (Vair)
Vair = Vma - Vbe
Volume of air = Volume of voids in mineral agg - Volume of effective binder
How do you calculate voids filled with asphalt per m^3 (VFA)
VFA = Vbe/Vma x 100
Voids filled with agg = Volume of effective binder / Volume of voids in mineral agg x 100
How do you calculate Marshall Stability?
Observed Stability x Stability Correction Ratio
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?
Coarse Agg = (1100kg) (1.1%/100) = 12.1kg
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)
f’cr = f’c + 1.4S
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)
f’cr = f’c + (2.4s - 3.5MPa)
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)
f’cr = 35Mpa + (1.4 x 1.5) = 37.1 MPa
