CIVL 215 - Exam Review UPDATED
ACTUAL QUESTIONS AND CORRECT
ANSWERS
Why Use Aggregates - CORRECT ANSWER 1. Cost
- aggregates are typically 70-80% of the volume of the concrete
- $8-9 per tonne vs $120 per tonne for cement
2. Dimensional Stability
- Significantly lower potential shrinkage and creep strains due to long term loading and drying - less
cracking
3. Better Durability
- 100% paste material would be highly susceptible to attack by chemicals
4. Strength
- Aggregates are stronger than paste
Gradation of Aggregates - CORRECT ANSWER Gradation determines the particle size
distribution (fine and coarse) of a representative sample of aggregate.
- Evaluated by a sieve analysis
- Plotted on a grain size distribution curve and must lie inside the ASTM grading requirements
(smaller seive size is fine)
1. Single size (open graded)
- Poor strength
- Not recommended
2. Gap graded
- Intermediate sizes omitted
- Good in rare cases
3. Well graded (dense graded)
- Economical
- Good strength
- good workability
,Grading limits: Coarse aggregates - CORRECT ANSWER 1. Maximum size - is the smallest
sieve through which 100% of the sample passes
2. Nominal Maximum Size - is the standard sieve opening immediately smaller than the smallest
through which all of the aggregate passes.
Fineness Modulus - CORRECT ANSWER - An index of the fineness of the aggregates
- The higher the fineness modulus the coarser the aggregate
- The smaller the number the larger percentage of finer material
- Should be between 2.3 and 3.1
- Obtained by adding the cumulative weight percentages retained on each of a specified series of
sieves and diving the sum by 100.
Moisture Absorption (concrete) - CORRECT ANSWER - Affects the strength of concrete
- Can have a large effect on accuracy of proportioning
- Water absorption test on aggregates must be measured
- Can be four different moisture states
1. Oven dry - all moisture is removed by heating the aggregate in an oven
2. Air dry - pore connected to the surface are partially full of moisture but surface is dry
3. Saturated surface dry - pore connected to surface are filled with water, but the surface is dry
4. Wet or moist - pores connected to the surface are filled with water and there is excess (free)
moisture on the surface
Cement Clinker - CORRECT ANSWER 1. Belite (C2S)
-Formed at 1200-1500 degrees
-Approximately 20-25% of the clinker phase in Portland cements
-much slower initial reaction with water
-Contributes to longer term strength gain (28 days and beyond)
-Exothermic reactions with water
2. Alite (C3S)
- Formed above 1250 degrees
-The most important cementing compound
-Approximately 55 to 60% of the clinker phase in portland cements
, -reacts with water to give most of the early strength of concrete
-Exothermic reaction with water (releases a lot of heat early in the hydration process)
3. Aluminate (C3A)
- formed above 1300 degrees
-Approximately 4 to 12% of the clinker
-Presence of aluminates is undesirable from an engineer point of view
-low percentage of C3A are more resistant to sulphate attack (durability)
- Rapid reaction with water (responsible for initial set)
-Reaction rate is controlled by the addition of gypsum
4. Ferrite (C4AF)
- Approximately 5 to 10% of the clinker
- Reduces the temperature required to produce alite (C3S) to save energy and hence reduce the cost
-It contributes little to strength
Types of Concrete and Their Use - CORRECT ANSWER 1. Type I aka 10 or GU
- When special properties of the other types are not required
- Susceptible to sulphate attack
- Used for floors, reinforced concrete buildings, pavements, bridges, reservoir pipes, masonry units,
precast concrete products
2. Type II aka 20 MS or MH
-when moderate sulphate exposure or moderate heat of hydration is required
- sulfate resistance is improved by a lower C3A content (below 7%)
-Used in seatwater
- Suitable for mass concrete works such as large piers, large footings, retaining walls, massive
structures, drainage structures
-Reduces temperature rise and temperature related to cracking. Good for placing in warm weather and
large structures
3. Type III aka 30 or HE
- When early strength is desired it sets and hardens rapidly
- Has highest heat of hydration similar to type I except particles ground finer
-When formwork must be removed rapidly and the structure must be put into service quickly. Forms
can be removed after 3 days ( 7 days for type I)
ACTUAL QUESTIONS AND CORRECT
ANSWERS
Why Use Aggregates - CORRECT ANSWER 1. Cost
- aggregates are typically 70-80% of the volume of the concrete
- $8-9 per tonne vs $120 per tonne for cement
2. Dimensional Stability
- Significantly lower potential shrinkage and creep strains due to long term loading and drying - less
cracking
3. Better Durability
- 100% paste material would be highly susceptible to attack by chemicals
4. Strength
- Aggregates are stronger than paste
Gradation of Aggregates - CORRECT ANSWER Gradation determines the particle size
distribution (fine and coarse) of a representative sample of aggregate.
- Evaluated by a sieve analysis
- Plotted on a grain size distribution curve and must lie inside the ASTM grading requirements
(smaller seive size is fine)
1. Single size (open graded)
- Poor strength
- Not recommended
2. Gap graded
- Intermediate sizes omitted
- Good in rare cases
3. Well graded (dense graded)
- Economical
- Good strength
- good workability
,Grading limits: Coarse aggregates - CORRECT ANSWER 1. Maximum size - is the smallest
sieve through which 100% of the sample passes
2. Nominal Maximum Size - is the standard sieve opening immediately smaller than the smallest
through which all of the aggregate passes.
Fineness Modulus - CORRECT ANSWER - An index of the fineness of the aggregates
- The higher the fineness modulus the coarser the aggregate
- The smaller the number the larger percentage of finer material
- Should be between 2.3 and 3.1
- Obtained by adding the cumulative weight percentages retained on each of a specified series of
sieves and diving the sum by 100.
Moisture Absorption (concrete) - CORRECT ANSWER - Affects the strength of concrete
- Can have a large effect on accuracy of proportioning
- Water absorption test on aggregates must be measured
- Can be four different moisture states
1. Oven dry - all moisture is removed by heating the aggregate in an oven
2. Air dry - pore connected to the surface are partially full of moisture but surface is dry
3. Saturated surface dry - pore connected to surface are filled with water, but the surface is dry
4. Wet or moist - pores connected to the surface are filled with water and there is excess (free)
moisture on the surface
Cement Clinker - CORRECT ANSWER 1. Belite (C2S)
-Formed at 1200-1500 degrees
-Approximately 20-25% of the clinker phase in Portland cements
-much slower initial reaction with water
-Contributes to longer term strength gain (28 days and beyond)
-Exothermic reactions with water
2. Alite (C3S)
- Formed above 1250 degrees
-The most important cementing compound
-Approximately 55 to 60% of the clinker phase in portland cements
, -reacts with water to give most of the early strength of concrete
-Exothermic reaction with water (releases a lot of heat early in the hydration process)
3. Aluminate (C3A)
- formed above 1300 degrees
-Approximately 4 to 12% of the clinker
-Presence of aluminates is undesirable from an engineer point of view
-low percentage of C3A are more resistant to sulphate attack (durability)
- Rapid reaction with water (responsible for initial set)
-Reaction rate is controlled by the addition of gypsum
4. Ferrite (C4AF)
- Approximately 5 to 10% of the clinker
- Reduces the temperature required to produce alite (C3S) to save energy and hence reduce the cost
-It contributes little to strength
Types of Concrete and Their Use - CORRECT ANSWER 1. Type I aka 10 or GU
- When special properties of the other types are not required
- Susceptible to sulphate attack
- Used for floors, reinforced concrete buildings, pavements, bridges, reservoir pipes, masonry units,
precast concrete products
2. Type II aka 20 MS or MH
-when moderate sulphate exposure or moderate heat of hydration is required
- sulfate resistance is improved by a lower C3A content (below 7%)
-Used in seatwater
- Suitable for mass concrete works such as large piers, large footings, retaining walls, massive
structures, drainage structures
-Reduces temperature rise and temperature related to cracking. Good for placing in warm weather and
large structures
3. Type III aka 30 or HE
- When early strength is desired it sets and hardens rapidly
- Has highest heat of hydration similar to type I except particles ground finer
-When formwork must be removed rapidly and the structure must be put into service quickly. Forms
can be removed after 3 days ( 7 days for type I)
