CE MATERIALS-EXAM 2 QUESTIONS AND ANSWERS
How does one perform a concrete mix design on paper according to the ACI (Absolute
Volume) method? - Answers :(1) Determine Required Average Compressive Strength
(2) Determine Water Cement Ratio
(3) Determine Mixing Water Requirement & Air Content
(4)Calculate Required Cement Content
(5) Determine Coarse Aggregate Content
(6) Determine Fine Aggregate Content
(7) Adjustments for Agg. Moisture
(8) Summary of Mix Ingredients
What is the specific gravity of cement? - Answers :125.45 pcf
What is the density of water? - Answers :62.4 lb/ft^3
How do we verify or make the necessary adjustments in a concrete mix design if the
proportioning of the other mix ingredients is kept the same? - Answers :
What are the effects of air-entraining admixture on the workability of fresh concrete if
the proportioning of the other mix ingredients is kept the same? - Answers :Improved
work-ability of fresh concrete.
What are the effects of air-entraining admixture on the strength of hardened concrete if
the proportioning of the other mix ingredients is kept the same? - Answers :Each
percent of entrianed air reduces the compressive strength of concrete by about 2 to 6%.
What are the effects of air-entraining admixture on the density of hardened concrete if
the proportioning of the other mix ingredients is kept the same? - Answers :Density is
decreased, since minute air bubbles are entrianed in the cement paste.
What are the effects of air-entraining admixture on the durability of hardened concrete if
the proportioning of the other mix ingredients is kept the same? - Answers :Improved
freeze-thaw resistance, resistance to deicers and salts (damage due to pressure
caused by formation of salt crystals), sulfate resistance, and resistance to alkali-silica
reactivity.
Why can air entrainment in concrete improve its durability? - Answers :Air entrainment
can improve freeze-thaw resistance, resistance to deicers and salts (damage due to
pressure caused by formation of salt crystals), sulfate resistance, and resistance to
alkali-silica reactivity.
What are the effects of water reducing admixture on the properties of fresh and
hardened concrete, if the proportioning of the other mix ingredients are kept the same? -
Answers :1. Increase the workability of the fresh concrete without addition of more
cement and water.
, 2. Achieve higher compressive strength without increasing the cement content or
reducing the workability of the fresh concrete.
3. Reduce the cement content without reducing the strength or the workability of the
concrete.
4. Produce high early strength by using super plasticizers (combined effect of using a
lower w/c and the higher rate of hydration due to the super plasticizer).
What are the effects of accelerating admixture on the properties of fresh and hardened
concrete, if the proportioning of the other mix ingredients are kept the same? - Answers
:1. Accelerates setting. Reduces both initial and final setting times.
2. Increases compressive strength and elastic modulus at early age.
3. Improves workability of fresh concrete and reduces bleeding.
4. Improves water tightness and resistance to freezing and thawing at early age.
5. Increases the heat of hydration.
6. Reduces the resistance to sulfate attack.
7. Aggregates alkali-aggregate reaction.
8. Increases shrinkage, volume change, and creep.
What are the effects of gas forming admixture on the properties of fresh and hardened
concrete, if the proportioning of the other mix ingredients are kept the same? - Answers
:It is added to concrete to form air bubbles in the concrete to form lightweight cellular
concrete. A commonly used gas forming agent is aluminum powder.
What are the effects of corrosion inhibitor on the properties of fresh and hardened
concrete, if the proportioning of the other mix ingredients are kept the same? - Answers
:It is added to concrete to reduce the corrosion of steel rebar in concrete. A commonly
used corrosion inhibitor is calcium nitrite.
What are the effects of fly ash on the properties of fresh and hardened concrete, if the
proportioning of the other mix ingredients are kept the same? - Answers :1. Improve
workability of fresh concrete, when fly ash is used.
2. Improve resistance to thermal cracking, when fly ash is used as partial Portland
cement replacement. This is due to the lower heat of hydration.
3. Improve resistance to sulfate, acid water, and seawater.
How does one perform a concrete mix design on paper according to the ACI (Absolute
Volume) method? - Answers :(1) Determine Required Average Compressive Strength
(2) Determine Water Cement Ratio
(3) Determine Mixing Water Requirement & Air Content
(4)Calculate Required Cement Content
(5) Determine Coarse Aggregate Content
(6) Determine Fine Aggregate Content
(7) Adjustments for Agg. Moisture
(8) Summary of Mix Ingredients
What is the specific gravity of cement? - Answers :125.45 pcf
What is the density of water? - Answers :62.4 lb/ft^3
How do we verify or make the necessary adjustments in a concrete mix design if the
proportioning of the other mix ingredients is kept the same? - Answers :
What are the effects of air-entraining admixture on the workability of fresh concrete if
the proportioning of the other mix ingredients is kept the same? - Answers :Improved
work-ability of fresh concrete.
What are the effects of air-entraining admixture on the strength of hardened concrete if
the proportioning of the other mix ingredients is kept the same? - Answers :Each
percent of entrianed air reduces the compressive strength of concrete by about 2 to 6%.
What are the effects of air-entraining admixture on the density of hardened concrete if
the proportioning of the other mix ingredients is kept the same? - Answers :Density is
decreased, since minute air bubbles are entrianed in the cement paste.
What are the effects of air-entraining admixture on the durability of hardened concrete if
the proportioning of the other mix ingredients is kept the same? - Answers :Improved
freeze-thaw resistance, resistance to deicers and salts (damage due to pressure
caused by formation of salt crystals), sulfate resistance, and resistance to alkali-silica
reactivity.
Why can air entrainment in concrete improve its durability? - Answers :Air entrainment
can improve freeze-thaw resistance, resistance to deicers and salts (damage due to
pressure caused by formation of salt crystals), sulfate resistance, and resistance to
alkali-silica reactivity.
What are the effects of water reducing admixture on the properties of fresh and
hardened concrete, if the proportioning of the other mix ingredients are kept the same? -
Answers :1. Increase the workability of the fresh concrete without addition of more
cement and water.
, 2. Achieve higher compressive strength without increasing the cement content or
reducing the workability of the fresh concrete.
3. Reduce the cement content without reducing the strength or the workability of the
concrete.
4. Produce high early strength by using super plasticizers (combined effect of using a
lower w/c and the higher rate of hydration due to the super plasticizer).
What are the effects of accelerating admixture on the properties of fresh and hardened
concrete, if the proportioning of the other mix ingredients are kept the same? - Answers
:1. Accelerates setting. Reduces both initial and final setting times.
2. Increases compressive strength and elastic modulus at early age.
3. Improves workability of fresh concrete and reduces bleeding.
4. Improves water tightness and resistance to freezing and thawing at early age.
5. Increases the heat of hydration.
6. Reduces the resistance to sulfate attack.
7. Aggregates alkali-aggregate reaction.
8. Increases shrinkage, volume change, and creep.
What are the effects of gas forming admixture on the properties of fresh and hardened
concrete, if the proportioning of the other mix ingredients are kept the same? - Answers
:It is added to concrete to form air bubbles in the concrete to form lightweight cellular
concrete. A commonly used gas forming agent is aluminum powder.
What are the effects of corrosion inhibitor on the properties of fresh and hardened
concrete, if the proportioning of the other mix ingredients are kept the same? - Answers
:It is added to concrete to reduce the corrosion of steel rebar in concrete. A commonly
used corrosion inhibitor is calcium nitrite.
What are the effects of fly ash on the properties of fresh and hardened concrete, if the
proportioning of the other mix ingredients are kept the same? - Answers :1. Improve
workability of fresh concrete, when fly ash is used.
2. Improve resistance to thermal cracking, when fly ash is used as partial Portland
cement replacement. This is due to the lower heat of hydration.
3. Improve resistance to sulfate, acid water, and seawater.
