Admixtures

Question 1

What are the effects of air entraining admixture on the workability of fresh concrete, strength of hardened concrete, density of hardened concrete, and durability of hardened concrete.

Answer 1

-Minute air bubbles, 10 to 100 micrometers in diameter are entrained in the cement paste. these air bubbles are not interconnected and are well distributed. The permeability of the concrete is not increased
-Increases workability of fresh concrete
-increases compressive strength by 2 to 6% of hardened concrete
-

Question 2

What are the effects of water reducing admixture on fresh and hardened concrete?

Answer 2

Increases workability of fresh concrete without adding water
Higher compressive strength without increasing cement content
Reduces the cement content without reducing the strength or workability
Produces high early strength by using super plasticizers (high range water reducing admixture)

Question 3

What are the effects of accelerating admixture on fresh and hardened concrete

Answer 3

• Used to accelerate strength development of concrete at an early age
• Improves workability and reduces bleeding in fresh concrete
• Increases compressive strength and elastic modulus at early age in hardened concrete
• Increases heat of hydration, reduces resistance to sulfate attack, increases shrinkage, volume change and creep.

Question 4

What are the effects of retarding admixture on fresh and hardened concrete

Answer 4

-Delays initial set of concrete when more time is needed

Question 5

What are the effects of gas forming admixture on fresh and hardened concrete

Answer 5

Added to concrete to form air bubbles in the concrete to form a lightweight cellular concrete. Ex aluminum powder

Question 6

What are the effects of corrosion inhibitor on fresh and hardened concrete

Answer 6

Used to reduce the corrosion of steel reinforcing bars in concrete. Ex Calcium Nitrite

Question 7

What are the effects of fly ash on fresh and hardened concrete

Answer 7

Improve workability fresh concrete, improve resistance to thermal cracking

Question 8

What are the effects of ground blast furnace slag on fresh and hardened concrete

Answer 8

Improve workability fresh concrete, improve resistance to thermal cracking

Question 9

What are the effects of silica fume on fresh and hardened concrete

Answer 9

High strength concrete, reduced permeability

Question 10

What are the differences between normal water reducing admixture, a superplasticizer, and a plasticizing admixture

Answer 10

Normal water reducing admixture reduces the water demand to produce a given consistency in fresh concrete by 5-10%
High range water reducing admixture (super plasticizer) reduces the water demand to produce a given consistency in fresh concrete by atleast 12%.
Plasticizing admixture is added to concrete to produce flowing concrete (slump of greater than 7.5” while maintaining a cohesive nature) without further addition of water