Admixtures

Question 1

What are admixtures

Answer 1

Chemicals added to cement paste to change its properties

Question 2

How much of the cement weight is admixture typically

Answer 2

5%

Question 3

What are the four main types of admixture

Answer 3

Superplasticiser, air entraining agent, accelerator, retarder

Question 4

What are superplasticisers and its applications

Answer 4

Reduce surface tension of water which allows cement grains to disperse, improving workability without needing more water so increases strength.

Question 5

What are the chemical functional groups in a superplasticiser

Answer 5

Anionic polar group joined to a polar and hydrophilic carbon chain

Question 6

What are air entraining agents and its applications

Answer 6

Creates stable air voids that allows the water inside the concrete to expand into when freezing without damaging the microstructure

Question 7

What are the chemical functional groups in air entraining agents

Answer 7

Anionic polar group joined to a nonpolar and hydrophobic carbon chain

Question 8

What are accelerators and its applications

Answer 8

Make the hydration of cement occur faster (which also releases heat faster) . This allows concrete to set in low temperatures

Question 9

What are retarders and its applications

Answer 9

Makes the hydration of cement occur slower. Allows wet concrete to be transported for longer times, makes concrete set with fewer cracks in hot weather, prevents formation of cold joints

Question 10

What are cold joints

Answer 10

When concrete is poured in layers, if the layer above sets before the one on top, this forms a crack at the boundary