Materials:Hydration – Aggregates Concrete Mix Design

Question 1

What is microstructure?

Answer 1

Microstructure is how the cement looks under a microscope

Question 2

What is hydration

Answer 2

Hydration is the process which the materials react with water

Question 3

What is setting time?

Answer 3

The setting time is the time of which the reaction ha s attained a certain level of strength

Question 4

What is phase assemblages?

Answer 4

Phase assemblages is the reaction of products

Question 5

What is the pore structure?

Answer 5

The pore structure is the voids around the phase assemblages

Question 6

What is CSH?

Answer 6

CSH is what gives concrete its strength

Question 7

What is CH?

Answer 7

CH doesn’t contribute to the strength but it is important to fight against corrosion and is important for maintaining concrete integrity

Question 8

What is flash setting?

Answer 8

Flash setting is when the cement sets very quickly but has no strength

Question 9

How do we stop flash setting?

Answer 9

We stop flash setting by adding calcium sulphate (2CSH2)

Question 10

What does calcium sulphate do and why?

Answer 10

Calcium sulphate controls how the C3A reacts and does it over time by exposing a little at time. This is because the C3A wants to react fast with water and so we need to slow it down or it will have no strength.

Question 11

What does adding more water do to cement?

Answer 11

Adding more water leads to more pores which means more voids/ holes which isnt a good thing as it can reduce strength.

Question 12

What i the normal water to cement ration?

Answer 12

40%-60%

Question 13

What are capillary pores?

Answer 13

paces left behind after the water has been consumed

Question 14

What are gel pores?

Answer 14

Gel pores are pores between the sheets

Question 15

What is entrapped air voids?

Answer 15

Air bubbles inside the concrete which is bad as it creates spots of weakness

Question 16

Why can a lower water to cement ratio be good and bad?

Answer 16

-Good because it means that the concrete will have good strength and be durable
-Bad because it makes the concrete less workable

Question 17

What is stoichiometry?

Answer 17

The water to cement ratio is 22% which is just enough to hydrate all the cement but it makes it unworkable

Question 18

What is the practical w/c ratio?

Answer 18

Practically, 40%-65%

Question 19

What is the conflicting role of water?

Answer 19

-Too little = high strength but not workable
-Too much leads to loss of strength

Question 20

What is curing?

Answer 20

Curing is the process where you keep the concrete moist and you stop the initial water added from escaping