Mix Design

Question 1

How is compressive strength of concrete modelled?

Answer 1

Via a normal distribution

Question 2

What is characteristic strength?

Answer 2

The least value of the concrete strength at which the structure can be expected not to fail

Question 3

Why ought you to aim for minimal cement in concrete?

Answer 3

It is expensive and generates heat and shrinkage in hydration

Question 4

What are the 6 stages of mix design?

Answer 4

1. Determining target mean strength and w/c ratio
2. Finding the amount of free water required
3. Calculating cement concrete
4. Determining the total wet aggregate weight
5. Figuring out the proportion of coarse to fine aggregates
6. Performing trial mixes and adjusting mix accordingly

Question 5

In notation C40/50, what do the numbers refer to?

Answer 5

40 is the cylindrical compressive strength

50 is the cubic compressive strength - this is typically the number taken as characteristic strength

Question 6

If the concrete strength is off, what can be adjusted?

Answer 6

Cement content
(Water content must not be changed)