T1-0: Intro

Question 1

Define hydraulic cement

Answer 1

Powder that sets and hardens as a result of chemical reactions with water

Question 2

Define cement clinker

Answer 2

Unground cement

Question 3

Define concrete

Answer 3

Cement and aggregate (ie. sand & stones) and water

Question 4

Define mortar

Answer 4

Cement and sand (fine aggregate) and water

Ie. concrete without coarse aggregates

Question 5

Define cement paste

Answer 5

A mixture of cement and water in such proportions that setting and hardening occur

Question 6

Define concrete setting

Answer 6

Stiffening without significant development of compressive strength

Question 7

Define concrete hardening

Answer 7

Significant development of compressive strength

Question 8

Define concrete hydration

Answer 8

The totality of the changes that occur when anhydrous cement is mixed with water

Question 9

What is porosity?

Why is it necessary to minimise porosity?

How is this visualised?

Answer 9

Porosity is the space left between the packed particles (measurement of voids)

It is necessary to optimise the packing of particles to make a strong concrete, to minimise porosity

In mortar, the combination has lower voids ratio than the components (fine aggregates, cement), to minimise porosity

Visualised using a voids ratio diagram

Question 10

Define the voids ratio if a particulate material

Answer 10

The ratio of voids to solids

Question 11

How is a voids ratio diagram constructed?

Answer 11

• The voids ratios of the coarse and fine components of a two-material mixture are plotted on the left and right vertical axes respectively
• The volume fraction of the fine component, n, is plotted on the horizontal axis

Question 12

Describe how to use voids ratio diagrams for mortar and concrete

Answer 12

For mortar:
- the minimum porosity is determined by considering the void ratios of the coarse (sand) and fine (cement) particles

Concrete can then:
- be treated as coarse aggregate in a mortar matrix
- the minimum porosity composition of the mortar having been determined first

Question 13

How can high-performance/high-strength concrete be achieved?

Answer 13

• Put in less water
• Minimise porosity (space between particles)
• For coarse aggregates, crushed aggregates with a rough surface is better than gravel with a round surface (for high-strength concrete)