Pavement Types

Question 1

What are the two types of pavements?

Answer 1

Flexible (asphalt) (is called flexible because the pavement flexes/ bends to accomodate loads and rigid (Portland cement concrete- these are stiff pavements that do not bend).

Flexible pavements distribute load over a smaller area and rely on combo of layers for transmitting load to subgrade. Rigid pavements distribute load over wide subgrade area.

Question 2

What main purposes should pavements have?

Answer 2

1) Load support- Pavements are stiffer most materials and can help with resisting loads without excessive deformation or cracking
2) Smoothness- for ride comfort and vehicle operating costs
3) Drainage- for avoiding moisture problems such as mud and ponding

Question 3

Describe material layers in Flexible pavement

Answer 3

Highest load bearing capacity layer at the top
Surface course- top layer provides characteristics such as friction, smoothness, noise control, rut resistance, and drainage. Sometime it’s divided into two layers wearing top course and binder bottom course

Binder course

Base course- provides additional load distribution and helps with drainage

Subbase course- there for structural support. prevents fines from subgrade going into pavement structure and helps with drainage. This layer is not always needed but made from crushed aggregate and engineered fill.

Capping- intended to low CBR subgrades

Subgrade- is the insitu material/ soil. It must have load bearing capacity

Question 4

What determines the pavement layer thicknesses?

Answer 4

Subgrade stiffness
Drainage characteristics
Traffic load

Question 5

What is load bearing capacity affected by?

Answer 5

• Degree of compaction
• Soil type
• Moisture content

Question 6

If the subgrade/ soil is weak what can you do?

Answer 6

1) Remove and replace with higher quality fill- but can be expensive
2) stabilisation with a cementitious or asphaltic binder (such as lime/ portland cement or emulsified asphalt) to help increase subgrade stiffness
3) or adding a base layer that spreads loads over larger subgrade area

Question 7

What two things should subgrade offer?

Answer 7

1) Stiffness- resistance to deformation
2) Load bearing capacity (Strength)