MODULE 5: UNIT 1 Flexible Pavement

Question 1

costliest items associated with highway construction and maintenance

Answer 1

Pavements

Question 2

two types of pavement structures:

Answer 2

flexible pavements and rigid pavements

Question 3

usually require specialized designs

Answer 3

• Composite pavements (which are made of both rigid and flexible pavement layers)
• continuously reinforced pavements
• post-tensioned pavements

Question 4

its function is to distribute the traffic load stresses to the soil (subgrade) at a magnitude that will not shear or distort the soil.

Answer 4

pavement

Question 5

constructed with asphaltic cement and aggregates and usually consists of several layers

Answer 5

flexible pavement

Question 6

The lower layer of the flexible pavement is called the ________ (the soil itself).

Answer 6

subgrade

Question 7

The next layer of the flexible pavement is the __________, which usually consists of crushed aggregate (rock). This material has better engineering properties (higher modulus values) than the subgrade material in terms of its bearing capacity.

Answer 7

subbase

Question 8

The third layer of flexible pavement is the ____________ and is also often made of crushed aggregates (of a higher strength than those used in the subbase), which are either unstabilized or stabilized with a cementing material.

Answer 8

base layer

Question 9

The top layer of a flexible pavement is referred to as the ___________. It is usually made of asphaltic concrete, which is a mixture of asphalt cement and aggregates.

Answer 9

wearing surface

Question 10

to protect the base layer from wheel abrasion and to waterproof the entire pavement structure. It also provides a skidresistant surface that is important for safe vehicle stops.

Answer 10

wearing layer

Question 11

occurred whenever cracking, rutting, or other surface distresses became visible.

Answer 11

pavement failure

Question 12

Pavement engineers conducting the ________________ were faced with the task of combining the two failure definitions so that a single design procedure could be used to satisfy both critics.

Answer 12

AASHO Road Test

Question 13

was developed by Carey and Irick [1962] to handle the question of pavement failure.

Answer 13

Pavement Serviceability-Performance Concept

Question 14

the historical record of the performance of the
pavement.

Answer 14

performance curve

Question 15

known as the present serviceability index, or PSI.

Answer 15

Pavement performance,

Question 16

the ___________________ of a pavement can be measured. This is usually done by a panel of raters who drive over the pavement section and rate the pavement performance on a scale of 1 to 5, with 5 being the smoothest ride.

Answer 16

present serviceability index

Question 17

causes the pavement to deteriorate, and, as expected, the serviceability rating drops.

Answer 17

accumulation of traffic loads

Question 18

It has been found that new pavements usually have an initial PSI rating of approximately ___________.

Answer 18

4.2 to 4.5

Question 19

True or false:
The point at which pavements are considered to have failed (the TSI) varies by type of highway. Highway facilities such as interstate highways or principal arterials usually have TSIs of 2.5 or 3.0, whereas local roads can have TSIs of 2.0.

Answer 19

true

Question 20

The basic equation for flexible-pavement design given in the 1993 AASHTO design guide permits engineers to determine a structural number
necessary to carry a designated traffic loading.

Answer 20

Flexible-Pavement Design Equation

Question 21

used to modify the thickness of the lower pavement layers (base and subbase) to take into account a material’s drainage characteristics.

Answer 21

Drainage coefficients

Question 22

A value of ___ for a drainage coefficient represents a material with good drainage characteristics (a sandy material).

Answer 22

1.0

Question 23

true or false:
A soil such as clay does not drain very well and,
consequently, will have a lower drainage coefficient (less than 1.0) than a sandy material.

Answer 23

true