MODULE 5: UNIT 1 Flexible Pavement Flashcards
costliest items associated with highway construction and maintenance
Pavements
two types of pavement structures:
flexible pavements and rigid pavements
usually require specialized designs
- Composite pavements (which are made of both rigid and flexible pavement layers)
- continuously reinforced pavements
- post-tensioned pavements
its function is to distribute the traffic load stresses to the soil (subgrade) at a magnitude that will not shear or distort the soil.
pavement
constructed with asphaltic cement and aggregates and usually consists of several layers
flexible pavement
The lower layer of the flexible pavement is called the ________ (the soil itself).
subgrade
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.
subbase
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.
base layer
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.
wearing surface
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.
wearing layer
occurred whenever cracking, rutting, or other surface distresses became visible.
pavement failure
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.
AASHO Road Test
was developed by Carey and Irick [1962] to handle the question of pavement failure.
Pavement Serviceability-Performance Concept
the historical record of the performance of the
pavement.
performance curve
known as the present serviceability index, or PSI.
Pavement performance,
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.
present serviceability index
causes the pavement to deteriorate, and, as expected, the serviceability rating drops.
accumulation of traffic loads
It has been found that new pavements usually have an initial PSI rating of approximately ___________.
4.2 to 4.5
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.
true
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.
Flexible-Pavement Design Equation
used to modify the thickness of the lower pavement layers (base and subbase) to take into account a material’s drainage characteristics.
Drainage coefficients
A value of ___ for a drainage coefficient represents a material with good drainage characteristics (a sandy material).
1.0
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.
true
