Question

17. List three computer programs that may be used to calculate pavement responses in flexible pavements.

18. In terms of fatigue cracking, a damage index, D, of 1.0 means that the roadway

19. List the three types of distortion.

20. __   ___           and __ _     __ are two mechanisms that cause rutting.

Answer 1

List the three computer programs that may be used to calculate pavement responses in flexible pavements.

Ans. a) MichPave - It is a non linear finite element program for flexible pavement analysis. The displacements, stresses and strains in the pavement layers due to a single circular wheel load can be computed using this software. This software uses empirical equations to calculate rut depth and fatigue life of the pavement.

b) Chevron - It is a linear elastic layer analysis program

c) Kenlayer - This software is used to determine pavement response for both thin and thick HMA layers.

In terms of fatigue cracking a damage index of 1 means that the roadway will be subjected to fatigue cracking once the index becomes equal to or greater than 1.

List the three types of distortion

a) Rutting - Subgrade exhibits wheelpath depressions due to loading as a result of compaction and mix design problems. Pavement settles into these depressions causing surface ruts.

b) Corrugation - It is the formation of ripples in the asphalt due to poor subgrade amalgamation and heavy traffic.

c) Upheaval - This is localised swelling in the pavement due to frost or moisture action causing the aggregates to expand.

Insufficient compaction (if not compacted sufficiently, the subgrade layer tends to get compacted under the action of loads) and improper mix design (excessive asphalt content, insufficient aggregate particles) are two mechanisms that cause rutting.