A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
Level Two (Advanced FAQs)
Part II: Pavement Design
1. What is the principle of asphalt mix design? (AMD1)
The main objective of asphalt mix design is to achieve a mix with
economical blending of aggregates with asphalt to achieve the following
[61]:
(i) workability to facilitate easy placement of bituminous materials without
experiencing segregation;
(ii) sufficient stability so that under traffic loads the pavement will not
undergo distortion and displacement;
(iii) durability by having sufficient asphalt;
(iv) sufficient air voids
In asphalt mix design, high durability is usually obtained at the expense of
low stability. Hence, a balance has to be stricken between the durability
and stability requirements.
2. What is Marshall Mix Design for bituminous materials? (AMD2)
The Marshall Mix Design method was originally developed by Bruce
Marshall of the Mississippi Highway Department in 1939. The main idea of
the Marshall Mix Design method involves the selection of the asphalt
binder content with a suitable density which satisfies minimum stability and
range of flow values.
The Marshall Mix Design method consists mainly of the following steps:
(i) Determination of physical properties, size and gradation of
aggregates.
(ii) Selection of types of asphalt binder.
(iii) Prepare initial samples, each with different asphalt binder content.
For example, three samples are made each at 4.5, 5.0, 5.5, 6.0 and
6.5 percent asphalt by dry weight for a total of 15 samples. There
should be at least two samples above and two below the estimated
optimum asphalt content.
(iv) Plot the following graphs:
(a) Asphalt binder content vs. density
(b) Asphalt binder content vs. Marshall stability
274