Abstract:
Hot-mix asphalt, (HMA), is a one of composite material that used for
pavement. For this research, HMA is prepared by using Marshal Method for
mix design. Marshal method assumes that the bitumen is a binder that binds
the aggregate together to form the so-called HMA.
The research shows that this assumption represents a main defect in
Marshal Method, MM. This defect affects other parameters of HMA,
specially, the procedure of finding "optimum asphalt content" and the
dispersions of quality control data of field. These problems make the Marshal
Method unreliable. Hence, the produced HMA definitely will be Instable.
To proof the unreliability of MM, the research assumes that the
"volume of bitumen paste", BP, is the material that binds the aggregate
together to form so-called HMA. The bitumen paste is the mixture of bitumen
binder, mineral filler, cement dust, and air voids.
The research solves the above said problems by follow two approaches:
one is the "elasticity approach" and the other is the "dispersion of field data
approach".
Generally, in composite materials that their elasticity affected by the
degree of stress-concentration. For HMA the stress-concentrations are the
"porosity data" which consists mainly of air voids and voids in mineral
aggregate. Therefore, the elasticity of HMA changes as the porosity changes.
The porosity is the measurement of voids in bitumen paste. The research gives
categories to this porosity such that high porosity, nonporous, and ideal
porosity. The last category is the one that responsible of the isotropy of the
asphalt pavement.
The "dispersion of field data approach" compares the porosity filed data
against those of mix design to know whether they coincide or not?
The findings are summarized as follows:
1. The Hot Mix asphalt is not elastic
2. The porosity data of the field not coincide with the design values.
III
These findings stand as a proof of incapability of Marshal Method to control
the quality of the field and to produce stable asphalt pavements.
To solve the two drawbacks mentioned above, the research proposed
three criteria of optimum asphalt content, ideal porosity and stability to fulfill
the requirements of stable hot mix asphalt.
