Evaluation of Stability of Asphalt-Pavements Study to Verify Marshal Method Case Study : Qassim-Madina Expressway

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.