نمونه متن انگلیسی مقاله
The present study gives a new understanding about bitumen's colloidal behavior, related to its chemical composition, microscopic structure and rheological properties. Bitumens possess a strong temperature dependence of rheological properties, governed by the interaction of the individual constituents. Much importance is given to the colloidal index of the bitumen, based on the ratio of the four main chemical components (asphaltenes, resins, aromatics, saturates). Increasing one of these constituents fundamentally changes the structure and the rheological behavior of bitumen. Therefore, a gel bitumen contains high asphaltene/resin concentrations, leading to a network structure with high rigidity and elasticity (high IG*I, low 0), whereas a sol bitumen possesses a high resiniasphaltene ratio, forming domains of coherent asphaltene micelles which lead to a good time-temperature equivalence in the Black space but also high viscous behavior.
What are bitumens? Bitumens are important factors in road construction and roofing systems. They possess strong temperature dependent rheological properties, governed by the chemical-physical interactions of their individual constituents. Another approach is their chemical composition or their fractionating by distillation in narrow molecular weight determination by GPC, Iatroscan or liquid chromatographyl-5,11. More recently, new approaches were used to define bitumens or bitumen's heavy constituents as RMN, scattering techniques and scanning or tunneling force microscopy6-1O. In a general way all bitumens are classified in terms of 'grade' by penetration and ring and ball softening point measurements. However, a simple compositional analysis shows that a same grade bitumen does not have the same chemical composition (Table 1) or the same rheologicaVphysico-chemical behavior when in contact with polymers, acids or stones. So the question still remains, what really is bitumen? What is the relationship between the bitumen's rheology, composition and structural arrangement?