Asphalt rheology

Briscoe, O.E. (Ed.) Asphalt Rheology Relationship to Mixture, ASTM Spec. Publ. 941, American Society for Testing and Materials Philadelphia, PA, 1987. 

W. O. Yandell, in O. E. Briscoe, ed., Asphalt Rheology Relationship to Mixture, ASTM Special Publication No. 941, ASTM, Philadelphia, Pa., 1985. 

These few application examples in the nonfood industrial sectors can be easily extended by a long range of specific actual uses. Some other examples are as an antidusting agent on sandy roads, viscosity enhancer in brick production, mosquito control systems and asphalt rheology. 

The influence of the composition of asphalt has been recognized, for many years, as being an important factor in controlling the performance of such materials. Furthermore, rheological properties have always been associated with composition but, in order to utilize compositional data effectively, more definitive correlations between composition and properties are needed (46—48). 

This equation is based on the approximation that the penetration is 800 at the softening point, but the approximation fails appreciably when a complex flow is present (80,81). However, the penetration index has been, and continues to be, used for the general characteristics of asphalt for example asphalts with a P/less than —2 are considered to be the pitch type, from —2 to +2, the sol type, and above +2, the gel or blown type (2). Other empirical relations that have been used to express the rheological-temperature relation are fluidity factor a Furol viscosity P, at 135°C and penetration P, at 25°C, relation of (H—P)P/100 and penetration viscosity number PVN again relating the penetration at 25°C and kinematic viscosity at 135 °C (82,83). 

Rheological investigations of asphalts by Traxler and associates (123,124), Lee et al. (51), Pfeiffer and Van Doormaal (94), Thelen (117), Mack (60), and others show the following to be characteristic colloidal properties. 

Mack (58, 59) points out that asphaltenes from different sources in the same petro-lenes give mixtures of approximately the same rheological type, but sols of the same asphaltenes in different petrolenes differ in flow behavior. Those in aromatic petrolenes show viscous behavior and presumably approach true solution. Those in paraffinic media show complex flow and are considered to be true colloidal systems. Pfeiffer and associates (91) consider that degree of peptization of asphaltene micelles determines the flow behavior. Thus, a low concentration of asphaltenes well peptized by aromatic petrolenes leads to purely viscous flow. High concentrations of asphaltenes and petrolenes of low aromatic content result in gel-type asphalts. All shades of flow behavior between these extremes are observed. 

MALTHA. A black, viscous, natural bitunvon consisting of a complex mixture of hydrocarbons. Ils viscosity and rheological properties lie bciwccn those of crude oil and scmisnlid asphalt. It is the chief component of Alhabaska oil sands. 

Example 6.14 Squeezing Flow between Two Parallel Disks This flow characterizes compression molding it is used in certain hydrodynamic lubricating systems and in rheological testing of asphalt, rubber, and other very viscous liquids.14 We solve the flow problem for a Power Law model fluid as suggested by Scott (48) and presented by Leider and Bird (49). We assume a quasi-steady-state slow flow15 and invoke the lubrication approximation. We use a cylindrical coordinate system placed at the center and midway between the plates as shown in Fig. E6.14a. 

Rheology of SA Binders. Conventional test methods such as softening point, viscosity, penetration, Fraas break point, ductilities, etc. have been used to characterize the rheology of SA binders (11). The physical structure of SA binders is complex, and the sulfur-asphalt and sulfur-aggregate interaction make correlations to asphalt and to binder properties for aggregate rather difficult. 

While asphalt itself consists of a complex colloidal dispersion of resins and asphaltenes in oils, introduction of liquid elemental sulfur, which on cooling congeals into finely dispersed crystalline sulfur particles and in part reacts with the asphalt, necessarily complicates the rheology of such a SA binder. Differences and changes with SA binder preparation, curing time, temperature etc. must be expected and may be demonstrated by viscosity characteristics. 

Several natural materials (waxes, clays, and asphalts) have rheological properties similar to synthetic products, but because they are not polymeric, are not considered true plastics. Certain proteins (casein, zein) are natural high polymers from which plastics are made (buttons and other small items), but they are of decreasing importance. 

Asphalt is a viscoelastic material whose rheological properties reflect crude type and, to a lesser extent, processing. The ability of asphalt to perform under many conditions depends on flow behavior. Asphalt films or coatings showing no appreciable change from original conditions are usually desired, that is, they should allow some structural movement without permanent deformation. 

Distillate cut 3 obtained from bulk separation is still dark colored which may indicate the presence of small quantities of asphaltic material (20). Figure 3 indicates that it is possible that a composite of compounds, besides carboxylic acids, may be required to yield optimal recovery. In order to understand the mechanism of oil recovery, the contribution of a given individual fraction to ultra-low surface tension characteristics and the contribution of various combinations of individual fractions contribute greatly to viscosity behavior. Therefore, interfacial rheology may be dependent on the appropriate composition of the crude oil. 

It is assumed that contact between mineral fines and asphalts results in migration of polar organic asphalt molecules to polar sites on mineral surfaces. This aggregate induced interaction results in changes in asphalt microstructures. Currently, no standard binder test is in use to determine the aggregate-induced effects of asphalt microstructure on the rheological properties of asphalt binders (adhesion), nor is there a mixture test that determines the contribution of these physicochemical effects on the properties of asphalt-aggregate mixtures. 

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