Asphalt grading

Asphalt (referred to as bitumen in some parts of the world) is produced from the distillation residuum. In addition to road asphalt, a variety of asphalt grades for roofing and waterproofing are also produced. Asphalt has complex chemical and physical compositions, which usually vary with the source of the crude oil, and it is produced to certain standards of hardness or softness in controlled vacuum distillation processes (Barth, 1962 Bland and Davidson, 1967 Speight, 1999, and references cited therein Speight and Ozum, 2002). 

Asphalt Grade o/w S in Binder Coefficient, Kv(cm/sec) Predicted Flooding Rainfall Intensity Ip, (in/hr)... 

Sulfur-Extended Mastic Mixes. The use of sulfur in mastic or Guss-asphalt mix type formulations extends the use of this material. For example, softer asphalt grades may be used, and the mixes may be placed at lower temperatures. Using sulfur would permit variation in mix workability and control of the mechanical properties of the mixes and would extend the variety of aggregates that may be used. 

Asphalt (bitumen) also occurs in various oil sand (also called tar sand) deposits which occur widely scattered through the world (17) and the bitumen is available by means of various extraction technologies. A review of the properties and character of the bitumen (18) suggests that, when used as an asphaltic binder, the bitumen compares favorably with specification-grade petroleum asphalts and may have superior aging characteristics and produce more water-resistant paving mixtures than the typical petroleum asphalts. 

The hquid cutback asphalts are prepared in a number of viscosity grades, ranging generally from 70 to 6000. The grade number indicates the viscosity at 60°C. 

The Federal specifications stipulated that only those asphalts that had been demonstrated by service tests as satisfactory for the intended use would be accepted. The specifications also indicated the type and location of constmction and the relative amount of traffic for each of the grades. The AASHTO specifications indicated that the use of each grade depended on the type of road, climate, and traffic. The ASTM suggested the type of constmction for which each grade would be used. 

Asphalts are usually specified in several grades for the same industry, differing in hardness or viscosity (95). However, with the changing nature and composition of cmde oil feedstocks over the past two decades, performance and supply factors are also an important consideration (95). 

Specifications for paving asphalt cements usually include five grades differing in either viscosity or penetration level at 60 °C (Table 8) (ASTM D496). Susceptibihty of viscosity to temperature is usually controlled in asphalt cement by viscosity limits at a higher temperature such as 135 °C and a penetration or viscosity limit at a lower temperature such as 25 °C. 

If straight-mn asphalts are reduced to a hardness below 300 penetration (30 mm), they are termed asphalt cements. For hot-mix paving, either the AC-10 viscosity grade or the next harder AC-20 grade is commonly specified. 

Liquid Asphalt. Liquid asphalt products comprise cutback asphalts and emulsions. A number of grades of different viscosities are available, which permit appHcation from ambient temperatures to 150°C. The lower viscosity products are used for dust-laying purposes and as tack coats, prior to laying asphalt surface courses. The heavier grades are used for mix-in-place road mixes. 

Only those grades of emulsified asphalt in general use have been indicated herein. It is possible that under certain variation of aggregates and/or climatic conditions, additional selections might be appropriate. Where the use of emulsified asphalt for appHcations other than those Hsted in the table are contemplated, the emulsion suppHer should be consulted. 

In addition to the paving grades of emulsions, a variety of products are available that are suitable for industrial uses, for paper sidings, and for use in the roofing appHcation field. Asphalts emulsified with colloidal clays are especially suitable for outdoor appHcations because of their exceUent weathering properties. Some of these products have been adapted for use with roofing systems, either with bmsh or spray appHcation. 

Since the propane deasphalting operation is primarily directed toward the manufacture of lubes with asphalt as a by-product, the grades of asphalt produced from a deasphalter are usually limited. In some cases considerable blending must be done (frequently with extract oils) to provide the variety of grades required by the consumer. 

---