1.2.1.1  Roofing Asphalt

The distillation of crude petroleum yields bitumen residues that are called asphalt. Asphalt qualities are determined by the nature of the crude oil used and by the refinery process.

In Canada, asphalt is classified in accordance with CSA 123.4 Asphalt for Constructing Built-up Roofing Coverings and Waterproofing Systems. This standard covers three types of asphalt that are typically used in Canada.

• Type 1: asphalt for use on built-up roofs with slopes less than or equal to 1:16 (6.25⁰) and for use as waterproofing below ground level when not exposed to surface temperatures above 25°C (77°F).
• Type 2: asphalt for use on built-up roofs with slopes less than or equal to 1:8 (12.5⁰) and for use as waterproofing above ground level on vertical surfaces not exposed to direct sunlight.
• Type 3: asphalt for use on built-up roofs with slopes greater than 1:8 (12.5⁰) for exposed applications or for use as waterproofing above ground level on vertical surfaces not exposed to direct sunlight.

Physical properties of asphalt are also covered in the standard including softening point, flashpoint and equiviscous temperature (EVT).

Softening Point

The softening point of asphalt roughly corresponds to the temperature at which the material commences to melt. The softening points for the different types of asphalt are as follows:

Flashpoint and Auto-Ignition

The flashpoint is the temperature at which the material gives off vapour sufficient to form an ignitable mixture with air. This occurs near the surface of the liquid asphalt in the heating vessel. The minimum flashpoint temperature of 260°C (500°F) is a work safety requirement. The actual flashpoint temperature of packaged or bulk asphalt products depends on the type of crude oil used in the manufacture of the asphalt.

When the ratio of gas to air above the surface of the hot asphalt reaches the proper proportions, the mixture becomes explosive. The auto-ignition temperature of this flammable vapour is the lowest temperature at which a chemical reaction within the mixture will occur and the vapour will self-ignite. Auto-ignition normally occurs at a temperature approximately 50°C (122°F) higher than the flash point temperature. It is not necessary to have a spark or flame for auto-ignition of the asphalt. A surface heated to the required temperature, such as a hot motor or smokestack, in contact with the asphalt vapour will cause it to ignite.

Equiviscous Temperature (EVT)

The equiviscous temperature (EVT) is the temperature at which a bitumen attains the proper viscosity for built-up membrane application. The recommended EVT is determined by the chemical composition of the material. According to the standard, each supplier/ manufacturer is to provide information regarding the recommended EVT on the packaging or bill of lading.

1.2.1.2 Coal Tar Pitch

Coal tar pitch is a by-product obtained during the production of coke from bituminous coal. The softening point for coal tar pitch is approximately 60°C (140°F) and its flashpoint varies from a minimum of 110°C (230°F)