Bitumen (Asphalt)

The term bitumen refers to a substance produced through the distillation of crude oil. Bitumen is known for its waterproofing and adhesive properties and is commonly used in the construction industry, notably for roads and highways. Production occurs through distillation, which removes lighter crude oil components like gasoline and diesel, leaving the heavier bitumen behind. Deposits can also occur naturally at the bottom of ancient lakes, where prehistoric organisms have decayed and been subjected to heat and pressure.Bitumen is a byproduct of crude oil. It is composed of complex hydrocarbons and contains elements like calcium, iron, sulfur, and oxygen. The quality of material and ease of production depends on the source and type of crude oil from which it is derived. It was first used for its natural adhesive and waterproofing characteristics, helping to bind building materials together, as well as to line ship bottoms.

Bitumen can deform permanently under heavy loads. Continued stress on the material can result in cracking. It oxidizes, which can leave the asphalt brittle. The way its shape is affected depends on a few things, including the composition of the asphalt mixture and the ambient temperature.As noted above, bitumen isn’t just produced by distilling crude oil; it’s also a naturally-occurring product. The term is also used to refer to oil sands or partially consolidated sandstone containing a naturally occurring mixture of sand, clay, and water that is saturated with a dense and extremely viscous form of petroleum.

Properties of Bitumen

Adhesion: Bitumen has the ability to adhere to a solid surface in a fluid state depending on the nature of the surface. The presence of water on the surface will prevent adhesion.

Resistance to Water: Bitumen is water-resistant. Under some conditions, water may be absorbed by minute quantities of inorganic salts in the bitumen or filler in it.

Hardness: To measure the hardness of bitumen, the penetration test is conducted, which measures the depth of penetration in tenths of mm. of a weighted needle in bitumen after a given time, at a known temperature. Commonly a weight of 100 gm is applied for 5 sec at a temperature of 77 °F. The penetration is a measure of hardness. Typical results are 10 for hard coating asphalt, 15 to 40 for roofing asphalt and up to 100 or more for waterproofing bitumen.

Viscosity and Flow: The viscous or flow properties of bitumen are of importance both at high temperature during processing and application and at low temperature to which bitumen is subjected during service. The flow properties of bitumen vary considerably with temperature and stress conditions. Deterioration, or loss of the desirable properties of bitumen, takes the form of hardening. Resultantly, a decrease in adhesive and flow properties and an increase in the softening point temperature and coefficient of thermal expansion.

Softening point: Softening point is the temperature at which a steel ball falls a known distance through the bitumen when the test assembly is heated at a known rate. Usually, the test consist of a (3/8)in dia steel ball, weigh 3.5 gm, which is allowed to sink through a (5/8) in dia, (1/4) in the thick disk of bitumen in a brass ring. The whole assembly is heated at a rate of 9 °F per min. Typical values would be 240 °F for coating grade asphalts, 140 °F to 220 °F for roofing asphalt and down to 115 °F for bituminous waterproofing material.

Ductility: The ductility test is conducted to determine the amount bitumen will stretch at a temperature below its softening point. A briquette having a cross-sectional area of 1 in2 is placed in a tester at 77 °F. Ductility values range from 0 to over 150 depending on the type of bitumen.

Bitumen Grades

Bitumen grades range from the softer, more malleable variants used in colder regions to the harder, sturdier ones perfect for warm climates.

• Oxidized Bitumen: A Hardened Solution

Oxidized bitumen, also known as blown bitumen, is produced by passing air through the raw bitumen at high temperatures. This process increases the bitumen’s softening point and viscosity, resulting in a harder, more stable material. Oxidized bitumen is commonly used in roofing applications, such as waterproofing and insulation, due to its excellent adhesive properties and resistance to water and extreme weather conditions.

• Penetration Bitumen: The Versatile Standard

Penetration bitumen, named after the penetration test used to measure its consistency, is the most commonly used grade of bitumen in road construction. Its versatility stems from its ability to be mixed with various aggregates, making it suitable for a wide range of pavement types. This grade of bitumen is graded based on penetration values, with lower values indicating a harder, more viscous material.

• Emulsion Bitumen: The Water-friendly Alternative

Emulsion bitumen is a blend of bitumen, water, and emulsifying agents that form a stable, homogeneous mixture. This grade of bitumen is typically used in cold weather or environmentally sensitive areas, as it does not require heating for application. Emulsion bitumen is utilized for road maintenance, surface dressing, and tack coats due to its fast-setting properties and ability to bond with damp surfaces.

• Performance Grade Bitumen: The Industry Standard

Performance grade (PG) bitumen is a modern classification system developed to address the limitations of older grading methods, such as penetration and viscosity grading. PG bitumen is designed to withstand specific temperature and performance requirements, making it suitable for various climates and traffic conditions. This grade of bitumen is widely used in road construction and pavement maintenance.

• Polymer Modified Bitumen: The Durable Upgrade

Polymer modified bitumen (PMB) is the result of blending raw bitumen with polymers, such as styrene-butadiene-styrene (SBS) or ethylene-vinyl acetate (EVA). This modification enhances the bitumen’s elasticity, resistance to deformation, and durability. PMB is ideal for heavy-duty pavements, airport runways, and bridge decks, as it can withstand heavy traffic loads and extreme temperature fluctuations.

• Viscosity Grade Bitumen: The Temperature-tailored Option

Viscosity grade (VG) bitumen is a classification system that measures the bitumen’s viscosity at specific temperatures. This grading system ensures the material’s performance at various temperature ranges, making it ideal for regions with fluctuating weather conditions. VG bitumen is primarily used in road construction and maintenance, as it offers improved adhesion, workability, and durability.

• Cutback Bitumen: The Easy-to-Apply Choice

Cutback bitumen is created by blending raw bitumen with a solvent, such as kerosene or naphtha, which reduces its viscosity and makes it easier to apply. This grade of bitumen is often used in road construction and maintenance, as it can be applied at lower temperatures and does not require specialized equipment. However, due to environmental concerns associated with the evaporation of solvents, the use of cutback bitumen has been limited in recent years.