Bitumen is used in roads, roof membranes, car parks, and sealing systems—but not all grades are the same. If the material isn’t matched to traffic load, climate, or surface movement, it breaks down fast. Cracks appear, softening begins, and repairs follow.
This happens more often than it should. Surfaces show early rutting, joints lift, and waterproofing fails—despite being installed correctly. The problem usually starts with poor grade selection.
A surface exposed to heat needs a grade with thermal resistance. A high-traffic area needs better recovery under pressure. Without this match, the material fails in months—not years.
This guide explains how bitumen is graded, what each grade is made for, and where it performs best. Whether you’re working on access roads, roof systems, or seal joints, the right grade keeps the surface stable and cuts down future repair work.
What Is Bitumen Made From?
Bitumen is a dense, dark substance made mostly of hydrocarbons. It comes from refining crude oil, though some types occur in natural deposits. Its adhesive and waterproof properties make it a key material in civil works, roofing, and insulation systems.
Once refined, bitumen is classified based on how it behaves under heat, load, and movement. These behaviours define its grade and application. The more refined the product, the more stable it becomes across temperatures and site conditions.
Natural vs Refined Bitumen
There are two broad categories:
Natural Bitumen
This form is mined from rock or sand. Tar sands and oil sands are examples. It’s brittle under temperature changes and prone to cracking without additives. For this reason, it’s often limited to waterproofing or older-style insulation uses.
Refined Bitumen
Crude oil goes through distillation to produce consistent bitumen. Additives or modifiers are often mixed in to improve flexibility, adhesion, or performance under extreme temperatures. This is the form most often used in roads, roofing, and infrastructure.
Refined bitumen is easier to control across climate zones and load types. This makes it preferred for most commercial work.
Grades of Bitumen Based on Penetration
Penetration grades define how soft or hard the bitumen is at a set temperature. It’s measured in tenths of a millimetre.
- Hard Grades (<50) – Used in waterproofing and insulation. These grades don’t deform easily under pressure but can crack in heat changes.
- Medium Grades (50–150) – Used in most road and paving projects. These allow movement under vehicle load without cracking.
- Soft Grades (>150) – Used in high-density traffic zones that demand more flexibility.
Selecting the wrong grade for a surface load often leads to rutting, bleeding, or surface fatigue.
Performance Graded Bitumen (PGB)
PGB is selected based on how it performs under specific traffic and climate conditions. Instead of just hardness, this grading looks at:
- Rutting resistance
- Thermal cracking resistance
- Elastic recovery
Each PGB is labelled with two values (e.g. PG 64-22):
- First number = max temperature it can handle without deforming
- Second number = lowest temperature before it cracks
PGB is used for:
- High-traffic motorways
- Airport runways
- Freight corridors
- Ports and loading docks
Because PGB is selected based on function, it reduces failures due to seasonal movement or heavy load impact.
Viscosity Graded Bitumen
Viscosity grading focuses on how the material flows at a given temperature. It’s crucial in hot mix and spray seal applications.
- High Viscosity (>180 Poise) – Best for sealing, tank linings, and areas needing slow flow or high resistance.
- Medium Viscosity (80–180 Poise) – Common in road surfacing. Flows well during application but hardens on cooling.
- Low Viscosity (<80 Poise) – Used in spray seal work or priming surfaces with light aggregate bonding.
Viscosity matters when determining how the bitumen will perform during application and in-place once cooled. Matching flow rate to climate and mix temperature avoids binder separation or poor coverage.
Specialised Bitumen Types
Modern infrastructure uses bitumen in engineered forms:
Cutback Bitumen – Mixed with a solvent to lower viscosity. Used in cold weather priming and surface preparation.
Emulsified Bitumen – Mixed with water and additives. Common in chip sealing, slurry surfacing, and temporary fixes.
Modified Bitumen (PMB) – Mixed with polymers for elasticity. Used in roofing, bridges, and high-stress zones that face movement or vibration.
Each version is selected based on site behaviour and end-use demands—not just surface appearance.
Bitumen in Road Construction
Most road projects in Australia use a combination of medium-grade and viscosity-rated bitumen. In sealed roads, bitumen binds the aggregate in hot mix asphalt. In sprayed seals, it acts as the base layer for stone coverage.
Where extreme weather or traffic loads apply, performance graded bitumen replaces standard grades to improve longevity.
See how Road Ways handles bitumen road construction across different zones and load types.
Bitumen in Roofing and Waterproofing
Bitumen is widely used in flat and pitched roof systems. It provides water resistance and UV shielding. In roofing, it’s layered into sheets (modified or oxidised) or applied as hot liquid.
For waterproofing, bitumen membranes protect foundations, basements, and retaining walls from ground moisture. Hard grades with high viscosity are preferred to prevent flow and cracking.
Applications include:
- Torch-on membranes
- Bituminous paint under screeds
- Joint sealing between pre-cast elements
Bitumen in Industrial Insulation
Bitumen acts as both an insulator and a dampener. In wall cavities, it limits heat transfer. Between slabs, it blocks noise and vibration. It’s also applied in acoustic flooring systems or HVAC panel gaps.
These products are built using modified bitumen with high elastic recovery, so the insulation layer remains intact over years of compression and climate exposure.
Bitumen in Sealants and Adhesives
Bitumen is used in sealant compounds for expansion joints, service entries, and roofing seams. It’s also present in adhesives for roofing felt, shingles, and membrane layers.
When applied hot, it forms a flexible bond that absorbs movement. When cooled, it hardens into a weather-resistant seal.
Roofing, flooring, and structural expansion joints all benefit from the long-lasting sealing capacity of medium or modified bitumen.
Bitumen in Non-Road Applications
In industrial tanks, ponds, or bunds, bitumen liners reduce evaporation and prevent chemical seepage. It’s also used in protective coatings for pipelines and metal sheets, slowing corrosion.
Cabling, ducting, and waterproof packaging sometimes rely on thin bitumen coatings to keep moisture out and structure stable.
Bitumen has a broad role across infrastructure—not just on roads.
Final Advice from Road Ways
Bitumen failure usually traces back to a mismatch between material grade and site needs. Whether it’s a driveway or a port accessway, every site demands the right bitumen type, grade, and mix for its environment.
At Road Ways, we match each application to a tested material grade that fits:
- The traffic type
- Surface use
- Temperature shifts
- Moisture levels
- Surface fall or drainage setup
Reach out if your surface project requires stability, load tolerance, or weather resistance that lasts.
