The Essential Facts On Road Seals In Australia
Australia has an expansive road network covering huge distances, but not all roads are created equally. In our cities and larger regional areas, where of our population is concentrated, our roads need to be robust to withstand extensive use without the need for constant repairs.
While sealed roads form an important part of our nationwide road network, there are vast distances between our cities and densely populated areas that are less frequently used and, therefore, subjected to far less wear and tear. In these areas it is far more economical to use a means of road construction or sealing that is low-cost and lower maintenance. Here are the essential facts about Australian road seals.
What Are Road Seals?
Our roads are comprised of three layers: the subgrade or formation (the base), the pavement, and the surface – also known as the road seal. The road seal serves to protect the more expensive pavement and road base by taking the brunt of regular use and exposure to the elements. When the road seal breaks down or sustains damage, the pavement can be resealed to preserve the road and prevent the need for extensive and costly repairs to the lower layers of the road.
Why Do We Need Road Seals?
Sealed roads provide a better surface for road users, prevent degradation of the road surface, and lessen the need for constant, time consuming and costly road maintenance. There are several methods of road construction and sealing used in Australia, and the method chosen will generally depend on a range of factors, including current and projected usage, local environmental considerations, and cost-effectiveness.
What Are the Different Types of Road Seal?
Hot bitumen seals
Hot bitumen seals are the most common type of spray seal used on bitumen road surfaces in Australia. Bitumen is produced in several different grades – some hard and brittle, some fluid and soft – but must be liquidised so that it can be pumped and sprayed onto the road surface.
To do this, the bitumen is heated to between 160-220 degrees Celsius, and a cutter agent or oil, such as kerosene, is added to the bitumen to temporarily reduce its viscosity, which helps it properly soak into the road surface and adhere to both the surface and the aggregate that will be spread on top of it and rolled into it.
Emulsion seals
A bitumen emulsion is a mixture in which bitumen is dispersed in water to produce microscopic bitumen droplets that have a positive (fast), negative (slow) or neutral charge, which affects the rate at which the bitumen sets.
These droplets are formed by using chemical emulsifiers and a homogeniser (a piece of equipment that forces substances through tiny openings against a hard surface, creating shear forces that blend the substances together) to combine bitumen and water. Although similar to standard spray seals, the bitumen/water emulsion allows for successful application at lower temperatures.
The addition of polymers (plastics) during the emulsification process produces a ‘polymer modified bitumen emulsion’. Polymer modified emulsions have excellent elastic and adhesive properties that create a strong bond between the bitumen binder, base and aggregate.
Dust seals
Dust seals are intermittent seals applied to the existing surface of dirt and gravel (unsealed) roads, with minimal road drainage, road formation and road pavement construction, for the purposes of dust suppression.
For many councils, the application of a dust seal is a low cost, risk-based solution that provides a sealed roadway in locations where it is not economically viable to conduct road works to standard engineering specifications.
Hot mix asphalt
Hot mix asphalt (also known as asphaltic concrete) is a mixture of aggregate, sand, and filler that is heated to approximately 160 degrees Celsius while adding hot bitumen. The size of the aggregate used in the mixture depends on where the asphalt is to be laid – for example, larger-diameter aggregate is used for roads, smaller-diameter aggregate is used in driveways, carparks, and sports courts.
Primerseal
Primerseal is a spray seal treatment applied in a single stage. It is not intended to be a long-wearing surface and is usually covered by an asphalt overlay or final seal one to three years after being laid.
Rather than priming the granular road surface, a liquid primer-binder (typically, a cutback bitumen, generally comprised of bitumen, cutter oil and an adhesive agent) is sprayed onto the prepared road surface and then covered with a layer of aggregate. The primer-binder penetrates and adheres to the road surface and holds the aggregate in place. The surface is then rolled and can be immediately opened to controlled traffic.
Spray seals
Spray seals, also sometimes known as “sprayed seals”, “chip seals” or, simply, “bitumen seals”, are constructed by pouring aggregate over a waterproof binder. There are several types of spray seals, including primer seal, two coat seals, final seals and reseals.
The binder – a hot mixture of bitumen and kerosene – is sprayed onto the road surface, forming a waterproof barrier. This waterproof membrane is then covered with a thin layer of aggregate, which is rolled into the bitumen. A polymer or crumb rubber may be added to the bitumen to enhance the strength and flexibility of the surface.
Two coat seals
Two coat seals are comprised of a layer of bitumen containing large pieces of aggregate, which is then sealed with a second layer of bitumen containing smaller pieces of aggregate. This kind of road treatment is more hard-wearing than a typical spray seal and is particularly resistant to stripping caused by turning traffic, due to the combination of large and small aggregate.
Northern Highways Bitumen – The Answer To All Your Road Seal Questions
For more information on road seals, consult the road seal specialists at Northern Highways Bitumen. With years of experience and expert knowledge on road surface sealing, you can trust Northern Highways Bitumen to give you reliable advice on which road seal solution will best meet your needs.
To find out how we can help you or your organisation with all your road sealing requirements, contact Northern Highways Bitumen for an obligation free quote today. Give us a call on 1300 858 751, send us an email at sales@northernhighwaysbitumen.com.au, or complete our Enquiry Form and one of our friendly staff will get back to you.
