Asphalt concrete is a graded mixture of aggregate and filter with asphalt; hot or cold and rolled.
It is used in building surface operations such as runways, taxiways, airports, road surfaces, aprons, and parking lots.
Here we will learn about Asphalt concrete, types of asphalt concretes & much more.
Introduction to Asphalt concrete:
In short, asphalt concrete is a composite material consisting of a grade of aggregate and asphalt used as binder mixed together then molded into layers and compacted, it is also being used as a core for embankment dams.
It is also called special concrete consisting of a mixture of graded concrete and hot asphalt to be applied and spread.
This concrete is also referred to as a “blacktop”, especially in North America.
Components of asphaltic concrete:
- Careful selection of binders and aggregate.
- Volumetric proportioning of ingredients.
- Evaluation of the finished products.
Types of Asphalt Concrete:
1.Hot mix asphalt concrete (HMAC or HMA):
It is produced by heating the asphalt binder and drying the aggregates to remove the moisture from it, before mixing.
The mixture is usually collected at about 150 °C for new asphalt, 166 °C for polymer modified asphalt and 95 °C for asphalt cement paving; condensate when the asphalt is sufficiently sizzling.
The HMAC is a type of asphalt commonly used for high traffic pavements of highways, airports, and race tracks.
2.Warm Mix Asphalt Concrete (WMA):
This type of concrete is also produced by adding zeolites, waxes, asphaltic emulsions or water to asphaltic binder before mixing.
Such concrete emits less CO2, aerosols and vapour, demonstrating its advantage.
The lower laying temperature furthers the rapid availability of the floor to be used, which is extra advantageous for construction sites with vital time schedules.
Adding additives such as zeolites, waxes, and asphalt emulsions to hot mixed asphalt can cause easy condensation and allow for cold weather or longer stays.
3.Cold mix asphalt concrete:
This type of concrete is produced by blending the asphalts in water with the soap as essential before mixing with the aggregates.
When concrete is in a blended state, asphalts is less viscous and the mixture becomes easier to work and compact.
Cold mixes are commonly used as batching materials for service roads subject to low traffic.
4.Cut-back asphalt concrete:
This type of concrete is produced by dissolving the binder in kerosene or other lighter fraction of petroleum before mixing with the aggregate.
When it is in the dissolved state, the asphalt is much less viscous and the mixture turns into simpler to work.
After inserting the mixture down, the lighter fraction evaporates.
This increases pollution from volatile organic compounds present in the volatile fraction, so the cut-off asphalt has been largely replaced by emulsion of asphalt.
5. Mastic asphalt concrete or sheet Asphalt:
This type of concrete is formed by heating exhausting grade blown bitumen in a mixer until it has change into a viscous liquid after which the aggregate mix is added.
The bitumen aggregate mixture is matured for about 6 to 7 hours as soon as it is prepared, the mastic asphalt mixer is taken to the highway construction work.
It is normally positioned to a thickness of about 20- 30 mm for pavement and highway applications, it is laid to a thickness of 10 mm for flooring or rooftop.
Rarely, an additive such as polymers and ant stripping agents can be added to improve the properties of the final product.
6. Natural asphalt concrete:
This type of concrete might be produced from the bituminous rock which is found naturally in some parts of the world.
Advantages of Asphalt Concrete:
- It is less expensive than concrete, takes less time to build an road.
- This thick asphalt structure is long-lasting and only requires surface maintenance.
- They are fast and cost-efficient, especially for city and country roads.
Disadvantages of Asphalt Concrete:
- They are less durable and become softer in hot climates.
- When the asphalt is not laid properly, it causes cracks and issues.
- This construction method requires heavy equipment to be installed, no matter what type of asphalt has been used.
For asphalt concrete, the mix design includes aggregates, combination of crushed stone, gravel and asphalt with asphalt emulsion.