What is Bituminous Concrete | Application Example and Uses

When it comes to highway construction, there are two distinct types: asphalt roads and concrete roads. While concrete roads have some edges, over 90% of roads are made of asphalt, also known as bituminous concrete roads, mainly due to better cost-performance, use of unskilled laborers, and, of course, aesthetics. Read on to learn about bituminous concrete roads, their construction, and more.

What is Bituminous Concrete?

Bituminous concrete is a type of building material widely used for paving highways, service roads, parking lots, etc. The product is composed of a mixture of stone and other aggregate elements, held together by a binding agent.

This binding substance is called Bitumen, which is a by-product of the petroleum refinement process. When heated, it becomes thick and sticky, similar to tar. And as it cools, it solidifies into a dense surface. In many parts of the world, bituminous concrete is also frequently referred to as asphalt.

Notwithstanding the similarity in their names, Bituminous Concrete differs significantly from regular concrete and doesn’t contain cement. While the majority of surfaces made of cement are white or gray, bituminous concrete is distinguished by its characteristic black color. 

Applications of Bituminous Concrete

Bituminous concrete is a solid, long-lasting substance that can withstand weathering and moisture. Additionally, the cost of production and maintenance is not too high. These elements have made it a well-liked option for numerous applications, such as:

1. Road construction

The most typical material used in road building is bituminous concrete. It serves as a base for roads as well as the material utilized to create the road surface.

2. Sidewalks, service roads, and driveways

Bituminous concrete is often the first choice for the construction of driveways, sidewalks, and other paved surfaces. It is also sometimes used to create play areas and other surfaces that require a long-lasting, slip-resistant characteristic.

3. Repairing of roads

Bituminous Concrete (BC) mix is frequently poured over worn-out roads to repair or fill in holes and irregularities. It is also laid directly over a gravel base layer to create new roadways and parking lots. After the bituminous concrete has been poured onto the road, big paving machines come into play for compacting and smoothing the surface.

Bituminous Concrete Mix Design

Bituminous concrete is made up of coarse aggregate, fine aggregate, mineral filler,  and bitumen, which result in a high degree of stability and toughness. The required density can be achieved by using properly sized aggregates and mineral fillers combined with the right amount of bitumen.

Bitumen 

Viscosity-graded bitumen or Polymer-modified bitumen should be used that is needed to comply with IRC & MORTH specifications, obtained from an approved source.

Coarse Aggregate

Crushed rock, crushed gravel (shingles), and crushed air-cooled slag that has been sifted through a 2.36 mm screen make up coarse aggregates. They must be free of dust, soft or friable materials, organic material, and other harmful things. They must also be rigid, sturdy, and cubical in shape.

Fine Aggregate

Crushed stone that has been retained on a 75-micron filter after passing through a 2.36 mm sieve makes up fine aggregates. They must be free of dust, soft or friable matter, organic material, and other harmful materials. They must also be clear, hard, sturdy, dry, and clean. 

Filler

Hydrated lime or cement that has been finely separated, as determined by the Engineer, shall be the filler. The filler must meet the grading specifications listed in MORTH’s table 500-8. 

Desirable Properties of BC Mix

• Stability: Sufficient resistance to deformation when repeated or sustained enough resistance to deformation when subjected to repeated or prolonged stresses.

• Durability: The ability to withstand deterioration caused by weathering or abrasive forces. Defeat against weathering or the abrasive powers of traffic.

• Flexibility: Refers to a bituminous mixture’s capacity to bend repeatedly without cracking and to adapt to base course shape changes. 

• Skidproof: To provide sufficient resistance to the sliding of Provide adequate resistance to prevent tire skidding.

• Impervious: Should minimize rainwater seepage. 

What Should be the Density of Bituminous Concrete?

Bituminous Concrete or Asphalt is a hot-mixed, hot-laid, plant mixture of well-graded, dried aggregates, filler, and paving bitumen in the best ratios possible depending on the requirements. 

When compacted, the mixture forms a dense material layer atop a previously manufactured granular, modified granular, or Dense Bituminous Macadam (DBM) that is 25–100 mm thick (preferably 2.243 g/cubic cm).  

Bituminous Concrete Paving Procedures

The following steps are involved in the construction of a BC road 

1. Preparing the existing base course layer: Identifying the potholes and other imperfections on the existing base course layer and filling them with premix chippings at least a week before installing the surface course.
2. Application of Tack Coat: Bitumen is applied for a tack coat at a rate of 6.0 to 7.5 kg per 10 sq.m. area. For non-bituminous bases, the rate should be 7.5 -10 kg. per 10 sq.m. for an ideal tack coat layer.
3. Placement of premix: Premix produced in a hot mixed plant is spread by a mechanical paver at 121 to 163 degrees Celsius. Accurate layer and camber checking is performed
4. Rolling: After the mix has been spread out across the base course, it is fully compacted at a speed of no more than 5 km/h by a road roller. 
5. Quality control: Regular checking is needed for the grading of aggregate, the temperature of aggregate, bitumen quality, and the temperature of mixing and compaction. Every 100 tonnes of mix released by the hot mix plant requires the collection and testing of at least one sample.
6. Finishing the surface: A 3.0 m straight edge should be used to inspect the surface of the newly constructed road. In a length of 300 m, the longitudinal undulations shouldn’t be more than 8.0mm, and there shouldn’t be more than 10 undulations that are higher than 6.0mm. 

Advantages of Bituminous Concrete

Although it doesn’t have the same strength as conventional concrete, asphalt paving is still the most often utilized material in road construction. Bituminous concrete roads have the benefits listed below:

• Simple yet sturdy: They are relatively simple to repair or refinish, and they are sturdy enough to withstand years of traffic load. 
• Smoother and less noisy: The BC roads offer a smoother and quieter driving experience than cement concrete roads and therefore aid in lowering noise pollution near major roads and highways.
• Lower cost: Both initial and lifetime maintenance costs of bituminous concrete roads is less compared to cement concrete roads. 
• Gradual decay: The process of BC pavement deforming and failing gradually. Cement concrete pavements produce brittle failures.

Roads made with bituminous concrete (BC) are likewise completely recyclable, albeit recycled components might not be as durable as new ones. To make recycled asphalt stronger and more resilient, some producers mix recycled tires or glass aggregate into the mixture.

Disadvantages of Bituminous Concrete Roads

Many of the negative aspects of bituminous concrete are related to how it affects the environment. Asphalt’s bituminous binding components come from fossil fuels. Fossil fuels are not only non-renewable and scarce, but they also play a variety of roles in pollution. Toxic gasses are released into the atmosphere during the fuel extraction process, causing both poor air quality and global warming.