What is Milling in Road Constructions

What is Milling in Road Constructions

Milling in road construction gives a new lease of life to worn-out roads. Asphalt roads are often found to have developed cracks and potholes, especially after the rainy season. Sometimes, the road level may also need to be lowered to match the surroundings. Milling makes road reconstruction green, ecological, and cost-effective.

What is milling in road construction?

Pavement milling, asphalt milling, cold milling, or cold planing is a process of recycling bituminous concrete for road reconstruction. This involves the removal of a portion of the paved surface, such as roads, driveways, bridges, or parking lots.

Because of asphalt milling, the height of the road does not increase because fresh asphalt is laid down in place of old asphalt, which is removed and recycled. Asphalt milling involves removing the top layer of asphalt to a specified depth without disturbing the underlying subbase.

After being extracted from the surface of the damaged road, asphalt pieces are transported to a processing plant, where they are broken down and converted into gravel-size aggregates.

Next, the asphalt aggregates are reactivated by mixing them with other materials, including sand, stone, gravel, and binding agents such as bitumen, to create a stronger and more durable paving material.

What are some other purposes of milling in road construction? 

Milling can also reduce surface distress, resulting in a better driving experience and/or longer roadway life. Milling can help to solve the following problems:

  • Ravelling: It is a condition when aggregates are separated from the binder and lie loose on the road
  • Bleeding: This happens when the binder (bitumen) comes up to the surface of the road
  • Rutting: the creation of longitudinal depression in the pavement along the line of movement, commonly in the wheel path
  • Shoving: This results in the formation of ripples, a washboard-like action in the opposite direction of travel
  • Ride quality: swells, bumps, sags, or depressions in the road surface
  • Accidental and/or fire-related damage

Milling is also used to control or adjust the height of a portion or the entire length of the road. Heights and clearances of other road structures, such as curb reveals, manhole and catch basin heights, shoulder and guardrail heights, and overhead clearances, can be controlled in the same way. 

Another application of milling is to vary the slope or camber of the road, as well as make grade adjustments to aid in drainage.

What are the different methods of milling? 

There are three major forms of road milling for coping with various circumstances. Each milling method necessitates specialised equipment and skills.


Fine milling is used to repair and renew the surface layer of pavement. The procedure involves removing the damaged surface asphalt, repairing the foundational damage, and then resurfacing the surface with fresh asphalt. And finally, smoothing and levelling the new asphalt surface.


Planning is commonly used in repaving major highways. Its goal is to create a flat surface for vehicles to be used for residential, industrial, or commercial purposes. 

The planing procedure entails removing the entire damaged pavement rather than just the surface, creating aggregate from the removed particles, and adding the aggregate to the rebuilt pavement.


Micro milling, as the name implies, removes only a small layer of asphalt (approximately one inch or less) rather than the entire surface or pavement. It is primarily used for maintenance rather than repair. 

This is a proven way to keep the pavement from deteriorating. In micro milling, a revolving milling drum with numerous carbide-tipped cutting teeth, also known as road milling teeth, is utilised. 

Rows of road-milling teeth are used to create a relatively smooth surface. However, unlike traditional milling drums, micro-milling drums merely mill the surface to a shorter depth while addressing the same road issues.

How is milling done?

The milling operation uses road milling machines or cold planers. However, there are other equipment used in the operation, such as water trucks, dump trucks, sweepers, and hot-mix plant. The asphalt chunks are removed, chopped, compacted, and redistributed by this machinery working together. The general procedure for milling a road includes the following steps:

1. Excavating the surface layer of the road

A milling machine excavates and grinds the asphalt surface. Also called a cold milling machine, this consists of a drum with rows of teeth across its curved surface that moves over the surface of the pavement. As a result, asphalt pieces are removed and ground by the teeth and sheer weight of the drum. 

You can adjust the machine to obtain the required size of chunks based on the amount of existing surface that needs to be removed.

2. The removal of milled pieces and their loading into a dump truck

The milling machine screens the crushed asphalt after it passes through the grinder. The asphalt millings are cleaned using a vacuum and then moved to a conveyor system in front of the machine.

The asphalt chunks are then transferred to dump trucks for sending to a RAP plant for recycling.

3. Cleaning of the milled surface

The process of breaking up the current asphalt generates a lot of dust and debris. The surface must be completely cleaned before new asphalt can be applied.

A sweeper removes any remaining asphalt pieces, resulting in a smooth surface for repaving.

4. Fresh asphalt aggregates are poured 

The new asphalt can be laid once the surface has been cleared of any dust and debris. It should easily bind to the new surface if properly prepared.


What are the different types of milling machines?

There are 3 main categories of milling machines as given below:

Based on the milling form

Milling machines are classified into two types based on their milling form: cold milling machines and hot milling machines. Cold milling is characterised by high power, rapid tool wear, and the use of cutting material according to particle size. It can be outfitted with sprinklers to spray water, which is very common. 

The hot milling machine, which facilitates hot recycling, is more complex as a result of the incorporation of heating equipment and requires a strong base layer to bear its weight. However, hot recycling offers cost-effectiveness compared to cold milling. 

Based on structural characteristics

It is classified as forward milling or reverse milling based on the rotation direction of the milling rotor. When the milling machine is running, the rotor rotates in the same direction as the wheel, indicating that it is forward milling; otherwise, it is reverse milling.

Based on the rotation direction 

It is classified into two types based on its structural characteristics: wheel type and track type. The wheel type has strong mobility and easy transition, making it ideal for small and medium-sized road operations; the crawler type is often a large milling machine with a milling width of more than 2000mm.