Cold Mix Asphalt

 Cold Asphalt/Asphalt Emulsion

Cold asphalt is green technology for construction of bituminous road which complies mixture of Bitumen Emulsion, Aggregates and Filler. It has many uses in road construction and maintenance. Asphalt emulsion is also often used as an alternative to hot mix asphalt for cold processes such as chip sealing or slurry sealing. Nowadays, Cold Asphalt Emulsion are used for mixing and spraying in road construction and road maintenance especially patch works, potholes repair, emergency road construction. It is efficient in all types of weather/climate : hot, cold or even wet.

Ingredients of Cold Asphalt

1) Bitumen Emulsion (Binder)

2) Aggregate for 20mm thick - 13.2mm down, 9.5mm down, 6mm down

3) Aggregate for 40mm thick - 37.5mm down, 19 mm down, 6mm down

4) Mineral Filler (Lime or cement or non-plastic materials)

Process for the preparation of a cold mix asphalt paving

In conventional cold mix processes, the liquid asphalt is in the form of an asphalt emulsion. The asphalt emulsion is then blended with a sized aggregate to form a cold mixture useful for asphalt pavement. The aggregate then cements into a hard pavement that is essentially identical to the hot mix bituminous asphalt.

• Prepare batch of 0.05 m3 of aggregate (mixture in ratio) and feed into concrete mixture or lay on ground (if manual).

• Pour 8.75 lit of Rapid Setting/Medium Setting Emulsion into concrete mixture or over aggregate (if manual).

• Allow mixing for 45 sec until all the aggregate are well mixed in emulsion. Quickly spread the grey aggregate mix over surface to be lay. If hand mixed, mix until all the aggregate turns grey in color. Mix water to increase workability.

• Compact the overlay cold mix with tandem with 2 pass. 

• Make final roll by tandem roller and the road is ready to serve.

Bitumen Emulsion 

Bitumen emulsion is a mixture of fine droplets of bitumen and water. But as the bitumen is a petroleum product it doesn't mix with water and as it is sticky in nature, it doesn't easily gets disintegrated into fine droplets. To overcome this problem an emulsifier is used. Emulsifier keeps the bitumen in its fine droplet state by disallowing it to mix with other droplets. As the droplets are very fine they suspend in water. “Therefore, bitumen emulsion is a dispersed liquid consisting of three products, i.e. water, bitumen and emulsion”. Generally, the amount of bitumen in the bitumen emulsion is 55 to 65%, the amount of water 35 to 45 %, and the amount of emulsifiers should be a maximum 0.5% of bitumen emulsion’s weight.

Types of Bitumen Emulsion:

(A) Based upon the time taken by the emulsion to evaporate the water and between particles to separate from water, bitumen emulsion is further classified into 3 types based on setting time:

1) Slow Setting (SS) 2) Medium Setting (MS) and 3) Rapid Setting (RS)

(B) Based upon the type of surface charge, they are divided into 2 types,

1) Anionic Bitumen Emulsion and 2) Cationic Bitumen Emulsion

Cationic emulsifiers, for example, form a layer of positive charge around the bitumen droplets that prevent them from joining each other.

This makes bitumen dispersion in water more durable.

The electronic charge of bitumen emulsion decides on what kind of surface it should be used.

Some aggregates (such as marble aggregates) mix well with anionic bitumen emulsion and some others are a better solution to cationic bitumen emulsion (such as granite aggregates).

Both cationic and anionic bitumen emulsions are categorized according to the setting time.

Below table shows various categories of bitumen emulsion and their globally standard names.

Bitumen Emulsion Application

It is used in road construction and maintenance, as well as for waterproofing and sealing applications. 

This type of bitumen is used in various methods of road construction including tack coats, chip seals, slurry seals and micro surfacing.

Tack Coat:

Bitumen emulsion especially CRS-1 and CRS-2 are the best choice for tack coats between layers of asphalt pavement.

For running tack coats, the best temperature is 10 to 15 degrees Celsius.

Chip Seals:

It is possible to use bitumen emulsion to renovate and waterproof old roads.

Chip seals are one of the most cost-effective methods of pavement preservation, since they protect underlying pavement from oxidation and aging.

Generally speaking, chip seals are typically used on rural roads carrying lower traffic volumes.

Slurry Seals:

In order to give a uniform texture to roads, engineers use slurry seals.

This mixture of bitumen emulsion, aggregates and mineral fillers is sprayed on the pavement to seal it and make the surface weather-resistant.

Slurry sealing is also used in the maintenance of asphalt pavements and it helps to reduce road surface damage due to bitumen oxidation, but cannot increase its structural strength.

Micro Surfacing:

Micro surface is another form of slurry in road construction, which is composed of polymer modified bitumen emulsion.

The existence of dense-graded aggregates in this mixture makes it stronger and more durable than a slurry seal.

A specialized machine is used to apply the mixture on existing pavements, which carries all components and mixes them on-site. The mixture is then spread onto the road surface.

Bitumen Emulsion Packaging

For bitumen emulsion, there are several types of packaging, including :

• Barrel
• IBC
• Flexi tank
• Reconditioned drums

Now a days, ready to use cold asphalt in 25kg pails packaging also available which does not require any mixing or hitting. Coverage area is 1m2 of 25mm thick by 25 kg clod asphalt pack.

Application for a Pat-hole Repair by ready to use cold asphalt: