An Introduction About Anti Stripping Agents
Anti stripping agents modify the chemical structure of bitumen. They are complex chemicals that guarantee a perfect adhesion of the bitumen film on the aggregate surface. Oppose the disgregating action of water, they increase the wettability of bitumen, the resistance to the mechanical and cyclic strains. Increase the durability of bituminous mixtures, guarantee resistance, allow to extend the production- to-lay times, easing the compaction.
Anti stripping agents are the chemical compounds, which renders minimum stripping (breaking) of bonds between the aggregate surface and the bitumen. The stripping is attributed to water which gets between the bitumen film and the aggregate surface. The aggregate surface is having greater attraction to water than for bitumen owing to hydrophilic nature of aggregate. This leads to the breaking of adhesive bond of bitumen to aggregate.
The natural stones aggregate mostly used for road construction and the surface treatment in India generally do not conform to the stripping requirements viz 5% (max) specified.
To achieve good bong between aggregate and bitumen the anti stripping agents are used. The types of anti stripping agents used are Fatty amines and Tallow Diamine, and Fatty amino and Immidazoline derivatives. In General literature, it is claimed that the use of anti stripping agents had resulted in a substantially longer lasting asphalt pavement and improved tensile strength saving in maintenance and repair cost from base course to surface mixes.
Importance of Anti-Stripping Agent
The Premature failure of Bituminous Pavements due to action of water is the most common problem and single largest factor causing early pavement distress. The most important reason contributing to this condition is improper adhesion between bitumen and commonly used aggregates, salt contamination of water/soil and water drainage problems. Majority of aggregate show high value (as high as 70%) and most of them fail miserably in bitumen adhesion properties. These conditions prevail across continents, thus all around the world, Anti-Stripping Agents are recommended and used to extend pavement life.
Advantages of Anti-Stripping Agent
In addition to reduce water damage to Bituminous Pavements it provide following benefits :
- Provide saving by optimizing the Bitumen requirement in the mix.
- Help utilize locally available aggregates to save in transportation
- Provide fast coating of chips due to surface active action.
- Reduce requirement of fines in the mix.
- Help in easy compaction of the mix ensuring better surface texture.
- Improve Retained Marshall Stability for high rainfall area.
- Help the construction of roads during damp climate.
- Save road from freeze-thaw in snow-bound areas.
- Save upto 50% in maintenance cost.
- Help in stable road maintenance even using wet aggregates.
- Cost effective.