What is differences between anionic & cationic Emulsion?

Bitumen Emulsions need to be classified by their ionic charge into cationic or anionic. Since water bitumen emulsions are used intensively as binding and film-forming material in construction, two types of emulsifiers are used: anionic and cationic. Cationic emulsions begin with a “C” If there is no C, the emulsion is usually an anionic. The charge is important when designing an emulsion for compatibility with certain aggregates.

The next set of the specification describes how quickly an emulsion will set or coalesce. RS (Rapid Set), MS (Medium Set), SS (Slow Set), and QS (Quick Set) are the setting-grades. Also, the adhesion used for bitumen emulsion that depends on the electrical charges in the bitumen emulsion particles and the surface of the rock material. The type of load is effective on the desired quality.

Chemical surface-active agents, which serve as emulsifiers, are classified by the electrochemical charge that is attained when they dissociate in a water solution, for example, cationic bitumen emulsion is suitable for siliceous (negatively charged) materials.

In the case of anionic emulsions, the chemical charge is negative. The chemical type and quantity of surface-active agent used in the manufacturing process govern the process in which the resulting asphalt emulsion can be used. Negative charges less commonly used for materials having positive charges (such as lime).

Cationic systems have a significant advantage over anionic emulsions. Most of the fillers used in road construction have a limited amount of positively charged particles, which can attract the negatively charged particles of the anionic emulsion. Therefore, it is more difficult to create a uniform structure and ensure a high degree of adhesion with an anionic surfactant. When using anionic emulsion, bitumen should be modified by additives, while in the cationic emulsion, the emulsifier itself serves as an adhesion additive. Unlike cationic emulsions, which readily interact with alkaline and acidic minerals, anionic emulsions are less versatile and work well only with alkaline minerals. The amount of emulsifier applied influences emulsion breakdown rate, the time until the bitumen precipitating from the emulsion, returns to its original state.

Almost all surfaces have a net negative charge. The strength or intensity of this negative charge may be different from material to material. Because of this phenomenon, anionic and cationic emulsions break in different ways.  Due to the chemistry of emulsions, they may react differently in specific weather and application conditions. The effective issues are weather, aggregate condition or emulsion used. The production of both Anionic & Cationic Bitumen Emulsions in correspondence to ASTM D977-12 and EN 13808-2005.

Performance of Anionic Emulsion Bitumen at the road:

In an application of anionic emulsion, negatively charged drops of asphalt are applied to a negatively charged surface. All components repel each other. The only way the emulsion can break is through the loss of water by evaporation. As more and more water is lost through evaporation, the particles are forced closer and closer together until they can no longer be separated by a film of water. At this point, droplets coalesce into larger and larger drops and ultimately a sheet of asphalt on the road

Performance of Cationic Emulsion Bitumen at the road:

In an application of cationic emulsions, the bitumen drops are immediately attracted to the surface and begin to break. The emulsion also loses water by evaporation. Thus the cationic emulsion has two breaking mechanisms at work and will break faster than a corresponding anionic emulsion.

Abbreviation on Emulsion bitumen

  • RS = rapid set
  • SS = slow set
  • QS = quick set
  • MS = medium set
  • HF = high float
  • C = Cationic
  • AE = anionic emulsion
  • h = hard penetration
  • P,M or L = modified with polymer or latex
  • 1 = low viscosity, stored @ cooler temps
  • 2= high viscosity, stored @ higher temps
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