Based on the degree of dispersion all bitumen emulsions can be divided into poly- and monodispersed emulsions. In most cases, road bitumen emulsions are polydispersed but it doesn’t mean than monodispersed emulsion doesn’t have any applications. Monodispersed bitumen emulsions help to make materials with high optic properties and coloured materials with a minimum amount of dye.
Dispersion influences many properties of bitumen emulsions. including viscosity and lability. Technically, a droplet of the proper size can be obtained by:
- using a special additives;
- selection of emulsifier type;
- selection of disperser type and operation methods.
The following principles should also be considered. Lability of polydispersed emulsions depends on the average droplet diameter. The bigger it is, the higher the lability. Conversely, material viscosity depends on emulsion droplet size deviation from their average size. Less deviation means higher viscosity. If the deviation is zero, the viscosity is at maximum, which means that the size of all the droplets in the monodispersed emulsion is the same.
The required lability can be obtained by selecting the proper dispenser operation mode, allowing to create droplets of a specified size without changing the composition of the emulsion. This effect can be achieved by changing of rotation speed of colloid mill rotor and/or by increasing the clearance between the rotor and the stator. This will save time and cut product costs.
During storage, the droplets of a monodispersed emulsion move. This leads to stratification and loss of consumer appeal, and, in some cases, even to complete breaking of the emulsion.
Monodispersed emulsions can be produced by one of the three methods:
- By phase shift control, setting shearing load and creating laminar flow;
- By squeezing dispersed material through a porous membrane with precisely calibrated orifices;
- By installation of capillaries in a tube of bigger diameter inside which water and emulsifier flow.
Thus, consumer appeal of bitumen emulsions can be significantly improved due to control of bitumen droplet size.
One of the promising directions is the development of an emulsion which changes color if illuminated by headlights, indicating road centerline and shoulders for traffic safety.