Factors influencing the properties of bitumen emulsions
Production of emulsion binder with required parameters implies consideration of the main dependencies of bitumen emulsion creation and formation.
Let us first formulate the main required properties of bitumen emulsions.
First of all, as was mentioned above, emulsification is a process which allows even distribution of bitumen on the treated surface. Therefore, bitumen emulsion must, being fluid for transportation of bitumen into the pores and small cracks, ensure formation of a specific thickness of binder film.
It is also worth noting, that the properties of bitumen film, i.e. adhesion to stone material or treated surface of road coat, cohesion of the binder and stability to various factors are provided for by the properties of bitumen. In case of emulsion, the task is to get bitumen to restore its properties as soon as possible after emulsification, which is attained in three stages, including the ability to:
- relatively easy emulsify bitumen;
- easy creation of even bitumen film of required thickness on the treated surface;
- quick and complete return of original qualities or better. This process is usually called formation. Formation time, a parameter of emulsion, often includes the formation of bitumen precipitating out of the emulsion.
Emulsion as material works full scale only during the second stage. In this case it must have the following main properties:
- be stable and not break into water and bitumen for the time required by the process;
- possess the required viscosity and dispertion;
- ensure the capability of settling on treated surface and traction of the bitumen binder film with it;
- cease to exist as soon as possible after completion of the required process cycle, i.e. break down into water and bitumen, leaving in the required position in the form of thin film. This process is characterized by breakdown rate.
During the third stage, apart from emulsion breakdown rate which starts partially during stage two, water is removed from treated surfaces and then bitumen film is formed, i.e. plasticizer and flux removal and “settling” of bitumen. The processes during this stage, apart from water removal, depend exclusively on bitumen properties and the possibility and rate of removal of process additives from it (plasticizers or flux).
Here we do not look in detail into formation of binder and removal of water from mineral-emulsion
To convert bitumen to emulsified (liquid) state and ensure decrease of interfacial tention at the border of bitumen and water phases, emulsifier and stabilizers must be introduced..
Production of emulsion from two mutually indissoluble DP and DM requires that charge of the liquids be similar; in order to do this emulsifier is introduced, which adsorbs on the border of phase separation and lowers interfacial tension of water and equalizes polarity of the phases.
The process is influenced by a range of factors.