Breaking rate of bitumen emulsion

The breaking rate can be changed by altering the emulsion composition, namely, the amount of emulsifier, bitumen and additives. In a cationic bitumen emulsion, if the amount of emulsifier and the bitumen content is reduced, or if the amount of acid or the acid/emulsi-fier ratio is increased, the rate of breaking is reduced. Additionally, a reduction on the size of the bitumen globules and its size distribution also reduces the breaking rate. In case an increase of breaking rate is required, fluctuation of the above parameters should be reversed (Nikolaides 1983). 

The evaporation rate of water has a direct impact on the rate of emulsion breaking. Since the evaporation rate is related to the climatic conditions, the rate of emulsion breaking increases when the ambient temperature and the wind velocity increases or when the relative humidity is reduced. Hence, the emulsion used should be susceptible as little as possible to the abovementioned factors. Cationic emulsions seem to be more susceptible to the above factors. 

Physical and chemical characteristics of aggregates affecting the breaking rate are the particle size distribution and the maximum particle size of the aggregate mixture (both related to the aggregate specific surface area, the relative moisture content, the surface texture, the origin of parent rock material and the amount and type of filler). 

When the specific surface area of aggregates increases, which means that more fine aggregates are in the mixture, the bitumen emulsion breaks faster. Likewise, an increase of the breaking rate is observed when the filler percentage increases. However, the effect on the breaking rate differs if the filler is cement, limestone or lime, for a given bitumen emulsion. Nevertheless, the impact of the amount of filler is greater than the type of filler used. 

In the beginning of the 1990s, an additive that fully controlled the breaking rate of the emulsion, depending on the type of application, was developed. The additive was an aqueous solution (neutraliser) in oil (reverse emulsion) and it was added to the bitumen emulsion shortly before its use. This additive gave excellent results both on surface dressings and on cold bituminous mixtures of any type with conventional or modified bitumen (Redilius 1993). 

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