Suitability of chitosan as an emulsifier for cationic bitumen emulsions and its behaviour as an additive to bitumen emulsion

Abstract

Chitosan contains amine and amino groups which have the ability to generate cationic type surfactants when combined with H+ ions. It has a high potential for use as a cationic emulsifier for negatively charged siliceous aggregates for paving of roads in Sri Lanka. Water soluble Chitosan was tested for suitability as an emulsifier in the production of cationic bituminous emulsions. The amine emulsifier currently in use was fractionally replaced with Chitosan and tested for emulsion properties; emulsion viscosity, storage stability, settlement, sieve test and breaking of emulsion. The viscosity of the emulsion was found to increase significantly from 16 SFS to 50 SFS and from 20 SFS to 72 SFS for Cationic Rapid Setting type (CRS1) emulsion and Cationic Slow Setting type (CSS1) emulsions respectively. For both types of emulsions, an exponential growth in viscosity was found to occur at a critical Chitosan to bitumen ratio of 0.0028. Results of storage stability indicated a tendency for floating, while in the presence of Chitosan, within the first 24 h of preparation. However, a settling tendency developed for both types of emulsion when in longer storage as indicated by a 5 day settlement test. A new model based on the interaction between reactive groups of Chitosan and bitumen emulsion droplets was proposed to describe the effect of Chitosan on bitumen emulsion.