A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
Fig. Position of application of prime coat
19. Why is it necessary to ensure cleanliness of bituminous pavement
before applying tack coat? (C5)
Surface preparation of bituminous pavement is essential in proper
application of tack coat. The entire surface has to be cleared of debris, dust
and soils. Otherwise, the tack coat would stick to the debris left on the
pavement instead of adhering to the pavement. When delivery or
placement equipment is driven over tack coat, it tends to stick to the tire’s
of the equipment instead of pavement.
20. What are the differences between anionic emulsions and cationic
emulsions?
Bitumen emulsions consist of particles of bitumen dispersed in water by
using emulsifying agent. When the emulsion breaks, it represents a
change from a liquid to a coherent film with bitumen particles coagulating
together. The sign of breaking is the change of colour from brown to black
as the colour of emulsion and bitumen is brown and black respectively.
There are in common two broad types of emulsions, namely anionic
emulsions and cationic emulsions. The breaking of anionic emulsions is
dependent on the evaporation of water from bitumen emulsion. As such, it
poses difficulty in wet weather condition. However, for cationic emulsions,
instead of relying on the evaporation of water the breaking is achieved by
chemical coagulation. Hence, cationic emulsions are particularly useful in
wet weather conditions [66].
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