14
presence in the road surface is not always an advantage, and,
unless the soap is carefully chosen, may be the reverse.
7. No bituminous emulsion can be stored indefinitely;
probably six to eight weeks would be the limit of safe
storage in Hong Kong. After that period the asphalt
mass to the
gradually separates out and falls in a viscous
bottom of the containing drums; the soap in the emulsion also
deteriorates and no amount of "rolling" the drums will re-mix
it. If hard water were used in making the emulsion and the
Soap a cheap soap, either or both of these circumstances
would lead to still earlier deterioration of the emulsion.
8. Bituminous emulsion freshly made and of good
T
quality may be suitable for surface dressing bitumenised
roads, or used "blinded" with gravel on wood pavement
in certain climates, but as a substitute for "hot-mix" in
road construction, price for price, we are of opinion that
it is not to be considered.
9. If bituminous emulsion is to be used at all we
recommend that it should be made by the Public Works
Department, locally, and in the Fourth Crown Agents' Bulletin
Article VII (acopy of which is attached) the method of
manufacture and also the plant requisite for the process are
described in detail.
It will be seen that the cost of the
plant is not excessive and the saving effected by making the
emulsion on the spot exactly and only when required, compared
with the importation of any of the proprietary brands would
be considerable.
I have the honour to be,
Sir,
Your obedient servant,
Wat wichhart
for Crown Agents.