BETTER ROADS

Ashburton Guardian, Volume 71, Issue 35, 21 November 1950, Page 6

BETTER ROADS

VALUE OF RESEARCH Physico - chemical studies have cheapened road maintenance, says an English report. One common upkeep method is to spray on to the road surface a film of tar or bitumen, which is immediately dressed with chippings. If the weather is good, film and dressing adhere into a sound protection. Rain on the other hand, prevents adhesion between coating and stone chips. Passing traffic scatters them and soon wears ruts in the loose stone. The costly task has then to be done again. A method of securing dressings urn der bad weather conditions has been evolved by Road Research Laboratory, Harmondsworth, England, a part of Britain’s Department of Scientific and Industrial Research. Fundamentally, the problem was that of promoting adhesion between the bituminous film—the binder —and the surface of the stone dressings. Both elements underwent minute study.

Attempts were first made to increase the binder’s adhesiveness in the presence of water by adding wetting agents to it. Under test, this method gave poor results. Next, chippings were investigated. They were found, as stored in piles prior to use, to be generally wet, apart from those on the outside. Thus, when scattered on the binder, a moisture coating separates the stone from the bituminous film. In good weather, the wetness quickly dries off, with rapid adhesion; damp or cold weather prevents di’ying out, and no adhesion occurs. The solution, proved by controlled experiment in the rainier districts of Britain, consists in displacing the harmful moisture. This is done by treating the chips at quarry or roadside with a solution of creosote and a wetting agent cetyl pryidinium bromide. They will then adhere firmly and subsequent rain will not break the bond created.