ROAD MAINTENANCE

Hokitika Guardian, 23 February 1931, Page 7

ROAD MAINTENANCE

VIRTUES OF TAR. Air T. Dix, Cambridge, read a paper on “Tile Value of Tar to Small Gasworks” last week at the Gas Institute Conference at Dunedin. He said: “It might be asked why it should be considered necessary to send out statements about tiie virtues- of tar. Surely it must be admitted that the experience of the last 30 years has firmly proved that tar is an ideal road-making and road-preserving material, but the very feet that it has proved so successful ever since it was first used has led to its virtues being taken for granted. Little or no publicity has been given to the fact that tar was just as capable of meeting the exact requirements of the road-maker of to-day as it was first used many years ago. This may seem rather out of place to be read at a Gas Conference, but I would like to have the opportunity of explaining what success we have had and the pro-

cess we put the tar through in a works the size of Cambridge. The large dehydrating plants in the cities are not possible in a small gasworks, so I would like to give a description of our small plant which is giving every satisfaction in the preparation of tar for roads. The plant consists of an ordinary 600-gallon second-hand boiler, fitted on a brick foundation, and lagged with a coating of ashes. The outlet pipe consists of n H inch pipe three feet high, then a one-inch pipe is led to n coil submerged in water constantly flowing when the plant is working. The plant is a very crude one, and could easily he erected in nny small gasworks at a comparatively small cost. The question why is it necessary to dehydrate tar may bo bnought forward. Well, the answer

is this: Tar in its crude form is not a suitable compound for road-making, but when properly dchyrated is second to no other material for that purpose. In Cambridge dehydrated tar coated with fine sand was tried on a section of road subjected to very heavy and fast traffic for approval or otherwise of the Main Highways Board. This road was given two coats of tar and sand the first year, and one coat the next two years, and gave entire satisfaction. After an inspection by the Highways Board, it was decided to approve of a tar-scalec! road from Cambridge to Hamilton, a distance of 13 miles, provided the tar was prepared to the same specification as the piece iust mentioned. In Cambridge the tar is pumped from the tar well, then run across to the boiler, no extra labour being necessary. It is then boated slowly until the light oils, etc..

have evaporated, which generally takes about four hours. The firing from now on is vei-y heavy, and continues so until the tar has been heated to 200 degrees to 212 degress Centigrade. When this heat has been obtained the fire must not be drawn, and tile tar left to cool. The only satisfactory method we found after a lot of experimenting was to bank the fire up and let the tar toughen until two days after the boiling. Wo also found that the tar was too hot to work satisfactorily tlic day after boiling. The spirits of tar and phenoils that come away we use in the exhauster with good results, and hv this have saved a considerable amount of money by supplying our own product instead of purchasing from outside. Local body engineers arc very hard to please, and often place obstacles in the way of tar ; but if we are able to show them we have a material that is of good quality, the prospects of commanding ft ready sale for our tar should he much brighter. There i c quite a lot of cold emulsion bitumen coming on the market at a fairly reasonable cost, but there need be no fear of that for first coat work, as there is no material known that can take the place of tar for the first or second coat on a gravel or sand rontf. We in Cambridge sell dehydrated tar to the Sttreets Department at 9d per gallon, and have no trouble to sell all we make. The cost of dehydrating tar works lout at' 'approximately Id per gallon, so you see it is a paying proposition to have a good material to offer at a reasonable price. I do not wish .to make a long subject of this paper, but am of the opinion that small gasworks can enjoy the same benefits as largo ones if they desire to do no. I trust that this will have been of some use to serve as a coble to the good qualities of tar, nnd that it. will he the means of a better tar being supplied to local engineers from smaller gasworks than before, as we all have to remember that unless we supply the correct material we cannot expect to get busine's and success with local body engineers, who will not risk their reputation on an inferior article. ” A vote of thanks was passed to Mr Dix for his paper. i