MODERN ROAD CONSTRUCTION

Taranaki Daily News, 22 April 1921, Page 7

MODERN ROAD CONSTRUCTION

SOME USEFUL SUGGESTIONS. Mr. C. Skitrop, C.E., late engineer to the Bitumen Road Binder Co., Ltd., and an acknowledged authority on road construction, writes to the editor:— As several-of the Taranaki local bodies contemplate large sums of money in the near future in laying down so-called permanent highways, dt is advisable to consider carefully what class of material will give the greatest service. In the pafet tar has been used chiefly on account of its comparative cheapness and the ease with which it can be sprayed, but owing to the tremendous cost of maifitenance, I think the local bodies who have used it for any length of time would like to hear of something within their reach financially that would give more satisfactory results. Taranaki possesses some of the finest tar roads in the Dominion, but to keep them so requires continual attention and expenditure of money. A tarred road surface, to keep it in good order, requires a top-dressing once every year, and sometimes oftener. If neglected for a year or two the surface breaks up, and the road has to be laid down anew.

In the construction of modern highways three classes of materials are in general use:—Concrete, bitumen and

Concrete, which is no doubt the most durable material, is also the most costly in construction, and has to be surface dressed with a bituminous wearing blanket every 5 to 10 years, according to the amount of traffic passiiig over it, otherwise the surface of the concrete becomes frayed and pitted.

Bitumen is the next best material. It is comparatively cheap iii construction, costing very little more than tar. It is, however, more difficult to lay down than either concrete or tar. The cost of maintenance is the same as for concrete, that is, a top dressing every 5 to 10 years, according to the amount of traffic passing over it.

Bitumen has one disadvantage over concrete in that it is not a uniform material, there being several grades on the market and only a few of them are suitable for road construction in-our climate. As a rule two, or sometimes three, grades have to be used, and combined with a suitable flux and mixed at a given temperature. If the proper grades of bitumen are used and combined with a suitable flux there is no fear of failure. All bitumen should be tested to determine its specific gravity, penetration, melting point, cementitiousness, brittleness, and solubility. The flux is of a chemical nature, and should be stable at the temperature which it is called upon to withstand, that is to say, it should contain no component volatile at such a temperature, and it should be of such a nature chemically that its components will form a homogenous solution with the different grades of bitumen with which it is combined.

I feel quite certain from personal experience that tar will not solve the problem of modern road construction. There are only two materials that will stand our traffic and climatic changes. They are concrete and bitumen. If any local body is sufficiently interested in this question I shall be pleased to give them the benefit of my experiences in bituminous road construction, covering a period of seven years,, in different parts of the Dominion.

In conclusion, I wish to say that my motive in writing this is not to belittle tar as a road binder. It has served its purpose in the evolution of modern roads, but with the increase in motor traffic the maintenance question becomes a very serious one. A road surface that has to be top-dressea every year cannot be termed permanent. As a comparison of maintenance cost I will mention just one ease that has come under my observation—bitumen and tar laid on the same street under the same conditions. The tarred portion has been top-dressed four times, and is now in a. worn-out condition. The bituminous portion has never been top-dressed, and is in perfect order.