THE USE OF BITUMEN IN MODERN ROADS.
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How Tractive Effort is Greatly Reduced and Various Other Advantages Afforded by the Employment of Asphalt in Road Making.
By J. S. KiRick, C.B E., M.Inst.CE T0 NO USER of our road system does a good road surface mean more than to the owner of commercial vehicles. Vibration caused by inequalities in a road results in increased fuel consumption, higher maintenance charges and general decrease of efficiency; conversely, good roads mean cheaper haulage, which, in business, should reflect upon. the price paid for commodities by the consumer.
One so frequently hears the argument, particularly used by farmers and to a less extent by those interested in hunting, that the modern road is built for the motorist. Why not be honest and admit that road surfaces are, and at the same time state that only surfaces which are constructed upon modern methods will stand up to mechanical traction? That these are most suitable for motorists is but an incident. The large and increasing number of mechanically propelled vehicles now using our highways necessitates surfaces which will withstand the abrasive action of steel-shod wheel, and also the disintegrating action of rubber tyres.
The hard, but slightly resilient and impervious; road surface has come to stay, and horses in the country must get used to them as their town cousins have done. "
Teams of oxen were once good enough for haulage purposes, but have been discarded for more economical methods. If the trader were justified in utilizing such cheaper haulage, why should not those responsible for highway maintenance be equally justified in providing surfaces which are so much cheaper to maintain than those 'which were once thought to be sufficient, but are now effete? Whilst it will not be disputed that the value of roads to every member of the community is much in expess of the actual cost per capita to every man, woman and child in these islands, there is equally no doubt that the burden of rates and taxes is near-, ing the bearable limit. It is for this reason that highway engineers must adopt methods which, whilstsatisfying traffic requirements, are not prohibitive on the score of initial cost and subsequent upkeep.
Bitumen as a Road Material..
Modern thought in highway engineering is turning towards the use of bitumen as a solution of the problem, or until something even more promising is. available.
Bitumen, whether obtainable from the distillation of asphaltic oils or from the lake in Trinidad, has a great many advantages for use in road construction. it.is little affected by climatic changes experienced here. It does not readily oxidize, thus retaining its nature indefinitely and, further, it " stays put." In using this Americanism the expression is intended to explain that heavy traffic, even units sometimes known to be laden above the statutory limits and travelling at speeds in excess of those recognized by law, does not displace a well:constructed road in which bitumen has been employed as the binding agent.
Many well-known county surveyors have definitely adopted the policy of laying asphalt surfaces on their trunk roads, being of the opinion that such surfaces are the cheapest and best, having regard to their initial cost and subsequent maintenance.
Traffic must still increase by leaps and bounds, particularly that used for commercial purposes. It is the life blood of the nation coursing along its arteries if the roads are good and through them if they are bad, and _anyone who impedes traffic, by grandmotherly legislation, bad roads, or faulty mechanical design, can only deserve condemnation.
A good, sound permanent way is essential-for the railway, engine, and equally essential for the road vehicle. 1 Concrete sleepers were discarded by railway engineers because they were found to be insufficiently resilient. The same reason holds good for providing an asphaltic road surface, and this-is best provided by using bitumen as the cement with which to hold a mineral aggregate in position. We thus have an asphalt surface cheap to construct, impervious to water, and sanitary.
The Lessening of Tractive Effort.
• Owners of mechanically propelled vehicles should strongly advocate the general adoption of asphalt for many and weighty reasons, an important one being that the required tractive effort on surfaces of this character is very much less than on any other form of pavement. One well-known borough engineer published, some little time ago, the following ascertained figures, which it is suggested are worthy of very careful consideration.
Tractive Effort to Overconie Road Resistance. Approx. lb.
Type of Road. per ton.
.Asphaltic surface ... 40 Granite paving 50 Tar macadam 63 Wood pavement ... 70 Waterboun d macadam 90 (These figures appear to us to be high.—En.) If the cost of haulage per ton-mile is anything like proportionate to .the tractive effort required, then these figures prove fairly conclusively that asphalt surfaces are, by far, the most economical to the road user, as it is suggested they are for those responsible for ;heir provision and maintenance.
With the inunense quantities of bitumen now called for by practically every local authority throughout the country, it is of the utmost importance that not only shall there be ample supplies, but that they should be standardized, and the quality maintained without variation to an exacting specification in order to secure the fullest efficiency in their use. In this connection it is of interest to note that the proprietors of the most widely used bitumen marketed in this country have evolved specifications for grades of bitumen most suitable for this climate. and constant care and vigilance are exercised in their laboratories and refineries to maintain the high standards achieved. It may be remarked in closing that each year that passes brings proof that these endeavours are more and more appreciated