ROADS OF THE FUTURE.

Hawera & Normanby Star, Volume XLII, Issue XLII, 6 January 1923, Page 5

ROADS OF THE FUTURE.

THE IDEAL SURFACE. (London Correspondent). , ' Somewhere down near Arundel recently engineers discovered an abandoned grass-grown Koman road which, was made in -a similar manner 'to the most up-to-date sections of roadway in England I to-day. It was made ;of bitumen,. and geologists were able to, demonstrate that the bitumen came from Egypt. In the ancient civilisation of Peru bitumen roads seem also to have been constructed, • while the substance is mentioned in the Book of Genesis as being used as a-cementing material; in the construction of the Tower of Babel. With the development of travel and commerce along the main roads of this country during the past decade engineers have had to improve on the old water-bound metal roads, and they turned to tar for a surface dressing. It was a vast improvement for purposes of light motor traffic, hut the traffic had been growing even- heavier and heavier, and the ' provision and maintenance of roads equal to the strenuous demands now made upon them has become an absorbing study to every road engineerSooner or later the same subject will be a very vital one in New 'Zealand, and no doubt some idea of what is being done in this country will be of interest. To the ordinary pedestrian a road is just a road. After conversation with a few experts the road over which one passes becomes a thing to be examined with interest. From two such experts I have recently obtained a good deal of information. The one, an officer in-charge of a Government experimental station, spoke as one without any interest in any special form of road-making. The other, whose business it was to push the sale of bitumen for a certain world-famous old firm, spoke naturally with a certain bias towards this latest method of construction. For a good many years complaints have come from many quarters that the draininjgs from the surface of tarred roads killed fish' in adjacent streams, and some- time ago the Government set up an experimental station under the joint Ministries of Agriculture and Fisheries and Transport to ascertain whether tar was poisonous and if so whether some suitable substance could be suggested w?hich was not poisonous to fish life. Experiments; have shown that tar in any appreciable quantity is invariably fatal to fish life, while on the other, hand bitumen has not been injurious to fish, and so far as those carrying out\the experiments are • aware there is no poison in the substance. Corporations and companies interested in the disposal of tar in this country are, of course, many in number, besides being extremely influential, so that any report detrimental to their industry is„ sure to be extremely unpopular. Nevertheless, public opinion is beginning to grasp some elementary facts—that tair is not especially cheap, its life is not particularly lengthy, it is by no means a good binding materia,!, and its low melting point is a particularly objectionable feature in hot weather. These facts were borne out Iby the Government official in question, ' who was also a civil engineer. 'His advocacy of bitumen as a road-forming material was even mare enthusiastic than,the advocacy of the trade representative.- Bitumen roads have been constructed at-, the experimental station and subjected to very severe . tests. One has been down for two years, and its present condition is even i better than at first. This is owing to r I the tendenov the substance has of ;flow- , j ing very slowly into any holes ar sub- ' stances, and always finding for itself

a level surface. Thus should particularly heavy traffic make an impression I it also crushes the surface grit stiil finer, and the bitumen binds all the tighter, and in a. very short time ireadjusts itself to the proper level. SELF-SEALING; TENDENCY. -This self-sealing tendency prevents any water from penetrating, and no injury can be done to the roads by frost. In the case of tar,1 once the surface is broken there is no self-sealing, and the water penetrates, the frost comes, and the road is still further disintegrated. How long,the bitumen ! road will last without attention has not yet been ascertained, as no roads laid in England in this way have yet re-' quired attention. Firom' America, how-i ever, there comes the testimony of Professor S. C. Peckham, who refers in his standard, work oh Solid Bitumens' to the bitumen-surfaced streets of j Kansas City, which notwithstanding the j violent extremes of temperature and the enormous traffic, have shown no signs of wear after a pdribd of seventeen years. The British Government exhibition "tank" did no damage to the bitumen-surfaced streets of the American cities in which it demonstrated. Before proceeding further it may be well to mention how bitumen is procured. It is, of course, a product of the crude petroleums drawn from the oil wells in various parts of the world. As the benzines, kerosenes, gas and flux oils al} have boiling points lower than those of bitumen, these products boil off first when heat is applied, leaving the bitumen behind, a dark thick substance not unlike treacle, which, as its temperature decreases, solidifies to p, hardness which is regulated by the extent of the distilling prol dess. ■ ' -. A USE FOUND FOR CLINKER, ! There are several methods employed m the formation of bitumen roads. However well the, surface is constructed, the success of the road depends primarily upon efficient drainage and the stability and permanence of the foundation. Having these factors, the question then becomes one of final' surfacing. But bitumen has been used very largely in street formation in some of the larger cities of England! Not long ago destructor clinker was a substance municipal authorities had to pay ,people to cart away. Now a use has 'been found for it. Carefully selected clinke*r is crushed and screened, and the half-inch, material is used for the subcrust of the roads. The clinker is heated, an sand dryers to a temperature of 300dg. Fahr.. and is mixed with the heated bitumen in a steam-jacketed mixer. For this sub-crust approximately 10 per cent, of bitumen is used. After mixing, and whilst as hot as possible, the material is placed on the road which is to be surfaced. It is then spread to a sufficient thickness to give after rollins a consolidated depth of IJ inches. Clinker for the wearing surface consists of -material passing |-inch mesh screen, and it is mixed with 15 per cent, of bitumen. Sufficient material for the - wearing surface is carefully imposed to give a thickness after rolling of H-inch, making a total of 2 inches for the two layers. Rolling is carried out until it is impossible to make'further impressions* and then the surface is dusted over with cement or limestone dust, after which the road is ready for traffic. Similar streets have been laid down in London, tbe mineral aggregate consisting of hardstone, slag, limestone, or gravel, with-graded sands mixed with about 9 per cent, of bitumen for a top dressing. In a number of localities country roads have been formed in a very simple way. Ordinary hard rock broken to 2-inch _auge is evenly spread three inches in depth and lightly rolled. Two gallons of bitumen peir super yard of road is poured on. A sprinkling of chippings is laid, and rolling is continued, and a sealing coat is applied by means of pails and squeegees.

FOR COUNTRY ROADS. t / Where something much less expensive is required, slich as in the case of the mam country roads of New Zealand, where the metal is substantial and the surface only .requires attention, another process is quite effective. This isjust a surface dressing. The road, wnen dry, is swept clean of all dust. Bitumen is i raised to a temperature of 300deg. Fahr.. and spread on the road with pails and squeegees, the quantity being one gallon to five or six square yards qf surface. Directly after the dressing is made, chippings of £-inch limestone are sprinkled on, and "these in due course become ground. up in the bitumen. Roads pf this nature have been laid in some parts of England for two years only, but so far there has been no sign of their wearing. The great advantage of bitumen is that it retains its character for all time practically, whereas in the case of tar the various constituents evaporate rapidly and leave only a crumbling carbon. NATURAL ASPHALT. With improved methods for gas making in England, the quality of tar has' deterobrated a good deal; and the present practice is to mix bitumen with the tar to 9_ffen, it up and bring it up to a uniform standard. In some parts of the world people have a preference. for natural asphalt taken from the pitch lakes, but it is pointed out that the natural asphalt has no advantages over the made-up mixtures of bitumen and: gravel. , These pitch lakes have been formed at some time by the oil bursting through the earth's surface. In due course the lighter fractions evaporated, leaving the bitumen to mix up with the debris and the soil, the proportion of mineral matter being about- 36 per cent. Thus the natural asphalt is exactly the same as what is. artificially made, but in the case of the former one is paying for.-the transport of a great proportion, of mineral aggregate which could«be more conveniently obtained. - * . THE PRICE.' An instance is quoted of a certain urban district council with a tarred road beside: a fishing stream having to pay £4000 damages for destruction of fish. A certain firm dealing in bitumen has now submitted bitumen for the tar, and has, in addition, given the Council an indemnity against any future damage to the fish. . Finally, it is main-, tamed that where 3£d is spent for tar in road construction, only 4*d need be spent on bitumen. The advantages in favour of the latter point to its more /general usei "Whether it would be a pacing proposition in New Zealand, , with the added freight j is a question for ! others to decide. j