ROADS.

Taranaki Daily News, Volume LIII, Issue 243, 20 February 1911, Page 3

ROADS.

i THEIR MAKIXC AND PRESERVATION

(Contributed). I Binding materials of roads are largely inlluenced bv rainfall, usually less material being applied where there are frequent rains. Itoads should conform to a Hat surface for heavy tropical rains, otherwise they become rutted. For mechanical street-watering river water is objectionable, unless it passes through an efficient system of filtration, because the water contains much matter in suspension, which, as the roads become dry, and high winds prevail, is wafted in dust particles into dwelling-houses, consequently rendering them insanitary. Toughness is the chief desideratum in selecting rocks for road material. They may be tested by the use of the stonehammer, or by the scratching test. Rocks «f finer texture are generally more tough than those of a coarse crystalline nature. Graded ledge rock is always preferable for use to field boulders, because with the latter evenness of surface is with difficulty maintained. The accepted order of'rocks for macadamising roads is that trap rock stands firstJn importance, being followed in durability, successively bv felsites, hornblehdi,c granites, hard limestones, schists, and quartz-, ites.

The making of a good road has been said to depend upon four factors, viz., the proper aggregate, agglutinative, mixing, and consolidation. Materials of a cementitiods nature should be used in just sufficient quantities to bind the dust into particles, rendering the granulations or clippings too heavy to be moved by normal wind force. Road-rollers that are excessively heavy produce large quantities of dust, as well as returned sweepings, or the wear and tear of the materials from traffic. A roller o.f ten tons in weight consolidates on-an average thirty tons of stone per day. The difficulty of treating many colonial roads with tar, particularly when composed of loose earth materials such as are frequently found in New Zealand, is that successful binding is almost impossible in its application. For the advantageous use of tar in any form roads must be first well made 'of firm road metal. In main streets of towns where the available hard metal of the district has been accumulated, tar is frequently used for roads and footpaths, yet observation shows the tar surface is often lacking in solidification. When used, grit arising from a tarred road is nothing in its evil effects in comparison with a road untreated. By regular washing and cleansing, the dust on a tarred surface can be reduced to a minimum. In some parts water gas tar has been applied as a dust preventative. This can be quickly put on, and the cost is low in current expenditure, the chief objection being that it is not lasting, thus spraying must be repeated annually. Unless prepared to go to the expense of specially manufacturing coal tar for road and other local application, a borough must be content with the supplies available from gas works. The binding power of coal tar is contained in the bitumens. Other substances contained in it are variable according to the process and temperature of distillation. Excessive water may conclusively be thought to be present in the compound whenever the tar foams. Too much ammonia is identifiable on a trial surface becoming brittle after continuous rainfall. Naphthalene, anthracene and free carbon are almost valueless constituents, for they reduce the binding power and water-proof-ing qualities. Oily constituents are generally valuable, as- they thin the compound, making it much easier to spread or apply in other ways. There is no reliable simple test for bituminous materials. Chemically analysed and tested, coal tar most nearly approaches the realisation of desirable standardised treatment: • • Refined tar must be uniform in color, character, appearance and viscosity. The latter.quality is found by passing the fluid through a' viscosimeter orifice. Coal, tar snouid , contain no body that distills at a lower temperature than 225 degrees centigrade, nor over 10 per cent, by weight distilled below 270 degree C. There should be 65 per cent, by weight of pitch or bituminous material remaining after all bodies have been distilled by heating up to 300 degrees C. Its bending and break ing weights have been tested by experts, by mixing 12% per cent, of the fluid with 87 ] /» per cent, of sand, formed into briquettes and allowed to harden for a week at ordinary room temperature.

The advantage of using some of the patented dust preventatives is that no heating process is necessary at the municipal yard, or on the highway. As an instance., the "Tarflux" compound may be mentioned. This compound can be applied in any state of weather. A special' distributor is used, resembling' in form an ordinary water-cart, with the attachment of an agitating apparatus which keeps the compound thoroughly mixed during the time of application. The tar is taken in a cold state exactly as received from gasworks, being mixed up where required on the roadside simply by the addition of the patented chemical compound and water to the fold tar. Aihen this compound is applied to the road, the tar remains on the. surface, whilst the other constituents are absorbed by the soil, which by their aid is kept in a moist condition, the tar on the road surface by its adhesiveness preventing evaporation. It is rendered uninflammable and dries quickly, leaving the road with the appearance of having been asphalted. This covering is, besides, waterproof, and it is claimed the life of a road so treated is increased fully 10 per cent. I In England' another extensively uscdi patented composition is "Tarmac." Although the first cost of this exceeds some classes of macadamised roads, it is on evidence economical in the long run through saving in maintenance and scav-1 enging. In this, however, the tar composition is consolidated with stone, variously guaged and rolled, as in making an ordinary macadam road. The thickness of customary consolidations are 4in or 3in, according to the requirements for highway traffic. In the first case, one ton laid 4in thick covers S sup. yds. This material has been much used in making the approach drives to public institutions. The object in laying out roadways consists in due consideration i of the direction, lines and widths of principal and subsidiary streets; in observation of prevailing winds, higher requirements, readiness of access, and preservation of scenery. From conferences in England and U.S.A. regarding standarisation of roar statistic.*, the following are drawn up as the basis of proposals:—There should be classification, for districts. Making and maintenance statistics should be tabulated for the individual costs of coating, lotting anil patching. The expenditure should be observed for surface tarring, or any special treatment; also for scavenging and watering. The preparation of traffic returns, and the adoption of uni-, form road signs. Systems »f road alignment include rectangular, triangular, radiating and irregular methods. Owing to the high speed of motor vehicles, the diagonal (derived from the radiating) or the triangular forma! systems meet well stroightness and directness of route from one part of a large city to another. Extreme width of 'a road only incre:*es the expanse from which dust arises, .unless broad crass' verges are allowed to remain or artificial coatings ronder them unnecessary.

Recently .some experiments were made in Canada with the residue of a sulphite [ factory by utilising the liquor with other f substances as a road binder. Sulphur, lime and gum were the chief factors, being blended into a thing viscous fluid applicable by sprinkling, which after a few repeated (rials apparently served well as | a dust layer through rapidly setting into i a firm surface.