Road Widenings and Motor Roads.
Page 18
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By John A. Brodie, Wh. Sc. , Inst. C. E. , I.Aslech. E.*
Such mixtures have long been used in preference to tar in this district for jointing the hard Carnaryonshire setts commonly used, and, when some of these pavements were being pulled up after a twenty years' life, the combination of pitch, tar-oil, gravel and shingle was found to be adhering perfectly to the stone, and to be in better condition than the best mixtures obtainable from pitch and oil materials at the time being supplied under annual contracts, and some of the material was in fact re-used. With the help of chemical analysis a specification was prepared both for pitch and ail, and every delivery of these materials is now chemically tested, and, if found not to comply strictly with the specification, is rejected. It was found that with unvarying materials a uniformly tempered pitch mixture became a cornDaratively simple matter, As a simple and practical test this mixture when cooled in water at 6odeg. Fahr. should stretch at least 6 feet before breaking, and the threads so rormed should pull out very finely indeed. It should also when doubled into a length of about a foot bear hitting lard on an iron or stone surface without showing signs of :racking. Immediately before being used an equal bulk of hot sand mixed with a small percentage of lime or cement shotild be stirred into the pitch and oil mixture and kept :ontinuously stirred until applied to the joints or the macidam, as the case may be. This mixture has been used in Tiy department for many years, has never been patented, and forms a very useful basis from which experiments in all directions with a view to improvements may usefully be -nade by road engineers who require an impervious grouting ither for hard setts or macadam.
The Dust Nuisance.
Another matter which is of importance to the members of his Association at the present time is the removal or aboli:ion of dust from macadam roads, which though not caused )3, the fast and light motor traffic, is undoubtedly lifted from he roadways and becomes a great nuisance both to the ndinary user of the roadway and to the Owner of property tdjoining it. This subject has for some time been receiving e great deal of attention from road engineers, and also from t large number of manufacturers who are endeavouring to thtain Materials which will enable the road engineers to arovide a satisfactory dustless road surface, The first maerials to be experimented with in this country were pro bably the heavy petroleum and coal-tar oils. Undoubtedly the results were very satisfactory so long as the weather remained dry and warm. The mud formed during wet weather was, however, found to be objectionable, and complaints were received as to injury to coachwork, and so far as I am aware this material is not now being used on any very large scale. Important trials have recently been carried out near London with tar mixtures and tar-spraying machines which have been largely attended by the leading road surveyors in the kingdom. Another step was taken when it was found possible to dissolve oils in water and apply them to the surface of the road through an ordinary watercart. Deliquescent materials such as chloride of calcium, which have been used for the purposes of keeping down dust in this city for many years, when dissolved in water and spread in the usual way also give satisfactory results. Whilst all these methods of surface spreading are interesting, and may probably be the best way of keeping down dust on existing macadam roads, I look upon surface sprinkling generally, and especially with mixtures which are readily acted upon by water, as merely temporary applications, which, however, are serving a useful, even if only a temporary, purpose in reducing dust on roads; but I think that the better and more lasting results are likely to be obtained where the whole of the interstices for a sufficient depth below the surface are filled and the stone coated with a waterproof material.