Evening Republican, Volume 17, Number 140, Rensselaer, Jasper County, 12 June 1913 — Home Course In Road Making [ARTICLE+ILLUSTRATION]

Home Course In Road Making

IX.—The Gravel Road.

By LOGAN WALLER PAGE,

Director Office of Public Roads, United States Department erf Agriculture. Copyright by American Press Asso- ‘ elation, 1912.

GRAVEL may be defined as a , mass of small fragments of stone which have been more or less rounded through the action of water and which have been deposited by the same agency along sluggish river channels or about the margins of lakes or other bodies of water. It may have been formed from the hard rocks along the seashore, the fragments of which, dislodged by the elements, fall Into the water and are washed back and forth through the action of the waves, gradually becoming rounded and smaller. 0 the New England states and other of the states lying north of the Potorhac and Ohio river region gravel

pits, which are frequently termed glacial gravels on account of their or indirect association with ice action, are quite widely distributed, and these have been and may be used to a greater or less extent In road improvement During recent geological history of the continent the Atlantic and gulf borders have been submerged at Intervals. The ocean has advanced inland a number of times. During each of these periods of continental submergence the harder rock remanents along the inner margins of the ocean’s advance have been rounded, worn down, deposited and redeposlted with varying proportions of sands and loams and clays, thus forming beds of gravel, which are today available for road bnllding purposes. Gravel roads and macadam roads niifro have often received sweeping condemnations as unsatisfactory when the cause of failure was poor construction and not the character of the material used. The need of care in grading and drainage in the construction of macadam roads is tfeing quite generally recognized, but unfortunately many amateur road builders seem to think that gravel roads may be constructed by simply piling gravel on the surface and leaving it to be packed by the passing traffic. In point of fact, the grading and drainage and other details in connection with the construction of a gravel road should be done with as much care and thoroughness as In the case 6T a macadam road.. Moreover, in the one case as in the other specifications must be adapted to varying local conditions. Of course, the gravel itself must be selected with care. That which contains a sufficient quantity of binding material so that it stands as a vertical wall when it is being excavated is generally the best, for the reason that this same binding material will re-cement the gravel when used for road building. There are three Important qualities which should be possessed by road building gravel—hardness, toughness and cementing or binding power. Of these three qualities the last is the moat Important. This binding quality is due in part to the presence of oxide -of iron, lime or ferrngineoqp clay and in part to the angular shape and size of the pebbles composing the gravel. Blue gravel is universally conceded to be the best for road construction, because it is usually derived from trap rock. As the pebbles composing the gravel retain the characteristics which they formerly possessed as a part of the larger rock Itself, it follows that as trap rock is considered an excellent material for road building, trap rock gravel should occupy the same relative rank among the gravels Limestone is, generally speaking, a soft rock, and consequently .limestone gravel, which la quite rare, - will usually be found ■oft and will wear rapidly. Quartz possesses practically no binding power, although it is very hard. Therefore gravel which contains an exceptionally large percentage of quartz will not prove successful, as it will fall to consolidate unless it contains binding material. or unless a good binder is added. In order that the material may hind readily the pebbles should' be angular and shonld vary in size so that the maaller fragments may fill the voids

fietweeri the larger'pieces. TJrSv® obtained from streams & usually interior to pit gravel for the reason that the action of the water has worn the pebbles smooth and practically all the fine binding material has been moored by the same agency. Even if clay or learn 1b mixed with river or creek gravel the result is not likely to be as satisfactory as that obtained by the use of pit gravel. Pit gravel frequently contains too much clay or earthy matter, while river gravel may have too much sand. In such cases It Is sometimes advisable to screen the gravel so as to eliminate the material which is too fine or that Which' •is too coarse The screen should be similar to that which is used in preparing material for a macadam road. In the handling of the gravel care should be exercised not to separate the binding material from it, nor should, this binding material be allowed to settle to the bottom in spreading the material over the road surface. It will often be found advisable to spread a thin layer of such binding material over the surface after the material has been distributed and rolled, and after this the surface should be sprinkled and rolled again or else rolled while still damp from the rains. A large part of the gravel found in the Atlantic coastal plane is sufficiently fine and uniform to render unneces-

sary any assorting for road building purposes, but when the gravel, especially that which is to conr’itute the surface layer, contains large pebbles these should be removed and either thrown aside or else raked into the foundation or recrushed. At least (50 per cent by weight of the gravel should be pebbles above one-eighth inch In sice, and there should be no pebbles in the bottom layer that will not pass through a two and a half or three inch ring, and in the top layer there should be no pebbles which will not pass through a one and one-half lneh ring. Not over 20 per cent of the mass should be clay, and this should be uniformly mixed and should contain no large lumps. Ten or 15 per cent of clay produces better results than 20 per cent.

If the foundation or roadbed is loose it should be carefully rolled. It is quite as important to have a solid foundation for a gravel road as for a macadam road. Gravel will compact to about 80 per cent of its depth, loose measure, provided earth shoulders fi.ro placed on both sides of the road to prevent the wasting away of the gravel on the sides. If gravel is abundant, however, these shoulders may be built of gravel Instead of with earth, or the road may be surfaced with gravel from shoulder to shoulder. If the compacted depth of the gravel toad Is to be eight inches and the width twelve feet it will take about 2,250 cubic yards of gravel to the mile, and it is best to make the first layer about six Inches in depth, loose measure, and the second layer about four indies in depth, loose measure. Gravel should not be dumped directly on the road, as this will usually result in a rough, uneven surface. If specially devised spreading wagons are not used the gravel should be dumped on boards and spread from them on to the road.

The gravel should be placed on the road commencing at the end nearest the gravel pit, dn order that the teams will aid in packing the material. A spike or tooth harrow may be used to advantage in spreading the material, but if the gravel contains only a small amount of binding material the harrow should not be used, as it will have the effect of bringing the larger pebbles to the surface and shaking the binding material to the bottom. Bach layer of gravel should be rolled separately. The rolling should begin at the sides and continue toward the center until the surface is thoroughly compacted. The surface layer should

be sprinkled while the roiling Is in progress, but if a roller and sprinkler are net available the road should be eenstrncted if possible in the spring of the year, as the successive rains will cense the material to pack much better than, if 4be road were built in the dry hot summer or early fall. If the gravel is lacking in suitable binding material and clay or loam is available a limited quantity of anch material may be spread over the surface. The clay should be used very sparingly, however, as it absorbs water and causes the road to become soft and muddy in wet weather and dnsty in dry weather. When the clay dries It contracts and causes the road to crack. Clay is also affected by frost. The same may be said of loam. The best binder of allls Iron oxide, which la frequently foundr coating the pebbles. Vary satisfactory results may be obtained by surfacing the gravel road with a thin layer of limestone or traprock screenings. v The split log drag or some similar device may be used to good advantage In maintaining the gravel road.

A POOBLY BUILT GRAVEL BOAS.

A PROPERLY CONSTRUCTED GRAVEL BOAS.