When the road is formed in rock cuttings it is advisable to spread a layer of sand or other material of light nature, so as to fill up the irregularities of the surface as well as to form a cushion for the road material to rest on.
Spreading the Stone. The stone should be hauled upon the roadbed in broad-tire two-wheeled carts and clumped in heaps and be spread evenly with a rake in a layer which should be of a depth of 41 inches.
Watering. Wetting the stone expedites the consolidation, decreases crushing under the roller, and assists the filling of the voids with the binder. It should be applied by a sprinkler and should not be thrown on in quantity or from the plain nozzle of a hose.
Excessive watering, especially in the earlier stages, tends to soften the foundation, and care should be exercised •in its appli cation.
Binding. As the voids in loosely spread broken stone range from 35 to 50 per cent of the volume, and as no amount of rolling will reduce the voids more than one-half, it is necessary, in order to form an impervious and compact mass, to add some fine material which is called the binder. It may consist of the fragments and detritus obtained in crushing the stone. When this is insufficient, as will be the ease with the harder rocks, the deficiency may be made up of clean sand or gravel. The proportion of binder should slightly exceed the voids in the aggregate; it must not be mixed with the stones, but should be spread uniformly in small quantities over the surface and rolled into the interstices with the aid of water and brooms.
As the quality of the binding used is of vital importance, the employment of inferior material, such as road scrapings or material of a clayey nature, should be avoided, even if the initial cost of the work should be greater when a good binding material is used.
Stone consolidated with improper binding material may present a good appearance hmnediately after being rolled and be otherwise an apparently good piece of work, still.in damp weather a consider able amount of "licking up" by the wheels of the vehicles will take place, which reduces the strength of the coating and causes the sur face to wear unequally.
By the application of an immoderate quantity of binding of any description the stone coating will become unsound or rotten in con dition, and if the binding be of an argillaceous nature, it will expand during frost, owing to its absorbent properties, and cause the dis placement of the stones. The surface will become sticky, which seriously affects the tractive power of horses, while the road itself will suffer by the irregular deterioration of the surface.
The use of such material as mentioned for binding enables rolling to be accomplished in much less time than when proper bind ing is used, and the cost of consolidating the stone may be reduced by 25 per cent; but, on the other hand, the stone coating which will probably contain under these circumstances from 30 to 40 per cent of soft and soluble matter, and possibly present a smooth surface immediately after being rolled, will quickly become "cupped" by the wheel traffic, a humpy surface being the result. This is caused by the irregular wear, while the lasting qualities or "life" of the coating will be shortened, giving unsatisfactory results to those traveling over the road, and the work of renewing the surface of the road in this manner may prove a failure on economical grounds. There can be no doubt, and it is now being more generally recog nized, that sand as a material for binding in connection with rolling operations, when applied in a limited but sufficient quantity, pro motes the durability of the stone coating, while the general results are equally satisfactory; a firm, compact, and smooth surface is obtained, and the subsequent maintenance of the rqad is minimized.
A great amount of rolling is necessa.y when sand is employed as a binding material, but economy is promoted, and the results are more satisfactory when sand is used than by the use of the material which gives to the stone an appearance only of having been properly consolidated. If clean sand be used in combination with the screen ings from the crusher a very satisfactory surface will be obtained.