Rocks belonging to the same species and having the same name, such as traps, granites, quartzites, etc., vary almost as much in different localities in their physical road-building properties as they do from rocks of distinct species. This variation is also true of the mineral composition of rocks of the same species, as well as in the size and arrangement of their crystals. It is impossible, therefore, to cla.s.sify rocks for road-building by simply giving their specific names. It can be said, however, that certain species of rock possess in common some road-building properties. For instance, the trap[8] rocks as a cla.s.s are hard and tough and usually have binding power, and consequently stand heavy traffic well; and for this reason they are frequently spoken of as the best rocks for road-building. This, however, is not always true, for numerous examples can be shown where trap rock having the above properties in the highest degree has failed to give good results on light traffic roads. The reason trap rock has gained so much favor with road-builders is because a large majority of macadam roads in our country are built to stand an urban traffic, and the traps stand such a traffic better than any other single cla.s.s of rocks. There are, however, other rocks that will stand an urban traffic perfectly well, and there are traps that are not sufficiently hard and tough for a suburban or highway traffic. The granites are generally brittle, and many of them do not bind well, but there are a great many which when used under proper conditions make excellent roads. The felsites are usually very hard and brittle, and many have excellent binding power, some varieties being suitable for the heaviest macadam traffic. Limestones generally bind well, are soft, and frequently hygroscopic. Quartzites are almost always very hard, brittle, and have very low binding power. The slates are usually soft, brittle, and lack binding power.
The above generalizations are of necessity vague, and for practical purposes are of little value, since rocks of the same variety occurring in different localities have very wide ranges of character. It consequently happens in many cases, particularly where there are a number of rocks to choose from, that the difficulty of making the best selection is great, and this difficulty is constantly increasing with the rapidly growing facilities of transportation and the increased range of choice which this permits. On account of their desirable road properties some rocks are now shipped several hundred miles for use.
There are but two ways in which the value of a rock as a road material can be accurately determined. One way, and beyond all doubt the surest, is to build sample roads of all the rocks available in a locality, to measure the traffic and wear to which they are subjected, and keep an accurate account of the cost both of construction and annual repairs for each. By this method actual results are obtained, but it has grave and obvious disadvantages. It is very costly (especially so when the results are negative), and it requires so great a lapse of time before results are obtained that it cannot be considered a practical method when macadam roads are first being built in a locality. Further than this, results thus obtained are not applicable to other roads and materials.
Such a method, while excellent in its results, can only be adopted by communities which can afford the necessary time and money, and is entirely inadequate for general use.
The other method is to make laboratory tests of the physical properties of available rocks in a locality, study the conditions obtaining on the particular road that is to be built, and then select the material that best suits the conditions. This method has the advantages of giving speedy results and of being inexpensive, and as far as the results of laboratory tests have been compared with the results of actual practice they have been found to agree.
Laboratory tests on road materials were first adopted in France about thirty years ago, and their usefulness has been thoroughly established.
The tests for rock there are to determine its degree of hardness, resistance to abrasion, and resistance to compression. In 1893 the Ma.s.sachusetts Highway Commission established a laboratory at Harvard University for testing road materials. The French abrasion test was adopted, and tests for determining the cementing power and toughness of rock were added. Since then similar laboratories have been established at Johns Hopkins University, Columbia University, Wisconsin Geological Survey, Cornell University, and the University of California.
The Department of Agriculture has now established a road-material laboratory in the Division of Chemistry, where any person residing in the United States may have road materials tested free by applying for instructions to the Office of Public Road Inquiries. The laboratory is equipped with the apparatus necessary for carrying on such work, and the Department intends to carry on general investigations on roads. Part of the general plan will be to make tests on actual roads for the purpose of comparing the results with those obtained in the laboratory.
Besides testing road materials for the public, blank forms for recording traffic will be supplied by the department to any one intending to build a road. When these forms are filled and returned to the laboratory, together with the samples of materials available for building the road, the traffic of the road will be rated in its proper group, as described above; each property of the materials will be tested and similarly rated according to its degree, the climatic conditions will be considered, and expert advice given as to the proper choice to be made.
FOOTNOTES:
[7] By Logan Waller Page, expert in charge of Road Material Laboratory, Division of Chemistry.
[8] This term is derived from the Swedish word _trappa_, meaning steps, and was originally applied to the crystallized basalts of the coast of Sweden, which much resemble steps in appearance. As now used by road builders, it embraces a large variety of igneous rocks, chiefly those of fine crystalline structure and of dark-blue, gray, and green colors.
They are generally diabases, diorites, trachytes, and basalts.--PAGE.
CHAPTER V
STONE ROADS IN NEW JERSEY[9]
As New Jersey contains a great variety of soils, there are many conditions to be met with in road construction. The northern part of the state is hilly, where we have clay, soft stone, hard stones, loose stones, quicksand, and marshes. In the eastern part of the state, particularly in the seash.o.r.e sections, the roads are at their worst in summer in consequence of loose, dry sand, which sometimes drifts like snow. In west New Jersey, which comprises the southern end of the state, there is much loose, soft sand, considerable clay, marshes, and low lands not easily drained.
In addition to the condition of the soil, there is the economic condition to be considered. In the vicinity of large towns or cities, where there is heavy carting by reason of manufactories and produce marketing, it is necessary to have heavy, thick, substantial roads, while in more rural districts and along the seash.o.r.e, where the travel is princ.i.p.ally by light carriages, a lighter roadbed construction is preferred. In rural districts, where the roads are used for immediate neighborhood purposes, an inexpensive road is desirable. The main thoroughfares have to be constructed with a view to considerable increase of travel, as farmers in the outlying districts who formerly devoted their time to grazing of stock, raising of grain, etc., find it more profitable to change the mode of farming to that of truck raising, fruit growing, etc.
The road engineers of New Jersey find that they cannot follow old paths and make their roads after one style or pattern. Technical engineering in road construction must yield to the practical, common-sense plan of action. An engineer with plenty of money and material at hand can construct a good road almost anywhere and meet any condition, but with limited resources and a variety of physical conditions he has to "cut the garment to suit the cloth." We start out with this dilemma. We must have better roads, and our means for getting them being very limited, if we cannot get them as good as we would like, let us get them as good as we can.
Let me give a practical ill.u.s.tration. Stone-road construction outside of turnpike corporations in West Jersey was begun in the spring of 1891. I was called on by the township committee of Chester Township, Burlington County, to construct some roads. Moorestown is a thriving town of about three thousand inhabitants in the center of the township. The roads to be constructed, with one exception, ran out of the town to the township limits, being from one-half to three miles in length. The roads were generally for local purposes. There were ten roads, aggregating about eleven miles. The bonding of the township was voted upon, and it was necessary, in order to carry the bonding project of $40,000, to have all these roads constructed of stone macadam. The roads to be improved were determined on at a town meeting without consulting an engineer as to the cost, etc., so that the plain question submitted to me was, Can you construct eleven miles of stone road nine feet wide for $40,000? The conditions to be met were these: There was no stone suitable for road-building nearer than from sixty to eighty miles; cost of freight, about seventy-five cents per ton; the hauls from the railroad siding averaged about one and three-quarter miles; price of teams in summer, when farmers were busy, about $3.50 per day. In preparation for road construction there were several hills to be cut from one to three feet; causeways and embankments to be made over wet and swampy ground. For this latter work the property holders and others interested along the road agreed to furnish teams, the township paying for laborers. The next difficulty was the kind of a road to build. As the width was fixed at nine feet as a part of the conditions for bonding, there seemed only one way left to apply the economics--that was, in the depth of the roads.
On the dry, sandy soils I put the macadam six inches deep; this depth was applied to about six miles of road. On roads where the heaviest travel would come the roadbed was made eight inches deep. On soils having springs and on embankments over causeways the depth was ten inches with stone foundation, known as telford. Where springs existed, they were cut off by underdrains.
It had been the practice of engineers in their specifications to call for the best trap rock for all the stone construction. As this rock is hard to crush and difficult to be transported some seventy or eighty miles to this part of New Jersey, I found that in order to construct all of the road from this best material it would take more money than the bonds would provide; so I had half of the depth which forms the foundation made of good dry sedimentary rock. Of course, in this there is considerable slate, but the breaking is not nearly so costly as the breaking of syenite or Jersey trap rock, and there was a saving of thirty per cent. As the surface of the road had to take all the wear, I required the best trap rock for this purpose.
Since the construction of these roads in Chester Township, roads are now built under the state-aid act by county officials and paid for as follows: One-third by the state, ten per cent by the adjoining property holders, and the balance (56-2/3 per cent) by the county. The roads constructed under this act are generally leading roads and those mostly traversed by heavy teams. They are constructed similarly to those in Chester Township, excepting that they are generally twelve feet wide and from ten to twelve inches deep. Many of them have a telford foundation, which is now put down at about the same price as macadam, and meets most of the conditions better than macadam. The less expensive stone is used for foundations, and the best and more costly for surface only. In this way the cost of construction has been greatly reduced.
In regard to the width, a road nine or ten feet wide has been found to be quite as serviceable as one of greater width, unless it is made fourteen feet and over. It is not claimed that a narrow road is just as good as a wide road, but it has been found better to have the cost in length than in width in rural districts. In and near towns, where there is almost constant pa.s.sing, the road should not be less than from fourteen to twenty feet in width. The difficulty in getting on and off the stone road where teams are pa.s.sing is not so great as is supposed.
To meet this difficulty in the past, on each side of the road the specifications require the contractor to make a shoulder of clay, gravel, or other hard earth; this is never less than three feet and sometimes six to eight feet in width, according to the kinds of soil the road is composed of and the liability of frequent meeting and pa.s.sing.
In rural districts the top-dressing of these shoulders is taken from the side ditches; gra.s.s sods are mixed in when found, and in some cases gra.s.s seed is sown. As the stone roadbed takes the travel the gra.s.s soon begins to grow, receiving considerable fertilizing material from the washing of the road; and when the sod is once formed the waste material from the wear of the road is lodged in the gra.s.s sod and the shoulder becomes hard and firm, except when the frost is coming out.
Another mode of building a rural road cheaply and still have room for pa.s.sing without getting off the stone construction is to make the roadbed proper about ten feet wide, ten or twelve inches deep; then have wings of macadam on each side three feet wide and five or six inches deep. In case ten feet is used the two wings would make the stone construction six feet wide. If the road is made considerably higher in the center than the sides, as it should be, the travel, particularly the loaded teams, will keep in the center, and the wings will only be used in pa.s.sing and should last as long as the thicker part of the road.
The preparation of the road and making it suitable for the stone bed is one of the most important parts of road construction. This, once done properly, is permanent. Wherever it is possible the hills should be cut and low places filled, so that the maximum grade will not exceed five or six feet rise in one hundred feet; where hills cannot be reduced to this grade without incurring too much expense, the hill, if possible, should be avoided by relaying the road in another place.
Wherever stone roads have been constructed it has been found that those using them for drawing heavy loads will increase the capacity of their wagons so as to carry three or four times the load formerly carried.
This can easily be done where the road has a maximum grade of not greater than five or six per cent, as before stated; but when the grade is greater than this the power to be expended on such loads upon such grades will exhaust and wear out the horses; thus a supposed saving in heavy loading may prove to be a loss.
In the preparation of the road it is necessary to have the ditches wide and deep enough to carry all the water to the nearest natural water way.
These ditches should at all times be kept clear of weeds and trash, so that the water will not be retained in pools. Bad roads often occur because this important matter is overlooked.
On hills the slope or side grade in construction from center of road to side ditches should be increased so as to exceed that of the longitudinal grade; that is, if the latter is, say, five per cent, the slope to side should be at least six per cent and over.
Where the road in rural districts is on rolling ground and hills do not exceed three or four per cent, it is an unnecessary expense to cut the small ones, but all short rises should be cut and small depressions filled. A rolling road is not objectionable, and besides there is no better roadbed for laying on metal than the hard crust formed by ordinary travel. In putting on the metal, particularly on narrow roads, the roadbed should be "set high;" it will soon get "flat enough." It is better to put the shouldering up to the stone than to dig a trench to put the stone in. If the road after preparation is about level from side to side and the stone or metal construction is to be, say, ten inches deep, the sides of the roadbed to receive the metal should be cut about three inches and placed on the side to help form the shoulder; the rest of the shoulder, when suitable, being taken from the ditches and sides in forming the proper slope. The foundation to receive the metal, if the natural roadbed is not used and the bed is of soft earth, should be rolled until it is hard and compact. It should also conform to the same slope as the road when finished from center to sides. If the bed or foundation is of soft sand rolling will be of little use. In this case care must be taken to keep the bed as uniform as possible while the stone is being placed on the foundation.
When the road pa.s.ses through villages and towns the grading should reduce the roadbed to a grade as nearly level as possible. It must be borne in mind that the side ditches need not necessarily always conform to the center grade of the road. When the center grade is level the side ditches should be graded to carry off the water. In some cases I have found it necessary to run the grade for the side ditches in an opposite direction from the grade of the road. This, however, does not often occur. The main thing is to get the water off the road as soon as possible after it falls, and then not allow it to remain in the ditches.
And just here the engineer will meet with many difficulties. The landowners in rural districts are opposed to having the water from the roads let onto their lands, and disputes often arise as to where the natural water way is located. This should be determined by the people in the neighborhood, or by the local authorities. I have found in several cases, where the water from side ditches was allowed to run on the land, that the land was generally benefited by having the soil enriched by the fertilizing matter from the road.
After the roadbed has been thoroughly prepared, if made of loam or clay, it should be rolled and made as hard and compact as possible. Wherever a depression appears it should be filled up and made uniformly hard. Place upon it a light coat of loam or fine clay, which will act as a binder.
If the roller used is not too heavy it may be rolled to advantage, but the rolling of this course depends upon the character of the stones. If the stones are cubical in form rolling is beneficial, but if they are of shale and many of them thin and flat, rolling has a tendency to bring the flat sides to the surface. When this is the case the next course of fine stone for the surface will not firmly compact and unite with them.
When the foundation is of telford it is important that stones not too large should be used. They should not exceed ten inches in length, six inches on one side, which is laid next to the earth, and four inches on top, the depth depending on the thickness of the road. If the thickness of the finished road is eight inches, the telford pavement should not exceed five inches; if it is ten or more inches deep, then the telford could be six inches. It need in no case be greater than this, as this is sufficient to form the base or foundation of the metal construction. The surface of the telford pavement should be as uniform as possible, all projecting points broken off, and interstices filled in with small stone. Care should be taken to keep the stone set up perpendicular with the roadbed and set lengthwise across the road with joints broken. This foundation should be well hammered down with sledge hammers and made hard and compact. Upon this feature greatly depends the smoothness of the surface of the road and uniform wear. If put down compactly rolling is not necessary, and if not put down solid rolling might do it damage in causing the large stones to lean and set on their edges instead of on the flat sides. I refer to instances where the road is to be ten inches and over. Then put on a light coat or course of one and one-half inch stone, with a light coat of binding, and then put on the roller, thus setting the finer stone well with the foundation and compacting the whole ma.s.s together.
After the macadam or telford foundation is well laid and compacted, the surface or wearing stone is put on. If the thickness of the road is great enough, say twelve or fourteen inches, this surface stone should be put on in courses, say of three and four inches, as may be required for the determined thickness of the road. On each course there should be applied a binding, but only sufficient to bind the metal together or fill up the small interstices. It must be remembered that broken stone is used in order to form a compact ma.s.s. The sides of the stone should come together and not be kept apart by what we call binding material; therefore only such quant.i.ty should be used as will fill up the small interstices made by reason of the irregularity of the stone. Each course should be thoroughly rolled to get the metal as compact as possible.
When the stone construction is made to the required depth or thickness, the whole surface should be subjected to a coat of screenings about one inch thick. This must be kept damp by sprinkling, and thoroughly rolled until the whole ma.s.s becomes consolidated and the surface smooth and uniform. Before the rolling is finished the shoulders should be made up and covered with gravel or other hard earth and dressed off to the side ditches. When practicable these should have the same grade or slope as the stone construction. This finish should also be rolled and made uniform, so that, in order that the water may pa.s.s off freely, there will be no obstruction between the stone roadbed and side ditches. To prevent washes and insure as much hardness as possible on roads in rural districts, gra.s.s should be encouraged to grow so as to make a stiff sod.
For shouldering, when the natural soil is of soft sand, a stiff clay is desirable. When the natural soil is of clay, then gravel or coa.r.s.e sand can be used, covering the whole with the ditch sc.r.a.pings or other fertilizing material, where gra.s.s sod is desirable. Of course this is not desirable in villages and towns.
For binding, what is called garden loam is the best. When this cannot be found use any soft clay or earth free from clods or round stones. It must be spread on very lightly and uniformly.
Any good dry stone not liable to disintegrate can be used as metal for foundation for either telford or macadam construction. For the surface it is necessary to have the best stone obtainable. Like the edge of a tool, it does the service and must take the wear. As in the tool it pays to have the best of steel, so on the road, which is subject to the wear and tear of steel horseshoes and heavy iron tires, it is found the cheapest to have the best of stone.
It is difficult to describe the kind of stone that is best. The best is generally syenite trap rock, but this term does not give any definite idea. The kind used in New Jersey is called the general name of Jersey trap rock. It is a gray syenite, and is found in great quant.i.ties in a range running from Jersey City, on the Hudson River, to a point on the Delaware between Trenton and Lambertville. There are quant.i.ties of good stone lying north of this ledge, but none south of it.
The best is at or near Jersey City. The same kind of stone is found in the same ranges of hills in Pennsylvania, but in the general run it is not so good. The liability to softness and disintegration increases after leaving the eastern part of New Jersey, and while good stone may be found, the veins of poorer stone increase as we go south and west.
It is generally believed that the hardest stones are best for road purposes, but this is not the case. The hard quartz will crush under the wheels of a heavy load. It is toughness in the stone that is necessary; therefore a mixed stone, like syenite, is the best. This wears smooth, as the rough edges of the stone come in contact with the wheels. It requires good judgment based on experience to determine the right kind of stone to take the constant wear of horseshoes and wagon tires.
If good roads are desired, the work is not done when the road is completed and ready for travel. There are many causes which make repairing necessary. I will refer to only a few of them. Stone roads are liable to get out of order because of too much water or want of water; also, when the natural roadbed is soft and springy and has not been sufficiently drained; when water is allowed to stand in ditches and form pools along the road, and when the "open winters" give us a superabundance of wet. Before the road becomes thoroughly consolidated by travel it is liable to become soft and stones get loose and move under the wheels of the heavily loaded wagons. In the earth foundation on which the stone bed rests the water finds the soft spots. The wheels of the loaded teams form ruts, and particularly where narrow tires are used.
The work of repair should begin as soon as defects appear, for, if neglected, after every rain the depressions make little pools of water and hold it like a basin. In every case this water softens the material, and the wagon tires and horseshoes churn up the bottoms of the basins.
This is the beginning of the work of destruction. If allowed to go on, the road becomes rough, and the wear and tear of the horses and wagons are increased. Stone roads out of repair, like any common road in similar condition, will be found expensive to those who use and maintain them. The way to do is to look over a road after a rain, when the depressions and basins will show themselves. Whenever one is large enough to receive a shovelful of broken stone, sc.r.a.pe out the soft dirt and let it form a ring around the depression. Fill with broken stone to about an inch or two above the surface of the road. The ring of dirt around will keep the stone above the surface in place, and the pa.s.sing wheels will work it on the broken stone and also act as a binder. The whole will work down and become compact and even with the road surface.
The ruts are treated in the same way. Use one and one-half inch stone for this; smaller stones will soon grind up and the hole appear again.
The second cause of the necessity for road repairs is want of water.
This occurs in summer during hot, dry spells. The surface stone "unravels;" that is, becomes loose where the horses travel. This condition is more liable to be found on dry, sandy soils, and where the roadbed is subject to the direct rays of the sun, and where the winds sweep off all the binding material from the surface. In clay soil there is little or no trouble from "unraveling." The cause being found, the remedy is applied in this way: Put on water with the sprinkler before all the binding material is blown off. If the hot, dry weather continues, sprinkling should continue. Do this in the evening or late in the afternoon.
The next mode is to repair the road by placing the material back as it was originally. The loose stones are placed in the depressions and good binding material--garden loam or fine clay--is put on, then roll the whole repeatedly and dampen by sprinkling as needed until the whole surface becomes smooth and hard. Care must be taken that too much binding material is not used. If too much is used it will injure the road in winter when there is an excess of water.
When a road has been neglected and allowed to become uneven and rough, or is by constant use worn down to the foundation stones, there should be a general repairing. In the first place, if it is the roughness and unevenness that is the only defect, this may be remedied by the use of a large, heavy roller with steel spikes in its rolling wheels. This will puncture the surface so that an ordinary harrow will tear up the surface stones. Then take the spikes out of the roller wheels, and, with sprinkling and rolling, the roadbed can be repaired and made like a new road. But if the cause of the roughness is from wearing away of the stone, so that the surface of the road is brought down to or near the foundation, then the road needs resurfacing. The mode of treatment is the same as in the other case.
In districts where there is stone suitable for road construction the county, town, township, or other munic.i.p.ality, proposing to construct stone roads, should own a stone quarry and a stone crusher. For grading and preparing the road for construction, dressing up sides, clearing out side ditches, etc., a good road machine is necessary. For constructing roads and repairing them a roller is necessary, the weight depending upon the kind of road constructed. If the road is not wide a roller of from four to six tons is all the weight necessary. The rolling should be continued until compactness is obtained. For wide, heavy roads a steam roller of fifteen tons can be used to advantage. A sprinkling wagon completes the list that is necessary for the county or town or other munic.i.p.ality constructing its own roads.