ROAD MAKING MATERIALS

The available road materials in Arkansas, their kinds, distribution and relative value are briefly discussed. The emphasis will be placed on those materials that are more or less suitable for topdressing because it is the surface that receives the wear. The foundation for this surface must resist pressure, but it is subjected to relatively little friction once the road-bed becomes well settled.

Inferior Materials

Characteristically, the inferior materials are utilized because of ease of crushing or immediate availability in certain regions. These materials are subject to easy pulverization under wheels giving rise to dust in dry weather and mud in wet weather. In the wet weather such roads develop ruts and "chuck-holes" very readily. Such roads rapidly wwear out and the upkeep is costly. Only in rare cases will the initial low cost plus the high cost of subsequent repairs justify the use of inferior material instead of a higher initial cost of better material with consequent reduced cost of upkeep.

Among the inferior materials may be listed the following, in order of value:

1. Shale is a name applied to a rock composed essentially of clay. The term "slate" or "soapstone" is frequently in common use, though erroneously. Regardless of names, the fact that pure shale. is composed almost wholly of clay, will make it unnecessary to go into detail regarding the inadvisability of using such a rock for road metal. In a very short time, such a road would simply be a clay or mud road, and the outstanding drawbacks of such a highway are well known. But a sandy shale may make a fairly good road, as is shown later.

2. The term "clean sandstone" is applied to a sand rock that is composed of sand grains alone, the dominant grains consisting of quartz. Such a rock pulverizes rapidly into a very loose sand under traffic and instead of a firm roadway that will not wear out quickly a surface is formed into which wheels readily sink and composed of such loose material that every rain will tend to carve gullies along the wheel tracks as well as cross ditches where the water runs off of the road into the side drainage lines. Consequently the cost of upkeep where clean sandstone is used in a road will be higher.

3. Syenite or "granite" as the term is incorrectly used in Arkansas, is a little better than either of the above mentioned rocks for road metal. However, the syenite is composed almost wholly of feldspar, which weathers readily to clay. This alteration is the more rapid, the finer the syenite is pulverized. Therefore as the traffic grinds up the larger rock fragments, alteration to clay is hastened and a road surface is formed that offers all of the objections mentioned in regard to a clay shale.

4. Limestone does not undergo any rapid chemical change upon weathering in a roadway, but is a rock that is easily reduced to powder because of its brittleness and inability to withstand scratching or breaking when rubbed against other rocks. Thus the traffic over a limestone surface road develops a fine white powder that is blown about as dust and a coarser-grained texture that causes the limestone to wash as does sand.

Superior Materials

Characteristically, the superior materials are composed of rocks that resist the frictional wear of traffic, combined with some materials that may be softer but have the power of cementing the harder materials together, thus yielding a surface that will wear at a minimum rate.

Experience has shown that the following rocks are very good for use in making hard surfaced roads:

1. Novaculite is a hard rock and resists the wear of traffic very well. The main objections to the use of this rock for surfacing roads are found in the tendency to develop sharp edges and points of knife-like character, and the lack of binding materials. Where fragmental novaculite occurs intimately mixed with red residual clays, it would have all of the advantages of chert, which are discussed later.

2. Sandy shales contain quite a large amount of sand grains and are thus distinguished from clay shales. The sand grains are mainly of quartz. This quartz resists frictional wear of traffic and the clay acts as a sort of cement. If the sand grains are sufficiently abundant, the clayey cement is partially protected by them from surface wear and thus keep down the rate of rain wash. However, in prolonged periods of wet weather these same roads will become soft and consequently rough.

3. Gravels make a very good road metal if they are not clean washed, i. e., if there is some clay or other cementing material left with them. The cheapness due to wide distribution and to the fact that there is no cost of crushing renders the use of gravel for road work of great importance. As gravels are composed of rocks that have resisted the frictional wear due to the, action, of, running water, they will resist the wear of traffic. If there is sufficient clay, lime or iron material, or combination of these three materials, to form a good binding cement, the cost of upkeep of a gravelled road will be relatively small. If these binding materials are absent, a gravelled road is very unsatisfactory.

4. Chert or "flint rock" is hard and resistant to frictional wear. It usually is associated with and occurs in residual clays that make a good stiff natural binder that does not readily wash or become dusty. Consequently, the natural occurrences of "flint rock" offers one of the best road metals that occurs in Arkansas. Chert is an amorphous or crypto-crystalline form of quartz and the residual materials in which it is usually imbedded are clays highly impregnated with iron oxides and some carbonates of lime and magnesia, all of which have a hardening or cementing effect under the combined influence of weathering and traffic.

Distribution

Argillaceous or clay shales may occur in rocks of any age from Ordovician to Tertiary. The Chattanooga, Fayetteville, and some others are examples occurring in the northern part of the State. In and south of the Boston Mountains such shales are common. They also abound in the Ordovician area about Hot Springs, and Mena, Polk County, though they by no means form the only, or even the greater part of the rocks in the area mentioned.

Clean sandstones occur in all of the areas mentioned under argillaceous shales. (See "Building Stones.")

Syenites or "granites" occur in Pulaski, Saline and Hot Spring Counties and in a few small dikes in Garland, Montgomery, and a few other counties.

Limestones are most abundant in the region north of the Boston Mountains and west of the St. Louis, Iron Mountain & Southern Railway. (See "Building Stones.")

For distribution of novaculites see map, page 240.

Arenaceous or sandy shales abound in the lower coal measures of the State in the region south of the north face of the Boston Mountains, north of the Fourche and Petit Jean Mountains, and west of the St. Louis, Iron Mountain & Southern Railway. As there are also many argillaceous or clay shales in this area, one must guard against a confusion of the two when selecting a road surfacing material. ·

Gravels occur abundantly along Crowley's Ridge in eastern Arkansas; in Sevier, Howard, Pike, Hempstead, Clark, Dallas, Saline, Grant, Hot Spring Counties; along the courses of the Ouachita, Arkansas, White, and Black rivers, as well as in small deposits along streams in southeastern Arkansas. (See "Sand and Gravel.")

Chert is widely distributed throughout the area lying north of the Boston Mountains and west of the Iron Mountain Railway. For a detailed location of chert beds, see geological map of Arkansas and trace the outcrops of the Boone formation. Rocks older than the Boone furnish chert in Randolph, Sharp, Fulton, Izard, and Baxter Counties.

Road materials are thus seen to be widely distributed in all parts of the State except in the alluvial bottom lands of the eastern part. Even here local gravel deposits are frequently available. When the cost of road building is considered in an area where road materials are shipped in, it is observed that the road materials of Arkansas constitute an asset that is directly proportional in value to the public's estimate of the value of good roads.

Producers

For list see producers under "Sand and Gravel," page 238, “Sandstone and Quartzite," page 81, and "Novaculite," page 180.

Bibliography of Road Making Materials
1894

U. S. Department of Agriculture, Office of Road Inquiry, Bulletin 4.

1896

Branner, J. C., "Road Making Materials in Arkansas" (Report to W. G. Vincenheller, Commissioner of Mines, Manufactures and Agriculture).—Arkansas Bureau of Mines, Manufactures and Agriculture, Fourth Biennial Report, pp. 99-101. Same republished in Fifth Biennial Report, 1898. Available for consultation at most public libraries.

See also bibliographies under "Sand and Gravel," page 239; "Sandstone and Quartzite," page 80, and "Novaculite," page 180.

SAND AND GRAVEL

(See also "Glass Sand" and "Road Building Materials")

Uses.-Arkansas sand is used as a concrete aggregate, with mortar, as a base for brick pavements, for railway braking, etc. (See also "Glass Sand.")

Sand and gravel are used principally as road material, as railroad ballast, and as a concrete aggregate.

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Occurrence. Sand and gravel are widely distributed throughout the State. In the Coastal Plain or lowland region of southwest Arkansas, the gravel deposits are found either as stream deposits or higher land deposits. The higher land deposits are known as the Terrace gravels. The most persistent gravel bed in this portion of the State is known as the Pike gravel member of the Trinity formation (Lower Cretaceous). This extends irregularly across Pike, Howard, and Sevier Counties, near the northern edge of the Coastal Plain. The bed is from twenty to fifty feet thick. Another valuable bed is the Ultima Thule gravel lentil of the Trinity formation which is exposed northeast, north, and northwest of De Queen. This lies immediately south of the Pike gravel.

The largest gravel pit in southern Arkansas is that of the Ball Benton Gravel Company at Benton, Saline County. The gravels there are for the most part well rounded, quartzite gravels and are terrace gravels of Quaternary age. They occur in beds which are in some places fifty feet in thickness.

Crowley's Ridge in eastern Arkansas contains immense quantities of gravel which are frequently exposed in road cuts and in a few of the railway cuts. In many instances, the gravel extends to the tops of the ridge. Crowley's Ridge extends through Clay, Greene, Craighead, Poinsett, Cross, and St. Francis Counties.

The beds and bars of the Arkansas, Ouachita, Saline, and White Rivers furnish very great quantities of sand and gravel.