Evening Republican, Volume 17, Number 14, Rensselaer, Jasper County, 16 January 1913 — Home Course In Road Making [ARTICLE+ILLUSTRATION]

Home Course In Road Making

VIIL—The Sand-Clay Road. ■ <*, u '

By LOGAN WALLER PAGE, Director Office of Public Road*, United States Department of Agriculture.

a SAND-CLAY road Is composed of sand and clay mixed in such proportions as to form a compact and firm support to traffic. The perfect sand-clay road should be neither sticky nor sandy. The sand and clay may form a natural mixture, in which case the road is termed a “natural sand-clay road.” The two materials may have become mixed in the fields along the road by

successive cultivation of the soil, and if this soil is used in the construction of a road it is known as “top soil road.” There are many varieties of clay and consequently a wide variation in the characteristics of a sand-clay road. The quality of the sand is a variable factor, as it may range all the way from fine, dust-like particles to coarse grains and gravel and may be perfectly clean or mixed with loam and other material. In consequence of these wide differences in the materials constituting sand-clay roads it is impossible to maintain a uniform standard as to quality of the road or methods of construction.

Not all but most sand consists of tiny grains of quarto. While quarto to one of the hardest minerals known, It possesses practically no binding or cementing power. The grains of sand, Instead of cohering in a tough mass under the Impact of traffic and the action of water, remain loose and shifting. Fine sand when dry to easily displaced by the wind, which produces In this way the ever shifting sand hills. No road is so difficult to travel as one through fine sand. If clay has been carried In small quantities by running water and deposited as sediment It to known as “sedimentary clay.” If the feldspathic rock has been disintegrated In place by water the clay Is known as “residual clay.” The sedimentary clay, having been carried in the form of fine particles, is finer grained than the residual clay and to more sticky and plastic. In contrast with sand, which possesses no binding power, but to very hard, clay Is a powerful binder, but does not possess the quality of hardness. It to evident that In the construction of a sand-clay road the important property in the clay to Its plasticity or tendency to become sticky and elastic when mixed with water. The clays which are most plastic are called “ball clays.” Another Important property which Is possessed by clays in widely varying degrees Is the porosity or capacity for rapid absorption of water. Clays which possess this quality in the highest degree fall to pieces under the action of water. These days are ealled “slaking clays.” It will readily be seen that the plastic or ball clays will form a better and more powerful binder for sand-clay roads than will the slaking clays; but, on the other hand, they will be much more difficult to mix, as they disintegrate with far leas rapidity.

The shrinkage of clay to an Important characteristic in connection with the building of roads. When water to mixed with results, and when the watir evaporates the clay contracts. This characteristic of expansion is much more pronounced In some clays than in others, and it must ba apparent that the clays which expand the least are preferable for road building. The ttfeory of the sand-clay- road to very similar to the theory of the macadam road. In the latter rock dnst and screenings fill the voids between the angular fragments of stone and when wet serve as a cement or binder. The grains of sand may be likened to the angular fragments of stone and slay to the rock dust binder. In the most successful sand-clay road Just a sufficient amount of clay Is used to fill the voids between the grains of sand. In this way the sand sustains tibe wear, while the clay serves as f

6!nder. If lob mu?h sand'is result will be loose sand on the surface; if too much clay is used the surface of the road will become sticky after rains. The best mixture of sand and clay can be made when the materials are wet, and particularly la this true of the plastic or ball days. If the clay is a plastic or ball clay much greater effort will be necessary to obtain a complete mixture; If it Is a slaking day' the will be much more readily obtained. This kind of clay is mot as satisfactory, however, as the ball day, as Its binding powers are much less. In selecting clay for road purposes It is always best to select the stickiest clay available. A common test is to wet the thumb and place It against a piece of day. If the clay will not stick to the thumb it is safe to assume that it will be a poor binder In a sand-clay road. As the desirable proportions of sand and clay are such that the particles of clay barely fill the voids between the grains of sand, it is well in determining The quantity of clay to be applied to a sand road or sand to be applied to a clay road to know approximately bow much is needed. A simple method for determining the relative quantity is to take two glasses of the same size and fill one with dry sand which it is proposed to use and the otherrwith water. The water should then be poured carefully ip the glass of sand and allowed to trickle down through the sand until it reaches the bottom of the glass. When the water has been poured into the glass of sand to the point of overflowing we may assume that the voids between the grains of sand have been filled, and consequently the amount of water taken from the full glass would represent the volume of clay needed to fill the voids In a volume of sand equal to that iH*the other glass. It is better to use a little less clay than would appear to be necessary, as the tendency Is to overestimate the amount needed.

Good drainage is the most essential feature of the sand-clay road just as it is of all other types of road. A sandy or gravelly soil affords better natural drainage, and if the sand is present to an exceptional extent the only provision necessary for drainage will be to crown the surface of the road in the same manner as prescribed for earth, gravel or macadam roads. If the road Is located through land that is so low as to be continually wet it will be necessary In addition to crowning the road to provide wide ditches on each side and to raise the roadbed a little higher than the surrounding country. After proper drainage has been secured the roadbed should be crowned, beginning near the source of supply of the clay or sand. The clay should then be spread to a depth of from six to eight inches in the center, sloping off gradually to a thin layer at the sides. Upon the clay should be placed a thin covering of sand. If the clay Is of the plastic kind it will then be necessary to plow and harrow It, advantage being taken of rains to puddle the surface with a disk harrow. Sand should be gradually added until the surface of the road ceases to ball and cake.

If the clay Is placed on sand to a depth of six Inches a cubic yard of clay will cover fifty-four lineal feet; consequently a sixteen foot road treated in this manner would require one cubic yard of clay for each three feet of length. A mile of sixteen foot road would therefore require 1,700 cubic yards of clay. If th% clay subsoil is to be treated with sand it should be plowed and harrowed to a depth of about four Inches. On this prepared subsurface should be placed from six to % eight inches of clean sand, spread thickest at the center and sloping to the sides In much the same manner as the clay Is applied to a sand road. These materials should then be mixed dry instead of the wet mixing, which is preferable when clay is applied to sand. This is preferable because the clay can be better pulverized when In a dry state. After dry mixing the road should be puddled following the first heavy rain. When the materials are thoroughly mixed and puddled a road

machine or grader should be used to give proper crown to the road, and if a roller is available the road can be lag)roved by the use of It Aa It to Impossible lo determine exactly the proportions of sand and clay to be used In the first-place, it to necessary to give careful attention to the aandcluy road for a considerable time after it Is completed. In order that additional sand or clay may be applied as needed. In 1904 there were only 2,900 miles es saud clay roads In the United States, bet at the present time there are approximately 25,000 miles

MIXING THE SAND AND CLAY.

A SAND-CLAY ROAD.