Road construction

Dec. 12, 1939.

A. R. CHAMBERS

ROAD CONSTRUCTION

Filed June 21, 1937

2,183,253

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/W£7VTOR:

ALLISON ROBERT CHAMBERS

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ATTORNEY

Patented Dec. 12, 1939

2,183,253

UNITED STATES PATENT OFFICE

2,183,253

ROAD CONSTRUCTION

Allison Robert Chambers, New Glasgow, Nova Scotia, Canada

Application June 21, 1937, Serial No. 149,434 In Canada September 12, 1936

Claims. (Cl. 94—25)

This invention relates to an improved base construction for roads or highways, culverts, foundations, telegraph poles, posts and the like.

The object of the invention is to overcome the 5 damaging effect of frost caused by heaving. It has been observed that ice-lenses form and grow in the sub-base of roads at depths of one, two or more feet below the surface and these give rise to frost heaves and the so-called “boils” in 10; the. road when climatic temperatures rise sufficiently. Sub-soil temperatures at these depths are rarely lower than 15-20° F. The invention contemplates lowering the freezing point of water in the sub-base to or below these temperatures 15' to prevent the formation of ice-lenses. In placing foundations for buildings, machinery, telegraph poles, fence posts, bridges and culverts, somewhat similar conditions prevail. Although culverts are normally a substantial distance be20: low the road surface, the open end of the culvert . permits the frost to enter the ground beneath it and: the road surface is frequently pushed up by the freezing of sub-surface water.

The. accompanying drawing illustrates the in25 vention; Figures 1 and 2 as indicated illustrating road construction.

In accordance with the invention the sub-base of the construction to be stabilized against frost is impregnated with a water soluble electrolyte, 30 soluble to such an extent as to lower the freezing point of soil water therein to a point below the temperature to which it is commonly reduced during the cold season. This sub-base is rendered impervious to water by treatment with a water35 proofing binder so as to retain therein the electrolyte. On this waterproof sub-base is preferably laid a base course, composed of a soil mixture stabilized with water soluble electrolyte, to the desired depth. In the case of a base for poles, 40 posts or the like the walls and bottom of the hole is coated with a tar or asphalt emulsion, bitumen or the like.

The invention will now be described in detail with particular reference to road construction.

In carrying out the invention in practice, when grade and line of the road have been established and the surface brought to a pre-determined subbase level, this surface is scarified to a depth of, for example, 6 to 8 inches and a water soluble 50 electrolyte, preferably common salt, is thoroughly mixed, as by repeated blading, with the sub-base material, in proportions determined from, an analysis of the sub-base material and the temperature against which frost protection is desired.

As a guide to the determination of the amount of electrolyte to be used, the following formula, which is applicable to the use of sodium chloride, may be employed. It will be apparent that for other electrolytes the quantity m will require revision. B=165aa:2/277i in which 5

B—tons of salt per mile.

a—-% by weight of sub-base material passing standard U. S. 40 screen, expressed as a decimal fraction. ₁₀ x—the average specific gravity of . sub-base material.

y—the thickness in feet of the sub-base layer.

z—the width of the road in feet.

m—% of salt required to protect against a cer- _lgtain temperature, as indicated, for illustration, in the following table and expressed as a decimal.

<td> Percent salt in sol/ fines</td><td> Freezing point</td>

<td></td><td> °F.</td>

<td> 1.25_________________________________________ .</td><td> 26</td>

<td> 2.50________________________________________________</td><td> 19</td>

<td> 3.75________________________________________________</td><td> 13</td>

<td> 5.00________________________________________________</td><td> 5</td>

<td> 6.25________________________________________________</td><td> -6</td>

<td></td><td></td>

To illustrate, if a sub-base course 20 feet wide and 6 inches deep is to be protected against a temperature down to 13° F. and analysis shows the sub-base to contain 20% of fines of the character 30 described and to have a specific gravity of 1.3, the salt requirements would be

Β=165α:χ.2χ 1.3χ.5χ20χ.0375=16.1 tons per mile of road

The mixture is then placed in position, moistened and compacted by rollers, trucks or any other convenient means.

The above formula and figures are for illustrative purposes and it will be understood that 40 the amount of salt to be used under a given set of conditions may be determined by trial or otherwise as desired. The salt may be applied in solution where penetration to the required depth permits and conditions are such as to make this more 45 economical.

As a means of further increasing the strength of the sub-base, the moist salt treated sub-base may be allowed to dry for a time to permit the formation of an interlocking network of crystal- 50 line particles throughout the structure. The increase in strength thus afforded appears to be due to the reduction of voids and to the intrinsic nature of the rock structure of the crystals themselves. 55

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The sub-base thus prepared is rendered impervious to water by application of standard tar or asphaltic primer at the rate of say 0.5 gallon per square yard. If desired a thin layer of fine 5 gravel may be rolled in and recoated as above to more effectively confine the electrolyte in the subbase material. This seal coat should protect the salt in the sub-base material from being leached out and thus retain the salt in the region of the 10 origin of the frost trouble.

In cases where water may enter the sub-base from below or the sides thereof it is preferable to coat with waterproofing the bottom and sides of the sub-base excavation before replacing the 15 backfill with the electrolyte therein in order to further insure the retention of the electrolyte.

The base course is then laid and consists of gravel, sand and clay of such size, gradation and proportions as to give a stabilized aggregate ac20 cording to well known practice. Salt is preferably uniformly mixed with this material in proportions of about 15 tons per mile of roadway 20 feet wide for a base course 3 inches thick. This course is preferably placed in layers each of which is 25 dampened and compacted in place before the next is laid. This gives a dense and strong base which is preferably allowed a period of seasoning in actual use before the wearing surface is applied.

In many cases this may be used as the wearing surface but if a more permanent surface is desired cement, concrete or other bonded aggregate may be applied as in standard practice.

In preparing the base for culverts, piers, and 35 other foundations the base soil is excavated and after the electrolyte is mixed therewith the mixture is returned into place with the waterproofing to retain the electrolyte in the base soil.

In the case of pole or post holes after the base ₄₀ and wall of the hole are coated with waterproofing composition, the back-fill in which the electrolyte has been mixed is tamped into place about the pole, a thin layer of waterproofing composition is preferably placed thereover and the same is covered with earth to protect it from surface traffic around the pole. The salt electrolyte protects the pole from fungus growth and this substantially prolongs the life of the pole.

In constructing runways for flying fields or 5 earth dams and reservoirs it is advantageous to place a thin layer of the waterproofing material at intervals as the electrolyte-stabilized soil mixture is laid to improve retention of the electrolyte in the soil concrete. 10