Popular Science Monthly/Volume 81/August 1912/Trinidad and Bermudez Asphalts and their Use in Highway Construction II
|TRINIDAD AND BERMUDEZ ASPHALTS AND THEIR USE IN HIGHWAY CONSTRUCTION. II|
NEW YORK CITY
The Bermudez Asphalt Deposit
From the mouth of the Orinoco, the northeastern coast of Venezuela, which faces Trinidad, is low and consists of vast mangrove swamps, through which run deep tidal estuaries. That portion forming part of the State of Bermudez extends inland for many miles. It lies on the opposite side of the Gulf of Paria from Trinidad. About 30 miles in an air line from the coast the asphalt deposit, known as the Bermudez pitch lake, is found at the point where a northern range of foothills comes down to the swamp. The Guanaco River, a branch of the San Juan, one of the large cahos or estuaries of this region, at about sixty-five miles, in its winding course, from its mouth, runs within three miles of the deposit, but it is five or six miles to a suitable wharfage site. On the other hand, towards the north, a road runs to the hills and to the village of Guaryquen. These are the means of communication with the deposit. The so-called lake is situated between the edge of the swamp and the foothills in what might be termed a savanna. It is an irregular-shaped surface with a width of about a mile and a half from north to south and about a mile east and west. Its area is a little more than 900 acres, and it is covered with vegetation, high rank grass and shrubs, one to eight feet high, with groves of large moriche palms, called morichales. One sees no dark expanse of pitch on approaching it as at the Trinidad pitch lake, and except at certain points where soft pitch is welling up, nothing of the kind can be found. The level of the surface of the deposit does not vary more than two feet and is largely the same as that of the surrounding swamps. In the rainy season it is mostly flooded and at all times very wet, so that any excavation will fill up with water. . These conditions make it difficult to get about upon it or to excavate pitch easily.
It is readily seen that this deposit is a very different one from that in the pitch lake of Trinidad. It seems to be in fact merely an overflow of soft pitch from several springs, over this large expanse of savanna, and one which has not the depth or uniformity of that at Trinidad.At different points there is at most a depth of 7 feet of material,
while the deepest part of the soft maltha is only 9 feet and the average of pitch below the soil and coke only 4 feet. At points there is not more that 2 feet of pitch, and in the morichales or palm groves it is often 5 feet below the surface. At several points scattered over the surface are areas of soft pitch, or pitch that is just exuding from springs. The largest area is about 7 acres in extent and of irregular shape. This has little or no vegetation upon it, and from the constant evolution of fresh pitch is somewhat raised above the level of the rest of the deposit. This soft asphalt has become hardened at the edges, but when exposed to the sun is too soft to walk upon. The material is of the nature of a maltha and it is evidently the source of all the asphalt in the lake, from these exudations the pitch having spread in every direction, so that no great depth of pitch is found even at this point.
A careful examination of the surroundings shows that in one respect there is a resemblance between the point of evolution of the soft pitch at the Bermudez and at the Trinidad lakes. Gas is given off in considerable quantities at both places, and in both cases consists, partly, at least, of hydrogen sulphide.The consistency of the soft pitch at the center of the Bermudez lake is much thinner than that of the Trinidad lake. It will run like a heavy tar and does not evolve gas in the same rapid way or harden as quickly after collection. It therefore does not retain the gas which is generated in it, nor does the deposit as a whole do so to the same extent as the Trinidad pitch.
The general surface of the lake is very irregular and hard. There are many very narrow and irregular channels or depressions from a few inches to four feet deep, filled with water, and, not being easily distinguished, one often falls into them. At the foot of the growth of grass and shrubs are ridges of pitch mingled with soil and decayed vegetation, which have been plainly coked and hardened by fires originating in the surface growth. When this hardened material which forms only a crust is removed, asphalt of a kind suitable for paving is found. The crust is from a foot and a half to two feet in depth and very firm, while the asphalt underneath would not begin to sustain the weight which that of the Trinidad pitch lake does easily. There are breaks in the crust here and there through which soft pitch exudes, as has been described.
It appears, therefore, that the Bermudez deposit owes its existence to the exudation of a large quantity of soft maltha, which is still going on and which has spread over a great area; that this has hardened spontaneously in the sun, and has also, by the action of fire, been converted over almost the entire surface into a cokey crust of some depth, beneath which the best material lies, and that here and there are scattered masses of glance pitch produced in a similar way from the less violent action of heat. There is no evidence of a general movement and mingling of the mass of this deposit in any way that would produce a uniformity of composition, as seen in the Trinidad pitch lake, although there is a certain amount of gas evolved at the soft spots where maltha exudes and some gas cavities are found in the general mass of the pitch beneath the crust. As the asphalt below the crust of the deposit is the only portion of value for paving, the question has arisen as to its uniformity.
An examination of a series of samples collected in 1894 shows that the asphalt from the Bermudez deposit may vary very largely in the amount of water which it contains, from 11 to 46 per cent. None of it, however, is present in the form in which it occurs in Trinidad asphalt. It is not emulsified with the bitumen, but is all adventitious surface water. The percentage of oils which it volatilizes at about 400° F. varies from 16 to 6 per cent., consequently the consistency is far from uniform. The material carefully selected for use industrially is fairly constant in character, however, and when carefully refined has the following proximate composition:
The Composition of Refined Bermudez Asphalt
|Specific gravity, 77/77° F., orig. substance dry||1.082|
|Color of ponder or streak||Black|
|Hardness—original substance—at 77° F||Soft|
|Flows (melting point N. Y. T. L. method)||151°||F.|
|Penetration at 77° F., 5 sec, 100 grams, No. 2 needle||3||.0 mm.|
|Loss 20 grams 325° F., 7 hours, 24 dish||2||.9 per cent.|
|Character of residue||Smooth|
|Penetration at 77° F., 5 sec, 100 grams, No. 2 needle||1||.2 mm.|
|Loss 20 grams 400° F., 7 hours, 244 dish||7||.2 per cent.|
|Character of residue||Smooth|
|Penetration at 77° F., 5 sec, 100 grams, No. 2 needle||.4 mm.|
|Loss 50 grams at 325° F., 24 hours, 28 4 dish||3||.9 per cent.|
|Character of residue||Smooth|
|Penetration at 77° F., 5 sec, 100 grams, No. 2 needle||.5 mm.|
|Bitumen soluble in CS2 air temperature (70° F.)||94||.6 per cent.|
|Difference||1||.5 per cent.|
|Inorganic or mineral matter||per cent.|
|Bitumen soluble 88° naphtha, air temperature (70° F.)||67||3 per cent.|
|This is per cent, of total bitumen||71||.2 per cent.|
|Carbenes—per cent. bit. insol. CCl4 air temp. (70° F.)||None|
|Bitumen yields on ignition: Residual coke||12||.9 per cent.|
|Sulphur||5||.5 per cent.|
It appears from the above that the Bermudez asphalt is differentiated completely from that found in the Trinidad pitch lake, by the absence of
emulsified water and mineral matter. It is a much purer bitumen, a fact of no importance as far as its technical application in street paving is concerned, since the fine mineral matter or filler must be added to any asphalt cement in its use in such construction, but which is of advantage where the material is to be used in the construction of bituminous broken stone highways by the penetration process, owing to the greater ease with which the purer and more liquid material will enter into the voids of the broken stone.
The ultimate composition of the pure bitumen of Bermudez asphalt is much the same as that of the bitumen in Trinidad asphalt, as can be seen from the following comparison:
Bermudez asphalt contains, like the Trinidad, a high percentage of sulphur, varying, however, according to the degree to which the material has become hardened at different points in the deposit. The softest material contains the largest percentage.
In this connection I would say that in a paper read before the New York Section of the Society of Chemical Industry in November, 1897, and published in the Journal of the Society for January, 1898, I stated that, in my opinion as the results of investigations extending over eleven years:
This conclusion was based on the fact that an ultimate analysis of the pure bitumen from fourteen solid asphalts from various parts of the world, showed the presence of from 9.76 to 4.78 per cent, of sulphur, while in the softer forms of bitumen which rapidly harden on exposure to the atmosphere, or on heating, notable amounts of sulphur, 2.0 per cent, or over are found.
The same conclusion seems to have been arrived at, independently and apparently without a knowledge of my investigations, by Dr. D. Holde, of the Royal Testing Laboratory near Berlin. In his book on mineral oils and fats he says:
steam, when the amount of the latter in the chloroform extract which is insoluble in benzol is at least 7.5 per cent, and the asphalt, separated according to the method of Marcusson and Erckmann, contains 1.4-3.1 per cent, of oil with at the most 0.6 per cent, paraffin.
A bitumen would be called a petroleum residual pitch if it contains at most 1.7 per cent, of sulphur, even in the chloroform extract prepared as previously described and further 26-59 per cent, of oil in which the paraffin amounted to 3.3-16.6 per cent.
These conclusions of Holde are confirmed by my own data given in the paper to which I have referred, and are of the greater value on that account.
It appears, therefore, that a native solid asphalt is characterized by the fact that it contains sulphur, and the same thing is true, though in a lesser degree, of the softer bitumens from which it is derived.
Aside from the mere fact that sulphur is present in asphalt it is undoubtedly true that some of the most important physical characteristics of the material and those which distinguish it from the residual pitches are due to its presence, that is to say, the greater lack of susceptibility to change in consistency with change of temperature in the solid asphalts than is the case of the residual oils and pitches.
It is the presence of such a large amount of sulphur derivatives in Trinidad and Bermudez asphalt which makes them so desirable for use in highway construction, as compared with the residual pitches prepared from petroleum oil, which contains practically no sulphur derivatives.
In proximate composition Bermudez is very similar, as far as the bitumen is concerned, to that of the Trinidad material. The proportion of malthenes is slightly larger, and the asphalt in consequence somewhat softer, but in general, it is of a very similar character.
Shipping the Asphalt
As will be seen in the accompanying illustrations, the crude asphalt is won from the surface of the pitch lake by laborers with picks, in the form of flakes which have been mentioned. Those are thrown into
Much the same process is carried out at the Bermudez deposit, but the asphalt is carried from the lake to the shore of the river on a railway instead of by cableway. In either case, the crude material having been dumped into the hold of the vessel, runs together into a compact mass during the voyage to the United States. In consequence, it must be again picked out by laborers as it lies alongside the pier, and loaded into skips in which it is raised and again dumped into others, which are carried by a small railway to large storage bins holding several thousand tons, where it is again hoisted and dumped for storage until it is refined. Of course, in these bins it again runs together into a solid mass. As a supply is needed for refining, it is picked out and transferred to large rectangular tanks holding a hundred tons each, which are provided with gangs of pipe carrying steam at a pressure of 125 pounds and of about 325° F. This heat removes the water and melts the pitch.
Agitation is provided by passing some of the live steam through the crude material while it is heating. When there is no further evolution of steam and the melted mass has become tranquil, it is drawn off from the bottom of the tanks into open cement barrels placed on flat cars. These are not filled at once, but are topped off after the first filling has cooled, so that there shall be no loss of material. The product obtained in this way is the refined asphalt of commerce, and is in shape for shipment to whatever point there may be demand for it.
It may be interesting to note that the amount of crude material shipped from Trinidad during recent years, has reached as high as 180,000
tons per year, while that from the Bermudez deposits has reached as high as 47,000 tons but is rapidly increasing. The entire amount shipped from Trinidad since 1867 has reached three million tons, which would be equivalent to 180 million square yards of sheet asphalt pavement.
Service Tests of Trinidad Asphalt
Trinidad asphalt being for many years the only available supply of such material, it was the only one used in the early days of asphaltic highway construction in the United States. It has been subjected to the most varied environment with the most satisfactory results. There are in existence to-day three pavements which are worthy of consideration, as showing its capacity to meet different kinds of traffic and different climatic conditions.
A sheet asphalt pavement was laid in 1879 of Trinidad asphalt, on Vermont Avenue in Washington, between H and I Streets. This pavement is still in existence, and during that period has cost only in the neighborhood of ten cents a square yard, for maintenance for the entire period. It is apparently good to-day for ten or fifteen years more. This street is one of very moderate travel, delivery wagons and pleasure vehicles, and being very broad, over 100 feet, this is well distributed The pavement is typical of what Trinidad asphalt will do under such conditions for a long period of time.
Another striking piece of Trinidad sheet asphalt pavement is that on Fifth Avenue in New York, between 10th and 59th Streets. This was laid under the personal direction of the writer in 1896 and 1897, and has
withstood the very heavy travel which Fifth Avenue carried in a most satisfactory way for fifteen years, the number of vehicles passing any one point, when the travel is the greatest, being at the rate of as high as 14,000 in ten hours. No other smooth surface pavement in any country has withstood the conditions existing on Fifth Avenue with an equally satisfactory result.
The third type of Trinidad sheet asphalt pavement is that found on the Victoria-Thames Embankment in London, the first portion of which was put down by the writer in 1906, upon old macadam and a course of Trinidad asphalt concrete. Much the larger portion of the embankment has since that time been paved with this same form of construction, other forms having been removed in the meantime as unsatisfactory and replaced by it. The surface of the Embankment is rarely dry from November to April, and it carries the very large traffic which proceeds from Westminster to the city. This serves as a striking evidence of the ability of Trinidad asphalt to resist dampness and to carry heavy travel in such a climate and in such a city as London, without deterioration.
I may further illustrate the uses of Trinidad and Bermudez asphalt by citing bituminous broken stone surfaces which have been constructed with these asphalts in Massachusetts and in the State of New York, which have been in use for at least three years, and have given the greatest satisfaction, the most striking feature of these roads being that the bituminous binding material is not drawn to the surface by the hot summer sun, but remains in the road where it is placed, with the greatest stability. Surfaces of this kind have furnished the most satisfactory service tests which are at present available, of a bituminous broken stone construction.
- Soft material, maltha.