half inches, nor more than inches long, not less than two and one eighth inches, nor more than two and one half inches wide, not less than three and one half inches, nor more than four and one fourth inches deep. All paving brick must be homogeneous and compact in structure, free from loose lumps of uncrushed clay or from laminations caused by the process of manufacture or fire cracks or checks of more than superficial character or extent. All brick so distorted in burn

ing as to lay unevenly in the pavement shall be rejected. All brick shall be free from lime or magnesia in the form of pebbles and shall show no signs of cracking or spalling on remaining in water ninety-six (96) hours.

The brick shall have a specific gravity of not less than 2. They shall not absorb more than 3 per cent. of water when dried at 212 degrees Fahrenheit, and immersed for twenty-four hours in water.

The bidders shall submit twenty-five samples of the brick they propose using. A portion of these bricks shall be subjected to such physical tests as the board of public improvements shall deem necessary,* and the remainder shall be retained as samples of the material to be furnished and used. Any brick which does not stand the tests satisfactorily will be rejected, and no bid contemplating the use of the rejected brick shall be entertained. Samples may be submitted by manufacturers, in which case the bidder proposing to use brick of such manufacture will not be required to submit samples. The quality of the brick furnished must conform to the samples presented by the manufacturers and kept in the office of the street commissioner.

All brick may have a proper shrinkage but shall not differ materially in size from the accepted samples of the same make, nor shall they differ greatly in color from the natural color of the well burned brick of its class and manufacture.

No bats or broken brick shall be used except at the curbs where nothing less than a half brick shall be used to break joints. The bricks to be laid in straight lines and all joints broken by a lap of at least two inches, to be set upon the sand in a perfectly upright manner as closely and compactly together as possible, and at right angles with the line of the curb, except at street intersections where they are to be laid as the street commissioner may direct.

The pavement to be thoroughly rammed two or three times, as may be directed by the street commissioner, with a paver's rammer, weighing not less than seventy-five pounds, or a roadroller weighing not less than three nor more than six

tons.

* Tests similar to those described in the previous article are required.

All the joints in the pavement shall be completely filled with clean coarse river sand, and an additional layer of sand not less than one inch in depth shall be spread uniformly over the whole surface of the pavement. The joints may be filled with hot pitch or asphaltum, with some sand or gravel at bottom, or with cement grout, this latter being now (1895)recommended in order to prevent the brick from chipping on the edges. On steep grades, however, this would give too smooth a surface. ST. L.

Following the above specification is a "maintenance clause," similar to that given in the following article, providing for the maintenance of the pavement in good repair for a period of nine years. The contract price provided also for an annual sum to be paid for maintenance, and the bond given by the contractor covered the maintenance, as well as the original construction.

The tests to which the brick are submitted under this specification are the same as those given in Art. 133.

135. Specification for Asphaltum Pavement. After describing the preparation of the roadbed, curbing, concrete foundation, having a depth of five inches, etc., the following specifications of the asphaltum body and wearing surface are employed.

BINDER.

The second or binder course will consist of a fine bituminous concrete composed of clean broken stone, slag or gravel, not exceeding one and one half (12) inches in their largest dimensions, thoroughly screened, and asphaltic cement made from lake asphalt, as below described. The stone, slag or gravel, will be heated by passing through revolving heaters and thoroughly mixed by machinery with the asphaltic cement in the proportion of not less than fifteen gallons of the asphaltic cement to one (1) cubic yard of stone, slag or gravel. The mixture will be so made that the resulting binder has life and gloss without an excess of cement. Should it appear dull from over heating or lack of cement it will be rejected. This binder will be hauled to the work and spread on the base with hot iron rakes, and immediately rammed and rolled with hand and steam rollers while in a hot and plastic condition, until it has a thickness of one and one half (12) inches. The upper surface will be made exactly parallel with surface of the pavement to be laid.

WEARING SURFACE.

Upon this binder course thus prepared shall be laid a wearing surface or pavement proper, the basis of which shall

be composed of lake asphalt unmixed with any of the products of coal tar, of a nature and quality proved to be durable and proper by having been in successful use in roadway pavements in one or more cities of the United States for a period of at least two years and in an amount greater than five thousand square yards in each of said cities.

The wearing surface shall be composed of

Ist. Refined lake asphaltum.

2d. Heavy petroleum oil.

3d. Clean sharp sand.

4th. Fine powder of carbonate of lime.

Refined asphalt shall be smooth and free from lumps of unmelted pitch or organic matter not bituminous.

It shall not at any time reach a temperature over 375 degrees Fahrenheit. The asphaltic cement shall be prepared from such refined asphalt as may be approved by the street commissioner, and suitable heavy petroleum oil or other approved solvent.

The heavy petroleum oil, which may be the residum by distillation of the petroleum oils as found in the market, generally contains water, light oils, coke, and a gummy substance soluble in water. This petroleum oil is freed from all impurities and brought to a specific gravity of from 18 degrees to 22 degrees Beaume, and a fire test of 250 degrees Fahrenheit.

To the melted asphalt, at a temperature of not over 325 degrees Fahrenheit, the oil, after having been heated to at least 150 degrees Fahrenheit, is to be added in suitable proportions to produce an asphalt cement. To accomplish this, from 15 to 21 pounds of oil per 100 of refined asphalt will be required. As soon as the oil has begun to be added, suitable agitation, be means of an air blast or other acceptable appliances, will commence and be continued till a homogeneous cement is produced. The appliances for agitation shall be such as to accomplish this in at least ten hours, during which the temperature shall be kept at from 290 degrees to 325 Fahrenheit, and no higher. If the cement then appears homogeneous and free from lumps and from inequalities, as shown by samples from different parts of the still, it may be used. Should it not prove homogenous, such deficiencies as may exist shall be corrected by the addition of hot oil or melted asphalt, in the necessary proportion.

They shall be mixed in the following proportions by weight:

Pure asphalt

Heavy petroleum oil

.....

100 parts.

15 to 20 parts.

The asphaltic cement being made in the manner above described, the pavement mixture shall be formed of the following materials, and in proportion stated:

Limestone dust shall be an impalpable powder of carbonate of lime, the whole of which will pass a 30-mesh screen, and at least 75 per cent. pass a 100-mesh screen.

The sand and asphaltic cement are heated separately to about three hundred degrees Fahrenheit. The pulverized carbonate of lime, while cold, is mixed with the hot sand in the required proportions, and is then mixed with the asphaltic cement at the required temperature, and in the proper proportion, is a suitable apparatus, which will effect a perfect mixture.

The pavement mixture, prepared in the manner thus indicated, shall be laid on the foundation. It shall then be carefully spread, by means of hot iron rakes, in such manner as to give a uniform and regular grade, and to such depth that after having received its ultimate compression, it shall have a thickness of two inches. The surface shall then be compressed by rollers; after which a small amount of hydraulic cement shall be swept over it, and it shall then be thoroughly compressed by a steam roller, weighing not less than ten (10) tons, in order to get a thoroughly compressed wearing surface, the rolling being continued as long as it makes an impression on the surface.

The powered carbonate of lime shall be of such degree of fineness that 5 to 15 per centum by weight of the entire mixture for the pavement shall be an impalpable powder of limestone, and the whole of it shall pass a No. 26 screen. The sand shall be of such size that none of it shall pass a No. 80 screen, and the whole of it pass a No. 10 screen.

In order to make the gutters, which are consolidated but little by traffic, entirely impervious to water, a width of twelve inches next the curb shall be coated with hot pure asphalt and smooth with hot smoothing irons, in order to saturate the pavement to a certain depth with an excess of asphalt.

TOOLS AND SAMPLES OF MATERIALS.

The contractor shall furnish and have on the line of work at all times, a complete and sufficient plant of tools, rollers, carts, etc., as may be determined by the street commissioner, to carry on the work in an expeditious and workmanlike manner, also furnish samples of the crude lake asphalt to be used in the work, properly labeled, also samples of the wearing surfaces as prepared for use, and the statement of the amount of each material used in making up the pavement mixtures, when called for by the street commissioner.

In order that the asphalt may be fully tested, each bidder must deposit with the street commissioner, at least three days before making his bid, samples of materials he intends to use, together with certificates and statements as follows:

1st. A specimen of the crude asphaltum not less than five (5) pounds in weight with a certificate stating the place from whence the asphaltum was taken.

2d. A specimen of the asphaltic cement not less than five (5) pounds in weight with a statement of its composition, and also a statement of the composition of the proposed wearing surface.

3d. A sample of the pavement surface showing the Asphalt after two years' actual use in a street, said sample be not less than one foot square and to be accompanied by a certificate from the proper city official showing the time during which said pavement has been in use on the street on which it was laid, and the certificate shall further show that the pavement from which the sample is taken, or similar pavement, has been in successful use on one or more roadways in said city for a period longer than two years, and in an amount greater than five thousand (5000) square yards.

4th. A statement of the location and the capacity in square yards per day of the works or factory where the paving material is to be prepared.

Specimens must be furnished to the street department as often as may be required during the progress of the work.

MAINTENANCE.

The said -, party of the first part, expressly guarantees to maintain at grade and surface in good order the aforesaid work of reconstruction throughout and at the end of the full period of nine years, commencing one year after the said work of reconstruction is completed and accepted, and binds himself, his heirs and assigns to make all repairs which may from any imperfection in said work or materials or from any rotting, crumbling or disintegration of the materials, become necessary within that time; and the party of the first part shall, whenever notified by the street commissioner that repairs are required, at once make such repairs at his own expense, and if they are not made within the proper time, the street commissioner shall have power to cause such repairs to be made, and the cost thereof shall be paid out of the fund provided for the payment of contracts for street maintenance, and the amount shall be deducted from any money then due under the contract, or which may thereafter become due. At the end of the nine-year period the street commissioner must determine whether or not the street is in good order at grade and surface, and the principal and his sureties under this con