Asphalts. - The Refined Asphalts, Fluxes, and Asphalt Cement used, must comply in all respects with the requirements specified for these materials under Asphalt Pavement Item 54.

Stone. - The stone shall be sound, hard, crushed granite, limestone or crushed gravel bowlders, free from dust and all foreign materials, all passing a one-half-inch screen, and not more than 40% retained upon a screen with one-quarter inch round holes.

Sand. - The sand shall be hard-grained and moderately sharp. It shall be free from loam or any other foreign material, and shall be so graded as to produce in the finished surface mixture, the mesh requirements hereinafter specified.

Filler or Stone Dust. - The filler shall be ground Portland cement, silica or limestone dust, and shall be of such fineness that at least 65% will pass a 200-mesh sieve.

wearing surface

Mixture Composition. - The wearing surface shall consist of asphaltic cement, filler, sand and stone as heretofore specified, proportioned by weight so that the resulting mixture will contain average proportion of the whole, as follows:

Bitumen .....................................................................

7%

to

9%

Mineral

passing

200

mesh

........................................

6%

to

11%

"

"

80

(4

............................................

6%

to

15%

"

"

40

"

........................................

10%

to

25%

"

"

10

"

..........................................

10%

to

20%

"

"

4

"

.........................................

10%

to

40%

,,

"

2

"

.............................................

5%

to

20%

Total.................................

40%

to

55%

Sieves to be used in the order named.

The proportions of the above materials, sand stone, filler and bitumen may be varied within the limits designated above in the discretion of the Chief Engineer, and said limits as to composition are intended to provide for such reasonable variations as may be rendered necessary by the kind of available materials, and the character of the work to be done. The minimum amount of bitumen above specified may be only used, however, when the mixture contains the maximum of aggregate coarser than ten mesh.

The item designated as passing 200-mesh sieve includes filler, fine sand passing a number 200-mesh sieve, and such 200-mesh mineral dust as is naturally self-contained in the asphaltic cement.

Mixture Preparation. - The aggregate shall be thoroughly dried before, mixing with the asphaltic cement, in driers of the revolving type, which shall be so constructed and operated as to thoroughly agitate and turn the material during the process of drying.

The mineral aggregate and the asphaltic cement shall be heated separately to about 300 degrees Fahrenheit. The hot mineral aggregate shall be separated into two sizes, and stored in separate bins. By means of a 6 or 8-mesh screen, the sand portion of the mineral aggregate shall be collected in one bin, and the rejection from a 6 or 8-mesh screen shall be collected in another bin. Provision must be made for weighing out separately the required proportions of materials from each bin.

The asphaltic cement shall be melted in a tank arranged so that the heat can be properly and easily controlled and regulated. When melted and raised to a temperature of three hundred (300) degrees Fahrenheit it shall be combined in the specified proportions with the hot sand, stone and stone dust, and be immediately mixed in a mixer with revolving blades until a thorough, intimate and uniform mixture of the ingredients has been accomplished, and until all the mineral particles have become evenly and thoroughly coated with the asphaltic cement. The mixer shall be so arranged as to retain the heat during the process of mixing, but shall not be exposed directly to the action of the fire.

The maximum temperature of the aggregate at the mixers shall in no case be in excess 6f three hundred seventy-five (375) degrees F., and the maximum temperature of the asphaltic cement shall not exceed three hundred twenty-five (325) degrees F. at the discharge pipe. The filler, mineral aggregate, and asphaltic cement shall be mixed at the required temperature, and in the proper proportions so as to effect a thoroughly homogeneous mixture.

In producing the mixture, the proportions of asphalt cement and mineral aggregate must at all times be determined by actual weighing with scales, and shall be verified as often as may be required by the Chief Engineer.

Laying. - The asphalt wearing surface mixture as prepared above shall be hauled to the work in wagons or trucks, provided with canvas or other suitable covers. The mixture shall be dumped in such a manner that all of it must be loosened and turned before being raked. If considered necessary by the Chief Engineer to secure proper handling and even distribution of the mixture, the wagons shall be dumped upon sectional platforms from which all of the mixture must be handled and distributed. The wearing surface mixture shall be raked while hot over the clean foundation to such thickness that after receiving ultimate compression by rolling, it shall have a depth of two (2) inches.

Initial compression shall be effected by means of a roller of five (5) tons weight, immediately after which fine dry sand in sufficient quantities to completely fill all superficial interstices shall be swept over the surface.

The rolling shall then be continued with a roller of ten (10) tons weight, until all roller marks have disappeared and the surface has become uniformly smooth, and free from elevations and depressions greater than one-quarter (1/4) inch under a six (6) foot straight-edge placed longitudinally of the street. Rolling shall be carried on continuously at the rate of not more than two hundred (200) yards per hour. The final rolling above specified shall be done with a three (3) wheel roller if the Chief Engineer so directs.

Along the curb and around the manholes and other obstructions in the street where the roller can not reach, the compression shall be secured by the use of hot iron tampers. The tamping shall be done as quickly as possible after the material is spread, and while it is still hot and plastic.

No portion of the wearing surface shall be laid when the surface of the concrete base is wet. Before the paving mixture is laid the entire exposed surface of the roadway face of the gutter flag and of the iron frames of manholes and catch basins shall be thoroughly painted with the pure asphaltic cement.

The paving shall be done as nearly continuously as possible, so the joints between the hot and cold material shall be as far and as few as possible. When a joint is unavoidable, the section of cold material shall be roughly brought down to a feathered edge, and the surface where the joint is to be made, painted over with pure asphaltic cement, the hot material raked over the feathered edge and thoroughly rolled. Upon the completion of the improvement the gutters shall be cleaned and the street kept barricaded for a period of twenty - four (24) hours.

The Contractor shall furnish all facilities for plant inspection by the Chief Engineer, and shall provide proper place and equipment for testing aggregates and penetrations of asphaltic cement.

Payment. -The cost of replacing gutter flagging and crossings will be included in price bid for concrete per cubic yard.

The readjusting of existing pavements at the intersections will be paid for as repaving under the appropriate heads. All concrete used in filling holes will be paid for at the price bid per cubic yard. The readjusting of manholes will be paid for as such.

Where the asphaltic pavement is laid over old block pavements, any binder used in filling depressions shall be paid for by the cubic foot as Extra Binder Item 53.

The price bid for asphaltic concrete pavement per square yard shall include all the balance of the work of laying the pavement complete.