(a) The base for all asphaltic installations shall be five inches in finished depth, and such base shall be of limestone ranging from two (2") inches to one-half (½) inch screen, and all loads delivered shall be of uniform mix without segregation of sizes. This material shall be evenly spread over the rolled sub-grade and thoroughly consolidated with a power roller of at least five (5) tons weight. Voids shall be filled with fine screenings after the initial rolling and the surface sprayed with water during the final roller operation. The finished top base shall be uniform in surface and shall show no loose aggregates.
(b) An alternate base may be made by using Portland cement concrete four (4") inches in depth. Such concrete shall be composed of one (1) part cement, two and one-half (2½) parts sand and four (4) parts limestone. Only enough water shall be hand-tamped in place on the rolled sub-grade. A covering of burlap or heavy paper shall be left on for a period of at least six (6) days before applying the two (2") inch asphalt surface.
(c) When the base has thoroughly dried to the satisfaction of the City Engineer, the two (2") inch asphalt wearing surface may be laid. On the foundation, as heretofore required, there shall be laid the bituminous concrete wearing surface, which shall consist of a mineral aggregate mixed with bituminous cement and laid as hereinafter specified. This wearing surface shall have a thickness of two (2") inches after thorough compression with a roller weighing at least five (5) tons.
(d) The mineral aggregate shall consist of a mixture of broken stone and sand to which in some cases may be added a small quantity of stone dust or Portland cement. Any sound, durable stone such as trap rock, blue limestone, or granite, usually considered suitable for macadam surface, may be used. The stone must be broken as nearly cubical as practicable and shall not show distinct planes or cleavage or crystalline faces and shall not crush or split under the roller when being consolidated in the installation. For the wearing surface the stone shall vary in size from that passing a one and one-fourth inch screen to that held on a one-fourth (¼") inch screen. The dust or fine screenings shall be removed from the stone if excessive and irregular in quality. The sand shall be similar in character to that commonly used in sheet asphalt mixtures. It shall be hard-grained and moderately sharp, free from loam or other foreign material and vary in size from that passing a one-fourth (¼") inch screen to dust passing a 200 mesh screen. There shall not be over five percent (5%) passing the 200 mesh and not over thirty percent (30%) on the ten (10) mesh screen. The dust which may be added to the mixture shall be either Portland cement or finely ground limestone. Not over four percent (4%) by weight shall be added to any bituminous concrete mixture and a screening of the combined aggregate should not be over six percent (6%) of 200 mesh material.
(e) The proportions of the various ingredients composing the bituminous concrete shall be approximately three (3) parts of stone to two (2) parts of sand, to which shall then be added bituminous cement sufficient so that from seven (7%) to ten percent (10%) by weight of the mixture shall be bitumen soluble in carbon disulphide.
(f) The mineral aggregate shall, before mixing with the bituminous cement, be dried and heated in driers of approved type in which the material does not come into contact with fire or flames. The driers shall be of the revolving type, agitating and turning the material during the process of drying. When the aggregate is thoroughly dried and heated to a temperature from 250 degrees to 355 degrees Fahrenheit, depending upon the climatic conditions and the bituminous cement used, it shall be immediately, before being cooled or exposed to moisture, mixed in a box known as the “pug type” with the hot bituminous cement, as hereinafter specified. If stone dust is used, such material shall be introduced directly into the mixer without passing through the drier.
(g) The asphaltic cements used as the binding material shall be prepared from refined oils having asphaltic base. The material shall be prepared with asphaltic petroleum oils, to produce the required consistency. The asphalt shall be homogeneous, free from water, and shall not foam when heated to 175 degrees Centigrade. Such asphalt shall meet the following requirements:
(1) | Specific gravity 25°C, not less than | 1.01 |
(2) | Flash point, not less than | 175°C |
(3) | Softening point | 40° - 55°C. |
(4) | Penetration 25°C, 100 gr. 5 sec | 80 - 90 |
(5) | Loss at 163°C 5 hours | 1° maximum |
(6) | Penetration residue, 25°C, 100 gr 5 sec. At least | 55 |
(7) | Total bitumen, at least | 99.5 |
(8) | Organic, insoluble | .02 maximum |
The contractor must certify in writing to the City Engineer of his inspector, the character of the asphalt and the source of supply which he contemplates using, prior to beginning the work.
(h) The mixture shall be spread by shoveling into place on the foundation and leveling with heated metal rakes so that when compressed by self-propelled roller weighing at least five (5) tons, it shall be two (2") inches in thickness with surface even and true to grade. Along the curb and around manholes, meter boxes and other obstructions where the roller cannot reach, the compression shall be obtained by hot iron tampers. As soon as temperature will permit, the mixture shall be rolled and the rolling continued lengthwise and diagonally until all roller marks have disappeared and the surface give indication of no further compressibility. When a joint is necessary, the material shall be trimmed to a rough feather edge, painted with asphaltic cement, and the hot material then raked over the joint and thoroughly tamped and rolled. The process of laying must be continuous throughout each day’s operation to avoid unnecessary joints or lack of cohesion between the different batches delivered and installed.
(i) As soon as possible after the rolling of the mixture is finished and while the surface is still warm and clean a coat of pure asphalt cement, heated to a temperature of from 280 degrees to 320 degrees Fahrenheit shall be spread over the surface and evenly distributed with rubber squeegees or roofing mops. Only sufficient material shall be used to flush the surface voids without leaving an excess. Immediately over this cement application of a top dressing of torpedo sand or fine gravel, free from dust, which must be thoroughly dried and heated shall be spread and rolled into the surface. A small excess of gravel may be left to be worn in or away by traffic.
(Ord. 1999-02. Passed 1-11-99.)