FLEXIBLE SURFACE COURSES ITEM P-401 BITUMINOUS SURFACE COURSE 401-1.1 DESCRIPTION This item shall consist of a surface course composed of mineral aggregate and bituminous material, mixed in a central mixing plant and placed on a prepared course, in accordance with these specifications and in conformity with the dimensions and typical cross section shown on the plans, and with lines and grades established by the engineer. When called for or shown on the plans, the surface course shall be constructed in two or more courses. Each shall be constructed to the depth, typical section, or elevation required by the plans. The leveling, binder, or base course shall be rolled, finished, and approved be. fore the placement of the surface course, in the manner specified. 401-1.2 DETERMINATION OF PERCENTAGE OF BITUMINOUS MATERIAL. The percentage of bituminous material, by weight, to be added to the aggregate shall be fixed by the engineer on the basis of preliminary laboratory tests and field sieve analysis on the aggregate furnished, and shall be within the range as shown in the table. 401-1.3 JOB MIX FORMULA. No work shall be started on the project, nor any mixture accepted therefor, until the contractor has submitted samples of the materials intended for use and the engineer has established a satisfactory job mix formula based upon tests of the materials furnished. The formula shall be submitted in writing by the engineer to the contractor, indicating the definite percentage for each sieve fraction of aggregate, and for bituminous cement; also the intended temperature of completed mixture at the time it is discharged from the mixer. The material furnished shall conform to the approved job mix formula within the tolerances specified herein: MATERIALS 401-2.1 AGGREGATE. The aggregate shall consist of crushed stone, crushed gravel, crushed slag, screenings, gravel, sandgravel, sand, or other natural, granular, approved material having essentially the same qualities and meeting all the requirements when combined within the limits for gradation. For the surface course at least forty (40) percent by weight of the mineral aggregate, including filler, shall have been produced by the crushing of stone, slag, or gravel. When produced from gravel, only those particles having one or more fractured faces shall be considered as crushed. Aggregate containing forty (40) percent to one hundred (100) percent crushed material will be required in surfaces to withstand parking and locked-wheel turns on special sections. These sections are ends of runways, plane-parking areas, apron areas, or such sections subjected to similar wear and loads. The percent of crushed aggregate required will be indicated in the proposal. The aggregate shall be tough, durable, and sound. The aggregate shall consist of angular fragments reasonably uniform in density and quality and shall not contain more than eight (8) percent of either thin, elongated, and soft pieces, or dirt, or other objectionable matter. The coarse aggregate when tested in accordance with the Los Angeles Rattler Test, after five hundred revolutions, shall have a percent of wear of not more than forty-five (45) according to the A. A. S. H. O. Method T-96. The coarse aggregate shall not show evidence of disintegration, nor show a total loss greater than twelve (12) percent when subjected to five cycles of the sodium sulphate accelerated soundness test using A. A. S. H. O. Method T-104. Slag shall be air cooled, blast furnace slag, and shall have a compact weight of not less than seventy (70) pounds per cubic foot. The portion of the material retained on a No. 4 mesh sieve shall be known as coarse aggregate; that portion passing a No. 4 mesh sieve shall be known as fine aggregate, and the material passing the No. 200 mesh sieve shall be known as filler. The composite material shall meet the requirements for one of the gradations given in Tables 1 or 2, using A. A. S. H. O. Methods T-11 and T-27. That portion of the fine aggregate, including any blended filler, passing a No. 40 mesh sieve shall have a plasticity index of not more than 6, as determined by A. A. S. H. O. Method T-91, and a liquid limit of not more than 25 as determined by A. A. S. H. O. T-89. The composite aggregate shall be free from vegetable matter, lumps or balls of clay, adherent films of clay, or other matter that will prevent thorough coating with bituminous material. The bituminized aggregate shall have a swell of not more than one and one-half (11⁄2) percent as determined by A. A. S. H. O. Method T-101. Prior to final acceptance of the proposed aggregate to be used, the inherent characteristics of said aggregate relative to stripping shall be determined. This shall be done by preparing a test sample of the paving mixture in conformity with the specifications contained herewith. After the mixture has been made it shall be spread out in a loose thin layer and allowed to air-season for twenty-four (24) hours before testing. A suitable size sample (approximately one-half (1⁄2) contents of container) shall be tested by placing it in a glass jar fitted with a tight screw cap. The sample shall be completely covered with distilled water at a temperature between 80° F. and 100° F. The jar shall be thoroughly cleaned and free from any traces of soap or other saponifiable material. The jar and contents shall be allowed to stand for a period of twenty-four (24) hours. Then the sample shall be vigorously shaken for a period of fifteen (15) minutes. The sample of mixture shall be examined for stripping. If stripping or sloughing. off of the bituminous coating occurs, it will be necessary to treat said aggregate by a method which has proven successful in changing the material from a hydrophilic to a hydrophobic state or the aggregate shall be rejected. 401-2.2 FILLER. If filler, in addition to that naturally present in the aggregate, is necessary it shall consist of stone dust, loess, Portland cement, or other approved mineral matter. Stone dust shall be specified and used with sand-asphalt surface courses. The filler material shall meet the requirements of A. A. S. H. O. Specification M-17. 401-2.3 BITUMINOUS MATERIAL. The bituminous material to be mixed with the mineral aggregate at the central plant shall conform to the grade, requirements, and specifications as follows: The asphalt cement for hot central-plant mix shall meet the requirements of A. A. S. H. O. Specification M-20 or M-22. (The penetration of petroleum asphalt shall be between 100 and 150. The penetration of native asphalt cement shall be between 85 and 150) A limited range or grade shall be selected for each project, such as 85100, 100-120, or 120-150. The penetration grade shall be indicated in the proposal, shown on the plans, or as directed by the engineer. Petroleum asphalt cement shall not be cracked. NOTE: When native asphalt cement contains mineral filler, the penetration grade selected will depend upon the amount of inorganic filler present. 401-2.4 HYDRATED LIME. The hydrated lime shall meet the requirements of the A. S. T. M. Designation C-6. COMPOSITION The mineral ag 401-3.1 COMPOSITION OF MIXTURE. gregate for the surface course shall be of such size that the percentage composition by weight, as determined by laboratory sieves, will conform to one of the following gradations. The percent by weight for the bituminous material shall be within the limits given. 1 The 1⁄2-inch maximum gradation shall not be used in preparing mixtures for turnarounds and parking areas. TABLE 2.-Sand-Asphalt Surface Course [This table will not be considered unless its use is permitted in the Sieve size proposal] Percentage passing sieves (square openings) D 36" maximum In the table the percentages of asphalt cement are given for stone, gravel, and slag aggregates. If the total aggregate is composed of slag, the percentages of bituminous material shown shall be used. Where only a part of the aggregates is slag, the increase in bituminous material shall be made in a corresponding proportion. The gradations in these tables represent the limits which shall determine suitability of aggregate for use from the sources of supply. The final gradations decided on within the limits designated in the table shall be uniformly graded from coarse to fine, and shall not vary from the low limit on one sieve to the high limit on the adjacent sieves, or vice versa. The selection of any of the gradations shown in the tables shall be such that the maximum-size aggregate used shall not be more than one-half (2) the thickness of the layer of the surface course being constructed. A sample of the coarse and fine aggregates shall be washed to determine the percentage of the total material passing the No. 200 mesh sieve. Of the amount of the material passing the No. 200 mesh sieve, at least one-half (1⁄2) shall pass the No. 200 mesh sieve by dry sieving. The composition limits tabulated shall govern, but a closer control appropriate to the job materials will be required for the specific project in accordance with a job-mix formula. The weights for the measurement of the bituminous mixtures should be based on the bulk specific gravity of aggregates of 2.65. Proportionate corrections shall be made when the aggregates furnished on the job (job aggregate) have bulk specific gravities above 2.75 or below 2.55. 401-4.1 CONSTRUCTION METHODS WEATHER AND SEASONAL LIMITATIONS. The surface course shall be constructed only when the surface upon which it is to be placed is dry, when the atmospheric temperature is above 40° F., and when the weather is not foggy or rainy. The temperature requirement may be waived, but only when so directed by the engineer. 401-4.2 EQUIPMENT. (a) General. All methods employed in performing the work and all equipment, tools, and other plant and machinery used for handling materials and executing any part of the work shall be subject to the approval of the engineer before the work is started, and whenever found unsatisfactory shall be changed and improved as required. All equipment, tools, machinery, and plant used must be maintained in a satisfactory working condition. (b) Mixing Plant. The paving plant used by the contractor in the preparation of the bituminous concrete shall comply with the following requirements: The drier shall be suitably designed to heat and dry the aggregate to specification requirements and to continuously agitate the aggregate during heating. The drier shall be capable of preparing aggregate to the full rated capacity of the paving plant to meet the specification requirement. A dial thermometer or other approved thermometric instrument shall be so placed at the discharge chute of the drier as to automatically register or indicate the temperature of the heated aggregate. All plant screens shall be designed, constructed, and operated so as to screen all aggregates to appropriate fractions as established by the engineer and as necessary to meet the job mix tolerances. The plant shall have storage bins, protected from the weather, of sufficient capacity to furnish the necessary amounts of all aggregates when operating at the maximum rated capacity of the plant. The |