ITEM P-410 ASPHALT CONCRETE SURFACE COURSE (Liquefier Type) DESCRIPTION 410-1.1 This item shall consist of a surface course composed of mineral aggregate and bituminous material, mixed in a central mixing plant, and placed on the prepared base 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. 410-1.2 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. 410-1.3 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 temperature of the aggregate at the time it is placed in the mixer. The material furnished shall conform to the approved job mix formula within the tolerances specified herein: JOB MIX TOLERANCES Aggregate passing sieve No. 4 and larger____ Liquefier MATERIALS 410-2.1 AGGREGATE. The aggregate shall consist of crushed stone, crushed slag, and screenings of these materials. The aggregate and screenings used in any one project shall be the same kind of aggregate. The surface covering or sealing material shall consist of approved, clean, dry coarse sand. Screenings may be used when approved. The aggregate shall be tough, durable, and sound. The aggregate shall consist of angular fragments reasonably uniform in density and quality and reasonably free from thin, elongated, or soft pieces, dirt, or other objectionable matter. The coarse aggregate, when tested in accordance with the Los Angeles Rattler Test, after five hundred (500) 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 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. Slag shall be air-cooled, blast furnace slag, and shall have a compact weight of not less than sixty-five (65) pounds per cubic foot. The crushed aggregate shall not show evidence of disintegration, nor show a total loss greater than twelve (12) percent when subject to five (5) cycles of the sodium sulphate soundness test using A. A. S. H. O. Method T-104. 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 a sample mixture has been made it shall be spread out in a loose thin layer and placed in a constant temperature, ovencontrolled to 140° F., for twenty-four (24) hours before testing. A suitable size sample (approximately one-half (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. 410-2.2 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 shall meet the requirements of the A. A. S. H. O. Specification M-20 or M-22. The penetration of petroleum asphalt cement 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 85-100, 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. 410-2.3 LIQUEFIER. The liquefier shall meet the requirements of the A. A. S. H. O. Specification M-83. The grade shall be the light grade unless otherwise indicated in the proposal. 410-2.4 HYDRATED LIME. The hydrated lime shall meet the requirements of the A. S. T. M. Designation C-6. COMPOSITION OF MIXTURE 410-3.1 GRADATION. The mineral aggregate for the surface course and sealing material shall be of such size that the composition by weight, as determined by laboratory sieves, shall conform to the following gradations: ingredients shall be combined within the following percent by weight as may be directed by the engineer: The sealing material shall be prepared in the paving plant and be proportioned by weight, as directed by the engineer. Asphalt Cement_ Sand___. Liquefier Percent 2.0 to 3.5 96.5 to 98 0.5 to 1.5 CONSTRUCTION METHODS 410-4.1 WEATHER LIMITATIONS. Surface course shall be constructed only when the surface is dry, when the atmospheric temperature is above 50° F., and when the weather is not foggy or rainy. The temperature requirement may be waived, but only when so directed by the engineer. 410-4.2 EQUIPMENT. (a) General. All methods employed in performing the work and all equipment, tools, 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 surface course shall comply with the following requirements: The plant shall include a drier capable of heating evenly the aggregate necessary to continuously supply the mixing unit at its operating capacity, and of removing moisture from the aggregate to the limit herein prescribed without burning or overheating any portion. The equipment for mechanical cooling of the drying aggregate to the temperature prescribed for mixing shall be used, of capacity ample to keep the mixer supplied at its operating capacity, except in plants provided with dry, enclosed, storage space and mechanical aerating equipment adequate to accomplish satisfactorily the specified cooling of the dried aggregates without sweating or other deconditioning; in such plants, driers complying with all requirements except capacity, shall be used. For plants designed for mechanical cooling supplemented by dry storage, the requirements for mechanical aerating of the aggregate as it is being stored may be waived for material entering the storage space at atmospheric temperature. 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 bins shall provide two or more compartments, so proportioned as to insure adequate storage of appropriate fractions of the aggregate and mineral filler. Each compartment shall be provided with an overflow pipe or other device which meets the approval of the engineer, of such size and at such locations as to prevent backing-up of material into other compartments. All aggregate shall be dried and, after drying, shall be stored in the respective compartment where it can be held or fed to the weigh box. The storage of dried aggregate in the open-air or undertarpaulin covers will not be permitted, and dried aggregate may be stored only in covered bins as herein provided. The plant shall have a capacity not less than twenty-five (25) tons of mixed material per hour based on continuous operation. The plant shall have a weigh box of such capacity to hold a maximum amount of material for one batch, not less than 2,000 pounds. The weigh box or hopper shall be supported on fulcrum and knife edges so constructed that they will not be easily thrown out of alignment or adjustment. Said weighing hoppers must be free from contact on all edges, ends, or sides with any supporting rods or columns or other equipment that will in any way affect its proper functioning. In addition there must be sufficient clearance between the hopper and supporting devices so that foreign materials will not accumulate. The discharge gate of the weigh box shall be so hung that the aggregates will not be segregated when dumped in the mixer. If necessary to correct any such tendency, baffles shall be inserted or other means provided to discharge the materials in a blended condition. The discharge gate shall be sufficiently tight to prevent leakage of fine aggregate into the mixer. Scales for the weigh box may be either of the beam or springless dial type and shall be of a standard make and design, sensitive to onehalf (2) percent of the maximum load that may be required. When of the beam type, there shall be a separate beam for each kind of material, and there shall be a "telltale" dial scale attached which will start to function when the load being applied is within one hundred (100)) pounds of that desired. Sufficient vertical movements shall be provided for the beams to permit the "telltale" dial scale to function properly. Each beam shall have a locking device designed and so located that the beam can easily be suspended or thrown into action. Beam scales shall be balanced on knife edges and fulcrums, and be so constructed that they cannot be easily thrown out of alignment and adjustment. Dial scales shall be of a standard make and of sufficient size that the numerals on the dial can be read at a distance of not less than twentyfive (25) feet. The dials shall be of the compounding type having full complement of index pointers. Any pointers so placed as to give excessive parallax errors shall not be used. The scales shall be substantially constructed, and makes of this type of scale which easily get out of adjustment shall be replaced with other makes when so ordered. All dial scales shall be so located that they will be in plain view of the operator at all times. Scales for the weighing of asphalt cement shall conform to the specifications for the aggregate scales except that beam scales shall be equipped with a tare beam and a full capacity beam. The value of the minimum graduation in any case shall not be greater than two (2) pounds. Dial scales for weighing the asphalt cement shall not have a capacity of more than twice the weight of the material to be weighed, and shall read to the nearest pound. The asphalt weigh bucket shall be steam-jacketed and have a capacity equal to ten (10) percent of the maximum capacity of the mixer. It shall be supported on fulcrums and knife edges in the same manner as the weigh box. Tanks for storage of asphalt cement shall have a total capacity sufficient for one (1) day's run, and shall be capable of heating the asphalt cement with an effective and positive control of the heat at all times |