tractor drawn. The grader shall have a wheel base of not less than fifteen (15) feet, shall have a blade not less than ten (10) feet long, and be equipped with wheels of sufficient width to prevent excessive rutting.

If aeration is not necessary prior to compaction the mixed material may be placed and spread by a mechanical spreader and finisher.

(4) Rolling Equipment. (a) The pneumatic roller shall consist of pneumatic tires arranged in a manner so as to provide a satisfactory compacting unit. The roller shall have an effective rolling width of at least sixty (60) inches and shall give a compression of at least 275 pounds per inch of width of tread when fully loaded. The tires shall be uniformly inflated. The roller and operating power unit shall meet the approval of the engineer. The weight of the roller shall be increased as the rolling progresses to the maximum degree obtainable without detrimental results to the course being compacted.

(b) The steel-wheel rollers shall be of the self-propelled tandem or three-wheel type weighing not less than five (5) tons and not more than ten (10) tons. The wheels on the roller shall be equipped with adjustable scrapers which shall be used when necessary to clean the wheel surface. Rollers shall also be equipped with tanks and sprinkling apparatus which shall be used to keep the wheels wet and prevent the surfacing material from sticking. The rollers shall be maintained in good condition and be operated by experienced rollermen.

204-4.3 PREPARATION OF UNDERLYING COURSE. The underlying course upon which the base course is to be placed shall be properly prepared, smooth and fully compacted. It shall be cleaned of all loose material and deleterious matter and when tested with a sixteen (16) foot straightedge shall show no deviation in excess of three-eighths (%) inch.

204 4.4 PLACING MINERAL AGGREGATE. If borrow or foreign aggregate is used, it shall be transported to the site of paving in trucks equipped with pneumatic tires. Both speed and load shall be regulated by the engineer in order to reduce the possibility of damage to the existing surface. The aggregate existing or otherwise shall be formed in windrows in such quantity and proportions as to provide sufficient total aggregate, conforming with the specified gradation, to produce a finished base course of the specified compacted thickness. The contractor may proportion the amount of coarse aggregate and mineral filler in the windrow by weighing with suitable equipment or by using any other methods or devices which will be equally as effective as weighing equipment in placing the amount of total aggregate necessary to satisfy the yardage requirements for the area to be covered. After the proportions of coarse aggregate and mineral filler have been adjusted if required to meet the gradation, the total loose aggregate shall be thoroughly mixed to the satisfaction of the engineer. It shall then be bladed into windrows of uniform cross sections for the final measurement and sampling for grading adjustment. The formation of windrows in advance of mixing shall be limited so as to prevent

water from standing on the subgrade or ponding between windrows in case of rain.

Care shall be exercised to prevent the aggregate from becoming mixed with subgrade, subbase, or shoulder material. The uniform windrows shall be left undisturbed until measuring and sampling are completed.

204-4.5 MOISTURE CONTENT OF AGGREGATE. Immediately prior to bituminizing, the aggregate to be treated shall be tested for moisture. If the moisture content is in excess of the maximum allowable percentage the aggregate shall be turned by blades or disc harrows, or otherwise aerated, until the moisture content is reduced. The prepared aggregate shall then be uniformly windrowed as before or spread uniformly for mixing.

204-4.6 MIXING. The aggregate, windrowed and prepared as specified above, shall then be mixed with the bituminous material by means of the traveling mixing plant and deposited ready for spreading.

The Portland cement and lime shall be added during the mixing procedure at the time and in the amounts required by the engineer. These materials shall not be used in tar mixtures.

The quantity of bituminous material as calibrated for continuous mixer shall be determined by the engineer, and introduced into the mixer. The mixing shall continue for such period as is necessary to coat all of the particles and obtain a homogeneous mixture.

Before spreading, the mixture shall be examined by the engineer who shall determine whether the mixing is complete and satisfactory. Should the mixture show an excess, deficiency, or uneven distribution of bituminous material, the unsatisfactory condition shall be corrected by the addition of the required aggregate or bituminous material, and by remixing. If necessary, the material shall be harrowed or disced and all compressed masses of material broken up. No spreading shall be done, except when authorized by the engineer.

204-4.7 SPREADING AND FINISHING. (1) General. Spreading shall not be started until the subgrade or subbase has been properly prepared, compacted, and approved by the engineer.

When in-place materials or aggregates are used in the base course mixture, the coarse aggregate between the 2-inch sieve and the 12inch sieve shall not exceed five (5) percent. Any material that will not pass the 21⁄2-inch sieve shall be culled out and removed from the base course.

Grade control between the edges of the runway shall be by means of grade stakes or steel grade pins placed in lanes parallel to the centerline of the runway, and at intervals sufficiently close that string lines may be stretched between the stakes or pins.

When practicable and to protect the subgrade and to insure proper drainage, the mixing and spreading of the base shall begin along the center line of the runway or taxiway on a crowned section or on the high side of the pavement with a one-way slope.

The base course shall not be placed in a layer thicker than four (4) inches compacted thickness. Each layer shall be spread, finished and compacted, as described herewith, before an additional layer is placed.

(2) Spreading and Blade Finishing. The mixture shall be placed in lanes parallel to the centerline of the runway and ending each days run for the full width of the lane.

After the mixing has been completed, the mixed material shall be spread to the required width and depth by a self-powered or tractordrawn blade grader, mechanical spreader, or other approved method. In spreading from a windrow, care shall be taken to prevent cutting into the underlying course. If necessary to prevent such cutting, a layer of the mixture approximately one-half (2) inch thick shall be left at the bottom of the windrow. The mixture shall be spread and cured in thin layers. The surface shall be continually bladed, disced, and dragged if necessary until a smooth, uniform surface, true to line, grade and cross section has been developed. Should the mixture show an excess, deficiency, or uneven distribution of bituminous material, such unsatisfactory conditions shall be corrected.

After the base course material has been mixed, spreading shall not be started if threatening weather is apparent. The engineer shall have control of the spreading, aeration, and rolling procedures, and no spreading shall be done without his consent. The contractor shall regulate his operations in a scheduled manner by mixing only such amounts that can be spread, aerated, and compacted within relative short periods. Those areas which become wet shall be dried and remixed with bituminous material when directed. The remixing, including application of additional bituminous material where required, shall be handled in such manner as to insure thorough and uniform coating of the aggregate. Any mixture that is unsatisfactory because of becoming wet or remains unsatisfactory after remixing shall be removed. Prior to final compaction, the moisture content of the base material shall have been reduced by aeration to three and one-half (32) percent or less.

204-4.8 COMPACTION OF MIXTURE. Aeration after mixing and prior to rolling shall be continued until the mixture is in suitable condition for proper compaction. After each layer has been placed and cured, it shall be thoroughly and uniformly compressed by rollers, as specified. Blading shall continue during the rolling only if so ordered by the engineer. Initial rolling shall be done with pneumatic rollers.

Initial rolling shall be done longitudinally, overlapping on successive trips by at least twelve (12) inches. Alternate trips of the roller shall be of slightly different lengths. Rolling shall continue until the surface is of uniform texture and degree of compaction and is true to grade and cross section. Final rolling shall be done with the tandem rollers. Rolling shall continue until a density is obtained which is at least ninety-five (95) percent of the maximum density obtainable on

the same mixture if compacted in a laboratory using the standard Proctor Method with all aggregate in the bituminous mixture passing the 2-inch mesh sieve. (Proctor Method, A. A. S. H. O. Method T-99 with mixture at a temperature of 140° F. placed in three layers with 25 blows per layer.)

The speed of the rollers shall at all times be slow enough to avoid displacement of the mixture. Any displacement occurring as a result of reversing the direction of the roller, or from any other cause, shall be corrected at once by the use of rakes and of fresh mixture where required. Sufficient rollers of the designated types shall be furnished to adequately handle the rate of spreading and aeration of the mixture.

Upon instructions from the engineer, the course shall be rerolled any time within two weeks after it is laid, and shall be subjected to diagonal rolling, crossing the lines of the first. If necessary to prevent adhesion of the mixture to the power roller, the wheels shall be kept properly moistened, but an excess of either water or oil will not be permitted. The rollers shall be in good condition and shall be operated continuously as far as practicable and in such a manner that all parts of the pavement shall receive substantially equal compression.

At all places not accessible to the roller, the mixture shall be thoroughly compacted with tampers. Such tampers shall weigh not less than twenty-five (25) pounds and shall have a tamping face area of not more than fifty (50) square inches. The surface of the mixture after compression shall be smooth and true to the established crown and grade.

Any mixture which becomes loose and broken, mixed with dirt, or in any way defective prior to acceptance, shall be removed and replaced, at the expense of the contractor, with fresh mixture which shall be compacted to conform with the surrounding area. Skin patching on an area that has been rolled shall not be allowed. Any mixture remaining unbonded after rolling shall be removed and replaced.

204-4.9 JOINTS. The mixture at the joints shall comply with the surface requirements and present the same uniformity of texture, density, smoothness, etc., as other sections of the course. In the formation of all joints, provision shall be made for proper bond with the previously placed base material for the full specied depth of the course. A straightedge shall be used across all joints to test and insure grade and contour of the surface.

204-4.10 SHAPING EDGES. While the base is being compacted and finished, the contractor shall trim the edges neatly to line.

204-4.11

SURFACE TESTS. The finished surface shall not vary more than three-eighths (%) inch for the base course when tested with a sixteen (16) foot straightedge applied parallel with or at right angles to the center line. Tests for conformity with the specified crown and grade shall be made by the contractor immediately after

initial compression by powered rollers and any variation shall be corrected by removing or adding materials and continuing the rolling.

204-4.12 THICKNESS. The thickness of the base course shall be determined by depth tests or cores taken at intervals in such manner that each test shall represent no more than 300 square yards. When the base deficiency is more than one-half (2) inch, the contractor shall correct such areas by removing the base material, replacing the base mixture, rolling, reshaping, and finishing in accordance with these specifications. The contractor shall replace at his expense the base material where borings are taken for test purposes.

204-4.13 MAINTENANCE. The surface of the base course shall be maintained in its finished condition until any surface course or surface treatment provided in the contract is placed thereon, and the contract is completed and accepted.

204-4.14 BITUMINOUS AND AGGREGATE MATERIAL CONTRACTOR'S RESPONSIBILITY. Samples of the bituminous and aggregate materials that the contractor proposes to use, together with a statement as to their source and character, must be submitted and approval obtained before use of such material begins. The contractor shall require the manufacturer or producer of the bituminous and aggregate materials to furnish material subject to this and all other pertinent requirements of the contract. Only those materials that have been demonstrated by service tests as satisfactory for the intended use will be accepted.

The contractor shall furnish vendor's certified test reports for each carload or equivalent of bituminous material shipped to the project. The report shall be delivered to the engineer before permission is granted for use of the material. The furnishing of the vendor's certified test report for the bituminous material shall not be interpreted as a basis for final acceptance. All such test reports shall be subject to verification by testing of samples of materials as received for use on the project.

204-4.15 FREIGHT AND WEIGH BILLS. Before the final estimate is allowed, the contractor shall file with the engineer receipted bills where railroad shipments are made and certified weigh bills when materials are received in any other manner, of the bituminous and paving materials actually used in the construction covered by the contract. The contractor shall not remove bituminous material from the tank car or storage tank until the initial outage and temperature measurements have been taken, nor shall he release the car or tank until the final outage has been taken by the engineer.

Copies of freight and weigh bills shall be furnished to the engineer during the progress of the work.

METHOD OF MEASUREMENT

204-5.1 The unit of measurement for base course laid shall be the square yard. The yardage to be paid for shall be the square yards of base course completed and accepted in accordance with the plans and specifications, or as directed by the engineer.