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Section 400

BITUMINOUS PAVEMENTS

Section 401.-PLANT MIX BITUMINOUS PAVEMENTS

GENERAL

Description

401.01 These specification include general requirements that are applicable to all types of bituminous pavement structures of the plant mix type irrespective of gradation of aggregate, kind and amount of bituminous material, or pavement use. Deviations from these general requirements will be indicated in the specific requirements for each type.

This work shall consist of constructing one or more bituminous bound layers on the prepared foundation in accordance with these specifications and the specific requirements of the type under contract, and in reasonably close conformity with the lines, grades, thicknesses, and typical cross sections shown on the plans within the tolerances specified or established by the Engineer.

Materials

401.02 Composition of Bituminous Mixtures (Job-Mix Formula). The bituminous mixtures shall be composed of a mixture of aggregate and bituminous material.

At least three weeks prior to production, the Contractor shall submit in writing a job-mix formula for each mixture supported by laboratory test data along with samples and sources of the components and viscosity-temperature relationships information to the Engineer for his testing and approval.

Each job-mix formula submitted shall propose definite single values for:

(a) The percentage of aggregate passing each specified sieve, based on the dry weight of aggregate. These target values shall be within the ranges shown in Table 703-4 or Table 301-1 as applicable.

(b) The percentage of bituminous material to be added, based on the total weight of mixture.

(c) The temperature of the mixture delivered on the road.

(d) The kind and percentage of additives to be used.

(e) The kind and percentage of mineral filler to be used.

In addition, the job-mix formula as submitted by the Contractor shall conform to the following:

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*For aggregates having maximum sizes over 1-inch, AASHTO T 165 will be modified to use 6-inch by 6-inch cylindrical specimens. The 6-inch cylinders will be compacted by the procedures outlined in AASHTO T 167 modified to employ ten repetitions of a molding load of 1,400 pounds per square inch with no appreciable holding time after application of the full load.

The mixture shall have a minimum dry compressive strength of 200 psi.

The mixture shall have a percent of air voids with the range of 5 to 7 percent.

Should a change in source of material be proposed or should a job-mix formula prove unsatisfactory, a new job-mix formula shall be submitted by the Contractor and be approved by the Engineer, in writing, prior to production.

Approval of new job-mix formulas may require laboratory testing and verification.

401.03 Bituminous Materials. The type and grade of bituminous material will be specified in the contract. The grade may be changed one step by the Engineer at no change in unit price.

Asphalt cement shall conform to subsection 702.01, for the grade specified.

Emulsified asphalts shall conform to subsection 702.03 for the grade specified.

Tar shall conform to subsection 702.08 for the grade specified.

401.04 Coarse Aggregate. Coarse aggregate (retained on the No. 8 sieve) shall conform to the quality requirements of Section 703.07, Aggregates.

401.05 Fine Aggregate. Fine aggregate (passing the No. 8 sieve) shall conform to the quality requirement of Section 703, Aggregates. The magnesium sulfate soundness test will not be used.

401.06 Mineral Filler. Mineral filler shall conform to the requirements of subsection 703.15 and 712.03 as applicable.

Construction Requirements

401.07 Bituminous Mixing Plant. Plants used for the preparation of bituminous mixtures shall conform to AASHTO M 156 with the following changes:

(a) Requirements for all plants.

(1) All projects involving 5000 Tons or more shall have automatic controls which coordinate the proportioning, timing and discharge of a batch of mixture by the single operation of a switch or button.

(2) Truck scales.-The bituminous mixture shall be weighed on approved scales furnished by the Contractor or on public scales at the Contractor's expense. Such scales shall be inspected and sealed as often as the Engineer deems necessary to assure their accuracy. Scales shall conform to the requirements of Section 109, and shall be sensitive to one half their minimum graduation, which shall not be greater than 10 lbs.

(3) Dust collector.-Paragraph 2.10 of M-156 is deleted. The following applies: The plant shall be equipped with a dust collector constructed to waste or return uniformly to the hot elevator all or any part of the material collected as directed, without the escape of objectionable dust into the atmosphere.

To comply with established air pollution limitations the contractor may be required to provide and use a wet scrubber or other protective device for further treatment of the effluent dust charged gases emanating from the mixing plant dust collector. The treatment will be considered adequate when the dust charge gases are measured for solids content by the control agency and the solids content is accepted by that agency as being within established limitations.

Liquids from a wet scrubber shall not be discharged directly into a live stream, lake or pond. The effluent shall first be circulated through sludge pits, tanks, or swamps. The resultant sedimentation, together with all other waste material developed by crushing and mixing operation, shall be covered, or otherwise acceptably disposed of, in connection with the cleanup work prescribed in subsection 106.02.

To prevent discharge of dust into the atmosphere, dustproof covers will be required over the screens.

(4) Paragraph 4.6.4 of M 156 is deleted.

(b) Requirements for dryer drum mixing plants:

(1) Dryer drum mixers shall have been specifically designed and constructed for the process and shall be capable of producing a uniform mixture. A positive means of controlling

mixing time shall be provided showing the rate of aggregate flow through the mixer per revolution and per minute at the plant operating speed and tilt.

(2) Calibrated cold feed proportioning-The cold feed shall be capable of being calibrated to assure full control of the mix gradation. The plant shall include means for accurately proportioning each size of aggregate and shall include aggregate bins divided into at least 3 compartments. Separate dry storage shall be provided for filler or hydrated lime when used. Each compartment shall have an outlet gate which can be cut off completely and shall be equipped with an automatic plant shutoff that operates when any bin becomes empty. The bins or aggregate feeding system shall be so constructed that samples may be readily obtained.

(3) Weight measurement of aggregate-Positive weight measurement of the combined cold feed shall be maintained to allow regulation of the feed gate and permit automatic correction for variations in load.

(4) Synchronization of aggregate feed and bituminous material feed. The bituminous feed control shall be coupled with the total aggregate weight measurement device in such a manner as to automatically vary the bitumen feed rate as necessary to maintain the required proportions. Means shall be provided for checking the quantity or rate of flow of bitumen into the mixing unit.

(5) Thermometric equipment—Thermometers shall be fixed in the bitumen feed line at the charging valve at the mixer unit, and at the discharge chute of the mixer unit, to register or indicate the temperature of the materials. The Engineer may require replacement of any thermometer by an approved temperature-recording apparatus for better regulation of the temperature of the materials.

(6) A method shall be provided for automatically compensating the bituminous content in the mix for moisture variations in the cold feed.

401.08 Hauling Equipment. Trucks used for hauling bituminous mixtures shall have tight, clean, smooth metal beds which have been thinly coated with approved material to prevent the mixture from adhering to the beds. Each truck shall have a cover of canvas or other suitable material of such size as to protect the mixture from the weather. When necessary, so that the mixture will be delivered on the road at the specified temperature, truck beds shall be insulated and covers shall be securely fastened. Trucks beds shall be drained prior to loading.

401.09 Bituminous Pavers. Bituminous pavers shall be self-contained, power-propelled units, provided with an adjustable activated screed or strike-off assembly, heated if necessary, and capable of spreading and finishing courses of bituminous plant mix material in lane widths applicable to the specified typical section and thicknesses shown on the plans.

Pavers shall be equipped with a control system capable of automatically maintaining the screed elevation as specified herein. The control system shall be automatically actuated from either a reference line or surface through a system of mechanical sensors or sensor directed mechanisms or devices which will maintain the paver screed at a predetermined transverse slope and at the proper elevation to obtain the required surface. When directed, the transverse slope control system shall be made inoperative and the screed shall be controlled by sensor directed automatic mechanisms which will independently control the elevation of each end of the screed from reference lines or surfaces.

The controls shall be capable of working in conjunction with any of the following attach

ments:

(1) Ski-type device of not less than 30 feet in length or as directed by the Engineer. (2) Taut stringline (wire) set to grade.

(3) Short ski or shoe.

The Contractor shall furnish the long ski, the short ski or shoe and furnish and install all required stakes and wire for a taut stringline.

Should the automatic control system become inoperative during the day's work, the Contractor will be permitted to finish the day's work using manual controls, however, work shall not be resumed thereafter until the automatic control system has been made operative.

The Contractor shall provide and have ready for use at all times enough tarpaulins or covers, as may be necessary, for use in any emergency such as rain, chilling wind, or unavoidable delay, for the purpose of covering or protecting any material that may have been dumped and not spread.

401.10 Rollers. Rollers shall conform to the requirements of Section 212.

401.11 Weather Limitations. The bituminous mixture shall not be placed when weather conditions prevent the proper handling or finishing of the mixture, when the underlying base course is wet, frozen, or when the average underlying surface temperatures are less than those specified in the following table;

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401.12 Conditioning of Existing Surface. Immediately before placing the bituminous mixture, the existing surface shall be cleaned of loose or deleterious material by brooming or other approved means.

Contact surfaces of curbing, gutters, manholes and other structures shall be painted with a thin, uniform coating of bituminous material prior to the bituminous mixture being placed against them.

401.13 Preparation of Bituminous Material. The bituminous material shall be heated so as to avoid local overheating and provide a continuous supply of the bituminous material to the mixer at a uniform temperature. The temperature of asphalt cement delivered to the mixer shall be as required to achieve a kinematic viscosity in the range of 150-300 centistokes, as determined by AASHTO T 201. Asphalt cement shall not be used while it is foaming nor shall be heated above 350°F. at any time after delivery to the project.

401.14 Preparation of Aggregates.

Aggregates for pugmill mixing shall be heated, dried and delivered to the mixing unit at a temperature within the range ± 30°F of the bitumen. Moisture content of the aggregate shall not exceed one percent at the time it is introduced into the mixing unit. Flames used for drying and heating shall be properly adjusted to avoid damage to the aggregate and to avoid soot on the aggregate. Moisture content of the mixture from drum-dryer plants shall not exceed 3 percent at the output, as determined by AASHTO T 110.

401.15 Mixing. The dried aggregates and the bituminous material shall be measured or gauged and introduced into the mixer in the amount specified by the job-mix formula.

After the required amounts of aggregate and bituminous material have been introduced into the mixer, the materials shall be mixed until a complete and uniform coating of the particles and a thorough distribution of the bituminous material throughout the aggregate is secured.

401.16 Control of Bituminous Mixture. The mixture furnished by the contractor shall conform to the job-mix formula, within the allowable deviations set forth in Table 401-1. When an individual acceptance test result exceeds these allowable deviations, the material is known to be defective and the lot will be evaluated in accordance with subsection 401.21. 401.17 Transporting, Spreading, and Finishing. The mixture shall be transported from the mixing plant to the point of use in vehicles conforming to the requirements of subsection 401.08.

The mixture shall be spread and struck off to the grade and elevation established. Bituminous pavers shall be used to distribute the mixture either over the entire width or over such partial width as may be practicable.

The longitudinal joint in one layer shall offset that in the layer immediately below by approximately 6 inches; however, the joint in the top layer shall be at the center line of the pavement if the roadway comprises two lanes of width, or at lane lines if the roadway is more than 2 lanes in width, unless otherwise directed.

On areas where irregularities or unavoidable obstacles make the use of mechanical spreading and finishing equipment impracticable, the mixture may be placed and finished by hand tools.

The mixture shall be placed at a temperature not less than 225 degrees F as measured in the truck just prior to dumping into the spreader.

When tar is used the mixture shall be placed at between 150°F and 225°F.

When production of the mixture can be maintained and when practical, pavers shall be used in echelon to place the wearing course in adjacent lanes.

401.18 Compaction. Compaction shall be performed in accordance with Section 212, Compaction Using Control Strips and Nuclear Testing Devices.

Unless otherwise directed, rolling shall begin at the sides and proceed longitudinally parallel to the road center line, each trip overlapping one-half the roller width, gradually progressing to the crown of the road. When paving in echelon or abutting a previously placed lane, the longitudinal joint should be rolled first followed by the regular rolling procedure. On superelevated curves the rolling shall begin at the low side and progress to the high side by overlapping of longitudinal trips parallel to the center line.

Along forms, curbs, headers, walls and other places not accessible to the rollers, the mixture shall be thoroughly compacted with hot hand tampers, smoothing irons or with mechanical tampers.

401.19 Joints, Trimming Edges, and Cleanup. Placing of the bituminous paving shall be as continuous as possible. Rollers shall not pass over the unprotected end of a freshly laid mixture unless authorized by the Engineer. Transverse joints shall be formed by cutting back on the previous run to expose the full depth of the course. When directed by the Engineer, a brush coat of bituminous material shall be used on contact surfaces of transverse joints just before additional mixture is placed against the previously rolled material.

The exposed edges of the completed mat shall be cut off true to the required lines. Material trimmed from the edges and any other discarded bituminous mixture shall be removed from the roadway and disposed of by the Contractor in an approved area out of sight from the road. 401.20 Finished Work Samples. The Engineer may require the Contractor to cut samples from the pavement for testing. Samples will be neatly cut by a core drill. The Contractor shall supply and finish new material to backfill voids left by sampling.

401.21 Acceptance Sampling and Testing of Bituminous Mixtures (Gradation and Bituminous Content). The Special Provisions will specify:

1. Acceptance sampling frequency

2. Point of acceptance sampling

3. Lot size

Acceptance samples will be random and be taken from each lot in accordance with subsection 106.03. If these samples, when tested, indicate that the lot contains no defective material, the lot will be accepted at the full contract price. If any test indicates that the lot contains defective material, the lot will be evaluated in accordance with Table 401-2.

If the lot fails to qualify for at least a 0.85 pay factor in accordance with Table 401-2, the Engineer may reject the lot. If the Engineer allows the material to remain in place, it will be paid for at a pay factor of 0.70.

The contractor may elect to voluntarily remove any defective lot and replace it with nondefective material to avoid a pay factor of less than 1.00. Any such new material will be sampled and accepted in accordance with this subsection.

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