The Table of Contents for this section is available.
The work covered by this section consists of the production, delivery, placement, and compaction of all types of asphalt plant mixed bases and surface courses.
The work shall include one or more courses of asphalt mixture constructed on the prepared surface in accordance with these specifications and any additional requirements of Sections 630, 635, 640, 645, 650, 652, and 654 which may be applicable; and in reasonably close conformity with the lines, grades, thickness, and typical sections shown on the plans or established by the Engineer.
Where the asphalt plant mix incorporates reclaimed asphalt pavement materials, the plant mix will be considered to be a recycled asphalt plant mix and the provisions of Section 611 will be applicable.
All materials shall meet the requirements of Division 10 referred to in the various sections of the specifications covering the type of plant mix being constructed.
610-3 COMPOSITION OF MIXTURES (JOB MIX FORMULA).
The asphalt plant mix shall be composed of a mixture of coarse and fine aggregate, asphalt cement, and mineral filler and other additives when required. The several aggregate fractions shall be sized, uniformly graded, and combined in such proportions that the resulting mixture meets the grading and physical requirements of a job mix formula issued by the Department. The percentage of asphalt cement and other additives, if required, will be established by the Engineer. Materials which will not produce a mixture within the full allowable tolerances required by these specifications will be rejected, unless otherwise approved by the Engineer.
The Contractor shall have on hand at the asphalt plant an approved job mix formula, issued by the Department, prior to beginning work. A previously approved master job mix formula which is still valid will fulfill this requirement. When the proposed combination of materials is not for a currently approved job mix formula, the Contractor shall submit to the Department's Materials and Tests Unit samples of all aggregates proposed for use at least 3 weeks prior to beginning production. The aggregate samples shall be taken by a Department representative or by the Contractor in the presence of a representative of the Engineer. The Contractor shall also submit in writing to the Engineer the proposed blend and source of materials. The Department will then prepare a mix design based on the Contractor's proposed combination of aggregates. Upon receipt of the mix design, and if in agreement, the Contractor shall then make written request to the Engineer for a master job mix formula based on the mix design. The Contractor shall make available to the Engineer at the field laboratory a copy of the approved job mix formula prior to beginning work.
The job mix formula with the allowable tolerances will be established within the design limits specified for the particular type of asphalt mixture to be produced. The formula for each mixture will establish the blend percentage of each aggregate fraction, a single percentage of combined aggregate passing each required sieve size, a single percentage of asphalt cement (by weight based on total mixture) to be added to the mixture, the percentage of non-strip additive to be added to the asphalt cement, a single temperature at which the mixture is to be discharged from the plant, and the required field density.
The job mix formula for each mixture shall be in effect until modified in writing by the Engineer.
All mixtures furnished for the work shall conform to the job mix formula within the tolerance ranges specified for the particular mix involved as specified herein.
Should a change in sources of aggregate materials be made, a new mix design and job mix formula will be required before the new mixture is produced.
When unsatisfactory results or other conditions make it necessary, the Engineer may establish a new job mix formula.
Mixtures produced simultaneously from different plants shall not be intermingled by hauling to the same paver on the roadway unless the mixtures are being produced from the same material sources and the same job mix formula.
In lieu of a job mix formula based on a mix design prepared by the Department, the Contractor may submit for review and request a job mix formula based on a mix design prepared by an approved mix design laboratory. The laboratory shall have been approved by the Engineer prior to submission of the mix design. The mix design shall be prepared in accordance with AASHTO T245 or ASTM D1559, recommended procedures in the Asphalt Institute publication "Mix Design Methods for Asphalt Concrete" MS2, Sixth Edition or later) using the Marshall Method of Test, automatic mechanical compaction hammer, and Department policies and procedures. The mix design summary and supporting data shall be submitted as an assembly on forms and in a format approved by the Department.
The Contractor shall submit all test data to the Materials and Tests Unit at least 10 days prior to scheduled production of the mix. The Engineer will establish the percentage of asphalt cement and other additives, if required, to be added to the approved mixture. The Engineer may request samples of the proposed materials to perform verification tests, if deemed necessary. If acceptable, the Engineer will issue a job mix formula in accordance with procedures described above.
610-4 WEATHER AND TEMPERATURE LIMITATIONS FOR PRODUCING AND PLACING ASPHALT MIXTURES
Asphalt mixtures shall not be produced or placed during rainy
weather, when the subgrade or base course is frozen, or when the
moisture on the surface to be paved would prevent proper bond.
Asphalt material shall not be placed when the air temperature,
measured in the shade away from artificial heat at the location
of the paving operations, is less than the following temperatures:
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| Asphalt Concrete
Base Course, Type HB; Asphalt Concrete Binder Course; or Sand Asphalt Base Course | ||
| Asphalt Concrete
Binder Course, or Sand Asphalt Base Course | ||
| Surface Course Materials | ||
| Surface Course Materials |
In addition, surface course material which is to be the final layer of pavement shall not be placed between December 15 and March 16 if it is 1" or greater in thickness or between November 15 and April 1 if it is less than 1" in thickness, and open-graded asphalt friction course, Type J-1, shall not be placed between October 31 and April 1, unless otherwise approved by the Engineer.
As an exception to the above, when in any day's operations the placement of a layer of asphalt base course material or binder material 1 1/2" or greater in thickness has started, it may continue until the temperature drops to 32°F.
610-5 ASPHALT MIXTURE PRODUCTION.
(A) General:
Plants shall be either the batch mixing type, the continuous mixing type, or the drum mixing type, and shall be so designed, equipped, and operated that the weighing, proportioning, and mixing of the materials will result in a uniform and satisfactory asphalt mixture meeting the requirements of these specifications.
Prior to production of the mix, aggregates shall be stockpiled for a sufficient period of time to facilitate the drainage of free moisture. The different aggregate sizes shall be kept separated until they have been delivered to the cold feeder. The separate stockpiles shall be readily accessible for sampling.
When mineral filler is required in the mix, it shall be fed or weighed-in separately from the other aggregates.
The asphalt cement and other additives, when required, shall be introduced into the mixture at the amount specified by the job mix formula. No working tolerance will be allowed. The dried and heated aggregates, and mineral filler, when required, shall be introduced into the mixing unit in amounts and at temperatures such that the mixture produced is within the limits of the job mix formula. A positive means of controlling mixing time shall be provided so as to obtain a complete uniform coating and mixing of the aggregate particles and thorough distribution of the asphalt cement throughout the aggregate.
Plants used for the preparation of asphalt mixtures shall conform to all requirements of Subarticle 6105(B). In addition, batch mixing plants shall conform to the requirements of Subarticle 6105(C), continuous mixing plants shall conform to the requirements of Subarticle 6105(D), and drum mixing plants shall conform to the requirements of 6105(E).
All asphalt plants shall meet the requirements of these specifications and shall have been certified by the Department. Certification shall be renewed every 3 years or at such shorter period as considered necessary by the Engineer. Any plant which is relocated, modified, or changes ownership shall be recertified prior to use.
Any completely automatically controlled asphalt plant which, due to the basic design of the plant, does not meet all the requirements of these specifications for conventional batch mixing, continuous mixing, or drum mixing may be utilized on a project by project basis provided a uniformly consistent mix meeting all mix requirements can be produced and the plant has been approved in writing by the Engineer.
(B) Requirements For All Plants:
(1) Equipment for Preparation of Asphalt Cement:
Tanks for the supplying of asphalt cement to the plant shall be equipped to uniformly heat and hold the material at the required temperature prior to introduction into the mixer unit. A circulating system for asphalt materials shall be provided and shall be capable of the proper mixing of additives. The system shall have adequate pump or pumps to charge the mixing unit and unload asphalt material simultaneously. Provision shall be made for measuring and sampling plant supply tanks.
When non-strip additive is to be added at the asphalt plant in lieu of at the terminal, the plant shall be equipped with an in-line blending system. The system shall be capable of metering the additive within plus or minus 10 percent of the amount specified. The metering device shall be interlocked with the asphalt cement control equipment in such a manner as to automatically vary the additive feed rate to maintain the required proportions. The additive shall be injected into the asphalt cement feed line prior to introduction into the aggregate. The feed line shall be equipped with a blending device to thoroughly mix the additive with the asphalt cement prior to mixing with the aggregate. The system shall be capable of being calibrated, checked and monitored for accuracy and amount used.
(2) Cold Aggregate Feed Equipment:
Cold bins and a feeder system shall be used to proportion the aggregates and feed them to the dryer. Separate cold bins shall be used for each size aggregate and each natural sand being used and shall provide a uniform and continuous flow. Separate dry storage shall be provided when mineral filler is required. The cold aggregate bins shall be equipped with feeder units having interlocking controls capable of maintaining a constant ratio between the relative quantities of each size aggregate at varying plant production rates.
Each cold feeder shall be capable of being easily and accurately calibrated to assure full control of the mix gradation.
(3) Dryer:
The plant shall include a dryer or dryers which continuously agitate the aggregate during the heating and drying process.
(4) Control Unit for Asphalt Cement:
Satisfactory means, either by weighing or metering, shall be provided to introduce the proper amount of asphalt cement in the mix.
(5) Thermometric Equipment:
(a) Asphalt Cement Thermometric Equipment:
A thermometric device of adequate temperature range shall be fixed in the asphalt cement feed line.
(b) Dryer Thermometric Equipment:
The dryer shall be equipped with an automatic burner control device which shall use an approved thermometric instrument, located in the discharge chute, to actuate the automatic controls.
(6) Pollution Control Equipment:
All plants shall be equipped with such pollution control equipment as is necessary to meet all applicable local, State, and Federal pollution requirements. All plants shall have been registered and certified by applicable environmental protection agencies prior to being certified by the Department.
(7) Safety Requirements:
Adequate safety devices shall be provided at all points where accessibility to plant operations is required. Accessibility to the top of truck bodies shall be provided by a platform or other suitable device to enable the Engineer to obtain sampling and mixture temperature data. All gears, pulleys, chains, sprockets, and other dangerous moving parts shall be thoroughly guarded and protected. Ample and unobstructed space shall be provided on the mixing platform. A clear and unobstructed passage shall be maintained at all times in and around the truck loading area. All work areas shall be kept free from asphalt drippings.
(8) Production Consistency:
Any asphalt plant that cannot consistently produce a high quality mix meeting the requirements of these specifications will be considered in non-compliance with these specifications and may have its certification revoked.
Upon a malfunction of required automatic equipment on a batch or continuous mixing plant, the plant may continue to operate manually for the following 2 consecutive working days, provided acceptable mixture is being produced.
When a malfunction of required automatic equipment on a drum mixer plant occurs, manual operation of the plant will not be allowed except that if, in the opinion of the Engineer, an emergency traffic condition exists, the plant may be allowed to operate manually until the unsafe traffic condition is corrected.
(C) Requirements For Batch Mixing Plants:
(1) Plant Scales and/or Weighing Devices:
Scales shall be accurate to 0.5 percent at anticipated scale settings that may be required.
Scales will be inspected and tested as often as the Engineer may deem necessary to assure their continued accuracy.
The Contractor shall have on hand not less than 10 50-pound weights for testing the plant scales.
(2) Screens:
Plant screens shall be provided which are capable of adequately screening aggregates to the specified sizes necessary to consistently produce a mixture meeting the requirements of the job mix formula. Screens shall be capable of removing all oversize materials.
(3) Hot Bins:
The plant shall include hot storage bins of sufficient capacity and number to supply the mixer with uniform material. Each compartment shall be equipped with adequate and convenient devices to provide for sampling. Each compartment shall be provided with an overflow pipe of such sizes and at such locations as to prevent any backing up of the material into other bins or interference with the operations of screens. The gates shall close tightly so that no material is allowed to leak into the weigh hopper.
(4) Weigh Box or Hopper:
The equipment shall include a means for accurately weighing each size of aggregate in a weigh box or hopper suspended on scales and of ample size to hold a full batch without running over. The gate shall close tightly so that no material is allowed to leak into the mixer while a batch is being weighed.
(5) Asphalt Cement Control:
The equipment used to measure the asphalt cement shall be accurate to plus or minus 0.5 percent by weight of the amount of asphalt cement required. The flow indicator, whether scale or metering device is used, shall be in full view of the operator.
The asphalt cement bucket shall be a non-tilting type with a removable top. The asphalt cement bucket, its discharge valve or valves, and distribution bar shall be adequately heated. Heating connections shall be so constructed that they will not interfere with the efficient operation of the asphalt cement scales. The capacity of the asphalt cement bucket shall be at least 15 percent in excess of the weight of asphalt cement required in any batch. The plant shall have an adequately heated quick-acting, non-drip, charging valve located near the asphalt cement bucket.
When a metering device is substituted for an asphalt cement bucket, the flow indicator shall have a capacity of at least 15 percent in excess of the quantity of asphalt cement used in a batch. The section of asphalt line between the charging valve and distribution bar shall be provided with a valve and outlet for checking the meter.
All of the asphalt cement required for one batch shall be discharged in not more than 15 seconds after the flow has started. The size and spacing of the distribution bar openings shall provide a uniform application of asphalt cement the full length of the mixer.
(6) Mixer:
The batch mixer shall be an approved type capable of producing a uniform mixture. If not enclosed, the mixer box shall be equipped with a dust hood to prevent loss of dust. The plant shall have a batch mixer with a rated capacity of not less than 3,000 pounds.
The clearance of blades from all fixed and moving parts shall be such as to insure complete coating of aggregates.
(7) Control of Proportioning and Mixing:
All plants shall have fully automated controls for proportioning and mixing. The mixer shall be equipped with an accurate interlocking timing device to control the operations of a complete mixing cycle.
The timing device shall be capable of being set at intervals of 5 seconds or less throughout a total cycle.
Mixing time will be established by the Engineer and means shall be provided by lock, cover, or other methods to prevent unauthorized changes in mixing time.
(D) Requirements for Continuous Mixing Plants:
(1) General:
All continuous mixing plants shall have fully automated proportioning and mixing controls and a rated capacity of at least 90 tons per hour.
(2) Aggregate Proportioning:
The plant shall include means for accurately proportioning each size of aggregate to consistently meet the requirements of the job mix formula.
The plant shall have a feeder capable of being accurately calibrated to uniformly produce the specified mixture.
(3) Screens:
Plant screens shall be provided which are capable of adequately screening aggregates to the specified sizes necessary to consistently produce a mixture meeting the requirements of the job mix formula. Screens shall be capable of removing all oversize materials.
(4) Hot Bins:
The plant shall include hot storage bins of sufficient capacity and number to supply the mixer with uniform material. Each compartment shall be equipped with adequate and convenient devices to provide for sampling. Each compartment shall be provided with an overflow pipe of such sizes and at such locations as to prevent any backing up of material into other bins or interference with the operations of screens. The gates shall be adjustable such that the rate of flow can be controlled.
(5) Synchronization of Aggregate Feed and Asphalt Cement Feed:
Satisfactory means shall be provided to afford positive interlocking control between the flow of aggregate from the bins and the flow of asphalt cement from the meter or other proportioning device. This control shall be accomplished by interlocking mechanical means or by other positive methods satisfactory to the Engineer.
(6) Mixer:
The plant shall include a continuous mixer of an approved type, adequately heated and capable of producing a uniform mixture. It shall be equipped with a discharge hopper with dump gates which will permit rapid and complete discharge of the mixture. The paddles shall be adjustable for angular position on the shafts and reversible to retard the flow of the mix. The mixer shall have a manufacturer's plate giving the net volumetric contents of the mixer at several heights inscribed on a permanent gauge. Charts shall be provided showing the rate of feed of aggregate per minute for the aggregate being used.
(E) Requirements for Drum Mix Plants:
(1) Aggregate Feed Equipment:
Each cold feeder shall be equipped with an automatic device which activates a warning alarm and/or flasher light when any bin becomes empty or when aggregate flow becomes restricted. The automatic device shall be interlocked into the plant control system so as to automatically stop production if normal aggregate flow is not resumed within 60 seconds.
(2) Scalping Screen:
A vibratory screening system capable of removing all oversize materials for the particular mix being produced shall be provided prior to entry of the aggregate into the dryer-drum mixer. The screening system shall be located in the aggregate flow prior to the material passing over the aggregate weighing system.
(3) Weight Measurement of Aggregate:
The system shall provide positive weight measurement of the combined cold aggregate feed rate by the use of belt scales or other approved devices. Means shall be provided to allow correction for variations in the moisture content of the cold aggregate. A continuous readout or other means that can be monitored in the plant control room and which indicates the aggregate dry-weight equivalent feed rate shall be provided. The aggregate weighing system shall be automatically interlocked with the asphalt cement flow to maintain the required proportions. The weighing system shall have provisions for easy and accurate calibration.
(4) Dryer-Drum Mixer Unit:
The drum mixer shall be specifically designed and constructed for the process and shall be capable of producing a uniform mixture. Heating shall be controlled to prevent damage to the aggregate and asphalt cement. The dryer-drum mixer shall have a rated capacity of at least 90 tons per hour when producing a finished mixture at 300F. with removal of 5 percent moisture.
(5) Asphalt Cement Controls:
A metering system capable of introducing the required amount of asphalt cement in the mix shall be provided. The system shall provide means of correcting the delivered asphalt cement flow rate for temperature and specific gravity variations. The flow meter shall be connected to the asphalt cement supply so as to measure and display only the asphalt cement being fed to the mixer unit. The meter readout shall be positioned for convenient observation by the plant operator.
Means shall be provided for checking the rate of flow of asphalt cement into the mixing unit. The rate of flow shall be accurate to 0.5 percent by weight of the amount of asphalt cement required.
(6) Synchronization of Aggregate Feed and Asphalt Cement Feed:
The asphalt cement feed control shall be interlocked with the total aggregate weight measurement device in such a manner as to automatically vary the asphalt cement feed rate as necessary to maintain required proportions. This control shall be fully automatic and interlocked in a manner that will stop all feed components if either the aggregate or asphalt flow stops.
(7) Asphalt Mixture Storage Facilities:
Hot mix surge storage facilities shall be provided and shall be adequate to minimize production interruptions during the normal day's operation. The hot conveyor facilities shall be enclosed and of a type and design that will prevent segregation and minimize heat loss of the mix. The mixture shall meet the requirements of the job mix formula when discharged from the storage bin.
Surge storage bins may be used providing the mix that is discharged from the bin meet the requirements of the job mix formula.
610-7 HOT MIX SILO STORAGE BINS.
Hot mix silo storage bins may be used providing the mix that is discharged from the bin meets the requirements of the job mix formula.
610-8 TRANSPORTATION OF ASPHALT MIXTURE.
The mixture shall be transported from the mixing plant to the point of use in vehicles which have tight, clean, smooth metal beds that have been sprayed with an approved release agent, or other approved material, to prevent the mixture from adhering to the beds. Excess release agent shall be removed prior to loading. Each load of mixture shall be fully covered with a canvas or other suitable material. All covers shall be so constructed and secured as to prevent the entrance of moisture and the rapid loss of temperature. A 3/8 inch diameter hole shall be provided on each side of the vehicle body near the center of the body and 6 inches above the bed of the vehicle for the purpose of inserting a thermometer.
The temperature of the mixture immediately prior to discharge from the hauling vehicle shall be within a tolerance of plus 15F. to minus 25F. of the specified job mix temperature.
610-9 SPREADING AND FINISHING.
Tack coat shall be applied in accordance with the provisions of Section 605.
Mixtures produced simultaneously from different plant sources shall not
be intermingled by hauling to the same paver on the roadway unless the mixtures are being produced from the same material sources and same job mix formula.
The asphalt mixture shall be spread and finished to the required grades, cross sections, thicknesses, and widths shown on the plans and typical sections and to uniform density and texture by a self-contained, power propelled paver. The paver shall be equipped and operated with a fully activated screed plate which is designed to be preheated for the full length whenever necessary. The screed shall be of adequate length to spread and finish the full uniform width travel lane being placed, unless otherwise permitted by the Engineer. The use of strike off devices, either mechanically or manually operated, will not be permitted in spreading and finishing the mixture placed in the uniform width travel lane. The paver shall be equipped with a receiving hopper and an automatically controlled distribution system which is capable of uniformly maintaining a proper head of material in front of the full length of the screed including screed extensions. The screed unit shall be equipped with a sliding shoe attachment which will form a slope on the edge of the mat to prevent edge raveling when the mixture is compacted.
A string line shall be placed by the Contractor for the first lane of each layer of mixture placed to provide alignment control for the paver, except that a string line will not be required when the first layer is placed adjacent to a curb section.
Pavers shall be operated at forward speeds consistent with satisfactory laying of the mixture, plant production, and material delivery in order to provide a uniform and continuous laydown operation. Coordination of the paving operation and the loading operation shall be adjusted to maintain an adequate amount of asphalt mixture in the paver hopper. The paver hopper shall not be allowed to become empty between loads. Should unevenness of texture, tearing, segregation, or shoving occur during the paving operation due to unsatisfactory methods or equipment, the Contractor shall immediately take such action as may be necessary to correct such unsatisfactory work. Throwing back excessive material will not be permitted.
Pavers shall be equipped with a screed control system which will automatically control the longitudinal profile and cross slope of the pavement by the use of either a mobile string line or a fixed string line. A 30-40 foot mobile string line shall be utilized unless a fixed stringline is required by the contract. The grade sensor shall be positioned at the approximate midpoint of the mobile reference system. When a fixed string line is required, grade stakes at 25 foot maximum intervals will be required for the finished pavement grade. The Contractor shall furnish and erect the necessary guide line for the equipment.
When placing adjacent lanes of the final surface course, the paver shall be equipped with a joint matching device which will automatically provide control of the depth of the mixture being placed so that, when compacted, it will match the depth of the existing lane.
The Engineer will waive the requirement for automatic cross-slope controls in areas where the use of such equipment is impractical due to irregular cross section or shape. Manual operation will be permitted in the construction of irregularly shaped and minor areas. In the case of malfunction of the automatic screed control equipment, the Contractor may manually operate the paver for the remainder of the work day provided this method of operation produces acceptable results. Work shall not be resumed thereafter until the automatic system is operative.
The Engineer will waive the requirement for use of pavers for spreading and finishing where irregularities or obstacles make their use impractical. The Contractor shall spread, rake, and lute the mixture by hand methods in these areas.
Roadway paving shall be as continuous as possible. Intersections, auxiliary lanes, and other irregular areas shall be paved after the main line roadway has been paved, unless otherwise approved by the Engineer.
Immediately after the asphalt mixture has been spread, struck off, and surface and edge irregularities adjusted, it shall be thoroughly and uniformly compacted. The degree of compaction required shall be in accordance with the applicable section of the specifications for the type of mixture being placed.
All final wearing surfaces except open-graded asphalt friction course, Type J-1, shall be compacted using a minimum of 2 steel wheel tandem rollers. Steel wheel tandem vibratory rollers which have been specifically designed for the compaction of asphalt pavements may be used, except that operation in the vibratory mode will be permitted only during the breakdown rolling phase on all final wearing surfaces 1 inch or greater in thickness. Operation in the vibratory mode will not be permitted during the rolling of open-graded asphalt friction course, during the finish rolling phase on any mix type or pavement course, or when the layer thickness is less than 1 inch.
Vibratory rollers shall have variable frequency and amplitude capability. The rollers shall be equipped with controls which automatically disengage the vibration mechanism before the roller stops when being used in the vibratory mode.
The Engineer may prohibit or restrict the use of vibratory rollers where damage to the underlying pavement structure, drainage structures, utilities, or other components is likely to occur or is evident.
Rollers used to compact the mixture shall be in good condition, capable of reversing without backlash. The rollers shall be operated with the drive wheels nearest the paver and at uniform speeds slow enough to avoid displacement of the mixture. Steel wheel rollers shall be equipped with wetting devices to prevent the mixture from sticking to the roller wheels.
The number and weight of rollers shall be sufficient to compact the mixture to the required density while it is still in a workable condition. Pneumatic-tired rollers with 2 tandem axles and smooth tread tires will be permitted for use in intermediate rolling.
Compaction rolling (including both breakdown and intermediate rolling) shall be completed prior to the mixture cooling below a temperature of 185F. Finish rolling shall be performed to remove roller marks resulting from the compaction rolling operations.
Rolling for open-graded asphalt friction course shall consist of 1 coverage with a tandem steel wheel roller weighing a maximum of 10 tons, with additional rolling limited to 1 coverage with the roller where necessary to improve the riding surface.
The use of rolling equipment which results in excessive crushing of the aggregate or excessive displacement of the mixture will not be permitted.
In areas inaccessible to equipment, the mixture shall be thoroughly compacted by the use of hand tampers or hand operated mechanical tampers.
610-11 DENSITY CONTROL AND DETERMINATION.
(A) General:
Where the mixture is to be compacted to a specified density in accordance with the applicable section of the specifications for the type of mixture being placed, the Engineer may utilize either nuclear density testing methods or daily cored sample testing methods.
(B) Pavement Samples (Cores):
When cored samples of the compacted pavement are required by either method, they shall be taken from the full depth of the course at locations designated by the Engineer. The samples shall be taken no later than the beginning of the next working day, unless otherwise permitted by the Engineer.
The Contractor may elect to cool the pavement layers by artificial methods to allow cutting the core samples as quickly as possible. No compensation will be made for the costs of artificial cooling.
All pavement specimens taken by the Contractor for density testing purposes shall be obtained utilizing a 6 inch core drill. The coring equipment shall be capable of taking a representative sample of the compacted pavement and shall have been approved by the Engineer. In the event a malfunction of the coring equipment occurs, the Contractor may utilize a diamond or carborundum saw or other approved means to obtain the required samples. The coring equipment shall be repaired and restored to use within three working days.
Where samples have been taken, the inside surfaces of the sample hole shall be cleaned, dried and lightly coated with tack coat and new material shall be immediately placed and compacted by the Contractor to conform with the surrounding area. A circular tamp or other device shall be used to achieve compaction.
Failure to provide samples may result in suspension of all project operations.
(C) Density Determination by Nuclear Methods:
(1) General:
When the Engineer elects to utilize nuclear methods as the means of density control, the provisions of this subarticle shall apply. The use of nuclear methods will include the establishment of the required density through the use of control strips constructed from materials actually being used on the project, and the determination of the density being obtained in test sections located throughout the project.
Asphalt plant mix will be tested with the nuclear density gauge in the backscatter mode. Additional information is provided in the "NCDOT Nuclear Gauge Operator's Manual". Copies are available upon request from the Department's Materials and Tests Unit.
(2) Control Strip:
(a) General:
A control strip is a section of material being tested having a minimum area of 400 square yards unless otherwise approved by the Engineer; and a layer depth not greater than the layer depth shown in the plans or required by the Specifications, whichever is less. Roadway control strips may be used to determine required density for shoulder material when approved by the Engineer. When shoulder control strips are deemed necessary by the Engineer, they shall be constructed to the full shoulder width. The location of a control strip shall be as directed by the Engineer. The material used in constructing the control strip shall consist of material from the same source and shall be of the same type as the material being tested. Each control strip is to remain in place and become a portion of the completed project. At least one control strip shall be constructed for each layer of material being tested. Additional control strips shall be constructed when a change is made of the source of materials, when a significant change occurs in the composition of the materials from the same source, or when deemed necessary by the Engineer.
(b) Equipment:
Equipment used in compaction of control strips shall have been approved by the Engineer prior to use. Where uniform density is not being obtained throughout the depth of the layer of material being tested, the type and/or weight of the compaction equipment shall be changed as necessary to achieve uniform density even though such equipment has been previously approved by the Engineer.
(c) Compaction:
After the material in a control strip is spread and shaped to the required width and depth, the compaction of the material shall begin. Compaction shall be carried out in such a manner as to obtain uniform maximum density over the entire control strip.
When asphalt mixtures are being compacted, the compaction rolling shall be performed at the maximum temperature at which the mix will support the rollers without moving horizontally. The compaction rolling shall be completed prior to the mixture cooling below a temperature of 185F.
(d) Target Density:
After the Contractor has completed compaction of the control strip, the Engineer will conduct 10 density tests, 2 each at 5 random core locations in the control strip. The surface of the material being tested shall be smooth prior to any tests being performed. The results of the 10 tests will be averaged and the resulting average density will be used in determining the target density for all test sections being constructed in conjunction with a particular control strip. The target density will be determined by dividing the average density by the average percent compaction of the five (5) core samples from the control strip. Test section densities will be expressed as a percentage of the target density.
The final density of the control strip shall be at least equal to the minimum density specified for the mix based on the appropriate laboratory density or maximum density as specified in Articles 6304, 6354, 6404, or 6454. In addition to determining the nuclear target density, the following procedures and tests will be performed to assure that the final density of the control strip meets the above density requirements:
1. Samples of the mix used in construction of the control strip shall be taken and an extraction, Marshall test, and maximum specific gravity test performed.
2. No later than the beginning of the next day following the completion of the control strip, the Contractor shall core 5 samples from the control strip as directed by the Engineer. The density of each cored sample will be determined in the field laboratory. Artificial cooling of the pavement layers by the Contractor will be permitted in order to obtain cored samples as quickly as possible. No compensation will be made for the cost of artificial cooling. Cored samples shall be taken in accordance with Subarticle 61011(B).
3. During the time between the completion of the control strip and the determination of the density of the cored samples, the Contractor will be permitted to continue to place pavement which will be accepted on the basis of the appropriate laboratory density or maximum density, provided all other specification requirements are met.
4. If the average density of the 5 cored samples is at least equal to the minimum density specified for the mix in Articles 6304, 6354, 6404, or 6454, and no individual sample is more than 1.0 percent below the minimum density, paving may continue in the normal manner.
5. If the average density of the 5 cored samples fails to meet the minimum density and/or one of the test values is more than 1.0 percent below the required density referred to in Item 4 above, the Contractor shall construct a new control strip and the provisions of Items 1 through 4 above will apply to the new control strip. If the second control strip also fails to meet the minimum density referred to in Item 4 above, placing of pavement shall cease until adjustments are made and a control strip constructed meeting such minimum density.
(3) Test sections:
(a) General:
A test section is the testing unit for compaction. The material used in a test section shall be from the same source and shall be of the same type as the material used in the application control strip. The depth of a test section shall be equal to that of the control strip previously constructed for use with the test section involved except in cases where roadway control strips are used to determine required density for shoulder material. The length of a test section shall be determined by the lay-down width as shown in the Nuclear Gauge Operator's Manual. Copies of this manual may be obtained from the Materials and Tests Unit.
(b) Acceptance Requirements:
The required density for asphalt plant mix shall be that percentage of the nuclear target density as required by Articles 6304, 6354, 6404, or 6454, for the applicable mix type.
The actual density will be determined by the average of 5 nuclear density tests made at random locations within 5 equal segments of the test section. This actual density will be compared to the nuclear target density, as determined in Article 61011(C)(2)(d), to determine compliance. In addition, no individual test within a test section shall be more than 3.0% below the minimum required density for the applicable mix type.
(D) Density Determination by Cored Sample Methods:
(1) General:
When the Engineer elects to utilize cored sample methods as the means of density control, the provisions of this subarticle shall apply.
(2) Obtaining Samples:
Cored samples shall be taken in accordance with the provisions of Article 61011(B).
(3) Procedures and Tests:
(a) General:
The required density shall be the density specified for the mix based on the appropriate laboratory density or maximum density as specified in Articles 6304, 6354, 6404, or 6454. The procedures and tests provided for in this subarticle will be performed to assure that the required density is obtained.
(b) Minor Production:
At the beginning of production of each mixture involving production quantities of less than 100 tons daily, samples shall be taken in accordance with the Department's Materials and Tests Manual (Group II, Minimum Sampling and Testing) to determine compliance with the job mix formula for gradation, asphalt cement content, and density.
(c) Normal Production:
On the first day of production of each job mix formula involving 100 tons daily or more, a control strip shall be constructed in accordance with the applicable provisions of Subarticle 61011(C)(2). Samples of the mixture shall be taken and an extraction, maximum specific gravity, and Marshall test will be performed to determine compliance with the job mix formula.
The Contractor shall provide for a minimum of 5 cored pavement samples from the control strip. Additional samples shall be provided at the frequency indicated in the Materials and Tests Manual. The samples placed in the control strip shall be defined as "process control samples".
No later than the beginning of the next day following placement of the pavement, the Contractor shall core all samples from the previous day's production as directed by the Engineer. The density of each cored sample will be determined by the Engineer in the field laboratory and the Contractor will be immediately advised of the actual results. Artificial cooling of the pavement layers will be permitted in order to obtain cored samples. No additional compensation will be made for the cost of artificial cooling.
If the average density of the 5 or more control strip samples meets the required density and no individual sample is more than 1.0 percent below the required minimum density, paving may continue in the normal manner. Cored samples shall then be taken in accordance with the frequency of sampling and testing indicated in the Materials and Tests Manual.
If the average density of the 5 or more control strip samples fails to meet the required density and/or one of the test values is more than 1.0 percent below the required minimum density, the Contractor shall construct a new control strip in accordance with the above provisions. If the production represented by the second control strip also fails to meet the above density criteria, placing of the pavement shall immediately cease until appropriate adjustments are made and a control strip consisting of not more than 5 truck loads is constructed meeting the required minimum density.
(A) Transverse Joints:
When the laying of the mixture is to be suspended long enough to permit the mixture to become chilled, a transverse joint shall be constructed.
If traffic will not pass over the end of the paving, a butt joint will be permitted, provided proper compaction is achieved. If traffic will pass over the joint, the Contractor shall construct a sloped wedge ahead of the end of the full depth pavement to provide for proper compaction and protection of the full depth pavement. The joint shall be constructed square to the lane alignment and all excess material shall be discarded. The Contractor shall place a paper parting strip beneath this wedge to facilitate joint construction unless waived by the Engineer.
Before paving operations are resumed, the Contractor shall remove the sloped wedge and cut back into the previously constructed pavement to the point of full pavement depth. The exposed edge of the previously constructed pavement shall then be lightly coated with tack coat.
When laying of the mixture is resumed at the joint, the construction of the joint shall be completed and tested in accordance with Article 61013 while the mixture is still in a workable condition.
(B) Longitudinal Joints:
Longitudinal joints shall be formed by allowing the paver to deposit the mixture adjacent to the joint to such depth that maximum compaction can be obtained along the joint. The joint shall be pinched by rolling immediately behind the paver.
When multi-lane multi-layer construction is required, the longitudinal joint in each layer shall offset that in the layer immediately below by approximately 6 inches. The joint in the top layer shall be constructed, where possible, between design travel lanes.
The surface of the plant mix base or pavement after compaction shall be smooth and true to the required cross section and grade. Any defective areas shall be corrected with satisfactory material which shall be immediately compacted to conform with the surrounding area. Any area showing an excess of asphalt cement shall be removed and replaced.
Each pavement layer will be tested by the Contractor and the Engineer at all joints and at other selected locations using a 10 foot straightedge furnished by the Contractor. The variation of the surface from the testing edge of the straightedge, when applied parallel to the centerline of the surface, shall not exceed 1/8 inch between any 2 contact points. Areas found to exceed this tolerance shall be corrected by the Contractor by removal of the defective work and replacement with new material unless other corrective measures are permitted by the Engineer. The work and materials required in the correction of defective work shall be provided by the Contractor at no cost to the Department.
The Contractor shall maintain the plant mixed base or pavement in an acceptable condition until final acceptance of the project. Maintenance shall include immediate repair of any defects or damage that may occur. This work shall be performed by the Contractor at no cost to the Department and shall be repeated as often as may be necessary to keep the base or pavement in an acceptable condition.
There will be no direct payment for the work covered by this section.
Payment at the contract unit prices for the various items covered
by Sections 615, 620, 622, 630, 635, 640, 645, 650, 652,
and 654 will be full compensation for all work covered by
this section.