Sampling and testing of hot-mix asphalt are two of the most important functions performed by QA/QC technicians to assure that a quality product is obtained.  Data derived from sampling and testing during production and placement of the mixture are used to control the production process and to determine whether or not the final product meets specification requirements. For these reasons, sampling and testing techniques and procedures must be followed exactly to ensure that results give a true picture of mix quality and characteristics. In addition to performing other responsibilities, a competent QA/QC technician must be able to get representative samples, conduct field tests, interpret the test data, relay the test results to appropriate parties and maintain accurate and adequate records and reports.

Once the job mix formula is issued and before actual construction begins, Mix Verification tests must be performed to determine any differences which may exist between the properties of the asphalt mix designed in the laboratory and the same asphalt mix produced in a batch or drum mix plant.  Even though the same material sources are used, quite frequently the plant-produced mix may exhibit different mix properties from that indicated by the mix design.  QC testing of the mixture during production is essential to ensure that a satisfactory mix is being obtained. In addition, the Department will perform QA sampling and testing as specified in Section 609-6 of the Standard Specifications.

The JMF based on the mix design produced in the laboratory should be treated only as a “start-up” JMF.  As production begins, the desired properties of the mix should be checked and monitored on the plant produced, field lab compacted asphalt mixture.  Tests that should be performed during manufacture and placement include: aggregate gradations, cold feed calibrations, asphalt binder content, Superpave volumetric properties, temperature, theoretical maximum density, in-place density, smoothness and visual inspections, and others as necessary.  All of the mix properties on the plant-produced mix should be within the ranges required by the JMF and also within the tolerances set by the QMS Specifications.  If the test results on the plant-produced mix indicate compliance with the QMS Specifications, the plant may continue to operate.  If one or more of the mix properties is outside the desired range, appropriate actions, as described elsewhere in the Manual, shall be taken immediately.

In addition to sampling and testing performed by QA/QC technicians on projects, assessments will be performed by the Materials and Tests Unit’s Independent Assurance (IA) personnel.  The Independent Assurance (IA) program assures that the personnel performing QMS testing on all projects remain proficient.  Part of this program also assures that the laboratory equipment used in the testing is properly maintained and calibrated.  This is achieved by taking samples (typically a split sample) at either the QC or QA labs and testing those samples at a Materials and Tests Unit facility.  The results are compared to a correlation rating system derived from statistical analysis of previous comparative tests.  If the results of the comparative samples are within the Excellent/Good range, no investigation is required.  If the results are in the Fair/Poor range, an investigation is initiated by IA personnel in an attempt to determine the reason for the disparity.  This investigation shall include, but is not limited to: analysis of all calculations performed and procedures used by the QA/QC personnel, investigation of the testing equipment used, and the personnel performing the IA testing.  Analysis of all test results, and if necessary, re-sampling and testing under observation, are other investigation tools available.  The IA personnel will normally coordinate their visits with the QA/QC technician in order to prevent unnecessary sampling.  The majority of IA samples will be split samples that are taken by the QA/QC technician and witnessed by the IA personnel.

Full cooperation should be given to the IA personnel to insure that their sampling requirements are met.  Any questions concerning the IA process should be directed to the head of that section at the Materials and Tests Unit, (919) 329-4200.

This Section describes in detail the sampling and testing frequencies, procedures and test methods utilized by NCDOT.  As everyone is aware, there is much concern by the Division of Highways, the Federal Highway Administration and Asphalt Industry Representatives about the quality of asphalt pavement construction in North Carolina.  Full cooperation and efforts by all parties is necessary in order to assure that pavements are produced and constructed so as to perform as intended.  If the Resident Engineer, QMS Technician, Contractor or others should have questions or need further clarification about the guidelines, procedures, or instructions noted in this Manual, please contact the Pavement Construction Section at any time.  All forms and worksheets utilized for Sampling and Testing of mix and aggregates are contained in Section 11 along with detailed instructions.

7.2 SUPERPAVE FIELD LABORATORY

For a contract with 5000 or more total tons (metric tons) of mix, the Contractor shall furnish and maintain a certified laboratory at the plant site.  The laboratory shall be furnished with the necessary space for equipment, and supplies for performing contractor quality control testing.  A minimum of 320 square feet (30 square meters), exclusive of toilet facilities is required for all QC labs.  A 500 square feet (47 square meters) facility is suggested.  The Contractor shall provide convenient telephone and fax machine access for QMS personnel at the plant site.  There should also be an organizational chart with phone numbers for QC personnel posted in the QC Lab.

For a contract with less than 5000 total tons (metric tons) of asphalt mix, the Contractor may conduct the quality control testing in a certified off-site laboratory.  The Contractor may utilize private testing labs and technicians provided the Department has certified them.  The Contractor is still required to have a QMS Level I certified technician at the plant site while producing mix for a NCDOT QMS project.

The laboratory testing equipment shall meet the requirements of the test methods herein, identified in Subarticle 609-5(C)2 - “Required Sampling and Testing Frequencies”.
Laboratory equipment furnished by the Contractor or his representative shall be properly calibrated and maintained.  The Contractor shall document and maintain calibration results of all equipment at the QC laboratory.  See Section 7.2.2 for QMS Lab Equipment Calibration Requirements.  The Engineer shall be allowed to inspect measuring and testing devices to confirm both calibration and condition.  If at any time the Engineer determines that the equipment is not operating properly or is not within the limits of dimensions or calibration described in the applicable test method, the Engineer may stop production until corrective action is taken.

The Contractor shall notify the Division QA Supervisor as to when the QC lab is ready for inspection and certification.  This should be done as much as possible in advance of the paving operation (approx. 10 days) so that the QA Supervisor can complete the QC Lab Certification Checklist and submit it to the Pavement Construction Engineer for approval and certification.  Once the field lab is certified, a copy of the checklist and certification will be forwarded to the Contractor.  This certification and Checklist shall be posted in the field lab at all times.  The paving operations shall not begin until the lab is certified.

The Department will maintain a Quality Assurance (QA) Lab in each Highway Division, which will normally be centrally located within the division.  This Division QA Lab will be for the purpose of performing all necessary tests in monitoring the Contractor’s QC process and for maintaining all documentation of this process.  It will be staffed by a Division QA Supervisor and several QA technicians.

7.2.1   QC LAB REQUIRED EQUIPMENT LIST FOR SUPERPAVE TESTING

The Pavement Construction Engineer maintains a listing of the required equipment for a QA Lab.  Copies of this list are also furnished to each QA Supervisor anytime updates are made.

7.2.2  QMS Lab Equipment Calibration Requirements

Laboratory equipment furnished by the Contractor or his representative shall be properly calibrated and maintained as specified below. QC process control may require additional calibrations to ensure accurate test results.

The Contractor shall document and maintain all QC records, forms and calibrations for a minimum of 3 years after completion.  It is recommended that all records be kept in one (1) binder.  This binder shall be readily available for review by the Department or its representative.  Periodically, each lab may be audited by the Department or its representative.  The audit will consist of an evaluation of calibration/verification records and random check of equipment for compliance.

Test methods and forms listed (Italics) are available through the NCDOT Materials and Tests Unit in Raleigh at (919) 329-4060.  If the M&T Forms listed are not utilized, then the replacement form must include the identical information listed on the referenced M&T Forms and be labeled clearly for each piece of equipment verified/calibrated.

A. Gyratory Compactors and Molds

   1. Internal Angle will be verified annually as per AASHTO PP 48*  (1.16° ± 0.02°)

   2. Pressure will be verified/calibrated every three (3) months, as per manufacturer specifications (600 kPa ± 18 Kpa)

   3. Rotation will be calibrated every three (3) months  (30.0 ± 0.5 gyrations per minute)

   4. Height will be verified daily, as used   (+/- 0.1 mm of plug height)

   5. The above verifications for each calendar year will be printed (if applicable) and kept in a folder/binder that will be labeled “Gyratory Compactor Verifications”.

   6. The above calibrations/verifications shall be performed if the compactor is moved from one location to another.  This calibration shall be performed within 2 weeks of moving the compactor.

   7. Maintenance on the compactor will be required annually. The required maintenance will be as per manufacturer recommendations and performed by the manufacturer or a certified representative (certified by manufacturer)    and will include internal angle verification.  Paperwork (or certification sticker affixed to device) shall be provided showing the following information:
        - Date of calibration/verification and maintenance
        - Value for internal angle
        - Type of internal angle device used
        - Personnel who performed calibration/verification
        - Any repair work performed

8.  Gyratory Molds will be uniquely identified** and the diameter measured annually by the manufacturer or a certified representative, using an internal bore gauge or equivalent measuring device.  The inside diameter of each mold shall be measured following the procedures of Test Method MT-36V and recorded on Form MT 36V or equivalent.  The average inside diameter shall be 149.90 mm to 150.10 mm (measured at room temperature).  If any mold fails to meet these requirements, it shall be taken out of service and replaced.  In order to assure the molds stay in good condition, it is important to clean them after each use utilizing an appropriate cleaning agent (Citrus cleaner, CRC, etc.).

9.   Mold measurement information shall be stored in a binder or folder.

* AASHTO PP 48 addresses the use of only the FHWA DAV device.  NCDOT approves the use of the Pine Instrument Rapid Angle Measurement Device as an acceptable means for determining the internal angle as well (contingent on future research results).

** Uniquely identified molds refer to individual molds that are permanently etched and can be matched with calibration paperwork and tracked over time.

The gyratory compactor time and date stamp shall be checked daily to ensure accurate information is displayed on the printout.  The gyratory compactor time and date shall be accurate and consistent with the time and date displayed on the certified weight certificate.

B. Balances and Water Tanks

   1. Balances - general purpose balances shall be calibrated annually using NIST Class F traceable weights by a registered scale technician through the North Carolina Department of Agriculture and Consumer Services Standards Division.  These balances shall be verified weekly by QA/QC lab personnel following the procedures in Test Method MT-3V and recorded on Form 3V or equivalent.

   2. Balances must meet requirements of AASHTO M 231, Table 2.  When calibrated annually, each balance shall have a certification/sticker that provides:
        a.   Date of calibration.
        b.   Scale technician who performed calibration

   3. If the balances are being used for bulk specific gravity or maximum gravity methods and utilize a suspended cable, the steel cable or wire shall be of the smallest practical size to minimize any possible effects of variable immersed length.  Also, the opening in the table or stand shall allow the cable free movement with no restrictions.  Linked chain of any kind will not be allowed.

   4. The water tanks shall be made of a non-corroding material and have provisions for automatic control of the water temperature as well as a circulation pump.  Each tank shall be equipped with a recording thermometer with its bulb located in the water.

   5. These water baths shall be maintained at 77°F ± 1.8°F (25°C ± 1°C).

   6. The tanks shall be deep enough to completely submerse the specimen and holder and be equipped with an overflow outlet for maintaining a constant water level.  The water tanks shall be visually inspected monthly and water replaced periodically.

   7. Water tanks and suspension apparatus must meet the requirements of AASHTO T 166, Section 4.

C.  Ovens and Water Baths

1.  Asphalt mix ovens - shall be a forced draft oven, thermostatically controlled, capable of maintaining any desired temperature setting from room temperature to at least 350°F (176°C).

2.  Ovens shall be in proper working order with doors that seal properly with no broken hinges.

3.  Ovens will be verified every six months using a . NIST traceable thermocouple thermometer and following the procedures of Test Method MT-2V and recorded on Form 2V or equivalent. If the temperature readout does not match the NIST thermocouple, it shall be adjusted so the temperature readout is correct.

4.  A record shall be kept of all annual verifications as well as any repairs made to the ovens and shall include the following:

a.  Date of last verification
b.  Temperature at which oven was verified
c.  Personnel who performed verification

5.  Water baths shall be thermostatically controlled and will be verified every six months using an . NIST traceable thermocouple thermometer and following the procedures of Test Method MT-2V and recorded on Form 2V or equivalent. If the temperature readout does not match the NIST thermocouple, it shall be adjusted so the temperature readout is correct

1.  Forced air ignition furnaces shall be capable of maintaining the temperature at 1072°F (578°C). The furnace shall have an internal balance capable of weighing a 3500 gram sample in addition to the baskets. Ovens shall be in good working condition. All safeguards shall be in place and shall function properly.

2.  Furnaces will be calibrated annually using a NIST traceable thermocouple thermometer. If the oven readout does not match the NIST thermocouple, it shall be adjusted so the temperature readout is correct.

3.  The internal oven balance shall be calibrated annually by a registered scale technician through the North Carolina Department of Agriculture and Consumer Services Standards Division using NIST Class F weights following Test Method MT-35V and the results recorded on Form 35V or equivalent. (8000 gram weight required)

4.  Each ignition furnace shall have a lift test performed monthly when the furnace is at room temperature, following the procedures of Test Method 35V(A). These results shall be recorded on Form 35V(A) or equivalent.

5.  The furnace time and date stamp shall be checked daily to ensure accurate information is displayed on the printout.  The furnace time and date shall be accurate and consistent with the time and date displayed on the certified weight certificate (load tickets)

        1.  Shakers and Sieves

a.  Shakers shall be routinely inspected visually and maintained.
b.  Sieves shall be visually inspected weekly following Test Method MT-11V and documented on Form 11V or equivalent.
c.  Any sieve that is damaged or broken shall be immediately replaced with a new sieve.

a.  Vacuum pumps used for maximum gravity testing shall conform to the standards of AASHTO T 209, Section 6.
b.  The vacuum system shall include a vacuum gauge, a water vapor trap, hoses, a vacuum pump, and a manometer (absolute pressure gauge).
c. The vacuum within the pycnometer shall be verified quarterly with an absolute vacuum gauge and the manometer should be adjusted accordingly. The system shall be verified following the procedures of Test Method 28V and documented on Form 28V or equivalent.  Additionally, this verification shall be conducted anytime maintenance or adjustments are performed.

a.  The test press shall be capable of loading at a speed of 2 inches/minute (50 mm/min).
b.  The test press shall be verified using the manufacturer’s recommended method which usually involves using a calibration spring or a calibrated load ring.
c.  The test press shall be verified annually and the verification data shall be stored and be available for review.

*(1)  Note: In lieu of aggregate stockpile gradations, the Contractor may furnish gradation quality control data conducted by the aggregate producer, which is representative of the Contractor's current stockpiles.

*(2)  Note: TSR not required for Mix Verification but acceptable to be done at that time.

7.3 QUALITY CONTROL (QC) MINIMUM SAMPLING AND TESTING SCHEDULE

Sampling and testing are methods of evaluating and documenting the quality of the product.  The QA/QC Technician must know what frequency of sampling and testing is required for both Plant and Roadway Operations, the manner and location in which samples are to be taken, and the number of samples required for a given day’s production.  It is the QC Technician’s responsibility to ensure that representative samples are obtained in accordance with the specific contract guidelines.  He/ She must also ensure that samples are properly identified with the time, date and location.  The QA/QC Technician shall know the procedures for tests he/she must conduct and should follow those procedures to ensure accurate results.  If laboratory testing of samples is required, the QA/QC Technician should follow-up to ensure that tests are made as scheduled and that results are promptly evaluated.

The Contractor shall maintain minimum test frequencies as established below.  All tests shall be completed within 24 hours of the time the sample was taken. If not completed within this time frame, production shall cease until the tests are completed.  An essential element of quality control is the ability to react and make changes if asphalt mix deficiencies occur.  Therefore, it is intended for all tests to be performed directly after being sampled to allow the producer to react to the test results.

Mix control criteria are the 2.36 mm and 0.075 mm sieves, % binder content, voids in the total mix (VTM), Dust/Binder Ratio (P0.075\PbEff), voids in the mineral aggregate (VMA) , %Gmm @ Nini and TSR.

The Contractor shall sample and perform a full test series on the completed mixture from each mix design per plant per year at the following minimum frequency during mix production.

If production is discontinued or interrupted before the accumulative production increment tonnage is completed, continue the increment on the next production day(s) until the increment tonnage is completed.  Obtain the random sample within the specified increment at the location determined in accordance with the most current edition of the Department’s HMA/QMS Manual.  When daily production of each mix design exceeds 100 tons (100 metric tons) and a regularly scheduled random sample location for that mix design does not occur during that day’s production, perform at least one partial test series as outlined in the schedule below.  These partial test series and associated tests do not substitute for the regularly scheduled random sample for that increment.

Should the Contractor fail to meet the Required Minimum Test Frequencies as outlined above, all mix without test representation shall be considered unsatisfactory.  If the Engineer allows the mix to remain in place, payment will be made in accordance with Article 105-3. Any additional quality control samples taken and tested at times other than the regularly scheduled random samples or directed samples which take the place of regularly scheduled samples will be considered Process Control (PC) samples and shall be designated accordingly on the appropriate forms.  Process Control test results will not be plotted on control charts nor reported to the Quality Assurance Laboratory.

During mix production the Contractor shall conduct quality control sampling and testing on the asphalt mixture consisting of:

I.   Full Test Series

Asphalt Mixture - 200 lbs. (91 kg) Sampled From Truck at Plant (Section 7.5)
(Split Sample Required.  Must be retained for 5 calendar days)

A. Binder Content, % (Contractor may select either option below):

1.   Ignition Furnace (AASHTO T 308 Modified)
2.  Other: Contractor may request and use other means (namely AASHTO T 164) of determining percent asphalt binder, subject to approval by the Engineer.

B. Gradation on Recovered Blended Aggregate from Mix Sample (AASHTO T 30 Modified) Grade on all of the sieves specified on   JMF.

C. Maximum Specific Gravity (AASHTO T 209 Modified, ASTM D 2041 Modified, or ASTM D 6857).

D. Bulk Specific Gravity of Compacted Specimens (AASHTO T 166), optional (ASTM D 6752), average of 3 specimens at Ndes  gyrations (AASHTO T 312 Modified)  (Specimens must be retained for 5 calendar days)

E. Air Voids (VTM), average of  3 specimens at Ndes  gyrations (AASHTO T 269)

F.   Voids in Mineral Aggregate (VMA) (calculation)

G.   Voids Filled with Asphalt (VFA) (calculation)

H. P0.075/Pbe Ratio

I.  % Maximum Specific Gravity at Nini  (calculation)

Asphalt Mixture –100  lbs. (45 kg) Sampled from the truck at plant (Section 7.5)
(Split Sample Required.  Must be retained for 5 calendar days)

A.  Binder Content, % Ignition Furnace (AASHTO T 308 Modified)
Note: Contractor may request and use other means (namely AASHTO T 164) of determining percent asphalt binder, subject to approval by the Engineer.

B.  Gradation on Recovered Blended Aggregate from Mix Sample (AASHTO T 30 Modified) Gradation required on all of the sieves specified on JMF

A.  Aggregate Stockpile Gradations (AASHTO T 27 and T 11)
(sampled from stockpiles or cold feed system as follows; split samples not required)

1. Coarse Aggregates (Approved Standard Sizes)
    a. At beginning of production *
    b. Weekly thereafter *
2.   Fine Aggregates (Stone Screenings, Natural Sands, Etc.)
    a.   At or within 1 week prior to mix verification  (Gradations Valid for Multiple Mix Designs),
    b.  anytime production is stopped due to plant mix gradation related problems,
    c.  weekly after mix verification*

B. Reclaimed Asphalt Pavement (RAP) Binder Content and Gradation (AASHTO T 308 Modified and AASHTO T 30 Modified.) Sampled from stockpiles or cold feed system at beginning of production & weekly thereafter.  Have RAP approved for use in accordance with Article 1012-1(G) and Table 1012-2 of the Standard Specifications. (Split Sample Required. Must be retained for 5 calendar days)

C. Reclaimed Asphalt Shingle Material (RAS) Binder Content and gradation (AASHTO T 308 Modified and AASHTO T 30 Modified) (sampled from stockpiles or cold feed system at beginning of production & weekly thereafter). Have RAS approved for use in accordance with Article 1012-1(F) of the Standard Specifications. (Split Sample Required. Must be retained for 5 calendar days.)

D. Combined Aggregate Moisture Content (AASHTO T 255) Drum Plant Only (sampled from stockpiles or cold feed system a minimum of once daily).

E. Tensile Strength Ratio (TSR) - (AASHTO T 283 Modified):

Option 1:
Mix sampled from truck at plant, tested, and results furnished to the Engineer within seven (7) calendar days after beginning production of each new mix design.  From the split sample, QC prepares and submits within 5 calendar days of the sample date, an additional set of specimens to the QA Lab for TSR testing. (Split Sample Required)
Option 2:
Mix sampled from truck at plant with one set of specimens prepared by the Contractor and then tested jointly by QA and QC at a mutually agreed upon lab site within first seven (7) calendar days after beginning production of each new mix design. Specimens must be tested on either a recording test press or a test press that maintains the peak load reading after the specimen has broken.

Note:  Additional TSR testing required prior to mix production in accordance with above procedures is required when a change is made in anti-strip additive dosage or when a new anti-strip additive source or grade is utilized, unless otherwise approved.  Other TSR test(s) may be directed as deemed necessary.  TSR testing is not required for mix verification, but may be performed at that time.

Prior to beginning production each day, the Contractor shall specify the projected tonnage of each mix type to be produced from a plant and furnish this information to the appropriate QA Lab on the QC-9 form, along with the random sample locations for that day's production.  (See Section 11 of this manual for detailed instructions for this form.) This tonnage is not project specific but plant specific.

The approximate location of each sample within the increments shall be determined by selecting random numbers from Table 7-1 in accordance with the procedures detailed in ASTM D 3665 Alternative 2 as modified by the Department.  This is the only acceptable means of determining random numbers for plant mix test locations.  The random numbers selected shall then be multiplied by the 750 tonnage increment.  This number shall then be added to the final tonnage of the previous increment to yield the approximate total tonnage when the sample is to be taken.  A copy of the certified weight certificate from the load the sample was obtained shall be attached to the QA/QC-1 form.

Sample tonnage(s) shall be computed to the nearest whole ton (metric ton).  This process shall be recorded on the QC-9 form prior to beginning production of each increment, with the original maintained at the QC Lab for inspection by the QA personnel.  This form should also be faxed to the appropriate QA Supervisor prior to production each day.  Instructions for completing the QC-9 form can be found in Section 11 of this Manual.

All regularly scheduled random samples shall be taken at the sample tonnage as determined above. The random sample locations shall not be made known to the plant operator in order to maintain the integrity of the random sampling process.  As an exception to these regularly scheduled random samples, a mix sample shall be taken and a full test series performed on mix incorporated into a control strip when proceeding on limited production procedures due to failing densities. When a mix sample is obtained in conjunction with a control strip, that sample will not substitute for the next randomly scheduled QC mix sample for that tonnage increment, nor shall it be plotted on the control charts. However, all applicable plant mix tests results shall be reported to QA.  The maximum specific gravity (Gmm) used to calculate percent compaction for the control strip placed shall be the individual Gmm for the sample of mix taken from the mix incorporated into the control strip. (See Section 10.10)

7.3.2  Sample Location for Aggregates, RAP & RAS
Section 609-5 (C)2 of the QMS Specifications requires aggregate samples be taken from either the stockpiles or the cold feed system and gradations be performed at the frequencies specified below :

A.  Coarse Aggregates (Approved Standard Sizes) Split samples not required

1.  At beginning of production
2.  Weekly thereafter

B.  Fine Aggregates (Stone Screenings, Natural Sands, Etc.)   Split samples not required

1.  At or within 1 week prior to mix verification (Gradations Valid for Multiple Mix Designs),
2.  Anytime production is stopped due to plant mix gradation related problems,
3.  Weekly after mix verification

C.  Reclaimed Asphalt Pavement (RAP) and Reclaimed Asphalt Shingle Material (RAS) Split samples required

1.  At beginning of production
2.   Weekly thereafter

The weekly requirement for both aggregate, RAP and RAS is defined as a calendar week unless there has been no production during that calendar week.

The Contractor must maintain records of all aggregate, RAP and RAS stockpile gradations and furnish these upon request to QA personnel.

7.4     MIX VERIFICATION,  JMF ADJUSTMENTS, AND CORRECTIVE ACTION PROCEDURE

Note: All forms referred to in this Section have detailed instructions in Section 11 of this Manual.

7.4.1  Mix Verification Requirement

The Contractor shall conduct field verification of the mix at each plant within 30 calendar days prior to initial production of each mix design, when required by the Allowable Mix Adjustment policy and when directed as deemed necessary. Prior to beginning mix verification, the Contractor shall ensure that all preliminary inspections and plant calibrations are either current or performed as indicated on the QC-11 form. Should initial mix production not occur within 30 days of the initial verification, the contractor must repeat the mix verification.  Mix obtained from NCDOT or non-NCDOT work may be used for this purpose provided it is sampled, tested, and the test data handled in accordance with current procedures in this manual and the following provisions. If non-NCDOT mix is used for this purpose, the appropriate QA Lab should be notified prior to performing the sampling and testing.

Mix verification tests will consist of those required on the QC-11 form which includes recovered aggregate gradation, binder content, dust-to-binder ratio, Maximum Specific Gravity (G_mm), Gyratory Bulk Specific Gravity (G_mb@N_des), Gyratory printouts for N_des gyrations, VTM, VMA, VFA, %G_mm@N_ini calculations, cold feed blend calibration and moisture content (if required).  Other preliminary inspections, calibrations, aggregate stockpile washed gradations, RAP and RAS binder content and gradation (if applicable), are required to be current and on file at the Contractor’s QC Lab.   A 200 pound (91 kg) sample of mix shall be taken for mix verification testing.  This 200 pound (91 kg) shall be quartered, bagged, tagged, and the QA and referee portions retained until either procured by or disposal permission is given by QA personnel.  Plant production shall not begin until all QC field verification test results have been completed and the mix has been satisfactorily verified by the Contractor’s Level II technician.  Satisfactory verification shall be when all volumetric properties meet the applicable mix design criteria except the gradation, binder content and %G_mm@N_ini are within the individual test limits for the mix type being produced.  In addition, QC shall retain records of these calibrations and mix verification tests and furnish copies (as required on the QC-11 form) to the Engineer for review and approval within one working day after beginning production of that mix.  Failure by the Contractor to fully comply with the above mix verification requirements shall result in immediate production stoppage by the Engineer.  Production of that mix shall not resume until all mix verification sampling and testing, calibrations, and plant inspections have been performed and approved by the Engineer.  Any mix produced that is not verified may be assessed a price reduction at the discretion of the Engineer in addition to any reduction in pay due to mix or density deficiencies.

The initial mix verification of all new mix designs shall be conducted with the plant set up to produce the aggregate blend and binder content in accordance with the initial JMF, unless otherwise approved by the Engineer.  If QC test results indicate that adjustments to the aggregate blend and/or binder content are necessary to obtain the desired volumetric properties, QC adjustments as deemed necessary may be made prior to any mix production to the project.  After these adjustments are made, all related test results and data substantiating the change must be furnished to the appropriate QA Supervisor, including the gyratory specimen printouts and the 0.45 power chart with the original and proposed blend gradations plotted if any blend / gradation change is being requested.  The QA supervisor will furnish this data to the Pavement Construction Engineer for approval, prior to production of that mix.  In addition, all test results and data for the initial mix verification (with the plant set up to produce the initial aggregate blend and binder content) shall also be furnished at that time.

If the Contractor and/or the Division QA Supervisor determine from results of quality control tests conducted during verification that adjustments to the JMF are necessary to achieve the specified mix properties, adjustments to the JMF may be made within the tolerances permitted by the specifications for the particular mix type being produced.  All Contractor requested JMF adjustments must be approved by the Pavement Construction Engineer and documented in writing before the new mix is produced for a NCDOT project.  If these mix adjustments achieve the desired mix properties, the Pavement Construction Engineer will be contacted by the Division QA Supervisor for this approval and issuance of a revised JMF.

The Contractor shall maintain records of all mix verification tests, calibrations and plant checks.  Failure to have results available may require additional mix verification tests prior to production of a mix.

7.4.2  Allowable Mix Adjustments

 Listed below are allowable mix adjustments during normal production, the extent of these adjustments allowed, and designation as to who is authorized to make and/or approve these changes. These allowable adjustments only apply during normal production of asphalt mixes.  (See Section 7.4.1 above for allowable changes during the plant mix verification process)

A.   Mix Changes Allowed By QC Without Prior QA Lab Approval (QA Notification Required).

1.  Cold feed blend change of ± 10% or less from the original JMF target blend percentage per aggregate, except a deletion of a sole source aggregate is not allowed.  QA may require rut testing prior to approval of mix change.  Blend changes to RAP/RAS are not allowed since neither of these may be varied from the JMF targets without Pavement Construction Engineer’s approval.
2.  Change in source of asphalt binder or mineral filler.
3.  Addition of new source RAP if gradation & binder content meet Table 1012-2 of the Standard Specifications and all mix properties of mix with new source RAP meets all Specification requirements.

B.   Mix Changes Allowed By QA Lab Without Pavement Construction Section’s Prior Approval.

1.  Change in JMF mixing temperature of up to plus or minus 15°F (8°C).
2.  Addition or deletion of a same source aggregate to better control mix properties (JMF change required).  Deletion of a sole source aggregate is not allowed.

C.   Mix Changes Allowed With Pavement Construction Specialist's Approval.

1.  Addition of new source RAP if gradation & binder content does not meet Table 1012-2 of the Standard Specifications.
2.  Change of JMF Control Data

a. Gradation requirements
b. Gmm, Gmb, Gsb, or Gse
c. % asphalt binder content change of ? 0.1 - 0.5 % from JMF target.

3.  Per aggregate cold feed blend change of 10 - 15 % of original JMF target.
4.   Any change in anti-strip source or dosage of 0.5% or less.
5.  Change in JMF mixing temperature greater than plus or minus 15°F (8°C).

D.   Mix Changes Only Allowed With Pavement Construction Engineer's Approval.

1.  % asphalt binder content change of greater than 0.5 % from JMF target.
2.  Per aggregate cold feed blend change greater than ?15 % of original JMF target.
3.  Any % RAP/RAS change from JMF target.
4.  Grade of asphalt binder being used.
5.  Any change greater than 0.5% in anti-strip dosage.
6.  Any change of the level of a mix type; i.e., S12.5D to a S12.5C or vice versa.

1.   Items C.1 and C.3 or D.1 thru D.4 require mix verification prior to normal production*

2.   Items contained in sections B, C or D require JMF change utilizing Form QMS-6

3.   If a JMF gradation change is requested due to a change in the aggregate blend, a 0.45 power chart with both the old and proposed gradation plotted must be submitted.

4. If Items C.4 or D.5 occurs, a TSR shall be required prior to normal production*

7.4.3  Control Charts (QA/QC-6 Form):

Standardized control charts shall be maintained by the Contractor at the Quality Control field laboratory on forms furnished by the Department or produced using the NCDOT QMS spreadsheet program.  For mix incorporated into the project, record full test series data from all regularly scheduled random samples, or directed samples which replace regularly scheduled samples, on control charts the same day the tests results are obtained.  Partial test series results obtained due to reasons outlined in Sub-Article 609-5(C)2 will be reported to Quality Assurance personnel on the proper forms, but will not be plotted on the control charts.  Process Control (PC) samples which are taken within an increment other than regularly scheduled random samples or directed samples that do not replace the scheduled random sample will not be plotted on control charts nor reported to Quality Assurance Laboratory Personnel.

Results of quality assurance tests performed by the Engineer will be posted on the Contractor’s control charts as data becomes available.

The following data shall be recorded on standardized control charts:

1. Aggregate Gradation Test Results:

a.   For each mix type: one sieve size smaller than the mix nominal maximum size.
b.   For all mix types: 2.36 mm and 0.075 mm sieves

2. Binder Content, %, Pb

3. Bulk Specific Gravity of Compacted Specimens at Ndes (AASHTO T 166 or ASTM D 6752)

4. Maximum Specific Gravity Determined by AASHTO T 209 Modified, ASTM D 2041 Modified, or ASTM D 6857

5. Percent Voids in Total Mix at Ndes Gyrations (AASHTO T 269)

6. Percent Voids in Mineral Aggregate at Ndes Gyrations

7. P0.075/Pbe Ratio

8. Percent Maximum Specific Gravity at Nini Gyrations

The moving average(s) shall be continuous except that a new moving average(s) shall be re-established only when:

1. A change in the binder percentage, aggregate blend or Gmm is made on the JMF, or

2. When the Contractor elects to stop or is required to stop production after one or two moving average values, respectively, fall outside the moving average limits as outlined in Subarticle 609-5(C)6,

3. Failure to stop production after two consecutive moving averages exceed the moving average limits occurs, but production does stop at a subsequent time, re-establish a new moving average beginning at the actual production stop point.

All individual test results for randomly scheduled or directed samples that replace randomly scheduled samples are part of plant quality control records and must be included in moving average calculations with the following exception.  When the Contractor’s testing data has been proven incorrect, use the correct data as determined by the Engineer in lieu of the Contractor’s data to determine the appropriate pay factor in accordance with Subarticle 609-5(C)(6).  In this case, replace the data in question and any related data proven incorrect.

7.4.4  Control Limits:
The following are established as control limits for mix production.  Control limits for the warning and moving average limits are based on a moving average of the last four (4) data points.  Apply all control limits to the applicable target source.

7.4.5  Corrective Actions
All required corrective actions are based upon initial test results and must be taken immediately upon obtaining those results.  In the event situations occur which warrant more than one corrective action and/or adjustment, give precedence to the more severe of these actions.  Stopping production when required takes precedence over all other corrective actions.  All corrective actions shall be documented.  QC personnel will not be held retroactively  responsible for any actions that would have been required as a result of replacement of QC data by Quality Assurance.

    A     Individual Test Exceeding Individual Test Limits

When any of the following occur, production of a mix shall cease immediately.

1.   When an individual test result for a mix control criteria (including results for required partial test series on mix) exceeds both the individual test control limits and the applicable specification design criteria, or,

2.  When two consecutive field TSR values fail to meet the minimum specification requirement, or,

3.  When two consecutive binder content test results exceed the individual limits.

Option 1:  Approval has been granted by the appropriate QA Supervisor.

Option 2: The mix in question has been satisfactorily verified in accordance with Article  609-4.  Normal production may resume based on the approval of the contractor’s Level II technician, provided notification and the verification test results have been  furnished to the QA Lab.

Acceptance of all mix failing to meet the individual test control limits (including results for both full and partial test series on mix) or minimum TSR requirements as described above will be determined in accordance with Article 105 3.  In addition, any mix, which is obviously unacceptable, will be rejected for use in the work.

Failure to stop production when required due to an individual test(s) not meeting the specified requirements shall subject all mix from the stop point tonnage to the point when the next individual test is back on or within the moving average limits, or to the tonnage point when production is actually stopped, whichever occurs first, to be considered unacceptable.  Failure to stop production when required due to two consecutive TSR tests failing to meet the specification requirements shall subject all mix from the stop point tonnage to the point when the next TSR test meets or exceeds specification requirement, or to the tonnage point when production is actually stopped, whichever occurs first, to be considered unacceptable.  In either case, this material shall be removed and replaced with materials, which comply with the specifications.  Payment will be made for the actual quantities of materials required to replace the removed quantities, not to exceed the original amounts.

    B     Moving Average Exceeding Moving Average Limits
The Contractor shall immediately notify the Engineer whenever moving average values exceed the moving average limits.
If two consecutive moving average values for any one of the mix control criteria fall outside the moving average limits, the Contractor shall cease production of that mix and make adjustments.  The Contractor may elect to stop production after only one moving average value falls outside the moving average limits.  In either case, a new moving average shall not be determined until the fourth test after the elective or mandatory stop in production.  Production of the mix in question shall not be resumed until one of the following has occurred:

Option 1:  Approval has been granted by the appropriate QA Supervisor.

Option 2: The mix in question has been satisfactorily verified in accordance with Article 609-4.  Normal production may resume based on the approval of the contractor’s Level II technician, provided notification and the verification test results have been furnished to the QA Lab.

If the process adjustment improves the property in question such that the moving average after four additional tests is on or within the moving average limits, the Contractor may continue production with no reduction in payment.

If the adjustment does not improve the property in question such that the moving average after four additional individual tests is outside the moving average limits, the mix shall be evaluated for acceptance in accordance with Article 105-3.  Reduced payment for or removal of the mix in question will be applied starting from the plant sample tonnage at the stop point to the sample tonnage when the moving average is on or within the moving average limits.  In addition,  any mix which is obviously unacceptable will be rejected for use in the work.

Failure to stop production and make adjustments as described above due to two consecutive moving average values falling unacceptable.  This material shall be removed and replaced with materials, which comply with the specifications, unless otherwise approved by the Engineer. Payment will be made for the actual quantities of materials required to replace the removed quantities, not to exceed the original amounts.

7.5.1  Aggregate , RAP and RAS Sampling

Since the reason for sampling aggregates is to determine the gradation, it is necessary that they be sampled correctly.  The results of a sieve analysis should reflect the condition and characteristics of the aggregate from which the sample is obtained.  Therefore, when sampling, it is important to obtain a representative sample.  Unless it is truly representative, tests apply to the sample only and not to the entire aggregate shipment or stockpile.  Accuracy in sampling is equally as important as accuracy in testing.

Sampling methods will be as specified in AASHTO T 2 and AASHTO T 168 Modified.  Sample sizes shall be at least 10 lbs. (4.5 kg) for fine aggregates and 25 lbs. (11 kg) for coarse aggregates, RAP, and RAS.  Samples of RAP and RAS shall be mixed and quartered as specified in “Reduction of Samples to Testing Size” below.  Split aggregate samples are not required, however, split RAP and RAS samples are required.

In many cases a representative sampling cannot be obtained by a single sample.  Multiple samples may be necessary to obtain a true picture of the properties of a stockpile or source of material.  As the maximum particle size in the aggregate increases, the size of the sample must increase to maintain accuracy in testing.  In addition, the number and types of tests determine the size sample needed.

There are four principal aggregate sampling points that are of concern at an asphalt plant.  These are (1) the source of materials, (2) the stockpile, (3) the coldfeed and (4) the hot storage bin at a batch plant.  When sampling at the source of materials, it would be well to remember one general rule.  It is easier to obtain a representative sample from the production stream, such as from the conveyor belt, than from trucks, storage bins or stockpiles.  However, if the sample is taken from the conveyor belt, it must be removed from the entire cross-section of the belt.  The same would be true when sampling from the chutes of cold feeders or hot bins at batch plants.

Getting a sample from a stockpile is not easy, and great care must be taken to obtain a truly representative sample.  Segregation usually occurs when the material is stockpiled, because the coarser particles will roll to the base of the pile.  If a stockpile of sand is to be sampled, it is usually only necessary to remove the dry layer where the segregation occurs and sample the damp material below.  Samples of coarse aggregates from stockpiles should be taken at or near the top and base, and at a number of locations in the stockpile.  To prevent further segregation while sampling, a board may be shoved into the pile just above the sampling area.  Another method of sampling coarse aggregate materials would be to expose the face of the stockpile from the top to the bottom, with a front end loader.  The samples could then be taken from the exposed face.  Another method would be to have the front end loader take a scoop from bottom to top and dump the material in a convenient location for sampling.  The sample bag could then be filled from various locations around the scoop of material.  Fine aggregate may also be sampled with a sampling tube approximately 1 1/4 in. (32 mm) in diameter and 6 ft. (1.8 m) long.

A sample of coarse or fine aggregate may be obtained by passing a container through the complete flow of that particular material under the cold storage bins.  If stockpile variation is to be determined, samples should be taken at various points and tested separately.  The outer layer of the stockpile should be pushed aside and not included in the sample because it may have dried and become segregated.  In sampling coarse aggregate, a board may be pushed into the pile at this point and the sample taken below the board.  This should be done near the top, middle and bottom of coarse aggregate stockpiles and then the three samples blended.  When sampling local sands from pits or proposed pits, using some type of auger, it is desirable to retain different strata as separate samples.

7.5.2  Numbering of Mix Samples

The numbering of all samples shall be the responsibility of the Contractor’s QC personnel.  QC sample numbers shall be assigned to all samples taken for mix that will be incorporated into a QMS project.  This QC sample number shall also be assigned to all related samples and tests. A separate series of numbers will be maintained for each mix design for each plant location.  Each series of numbers will begin with the first sample taken for each mix design at each plant location and will progress in sequential order until the end of the calendar year.  A new number series and accumulative tonnage will start over at the beginning of production each calendar year.

The sample numbers will be assigned to full test series as follows.  The first two digits will be the last two numbers of the current calendar year followed by a dash (-), followed by a sequence number beginning with one and progressing in numerical order as samples are taken. For example: 08-1 and 08-2 would be the first two samples taken in 2008 for a particular mix design at a particular plant location.

Partial test series mix samples will be numbered with the same number as the full test series sample number for that increment, except it will be followed by a P1 for the first partial test within a test increment, P2 for the second one in the same increment, etc.  For example, if two partial test samples were taken from the increment represented by sample number 08-2 above, these partial test sample numbers would be 08-2P1 and 08-2P2.  This numbering procedure applies regardless of whether or not a full test series sample has been taken for the applicable increment.

7.5.3  Sampling Mix From the Truck

Quality Control sampling will primarily be the Contractor’s responsibility. The Department will perform the Verification Sampling process.  The mix sampling and splitting process shall be in accordance with the procedures covered in Sections 7.5.5 and 7.5.6 of this Manual.

A suitable sampling platform shall be provided on which the technician is able to stand and sample the material in the truck bed.  It is recommended that the platform be constructed such that the truck is able to park on either side in order to prevent the technician from having to climb into the truck bed.  If it is not possible for the platform to be constructed in this manner then two appropriately constructed separate platforms shall be provided or the truck required to reverse direction so that the sample may be obtained.

7.5.4  Sampling Device

The shovel or other sampling device shall be of such size and configuration that each increment of a sample can be obtained in one attempt without spilling or rolling off.  In order to satisfy this requirement, use a flat bottom shovel, modified with 2 to 4 inch (50-100 mm) vertical sides attached to the shovel.

7.5.5  Sample Location in Truck

When the last batch has been dumped into the truck box, establish a point on the surface of the load, either at the high point, if some semblance of a conical shape exists, or near the middle of the truck box if the surface shows no such conical shape. Then establish at least three incremental sample points about midway between the previously established point and the sides of the truck and equally spaced around the load (see sketch below).

At each of these sampling points, remove the upper 6 - 12 inches (150 - 300 mm) of mix, insert the sampling shovel or other device into the mix and extract the sample material.  This sampling should begin at one of the three locations and then continue in a rotational manner in such a way as to insure that each container/bucket contains mix from each sampling point in the truck.  The total full test series sample shall weigh at least 200 lbs. (91 kg). All partial test series samples shall weigh at least 100 lbs. (45 kg).

7.5.6   Obtaining Mix Samples (Full and Partial Test Series)

Divide mix sample into QA and QC samples. The entire 200 lbs. (91 kg) sample for a Full Test Series or   100 lbs. (45 kg) for a Partial Sample will be taken from the truck in 4 separate buckets. Each bucket will have approximately 50 lbs. (23 kg) of material for a Full Test Series or 23 lbs. (10 kg) for a Partial Sample.  Each bucket shall also have material from each sampling point in the truck.

The two buckets that form the QA sample shall be put into two separate cloth sample bags furnished by the Contractor.  A white sample card (QC-7) shall be attached to the sample bag(s).  This sample shall be stored by the Contractor in a safe dry place for a period of up to 5 days, or until disposal permission is given by the Quality Assurance personnel, whichever occurs first.

One of the QC buckets shall be considered the QC referee sample.  This sample shall also be put in one or more cloth sample bags furnished by the Contractor. An orange sample card (QC-7), furnished by the Department, shall be attached to the sample bag(s).  The referee sample shall be stored by the Contractor in a safe dry place for a period of up to 5 calendar days, or until disposal permission is given by the Quality Assurance personnel, whichever occurs first. When the Department picks up its portion of a split sample, the matching “Referee Sample” shall be kept by the Contractor until disposal permission is given by the QA personnel.   In this case, the referee sample may not be disposed of in the 5 calendar days.  If differences exist between the QA and QC test results, the referee sample will then normally be tested jointly by QA and QC.

The remaining QC bucket shall be reduced in size to the appropriate test samples as indicated next.

7.5.7   QC Quartering (Mix Sample for Full and Partial Test Series)

Step 1  (QC):

The remaining bucket from the Contractor’s portion of the sample should be placed onto the splitting table. Mix the material thoroughly by turning the entire sample over three times with a flat bottom scoop. With the last turning, scoop the entire sample into a conical pile by depositing each scoop full on top of the preceding one.  Carefully flatten the conical pile to a uniform thickness and diameter by pressing down the apex with a masonry trowel. Divide the flattened mass into four quarters by inserting the quartering device and pressing down until the template is in complete contact with the splitting table surface.  The samples for the needed tests shall then be removed from the quarters according to the following sketch:

Step 2 (QC):
With the quartering device in place, material from each quarter (A, B, & C) from Step 1 (QC) should be scooped out and used to weigh out the necessary amount of mix for compaction of each Gyratory specimen as required.  Care should be taken when scooping from each quarter such that no segregation occurs.  Once the necessary amount of mix needed for each specimen is removed from each quarter, any remaining material should be discarded.

Step 3 (QC):
With the quartering device still in place, material from Quarter D from Step 1 (QC) should be scooped out and used to weigh out the necessary amount of mix for both a maximum specific gravity (Gmm) test sample and a binder content & gradation test sample. Any remaining material should be discarded.

Note:  For the above method of quartering to achieve proper test results, it is imperative that each bucket from 7.5.6 be filled in the rotational manner described such that each bucket contains mix from each sampling point in the truck.

7.5.8  QC Quartering (RAP or RAS Samples)

The 25 lb (11 kg) RAP or RAS sample shall be quartered by the Contractor to obtain the appropriate size sample for binder content and gradation test. Split portions of RAP or RAS samples will be retained for a period of 5 calendar days, commencing the day the sample(s) is tested, or until disposal permission from QA personnel is given, whichever occurs first. QA personnel will also take verification RAP or RAS samples directly from the cold feed or stockpile.

7.5.9  QA Quartering (Mix Sample for Full and Partial Test Series)

Step 1 (QA):

On samples that the Engineer elects to test, both bags containing the 100 lbs (45 kg) sample shall be brought to the QA Lab.  If this sample is a mix sample, reheating to a workable condition in an oven will be necessary for cold samples.

One of the bags should placed onto the splitting table. Mix the material thoroughly by turning the entire sample over three times with a flat bottom scoop. With the last turning, scoop the entire sample into a conical pile by depositing each scoop full on top of the preceding one.  Carefully flatten the conical pile to a uniform thickness and diameter by pressing down the apex with a masonry trowel. Divide the flattened mass into four quarters by inserting the quartering device and pressing down until the template is in complete contact with the splitting table surface.  The samples for the needed tests shall then be removed from the quarters according to the following sketch:
 
 

The remaining bag will be retained for possible referee testing if needed.

Step 2 (QA):
With the quartering device in place, material from each quarter (A, B, & C) from Step 1 (QA) should be scooped out and used to weigh out the necessary amount of mix for compaction of each Gyratory specimen as required.  Care should be taken when scooping from each quarter such that no segregation occurs.  Once the necessary amount of mix needed for each specimen is removed from each quarter, any remaining material should be discarded.

Step 3 (QA):
With the quartering device still in place, material from Quarter D from Step 1 (QA) should be scooped out and used to weigh out the necessary amount of mix for both a maximum specific gravity (Gmm) test sample and a binder content & gradation test sample. Any remaining material should be discarded.

7.5.10  QA Quartering (Aggregates, RAP & RAS)

When aggregate, RAP or RAS samples are taken by QA personnel, the reduction of samples to testing size shall be accomplished by either using a sample splitter or the quartering method. These samples will be taken at the specified frequency for quality assurance testing.

7.6 TEST PROCEDURES – GENERAL

All test procedures utilized by the Department are generally in accordance with AASHTO or ASTM standards.  Any modifications to these procedures are covered in detail in the following sections.  Other test procedures may be used by the Contractor provided they are preapproved by the Department.  Most of the acceptable Standard / Modified test procedures are covered next.  When specified test(s) applies to either or both parties (Contractor and/or Department), the same standard test procedures will be followed by each.

The following standard test methods from AASHTO and ASTM are referenced in the next sections: