Sampling and testing of the 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, QA testing will be performed at a minimum of 10 percent of the QC testing.

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 verified 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, maximum density (Rice test), 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 then be taken immediately.

In addition to sampling and testing performed by QA/QC technicians on projects, samples will be taken by the M & T Unit’s Independent Assurance Sample (IAS) Section personnel. The Independent Assurance (IA) program assures that the personnel and equipment performing the Quality Assurance testing on all projects remain proficient. This is achieved by taking samples (typically a split sample) at the QA labs and testing those samples at the Design Asphalt Laboratory of the Materials and Tests Unit. The results are compared to a correlation rating system derived from a 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 personnel and the personnel performing the IA testing. Analysis of the QC test results, and if necessary re-sampling and testing under observation are other investigation tools available. The IAS personnel will normally coordinate their visits with the QA/QC technician in order to prevent unnecessary sampling.  The majority of IAS samples will be split samples that are taken together by the QA/QC technician and the IAS personnel.

Full cooperation should be given to the IAS personnel to insure that their sampling requirements  are met.  Any questions concerning the IAS process should be directed to the head of that section at the Materials and Tests Unit.

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 of the guidelines 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. 500 square feet (47 square meters) is suggested. The Contractor shall provide convenient telephone and fax machine access for QMS personnel at the plant site.

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 to a QMS project.

The laboratory testing equipment shall meet the requirements of the test methods herein, identified in Subarticle 609-5(D) - “Required Sampling and Testing”.

Laboratory equipment furnished by the Contractor or his representative shall be properly calibrated and maintained.  All calibrations shall be documented and maintained in the QC Lab. (See Section 7.13 for Calibration Requirements & Frequencies for Gyratory Compactor).  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 maintain a record of calibration results of all equipment at the QC laboratory.

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.  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.

7.2.1   QC LAB REQUIRED EQUIPMENT LIST FOR SUPERPAVE TESTING
 
 

QUANTITY           DESCRIPTION

1 ea.                       Fax Machine
2 ea.                       Mercury Thermometers
1 ea.                       Digital Thermometer (0°-400°F). min with Probe
2 ea.                       Asphalt Dial Thermometer (50°-400°F. min.)
1 ea.                       Hot Plate (Electric)
1 ea.                       Sieve Shaker w/Timer
1 set                       Electronic Scales (12,000 gm min. capacity w/ center
1 ea.                      Stainless steel Weighing cradle
1 set                       Electronic Scales (8,000 gm min. capacity)
1 set                       Milk Scale
1 ea.                       Vacuum Pump or Water Aspirator
1 ea.                       Manometer
1 set                       Vacuum Pycnometer & Lid with Two Vacuum Hose Connections or Glass Flasks (Jar) for Rice Gravity
1 ea.                       Mechanical Agitation Device for Rice Sample
1 ea.                       Electric Timer with 15 minute Capacity or more
1 ea.                       Thermostatic Heater for Water Container
1ea                         Temperature chart recorder w/ remote probe
1ea.                        Immersion circulation pump
2 ea.                       Electric Fans minimum 16” (406mm)
1 ea.                       Water Trap for Vacuum Pump
1 ea.                       Bleeder Valve for Vacuum Pump Line
1 ea.                       Refrigerator, Apt. Size or Larger
2  ea.                      Metal Buckets, 10 qt. (10 L).
4 ea.                       Plastic Buckets, 5 gal. (19 L)
1 ea.                       Plastic Water Container w. Overflow min. 24” (610mm) Dia.
2 ea.                       Stencil Brushes
1 ea.                       Stainless Steel Bowl, 5 qt.  (5.0 L)
1 ea.                       Stainless Steel Bowl, 8 qt.  (8.0 L)
1 ea.                       Sampling Shovel with Modified Sides
1 ea.                       Metal Top Splitting Table, 3 ½'  x 3 ½' (1.1m X 1.1m) minimum
6 ea.                       Metal Mix Sample Pans,  12 ½” x 10 ½” (315mm X 265mm)
3 ea.                       Tin Containers w/Lids (approx. 2,000 gm size)
10 ea.                     Tin Containers w/Lids (approx. 1,200 gm size)
1 ea.                       Frying Pan, Cold Handle
1ea.                        Shop Vac w/ Hepa Filter
1set                        Calibration  Weights
1 ea.                      Masonry Trowel, Straight Sided
1 set                       Spatulas (1 @ 4” & 1 @ 6”)
1 ea.                      No. 2 Sampling Scoop -
2 ea.                      Large Spoons, 8” min. Length
1 pair                    Rubber Gloves
2 pair                    Welder’s Gloves
2 ea.                     Dust Brushes
2 ea.                     Wire Brushes
-  -  -                     Clean Rags
-  -  -                    *Wetting Agent (Calgon or Equivalent)
-  -  -                      Marking Crayons
-  -  -                      Large Cloth Sample Bags (Good Condition)

*Any Dispersing agent such as Calgon, Joy or other detergent, or soap which will promote the separation  of fine material.

2 ea.                     Lab Ovens 7.5 CF Total Capacity for Both.  Each must be forced air convection
1 ea.                    NCDOT Approved 150mm Gyratory Compactor w/Printer & Automatic Shutoff
1 ea.                    150mm Hydraulic Specimen Extractor
4 ea.                    150mm Gyratory Specimen Molds
1 ea.                    150mm TSR Breaking Head (if TSR checked at QC Lab)
4 ea.                    12” X15” (305mm X 380mm) Metal Mix Sample Pans
1 ea.                    Metric Ruler
1 set ea.              Sieves 203mm and 305mm  w/cover & pan
 

____50mm      ____19mm       ____4.75mm ____0.600mm **   ____0.075mm(3Each)
____37.5mm   ____12.5mm    ____2.36mm ____0.300mm **
____25.0mm   ____9.5mm   ____1.18mm ____0.150mm **

BINDER CONTROL METHOD

Must have equipment for at least one approved method.

1 ea.                    Approved Ignition Furnace

If Solvent Extraction Used:

1 ea.                    Centrifuge with 2 bowls
1 ea.                    Aluminum or Glass Beaker
-  -  -                   Filter Rings (For Centrifuge Bowls)
  -  -                    Ash Correction Equipment with Scales (Sensitivity of x.xxx gms)
1 ea.                    1,000 ml Graduated Cylinder
1 ea.                    100 ml Graduated Cylinder
-  -  -                   1 gal. plastic containers for obtaining solvent samples
 

FOLLOWING REQUIRED ONLY IF TSR TEST PERFORMED AT LAB SITE

1 ea.                   Loading Jack or Marshall Test Press w/ Calibration spring
1 ea.                   Hot Water Bath w/Agitator
1 ea.                   Infrared Thermometer (0°-400°F). min

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 evaluation of calibration/verification records and random spot check equipment for compliance.

Test methods and forms listed (Italics) are available through the NCDOT Materials and Tests Unit in Raleigh (919) 733-3563.  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 for reasons other than temporary replacement of a malfunctioning gyratory compactor.  This time frame shall be less than 3 months in duration.

   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 traceable** 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).

** Traceable molds refer to individual molds that are permanently labeled (etched) and can be 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. Scales and Water Tanks

   1. Scales – general purpose balances and scales shall be calibrated annually by a qualified technician using NIST traceable weights. These scales shall be checked weekly by QA/QC lab personnel following the procedures in Test Method MT-3V and recorded on Form 3V or equivalent.

   2. Scales must meet requirements of AASHTO M 231, Table 2. When calibrated annually, each scale shall have a certification/sticker that provides:
        a.  Date of calibration
        b.  Personnel who performed calibration/ verification

   3. If the scales are being used for bulk specific gravity or Rice maximum gravity methods and utilize a suspended cable, the steel cable or wire shall be 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 25°C ± 3°C (77°F ± 1.8°F).

   6. The baths shall be deep enough to completely submerse the specimen and holder and be equipped with an overflow outlet. 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 Hot 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 176°C within ± 5°C.

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

   3. Ovens will be verified weekly (when used) using a calibrated glass thermometer following procedures outlined in Test Method MT-2V and recorded on Form 2V or equivalent.

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

   5. A record shall be kept of all annually calibrations as well as any repairs made to the ovens and shall include the following:
        a. Date of last calibration
        b. Temperature at which oven was calibrated
        c. Personnel who performed calibration

   6. Hot water baths shall be thermostatically controlled and will be verified/calibrated every six months using a calibrated NIST traceable thermocouple thermometer and following the procedures of Test Method MT-2V and recorded on Form 2V or equivalent.

D.  Ignition Furnace

   1. Forced air ignition furnaces shall be capable of maintaining the temperature at 578°C (1072°F). 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 verified annually using a calibrated 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 verified annually using NIST 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 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.

E.  Various other lab equipment

   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.

   2. Vacuum Pump and System
        a. Vacuum pumps used for Rice testing shall conform to the standards of ASTM D2041, 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 calibrated quarterly with an absolute vacuum gauge and the manometer should be adjusted accordingly. Additionally, this calibration shall be conducted anytime maintenance is or adjustments are performed.
        d. The system shall be verified annually following the procedures of Test Method 28V and documented on Form 28V or equivalent.

   3. Marshall Test Press
        a. The test press shall be capable of loading at a speed of 50 mm/min (2 inches/minute).
        b. The test press shall be verified using the manufacturers 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 plot shall be stored and be available for review.
 

Items listed above shall adhere to Sub Article 609-5(B) in the Standard Specifications and in addition, failure to comply with these requirements may result in lab certification being suspended until all testing equipment meets calibration requirements.

*(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) SAMPLING AND TESTING SCHEDULE

Sampling and testing are methods of evaluating and documenting the quality of the work.  The QA/QC Technician must know what frequency of sampling and testing is for plant and Roadway Operations, the manner and location in which samples are to be taken, and the number of samples required for a given days production.  It is the QC Technician’s responsibility to ensure that representative samples are obtained.  He/ She must also verify that samples are identified with the proper time and date and the location of the source.  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.

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\Pb_EFF), voids in the mineral aggregate (VMA) and %Gmm @ Nini.

The Contractor shall sample and perform a full test series on the completed mixture from each mix design at the following minimum frequency during mix production.  A full test series shall consist of Items I - A thru I in the schedule below.

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 is not reached during that day’s production, perform at least one partial test series 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 and paid for at 50 percent of the unit bid price.

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

I.   Full Test Series
Asphalt Mixture –180 lbs. Sampled From Truck at Plant (AASHTO T 168) (Split Sample Required)

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 of determining percent asphalt binder, subject to approval by the Engineer.

B.  Gradation on Recovered Blended Aggregate from Mix Sample (AASHTO T 30 and T 11) Grade on all sieves specified on  JMF
C.  Maximum Specific Gravity (AASHTO T 209)
D.  Bulk Specific Gravity of Compacted Specimens (AASHTO T 166),  Average of  3 specimens at Ndes  gyrations
E.  Air Voids (VTM), average of  3 specimens at Ndes  gyrations
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)

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 of determining percent asphalt binder, subject to approval by the Engineer.

B.     Gradation on Recovered Blended Aggregate from Mix Sample (AASHTO T 30 and T 11) Grade on all 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 or AASHTO T 164 and AASHTO T 30) (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), Table 1012-2, of the Standard Specifications. (Split Sample Required. Must be retained for 5 calendar days)

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

D. Retained Tensile Strength (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.

E.   % Maximum Specific Gravity at Nmax. (Split Sample Required)

1.   Sampled from plant produced mix during mix verification
2.   3 specimens compacted at Nmax gyrations
3.  %Gmm @ Nmax calculated from average of  3 specimens.

F.   Uncompacted Void Content of Fine Aggregate, AASHTO T 304, Method A (Natural Sand Only).
        Performed at Mix Design and when directed as deemed necessary. (Split Sample Required)

G.  Reclaimed Asphalt Shingle Material (RAS) Binder Content and gradation (AASHTO T 308 modified or AASHTO T 164 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.)

The approximate location of each sample within the increments shall be determined by selecting random numbers from Table 1 of ASTM Method D3665 Alternative 2 (See Table 7-1 of printed version of 2004 QMS Manual) or by using the NCDOT computer program for the QC-9 form. These are the only two acceptable means of determining random numbers for plant mix test locations.  Whichever method is initially used to determine the random number, shall be used consistently. 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.  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.

The random sample locations shall not be made known to the plant operator in order to maintain the integrity of the random sampling process.

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) Splits 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 and cards 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 perform all preliminary inspections & plant calibrations as indicated on the QC-11 form.

Mix verification tests will consist of those required on the QC-11 form which includes preliminary inspection and plant calibrations, recovered aggregate gradation, dust-to-binder ratio, binder content, Maximum Mix Specific Gravity (Gmm), Gyratory Mix Bulk Specific Gravity (Gmb@Ndes and Nmax), Gyratory printouts for both Mdes and Nmax gyrations, VTM, VMA, VFA, %Gmm@Nini calculations, aggregate stockpile washed gradations, RAP extraction (if applicable), and moisture content(s).  The % Gmm@Nmax will be checked by both QA and QC as a part of mix verification.  QA should also compact specimens to Nmax during normal production as deemed necessary.  A 180-pound (82-kg) sample of mix shall be taken for mix verification testing.  This 180 pounds (82 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 meets the applicable mix design criteria except the gradation, binder content and
%Gmm@Nini 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 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 specimens 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 QA Approval (QA Notification Required).
    1.  Per aggregate cold feed blend change of ± 10% or less from JMF target, excluding the following:
        a.  Natural sand(s) shall not exceed the maximum limits in Table 1012-1A of Specifications.
        b.  Deletion of a sole source aggregate comprising 10% or less of the original JMF
    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 Authorized By QA Without Pavement Construction Section’s 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, except the addition of natural sand(s) shall not exceed the maximum limits in Table 1012-1A of the specifications.  (JMF change required)

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 reqm’ts.
        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 JMF target, except natural sand(s) shall not exceed the maximum limits in Table 1012-1A of Specifications.
    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 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.

7.4.3  Control Charts:
Standardized control charts furnished by the Department shall be maintained by the Contractor at the field laboratory.  All regularly scheduled random QC full test series sample test results on mix incorporated into the project shall be recorded on control charts the same day tests are conducted. Partial test series results obtained due to reasons outlined in Sub-Article 609-5(C)2 will be reported but will not be plotted on the control charts.

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 (measured)
• 4. Maximum Specific Gravity Determined by AASHTO T 209
• 5. Percent Voids in Total Mix at Ndes  Gyrations
• 6. Percent Voids in Mineral Aggregate at Ndes  Gyrations
• 7. P0.075/Pbe Ratio
• 8. Percent Maximum Specific Gravity at Nini  Gyrations

Both the full test series individual test values and the moving average of the last four (4) data points will be plotted on each chart.  The Contractor’s test data will be shown in black and the moving average in red.  The Engineer’s assurance data will be plotted in blue.  Denote the warning control limits with a dash green line, the moving average control limits with a dash blue line, and individual test limits with a dash red line.

The moving average(s) shall be continuous with the following exceptions. A new moving average(s) shall be re-established only when:

• 1. A change in the binder percentage or aggregate blend is made in 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 warning limits as outlined in Subarticle 609-5(C)6

All individual test results are part of the plant quality control record 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  Warning Bands
Warning bands are defined as the area between the warning limits and moving average limits.

7.4.6  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.

    A     Individual Test Exceeding Individual Test Limits
When any of the following occur, production of a mix shall cease immediately. Production of the mix in question shall not resume until approval is given by the Engineer.

• When an individual test result for a mix control criteria (full or partial test series) exceeds both the individual test control limits and the applicable specification design limits, or
• when two consecutive binder content test results exceed the individual limits, or
• when two consecutive field TSR values fail to meet the minimum specification requirement

In either case, this material shall be removed and replaced with materials, which comply with the specifications.

    B     Moving Average Exceeding Warning limits
The Contractor shall immediately notify the Engineer whenever moving average values exceed the warning limits.

If two consecutive moving average values for any one of the mix control criteria fall outside the warning 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 warning 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 approved by the Engineer.

 If the process adjustment improves the property in question such that the moving average after four additional tests is on or within the warning 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 stays in the warning bands, the mix shall be considered not to be within reasonably close conformity, but reasonably acceptable.  Reduced payment for 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 warning limits in accordance with the following table.
 
 

Failure to stop production and make adjustments as described above due to two consecutive moving average values falling outside the warning limits shall subject all mix produced from the stop point tonnage to the tonnage point when the moving average is back on or within the warning limits or to the tonnage point when production is actually stopped, whichever occurs first, to be considered unacceptable.  This material shall be removed and replaced with materials, which comply with the specifications, unless otherwise approved by the Engineer.

    C     Moving Average Exceeding Moving Average Limits
If the adjustment does not improve the property in question such that the moving average after four additional tests exceeds the moving average (JMF) control limits, the mix shall be considered not to be within reasonably close conformity with specifications.  If the Engineer determines the mix is reasonably acceptable based on test data and an inspection of the completed pavement and allows it to remain in place, the mix will be accepted in accordance with Article 105-3.  If the mix is determined to be unacceptable, the mix shall be removed and replaced with materials, which comply with the specifications.  In either case, the adjustment or removal, respectively, for 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 warning limits. In addition, any mix, which is obviously unacceptable, will be rejected for use in the work.

7.5  SAMPLING PROCEDURES

7.5.1  Numbering of 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 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: 02-1 and 02-2 would be the first two samples taken in 2002 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 partial test samples were taken from the increment represented by sample number 02-2 above, these partial test sample no’s. would be 02-2P1 and 02-2P2.

7.5.2  Sampling Mix From the Truck
Sampling will primarily be the Contractor’s responsibility, but the Department will perform the Verification Sampling process.  A suitable sampling platform shall be provided on which the technician is able to stand and sample the material in the truck bed.  The platform shall 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.

7.5.3  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.

7.5.4  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).

At these sampling points, remove the upper 4 to 6 inches (100-150 mm) of mix, insert the sampling shovel or other device into the mix to extract the sample increments and place increments in a sample container. The total full test series sample shall weigh at least 180 pounds (82 kg).  All partial test series samples shall weigh at least 90 pounds (41 kg).

7.5.5  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 Modified and AASHTO T 168 Modified respectively.  Sample sizes shall be at least 10 pounds (4.5 kg)  for fine aggregates and 25 pounds(11kg) for coarse aggregates and  RAP. Samples of RAP shall be mixed and quartered as specified in Reduction of Samples to Testing Size below.  Individual aggregate samples are not required to be retained.  However, individual RAP samples are required to be retained.

In many cases representative sampling cannot be made in a single sample, and it may be necessary to take a number of samples 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 ¼ in.(32 mm) in diameter and 6 ft.(1.8m) 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.

7.5.6  Reduction of Samples to Testing Size (Full and Partial Test Series)
Step 1.  - Mix Samples.
Divide mix sample into QA and QC samples. The entire 180 lb. (82 kg.) sample for a Full Test Series or  90 lb.(41 kg.) for a Partial Sample will be taken from the truck in 4 separate buckets. Each bucket will have approximately 45 lbs. (20 kg.) of material for a Full Test Series  or 23 lbs. (10 kg.) for a Partial Sample.  Each bucket will also have material from each sampling point in the truck.

The appropriate buckets shall be combined as indicated on the sketch to form the QA sample and the QC sample for further quartering.  The QA sample shall be put in one or more 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.

The test sample (A & D) shall be further quartered as specified in Steps 3 through 5 (QC) for testing.  The retained sample  (B & C) shall be put in cloth sample bags furnished by the Contractor. An orange sample card (QC-7), furnished by the Department, shall be attached to the sample bag.

The retained 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 be 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 retained sample will then normally be tested jointly by QA and QC.

Step 3. (QC) The 45+ lbs. (20 kg) of mix for testing from Step 2 (QC) (Mix) is to be reduced according to the following sketch.

Step 4.(QC)One half of  the 22+ lbs (10 kg) of mix from Step 3 (QC) (B & C quarters) is to be used for compaction of Gyratory specimens as required.

Step 5.(QC) The other half of  the 22+ lbs (10 kg) of mix from Step 3 (QC) (A & D quarters) shall be used to obtain a maximum specific gravity (Gmm) test sample.  Use two opposing quarters for the test sample.  The remaining mix may be retained for possible use, in the event that problems are encountered with the test sample mix for either the Gyratory or Gmm tests.  This portion may be disposed of as soon as it is evident that it is no longer needed.

7.5.7  QC Quartering (RAP Samples)
The 25 lb (11 kg) RAP sample shall be quartered by the Contractor to obtain the appropriate size sample for binder content and gradation test. Split portions of RAP 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 samples directly from the RAP cold feed or stockpile.

7.5.8  QA Quartering (Mix Sample for Full and Partial Test Series)
Step 1  (QA) On samples that the Engineer elects to test, the 90+ lbs (41 kg) sample from Contractor’s Step 1 is to be reduced according to the following sketch.  If this sample is a mix sample, reheating to a workable condition in an oven will be necessary for cold samples.

   Mix = 90+ lbs. (41 kg)
   Partial Sample 45+ lbs.

 The test sample (A & D) will be further quartered as specified  in Steps 3 through 5 (QA) for testing.  The remaining material (B & C) will be retained for possible Independant Assurance testing by the Central Materials & Tests Lab.

Step 2. (QA)  The 45+ lbs (20 kg) of  mix from step 2 (QA) is to be reduced according to the following sketch.

Mix = 45+ lbs. (20 kg)
Partial Sample = 22+ lbs. (10 kg)

Step 3. (QA)  The 22+ lbs (10 Kg) of mix from Step 3a (QA) (B & C) is to be used for compaction of Gyratory specimens.

Step 4. (QA)  The remaining 22+ lbs (10 Kg) of mix from Step 3a (QA) (A & D) will be used to obtain a maximum specific gravity (Gmm) test sample.  Use two opposing quarters for the test sample.  The remaining mix will be retained for possible use, in the event that problems are encountered with the test sample mix for either the Gyratory or Gmm tests.  This portion may be disposed of as soon as it is evident that it is no longer needed.

7.5.9   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.