This method of test covers a procedure for the determination of the particle size distribution of fine and coarse aggregates, using sieves with square openings.  It is not intended for use in the sieve analysis of aggregates recovered from asphalt mixtures or for the sieve analysis of mineral fillers.

7.7.1 Sieve Analysis (Gradation)
Aggregate gradation is the distribution of particle sizes expressed as a percent of the total weight.  A weighed quantity of thoroughly dried aggregate is shaken over a set of sieves having selected sizes of square openings.  The sieves are nested together such that the one having the largest opening is on top and those of successively smaller openings are placed beneath.  A pan is placed below the bottom sieve to collect all material passing through it.  The shaking of the aggregate is normally accomplished with a mechanical sieve shaker; however, the shaking may be done by hand.

The weight of material retained on each sieve is determined and expressed as a percent of the weight of the original total sample.  From this, one may determine the percent passing each sieve.  All NCDOT specifications for aggregates and asphalt mixes are based on “percent passing” the various sieve sizes. Sizes designated in inches means that each opening has that dimension on each side.  Numbered sizes denote that the sieve has that number of openings per linear inch.  For example, the No. 8 (2.36 mm) sieve has 64 (8 x 8) openings per inch2 (645 mm2). Fine aggregates are those that will generally pass the No. 8 (2.36-mm) sieve while coarse aggregates are generally retained on the No. 8 (2.36-mm) sieve

7.7.2  Gradation Tests of Aggregates

A.   Gradation tests will be run by the Contractor on stockpile aggregates, except when quarry QC gradations that are representative of current stockpiles, are furnished to the Contractor by the aggregate producer.

B.    The method of test for gradation determination of the aggregates will be in accordance with AASHTO T 11 and AASHTO T 27 .  Washed gradations (AASHTO T 11) will be performed on all aggregate samples.

C.    QC washed gradations (AASHTO T 11) will be performed on the first four (4) aggregate gradation samples of each job mix formula.  During this process a dry/washed gradation correction factor(s) will be determined by utilizing the QC-8 Form. Thereafter, the latest correction factor will be used for the 0.075 mm sieve and all other sieves with a correction factor of 1.0 percent or more.  The correction factor for the 0.075 mm sieve will be calculated to the nearest 0.1 percent, and all other sieves to the nearest 1.0 percent.  After a correction factor(s) is established, the correction factor(s) will be added to the dry gradation results for the next 8 gradation tests to determine the washed gradation of the aggregate.  This gradation will be reported to the nearest 1.0 percent except the 0.075 mm which will be reported to the nearest 0.1 percent. On each eighth (8th) test thereafter, a dry gradation and a washed gradation procedure will be performed and these results included on the QC-8 Form to establish a new moving average correction factor, which will then be used on the next 8 gradation tests.  Actual washed gradation results or dry gradations with the correction factors applied shall be the gradations plotted on the control charts.  Any time void problems (VTM or VMA) are encountered with a mix, washed gradations should be performed on all aggregate samples until the problem is resolved.  All dry/washed gradations’ differences should be included in calculating a new moving average correction factor.

D.   QA washed gradations (AASHTO T 11) will be performed on all aggregate gradations run for quality assurance purposes. Correction factors will not be used by the Division QA Labs.

E.   Calculations of the total percent passing each sieve size will be to the nearest whole number except that the 0.075 mm sieve will be to the nearest 0.1 percent (x.x). (Refer to the Significant Decimals Chart in Section 7.17.1 of this manual.)

The equipment shall consist of the following:

A.  Balance - The balance or scale shall be sensitive to within 0.1 percent of the weight of the sample to be tested.

B.  Sieves - The sieves with square openings shall be mounted on substantial frames constructed in a manner that will prevent loss of  material during sieving.  Suitable sieve sizes shall be selected to furnish the information required by the specifications covering the material to be tested.  The woven wire cloth sieves shall conform to the Standard Specifications for Sieves for Testing Purposes (AASHTO Designation M 92 Modified or ASTM Designation E 11 Modified).

C.  Oven - The oven shall be capable of maintaining a uniform temperature of 230°F. (110°C).  A hot plate may be satisfactory if turned to a lower temperature and the aggregate stirred to prevent  local overheating.

D.  Sieve Shaker - The sieve shaker shall be motorized, capable of providing a lateral and vertical motion to the sieves, accompanied by jarring action so as to keep the sample moving continuously over the surface of the sieve.  The sieve shaker shall have a timer that will automatically control sieving time.

A.    Samples for sieves analysis shall be obtained from the material to be tested by the use of a sample splitter or by the method of  quartering.  Fine aggregate sampled by the quartering method shall be thoroughly mixed and in a moist condition.  The sample for test shall be approximately of the weight desired and shall be the end result of the splitting or quartering method.  The selection of samples of an exact predetermined weight shall not be attempted.

B.    Samples of fine aggregate for sieve analysis shall weigh, after drying, approximately 100 to 400 grams.  In no case, however, shall the fraction retained on any sieve at the completion of the sieving operation weigh more than 4 g per inch2  (645 mm2) of sieving surface.

(1) The introduction of a sieve having larger openings than in the critical sieve, or,
(2) By the proper selection of the size of the sample.

C.   Samples of coarse aggregate for sieve analysis shall weigh, after drying, not less than an amount indicated in the following table:

* Shall be split into workable sample sizes depending upon use of 8” or  12” sieves.

Note: The Maximum Particle Size is defined as the sieve, which is one sieve size larger than the Nominal Maximum Particle Size. The Nominal Maximum Particle Size is defined as the sieve size which is one sieve size larger than the first sieve to retain more than 10 percent of the total material.

D. In the case of mixtures of fine and coarse aggregates, the material shall be separated into two sizes on the 2.36 mm sieve and the samples of fine and coarse aggregates shall be prepared in accordance with Paragraphs B. and C. above.

E. All samples shall be dried substantially to a constant weight at a temperature not exceeding 230°F.  (110°C)

A. The sample shall be separated into a series of sizes using such sieves as are necessary to determine compliance with the specifications.  The sieving operation shall be conducted by means of a lateral and vertical motion of the sieve, accompanied by jarring action so as to keep the sample moving continuously over the surface of the sieve.  In no case shall fragments in the sample be turned or manipulated through the sieve by hand.  Sieving shall be continued for a time of 10 minutes.  On that portion of the sample retained on the 2.36 mm sieve, the above described procedure for determining thoroughness of sieving shall be tested by using the hand method of sieving as described above.

B. The weight of each size shall be determined on a scale or balance conforming to the requirements specified in Equipment Section 7.7.3A.

The results of the sieve analysis shall be reported as total percentages passing each sieve.  Final percentages shall be reported to the nearest whole number, except the percentage passing the 0.075 mm sieve shall be reported to the nearest 0.1 percent.  Percentages shall be calculated on the basis of the total dry weight of the sample.  The QA/QC-1 form shall be used to report sieve analysis of coarse and fine aggregates.  For samples weighing 5,000 grams or more, it is recommended that sieves mounted in frames 16 in. (406 mm) in diameter or larger be used.

7.8      MOISTURE TEST (AASHTO T 255 Modified)

Since aggregate in a drum mix operation, unlike that of a batch operation, is weighed before drying, moisture content of the aggregate must be determined.  The weighing of aggregate and the metering of asphalt binder are interlocked electronically in drum mix operations.  To ensure proper metering of asphalt binder, adjustments for aggregate moisture must be made.  The moisture content of the aggregate should be determined and proper allowance made for the water content, prior to mixing.  Moisture determination shall be performed prior to starting of mixing and subsequently thereafter as changes occur in the condition of the aggregate.  A minimum of one (1) moisture test per day’s operation shall be performed by the QC technician at a drum mix plant operation.  Additional tests should be made when conditions in the stockpiles or supply change.

• Moisture tests will be performed on the aggregates in accordance with AASHTO T 255 Modified.
• Calculations of the percent moisture in the aggregate samples will be to the nearest 0.1 percent (x.x).  To determine the moisture content of aggregate being used, it is necessary to secure a representative sample of the aggregate.  When sampling, 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 storage bins or stockpiles.  When the sample is taken from the conveyor belt, it should be removed from the entire cross-section of the belt.  The size of the sample taken is determined by the maximum size aggregate.   Regardless of the size of the aggregate, the procedure for making an aggregate moisture determination is basically the same.  The steps for this procedure are outlined as follows:
• Obtain a representative sample of the material from the production line. (Conveyor  belt).
• Reduce the sample to a size that can be handled by the weighing device; either a sample splitter or the quartering method.
• Weigh aggregate sample and record weight.  (Wet Weight).
• Dry aggregate sample thoroughly.  The sample or samples are dried to constant weight on a hot plate or in an oven at a temperature of 230°F  (110°C).
• Weigh the dried sample and record weight (Dry Weight).  In weighing and handling the sample, extreme care must be taken to avoid any loss of the material, as this will affect the accuracy of the results.
• Determine moisture content.  The percent moisture is determined by the following formula:

7.9     SIEVE ANALYSIS OF RECOVERED AGGREGATE  (AASHTO T 30 Modified)

 This test method outlines the procedure for determination of particle size distribution of aggregate recovered from asphalt mixtures and RAP materials. These procedures are also used to determine the dry and washed gradations of the Recovered aggregates.

A.  Gradation tests will be performed in accordance with AASHTO T 30 Modified  Washed gradations  will be performed on the recovered aggregate from the mix only.  Dry gradations are acceptable to be run on RAP.

B. QC washed gradations  will be performed on the first four (4) aggregate gradation samples of each job mix formula.  During this process a dry/washed gradation correction factor(s) will be determined by utilizing the QC-8 Form. Thereafter, the latest correction factor will be used for the 0.075 mm sieve and all other sieves with a correction factor of 1.0 percent or more.  The correction factor for the 0.075 mm sieve will be calculated to the nearest 0.1 percent, and all other sieves to the nearest 1.0 percent.  After a correction factor(s) is established, the correction factor(s) will be added to the dry gradation results for the next 8 gradation tests to determine the washed gradation of the aggregate.  This gradation will be reported to the nearest 1.0 percent except the 0.075 mm which will be reported to the nearest 0.1 percent. On each eighth (8th) test thereafter, a dry gradation and a washed gradation procedure will be performed and these results included on the QC-8 Form to establish a new moving average correction factor, which will then be used on the next 8 gradation tests.  Actual washed gradation results or dry gradations with the correction factors applied shall be the gradations plotted on the control charts. All dry/washed gradation differences should be included in calculating a new moving average correction factor.  Any time void problems (VMA, VFA or VTM) are encountered with a mix, washed gradations should be performed on all aggregate samples until the problem is resolved.

C.  QA washed gradations  will be performed on all aggregate gradations run for quality assurance purposes. Correction factors will not be used by the Division QA Lab.

D. Final calculations of the percent passing each sieve size will be to the nearest whole number except that the 0.075 mm sieve will be to the nearest 0.1 percent (x.x).  Calculation of asphalt binder content will be to the nearest 0.1 percent (x.x).

7.9.2  Preparation of Sample

Note: The Nominal Maximum Particle Size is defined as the sieve size which is one sieve size larger than the first sieve to retain more than 10 percent of the total material.

7.9.3  Procedure

Dry all of the aggregate extracted from the mixture to a constant weight at a temperature not exceeding 230°F (110°C).  If a hot plate is used, stir the aggregate constantly while drying.  Cool and weigh the aggregate.  Then pour the sample into a stack of sieves containing the sizes required by the mixture, including the lid and pan. Shake in a motorized sieve shaker for ten minutes.  In order to check thoroughness of sieving, one or two of the smaller opening sieves may be shaken or tapped against the palm over a paper.

Begin by weighing the retained material on the largest opening size sieve, the material retained on each successive sieve shall be added and weighed with the aggregate from previous sieves.  Record the accumulative weights.

The total accumulated weight shall include that material in the pan which has passed the 0.075 mm sieve.  This weight should check within 0.1% of the weight of the extracted aggregate prior to sieving. If the Asphalt Binder Content is being controlled with the centrifuge the total aggregate weight is determined by adding the ash content in grams to the final weight of aggregate in the sieves and pan.

The accumulated weights may be converted to accumulated percentages by dividing each weight by the total aggregate weight. The same results are obtained by multiplying each accumulated weight by a constant.  This constant is derived by dividing 100 by the total aggregate weight.  To arrive at the percent passing each sieve size, subtract each accumulated percentage from 100%.

7.9.4  Report
The QA/QC-1 form will be used to record weights and calculate percent aggregate passing each sieve size. Report each sieve size to the nearest whole number except the amount passing the 0.075 mm sieve which is to be reported to the nearest one-tenth percent.

7.10  ASPHALT BINDER CONTENT CONTROL OPTIONS
The Contractor shall determine, prior to production of any mix, which method of the following tests will be used as the asphalt binder control. The Contractor may also utilize other innovative equipment or techniques to monitor the mix Binder content, subject to the approval of the Engineer.  Any method, including those listed as options in the Specifications, would need to be approved by the Department. Any tests or methods approved for use by the Engineer will be carried out according to the most current prescribed procedures. Binder content will be calculated and/or read to the nearest 0.1 percent (x.x) by whichever method used.

• IGNITION METHOD: (AASHTO T 308 Modified) The Contractor and/or Department may determine Binder content by using an ignition furnace. Results of each test must be recorded on either a standardized data sheet or a computer printout from a computerized ignition furnace.  This test data must be included with all other QC or QA test results for each sample tested.
• EXTRACTION METHOD: (AASHTO T 164 Modified) This method may be performed on the mix and on the RAP (when applicable) by the Department and/or the Contractor. The Contractor must request and receive approval from the Department prior to utilizing the extraction test on any NCDOT projects.  If extraction tests are utilized for the Contractor’s binder control method, ash correction samples will be taken and run on each extraction test.  If extraction test is not for purpose of checking Binder content, ash correction is not required. QA ash correction samples will be tested by the Division QA Lab to determine actual ash correction.  QC ash correction samples will be tested by the Contractor’s QC Lab to determine actual ash correction.  Ash corrections shall be calculated to the nearest 0.1 percent (x.x).

This standard may involve hazardous materials, operations, and equipment.  This standard does not purport to address all of the safety problems associated with its use.  It is the responsibility of whoever uses this standard to consult and establish appropriate safety and health practices and determines the applicability of regulatory limitations prior to use.

This method can be used for quantitative determinations of asphalt binder content and gradation in hot-mixed paving mixtures and pavement samples for quality control, specification acceptance, and mixture evaluation studies.  This method does not require the use of solvents.

The asphalt binder in the paving mixture is ignited using the furnace equipment applicable to this test method.  The asphalt binder content is calculated as the difference between the initial mass of the asphalt paving mixture and the mass of the residual aggregate, the calibration factor, and moisture content.  The asphalt binder content is expressed as mass percent of moisture-free mixture.

(A)  Equipment
 
(1)   Ignition Furnace—A forced air ignition furnace, capable of maintaining the temperature at 1072°F (578°C), with an internal balance thermally isolated from the furnace chamber accurate to 0.1 g  The balance shall be capable of weighing a 3500 gram sample in addition to the sample baskets.  A data collection system will be included so that the weight can be automatically determined and displayed during the test.  The furnace shall have a built in computer program to calculate change in mass of the sample baskets and provide for the input of a calibration factor for aggregate loss.  The furnace shall provide a printed ticket with the initial specimen mass, per minute specimen mass loss, temperature compensation, correction factor, corrected asphalt binder content (%), test time, and test temperature.  The furnace chamber dimensions shall be adequate to accommodate a sample size of 3500 grams.  The furnace shall provide an audible alarm and indicator light when the sample mass loss does not exceed 0.01 percent of the total sample mass for three consecutive minutes.  The furnace shall be equipped so that the door cannot be opened during the ignition test.  A method for reducing furnace emissions shall be provided.  The furnace shall be vented into a hood or to the outside and when set up properly shall have no noticeable odors escaping into the laboratory.  The furnace shall have a fan with the capability to pull air through the furnace to expedite the test and to reduce the escape of smoke into the laboratory.

(2)  Sample Basket(s) -- of appropriate size that allows the samples to be thinly spread and allows air to flow up through and around the sample particles.  Sets with two or more baskets shall be nested.  The sample shall be completely enclosed with screen mesh, perforated stainless steel plate, or other suitable material.

(3)  Catch Pan -- of sufficient size to hold the sample basket(s) so that aggregate particles and melting asphalt binder falling through the screen mesh are caught.
(4)  Oven -- capable of maintaining 257 ± 9°F (125 ± 5°C).
(5)  Balance -- of sufficient capacity and conforming to the requirements of AASHTO M231 Modified Class G2 for weighing specimen in basket(s).
(6)  Safety Equipment -- safety glasses or face shield, high temperature gloves, long sleeve jacket, a heat resistant surface capable of withstanding 1200°F (650°C) and a protective cage capable of surrounding the sample basket(s) during the cooling period.
(7)  Miscellaneous Equipment -- a pan larger than the sample basket(s) for transferring samples after ignition, spatulas, bowls, and wire brushes.

(B)  Preparation of Sample

(1)  The values in metric units are to be regarded as the standard. Obtain samples of aggregate in accordance with AASHTO T 2 Modified. Obtain samples of freshly produced hot-mix asphalt in accordance with AASHTO T 168 Modified. Obtain samples of asphalt binder in accordance with AASHTO T 40 Modified. The test specimen shall be the end result of quartering a larger sample taken in accordance with T 248. If the mixture is not sufficiently soft to separate with a spatula or trowel, place it in a large flat pan in an oven at 257°F ± 9°F (125°C ± 5°C).

(2)  The size of the test sample shall be governed by the nominal maximum aggregate size of the mixture and shall conform to the mass requirement shown below.  When the mass of the test specimen exceeds the capacity of the equipment used, the test specimen may be divided into suitable increments, tested, and the results appropriately combined for calculation of the asphalt binder content (weighted average). Specimen sizes shall not be more than 400 g greater than the minimum recommended specimen mass.

(C)  Calibration
The following three calibration factor methods may be affected by the size and source of aggregate in the mixture.  Accordingly, to optimize accuracy, a calibration factor for each aggregate type and / or each mix type will be established.  The calibration factor will be established using the actual ignition furnace that will be used for QC/QA testing.  One or more of the following procedures must be performed before any acceptance testing is preformed.  Certain aggregate types may result in unusually high calibration factors (>0.5%) and erroneous gradation results due to aggregate breakdown.  If either of these occur during procedure (A) then procedure (B) shall be followed.  If after that procedure is preformed, it also gives a calibration factor of >0.5, or a significant gradation change occurs, procedure (C) shall be followed.  If a question should arise as to whether a significant gradation change has occurred, the Department ‘s Pavement Construction Section should be contacted for assistance.

(D)  Individual Aggregate Samples

(1) Obtain individual aggregate samples in accordance with AASHTO T 2.

(2)   Split sample according to AASHTO T 248.

(3)   The size of the test sample shall conform to the mass requirement shown in Section 7.10.1(B).

(4) Samples must be preheated in a 125 ± 5°C (257 ± 9°F) forced air convection oven for a minimum 25 minutes or until a constant weight is maintained.  Do not preheat the sample basket(s).

(5) Perform aggregate gradation according to AASHTO T 27. (Do not wash sample)

(6) Set ignition oven temperature at 578°C (1,072°F).

(7) Set calibration factor on ignition furnace to 0.00 and ensure printer is on.

(8) Weigh and record the weight of the two sample baskets and catch pan (with guards in place).

(9) Evenly distribute aggregate into sample baskets (do not place any aggregate onto tray).  Ensure that sample is level in baskets.

(10) Weigh and record the specimen, baskets, catch pan, and basket guards.  Calculate and record the initial weight of the sample specimen.
 (Sample specimen = total weight minus weight of the sample basket assembly)

(11) Input the initial weight of the sample specimen in whole grams into the ignition furnace.

(12) Place sample into ignition oven, close door, and verify that sample weight (including basket) is correct.

(13) Press Start button.

(14) Burn ignition furnace for 40 minutes then press Stop.  Determine percentage of burn loss from print out of test.

(15) Perform aggregate gradation according to AASHTO T 27 on samples immediately after allowing to cool to room temperature.  Compare to original gradation in 7.10.1(D)S.

(16) Repeat this process for each aggregate in a mix.

(17) Multiply the percentage of  each aggregate in the mix times the percentage of burn loss for each aggregate.  Total these results for a calibration factor for that mix.

(18) Recycled Asphalt Pavement (RAP) will have an assumed calibration factor of 0.5%, unless prior test results verify a different calibration factor.

(19) If combined calibration factor is <0.5%, use that calibration factor.  If combined calibration factor is >0.5%, or if there is a significant gradation change in the aggregate, perform 7.10.1(E) below.

(20) Percentage of burn loss for individual aggregates shall be re-verified at least yearly.

(E)  Blended Aggregate Samples

(1)   Prepare two blended aggregate samples.  Size of samples shall be in accordance with section 7.10.1(B).

(2) Individual aggregates used to prepare the blended aggregate samples shall be sampled from stockpiled material.  The method used to combine the aggregates shall be the same procedure used during the mix design process.

(3)   Samples must be preheated in a 125 ± 5°C (257 ± 9°F) forced air convection oven for 25 minutes.  Do not preheat the sample basket(s).

(4)   Allow samples to cool and perform a gradation on one sample according to AASHTO   T 27. (Do not wash sample)

(5)   Burn both samples for 40 minutes and determine average percent burn loss in accordance with 7.10.1(D) 6 through 7.10.1(D) 14.  If the difference between the two calibration factors exceeds 0.15%, repeat the process for two more blended aggregate samples.  From the total of these four calibration factors, discard the high and the low, and average the remaining two.

(6)   Perform aggregate gradation (AASHTO T 27 ) on one burnt sample that is being used in the average calibration factor.  Compare this gradation to the gradation of the unburned “blank” specimen in 7.10.1(E) 4 to evaluate the amount of aggregate breakdown.

(7)  If final calibration factor is >0.5% or there is significant gradation change, perform 7.10.1(F) 3 below.

(F) Asphalt Mix Samples
(1) Prepare two mix samples within ±0.3 percent the optimum design binder content for the applicable mix.

(2) Size of sample shall be in accordance with section 7.11.2.

(3) Prior to mixing, prepare a butter mix at the design binder content.  The purpose of the butter mix is to condition the mixing bowl by providing a coating of asphalt binder and fines in the bowl.  Mix and discard the butter mix prior to mixing any of the calibration factor mix specimens to ensure an accurate binder content.  Aggregate used for the calibration factor specimens shall be sampled from stockpiled material.  The method used to combine the aggregates shall be the same procedure used during the mix design process. In addition a “blank” blended aggregate specimen shall be batched and tested for aggregate gradation according to AASHTO T 27. The washed gradation shall fall within the individual test limits for that mix type.  The freshly mixed specimens may be placed directly in the sample baskets.  If allowed to cool, the samples must be preheated in a 125 ± 5°C (257 +/- 9°F) forced air convection oven for 25 minutes.  Do not preheat the sample basket(s).

(4) Burn mix samples at 538°C (1000°F) in accordance with 7.11.4(I) of this procedure.  Determine percentage of burn loss in accordance with 7.11.3(A)G thru 7.11.3(A)M.  If the difference between the measured binder contents of the two samples exceeds 0.15 percent, repeat the process for two more tests and, from the four tests, discard the high and low result.  Determine the calibration factor by averaging the two remaining results.

(5) Perform a gradation analysis according to AASHTO T 27 on the residual aggregate from one of the burnt samples. Compare the gradation to the gradation of the unburned, “blank” specimen to evaluate the amount of aggregate breakdown.

(6) If the calibration factor is >0.5 % or if significant gradation change occurs, lower the test temperature to 482 ± 5°C (900 ± 8°F) and repeat the calibration process in 7.11.3(C) a thru 7.11.3(C)E. If the calibration factor continues to exceed 0.5 percent, lower the test temperature to 427 ± 5°C (800 ± 8°F) and repeat the same calibration factor process again.  The calibration factor obtained at 427 ± 5°C (800 ± 8°F) shall be averaged with the calibration factors from 7.11.3(A) and 7.11.3(B).  If all three results are within +/-0.08% of the average of these three, the calibration factor in 7.11.3(A) shall be used.   If any result is more than +/-0.08% from the average, use the calibration factor from the 427 ± 5°C (800 ± 8°F) burn.

(7) The temperature for testing HMA plant mix samples shall be the same temperature selected for testing mixture calibration factor samples in 7.11.3(C)F above.

(8) The calibration factor shall be re-verified each time there is a change in the mix ingredients, design or as required by the Engineer.


(G)  Test Method

(1) Preheat the ignition furnace to 1000°F (538°C) or as determined in the calibration procedure.

(2) Oven dry the HMA sample to a constant mass at a temperature of 221 ± 9°F (105 ± 5°C) or determine the moisture content of the samples according to AASHTO T 110 Modified.

(3) Enter the calibration factor for the specific mix to be tested as determined by the calibration method.

(4) Weigh and record the mass of the sample basket (s) and catch pan (with guards in place).

(5) Prepare the sample as described in Section 7.5.  Evenly distribute the sample in the sample basket(s) that have been placed in the catch pan, taking care to keep the material away from the edges of the basket(s).  Use a spatula or trowel to level the specimen.

(6) Weigh and record the total mass of the sample, basket(s), catch pan, and basket guards.  Calculate and record the initial mass of the specimen (total mass - mass of the sample basket assembly).

(7) Input the initial mass of the sample specimen in whole grams into the ignition furnace controller.  Verify that the correct mass has been entered.

(8) Open the chamber door and place the sample basket in the furnace.  Close the chamber door and verify that the sample mass (including the basket(s)) displayed on the furnace scale equals the total mass recorded in Section 7.11.4F within ± 5 grams.  Differences greater than 5 grams or failure of the furnace scale to stabilize may indicate that the sample basket(s) are contacting the furnace wall. Initiate the test by pressing the start/stop button.  This will lock the sample chamber door and start the combustion blower.

(9) Allow the test to continue until the stable light and audible stable indicator indicate the test is complete (the change in mass does not exceed 0.01 percent for three consecutive minutes).

(10) Use the corrected asphalt binder content (%) from the printed ticket.  If a moisture content has been determined, subtract the moisture content from the printed ticket corrected asphalt binder content and report the difference as the corrected asphalt binder content.
(11) Open the chambers door, remove the sample basket(s) and allow to cool to room temperature (approximately 30 minutes).

(H)  Gradation

(1) Allow the specimen to cool to room temperature in the sample basket(s).

(2) Empty the contents of the basket(s) into a flat pan.  Use a small wire sieve brush to ensure that any residual fines are removed from the baskets.

(3) Perform the gradation analysis according to AASHTO T 30 Modified and AASHTO T 11 Modified.

(I)  Report

Always report the corrected asphalt binder content, calibration factor, temperature compensation factor (if applicable), total percent loss, sample mass, moisture content (if determined) and test temperature. Report all ignition furnace % binder and gradation result information on the QA/QC-1 Form.  Also attach the entire original printed ticket from the ignition furnace to the QA/QC-1 Form.

(A)  Equipment
Centrifuge and bowls, filter rings, oven or hot plate, scales with capacity of 2000 grams sensitive to 0.1 gram, spatula, ladle, trowel, paint brush, beaker, or other suitable container to catch extract solution, frying pan or other suitable pan for drying aggregate.

(1) Solvent  - Trichloroethylene or any NCDOT approved Biodegradable Solvent.

(B)  Preparation of Sample

Note: The Nominal Maximum Particle Size is defined as the sieve size which is one sieve size larger than the first sieve to retain more than 10 percent of the total material.

A quartering table shall be used to mix and quarter the sample to a workable size.  Do not try to get an exact size sample.

Weigh the test sample which you have selected and place it evenly around the bowl.  The base mix will require two or more bowls unless a 3000 gram bowl is being used.  Here, a separate weight will be recorded for the mix placed in each bowl.  Cover the sample in the bowl with solvent and allow sufficient time for the solvent to dissolve the asphalt binder(not over one-hour) before proceeding.  During this time clean the rim of  the bowl, fit the filter ring on the bowl and tighten lid by hand, using about the same force each time.

(C)  Procedure
Place the bowl in the centrifuge and place beaker under the drain to collect the extract solution.  Start the centrifuge and gradually increase speed until solvent ceases to flow.  Allow machine to stop, add 200 ml. of solvent and repeat the above procedure.  Use sufficient 200 ml. solvent additions (not less than 3 additions) so that the extract is clear and not darker than a light straw color.

Remove the extracted aggregates from the centrifuge bowl(s) taking care not to lose any of the material in the process. Brush all aggregate from the bowl, lid and filter into a pan and dry.  Weigh the dried aggregate.

(D)  Ash Correction
If the Contractor elects to use the Extraction for Binder Content Control an ash correction must be obtained for each extraction performed.  To do this, collect all of the liquid extract from an extraction and place in a screw top plastic or metal container until the ash correction test is performed. Refer to AASHTO T 164 Modified, Method A for procedure of determining Ash Correction. To obtain the total ash weight of a mix sample, multiply the % ash by the total weight of the mix sample.

(E)  Calculations

(F)  Report
 Report percent Binder Content on the QA/QC-1 Form. Report results to nearest 0.1% (X.X).

This method is used to determine if the asphalt mixture actually being produced meets the requirements of the Specifications and/or if changes have occurred. This is one of the most important test the technician will conduct and is used in conjunction with the Maximum Specific Gravity (Gmm) test to determine a density-voids  (VTM) analysis of the mixture that is being produced.  It is at times also used to check %Gmm @ Nmax.  When checking VTM the mix is gyrated to the Ndes number of gyrations.  When checking %Gmm @ Nmax, the mix is gyrated to the Nmax number of gyrations.  Also, a back calculation is performed to check %Gmm at Nini.

The Superpave Gyratory Compactor field test procedure will be performed by the Contractor within each tonnage increment determined by the random sampling process and by the Department’s test on split samples taken by the Contractor.

The JMF will give the targets for maximum specific gravity (Gmm), bulk specific gravity of the compacted mix (Gmb) and percent air voids in the total mix (VTM). Due to normal testing error, material variations, changes that occur in the plant, and other possible causes, deviations from the established JMF values may occur. Therefore, occasional changes in the JMF values will need to be made based on the results obtained from QC/QA test data on actual mix production.

7.13.1  General Notes

 The following guidelines and tolerances will be utilized when comparing field bulk specific gravity of the compacted mix (Gmb), the field maximum specific gravity (Gmm), and the field VTM with JMF values to determine compliance and/or if a new JMF is needed.

A). A combined gradation (AASHTO T 30 Mod.), binder content test and maximum specific gravity (Gmm) (AASHTO T 209, ASTM D 2041 or ASTM D 6857) will be performed in conjunction with the Superpave Gyratory field test.

B.) VTM which is determined by use of the Superpave Gyratory field test and field Rice test is subject to a  ?2.0% Individual Test Control Limit against the JMF target VTM. (Refer to Subarticle 609-5 (G) of the QMS Specification).

C.) All Superpave Gyratory specimens will be tested using the 150 mm Superpave Gyratory method.

D.) The Height, Pressure, and Angle calibrations are required to be performed prior to initially using the Gyratory Compactor and at the minimum frequencies specified in Section 7.2.2.

 Refer to REDUCTION OF SAMPLES TO TESTING SIZE, Section 7.5.6 of this Manual.

7.13.3  Procedure

(A) Place 3 -150 mm Gyratory mold assemblies in a 300° - 310° F (149°C - 155°C) oven.

(B) Mix and quarter the sample material as described in “REDUCTION OF SAMPLES TO TESTING SIZE”. Weigh out the appropriate amount of mix to produce a compacted specimen height of 115 +/-5mm order to determine the approx. weight of uncompacted mix, the following formula may be used:

(C) After the proper loose mix sample weight is determined for the specimen, place the mix into a tarred pan approximately 15” x 18” (375 mm x 450 mm) and place pan and mix in a forced air oven. Repeat for two additional pans of mix.

(D) If necessary, heat the 3 pans of mix until the mix reaches a field mix compaction temperature recommended for the binder type. . The gyratory compaction temperature for Superpave mixes is as follows:

If mix temperature is at or above this compaction temperature, it is not necessary to put the mix in an oven since there is no curing time required.

(E) Place paper specimen protection disc, or comparable paper disc, in the bottom of the heated gyratory compaction mold.

(F) Introduce one pan of mix into a mold. Measure the temperature of the mix in the mold by placing a thermometer in the center of the specimen. Once the temperature is at the mix compaction temperature recommended for the binder type, place a specimen protection disc on the top of the mix and place mold assembly with mix into the Gyratory compactor and gyrate the number of Ndes gyrations given on the JMF. If mix is too hot, allow sufficient time to cool to above specified range before compacting.

(G) Place the mold assembly with mix into the Gyratory compactor and apply 600 kPa of pressure to the mixture and introducing the 1.25° angle, start the Gyratory compaction procedure. Gyrate to the specified Ndes number of gyrations, which is given on the JMF.  When checking % Gmm, gyrate to the number of gyrations specified on the JMF for Nmax.

(H) Procedures outlined in steps e. through g. should be done as quickly as possible as to not allow the mix to cool below the required temperature for that type Binder being compacted.

(I) When the compaction is complete, remove the compaction angle and raise the gyratory ram. Remove the mold assembly from the gyratory compactor. Extrude the specimen approx. 1 inch initially, then set under a fan to cool for approximately 5 minutes before complete extrusion of the specimen. Extrude the specimen by using the hydraulic jack being careful not to damage the specimen.

(J) Remove paper specimen protection discs. It is important to remove the paper specimen protection discs as soon as possible, because removal is difficult after the specimens have cooled.

(K) Place the three specimens in front of a cooling fan until they cool to room temperature. This may require 1 to 1.5 hours cooling time. It is helpful to set the specimen in front of the fan on some type material that absorbs heat. (Such as concrete)

(L) Smooth rough edges with a coarse brush, place on smooth and level surface, and properly identify by marking samples with QC sample number and proper suffix (i.e. 02-1a, 02-1b, and 02-1c).

(M) Determine bulk specific gravity (Gmb) using AASHTO T 166 or ASTM D6752.  Weigh the specimens in air, designating this weight as A.  Immerse the specimens in 77 ±2°F (25 ±1°C) water bath for 3 to 5 minutes and then weigh suspended in water, designating this weight as C.  Surface dry the specimens by blotting quickly with a damp towel and then weigh in air (include any water that may drain from voids in specimens), designating this weight as B.  Calculate the bulk specific gravity, Gmb, to three decimal places (x.xxx).

(M1) Determine the void content (VTM) of each specimen using the Gyratory bulk lab specific gravity (Gmb) of each specimen and the actual maximum specific gravity (Gmm) determined from the Rice Test using the formula given below and record results. The maximum specific gravity (Gmm) of the mixture (AASHTO T 209, ASTM D2041 or ASTM D6857) will be determined in conjunction with the Gyratory Test.

(M2) If checking % Gmm @ Nmax, the following formula will be used:

(N) Determine the average gyratory bulk specific gravity (Gmb) and void content (VTM) for the three specimens.  Discard an individual Gyratory bulk specific gravity that deviates more than ±0.015 from the average and recalculate the average, based on the remaining two specimens.  If more than one-value deviates by more than ±0.015, the entire set of results are considered suspect and a new set of specimens must be made and tested.

(O) If 2 consecutive sets of QA/QC Gyratory Bulk Specific Gravity results are outside the acceptable limits of precision, the QA Supervisor will designate one of the retained mix samples for the Contractor to cool to ambient air temperature for a period of 3 days, then reheat to 290°F. (143°C), then quarter for testing.  The Contractor shall then compact and test gyratory specimens.  Determine the Gyratory bulk specific gravity calibration factor, GmbCF, to use in comparing the average Gmb of an unreheated compacted sample to the average Gmb of a reheated compacted sample. The GmbCF will be considered accurate for the entire production of a particular mix design, but may be repeated at the discretion of the Contractor or the Engineer.   This correction factor is applicable for QA calculations only. If the GmbCF is between 0.9980 and 1.0020, it will be considered negligible and will not be used.

Determine the corrected average Gmb for reheated samples by use of the following formula.

Corrected Gmb = Gmb (Reheated) X GmbCF

(P) If 2 consecutive sets of QA/QC Gyratory Bulk Specific Gravity results are outside the acceptable limits of precision, the field mechanical Gyratory Compactors (QC & QA) will be calibrated with the mix design Gyratory Compactor.  This calibration will be accomplished by the following procedures:

(1) A 200 pound (91kg) sample of mix will be taken by QC personnel from the truck.

(2) This 200-pound (91kg) sample shall be quartered into 4 approximate 50 lb.  (23 kg) samples.  These four samples shall be put into four sample bags, labeled as Gyratory Compactor calibration samples, including date sample taken & JMF Number.  These four samples shall be distributed at that time as follows: Two bags to Contractor’s QC personnel (one for calibration and one for possible back-up), one bag to Department’s Division QA Lab, and one bag to mix design lab source.

(3) The above calibration samples will be cured at room temperature for a period of 3 days.

(4) A precise time will be selected for all 3 calibration samples to be placed into a 325°F (163°C) preheated forced air convection oven.  Samples will be left in oven for exactly 4 hours.

(5) Samples will then be removed from the oven and the procedures in 7.13.3.a. through 7.13.3.n. above will be followed.

(6) Determine the average gyratory bulk specific gravity of the 3 different sets of calibration samples.

(7) Determine the calibration correction factor by use of the following formula.

(8) The appropriate calibration correction factor will then be used to adjust all future QC and QA Gyratory Gmb results for that mix design.  This adjustment will be made by use of the following formula.

(9) If the calibration correction factor is between 0.9980 and 1.0020, it will be considered negligible and a correction factor will not be used.

(10) The Calibration Correction Factor may be reverified as necessary by the Engineer.

 This procedure is used to determine the maximum specific gravity (Gmm) of uncompacted asphalt paving mixtures.  This procedure determines the specific gravity of a “voidless” mixture of the aggregate and asphalt binder.  The maximum specific gravity procedure may be performed on either a loose sample of the mix or on previously compacted mixture, which has been reheated and broken apart, to facilitate removal of trapped air in the mixture.

The most important reason for knowing the maximum specific gravity of a paving mixture is to aid in calculating the percentage of air voids (VTM) in lab compacted specimens and/or in the final compacted mixture.  As was explained in Section 3, Mix Design, asphalt pavements must include a certain percentage (by volume) of air spaces or voids.  These spaces perform important functions and are significantly related to the performance and service life of the completed pavement.

Rice tests will be performed by both the Contractor and the Department on all mix samples. This procedure will be performed in conjunction with Gyratory testing on all asphalt mixes, along with binder content and gradation analysis. (An example of the maximum specific gravity determination worksheet is illustrated in Section 11.)

7.14.1  Sampling
Refer to REDUCTION OF SAMPLES TO TESTING SIZE, Section 7.5.6 of this Manual

7.14.2  Procedure

(A) Mix, quarter and select sample as described in Reduction of sample Sizes for testing. Weigh 2000 - 2500 grams of mix into a covered container.

(B) Cure sample in container in oven for 30 mins. not to exceed 1 hour at 290°F to 300°F (143-149°C).

(C) Spread mix uniformly in a large flat pan.  Thoroughly break up the mix and cool to ambient temperature using care not to fracture the mineral particles, so that the particles of the fine aggregate portion are not larger than ¼ inch(6.4 mm).  A portable electric fan shall be used to speed the cooling process.

(D) Place the entire amount of the sample in appropriate container (bowl, pot, or flask) and weigh.  Add water at 77°F (25°C) until the sample is covered approximately 2-3”(50-75 mm).  A few drops of a liquid detergent, to act as a wetting agent, may be added to the water to facilitate the release of entrapped air.

(E) Remove entrapped air by subjecting the contents of the container to a partial vacuum of 30 mm Mercury, ± 1mm, absolute pressure for 15 minutes.  The residual pressure of the container shall be measured by a manometer attached independently to the container.  The container and contents  shall be continuously shaken by a mechanical device in order to assist the removal of air bubbles.
 

(E1) Bowl or Pot -- Suspend the bowl or pot and contents in 77°F (25°C) water for 10 minutes.  Maintain water temperature of 77° ± 2°F (25°±1°C)  by adding hot or cold water, or more preferably by using a small submergible heater.  Weigh suspended sample.

(E2) Flask -- Place flask and contents in 77° ±2°F (25°±1°C)  water bath for 10 minutes.  Remove and fill flask to “fill line” with water at 77° ±2°F (25°±1°C).   Weigh filled flask.


(F) Drain water from sample, decanting water through a paper towel or 0.075 mm sieve to prevent loss of fine particles.

(G) Spread sample in a tared pan in front of an electric fan to speed evaporation and remove surface moisture.  The dry back pan may be lined with newspaper to speed up moisture removal.  After the pan is visibly dry, weigh at 15-minute intervals, and when the loss in mass is less than 0.5 g for this interval, the sample may be considered to be surface dry.  The procedure shall be accompanied by intermittent stirring of the sample.  Conglomerations of mix shall be broken up by hand.  Care must be taken to prevent loss of particles of mix.  The above dry back procedure shall be conducted on the first four samples tested during initial JMF production.  After that, the dry back may only be conducted on every eighth sample thereafter.  For those samples not checked for water pickup, the dry back correction factor shall be calculated based on the moving average difference for the previous four dry back tests.

(H) Calculate the maximum specific gravity (Gmm) of the test sample to three decimal places (x.xxx).

Where:
A = Weight in grams of samples in air before vacuum
               B = Weight in grams of surface dry sample in air after vacuum
C = Weight in grams of sample in water after vacuum

(I) If 2 consecutive QA/QC Rice Test Specific Gravity results check outside the acceptable limits of precision, the QA Supervisor will designate one of the retained mix samples for the Contractor to cool to ambient air temperature for a period of 3 days, to then reheat to 280°F (138°C) in an oven and to quarter for testing and determine the maximum specific gravity calibration factor (GmmCF).  The GmmCF will be used, by QA only, to determine the reheated maximum specific gravity.  Determine the maximum specific gravity calibration factor, GmmCF, to use in comparing the Gmm of an unreheated sample to the Gmm of a reheated sample.  The GmmCF will be considered accurate for the entire production of a particular mix design, but may be repeated at the discretion of the Contractor or the Engineer.

Note: If the GmmCF is between 0.9980 and 1.0020, it will be considered negligible and will not be used.

(J) Determine the corrected Gmm for reheated samples. (QA calculations only )

7.15     SPECIFIC GRAVITY OF COMPACTED ASPHALT MIXTURES (AASHTO T 166 or ASTM 6752)
This test procedure is used to determine the bulk specific gravity (Gmb) of compacted asphalt mixtures, including either Roadway cored samples, Gyratory specimens or other compacted specimens.  The bulk specific gravity of Gyratory specimens is used in the density-voids analysis in the mix design process and in field testing of the mixture.  The specific gravity of cored pavement samples is used for comparison with the Density Control Specific Gravity (Gmm) for density compliance purposes.

7.15.1  Equipment

• Balance sensitive to 0.1 gram and capacity of 5 kilograms or more.
• Wire basket of No. 4 mesh screen or other suitable means of suspending sample in water.
• Water Bath - For immersing the specimen in water while suspended under the balance, equipped  with an overflow outlet for maintaining a constant water level.

7.15.3  Sampling Compacted Asphalt Mix Pavement from Roadway
Samples taken from the compacted pavement shall have a minimum surface measurement of 6” (152 mm) in diameter, and shall extend the full depth of the course being placed.  The sample shall be cut in such manner as not to disturb the sample density and transported on a smooth surface sufficient to retain the shape of the pavement sample.  Placing a sheet of non-slick paper on the existing pavement ahead of the spreader facilitates removal of the cut sample. All roadway compacted core samples (both QC and QA samples) shall be transported to the proper QC lab by the Contractor.

7.15.4  Procedure

A.  Dry weight of sample - Allow all surface moisture to evaporate from the specimen and to cool to room temperature of 77° ± 1.8°F (25°±1°C). Weigh and record dry weight  (A).
B.  Suspend each specimen in water at 77° ± 1.8°F (25°±1°C) for 3 to 5 minutes and record immersed weight. (C).
C.  Remove the specimens from the water, surface dry by blotting with a damp cloth towel, and determine the surface-dry weight (B).
D. Calculate the roadway core bulk gravity of the test specimens as follows:

Where:
A = Weight in grams of the dry specimen in air.
B = Weight in grams of the saturated surface dry specimen.
C = Weight in grams of the specimen in water.

E.  Report Gmb of pavement samples on form QA/QC-5.

7.16 TENSILE STRENGTH RATIO (TSR) TEST (AASHTO T 283 - MODIFIED)

This procedure covers the preparation of specimens and measurement of diametral tensile strength resulting from the effects of saturation and accelerated water conditioning of asphalt mixtures in the laboratory.  The results are used to predict the long-term stripping susceptibility of the asphalt mixtures and to evaluate the effects of anti-stripping additives.

7.16.1  Frequency

1. The Contractor shall prepare one set of test specimens to be tested by QC personnel at the QC mix design or field lab site.

2. The 150 mm Superpave Gyratory Compactor specimens shall have a void content (VTM)  of 7.0 +/- 0.5%, except S 4.75mm mixes shall be compacted to a VTM of 13.0 +/- 0.5%.

3. The Gmm determined during the mix design process will be used to determine the VTM of the compacted specimens.

4. The compacted specimens must be tested on a test press meeting the requirements of AASHTO T 283 Modified.

5. Specimens will be tested in accordance with the latest procedures in AASHTO T 283 Modified.  The test data shall be submitted to the Asphalt Design Engineer on Form M&T 612 (QMS-2) along with all other required mix design data and forms for approval.

1. Contractor will sample, test, and furnish TSR results to the Engineer within 7 calendar days after beginning production of each new mix design.

1. When a change is made in the non-strip additive source or dosage of any mix design unless otherwise approved by the Engineer.
    (In this case, TSRs shall be performed by QC personnel and approved by the Engineer prior to production of any mix to the project)
2. When deemed necessary by the Engineer

2. 150 mm specimens shall have a voids in the total mix (VTM )of 7.0 +/- 0.5%. QC tested TSR specimens shall be retained at the QC lab for five (5) calendar days commencing the day the samples are tested or until disposal permission is given by QA personnel, whichever occurs first.

3. Contractor will prepare an additional set of specimens and submit these within 5 calendar days of obtaining the mix sample to the QA Lab for testing.

4. Along with these compacted specimens, the Contractor shall furnish 5000 grams of loose mix from the same sample. QA will perform Rice Test on approximately 2000 grams of loose mix. If QA results are within 0.025 of QC results, QA will use QC results to compute VTM.  If QA results exceed this 0.025 tolerance, the remaining loose mix will be tested jointly by QA and QC to determine the correct Gmm(Rice Test) to use.

5. If the QC’s first production TSR fails to meet the minimum TSR specification requirements, but does not exceed the individual  test control limit for that mix type, the contractor will immediately resample.  The Contractor will then compact 2 more sets of specimens for testing. The process specified in steps 1 thru 3 above shall be repeated.  If the first production TSR exceeds the applicable individual test control limits , production of that mix design will cease immediately and shall not resume until approval is given by the Engineer.

6.     If the QC's second production TSR results fail to meet the minimum TSR specification  requirement, the Contractor's production of that mix design shall be stopped until field tests indicate the minimum requirement has been met and approved by the Engineer.

7.  If any of the above QC test results meet minimum requirement but the corresponding QA results fail to meet the minimum requirement and the QA results are not more than 5% below minimum with no visual stripping in either set, the results will be considered reasonably acceptable. The determination of visual stripping will be by QA personnel. Any other failing results will be considered unacceptable, unless otherwise approved by the Engineer.

1. The Contractor may elect to sample and prepare one set of specimens to be tested jointly by QA/QC personnel at a mutually agreed upon lab site with the results being determined within 7 calendar days of beginning normal production. TSR testing will not be performed until both parties are present.

2. 150 mm specimens will have a (VTM ) of 7.0+/-0.5%. QA shall verify void content  prior to testing.

3. The Contractor will also furnish 5000 grams of loose mix from the  same sample the TSR sample was taken. This mix will be tested jointly to determine the Maximum Specific Gravity (Gmm).

4. If the first production QC TSR fails to meet the minimum TSR requirements for that mix type but does not exceed the individual TSR test control limits, or is not reasonably  acceptable as described in No.6 below, the Contractor shall immediately resample and compact another set of specimens for testing. The process specified in steps 1 thru 3 above shall be repeated.  If the first production QC TSR fails to meet the minimum and exceeds the individual  test control limits for that mix type, the contractor will immediately stop production of that mix design and not resume until given approval by the Engineer.

5.        If the QC's second production TSR results fail to meet the minimum requirement, or is not reasonably acceptable as determined in No.6 below, the Contractor's production of that mix shall be stopped until field tests indicate the minimum requirement has been met,   and approved by the Engineer.

6. When results fail to meet minimum requirements and the results are not more than 5% below minimum with no visual stripping, the results will be considered reasonably acceptable. The determination of visual stripping will be by QA personnel. Any other failing results will be considered unacceptable, unless otherwise approved by the Engineer.

7. If OPTION 2 is used, the specimens must be tested on a recording test press, or a test press that will maintain the peak load reading after the specimen has broken.

1. After the minimum specification requirement is met on plant produced mix, QA will obtain random verification TSR test samples as deemed necessary.  QA personnel will prepare, test, and furnish results of these verification TSR samples to QC within 7 calendar days of the sample being taken.

2. If verification TSR results do not meet the minimum requirement and the results are not more than 5% below minimum with no visual stripping the results will be considered reasonably acceptable.

3. If two consecutive randomly sampled and tested verification TSRs fail to meet the minimum requirement, or is not reasonably acceptable as described above, production of that mix design shall cease until additional TSR tests indicate the minimum requirement has been met and  approved by the Engineer.

4. At this point, the Contractor and QA personnel will sample, prepare and test all non-production TSR specimens together.  At this same time, another sample of the same mix will be taken and submitted by QA to the M & T Asphalt Design Engineer for TSR testing. Test results of the QA/QC TSR will be forwarded to the Design Engineer as soon as results are known. If QA/QC test meets the minimum requirement, the Design Engineer may elect not to perform the test on the split portion of this sample.

5. The Contractor has the option of preparing extra sets of specimens at any time for his own QC testing.  If he does so, these results will be forwarded to the QA Lab within 24 hours of the results being known.

(A) Laboratory prepared specimen

1. Prepare at least eight (8) gyratory test specimens using the same blend as the mix design and the Optimum Binder Content.
2. Compaction of the test specimens shall be completed using a gyratory compactor.
3. The compaction temperature for the specimen should be that recommended for the type Binder being used. (See Gyratory Test Procedures for temperatures)
4. The mixture shall be compacted to a height of 95 +/- 5 mm with 7.0 ± 0.5 % air voids, except type S 4.75mm which will be compacted to a void content of 13.0 +/- 0.5%. This level of voids may be obtained by adjusting the amount of mix placed into the gyratory compactor mold.
5. All other factors should remain constant during the compaction process.

(B) Plant Mixed prepared specimen

1. Obtain an 180 lb.(82 kg) sample of plant mix from a truck in accordance with Section 7.5 of this Manual.
2. Prepare at least 8 gyratory test specimen using plant-produced mix meeting the individual control limits of the applicable Job Mix Formula.
3. Compaction of the test specimen shall be by the use of a gyratory compactor.
4. Compaction temperature for the specimen should that recommended for the type Binder being used. (See Gyratory Test Procedures for temperatures)
5. The mixture shall be compacted to a height of 95 +/- 5 mm with 7.0 ± 0.5 % air voids, except type S 4.75 mm mixes which will be compacted to a void content of 13.0 +/-0.5%.  This level of voids may be obtained by adjusting the amount of mix placed in to the gyratory compactor mold. All other factors remaining constant during compaction process.

A. Allow the compacted specimens to cool to room temperature  77 °F (25 °C) .
B. Determine the height of each specimen from the Gyratory Printout.
C. Determine the Bulk Gravity (Gmb) of each specimen using the methods described in AASHTO T 166 Modified (“Bulk Specific Gravity of Compacted Asphalt Mixtures Using Saturated Surface-Dry Specimens”).
D. Determine the Rice Specific Gravity (Gmm) on an uncompacted sample of the same mix using the methods described in AASHTO T 209 Modified
E. Calculate Percent Air Voids (VTM) for each specimen.  All test specimens must have 7.0 +/- 0.5% voids, except S 4.75mm mixes must have 13.0 +/- 0.5% voids.
F. Sort specimens into two (2) subsets so that the average air voids of the two subsets are approximately equal.
G. Allow specimens to remain at room temperature for 24 hours before proceeding.

One subset will be tested dry and the other will be moisture conditioned before testing.

NOTE:  Both subsets should be tested at the same time.

DRY Subset

A. The three dry specimens should be stored at room temperature 77 °F (25 °C) until testing.
B. Before testing, the dry specimens shall be placed in heavy-duty leak-proof plastic containers.
C. The specimens shall then be placed in a 77 °F (25 °C) water bath for four (4) hours.
D. Remove the specimens from the water bath and place in the testing head. Care must be taken so that the load will be applied along the diameter of the specimen.
E. Apply the load to the specimen using the loading jack until the specimen fails.  The rate of loading should be constant at 2 in/min.(50 mm/min.). Record load at failure.
F. Remove the specimen from the machine and pull apart at the break in the specimen.  Inspect the interior surface for stripping and record the observations.

WET Subset

A. Place a specimen in the vacuum container supported above the container bottom by a spacer.
B. Fill the container with distilled water at 77 °F (25 °C) so that the specimen has at least one inch of water above its surface.
C. Apply a vacuum of 10 - 26 in. Mercury (13 - 67 kPa) for a short time to saturate the specimen.
D. The acceptable percent saturation is between 65 - 80 %,

E. Determine Percent Water Pickup by comparing SSD mass after saturation with SSD mass before Saturation.
F. Determine the Percent Saturation by comparing the volume of absorbed water after saturation with the volume of air voids before saturation.  Preferred saturation is approximately 72%.

1. If the Percent Saturation is between 65 - 80 %, proceed to the next step.
2. If the Percent Saturation is less than 65 %, repeat above steps a - c using more vacuum and/or time.
3. If the Percent Saturation is above 80 %, the specimen should be considered damaged and will be discarded.  Repeat above steps A - C on the remaining specimens using less vacuum and/or time.

G. After all of the wet subset has been correctly saturated, place the specimens in a water bath at 140 °F (60 °C) for 24 ± 1 hours.
H. Remove the specimens from the 140 °F (60 °C) water bath and place in another water bath at 77°F (25 °C) for 4 hours.  Dry sub set should also be put in a 77oF (25oC) water bath at this time.
I. Remove the specimens from the water bath and place in the testing head. Care must be taken so that the load will be applied along the diameter of the specimen.
J. Apply the load to the specimen using the loading jack until the specimen fails. The rate of loading should be constant at 2 in/min. (50 mm/min.). Record load at failure.
K. Remove the specimen from the machine and pull apart at the break in the specimen.  Inspect the interior surface for stripping and record the observations.
L. Visually compare the fractured surfaces of the wet and dry sub set of the pills and record these results.

The Tensile Strength Ratio (TSR) is a percentage of the median wet tensile strength compared to the median dry tensile strength. Median will be figured by the two remaining specimens after discarding the  high and low specimens of each subset.  It will be calculated in accordance with AASHTO T 283 (Mod.) and more specifically as required by the use of the Departments M&T 612 form and reported to the nearest 0.1 percent.

7.17      QMS CALCULATIONS

NOTE:  In order to monitor mix quality, several calculations are necessary other than those covered within specific test procedures.  This section covers those type calculations.

7.17.1  Significant Decimals

The following rule of “rounding off” shall be used in all calculations. When the digit to be dropped (one digit beyond significant digit) is 0, 1, 2, 3 and 4, the preceding digit will not change.  When the digit to be dropped (one digit beyond significant digit) is 5, 6, 7, 8 and 9, the preceding digit will be increased by one.
NOTE: Do not round one digit beyond the significant decimal prior to rounding to the specified significant decimal.

Example:   Significant decimal of 0.001
2.3954 will be 2.395 (Drop the 4 and leave the 5 as is)
2.3955 will be 2.396 (Drop the last 5 round up the first 5 to a 6)
 

NOTE:  Each internal calculation used to arrive at a final combined result shall be calculated to at least one decimal place farther than the specified significant decimal.

7.17.2  Voids in Total Mix (VTM) Calculation (AASHTO T 269)

 The air voids determination is a relationship between maximum specific gravity (Gmm) and Gyratory bulk specific gravity (Gmb).  Air voids can be calculated for both Gyratory compacted specimens and roadway compacted pavements (cores).

a.   Gyratory Compacted Specimens:

 Voids in Total Mix (VTM) for each specimen shall be calculated using the:
  - actual sample maximum specific gravity (Gmm) and the
  - actual bulk specific gravity (Gmb @ Ndes) of each specimen as follows:

Note: The VTM of the 3 specimens will be averaged to determine the VTM for the total sample.

b.   Roadway Compacted Specimens (cores):

In place pavement air voids for each core sample may be calculated using the:
- last moving average Gmm for that day’s mix and the
- pavement core sample Gmb as follows:

• Air voids shall be calculated to the nearest 0.1 percent (x.x).

7.17.3  Voids in Mineral Aggregate (VMA) Calculation
The VMA are the intergranular void spaces between the aggregate particles in a compacted paving mix that includes the air voids and the effective asphalt binder content, expressed as a percent of the total volume.

VMA is calculated using the combined aggregate bulk specific gravity (Gsb) from the mix design (unless field tests verify the Agg. Gsb to be significantly different than the mix design), the percent binder (Pb) from the field test, and the average specimen bulk specific gravity (Gmb @ Ndes) as follows:

 If field tests verify the combined aggregate bulk specific gravity (Gsb) has changed such that it will result in a 0.5% or more change in the calculated VMA, the revised field Gsb shall be used to calculate VMA.  Calculate VMA to the nearest 0.1 percent (x.x).

7.17.4  Voids Filled with Asphalt Binder (VFA) Calculation
The voids filled with asphalt binder determination is a relationship between the voids in the mineral aggregate (VMA) and the voids in the total mix (VTM).  The voids filled with asphalt binder (VFA) is a determination of the percentage of the voids in the mineral aggregate (VMA) that is filled with effective asphalt (not including absorbed asphalt).

VFA is calculated using:
- the sample VMA computed as indicated in 7.17.3 (from QA/QC-1SP) above and
- the average VTM as indicated in 7.17.2 (from QA/QC-1SP) above

The following formula is a “field” formula to be used by both QC and QA personnel to calculate % VFA.

 Calculate VFA to the nearest 1 percent (x%).

7.17.5  Aggregate Effective Specific Gravity (Gse) Calculation

The Aggregate Effective Specific Gravity (Gse) includes all void spaces in the aggregate particles except those that absorb asphalt.

Calculate the Gse value by using:
- actual individual Rice Test Gmm (until a moving average is established-See Note below)
- Pb from the field test,and
- Mix Design Gb

• Note : Once a Gmm moving average is established, calculate Gse using above formula and :

- the last Gmm moving average.
      - Pb from the field test , and
      - Mix Design Gb,

Calculate Gse to three decimal places (x.xxx).
 

7.17.6  Dust / Effective Binder (P0.075 / Pbe) Ratio Calculation
The Dust /Eff. Binder ratio is a relationship between the Effective (non-absorbed) Asphalt Binder(Pbe) and the amount of the P0.075  in   the mix. The Superpave Mix Design Specification requirement is 0.6 to 1.4 for all mixes.

A field calculation for the dust /eff. binder ratio (Number 1 below) can be used to check the Plant produced mix. If however, the results of this field calculation are outside the Mix Design tolerances, the Mix Design Calculation (Number 2 below) shall be used to obtain a more accurate result.

1.  FIELD CALCULATION FOR DUST/EFF. BINDER RATIO:

The field calculation for determining the dust/eff. binder ratio in the field produced mix uses the actual percent passing the Washed 0.075 mm Sieve, the Pb from the asphalt binder control method and the percent binder absorption from the Mix Design.

2.  MIX DESIGN CALCULATION FOR DUST/EFF. BINDER RATIO:

The calculation for the mix design dust proportion combines two other calculations. First the Absorbed Binder Content must be determined using the Effective Gravity (Gse) from the JMF, until a moving average is established. Also, the Mix Design aggregate bulk specific gravity (Gsb) is used unless the material percentages have changed enough to warrant recalculating the Gsb.

Note: Calculate the Dust / Binder ratio to the nearest 0.1 percent (X.X)

7.17.7  Percent Gmm @ Nini Calculation
The Percent Gmm @ Nini is a number representing resistance of a mix to compaction. It is a relationship between the specified number of gyrations that is placed upon the mix and the known Gmm. This is a percentage calculation of the volume of asphalt mix filling the known volume in the gyratory compaction mold.

Percent Gmm @ Nini is calculated using the actual Gmm (Rice) test from the current mix test and the results of the calculated individual Gmb @ Nini from the QA/QC-1 form.  The following formula is to be used by both QC and QA personnel to calculate % Gmm @ Nini.
%Gmm @ Nini =    (Average Gmb@Nini / Actual test Gmm) X 100
%Gmm @ Nini is expressed in percentage form and shall be calculated to the nearest 0.1 percent (x.x).

7.17.8  Percent Gmm @ Ndes Calculation
The %Gmm @ Ndes  is a percentage number related to the VTM in the mix at gyrations. It is the percentage that the mix bulk specific gravity achieved at the specified number of gyrations (Ndes) is of the known Gmm of the mix. This calculation is not normally made to calculate the VTM in the mix since the VTM is normally calculated in accordance with Section  7.17.2 based on actual test results on SGC specimens. However, they are related as follows.

7.17.9  Percent Gmm @ Nmax Calculation
The Percent Gmm @ Nmax is a number representative of the final in-place compaction of a mix. It is a relationship between the specified number of gyrations that is placed upon the mix and the known Gmm. This is a percentage calculation of the volume of asphalt mix filling the known volume in the gyratory compaction mold. This test is performed at mix verification and periodically there after.

Percent Gmm @ Nmax is calculated using the actual Gmm (Rice) test from the current mix test and the results of the average Gmb @ Nmax from the QA/QC-1A form.  The following formula is to be used by both QC and QA personnel to calculate % Gmm @ Nmax.

% Gmm @ Nmax is expressed in percentage form and shall be calculated to the nearest 0.1 percent (x.x).

7.18   ALLOWABLE RETESTING FOR MIX DEFICIENCIES

The Contractor may elect to resample and retest for plant mix deficiencies when individual QC test(s) exceed one or more of the mix property target(s) by more than the tolerances indicated below.  The retesting shall be performed within 10 days of the initial test results.  Retesting shall be approved by the Engineer prior to being performed and shall be in accordance with the Department’s “GUIDELINES FOR RETESTS OF PLANT MIX DEFICIENCIES”.  Retests for any mix deficiency other than as listed below will not be allowed unless otherwise permitted by the Engineer.  Acceptance of the mix in question will be based on the retest data in accordance with Article 105-3.  The Department reserves the right to direct the Contractor to resample and retest at any time or location.

• VTM   ---------- by more than +/- 2.5% from the target
• % Binder-------- by more than +/- 1.0% from the target
• VMA ----------- by more than minus 2.0% from minimum specification limit
• 0.075 mm sieve-- by more than +/- 3.0% from the target
• 2.36  mm sieve--- exceeds specification mix design limits and one or more of the above tolerances are also exceeded.
• TSR-------------  by more than minus 15% from minimum specification limit

1. QA Supervisor confirms QC test results as soon as possible after knowledge of it.  This will include testing of DOT’s split portion of sample and/or referee sample.
2. QA Supervisor verbally notifies Contractor, Division, and Resident Engineer of possible removal due to deficiency, as soon as possible.
3. QA Supervisor advises Contractor of option to retest and gives deadline for response.
4. Resident Engineer to follow up immediately with written documentation, including deadline.
5. Sampling for retests will be by coring in-place mix from roadway.
6. The increment of mix in question will be divided into sub-lots for testing.
7. If retests are requested by the Contractor, Resident Engineer will evaluate his proposal as soon as possible and give response.  Time frame for test, number of tests, type tests, location of samples, etc., must meet NCDOT minimum requirements.
8. If retests are allowed, QC sampling and testing shall be in DOT representative’s presence.  Testing shall be performed at the appropriate Contractor’s QC Lab, unless otherwise specified by the Engineer.
9. Contractor must also provide DOT with adequate QA samples
10. Retest results will be evaluated by Division, through consultation with Pavement Construction Section.  Contractor will be notified of decision in writing by Resident Engineer.

1. Increment tonnage in question shall be located by station numbers on the roadway.
2. Increment tonnage in question shall be divided into approximate equal sub-lots, unless otherwise approved.
3. Increment tonnage of 375 tons or more must be divided into 3 sub-lots
4. Increment tonnage of less than 375 tons will be divided into a minimum of 2 sub-lots, unless directed otherwise by the Engineer
5.   All sub-lots shall be marked on the roadway by the Contractor. Each sub-lot shall be cored at one random location sufficiently to yield enough mix to perform a full set of tests (% Binder, Gradation, Gmb , Gmm , VTM, and in-place Voids) Only one set of samples will be allowed in each sub-lot , unless otherwise approved.
6.  The area from which the cores were taken shall be saw-cut to square up the area, all excess material removed and the area immediately cleaned, tacked, filled with hot asphalt mix of the same type and compacted to conform to the surrounding area by the Contractor to the Engineer’s satisfaction.
7.   Full depth cores must be satisfactorily separated by mix layer by the Contractor
8.   All necessary traffic control shall be the Contractor’s responsibility
9.  Core samples from the same sub-lot will be combined for testing, samples from different sub-lots shall not be combined for testing.
10.  QC test results shall be reported on standard QMS forms separately by sub-lot.  All QC test results must be immediately furnished to the QA Supervisor
11.  Department personnel shall be present during all sampling and testing.  All testing shall be performed by the QC personnel at the appropriate Contractor’s QC Lab, unless otherwise specified by the Engineer
12.  The average test results from asphalt mix accepted and allowed to remain in place shall be used in place of the original plant test results. This would include QMS Forms and Charts used for acceptance.
13.  The increment tonnage in question will be evaluated and may be accepted based on each sub-lot’s test results in accordance with Article 105-3 of the Standard Specifications

Quality Assurance (QA) is the Department’s  process of insuring that the Contractor’s QC process and testing is an accurate representation to insure the quality of the mix produced. This process applies to all materials that are split during QC and QA testing, including asphalt mix, RAP, and RAS.  Quality assurance will be accomplished in the following ways:

1. by conducting assurance testing of split samples obtained by the Contractor at a frequency equal to or greater than 5% of the quality control frequency;
2. by periodically observing sampling and testing procedures performed by the Contractor;
3.   by monitoring required control charts exhibiting test results of control parameters;
4. by directing the Contractor to take additional samples at any time and any location during production (in lieu of the next scheduled random sample for that increment);
5. by testing verification samples taken independently of the Contractor’s quality control samples at a frequency equal to or greater than 10% of the quality control sample frequency; and
6. by any combination of the above

The Engineer will conduct assurance tests on both split QC samples taken by the Contractor and verification samples taken by the Department. These samples may be the regular quality control samples or a sample selected by the Engineer from any location in the process, or verification samples taken at random by the Department.  The frequencies will be equal to or greater than those specified above. The Engineer may select any or all split samples for assurance testing. Results of QA tests (including verification tests) will be provided to the Contractor within 3 working days after sample has been obtained.

Differences between the Contractor’s and the Department’s split sample test results will be considered acceptable if within the following limits:

In addition to the preceding limits of precision, RAP samples must be within the % binder and gradation tolerances specified in Table 1012-2. (See Section 8 of this manual)

In the event comparison test results are outside the above limits of precision or the quality assurance test results or verification test results are either outside the individual test control limits or fail to meet specification requirements, the Engineer will immediately investigate the reason for the difference.  If the potential for a pavement failure is present, the Engineer may suspend production in accordance with Article 108-7 while the investigation is in progress.  The Engineer’s investigation may include, but not be limited to the following :

1.  Joint testing of any remaining split samples,
2.  Review and observation of the QC technician’s sampling and testing procedures,
3.  Evaluation and calibration of QC testing equipment, and/or
4.  Comparison testing of other retained quality control samples.

The Engineer will periodically witness the sampling and testing being performed by the Contractor.  If the Engineer observes that the sampling and quality control tests are not being performed in accordance with the applicable test procedures, the Engineer may stop production until corrective action is taken.  The Engineer will promptly notify the Contractor of observed deficiencies, both verbally and in writing.  The Engineer will document all witnessed samples and tests.

7.19.1  Verification Sampling and Testing Guidelines for Plant Mix
 The FHWA Regulations for Quality Control/Quality Assurance programs utilized for acceptance of asphalt pavements contain specific requirements for verification sampling and testing.  These must be adhered to in order to conform to the FHWA requirements. The Engineer will obtain verification samples for testing independent of the Contractor’s quality control process.  These samples will be split for testing by the Department and optional testing by the Contractor.  The Department’s current guidelines related to mix testing for verification purposes are as follows:

a.) 180 Lb. (82 kg) sample taken at any point during production at either the plant site or on the roadway.  All samples shall be split in accordance with Section 7.5 of this manual with the appropriate portion being given to the Contractor for optional testing.  The referee portion of the sample shall be stored at the QA Lab until it is either needed for testing or determined that it is no longer needed.
b.) Sample shall be taken by either certified NCDOT Level I or Level II plant technician.
c.) Samples taken at a rate of 10% of the required number of QC samples
d.) Verification samples will be in addition to the 5% minimum required QA comparison test of the QC split samples.
e.) Verification test results shall be within the individual test control limits and meet all applicable specification requirements when compared to the appropriate JMF. If not, the QA Supervisor will investigate the reason(s) for the difference.  This investigation may include but not be limited to :

1)  Checking of QC and QA testing and weighing equipment to ensure accuracy
2)  Comparison of the QA verification test results to the results for QC split portion of  the verification sample,
3)  QA testing of the split portion of the QC sample,
4)  Retesting of QC prepared gyratory specimens of the QC sample and/or the split portion of verification samples,
5)  Testing of referee portion of verification samples by the NCDOT M&T Lab, and/or
6)  Further directed sampling and testing of the mix in question in accordance with procedures specified in Section 7.18.2 of this manual. (Sub-Lot procedures)

f.) These sampling requirements are per mix design per plant.
g.) Verification samples will be assigned numbers by the QA Supervisor.  These numbers will be per mix design per plant and will correspond to the QC sample numbers.  The number will begin with the year, followed by a dash, followed by the corresponding QC sample number for that 750 ton lot, followed by a “V”.  For example: 05-1V if from 1st QC lot,
05-12V if from 12th QC lot, etc.
h.) Documentation of verification sampling and testing will be on the appropriate QMS forms which will be maintained by the QA Supervisor in the appropriate plant file.  These samples shall be logged by the QA Supervisor on Form QA-3. If the verification sample results validate the QC results for the same 750 ton lot, these verification results shall be plotted on the Contractor’s QC charts for information.  Should the verification results and/or the investigation by the QA Supervisor determine the QC results for that same lot to be incorrect, the correct results as determined by the Department shall replace the QC applicable QC data on the control charts.
i.) Verification TSR tests shall be conducted at the frequency and in accordance with the procedures specified in Section 7.16.1 of this manual.

The Engineer will base final acceptance of the mix on the results of random testing made on split samples during the assurance process, verification samples, retests (if applicable) and validation of the Contractor’s quality control process as outlined above and in Subarticle 609-5(C) and Article 609-6.

Quality Control test results that have been proven incorrect, for any reason, will be replaced with the correct test results and related data as determined by the Engineer.  Quality Assurance comparison test results, verification test results, referee test results, and retest results may be used in making this determination.  Any one of these or none of these results may be used as the correct results.  Just because the referee sample is tested does not mean that its results will automatically be used.  The data and the extent of the replaced data is left to the discretion of the Engineer.  Assistance in making this decision is available through the Pavement Construction Section.