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.

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 such that the one having the largest opening is on top and those with 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 mean 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.

7.7.1 General

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 27.  For accurate determination of material finer than the No. 200 (75-um) sieve, the washing procedure from AASHTO T 11 Modified must be used.

C.  The Contractor has the option to either perform washed gradations on all QC gradation tests on recovered aggregate or perform limited washed gradations as outlined as next.  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 No. 200 (75-um) sieve and all other sieves with a correction factor of 1.0 percent or more.  The correction factor for the No. 200 (75-um) 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 No. 200 (75-um), 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 gradation differences should be included in calculating a new moving average correction factor.

D. QA washed gradations will be performed on all aggregate samples 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 No. 200 (75-um) sieve will be to the nearest 0.1 percent (x.x).  (Refer to the Significant Decimals Chart in Section 7.15.1 of this Manual.)

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 Wire-Cloth Sieves for Testing Purposes (AASHTO M 92).

C. 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.

D. Oven - The oven shall be capable of maintaining a uniform temperature of 230 ± 9°F (110 ± 5°C).  A hot plate may be satisfactory if turned to a lower temperature and the aggregate stirred to prevent local overheating.

E. Container - The container (bowl) shall be of sufficient size to contain the sample covered with water and to permit vigorous agitation without any loss of material or wash water.

F. Wetting Agent - any dispersing agent such as liquid dishwashing detergent which will promote separation of the fine material.

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 testing shall be approximately 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, a minimum of  300 grams.  In no case, however, shall the fraction retained on any sieve at the completion of the sieving operation weigh more than 4 g/in²  (7 kg/m²) of sieving surface.

Note:  This amounts to 200 grams for the usual 8 in. (203 mm) diameter sieve. The amount of material retained on the critical sieve may be regulated by:
(1)  Placing a sieve with larger openings than the overloaded sieve, above that 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 the amount indicated in the following table:

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.

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. Whenever the amount of material finer than the No. 200 (75-um) sieve is to be determined by washing, first test the sample in accordance with the steps for AASHTO T 11 Modified through the final drying operation.  Then, dry sieve the sample as required by AASHTO T 27.

The next 4 steps shall be followed whenever a washed gradation is performed:

A. Dry the sample at 230 ± 9°F (110 ± 5°C) to a constant weight and determine the weight to the nearest 0.1 gram.

B. The test sample, after being dried and weighed, shall be placed in a container and covered with water. Add a sufficient amount of wetting agent to assure a thorough separation of the material finer than the No. 200 (75-um) sieve from the coarser particles. The contents of the container shall be agitated vigorously and the wash water immediately poured over a nest of two sieves consisting of a No. 10 or No. 16 (2.00 or 1.18 mm) sieve over a No. 200 (75-um) sieve. The use of a large spoon to stir and agitate the aggregate in the wash water has been found satisfactory.

C. The agitation shall be sufficiently vigorous to result in the complete separation of all particles finer than the No. 200 (75-um) sieve from the coarse particles and bring them into suspension in order that they may be removed by decantation of the wash water. Care should be taken to avoid, as much as possible, the decantation of the coarse particles of the sample. The operation shall be repeated until the wash water is clear.

D. All material retained on the nested sieves shall be returned to the container. The washed aggregate in the container shall be dried to a constant weight at 230 ± 9°F (110 ± 5°C) and weighed to the nearest 0.1 gram.

E. If the test sample has not been tested as by according to the steps above, dry it to a constant weight at 230 ± 9°F (110 ± 5°C) and determine the weight to the nearest 0.1 gram.

F. The aggregate shall then be sieved over sieves of various sizes required by the specification covering the material to be tested, including the No. 200 (75-um) sieve. Nest the sieves in order of decreasing size of opening from top to bottom and place the sample on the top sieve.

G. Agitate the sieves by hand or by mechanical apparatus for a period of 10 minutes.  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.

Note:   It is important to limit the quantity of material on a given sieve so that all particles have opportunity to reach sieve openings a number of times during the sieving operation. If overloading of a sieve is suspected, the sieving adequacy should be checked as per the requirements of AASHTO T 27, Sections 8.3 and 8.4.

H. Determine the weight of each size increment by weighing on a balance conforming to the requirements of Equipment Section 7.7.3.A.  The total weight of the material after sieving should check closely with the original weight of the sample placed on the sieves.

I. If the sample has previously been tested by AASHTO T 11 Modified, add the weight finer than the No. 200 (75-um) sieve determined by that method to the weight passing the No. 200 (75-um) sieve by dry sieving of the sample.

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.

7.8.1  General

A. 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.

B. 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 nominal maximum aggregate size.   Regardless of the size of the aggregate, the procedure for making an aggregate moisture determination is basically the same.

A. Balance - the balance shall have sufficient capacity, be readable to 0.1 percent of the sample mass, or better, and conform to the requirements of AASHTO M 231.

B. Oven - a ventilated oven of appropriate size capable of maintaining a uniform temperature of  230 ± 9°F (110 ± 5°C).
(An electric hot plate with an appropriately sized pan would also be considered suitable).

7.8.4 Procedure

A. Determine the weight of the aggregate sample to the nearest 0.1 gram.  [Wet Weight].

B. Dry the sample thoroughly in the sample container by means of the selected source of heat, exercising care to avoid loss of any particles. Very rapid heating may cause some particles to explode, resulting in loss of particles. Use a controlled temperature oven when excessive heat may alter the character of the aggregate, or where more precise measurement is required. If a hot plate is used, stir the sample during drying to accelerate the operation and avoid localized overheating.

C. Determine the weight of the dried sample to the nearest 0.1 gram after it has cooled sufficiently not to damage the balance.  [Dry Weight].

D. Determine the moisture content of the sample.  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.  The results of this procedure are used to determine compliance of the gradation of the recovered aggregates with applicable specification requirements.

7.9.1  General

A.  Washed gradations will be performed on the recovered aggregate from the mix only.  Dry gradations are acceptable to be run on RAP.

B.  The Contractor has the option to either perform washed gradations on all QC gradation tests on recovered aggregate or perform limited washed gradations as outlined next. QC washed gradations can 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 No. 200 (75 um) sieve and all other sieves with a correction factor of 1.0 percent or more.  The correction factor for the No. 200 (75 um) 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 No. 200 (75 um) 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 No. 200 (75 um) 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).

A.  Balance - the balance shall have sufficient capacity, be readable to 0.1 percent of the sample weight or better, and conform to AASHTO M 231.

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 AASHTO M 92.

C. Oven - the oven of appropriate size, capable of maintaining a uniform temperature of 230 ± 9°F (110 ± 5°C).

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.

E. Wetting Agent - any dispersing agent, such as liquid dishwashing detergents, that will promote
 separation of the fine materials.

7.9.3 Sample
 The sample shall consist of the entire sample of aggregate obtained according to either AASHTO    T 164 or T 308 Modified.

7.9.4 Procedure

A. Dry the sample at 230 ± 9°F (110 ± 5°C) to a constant weight.

B. The test sample, after being dried and weighed, shall be placed in a container and covered with water. Add a sufficient amount of wetting agent to assure a thorough separation of the material finer than the No. 200 (75 um) sieve from the coarser particles. The contents of the container shall be agitated vigorously and the wash water immediately poured over a nest of two sieves consisting of a No. 10 or No. 16 (2.00- or 1.18-mm) sieve over a No. 200 (75 um) sieve. The use of a large spoon to stir and agitate the aggregate in the wash water has been found satisfactory.

C. The agitation shall be sufficiently vigorous to result in the complete separation of all particles finer than the No. 200 (75 um) sieve from the coarse particles and bring them into suspension in order that they may be removed by decantation of the wash water. Care should be taken to avoid, as much as possible, the decantation of the coarse particles of the sample. The operation shall be repeated until the wash water is clear.

D. All material retained on the nested sieves shall be returned to the container. The washed aggregate in the container shall be dried to constant weight at 230 ± 9°F (110 ± 5°C) and weighed to the nearest 0.1 gram.

E. The aggregate shall then be sieved over sieves of various sizes required by the specification covering the mixture, including the No. 200 (75 um) sieve. Nest the sieves in order of decreasing size of opening from top to bottom and place the sample on the top sieve. Agitate the sieves by hand or by mechanical apparatus for a period of 10 minutes.

F.  Record the weight of material passing each sieve and retained on the next and the amount passing the No. 200 (75 um) sieve. The summation of these various weights must check the dried weight after washing within 0.2 % of the total weight. 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%.

7.9.5 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 No. 200 (75 um) 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.

1.  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 the ignition furnace.  This test data must be included with all other QC or QA test results for each sample tested.

2.  EXTRACTION METHOD: (AASHTO T 164) 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 the extraction test is not for checking Binder content, an ash correction is not required.  QC ash correction samples will be tested by the Contractor’s QC Lab and QA ash correction samples will be tested by the Division QA Lab.  Ash corrections shall be calculated to the nearest 0.1 percent (x.x).

A.  General
This procedure can be used for the quantitative determination of asphalt binder content of hot-mixed paving mixtures by ignition of the asphalt binder at temperatures that reach the flashpoint of the binder in a furnace.  This method does not require the use of solvents.  The aggregate remaining after burning can be used for sieve analysis using AASHTO T 30 Modified.

This procedure may involve hazardous materials, operations, and equipment.  This procedure does not purport to address all of the safety problems associated with its use.  It is the responsibility of the user of this procedure to consult and establish appropriate safety and health practices.
 The asphalt binder in the paving mixture is ignited using the furnace equipment applicable to this procedure.  The asphalt binder content is calculated as the difference between the initial weight of the asphalt paving mixture and the weight of the residual aggregate, the calibration factor, and moisture content.  The asphalt binder content is expressed as weight percent of moisture-free mixture.

(B)  Equipment

(1) Ignition Furnace - a forced air ignition furnace that heats the sample by either convection or direct infrared (IR) irradiation method.  The convection type furnace must be 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 weight of the sample and provide for the input of a calibration factor for aggregate loss.  The furnace shall provide a printed ticket with the initial specimen weight, per minute specimen weight loss, temperature compensation, calibration 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 weight loss does not exceed 0.01 percent of the total sample weight 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 Baskets - baskets 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.

Note:  Screen mesh with maximum and minimum openings of No. 8 (2.36 mm) and No. 30 (600 um), respectively, has been found to perform well.

(3)  Catch Pan - a pan of sufficient size to hold the sample baskets so that aggregate particles and melting asphalt binder falling through the screen mesh are caught.

(4)  Oven - an oven capable of maintaining a temperature of 257 ± 9°F (125 ± 5°C).

(5)  Balance - a balance having sufficient capacity and conforming to the requirements of AASHTO M 231 Class G2 for weighing the sample and baskets.

(6) Safety Equipment - this equipment should include:  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 baskets during the cooling period.

(7) Miscellaneous Equipment – this equipment should include:   a pan larger than the sample baskets for transferring samples after ignition, spatulas, bowls, and wire brushes.

C. Sample

(1)  Obtain samples of aggregate in accordance with AASHTO T 2.  Obtain samples of freshly produced hot-mix asphalt in accordance with Section 7.5 of this Manual.  Obtain samples of asphalt binder in accordance with AASHTO T 40.  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 ± 9°F (125 ± 5°C) until it is workable.  Do not leave the sample in the oven for an extended period of time.

(2) The size of the test sample shall be governed by the nominal maximum aggregate size of the mixture and shall conform to the weight requirements shown below.  When the weight 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 500 grams greater than the minimum recommended specimen weight.

Note:  Large samples of fine mixes tend to result in incomplete ignition of the binder.

Sample Size for Aggregate

Nominal Maximum Aggregate Size (mm)	Minimum Weight Of Specimen (grams)
37.5 mm	4000 g
25.0 mm	3000 g
19.0 mm	2000 g
12.5 mm	1500 g
9.5 mm	1200 g
4.75 mm	1200 g

(3) The following three calibration factor methods may be affected by the type 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 occurs during procedure (3)a. then procedure (3)b. shall be followed.  If after that procedure is performed, it also gives a calibration factor of >0.5, or a significant gradation change occurs, procedure (3)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.

(3)a. 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 weight requirement shown in Section 7.10.1(B).

(4) Samples must be preheated in a 257 ± 9°F (125 ± 5°C) oven for a minimum of 25 minutes.  Do not preheat the sample baskets.

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

(6.1) For the convection-type furnace, set the ignition oven temperature to 1072°F (578°C).

(6.2) For the direct IR irradiation-type furnace, set the ignition burn profile to OPTION 2.

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

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

(9) Evenly distribute the aggregate in the sample baskets (do not place any aggregate on the  catch pan).  Ensure that the sample is level in the baskets.

(10) Weigh and record the total weight of 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 the door, and verify that the sample weight (including basket) is correct.

(13) Press the Start button.

(14) Burn the aggregate sample for 40 minutes and then press Stop.  Determine the percentage of burn loss from the printout of test.

(15) Perform an aggregate gradation according to AASHTO T 27 on samples immediately after allowing to cool to room temperature.  Compare to the original gradation in (3)a.(5).

(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 the combined calibration factor is <0.5%, use that calibration factor.  If the combined calibration factor is >0.5%, or if there is a significant gradation change in the aggregate, perform (3)b. below.

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

(3)b. Blended Aggregate Samples

(1) Prepare two blended aggregate samples.  The size of the 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 257 ± 9°F (125 ± 5°C) oven for a minimum of 25 minutes.  Do not preheat the sample baskets.

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

(5) Burn both samples for 40 minutes and determine the average percent burn loss in accordance with (3)a.(6) through (3)a.(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 factors.

(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 (3)b.(4) to evaluate the amount of aggregate breakdown.

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

(3)c. Asphalt Mix Samples

(1) Prepare two correction factor mix samples at the design asphalt binder content for the applicable mix.

(2) The size of the samples shall be in accordance with section 7.10.1(B).

(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 30 Modified.  The washed gradation shall fall within the individual test limits for that mix type.

(4) The freshly mixed specimens may be placed directly in the sample baskets.  If allowed to cool, the samples must be preheated in a 257 ± 9°F (125 ± 5°C) oven for a minimum of 25 minutes.  Do not preheat the sample baskets.

(5) Burn mix samples at 1000°F (538°C) in accordance with 7.10.1(G) of this procedure.

(6) Perform a gradation analysis according to AASHTO T 30 Modified on the residual aggregate from one of the burnt samples.  Compare this gradation to the gradation of the unburned, “blank” specimen to evaluate the amount of aggregate breakdown.

(7) Once all of the correction factor specimens have been burned, determine the measured asphalt binder contents for each sample by calculation or from the printed tickets.

(8) If the difference between the measured asphalt binder contents of the two samples exceeds 0.15 percent, repeat the two tests and, from the four tests, discard the high and low results. Determine the correction-factor from the two remaining results. Calculate the difference between the actual and measured asphalt binder contents for each sample. The correction-factor is the average of the differences expressed in percent by weight of the HMA.

(9.1) For the convection-type furnace, if the correction-factor exceeds 1.0 percent, lower the test temperature to 900 ± 8°F (482 ± 5°C) and repeat test. Use the correction-factor obtained at 900 ± 8°F (482 ± 5°C) even if it exceeds 1.0 percent.

(9.2) For the direct IR irradiation-type furnace, the DEFAULT burn profile should be used for most materials. The operator may select burn-profile OPTION 1 or OPTION 2 to optimize the burn cycle. OPTION 1 is designed for samples that require a large aggregate correction factor (greater than 1.0 percent) - typically very soft aggregate. OPTION 2 is designed for samples that may not burn completely using the DEFAULT burn profile.

(10.1) For the convection-type furnace, the temperature for testing HMA samples shall be the same temperature selected for testing correction factor samples for the furnace being used.

(10.2) For the direct IR irradiation-type furnace, the burn profile for testing HMA samples shall be the same burn profile selected for testing correction factor samples.

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

D. Procedure

(1.1) For the convection-type furnace, preheat the ignition furnace to 1000°F (538°C) or as determined in the calibration procedure.

(1.2) For the IR direct irradiation-type furnace, use the same burn profile as used during the calibration procedure.

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

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

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

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

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

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

(8) Open the chamber door and place the sample baskets in the furnace.  Close the chamber door and verify that the sample weight (including the baskets) displayed on the furnace scale equals the total weight recorded in Section 7.10.1(G)(6) within ±5 grams.  Differences greater than 5 grams or failure of the furnace scale to stabilize may indicate that the sample baskets 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.

Note:  The furnace temperature will drop below the set point when the door is opened, but will recover with the door closed and when ignition occurs.  Sample ignition typically increases the temperature well above the set point, depending on sample size and asphalt binder content.

(9) Allow the test to continue until the stable light and audible stable indicator indicate the test is complete (the change in weight does not exceed 0.01 percent for three consecutive minutes). Press the start/stop button. This will unlock the sample chamber and cause the printer to print out the test results.
Note: An ending weight loss percentage of 0.02 may be used with QA Supervisors approval when aggregates that exhibit an excessive amount of loss during ignition testing are used.  The precision and bias statement was developed using 0.01 percent.  Both precision and accuracy may be adversely effected by using 0.02.

(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 chamber door, remove the sample baskets, and allow to cool to room temperature (approximately 30 minutes).

(12) Gradation:

a. Allow the specimen to cool to room temperature in the sample baskets.

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

c. Perform the gradation analysis according to AASHTO T 30 Modified.

E. Report

Always report the corrected asphalt binder content, calibration factor, temperature compensation factor (if applicable), total percent loss, sample weight, 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. General

This procedure is used for the determination of the amount of asphalt binder in a paving mixture by cold solvent extraction.  The aggregate recovered from this procedure can be used for sieve analysis using AASHTO T 30 Modified.

B. Equipment

(1) Oven - an oven capable of maintaining a temperature of 257 ± 9°F (125 ± 5°C).

(2) Pan(s) - flat and of suitable size to warm test samples.

(3) Balance - a balance having sufficient capacity and conforming to the requirements of AASHTO M 231 Class G2 for weighing the sample and baskets.

(4) Hot Plate - electric, with an adjustable heating rate.

(5) Graduated Cylinders - one with either an 1000 or 2000 ml capacity.  An optional 100 ml capacity graduated cylinder can also be used for ash correction.

(6) Ignition Dish - for ash correction samples with at least a 125 ml capacity.

(7) Dessicator - of sufficient size to hold the Ignition Dish during cooling.

(8) Extraction Apparatus - consisting of a bowl matching the requirements of AASHTO T 164, Section 10, Figure 1, and an apparatus that will revolve the bowl at controlled variable speeds up to 3600 rpm.  The speed may be controlled manually or with a preset speed control.  There should be a beaker, or other suitable container to catch the extract solution for binder content determination.  The apparatus should preferably have explosion-proof features and installed in a hood or with an effective exhaust system to provide ventilation.

(9) Filter Rings - made of felt or paper, to fit the rim of the extraction bowl.

(10) Solvent - Trichloroethylene or any NCDOT approved Biodegradable Solvent.  All local, State, and Federal regulations shall be followed when hauling, using, storing, and discarding extractants and rinse water.  The Materials Safety Data Sheet should be adhered to closely to avoid fires and explosions.

C. Sample

(1) Obtain samples in accordance with Section 7.5 of this Manual.

(2) 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 ± 9°F (125 ± 5°C) until it is workable.  Do not leave the sample in the oven for an extended period of time.

(3) The size of the test sample shall be governed by the nominal maximum aggregate size of the mixture and shall conform to the weight requirements shown below.  When the weight 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 500 grams greater than the minimum recommended specimen weight.

D. Procedure

(1) Record the test sample weight to the nearest 0.1 gram.

(2) Place the sample evenly around the extraction bowl.

(3) 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.  Place the bowl containing the test portion and solvent in the centrifuge.  Dry the filter ring to a constant weight in an oven 257 ± 9°F (125 ± 5°C) and fit it around the edge of the bowl.  Clamp the cover on the bowl tightly and place a beaker or other container under the drain to collect the extract.

(4) Start the centrifuge revolving slowly and gradually increase the speed to a maximum of 3600 rpm until solvent ceases to flow from the drain.  Allow the machine to stop, add 200 ml. of solvent and repeat the above procedure.  Use sufficient 200 ml solvent additions (not less than three) so that the extract is not darker than a light straw color.  Collect the extract and the washings in an appropriate container for ash correction determination.

(5) Carefully transfer the filter ring and all of the aggregate in the centrifuge bowl into a tared metal pan.  Dry the material to a constant weight in an oven at 257 ± 9°F (125 ± 5°C).  The weight of the extracted aggregate (W2) is equal to the weight of the contents in the pan minus the initial dry weight of the filter ring.  Brush off any mineral matter adhering to the surface of the filter ring and add it to the extracted aggregate for sieve analysis.

(6) 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, Method A for procedure of determining Ash Correction.  To obtain the total ash weight of a mix sample, multiply the percent ash by the total weight of the mix sample.

(7) Calculate the % Binder (Pb) in the sample as follows:

E. Report

Report the 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.

7.11.1  General

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 Modified), binder content test (AASHTO T 308 Modified) and maximum specific gravity (AASHTO T 209 Modified or ASTM 2041 Modified or ASTM D 6857) will be performed in conjunction with the Superpave Gyratory Compactor field test.

(B) VTM which is determined by use of the Superpave Gyratory Compactor field test (Gmb) and maximum specific gravity test (Gmm) 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 utilizing the 150 mm Superpave Gyratory Compactor test method.

(D) Height, pressure, and external angle calibrations are required to be performed prior to initially using the Gyratory Compactor.  Periodic calibrations for height, pressure, internal angle and rotation shall be performed at minimum frequencies specified in Section 7.2.2.

A. Superpave Gyratory Compactor - An electrohydraulic or electromechanical compactor with a ram and ram heads as described in Section 4.3. The axis of the ram shall be perpendicular to the platen of the compactor. The ram shall apply and maintain a pressure of 600 ± 18 kPa perpendicular to the cylindrical axis of the specimen during compaction. The compactor shall tilt the specimen molds at an external angle of 22 ± 0.35 mrad (1.25 ± 0.02°) or an average internal angle of 20.2 ± 0.35 mrad (1.16 ± 0.02°), determined in accordance with AASHTO PP 48. The compactor shall gyrate the specimen molds at a rate of 30.0 ± 0.5 gyrations per minute throughout compaction.

B. Specimen Height Measurement and Recording Device - When specimen density is to be monitored during compaction, a means shall be provided to continuously measure and record the height of the specimen to the nearest 0.1 mm during compaction once per gyration.

C. Specimen Molds - Specimen molds shall have steel walls that are at least 7.5 mm thick and are hardened to at least a Rockwell hardness of C48. The initial inside finish of the molds shall have a root mean square (rms) of 1.60 ?m or smoother. Molds shall have an inside diameter of 149.90 to 150.00 mm and be at least 250 mm high at room temperature.

D. Ram Heads and Mold Bottoms - Ram heads and mold bottoms shall be fabricated from steel with a minimum Rockwell hardness of C48. The ram heads shall stay perpendicular to their axis. The platen side of each mold bottom shall be flat and parallel to its face. All ram and base plate faces (the sides presented to the specimen) shall be flat to meet the smoothness requirement in
 Section 4.2 and shall have a diameter of 149.50 to 149.75 mm.

E. Thermometers - Armored, glass, or dial-type thermometers with metal stems for determining the temperature of aggregates, binder, and HMA between 10 and 232°C.

F. Balance - A balance meeting the requirements of M 231, Class G 5, for determining the mass of aggregates, binder, and HMA.

G. Oven - A forced-draft oven, thermostatically controlled, capable of maintaining any desired temperature setting from room temperature to 350°F (176°C) within ±5°F (±3°C), for heating aggregates, binder, HMA, and equipment as required. The oven shall be capable of maintaining the temperature required for mixture conditioning in accordance with R 30.

H. Miscellaneous Items - Flat-bottom metal pans for heating aggregates, scoop for batching aggregates, containers (grill-type tins, beakers, containers for heating asphalt), large mixing spoon or small trowel, large spatula, gloves for handling hot equipment, paper disks, mechanical mixer (optional), lubricating materials recommended by the compactor manufacturer.

A. Mix and quarter the sample material as described in “Reduction Of Samples To Testing Size”, in Section 7.5.6 of this Manual.  Weigh out the appropriate amount of mix to produce a compacted specimen height of 115 ± 5 mm at the desired number of gyrations.  In order to determine the approximate weight of uncompacted mix, the following formula may be used:

Note:  This formula will give a weight, which is an estimate only.  If it does not produce the proper specimen height, trial and error should be then performed to determine the desired target weight for the proper height (115 ± 5 mm).

B. 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.

C. 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 the 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.

A. Place three (3) 150 mm Gyratory mold assemblies in a 300 - 310° F (149 - 155°C) oven for a minimum of 30 minutes prior to estimated beginning of compaction.

B. Verify that the settings on the compactor are as required by the specific JMF.

C. Once the compaction temperature is achieved, remove a heated mold assembly from the oven. Place a paper specimen protection disc in the bottom of the heated gyratory compaction mold.

D. 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 the mix is too hot, allow sufficient time for it to cool to above the specified range before compacting.

E. Place the mold assembly with mix into the Gyratory compactor and apply 600 kPa of pressure to the mixture and introduce the 1.25° external angle.  Gyrate to the specified Ndes number of gyrations, which is given on the JMF.

F. Procedures outlined in steps C. through E. 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.

G. When the compaction is complete, remove the compaction angle and raise the gyratory ram.  Remove the mold assembly from the gyratory compactor.

H. Extrude the specimen from the mold assembly.  Most mixes can be extruded immediately after compaction, however, some mix types may need a cooling period of 5 - 10 minutes before complete extrusion of the specimen, to insure the specimens are not damaged.

I. Remove the 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.

J. 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).

K. Identify each sample by marking with the appropriate QC sample number and proper suffix (i.e. 02-1a, 02-1b, and 02-1c).

L. Determine bulk specific gravity (Gmb) using AASHTO T 166 or ASTM D 6752.

M. Determine the void content (VTM) of each specimen using the bulk lab specific gravity (Gmb) of each specimen and the actual maximum specific gravity (Gmm) determined from the maximum specific gravity using the formula given below and record the results.

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 the gyratory specimens.  Determine the Gyratory bulk specific gravity calibration factor, Gmb CF, to use in comparing the average Gmb of an unreheated compacted sample to the average Gmb of a reheated compacted sample.  The Gmb CF 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 Gmb CF 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:

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 steps:

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

2. This 200 lbs. (91 kg) sample shall be quartered into 4 approximate 50 lbs. (23 kg) samples.  These four samples shall be put into four sample bags, labeled as Gyratory Compactor calibration samples, including sampled date & 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 7.11.3. 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 Gyratory Calibration Correction Factor (GCCF) may be reverified as deemed necessary by the Engineer.

Report the entire test results of each gyratory specimen at both Nini and Ndes on the QA/QC-1 Form.  Report results to nearest 0.1 mm (x.x).
 

7.12    MAXIMUM SPECIFIC GRAVITY (Gmm) OF ASPHALT PAVING MIXTURES (AASHTO T 209 Modified, ASTM D 2041 Modified or ASTM D 6857)

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.

7.12.1  General

A. 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.

B. Maximum specific gravity tests will be performed by both the Contractor and the Department on all full test series 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.)

C. Two procedures are outlined here:

• In the Rice Test method (AASHTO T 209 Modified, ASTM D 2041 Modified), dry, loose mix is placed in a vacuum container (bowl, pot, or flask) and covered with water.  A vacuum is then applied to reduce the residual pressure in the vacuum container and remove entrapped air from the mixture.  After the vacuum is released, the sample and container are immersed in a water bath and the volume of the mix sample is determined.  From the mass-volume relationship, the maximum specific gravity of the asphalt mixture can be calculated.

• In the Vacuum Sealing Method (ASTM D 6857), dry, loose mix is placed inside a plastic bag which is then placed inside a second plastic bag.  The double-bagged sample is placed into a vacuum chamber which automatically seals the plastic bag with the sample inside.  The bags are then removed from the vacuum chamber and placed into a large water tank equipped with a balance for weighing the sample under water.  The bags are then cut open to allow water to enter the bag and surround the sample.  The underwater weight of the mixture can be measured and from the mass-volume relationship, the maximum specific gravity of the asphalt mixture can be calculated.

7.12.2  Standard Test Method for Theoretical Maximum Specific Gravity and Density of Asphalt Paving Mixtures
(AASHTO T 209 Modified & ASTM D 2041 Modified)

A. Equipment

(1) Vacuum Container (may be one of the following):

(a) Vacuum Bowl - a metal or plastic pot or bowl with a diameter of approximately 7 to 10.25 in. (180 to 260 mm) and a bowl height of at least 6.3 in. (160 mm) shall be equipped with a transparent cover fitted with a rubber gasket and connections for the vacuum lines. Both the bowl and cover should be sufficiently stiff to withstand the applied vacuum pressure without visibly deforming. The hose connections shall be covered with a small piece of fine wire mesh to minimize the loss of any fine material.

(b) Vacuum Flask - a thick-walled volumetric glass flask with a capacity of approximately 4000 ml, fitted with a rubber stopper with a connection for the vacuum line. The hose connection in the flask should be covered with a small piece of fine wire mesh to minimize the loss of any fine material.

(2) Balance - capable of being read to the nearest 0.1 gram. For the pot or bowl method, the balance shall be equipped with a suitable apparatus and holder to permit weighing the sample while suspended below the balance. The wire suspending the holder should be the smallest practical size to minimize any possible effects of a variable immersed length.

(3) Vacuum Pump or Water Aspirator - capable of evacuating air from the vacuum container to a residual pressure of 30 mm of Hg (4.0 kPa) or less. A suitable trap shall be installed between the vacuum vessel and vacuum source to reduce the amount of water vapor entering the vacuum pump.

(4) Residual Pressure Manometer or Calibrated Absolute Pressure Gage - this manometer or calibrated absolute pressure gage shall be used to confirm the specified pressure is applied to the container and shall be capable of measuring residual pressure to 30 mm of Hg (4.0 kPa) or less. It is to be connected at the end of the vacuum line using an appropriate tube and either a “T” connector on the top of the container or by using a separate opening (from the vacuum line) in the top of the container to attach the hose.

(5) Vacuum Gage or Manometer - suitable for measuring the vacuum being applied at the source of the vacuum. This device can be connected directly to the vacuum source or be in the vacuum line close to the source.

(6) Thermometers - calibrated liquid-in-glass thermometers of suitable range with subdivisions and maximum scale error of 0.9°F (0.5°C), or any other thermometric device of equal accuracy, precision, and sensitivity shall be used. Thermometers shall conform to the requirements of Specification ASTM E 1.

(7) Water Bath - capable of maintaining a constant temperature of 77 ± 1.8°F (25 ± 1°C). The water bath must be large enough for entirely immersing the suspended vacuum container and equipped with an overflow outlet for maintaining a constant water level.

(8) Bleeder Valve - attached to the vacuum train to facilitate both the adjustment of the vacuum being applied to the vacuum vessel and the slow release of vacuum pressure.

(9) Mechanical Agitation Device - capable of applying a gentle but consistent agitation of the sample. This device shall be equipped with a means of firmly anchoring the container so that it does not move on the surface of the device.  Additionally, the device must be equipped with an electric timer with a minimum 15-minute capacity.

(10) Oven - an oven of appropriate size, capable of maintaining a uniform temperature of  230 ± 9°F (110 ± 5°C).

(11) Miscellaneous Items - pans of sufficient size for heating and cooling samples; spatulas and/or scoops for transferring mix samples.

B. Sample

(1) Mix, quarter and select sample as described as described in “Reduction Of Samples To Testing Size”, in Section 7.5.6 of this Manual. Weigh 2000 - 2500 grams of mix into a covered container.

(2) Mix design samples shall be cured and dried in an oven at 275 ± 9°F (135 ± 5°C) for a minimum of two hours, or as appropriate to match the mix design procedure being used. Longer drying time may be necessary for the sample to achieve a constant mass (mass repeats within 0.1 percent). For plant produced mix, samples need to be dried to a constant mass (mass repeats within 0.1% for consecutive 15-minute weighings) at a temperature of 221 ± 9°F (105 ± 5°C).

C.  Procedure

(1) Spread the mix uniformly in a large flat pan.  Thoroughly break up the mix using care not to fracture the mineral particles, so that the particles of the fine aggregate portion are not larger than 1/4 inch (6.3 mm). Cool to ambient temperature using a portable electric fan to speed the cooling process.

(2) Place the entire amount of the sample in the appropriate container (bowl, pot, or flask) and weigh.  Add water at 77°F (25°C) until the sample is covered completely.

(3) Remove entrapped air by subjecting the contents of the container to a partial vacuum of 27.5 ± 2.5 mm Hg (3.7 ± 0.3 kPa), absolute pressure for 15 ± 2 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.

(4) Gradually release the vacuum pressure using the bleeder valve and proceed with one of the following determinations:

(a) Bowl or Pot - Suspend the bowl or pot and contents (without the lid) in 77°F (25°C) water for 10 ± 1 minutes.  Maintain the water temperature at 77 ± 1.8°F (25 ± 1°C) by adding hot or cold water, or more preferably by using a small submergible heater.  Record the weight of the suspended sample.

(b) Flask - Place the flask and contents in a 77 ± 1.8°F (25 ± 1°C) water bath for 10 ± 1 minutes.  Remove and fill the flask to “fill line” with water at 77 ± 1.8°F (25 ± 1°C). Record the weight of the filled flask.

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

where,   A = weight of oven-dry sample in air, grams
                       C = weight of sample in water after vacuum, grams

Note:   For all mixes containing any aggregate having a water absorption of greater than 1.5%, the following dryback procedure must also be performed.  The Department reserves the right to require a dryback procedure for any maximum specific gravity test.  For a listing of quarries requiring the dryback procedure, contact the Materials and Tests Unit Asphalt Laboratory at (919) 329-4060.

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

(7) Spread the sample in a tared pan in front of an electric fan to speed evaporation and remove surface moisture.  The dryback pan may be lined with newspaper to speed up moisture removal.  After the pan is visibly dry, begin weighing it 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 dryback 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.

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

where,
A = weight of oven-dry sample in air, grams
B = weight of surface dry sample in air after vacuum & dryback, grams
C = weight of sample in water after vacuum, grams

(9) 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.

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

D. Report
Maximum Specific Gravity results should be determined using the QA/QC-2 Form.  If the Dryback Procedure is required, report the Rice Dryback Correction Factor data on the QA/QC-4 Form.  Report the final Maximum Specific Gravity value (Gmm) on the QA/QC-1 Form.

A. Equipment

(1) Balance - capable of being read to the nearest 0.1 gram. The balance shall be equipped with a suitable apparatus and holder to permit weighing the sample while suspended below the balance. The wire suspending the holder should be the smallest practical size to minimize any possible effects of a variable immersed length.

(2) Water Bath - with minimum dimensions to accommodate completely submerging the specimen in water while suspended and equipped with an overflow outlet for maintaining a constant water level.

(3) Vacuum Chamber - with a minimum 1.25 hp (0.93 kW) pump capable of evacuating a sealed and enclosed chamber to 5.6 mm Hg. The chamber shall be large enough to seal samples as large as 2000 grams. The device shall automatically seal the plastic bag and exhaust air back into the chamber in a controlled manner to ensure proper conformance of the plastic to the asphalt mixture. The air exhaust and vacuum operation time should be calibrated at the factory prior to initial use. The air exhaust system should be calibrated to bring the chamber to atmospheric pressure in 80 to 150 seconds after the completion of the vacuum operation. The vacuum system should be provided with a latch to control the chamber door opening.

(4) Absolute Vacuum Measurement Gage - a gage independent of the vacuum sealing device which can be placed directly inside the chamber to verify vacuum performance and the chamber door sealing condition of the unit. The gage shall be capable of reading pressure to 3 mm Hg (3 TORR).

(5) Plastic Bags - Internal Bags shall have random channels built into at least one side to aid in evacuating all air from the sample. The internal bags shall have a minimum opening of 12 in. (305 mm) and maximum opening of 13.5 in. (340 mm).  The External Bags shall have a minimum opening of 14.75 in. (375 mm) and a maximum opening of 15.5 in. (394 mm). Each bag shall be of material that will not adhere to asphalt film, puncture resistant, and impermeable to air. The bags shall have a minimum thickness of 0.004 in. (0.100 mm) and maximum thickness of 0.006 in. (0.152 mm). The combined apparent specific gravity of the two bags shall be provided by the manufacturer.

Note: Care should be taken to protect the bags during storage. Refer to the manufacturer’s procedures for safe handling and storage of bags.

(6) Holder - for water displacement of the sample having no sharp edges.

(7) Filler Plates - to position the sample and the bags in the same plane as the sealing bar.

(8)  Bag Cutting Knife or scissors - for opening bags during testing.

(9) Thermometers - calibrated liquid-in-glass thermometers of suitable range with subdivisions and maximum scale error of 0.9°F (0.5°C), or any other thermometric device of equal accuracy, precision, and sensitivity shall be used. Thermometers shall conform to the requirements of Specification ASTM E 1.

B. Sample

(1) Mix, quarter and select sample as described as described in “Reduction Of Samples To Testing Size”, in Section 7.5.6 of this Manual. Weigh 2000 - 2500 grams of mix into a covered container.

(2) Mix design samples shall be cured and dried in an oven at 275 ± 9°F (135 ± 5°C) for a minimum of two hours, or as appropriate to match the mix design procedure being used. Longer drying time may be necessary for the sample to achieve a constant mass (mass repeats within 0.1 percent). For plant produced mix, samples need to be dried to a constant mass (mass repeats within 0.1% for consecutive 15-minute weighings) at a temperature of 221 ± 9°F (105 ± 5°C).

C.  Procedure

(1) Spread the mix uniformly in a large flat pan.  Thoroughly break up the mix using care not to fracture the mineral particles, so that the particles of the fine aggregate portion are not larger than 1/4 inch (6.3 mm).

(2) Cool to ambient temperature using a portable electric fan to speed the cooling process.  Record the weight of the dry specimen in air as (B).

(3) Set the vacuum sealing machine according to the manufacturer’s recommendation to create at least a 5.6 mm Hg absolute pressure inside the chamber.

Note: For asphalt mixtures that contain polymers, the vacuum setting should be held at 99% of absolute vacuum for a minimum of five minutes. Follow the manufacturer’s recommendations when performing tests on polymerized mixtures.

(4)  If after examining the bags there are no punctures or cuts, weigh one internal and one external bag.

(5) Record the combined weight of the two bags as (A).

(6)  Place the entire sample in the internal bag. Ensure that none of the sample is lost during this transfer.

(7)  Place the empty external bag inside the vacuum chamber.

(8)  Place the internal bag containing the sample with the channel side (rough side) down into the external bag. The rough side is placed under the sample to protect against trapped air and to help in the evacuation of the air from the bag.

(9)  Spread the sample so that it is evenly distributed within the internal bag. Do not spread the sample by squeezing down on the sample from outside the bag.

(10) Push in the opening of the internal bag away from the opening of the external bag to prevent the opening of the internal bag from being sealed. Make sure that the opening of the internal bag is flat and that the opening is not restricted by a fold in the bag.

(11) Place the opening of the external bag over the seal bar, making sure the internal bag is not over the seal bar.

(12) Close the chamber door.

(13) Allow the vacuum chamber to remove the air from the chamber and the plastic bag. The vacuum chamber shall automatically seal the bag once the air is removed.

(14) Exhaust air into the chamber until the chamber door opens indicating atmospheric pressure within the chamber. The chamber door latch can be used to avoid automatic opening of the door after completion of the test.

(15) Remove the sealed sample from the vacuum chamber.  Perform a visual inspection of the bag and listen for any leaks.

Note: While transferring the sample to the water bath, handle the sealed sample with extreme care. Avoid any impacts with hard surfaces that could cause leaks in the bag and allow air to enter the sample.

(16) Immediately transfer the sample to the water bath at 77°F (25°C) equipped with a scale.

(17) Submerge the sealed bag containing the sample completely under water and cut open the external bag all the way across the top, leaving approximately 1 in. (25 mm) intact. When cutting the bag, make certain the sealed portion of the bag is at least 2 in. (50 mm) under water and remains under water throughout the entire process.

(18) Open both bags with your fingers and hold open for 10 to 15 seconds to allow the water to flow in the bags.

(19) Reach into the bag with one hand and for 40 to 60 seconds, break down all clumps with your fingers until there are no clumps larger than the maximum aggregate size used in the mixture. With the other hand, fold the opening of the bag around the arm that is used for breaking up the sample.

(20) Secure the sample over a suspended scale and allow the weight to stabilize. Make certain the bags or the suspension equipment is not contacting the sides or the bottom of the water tank and that no part of the plastic bag is breaking the water surface at any time.

(21) Allow the scales to stabilize, and record the weight of the mix and bags underwater as (C).

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

D. Report
The Maximum Specific Gravity data may be recorded on the manufacturer’s data collection table or similar form.  Report the final Maximum Specific Gravity value (Gmm)on the QA/QC-1 Form.

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.

7.13.1 General
Two procedures are outlined here:

• In the Saturated Surface-Dry Specimen method (AASHTO T 166), a compacted specimen is manually weighed in air, under water, and at the saturated surface-dry condition to determine the specimen’s bulk specific gravity (Gmb).

• In the Vacuum Sealing Method (ASTM D 6752), a compacted specimen is placed inside a plastic bag which is then automatically sealed in a vacuum chamber.  The sealed bag can then be placed into a large water tank equipped with a balance for weighing the sample under water.  From this weight-volume relationship, the bulk specific gravity of the specimen can be calculated.

A. Equipment

(1) Balance - capable of being read to the nearest 0.1 gram and equipped such that an apparatus can be suspended from the center of scale pan.

(2) Suspension Apparatus - the balance shall be equipped with a suitable apparatus and holder to permit weighing the sample while suspended below the balance. The wire suspending the holder should be the smallest practical size to minimize any possible effects of a variable immersed length. The suspension apparatus shall be constructed to enable the container to be immersed to a depth sufficient to cover it and the test sample during weighing. Care should be exercised to ensure no trapped air bubbles exist under the specimen.

(3) Thermometers - calibrated liquid-in-glass thermometers of suitable range with subdivisions and maximum scale error of 0.9°F (0.5°C), or any other thermometric device of equal accuracy, precision, and sensitivity shall be used. Thermometers shall conform to the requirements of Specification ASTM E 1.

(4) Water Tank - for immersing the specimen in water while suspended under the weighing device, equipped with an overflow outlet for maintaining a constant water level.

B. Sample

(1) Test specimens may be either laboratory molded from hot asphalt mixtures or cored samples from compacted roadway pavement.

(2) Samples taken from the compacted pavement shall have a minimum surface measurement of 6 in. (150 mm) in diameter, and shall extend the full depth of the course being sampled and tested. NCDOT specifications prohibit the placing of a separator medium such as a sheet of non-slick paper on the existing pavement ahead of the spreader to facilitate removal of the cored sample.  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.

(3) Specimens shall be free from foreign materials such as seal coat, tack coat, foundation material, soil, etc.

(4) If needed, specimens may be separated from other pavement layers by sawing or other suitable means. Care should be exercised to ensure sawing does not damage the specimens.

C. Procedure

(1) Dry weight of sample :

(a) Laboratory Molded Specimen - Allow all surface moisture to evaporate from the specimen and to cool to room temperature of 77 ± 9°F
(25 ± 5°C).  Weigh and record the dry weight (A).

(b) Cored Sample - Allow all surface moisture to evaporate from the specimen, all internal moisture to drain from the sample, and allow sample to cool to room temperature of 77 ± 9°F (25 ± 5°C).  Weigh specimens at 10-min. intervals until the mass loss is less than 0.5 gram for the interval.  Record the dry weight  (A).

(2) Suspend each specimen in water at 77 ± 1.8°F (25 ± 1°C) for 4 ± 1 minutes and record the immersed weight (C).

(3) Remove the specimen from the water, surface dry by blotting with a damp cloth towel as quickly as possible, and determine the surface-dry weight  (B).

Note: Damp is considered to be when no water can be wrung from the towel.  Each specimen shall be immersed and weighed individually.

(4) Calculate the specimen bulk gravity (Gmb) of the test specimen as follows:

where,
A = weight of the dry specimen in air, grams
B = weight of the saturated surface-dry specimen, grams
C = weight of the specimen in water, grams

D. Report

Report the Bulk Specific Gravity (Gmb) of laboratory-molded samples on form QA/QC-1.
Report the Bulk Specific Gravity (Gmb) of cored samples on form QA/QC-5.

Note:  All weights will be obtained when specimen and water temperatures are at 77 ± 1.8°F (25 ± 1°C).

7.13.3  Bulk Specific Gravity of Compacted Hot-Mix Asphalt Using Automatic Vacuum Sealing Method (ASTM D 6752)

A. Equipment

(1) Balance - capable of being read to the nearest 0.1 gram. The balance shall be equipped with a suitable apparatus and holder to permit weighing the sample while suspended below the balance. The wire suspending the holder should be the smallest practical size to minimize any possible effects of a variable immersed length.

(2) Water Tank - with minimum dimensions to accommodate completely submerging the specimen in water while suspended and equipped with an overflow outlet for maintaining a constant water level.

(3) Vacuum Chamber - with a minimum 1.25 hp (0.93 kW) pump capable of evacuating a sealed and enclosed chamber to a minimum pressure of 10 mm Hg in less than 60 s, when at sea level. The chamber shall be large enough to seal samples of 150 mm wide by 350 mm long by 150 mm thick. The device shall automatically seal the plastic bag and exhaust air back into the chamber in a controlled manner to ensure proper conformance of the plastic to the asphalt specimen. The air exhaust and vacuum operation time should be calibrated at the factory prior to initial use. The air exhaust system should be calibrated to bring the chamber to atmospheric pressure in 80 to 120 s, after the completion of the vacuum operation. The vacuum system should be provided with a latch to control the chamber door opening.

(4) Absolute Vacuum Measurement Gage - a gage independent of the vacuum sealing device which can be placed directly inside the chamber to verify vacuum performance and the chamber door sealing condition of the unit. The gage shall be capable of reading pressure to 3 mm Hg (3 TORR).

(5) Plastic Bags - bags used with the vacuum device shall be one of the two following sizes. The smaller bags shall have a minimum opening of 9.25 in.
(235 mm) and maximum opening of 10.25 in. (260 mm) and the larger bags shall have a minimum of 14.75 in. (375 mm) and a maximum opening of 15.5 in. (394 mm). The bags shall be of plastic material that will not adhere to asphalt film, is puncture resistant, capable of withstanding sample temperatures of up to 70°C, is impermeable to water, containing no air channels for evacuation of air from the bag. The bags shall have a minimum thickness of 0.004 in.
(0.100 mm) and maximum thickness of 0.006 in. (0.152 mm). The apparent specific gravity for the bags shall be provided by the manufacturer for each bag shipment. The apparent specific gravity provided for each size bag shall account for the different sample weights and bag weight used during testing.

Note: Care should be taken to protect the bags during storage. Refer to the manufacturer’s procedures for safe handling and storage of bags.

(6) Holder - for water displacement of the sample having no sharp edges.

(7) Specimen Sliding Plate - used within the chamber for reduction of friction on the plastic bags.

(8)  Bag Cutting Knife or Scissors - for opening bags during testing.

(9) Thermometers - calibrated liquid-in-glass thermometers of suitable range with subdivisions and maximum scale error of 0.9°F (0.5°C), or any other thermometric device of equal accuracy, precision, and sensitivity shall be used. Thermometers shall conform to the requirements of Specification ASTM E 1.

B. Sample

(1) Test specimens may be either laboratory molded from hot asphalt mixtures or cored samples from compacted roadway pavement.

(2) Samples taken from the compacted pavement shall have a minimum surface measurement of 6 in. (150 mm) in diameter, and shall extend the full depth of the course being sampled and tested. NCDOT specifications prohibit the placing of a separator medium such as a sheet of non-slick paper on the existing pavement ahead of the spreader to facilitate removal of the cored sample.  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.

(3) Specimens shall be free from foreign materials such as seal coat, tack coat, foundation material, soil, etc.

(4) If needed, specimens may be separated from other pavement layers by sawing or other suitable means. Care should be exercised to ensure sawing does not damage the specimens.

C. Procedure

(1) Dry weight of unsealed sample:

(a) Laboratory Molded Specimen - Allow all surface moisture to evaporate from the specimen and to cool to room temperature of 77 ± 9°F
(25 ± 5°C).  Weigh and record the dry weight (A).

(b) Cored Sample - Allow all surface moisture to evaporate from the specimen, all internal moisture to drain from the sample, and allow sample to cool to room temperature of 77 ± 9°F (25 ± 5°C).  Weigh specimens at 10-min. intervals until the mass loss is less than 0.5 gram for the interval.  Record the dry weight  (A).

(2) Select an appropriate size bag. For all 4 in. (100 mm) diameter samples and samples with 6 in. (150 mm) diameter and less than 2 in. (50 mm) thickness, use the bag with smaller opening size as specified in (A-5) above. For 6 in. (150 mm) samples with greater than 2 in. (50 mm) thickness, use the larger opening size bags as specified in (A-5) above. For samples that weigh more than 5500 grams or abnormally shaped samples, use the manufacturer’s recommendation for appropriate bag size and configuration.

(3) Inspect an appropriate size bag for holes or irregularities, record the bag weight and place a bag inside the vacuum chamber on top of the specimen sliding plate.

(4) Gently open the bag and place the specimen in the plastic bag on top of the specimen sliding plate, being careful to handle the bag in such a manner that would prevent a puncture. Avoid dropping or impacting the bag, and follow manufacturer’s recommendations for handling the specimens and the bags.

(5) Allow the vacuum chamber to remove the air from the chamber and the plastic bag. The vacuum chamber shall automatically seal the bag once the air is removed.

(6) Exhaust air into the chamber until the chamber door opens indicating atmospheric pressure within the chamber. The chamber door latch can be used to avoid automatic opening of the door after completion of the test.

(7) Remove the sealed sample from the vacuum chamber. Handle the sealed sample with extreme care to prevent puncturing the bag. Gently pull on the bag and if the bag easily separates from the sample, the bag may be punctured; repeat the sealing process with a new bag.

(8) Determine the weight of the sealed specimen in air by summing the weight in (1) & (3) above. Designate this weight as (B).

(9) Suspend each specimen in water at 77 ± 1.8°F (25 ± 1°C) and record the immersed weight  as (E).

(10) To ensure that there was a tight seal in the bag, remove the sample from the water and cut the bag open. Remove the sample from the bag and determine its weight. Record this weight as (C). Compare this weight with the initial dry weight in (1) above (weight (A)). If weight (C) is greater than weight (A) by 5 grams, then dry and retest the sample, otherwise continue with the calculation step.

(11) Calculate the specimen bulk gravity (Gmb) of the test specimen as follows:

where,
A = weight of the dry specimen in air, grams
B = weight of the dry, sealed specimen, grams
C = final weight of specimen after removal from sealed bag, grams
E = weight of the sealed specimen under water, grams
F_T = apparent specific gravity of the plastic bag at 77°F (25°C), provided by the manufacturer.

D. Report

Report the Bulk Specific Gravity (Gmb) of laboratory-molded samples on form QA/QC-1.
Report the Bulk Specific Gravity (Gmb) of cored samples on form QA/QC-5.

Note:  All weights will be obtained when specimen and water temperatures are at 77 ± 1.8°F (25 ± 1°C).

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.

7.14.1  General

A. Mix Design TSRs:

(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 4.75A mixes shall be compacted to a VTM of 13.0 ± 0.5%.

(3) The Maximum Specific Gravity (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.

B. Field TSRs:

OPTION 1:

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

(2) The 150 mm Superpave Gyratory Compactor specimens shall have a void content (VTM) of 7.0 ± 0.5%, except S 4.75A mixes shall be compacted to a VTM of 13.0 ± 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) The Contractor will prepare an additional set of specimens and submit these within five (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 the Maximum Specific Gravity 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 Maximum Specific Gravity (Gmm) 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) through (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 requirements, 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 made by QA personnel.  Any other failing results will be considered unacceptable, unless otherwise approved by the Engineer.

OPTION 2:

(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) The 150 mm Superpave Gyratory Compactor specimens shall have a void content (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 (6) below, the Contractor shall immediately resample and compact another set of specimens for testing.  The process specified in steps (1) through (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 (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 made 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.

C. Verification TSRs:

(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 the 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 are 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 Asphalt Design Engineer as soon as the results are known.  If the QA/QC test meets the minimum requirement, the Asphalt Design Engineer may elect not to perform TSR testing 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.

D. Additional TSR Testing is Required:

(1) When a change is made in the non-strip additive source or dosage of any mix design unless otherwise approved by the Engineer.

Note:  In this case, TSRs shall be performed by QC personnel and approved by the Engineer prior to production of that mix to the project.

(2) When deemed necessary by the Engineer.

A. Compactor - meeting the requirements of Section 7.11.2 (Superpave Gyratory Compactor)

B. Vacuum Container - meeting the requirements of Section 7.12.2 (Maximum Specific Gravity).

C. Vacuum Pump or Aspirator - meeting the requirements of Section 7.12.2 (Maximum Specific Gravity).

D. Manometer and Vacuum Gauge - meeting the requirements of Section 7.12.2 (Maximum Specific Gravity).

E. Balance and Water Tank - meeting the requirements of Section 7.13.2 (Bulk Specific Gravity).

F. Water Bath  - capable of maintaining a temperature of 140 ± 1.8°F (60 ± 1°C).

G. Water Bath - capable of maintaining a temperature of 77 ± 1.8°F (25 ± 1°C).

H. Bags or Containers - heavy-duty leak proof plastic bags or containers for temperature conditioning of specimens.

I. Loading Jack or Test Press - with ring dynamometer or load cell as required in AASHTO T 245 that produces a uniform vertical movement of 2 in. (50 mm) per minute.

K. Loading Strips - steel loading strips with a concave surface having a radius of curvature equal to the nominal radius of the test specimen.  The loading strips shall be 0.75 in  (19.1 mm) wide for specimens 150 mm in diameter. The length of the loading strips shall exceed the final compacted thickness of the specimens.  The edges of the loading strips shall be rounded by grinding.

Note:  The Lottman Breaking Head is an acceptable substitute for the Loading Strips.

L.  Oven - a forced-draft oven, thermostatically controlled, capable of maintaining any desired temperature setting from room temperature to 350°F ±5 °F (176°C ± 3°C).

M. Metal Pans - having a surface area of 75-200 in.2 (48,400-129,000 mm2) and a depth of 1 - 2 in. (25 - 50 mm).

A.  Laboratory-Mixed, Laboratory-Compacted Specimens:

(1) Prepare at least eight (8) gyratory test specimens using the same blend as the mix design and the optimum binder content. Compaction of the test specimens shall be completed using a Superpave Gyratory Compactor.

(2) After mixing, the mixture shall be placed in the required pan at a depth of approximately 1 in. (25 mm) and cooled at room temperature for 2 ± 0.5 hours. Then, the mixture shall be placed in a 140 ± 5°F (60 ± 3°C) oven for 16 ± 1 hours for curing. The pans should be placed on spacers to allow air circulation under the pan if the shelves are not perforated.
Note: If the minimum TSR value can be achieved without the curing period, the Engineer may waive this requirement once satisfactory results are shown.

(3) After curing, place the mixture in an oven for 2 hours ± 10 minutes at the compaction temperature ±5°F (3°C) prior to compaction.
Note: The compaction temperature for the specimen should be that recommended for the type binder being used (See Section 7.11.3 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 4.75A 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.

Note: Due to the elevated void content and potential instability of the specimens, ensure each is adequately cool and stable prior to removal from the mold.

B.  Plant-Mixed, Laboratory-Compacted Specimens:

(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 eight (8) gyratory test specimen using plant-produced mix meeting the individual control limits of the applicable Job Mix Formula. Compaction of the test specimens shall be completed using a Superpave Gyratory Compactor.

(3) No loose-mix curing as described in Section (A) above shall be performed on the plant-produced samples.  After sampling, place the mixture in an oven until it reaches the compaction temperature ±5°F (3°C).

Note: The compaction temperature for the specimen should be that recommended for the type binder being used (See Section 7.11.3 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 4.75A 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.

(5) All other factors should remain constant during the compaction process.

Note: Due to the elevated void content and potential instability of the specimens, ensure each is adequately cool and stable prior to removal from the mold.

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 Section 7.13 of this Manual.

D. Determine the Maximum Specific Gravity (Gmm) on an uncompacted sample of the same mix using the methods described in Section 7.12 of this Manual.

E. Calculate the Percent Air Voids (VTM) for each specimen.  All test specimens must have 7.0 ± 0.5% voids, except S 4.75A 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.

7.14.5  Preconditioning and Testing of Specimens

One subset will be tested dry and the other will be partially vacuum-saturated, and warm water conditioned before testing.  Both subsets shall be tested at the same time.

A. DRY Subset

(1) The four dry specimens should be stored at room temperature 77 °F (25 °C) until testing.

(2) Before testing, the dry specimens shall be placed in heavy-duty leak-proof plastic containers.

(3) The specimens shall then be placed in a 77 ± 1.8°F (25 ± 1°C) water bath for 2 hours ± 10 minutes with a minimum 1 in. (25 mm) of water above their surface.

(4) 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.

(5) Apply the load to the specimen using the loading jack until the specimen fails.  The rate of loading should be constant at 2 in. (50 mm) per minute.  Record load at failure.

(6) 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.

B. WET Subset

(1) Place a specimen in the vacuum container supported above the container bottom by a perforated spacer.

(2) Fill the container with distilled water at 77 °F (25 °C) so that the specimen has at least 1 in. (25 mm) of water above its surface.

(3) Apply a vacuum of 10 - 26 in. of Hg (13 - 67 kPa) for a short time (approximately 5 to 10 minutes) to saturate the specimen.

(4) The acceptable percent saturation is between 70 - 80 %.

Note:  Saturation times vary with vacuum pump type and condition.

(5) Determine Percent Water Pickup by comparing SSD mass after saturation with SSD mass before Saturation.

(6) 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 75%.

1. If the Percent Saturation is between 70 - 80 %, proceed to the next step.

2. If the Percent Saturation is less than 70 %, repeat above steps (1) - (3) 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 (1) - (3) on the remaining specimens using less vacuum and/or time.

(7) After all of the Wet Subset have been correctly saturated, place the specimens in a water bath at 140 ± 1.8°F (60 ± 1°C) for 24 ± 1 hours.

(8) Remove the specimens from the 140 ± 1.8°F (60 ± 1°C) water bath and place in another water bath at 77 ± 1.8°F (25 ± 1°C) water bath for
2 hours ± 10 minutes.

Note: The Dry Subset should also be put in the 77 ± 1.8°F (25 ± 1°C) water bath at this time.

(9) 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.

(10) Apply the load to the specimen using the loading jack until the specimen fails.  The rate of loading should be constant at 2 in. (50 mm) per minute.  Record load at failure.

(11) 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.

(12) Visually compare the fractured surfaces of the Wet and Dry Subset of the pills and record these results on the.

(13) The Tensile Strength Ratio (TSR) is the percentage that the average wet tensile strength is of the average dry tensile strength.  The averages will be computed from the two remaining specimens after discarding the high and low specimens of each subset.

7.15      QMS CALCULATIONS

Note:  In order to monitor mix quality, several calculations are necessary other than those covered within specific test procedures. Forms QA/QC-1(SP) and QA/QC-1A(SP) contain the majority of those calculations. This section covers significant decimals and those calculations in detail.

7.15.1  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.

7.15.2  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%).

7.15.3  Voids in Mineral Aggregate (VMA) Calculation
VMA is the intergranular void space between the aggregate particles in a compacted paving mix that includes both the air voids and the effective asphalt binder content, expressed as a percentage of the total volume.

VMA is calculated using the:

- combined aggregate bulk specific gravity (Gsb) from the mix design (unless field tests verify the  Aggregate Gsb to be significantly different than the mix design. See Note below),
- the actual percent binder (Pb) from the field test, and
- the average specimen bulk specific gravity (Gmb @ Ndes) from QA/QC-1SP as follows:

Note: 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 Gsb will be changed on the JMF and the new Gsb used to calculate VMA.

 Calculate VMA to the nearest 0.1 percent (x.x %).

7.15.4  Voids Filled with Asphalt Binder (VFA) Calculation
The voids filled with asphalt binder (VFA) 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 7.15.3 (from QA/QC-1SP) above and
- the sample average VTM as indicated in 7.15.2 (from QA/QC-1SP) above

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

7.15.5  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).

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.

7.15.7  Percent Gmm @ Nini Calculation
The Percent Gmm @ Nini is a percentage number indicating resistance of a mix to compaction.  It is the percentage that the mix bulk specific gravity achieved at the specified number of gyrations (Nini) is of the known Gmm of the mix. Lower percentages generally indicate more resistance to compaction and therefore, more rut resistance under traffic.

7.15.8  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.

7.16   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. Within one working day of the samples being taken, the area from which the cores were taken shall be saw-cut to square up the area, all excess material removed and the area 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)

The Engineer will immediately investigate the reason for differences if any of the following occur:

1.  QA test results of QC split sample does not meet above limits of precision, or
2.  QA test results of QC split sample does not meet the individual test control limits or the specification requirements, or
3.  QA verification sample test results exceed the allowable retesting tolerances.

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, and/or additional density core 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.

7.17.1  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. A 200 lbs. (91 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 allowable retesting tolerances specified in 609-5(C)7 of the specifications.   If so, QC test results for the applicable tonnage increment shall be used for acceptance in accordance with Article 105-3 of the Specifications.  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 7.16.2 of this Manual.

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 7.14.1 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.