Category:403 Asphaltic Concrete Pavement: Difference between revisions

Asphalt Test Results (Sec 403.17.1.1)

A copy of all random QC test results shall be furnished to the QA inspector no later than the beginning of the day after testing has been performed. All raw data and printouts must be included with the testing records. Raw data consists of all weights, measurements, etc. used to arrive at the final test results. Printouts include the gyration/height data from the gyratory compactor and the asphalt content ticket from the binder ignition oven or nuclear gauge. The QC testing records must be made available to the QA inspector at all times.

It is QC’s responsibility to take appropriate action if unsatisfactory mix is being produced. This may include making adjustments to the plant to bring the mix back into specification, sampling the mix from the roadway and performing informational testing, removing mix from the roadway, etc.

Informational Tests

An informational test is a test that QC may perform between random testing to determine whether or not the mix is within specifications. Informational testing is not required and may be performed at any time and at any frequency. Generally, informational testing will be performed early in the production period. The informational test may not be completed in full. For example, QC may only compact the gyratory specimens. Doing so will yield specimen heights and the contractor may or may not make production adjustments based on these heights. Informational test samples must be clearly marked as such if they are tested and stored in the field laboratory.

QC is not required to provide the QA inspector with informational test results, since informational tests cannot be used in the QC process to determine pay factors, The timing of random number locations being given to the contractor, typically 100 to 150 tons in advance, is meant to protect the integrity of the statistical sampling process. QA always has the option of taking its own informational samples.

Informational test data may be used to determine asphalt removal limits if it is adequately documented. It should not be used for QLA under any circumstances. To be considered adequately documented the following criteria should be met:

• The gyratory pucks should be clearly identified and labeled and made available for verification.
• The gyratory printout should be available.
• The printout from the AC test should be available.

If the preceding conditions are met and the gyratory specimens are used to troubleshoot the placement, the specimens can then be weighed and bulked to determine the volumetric properties. Data from informational tests is approximate. Its only legitimate use to the QA inspector is to help determine the point on the roadway where the mixture transitioned either above or below the removal limits. We don’t want to remove acceptable mix or leave unacceptable mix in place.

Removal Limits

As an example of how informational tests may be used to designate removal limits of failing QC samples, the following situation is provided. The random QC sample shown in the diagram below fell late in sublot ‘a’ and test results indicated that voids were below the limits for removal. By specification sublot ‘a’ should be removed. By the time the test results were available and corrective action was taken, the contractor had crossed into sublot ‘b’. Assuming that mix properties were acceptable at the beginning of sublot ‘a’, the actual limits of unacceptable material are indicated by the dashed lines.

Adhering strictly to the specification, it is likely that acceptable material early in sublot ‘a’ will be removed, and it is also likely that unacceptable material early in sublot ‘b’ will be left in place. An adequately documented informational test may be used to zero in on the transitions out of, and back into, acceptable mix. It doesn’t matter that the data is approximate, only that it is above the limit for removal.

Random tests within removal limits are to be replaced by an equal number of random QC test locations, regardless of tonnage. For example, if 750 tons replace an area covered by two random tests, the new tests would be randomly chosen in each 375 ton portion of the replaced mixture.

The resident engineer has the option to determine removal limits based on puck height, provided that the informational test data is consistent with previous production.

When the random QC density core is below or above the removal limits, additional cores may be cut using the following procedure to determine the area of removal. Locations 250’ parallel to the centerline, ahead and back of the failing QC location, will be determined by the engineer. Cores will be cut in these locations and tested. If both sets of cores are not below or above the removal limits, the 500’ section will be removed and replaced with acceptable material and a new random QC core will be cut with-in the new pavement. If either set of the cores are below or above the removal limits, the whole sublot or the area in which the density core represents is subject to removal.

Any sublot of material with air voids in the compacted specimens less than 2.5 percent shall be evaluated with Hamburg testing and removed and replaced with acceptable material by the contractor if the rut depth is greater than 14.0 mm.

Inertial Profiler Test Results (Sec 610)

Surface of the pavement should be thoroughly tested with an inertial profiler or straightedge as required by Sec 610. The procedures for testing with an inertial profiler and analyzing the results with the ProVAL software program are set forth in EPG 106.3.2.59 TM-59, Determination of the International Roughness Index.

Bituminous Quality Control Plan (Sec 403.17.2)

The contractor documents the QC method with a quality control plan (QC Plan*). The QC plan for Superpave mixes shall include the contact information of the contractor’s QC representative, lot and sublot sizes and how they will be designated, the test method for determining asphalt binder content, the number of cores to be cut for density determination, and the independent third party for dispute resolution. The QC plan is approved by MoDOT Construction and Materials and used as a contract document during mix production. Contractor technicians who perform materials testing shall be certified through the MoDOT Technician Certification Program (TCP).

• Note*: A QC Plan is not required for bituminous base (BB) and pavement (BP) mixes.

Up to 3 cores are allowed at each random location, but only if spelled out in the QC plan. In the drawing below, the cylinder represents the station and offset of the random location. Best management practice is for QA to mark that location on the pavement. The first density core should have that marking on it. Any additional cores should be taken along a straight line, parallel to the centerline, within 1 foot either side of the random location.

Plant Calibration (Sec 403.17.2.2)

See Bituminous Mixing Plants.

Retained Samples (Sec 403.17.2.3)

QC must retain the portion of each sample that is not tested after the sample has been reduced to testing size. This includes gradation, consensus, TSR, and volumetrics samples. The retained samples must be clearly identified in accordance with Standard Specification Section 403.17.2.3 and stored in the field laboratory for a minimum of 7 days. Also, all cores must be retained for a minimum of 7 days. Notwithstanding the 7 day minimum, retained samples should not be discarded until all comparison issues with the lot are resolved. If space at the field lab is an issue, the sample should be stored at the project office.

There is no legitimate reason for unidentified samples to be in the field laboratory. The QA inspector should insist that all test specimens in the field laboratory be marked as soon as they are cool enough. The identifying mark should be permanent, unique, and indicate what the sample is.

When running a QC split sample, the comparisons should be within the tolerances shown in the following table:

Gradation Sample (Sec 403.17.2.3.1)

QC will retain the portion of their gradation sample that is not tested. This includes the sample of the combined cold feed from a drum plant and all hot bin samples from a batch plant.

Loose Mix Sample (Sec 403.17.2.3.2)

A loose mix sample consisting of roughly 100 lbs. will be taken from the roadway behind the paver, in accordance with AASHTO T168, at the required frequency. The sample will be thoroughly mixed and quartered in accordance with AASHTO R47, or with an approved splitting/quartering device. Two opposite quarters will be retained for testing during the dispute resolution process, if necessary. The remaining two quarters will be mixed together and quartered again.

The required weight of mix, as listed on the JMF, will be taken from one quarter and used to compact a specimen in accordance with AASHTO T312. The mix will be compacted to Ndes gyrations while the mix temperature is within the molding range listed on the JMF. Using the opposite quarter, follow the same procedure for the second specimen. The Gmb of each specimen will be determined and the average will be used to calculate the air voids Va and the voids in the mineral aggregate (VMA). By specification, a minimum of two compacted specimens must be used to calculate these properties.

A third quarter will be used to determine the Gmm of the mix in accordance with AASHTO T209. The minimum sample size for each type of mix can be found in the training manual. This property is used to calculate the Va and density. The volume of the sample, which is needed in the calculation, can be determined by either the weigh-in-air method or the weigh-in-water method. The weigh-in-air method consists of weighing the sample and container (with the lid) completely filled with water in air. The weigh-in-water method consists of weighing the sample and container (without the lid) completely submerged in water.

The remaining mix should be mixed together and quartered again. To determine the binder content using the nuclear gauge, enough mix should be taken from opposite quarters. The required weight of mix is listed on the JMF. A moisture content sample should be taken from the same quarters. To determine the binder content using the binder ignition oven, enough mix should be taken from one quarter. The minimum sample size for each type of mix can be found in the training manual. A moisture content sample should be taken from the same quarter. Sometimes the ignition oven may not shut itself off. The oven may be shut off manually as long as 3 consecutive readings show less than 0.01% loss. The sample should be examined to assure that a complete burn has been achieved. This will be considered a valid test.

Quality Control Laboratory (Sec 403.17.3)

The contractor is required to provide an appropriately equipped QC laboratory, however, it is not required to be at the plant. The contractor is also required to provide office space at the asphalt plant for the QA inspector to work on records and reports. Usually, these two requirements are met with one structure, but not always. The intent of the specification will be met if the QA inspector is provided with suitable facilities at the plant, but the lab is located offsite at another location, such as between the jobsite and the plant. The laboratory should have internet access in the event that cell phone service is not available.

Calibration Schedule (Sec 403.17.3.1)

Calibrations and verifications of the testing equipment are very important. If the equipment has not been calibrated or verified as required, false test results may be obtained. The maximum intervals are given in Standard Specification Section 403.17.3.1. These frequencies are taken from the AASHTO test methods and/or the manufacturer’s recommendations.

Calibration Records (Sec 403.17.3.1.2)

Periodically, the QA inspector should check the QC calibration records to ensure that the equipment has been calibrated or verified in accordance with Standard Specification Section 403.17.3.1.

403.1.18 Quality Assurance (Sec 403.18)

Assurance Testing (Sec 403.18.1)

Under QC/QA, MoDOT performs quality assurance (QA) testing. QA testing is used to verify the QC results. MoDOT is also responsible for independent assurance sampling (IAS) to verify that both QC and QA are performing the testing correctly.

All QA samples will be at independent random locations from QC. Not testing at random locations introduces statistical bias that is not in the interest of either MoDOT or the contractor. As with informational QC tests for the contractor, the MoDOT inspector may select specific locations for informational QA loose mix or core samples at any time if there is concern about a problem area, however, these may not be used for PWL calculations.

For volumetric testing, QA must sample enough loose mix material to retain an adequate amount for a second test. This retained sample, as with the QC retained sample, may be used during dispute resolution. QA will randomly sample the mix from the roadway once per lot and perform volumetric testing. At the beginning of the project, QC and QA should be given the opportunity to witness each other’s sampling and testing procedures. Any discrepancies should be immediately resolved at the project level, if possible. QA should test a QC retained volumetric sample once per day to ensure that both QC and QA are testing correctly. These samples should also be chosen at random (do not consistently test the retained sample from the same sublot every lot or develop a pattern).

For density testing, QA cores shall also be randomly located within a sublot at a frequency of one per lot. However, in the interest of public safety a random QA core test location, such as one in the middle of a busy intersection, should be moved to the closest safe location at the same random transverse offset. When both QC and QA are confident in each other’s testing procedures and favorable comparisons have been obtained on the retained samples, testing of the QC retained volumetric samples may be performed at a reduced frequency as determined by the MoDOT inspector. QA should test a QC retained gradation sample at a minimum of once per week. A minimum of one QC retained consensus sample should be tested per project. QA test results will be furnished to the contractor no later than the day after testing has been performed. A QA/QC Checklist is attached.

For single lift overlays and small quantity, QA cores shall be cut in the same location as the QC core.

QA Core Chain of Custody (Sec 403.18.2)

The roadway inspector should ensure that the QA density cores taken from the roadway are the same ones tested in the lab. The preferred procedure is for a MoDOT inspector to take possession of the cores as soon as they are cut and deliver them directly to QA at the plant, so that testing can proceed without delay. When job circumstances make this procedure impractical and the contractor has to deliver the core, the roadway inspector should dry the core with a paper towel and mark the side with identifying marks, including lot and sublot, using a permanent felt-tipped marker. Regardless of who delivers the QA core to the lab, the core shall be placed in a tamper proof bag.

Aggregate Comparison (Sec 403.18.3)

A favorable comparison will be obtained when the independent QA sample(s) meets specifications. In addition, the QA test results of a QC retained sample must be within the following tolerances from the QC test results:

If a favorable comparison is not obtained, dispute resolution procedures should be initiated.

403.1.19 Acceptance of Material (Sec 403.19)

Random Numbers (Sec 403.19.1)

All random numbers for QC loose mix samples and cores shall be generated prior to the start of the project for every four sublots. A printout of those numbers will be sealed in an envelope, which will be signed and dated by both QA and QC parties. The QA inspector will keep the envelopes in his/her possession in a secure location. The envelope for every four sublots will be provided to QC at the end of the previous four sublots.

It is critical that QC (and QA) samples be taken at random locations, because any manipulation of the locations introduces bias. QC test results are used to statistically define a population of data and bias causes inaccuracy in that statistical calculation. Random numbers shall be generated by using the Asphalt Random Locations spreadsheet, in order to eliminate any question of bias. MoDOT inspectors can locate the Asphalt Random Locations sheet on the internal site.

QC samples that are used to determine the pay factors must be taken at the locations designated by the random numbers, unless circumstances warrant relocation. This could include close proximity to another QC sample location in the same production period (when QC is at a critical point in testing the previous sample), areas where mix must be placed by hand, etc. In these cases, using good judgment, QA has the authority to separate random samples by up to 200 tons. QC and QA need to work together in good faith to make this process run smoothly.

QC should be notified of the core location after rolling has been completed. QC should be notified of the loose mix sample location approximately 100 to 150 tons before the test. The intent is to give QC enough time to conclude any ongoing tests and collect the next samples. When the sampling for every four sublots is completed, the envelope for those sublots will be opened to demonstrate that the random numbers were not manipulated during production.

The independent QA sample must be taken at the location designated by a random number unless circumstances warrant relocation. This could include close proximity to a QC sample location in the same production period, areas where mix must be placed by hand, etc. If necessary, the random samples may be separated by 200 tons. The QA inspector shall place and seal the QA core in a tamper-proof bag immediately after extraction and mark the bag label with the project number, lot number, location and inspector signature. The test results from the independent QA sample will be compared to the QC test results to determine if the QC test results adequately define the characteristics of the entire lot. However, QA may take additional samples to determine if an area of concern complies with the specifications. The test results of these additional samples will not be compared to any QC test results.

Lots (Sec 403.19.2)

For the purposes of pay factor determination, the mat will be divided into lots with a minimum of 4 sublots per lot. The maximum sublot size is 1000 tons. If a full lot cannot be completed, the extra sublots will be added to the previous full lot and the pay factors will be determined on the large lot. If there is no previous lot, the mix will be treated as small quantities and Standard Specification Section 403.23.7.4.1 will apply.

If the target binder content is adjusted from the original JMF, a new lot shall begin. This will ensure that the binder content pay factor will represent the population of the adjusted mix. If the cold feed settings are adjusted from the original JMF alone, a new lot is not required. Adjusting the cold feed settings will change the G_sb and, therefore, the VMA of the mix. However, the VMA specification limits are based on the type of mix (see Voids in the Mineral Aggregate (VMA) (Sec 403.5.4) and do not change. The VMA is required to be within this range, even if changes are made to the JMF. A new lot sequence shall begin when a new mix design is established. The limits of adjustment can be found in Standard Specification Section 403.11.

Test and Pay Factor Items (Sec 403.19.3)

Regarding Note 'b', one core equals one sample and the results will be used to determine the density pay factor for the corresponding sublot. However, if stated in the QC Plan, a maximum of two additional cores may be taken per sublot. This gives a maximum total of three cores per sublot. One core must be taken at the location selected by random numbers. The remaining cores must be taken at the same transverse offset within one foot longitudinally of the location selected by the random numbers. If more than one core is taken per sublot, all of the cores will be combined into one sample. This means that the average density of the cores will be used to determine the density pay factor for the corresponding sublot.

Test Method Modification (Sec 403.19.3.1)

Binder Ignition Modification (Sec 403.19.3.1.1)

This specification adjusts the temperature of the binder ignition oven due to the breakdown of certain aggregate formations as a result of intense heat.

Rice Test (Sec 403.19.3.1.2)

If the absorption of any aggregate fraction used in the mix is greater than 2.0%, AASHTO T209 must be modified in accordance with Standard Specification Section 403.19.3.1.2. This procedure is called the dry-back method. The final surface-dry weight will be recorded in the APIW as “A2”. If necessary, the dry-back method should be performed on all samples taken in the first lot of mix produced. If the initial G_mm and the dry-back G_mm of a sample are within 0.002 of each other in all sublots of the first lot, the dry-back may be reduced to every fourth sublot. Otherwise, the dry-back will be required every sublot.

Miscellaneous Applications (Sec 403.19.3.2)

Small Quantities (Sec 403.19.3.2.1)

A mix that requires less than 4000 tons on a project is referred to as small quantities. Testing frequencies will be as stated in Standard Specification Section 403.19.3.2.1(b). If a project is initially setup with less than 4000 tons, pay factors will not be determined unless an adjustment is made to the approved QC plan before production begins. If a project is initially setup with more than 4000 tons but less than 4000 tons are placed, pay factor determination is not required and Standard Specification Section 403.23.7.4.1 will apply.

Dispute Resolution (Sec 403.19.4)

The vast majority of issues between QC and QA can be resolved by consulting the QC Plan, the Test Method or the contract documents. Dispute decisions should always be timely and made at the lowest appropriate level. However, if a dispute cannot be resolved within a few hours of taking these initial steps, it should be escalated.

Occasionally, the QC test may not represent the population or, due to individual differences in sampling and testing procedures, the QA and QC test results may not compare within the required limits. One of the first steps in resolution could be an immediate computation check, comparison of sampling and testing procedures, or split sample retests. Testing of the QC split sample or joint sampling and testing could determine if variations in the mix production or sampling and testing procedures are responsible for the differences. If resolution is not possible at the project level, either party may request that the approved independent third party test the mix. Third party test results will be binding upon both parties. The party whose results were incorrect will pay for the third party testing. Third party testing is costly and time consuming and should only be used when project level reconciliation is not possible.

403.1.20 Method of Measurement (Sec 403.22)

Weight Determination (Sec 403.22.1)

If a batch plant is used to produce the mix, the weight of the load will be determined by the batch weights. If the mix is produced in a drum plant, the weight of the load will be determined by weighing each load of mix. This can be accomplished with either a silo scale or a truck scale. These individual load weights will be added together for the total tonnage accepted for the project and rounded to the nearest 0.1 ton.

Full Depth (Sec 403.22.2)

(Sec 403.22.2.1)

The final driving surface area (length multiplied by width) of the pavement will be used as the area of all underlying lifts and courses. Any mix that is placed outside of this area, including the mix used to construct the 1:1 slope, will not be directly paid for.

(Sec 403.22.2.2)

Full depth pavements will be paid for by the square yard. If authorized changes are made to the contract quantity during construction or if errors are found in the contract quantity, the applicable completed pavement will be measured to the nearest 0.1 yd². The revision or correction will be added to or deducted from the contract quantity. If no changes are made or errors found, the pavement will not be measured and the contractor will be paid for the quantity of mix as shown in the contract.

Alternate Overlay (Sec 403.22.3)

An overlay project may be bid as Portland cement concrete or asphalt.

Field Established Quantity (Sec 403.22.3.1)

The field established plan quantity is the tonnage of mix that is determined from the set or adjusted profile. This will be the contract quantity for an asphalt overlay.

Overlay Measurement (Sec 403.22.3.2)

Overlays will be paid for by the ton. If authorized changes are made to the contract quantity during construction, the applicable completed pavement will be measured to the nearest 0.1 ton. The revision will be added to or deducted from the contract quantity. If no changes are made, the pavement will not be measured and the contractor will be paid for the quantity of mix as shown in the contract.

Pavement Testing (Sec 403.22.4)

See Density Samples in Paving Operations.

403.1.21 Basis of Payment (Sec 403.23)

Aggregate Variation (Sec 403.23.1)

The specific gravity of the aggregates used in the mix may fluctuate because of a variation in the quality of the rock within the quarry ledge. The gradation of the aggregate may also cause some fluctuation. However, this contribution is usually negligible. Because of such fluctuations, the quantity of aggregate used in the mix may vary from the quantity specified in the contract. Since this is expected and unavoidable, the contract unit price will not be adjusted.

Compacted Samples (Sec 403.23.2)

The cost of cutting QC cores is included in the contract. Therefore, no direct payment will be made. QA samples will be paid for at $75.00 per sample, per Standard Specification Section 109.15. If one QA core is cut per location, that core is equal to one sample. If more than one QA core is cut per location, the test results will be averaged and those cores will equal one sample.

Smoothness Adjustment (Sec 610.5)

Diamond Grinding (Sec 403.23.4.1)

Areas of the final driving surface that must be corrected by diamond grinding will be considered as a marred surface (Sec 610.5.3). A tack coat will not be applied to these areas. No direct payment will be made for diamond grinding.

Tensile Strength Retained Adjustment (Sec 403.23.5)

The tonnage represented by each QC TSR sample is subject to a pay adjustment that depends on the test results. The adjustments to the contract unit price are given in Standard Specification Section 403.23.5.

Continuing with the sampling example in Tensile Strength Ratio (TSR) (Sec 403.5.6), the contractor takes ten samples that represent 10,000 tons each. The last two samples represent 6,480 tons each. The contractor’s test results are shown in order in the table below. The price per ton is $35.00. The contract adjustment is calculated as follows:

Contract Adjustment = ((Percent of Contract Price-100)/100) * Price/ton * Tons

The Pay Factor Worksheet will automatically calculate the contract adjustment once the appropriate information has been entered. The contractor’s TSR results should be recorded in the Pay Factor Worksheet that corresponds with the lot that the sample was taken in.

Density Adjustment (Sec 403.23.6)

QC will take one unconfined longitudinal joint core per sublot, as specified in the QCP. These cores will be taken within 6 in. of the unconfined longitudinal joint. Unconfined joint cores can either be located at the same longitudinal location as the corresponding mat density cores or separate random numbers can be generated. The test results for each lot will be averaged to determine compliance with the specifications. Pay adjustments will be in accordance with the following table and will be applied to the corresponding tonnage represented by the core(s):

If pay reductions are necessary, the lower adjusted contract unit price of the PWL or the unconfined joint density adjustment will apply to the corresponding tonnage. For example, assume that the lot size is 4000 tons and that 1000 tons in the lot has an unconfined joint. The total pay factor for the lot due to volumetric testing is 105%. A longitudinal joint core is taken as required and the pay factor due to the unconfined joint density is 90%. As a result, a 10% reduction to the contract unit price will be applied to the 1000 tons represented by the unconfined joint and a 5% bonus will be paid for the remaining tonnage in the lot (3000 tons). On the other hand, if the pay factor due to the unconfined joint density were 100%, the 5% bonus would be paid for the entire lot. Longitudinal joint density is very important and this is an attempt to ensure that density is achieved. If it is not, the joint will ravel. Longitudinal joint core density testing will be waived if the contractor elects to mill off 6” of the unconfined joint edge.

Percent Within Limits (PWL) (Sec 403.23.7)

Superpave mixes contain a quality level analysis with statistically based incentive/disincentive pay factors. The QC tests are analyzed on each lot of mix and the pay is based on the percentage of the mix that statistically falls within the limits of the specifications. It is possible to have a given lot of mix with all tests falling within the specifications, but because of a large amount of deviation between test results, the percent within limits would be very low, giving the contractor a correspondingly low pay factor. Very consistent test results, with a correspondingly low standard deviation and high percent within limits, will produce high pay factors. Test results that are consistent may produce bonus pay factors while those that fluctuate within the specification limits will produce low pay factors.

The mean (x_a), standard deviation (s), Upper Quality Index (Q_u), Lower Quality Index(Q_l), and total percent within limits (PWLt) are calculated for each pay factor item in each lot using the equations given in Standard Specification Section 403.23.7. The PWL for an item can be determined using Table III in Standard Specification Section 502.15.8. To use this table, calculate the Q_u of the item and round the result to two digits (X.XX). Find the result in the left hand column of the table and move along the row to the right until reaching the column with the corresponding n-value. The n-value is the number of test results for the item in the lot. This process yields the upper percent within limits (PWL_u) of the item. Repeat this process to determine the lower percent within limits (PWL_l) of the item using the Q_l. Finally, calculate the PWL_t. If a Q-value is negative, subtract the PWL-value from 100. The Pay Factor Worksheet will automatically calculate the PWL_t for each pay factor item in each lot.

Quality Level Analysis (Sec 403.23.7.1)

Best management practice is for QA to review the QLA with QC before processing the report. Sec 403.23.7.1 requires QA to make the QLA no more than 24 hours after receipt of the contractor’s test results.

Acceptance (Sec 403.23.7.1.1)

The QC test results will be used to determine the PWL as long as QC and QA compare favorably. If a favorable comparison is not obtained, dispute resolution procedures should be initiated. If dispute resolution is carried out to independent third party testing and the QC test results have been determined to be correct by the third party, the QC test results will be used to calculate the PWL. If the QA test results have been determined to be correct by the third party, the QA test results will be included in the PWL calculation.

During the project, QA and QC should be given the opportunity to witness each other’s sampling, splitting and testing. Doing so will help avoid future conflict. For comparison of QC and QA cores, the density for the QA core will be calculated using the G_mm from the corresponding QC loose mix sample from the same sublot.

Comparison (Sec 403.23.7.1.2)

Copies of all test methods should be readily available in the field laboratory. Testing procedures must follow an approved test method. If either party has an issue with the other’s sampling, splitting or testing procedures, an objection should be raised at that time. By doing this promptly, the issue can be resolved while it is still possible to re-create the test. If a decision is made to test a retained sample, the test should be run jointly so that the testing procedure is removed as a possible variable for explaining the difference in results.

A favorable comparison is obtained when the QA test results of a random, independent sample are within two standard deviations of the average of the QC test results. This determination cannot be made until all random testing for the lot has been completed. If the QC test results vary within the specification tolerances, the standard deviation will be large. In fact, as the variability in the QC test results increases, the standard deviation also increases. This results in a wide comparison range and low pay factors. On the other hand, if there is little variability in the QC test results, the standard deviation will be small. The comparison range will be narrow and the pay factors will increase. In this case, a favorable comparison is obtained when the QA test results are within one-half of the specification tolerances of the QC average. For example, the specification tolerances for VMA are –0.5% to +2.0%. One-half of this range is 1.25%. Therefore, a favorable comparison is obtained if the QA test result is within ±0.6% of the QC average.

If the comparison is not favorable, the first step is to review both QC and QA test results to see if there is any noticeable error. If no errors are found, testing of the retained samples may be performed. Judgment must be used in determining which retained sample(s) to test. When testing a retained sample, the entire suite of tests (%AC, Va, and VMA) should be performed to verify the validity of the original test results. If the test results of the retained sample confirm the original test results, the original test results are used to determine the PWL. If the test results of the retained sample verify that the original test results were incorrect, the test results of the retained sample are used to determine the PWL.

If the QC and QA test results have been determined to be valid and the comparison is still unfavorable, the test results from the random, independent QA sample will be included in the PWL calculation. The QA test results of QC retained samples or the test results from any additional QA samples will not be used in the PWL calculation. As an example, lot 3 has been completed and consists of 4 sublots. A favorable comparison was not obtained but it was determined that the QC and QA test results are valid. Therefore, the PWL calculation will include the QC test results from all 4 of the sublots and the test results of the random, independent QA sample (n = 5).

When the random QA test results are included in the PWL calculation, all volumetric properties (%AC, VMA & VA) for that sample will be used, even if only one of the three properties has an unfavorable comparison.

For the random split sample comparisons of QC loose mix, a favorable comparison is obtained when the QA test results of a QC retained volumetric sample are within 0.010 of the QC G_mm test results, within 0.010 of the QC G_mb test results, and within 0.1% of the QC asphalt content test results. If larger variances occur, both QC and QA should investigate the sampling and testing procedures to identify and rectify the cause of the discrepancy.

Outliers (Sec 403.23.7.1.3)

If it is suspected that an individual QC test result is an outlier, the entire lot of QC test results may be checked in accordance with Standard Specification Section 403.23.7.1.2. The eligible measured test results are G_mb, G_mc, G_mm, and %AC. G_mb, G_mc, and G_mm shall be carried out to three decimal places (X.XXX) and the %AC shall be carried out to two decimal places (X.XX). On the other hand, V_a, VMA, and density are not eligible because these are calculated volumetric properties.

If an outlier is found, QC may test the retained sample from the corresponding sublot. Again, the entire suite of tests (%AC, G_mb, and G_mm) must be performed. If the test results from the retained sample confirm the original test results, the original test results will be used to calculate the PWL. If the test results from the retained sample do not confirm the original test results, the test results from the retained sample will be used to calculate the PWL.

When any change is made in the JMF, the previous test results cannot be used for future outlier calculations since the mix has changed. For example, if the contractor has made a change in sublot 2B and wants to check for an outlier in sublot 2D, the results from sublot 2A cannot be used since the mix is not the same.

Random Sampling (Sec 403.23.7.1.4)

See Random Numbers in EPG 403.2.19 Acceptance of Material (Sec 403.19).

Pay Factors (Sec 403.23.7.2)

The density (PF_density), asphalt content (PF_AC), VMA (PF_VMA), and air voids (PF_Va) pay factors are calculated for each lot using the corresponding PWL_t and the equations in Standard Specification Section 403.23.7.2. The total pay factor (PFT) is then calculated for each lot using the average of the individual pay factors. If coring is not required, such as on a leveling course or non-integral shoulders, the PFT will be calculated for each lot using the average of the PF_AC, PF_VMA, and PF_Va.

The contract adjustment is used to adjust the contractor’s pay to reflect the quality of the mix. The contractor may receive a bonus if the quality of the mix is good. On the other hand, if the quality of the mix is poor, a deduction will be applied. The contract adjustment is calculated by subtracting 100% from the PFT. The dollar amount of the bonus or deduction is determined by multiplying the unit bid price, the quantity of mix in the lot, and the contract adjustment (in decimal form) together.

Mix is typically produced and measured by the ton. Therefore, in order to eliminate confusion and excessive conversions on square yard projects (full depth pavements), the lots will be tracked by tonnage. When the pay factors are calculated at the end of the lot, the “Square Yard Calculator” in the Pay Factor Worksheet can be used to determine the square yards in the lot. This is best explained with an example:

On a full-depth paving project, the total thickness of the pavement is 12 in. and the contractor is placing two lifts of SP190, one 6 in. lift and one 4.25 in. lift. The final lift of SP125 is 2 in. thick. The lot size is 3000 tons. Suppose that one lot of SP190 has been completed. The total thickness of the pavement and the lift thicknesses are entered in the appropriate cells in the “Square Yard Calculator”. The length and width of the lot must be measured manually. The width of the lot is 12 ft., the length of the first lift is 4650 ft., and the length of the second lift is 3300 ft. Therefore, the area of the first lift is 6200.0 yd² (12 ft. * 4650 ft. = 55800 ft² * (1 yd²/9 ft²) = 6200 yd²) and is entered in the appropriate cell. The area of the second lift is 4400.0 yd²(12 ft. * 3300 ft. = 39600 ft² * (1 yd²/9ft²) = 4400 yd²) and is entered in the appropriate cell. The square yardage represented by each lift is calculated by multiplying the square yards by the lift thickness divided by the total pavement thickness. Therefore, the square yardage of the first lift is 3100.0 yd² (6200 yd² * (6 in./12 in.) = 3100 yd²) and the square yardage of the second lift is 1558.3 yd² (4400 yd² * (4.25 in./12 in.) = 1558.3 yd²). This lot represents 4658.3 square yards. This procedure is followed for the remaining lots.

Density Pay Factor (Sec 403.23.7.2.1)

Density is calculated using the G_mb of the core and the G_mm of the mix. The PF_density for each lot is calculated using the density test results of all of the sublots. Cores that are cut in half, as required by Standard Specification Section 403.15.4, will double the number of test results used to determine PFdensity. For example, suppose that the contractor is placing SP190 in 8” lifts and 4 cores are taken per lot, 1 per sublot. The lift is being placed thicker than 6 times the nominal maximum size aggregate used in the mix. By specification, the cores are to be cut in half and the density of each half determined separately. Therefore, 8 test results (as opposed to 4) will be used to determine the PF_density for the lot.

Asphalt Content Pay Factor (Sec 403.23.7.2.2)

The PFAC for each lot is calculated using the binder content test results of all of the sublots.

Voids in the Mineral Aggregate and Air Voids Pay Factor (Sec 403.23.7.2.3)

The V_a, VMA, and VFA are calculated using the average G_mb of the compacted gyratory specimens, the G_mm of the mix, the percent stone (P_s) of the mix, and the G_sb of the combined aggregate. The P_s is determined by subtracting the percent binder (P_b) from 100%. The G_sb will be that listed on the JMF. The PFV_a and PF_VMA for each lot are calculated using the V_a and VMA test results of all of the sublots.

Removal of Material (Sec 403.23.7.3)

If the PF_T for a lot is less than 50.0, the entire lot must be removed and replaced at the contractor’s expense. If the QC test results for density and/or air voids fall below the removal limits in any sublot, the affected mix must be removed and replaced at the contractor’s expense. The specifications state that the entire sublot must be removed. However, in some cases only a portion of the affected sublot(s) may require removal. Therefore, the limits of removal will be left up to the Resident Engineer's discretion. QC informational test results may be used to help define the limits of removal as long as the informational test(s) are well documented (see Asphalt Test Results (Sec 403.17.1.1) for the documentation requirements). The replacement mix will be sampled and tested as required. These test results will be used to calculate the PWL for the lot.

If the QA test results fall below the removal limits for density and/or air voids, the mix should stay in place if a favorable comparison has been obtained with the QC test results. Again, a favorable comparison signifies that the QC test results adequately define the characteristics of the lot and are, therefore, acceptable. If the QA test results fall below the removal limits and a favorable comparison has not been obtained, dispute resolution should be initiated to determine if the mix should stay in place.

For small quantities, if the laboratory compacted air voids are less than 2.5%, or the roadway density is less than 90.0% or more than 98%, the material should be removed and replaced. If asphalt content is above or below the target value by more than 0.3%, or if the roadway density is between 91.5% and 90%, the mixture may be allowed to remain in place with an appropriate deduction.

Miscellaneous Applications (Sec 403.23.7.4)

Small Quantities (Sec 403.23.7.4.1)

For small quantity projects consisting of less than 4000 tons, the statistical analysis of the mix is not required. Therefore, pay factors will not be determined. However, the mix must meet density, binder content, VMA, and V_a specifications. The testing frequencies are stated in Standard Specification Section 403.19.3.2.1(b). Density will be adjusted in accordance with the table in Standard Specification Section 403.23.7.4.1(b). TSR testing is also required.

The contractor may use the PWL pay factors for a small quantity if they are specified in their QC plan.

Base Widening and Entrances (Sec 403.23.7.4.2)

Single Lift or Leveling Course Work (Sec 403.23.7.4.3)

This specification does not apply to “mill and fill” projects.

403.2 Materials Inspection for Sec 403

403.2.1 Scope

To establish procedures for mix design of asphaltic concrete pavement, inspection and acceptance of bituminous mixture. Ingredients for use in asphaltic concrete pavement are to be inspected in accordance with the applicable sections of this Manual. Plant calibrations, if requested, will be performed in accordance with EPG 106.4 Plant Inspections.

403.2.2 Mix Design Procedure

In order for an asphaltic concrete mix formula to be approved, the contractor’s proposed job mix formula (JMF) shall be submitted as required in Specification Section 403.3.1. The time for approval starts when the completed design is delivered to the District. This time restarts when the District receives information omitted from the original JMF or corrected by the contractor. Review times include District and Central Office processing, therefore, each mix should be processed as soon as possible. When the contractor is not accepted as a participant in the AASHTO Proficiency Sampling Program, material sampling is required for mixture verification. Trial mix samples must be obtained and submitted to the Central Laboratory in accordance with Section 1001 of the Materials Manual. When possible, the JMF and correspondence should be transmitted electronically. The Materials Field Office e-mail address is MFO.

District Procedure

When the District receives a proposed trial mix formula, as required by the Standard Specifications, the mixture properties, components and proportions should be checked to ensure compliance with Specifications and that they are approved for the intended use. It may be necessary for the District to advise the contractor to make changes in the proposed mixture in order to comply with Department policies. The district shall provide AWP IDs and all pertinent information (gradation, deleterious, etc.) for each fraction of aggregate used in the mixture. A QC plan in accordance with Section 1001 of the Materials Manual covering each aggregate fraction should be on file in the District Office or received with the JMF. The target gradations shown on the QC plan and JMF must match. When the District is satisfied that the proposed mixture is acceptable, a copy of the JMF and the contractor's letter shall be submitted to the Materials Field Office, accompanied by a letter of transmittal with comments, any corrections made and recommendations. The transmittal letter shall contain the following information:

Project information – Job Number, Route, County, Contract Number.

Mixture Types

Grade and All Possible Sources of Asphalt Binder Intended for Use

Letting Date

Proposed Work – Type of Work, Job Location and Length

Annual Average Daily Traffic (AADT)

Total Trucks

Total Combination Trucks

Mix Use – Mainline, Shoulders, Outer Roads, Entrances, etc.

Quantity of Mix

Included in the letter should be information regarding the approximate date on which the contractor intends to begin placing the mixture on the roadway, the type of mixture needed first and whether the JMF is submitted for a 7-day review or verification. Information concerning plant location, type of plant to be used, etc., is beneficial.

If the mixture design is performed by a laboratory participating in the AASHTO Proficiency Sampling Program with a rating of 3 or more on the applicable test methods, trial mix material does not need to be submitted to the Laboratory unless one or more of the following conditions apply:

a. Nuclear calibration for MoDOT asphalt content gauges is needed.

b. Material for full verification of the mixture is requested by the Field Office.

c. District personnel have concerns over any aspect of the mix design.

Requests for previously approved mixes shall be submitted and will be approved in accordance with applicable portions of EPG 403 Asphaltic Concrete Pavement. Approved mixtures may be transferred within the time limit of 3 years from the approval date. Transfer requests for mixtures that exhibited poor performance or field problems should be denied.

Upon request by the contractor, the District has authority to change the source of mineral filler, hydrated lime, natural sand from the Missouri and Mississippi Rivers or asphalt binder. However, constant changing throughout a project should not be allowed. The contractor must provide reasonable justification for changing sources during the course of a project. Any adjustments should be made to the JMF to reflect changed properties caused by the new source. (e.g. Change in G_sb, gradation, asphalt content, etc.)

Approval of a new mix design shall be obtained prior to changing the source of aggregates used in a mixture.

Field Office Procedure

The Materials Field Office is charged with the responsibility of processing the mix formula. General procedures for processing an asphaltic concrete mix formula are as follows:

a. A letter from a District requesting a mix with a copy of the contractor's JMF and letter is received.

b. Contract Special Provisions for the project are checked for necessary items.

c. The urgency of the mix and the status of trial mix samples in the Central Laboratory are reviewed.

d. Grade of asphalt, possible sources intended for use and the percent asphalt recommended are reviewed.

e. Gradations of the individual aggregates are checked for specification compliance and compared with the gradations determined by the Laboratory.

f. All calculations on the proposed JMF are checked.

g. For verification, a one-point trial is prepared and submitted to the Laboratory.

h. When Central Laboratory tests are completed, the results are compared to the contractor’s and against the specifications. If the mixes tested cannot be used, the mixture will be rejected.

i. Formulas to check aggregate and mixture properties are shown in LS 403.

j. Absorption values obtained by AASHTO T85 or T85 Combined will be shown on the JMF for determining which mixtures require the optional dry-back procedure of AASHTO T209.

k. Upon JMF approval, a unique JMF number will be created and entered into AWP for each possible asphalt source. Each JMF will have a two letter suffix abbreviation for the binder supplier name and location.

403.2.3 Field Adjustments of Superpave Mix Design

The specification criteria are to be used to determine whether or not the mixture meets the specifications. When a mixture is field adjusted, the contractor is to notify the inspector prior to making the adjustment. A new G_sb is required when cold feed adjustments are made. A new lot will begin with any change in asphalt content. Adjustments beyond the limits set in the specifications will require a new mix design. Field adjusted mixture changes are not required to be sent to the Field Office, however, the District will track the changes to ensure proper material quantities are inspected.

403.2.4 Field Superpave Mix Design

When a field mix design is needed, the contractor must first notify the engineer (the Materials Field Office is to be notified immediately). During the design and verification process, no mixture is to be placed on the project. A plan for producing, sampling and verifying the proposed field mix design is to be agreed on between the contractor and the engineer. One hundred (100) pounds of loose mixture will be required in the Central Laboratory and the Materials Field Office will approve or deny the field mix design. In order to be accepted for use, the test results must meet all of the following:

a. Minimum VMA for the mixture type, i.e., 12.0 minimum for 250 mixes, 13.0 for 190 mixes, 14.0 for 125 mixes, and 17.0 for 125 SMA mixes.

b. Asphalt content within 0.3 % of the adjusted target. For example, if the contractor chose to lower the asphalt content from 5.0 percent to 4.8 percent for a field adjustment, the initial test results must be within 0.3 % of 4.8 percent.

c. Air voids of 4.0 +/- 0.5

d. TSR result is equal to or greater than 80%.

The contractor and Central Laboratory may run the moisture sensitivity test simultaneously. If the contractor’s test results meet the above criteria, and the results are verified by the Central Laboratory, the target VMA will be set at the contractor's test result, the target AC content will be set at the target set for the field mix design, and the air voids target will be set at 4.0.

403.2.5 Report

A letter of transmittal will accompany the approved mixture to the District Construction and Materials Engineer with distribution as follows:

The letter of transmittal and the approved mixture will be sent by electronic mail to the individuals listed above.

A copy of the approved formula accompanied by a letter of transmittal from the District Construction and Materials Engineer is to be forwarded to the contractor when an electronic mail address for the contractor has not been provided.

403.3 Laboratory Procedures for Sec 403

This establishes procedures for Laboratory testing and reporting of hot mix asphalt trial mixtures and field compacted density samples.

403.3.1 Procedure

403.3.1.1 Trial Mixtures

Test results and calculations required for asphaltic concrete trial mixtures are as shown in Batching below. Test results and calculations shall be recorded through AWP. Standard test procedures are as follows:

403.3.1.1.1 Batching

Aggregates shall be divided into the individual aggregate sizes down to either the minus No. 8 or minus No. 16 sieve except when inconsistencies occur during testing where it may be advantageous to divide to the minus No. 200 material.

403.3.1.1.2 Weigh each size aggregate according to the batch sheet in a tared pan and place into a larger pan for combining sizes. Repeat process for number of samples desired. The combined weight of a batch containing 3/4 in. plus material must be within 5 g of the target weight and a batch with minus 3/4 in. material must be within 3 g of the target weight. Otherwise, the sample shall be rebatched. If only one sample is out of tolerance, it may be swapped with the butter sample. The butter does not have to meet these tolerances.

403.3.1.1.3 Place samples and asphalt binder in an oven set at the mixing temperature. Heat in the oven a minimum of 2 hours. Aggregates may be heated no more than 28° C (50° F) above the mixing temperature in order to maintain the desired temperature throughout mixing.

403.3.1.1.4 Use a Hobart mixer with a wire whip to mix samples unless otherwise instructed to use a bucket mixer. Remove heated aggregate from oven and put in heated mixing bowl (bucket) that has been tared and weigh. Dry-mix thoroughly, then make a crater in the center of the aggregate to pool the binder. Calculate the proper binder weight for the actual weight of aggregate and add the binder to the aggregate to attain the proper weight. Recalculate the percent binder based on actual weights. If it is not within 0.02% of the target percent, add or remove binder to get within this tolerance. Mix until all aggregate is uniformly coated. The first batch shall be the butter. Scrape the mixing bowl with a spatula to remove as much of the mixture as possible. For each successive batch, the bowl should be scraped to the same level of removal as the butter. Calculation of the binder weight shall be as follows:

${\displaystyle BinderWeight={\frac {Wt.Agg.}{100-P_{b}}}x100}$

403.3.1.1.5 Split the mixtures batched in combined batches into individual specimens. Mixtures shall be placed in pans, at a depth of 1 to 2 in., then placed in a force-draft oven at the compaction temperature for the mixture and short-term aged for 2 hours. At one hour, stir Superpave mixtures making sure free binder and fines are scraped from the bottom and stirred evenly back into the mixture and place back in the oven. Other mixtures are aged with no stirring during the 2 hours.

403.3.1.1.6 After aging, stir mixtures, scraping binder and fines from the pan, and ensure all components are uniformly incorporated into the mixture.

403.3.1.1.7 The mixture shall be tested according to the appropriate test method.

403.3.1.1.8 Percent voids of the mixture (V_a) shall be calculated as follows:

${\displaystyle V_{a}=\left(1-{\frac {G_{mb}}{G_{mm}}}\right)x100}$

403.3.1.1.9 Percent voids in mineral aggregate (VMA) shall be calculated as follows:

${\displaystyle VMA=100-\left({\frac {G_{mb}xP_{s}}{G_{sb}}}\right)x100}$

Where:

P_s = Percent stone in mixture = 100 – Percent AC

G_sb = Bulk specific gravity of combined aggregate fractions

${\displaystyle G_{sb}={\frac {P_{1}+P_{2}+...P_{n}}{{\frac {P_{1}}{G_{1}}}+{\frac {P_{2}}{G_{2}}}+...{\frac {P_{n}}{G_{n}}}}}}$

Where:

P₁, P₂, P_n = Bin percentages by mass of aggregate

G₁, G₂, G_n = Individual bulk specific gravities of aggregate

403.3.1.1.10 Percent aggregate voids filled with asphalt binder (VFA) shall be calculated as follows:

${\displaystyle VFA=\left(1-{\frac {V_{a}}{VMA}}\right)x100}$

403.3.1.1.11 Limestone-Porphyry (LP) and SMA mixtures with porphyry requirements by volume of the plus No. 8 material shall be calculated as follows:

${\displaystyle \%Porphyry_{+No.8}=\left[{\frac {{\frac {\%R_{P1+No.8}}{G_{P1}}}+{\frac {\%R_{P2+No.8}}{G_{P2}}}...+{\frac {\%R_{Pn+No.8}}{G_{Pn}}}}{{\frac {\%R_{1+No.8}\times \;P_{1}}{G_{1}}}...+{\frac {\%R_{n+No.8}\times \;P_{n}}{G_{n}}}+{\frac {\%R_{P1+No.8}\times \;P_{P1}}{G_{P1}}}...+{\frac {\%R_{Pn+No.8}\times \;P_{Pn}}{G_{Pn}}}}}\right\rbrack \times \;100}$

Where:

%R_1+No.8, %R_2+No.8, %R_n+No.8 = Percent of plus #8 non-porphyry aggregate.(100-P_#8)

G₁, G₂, G_n = Bulk specific gravity of non-porphyry material by AASHTO T 85.

%R_P1+No.8, %R_P2+No.8, %R_Pn+No.8 = Percent of plus #8 porphyry aggregate. (100-P_#8)

G_P1, G_P2, G_Pn = Bulk specific gravity of porphyry material by AASHTO T 85.

403.3.1.2 Field Compacted Density Samples

Samples, as submitted from the field, may be routine or Independent Assurance Samples. Tests and calculations shall consist of specific gravity and percent density. Test results and calculations shall be recorded on work Forms "Asphaltic Concrete (Field Sample)" and "Report of Tests on Sample of Asphaltic Concrete".

Specific gravity of the field compacted sample shall be determined in accordance with AASHTO T166 except cores to be averaged may be tested as one sample or individually.

Percent density of the compacted sample shall be calculated as follows:

${\displaystyle PercentDensity={\frac {G_{mc}}{G_{mm}}}\times \;100}$

Where:

G_mc=Specific Gravity of Sample

403.3.2 Sample Record

403.3.2.1 Trial Mixtures

The sample record shall be completed in AWP, as described in AWP MA Sample Record, General, and shall indicate acceptance, qualified acceptance, or rejection. Appropriate remarks, as described in EPG 106.20 Reporting, are to be included in the remarks to clarify conditions of acceptance or rejection. Test results shall be reported on the appropriate templates under the Tests tab.

403.3.2.2 Field Compacted Density Samples

The sample record shall be completed in AWP, as described in AWP MA Sample Record, General, and shall include a notation in the remarks, "Material submitted for the determinations indicated". Test results shall be reported on the appropriate templates under the Tests tab.