S-1(2360) PLANT MIXED ASPHALT PAVEMENT – USE OF ADJUSTED AFT INSTEAD OF VMA FOR MIXTURE QUALITY AND ACCEPTANCE
Mn/DOT - Use with all SP2005-140 (2360 PLANT MIXED ASPHALT PAV’T.) projects.
Local agencies should only use after there has been discussion with consent from the Mn/DOT Bituminous Office.
NEW WRITEUP 12/7/07
SP2005-142.1
The provisions of the attached Combined 2360/2350 (Gyratory/Marshall Design) Specification of these Special Provisions is hereby modified as follows in order to use the calculated Adjusted Asphalt Film Thickness (Adj. AFT) instead of Voids in the Mineral Aggregate (VMA) to ensure adequate effective asphalt volume. VMA values will still be calculated for information purposes, but will not be used for acceptance criteria. The calculation of Adjusted AFT will be based on the calculated aggregate surface area (SA) and the effective asphalt content.
S-1.1AGGREGATE SURFACE AREA (SA)
The aggregate surface area (SA) shall be calculated by the following formula(1):
SA = 2 + 0.02a + 0.04b + 0.08c + 0.14d + 0.30e + 0.60f + 1.60g
Where:
SA = Aggregate Surface Area in SF/lb. of dry aggregate
a, b, c, d, e, f and g are the percent of total aggregate passing the #4, #8, #16, #30, #50, #100 and #200 sieves, respectively. The percent passing each of the sieves shall be rounded to the nearest 1 percent, except for the #200 sieve, which shall be rounded to the nearest 0.1 percent.
(1)Mixtures with a combined (-)#4 Gsb less than 2.580, or greater than 2.700, will have the calculated SA adjusted accordingly. The SA will be increased for mixtures with a combined (-)#4 Gsb less than 2.580, and decreased for mixtures with a combined (-)#4 Gsb greater than 2.700. The SA adjustment procedure is as follows: Adjusted SA = SA(2.650/Mixture -#4 Gsb). There will be no SA adjustment for mixtures with a combined (-)#4 Gsb between 2.580 and 2.700.
S-1.2ADJUSTED ASPHALT FILM THICKNESS (Adj. AFT)
Adjusted Asphalt Film Thickness (Adj. AFT)
Adjusted AFT = AFT + 0.06(SA-28)
Asphalt Film Thickness (AFT)
The asphalt film thickness (AFT) shall be calculated by the following formulas:
AFT = Pbe x 4870
100 x Ps x SA
Where:
AFT = Asphalt Film Thickness in microns
Pbe = Effective Asphalt Content as a percent of the total mixture
4870 = Constant Conversion Factor
Ps = Percent Aggregate in Mixture /100, or (100-Pb) /100
Pb = Percent Total Asphalt Cement in Mixture
SA = Calculated Aggregate Surface Area in SF/lb.
Example of AFT Calculation
Assume:Pb = 5.9%
Pbe = 4.9% (based on total mixture weight)
Combined (-)#4 Gsb between 2.580 and 2.700
% passing #4 = 73%
% passing #8 = 58%
% passing #16 = 42%
% passing #30 = 28%
% passing #50 = 17%
% passing #100 = 7%
% passing #200 = 5.4%
SA= 2+(0.02)(73)+(0.04)(58)+(0.08)(42)+(0.14)(28)+(0.30)(17)+(0.60)(7)+(1.6)(5.4) = 31.0 SF/lb.
AFT = (4.9)(4870) = 23,863 = 8.2 microns
(100)[(100-5.9)/100](31.0) (100)(0.941)(31.0)
Example of Adjusted AFT Calculation
Adj. AFT = 8.2 + 0.06(31.0-28.0) = 8.2 + 0.06(3.0) = 8.2 + 0.2 = 8.4 microns
The Adjusted AFT will be greater than the AFT if the SA is greater than 28.0 SF/Lb., and will be less than the AFT if the SA is less than 28.0 SF/Lb.
S-1.3MIXTURE DESIGN
(A)The Contractor's trial mix shall have a minimum Adjusted AFT of 8.5 microns.
(B)Table 2360.3-B2b is modified to add minimum Adjusted AFT requirements, and eliminate the VFA requirements. The minimum Individual and Moving Average (n=4) Adjusted AFT shall be 7.5 and 8.0 microns, respectively.
(C)The VMA requirements listed in Table 2360.3-B2c are eliminated; however VMA values shall still be calculated for information purposes.
S-1.4DOCUMENTATION (MIX DESIGN)
(A)Section 2360.3C5 is modified to include the percent passing the #16, #30, #50 and #100 sieves in addition to the sieves listed in Table 2360.2-E.
(B)Section 2360.3C13 (i) is modified to include Adjusted AFT. The VMA and VFA shall remain included for information purposes.
(C)Section 2360.3C13 is modified to add (k) "The calculated Adjusted Asphalt Film Thickness (Adj. AFT)"at each asphalt binder content.
(D)Section 2360.3C14 is modified to add (f) “The calculated Adjusted Asphalt Film Thickness (Adj. AFT)".
S-1.5MIXTURE DESIGN REPORT
The Mixture Design Report listed in Section 2360.3E will not include any VMA requirements.
S-1.6PRODUCTION SAMPLING AND TESTING RATES
(A)Table 2360.4-E titled "Production Sampling and Testing Rates" is modified as follows:
(1)To add that the adjusted asphalt film thickness (Adj. AFT) shall be calculated each time a gradation test is required. The calculation procedure to be used is illustrated in this Special Provision.
(2)The Sampling and Testing Rate for gradations is modified to “1 gradation per 900 metric tons (1000 tons), or portion thereof (minimum of one per day)”, or at the same rate as the QC Mixture Property (Gmm and Gmb) tests are required by the SCHEDULE OF MATERIALS CONTROL. All gradations will include the percent passing the #16, #30, #50 and #100 sieves.
(B)Section 2360.4-E6 is modified to “Testing to determine the blended aggregate gradation shall be determined every 900 metric tons (1000 tons), or portion thereof (minimum of one per day) on samples taken at the same time as the required mixture sample for a given increment.
S-1.7PRODUCTION DOCUMENTATION (Records)
Section 2360.4-F2a is modified to add (16) “calculated adjusted asphalt film thickness (Adj. AFT)”.
S-1.8PRODUCTION DOCUMENTATION (Control Charts)
Section 2360.4-G5 is modified to eliminate voids in the mineral aggregate (VMA) and replace with adjusted asphalt film thickness (Adj. AFT).
S-1.9JMF LIMITS
(A)Section 2360.4H is modified as follows:
“The production air voids and Adjusted AFT are based on the specified requirements as shown in Tables 2360.3-B2b (as modified by this Special Provision). Gradations and asphalt binder content limits are based upon the current Department reviewed Mixture Design Report. Gradation control sieves include each sieve shown in Table 2360.2-E. The mixture production targets are listed on the Mixture Design Report. JMF limits are the target plus or minus the limits shown in Table 2360.4-H (as modified by this Special Provision). JMF limits are used as the criteria for acceptance of materials based on the moving average. A moving average is the average of the last four test results.”
(B)Table 2360.4-H, JMF limits (N=4), is modified as follows:
(1)The VMA requirement is eliminated. The VMA will be calculated for information, but is not included in acceptance criteria.
(2)The JMF limits for the gradation sieves shall be the same as the “Broad Band” limits listed in Table 2360.2-E. The gradation JMF limits (for both Moving Average and Individual results) shall not exceed those listed in Table 2360.2-E.
S-1.10JMF ADJUSTMENT
(A)Section 2360.4J1, paragraph #3, is modified to exclude any reference to VMA.
(B)The last sentence of paragraph #3 is changed to:
“The JMF asphalt content may only be reduced if at least the last four Adjusted AFT production tests (calculations) average 8.5 microns or more, and have minimum Individual Adjusted AFT’s of at least 7.5 microns.
(C)Sections 2360.4J1 and 2360.4K are modified to “eliminate any reference to VMA”.
S-1.11FAILING MATERIALS
(A)Section 2360.4L2 is eliminated.
(B)Section 2360.4L3 is modified so that an individual gradation test which is outside the “Broad Band” gradation limits listed in Table 2360.2-E is a failure. It is not allowed twice the JMF limits.
(C)Table 2360.4-L3, Reduced Payment Schedule for Individual Test Results, is modified as follows:
(1)The VMA item is eliminated.
(2)Add “Adjusted AFT” as an item. The Pay Factors are 90% for an Individual Adjusted AFT less than 7.5 microns and 75% for an Individual Adjusted AFT less than 7.0 microns but greater than 6.0 microns.
(D)Section 2360.4L5 is eliminated.
(E)Add the following Section 2360.4L9, Individual Failure – Adjusted AFT.
“If an Individual Adjusted AFT result is less than 7.5 microns, but greater than 6.0 microns, the material is considered unsatisfactory and will be accepted at a reduced payment. Reduced payment will be 90 percent of the Contract bid price if the Adjusted AFT is less than 7.5, but equal to or greater than 7.0 microns. Reduced payment will be 75 percent of the Contract bid price if the Adjusted AFT is less than 7.0 microns but greater than 6.0 microns. If an Adjusted AFT result is 6.0 microns or less, the material is considered unacceptable, and the material is subject to removal and replacement at the Contractor’s expense. Reduced payment as outlined in Table 2360.4-L3 (as modified by this Special Provision), or removal and replacement, shall apply to all tonnage represented by the individual test (calculation). This tonnage includes all material placed from the sample point of the failing test (calculation) until the sample point when the test (calculation) result meets either 7.5 microns (to receive 100% payment), 7.0 microns (to receive 90% payment) or 6.1 microns (to receive 75% payment). When the failure occurs at the first test after the start of daily production, the tonnage subjected to reduced payment, or removal and replacement, shall be calculated as described above and shall include the tonnage from the start of production that day.”
(F)Add the following Section 2360.4L10, Moving Average Failure at Start-Up- Adjusted AFT
“The Moving Average (n=4) Adjusted AFT will not be calculated until the sixth test after the beginning of mixture production of that specific mixture. This calculation shall include the Individual results of test (calculation) # 3, 4, 5 and 6.
(G)Add the following Section 2360.4L11, Moving Average Failure – Adjusted AFT
“If the Moving Average (n=4) of the Adjusted AFT is less than 8.0 microns, the mixture is considered unsatisfactory, and will be accepted at a reduced payment. Reduced payment will be 80 percent of the Contract bid price. Tonnage subjected to replacement or reduced payment shall be calculated as the tons placed from the sample point of all Individual Adjusted AFT results less than 8.0 microns, which contributed to the Moving Average value that was less than 8.0 microns, to the sample point when the Individual Adjusted AFT is 8.0 microns or greater. When the failure occurs at the first test after the start of daily production, the tonnage subjected to reduced payment shall be calculated as described above and shall include the tonnage from the start of production that day.”
S-1.12QUALITY ASSURANCE
Table 2360.4-M titled “Allowable Differences (Tolerances) Between Contractor and Mn/DOT Test Results” is modified to add the sieves and tolerances listed in the following table:
Additional Fine Sieve Gradation TolerancesSieve size
/ Allowable Tolerance(% passing)
1.18 mm [#16] / 4%
0.60 mm [#30] / 4%
0.30 mm [#50] / 3%
0.15 mm [#100] / 2%
0.075 mm [#200] / * 1.2%
* The #200 sieve is not a new sieve, but the allowable tolerance has been changed.
The allowable difference between the Contractor and Mn/DOT verification Adjusted
AFT calculation is 1.2 microns.
The Contractor’s Adjusted AFT shall be calculated using his individual test values except for any individual test results that are out of tolerance. The individual test tolerances are listed in Table 2360.4-M (as modified by this Special Provision). The Contractor shall substitute any individual Mn/DOT test results that are resolved to be out of tolerance.
If the Adjusted AFT calculation is out of tolerance, the Mn/DOT Adjusted AFT calculation (based on Mn/DOT test results) will be Equalized and used for the Individual Adjusted AFT result, and calculation of Moving Average Adjusted AFT results. Equalization of the Mn/DOT Adjusted AFT result consists of increasing the original Mn/DOT value by 0.5 microns. This increased value will then be used for acceptance.
S-1.13VERIFICATION TESTING
Add calculated adjusted asphalt film thickness (Adj. AFT) to the mixture properties that will be used to verify the mixture quality for acceptance. The voids in the mineral aggregate (VMA) will be used for information, but not acceptance.