Annotated Literature Review for NCHRP Report 640 (2009)

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264 mm thick ARFCs. They are not sure whether this is due to the fact that the 25 mm thick ARFCs are on new pavements, while the 12.5 mm ARFCs are on old pavements. 1.70.8 Structural Design Scofield and Donavan do not provide any information on structural design. 1.70.9 Limitations Scofield and Donavan do not provide any information on limitations. 1.71 Sholar, G. A., G. C. Page, J. A. Musselman, P. B. Upshaw and H. L. Moseley. “Development of the Florida Department of Transportation’s Percent Within Limits Hot-Mix Asphalt Specification.” TRB 2005 Annual Meeting CD- ROM. Transportation Research Board. National Research Council, Washington, D.C. 2005. 1.71.1 General Sholar et al. provides a description of test data and methods used for the development for a percent within limits (PWL) specification for construction quality control of dense- graded hot mix asphalt HMA and open graded friction courses (OGFC) in Florida. The acceptance and payment for OGFCs are based on asphalt binder content and percent passing certain critical sieve sizes. Sholar et al mentions that data from recently constructed projects were used to develop the tolerances in this specification, and a system has also been developed for acceptance and payment of small quantity lots. They mention that a system has been developed to use independent sampling and statistical tests for acceptance and payment. Note that since this paper is focused on quality control and not specifically on permeable friction courses (PFC), only the portion relevant to PFC is reviewed and presented in the following paragraphs. 1.71.2 Benefits of Permeable Asphalt Mixtures No information on benefits of PFCs is given. 1.71.3 Materials and Design No information on materials and design of PFCs is given. 1.71.4 Construction Practices No specific information on construction practices is given. However, since the development of PWL and the data related to variability in asphalt binder content and gradations are related to construction of PFC, these are reviewed and presented below. Sholar et al mention that the development of the PWL system for open-graded friction course mixtures was done in the same way as done for dense-graded Superpave mixtures. However, the material properties used for payment, standard deviations and specification limits are unique for OGFCs.

265 Sholar et al indicate that the Florida Department of Transportation (FDOT) selected four asphalt material properties that were believed to relate most closely to the performance of open-graded friction course mixtures. For each of these properties, proper weightage was determined on the basis of engineering judgment to determine the relative contribution to the overall quality of OGFC. The four properties and the relative ratings are: 1) asphalt binder content (40%), 2) percent passing the 3/8 inch sieve (20%), 3) percent passing the No. 4 sieve (30%), and 4) percent passing the No. 8 sieve (10%). Sholar et al indicate that FDOT considered a sublot for OGFC mixes as 500 tons of asphalt mixture, with four sublots making up one lot of 2000 tons. They mention that the PWL system is utilized only for LOTs that contain three or more sublots. Production resulting in less than three sublots is treated separately as “small production”. The frequency of test for each asphalt mix property is one random test per sublot. Sholar et al provide a table with standard deviations of the critical OGFC mix properties on the basis of quality control data obtained from 5 projects, constructed by 7 contractors. Table 126 shows the variance and standard deviation of the different properties. Table 126: Variability of Test data from OGFC Projects (25 projects, 319 data points) Property Variance Standard Deviation Asphalt Binder Content, % 0.057 0.0238 Percent passing the 3/8 inch sieve 8.950 2.992 Percent passing the No. 4 sieve 4.422 2.103 Percent passing the No. 8 sieve 1.090 1.044 Sholar et al indicate that the FDOT used the method presented in the AASHTO Quality Assurance Guide Specification and NCHRP Report 447 to develop the specification limits for each asphalt mix. They mention that in this method, a 100 percent payment to the contractor is made if 90 percent of the test results are within the upper and lower specification test limits. Therefore, the specification limits must be established such that if a Contractor’s test data has representative variability and the mean of the test results is equal to the target, then 100 percent payment can be achieved. Sholar et al indicates that the standard deviations shown in Table 126 were multiplied by 1.645, since in a normal distribution 90 percent of the data is expected to lie between ± 1.645(standard deviation) from the mean value. In the derivation of the specification limits, Sholar et al mention that the median instead of the average standard deviation values were used. This was done in view of the fact that in the distribution of variance values, the median variance and the average variance were not found to be equal, and the DOT believed that the median value was more representative than the average value.

266 Sholar et al presents the derived specification limits (shown in Table 127), and mentions that the mathematically derived specification limit values were increased (and adopted, as shown in the column “Implemented Specification Limits”) on the basis of discussion with construction industry representatives, FHWA representatives and other Department personnel. Table 127: Specification Limits for OGFC Property Median Standard Deviation Calculated specification Limits (standard deviation * 1.645) Implemented specification limits Asphalt Binder Content, % 0.24 0.39 ±0.45 Percent passing the 3/8 inch sieve 2.99 4.92 ±6.00 Percent passing the No. 4 sieve 2.10 3.46 ±4.50 Percent passing the No. 8 sieve 1.04 1.72 ±2.50 Sholar et al indicate that for calculation of payment, the FDOT used the method presented in the AASHTO Quality Assurance Guide Specification. They indicate that for each asphalt material property, the following equation is used to determine the pay factor: Pay factor (%) = 55 + 0.5 x PWL, where: PWL = percent within limits The authors mention that with this system, the maximum pay factor that can be achieved for 100 percent of test results within the specification limits is 105, i.e. a five percent bonus in payment. They also mention that FDOT has specifications that have clauses for dealing with low pay factor material. Sholar et al mention that after the pay factor has been determined for each asphalt material property, a composite pay factor (CPF, with a maximum of 105) is calculated by multiplying the respective weights for each material property by the individual pay factors. There are also specifications to protect against low pay factor material. The authors mention that there are three ways for a Contractor to increase the percent within limits to increase the pay factor: 1) reduce the difference between the mean of the test data and the established target value, 2) reduce the variability of the test results, or 3) a combination of one and two. Sholar et al indicate that FDOT has developed small quantity pay tables that are similar in principle to the pay tables used prior to the development of the PWL system. Payment is based on the deviation of a test result or average deviation of two test results from the target value. Larger deviations from the target result in lower pay factors. No provision has been made for bonus in the small quantity pay table, since the intent of the

267 specification is to use the PWL concept as often as possible and to discourage the production of small LOTs resulting in only one or two test results. Sholar et al mention that the derivation of the values contained in the small quantity pay tables is based partially on the specification limits used in the PWL system and partially on negotiations with industry. Even though very little difference was found between variability of properties between large and small productions, provision for larger variability was kept in the table for small production in view of the contractors’ concerns that the variability for small quantities would be difficult to control. The pay table for open-graded friction course mixtures is shown in Table 128. Table 128: Pay Table for Small Production Property Pay Factor 1-Test Deviation 2-Test Average Deviation Asphalt Binder Content, % 1.00 0.90 0.80 0.00-0.50 0.51-0.60 >0.60 0.00-0.35 0.36-0.42 >0.42 Percent passing the 3/8 inch sieve 1.00 0.90 0.80 0.00-6.50 6.51-7.50 >7.50 0.00-4.60 4.61-5.30 >5.30 Percent passing the No. 4 sieve 1.00 0.90 0.80 0.00-5.00 5.01-6.00 >6.00 0.00-3.54 3.55-4.24 >4.24 Percent passing the No. 8 sieve 1.00 0.90 0.80 0.00-3.00 3.01-3.50 >3.50 0.00-2.12 2.13-2.47 >2.47 Notes: (1) Each density test result is the average of five cores. (2) In the event that the density of a LOT is less than 93.00% of Gmm, the Department will assess the pavement’s permeability in accordance with FM 5-565. If the coefficient of permeability is greater than or equal to 125 x 10-5 cm/s, the Engineer may require removal and replacement at no cost or may accept the pavement at 90% pay. The Contractor may remove and replace at no cost to the Department at any time. (3) If approved by the Engineer, based on an engineering determination that the material is acceptable to remain in place, the Contractor may accept the indicated partial pay. Otherwise, the Department will require removal and replacement at no cost. The Contractor may remove and replace at no cost to the Department at any time. Sholar et al provide information on the verification procedure used by FDOT. This procedure is necessary since the contractor’s quality control test data is used in the calculation of the payment amount for a given lot of hot-mix asphalt material. For verification, a DOT representative directs the contractor to obtain three split samples at a randomly selected point within the production of each sublot. The three split samples are required for the contractor, for verification testing and for resolution testing. The contractor performs tests on each sublot split sample. The verification technician

268 performs tests on one randomly selected split sample per lot. For both the contractor and verification technician, tests are conducted to determine the following six asphalt material properties: 1) maximum specific gravity of the asphalt mixture, 2) bulk specific gravity of the gyratory compacted asphalt specimen at the plant, 3) percent asphalt binder content, 4) percent passing the No. 8 sieve, 5) percent passing the No. 200 sieve, and 6) bulk specific gravity of roadway cores. The contractor and verification test results are required to meet between-laboratory precision values established in FDOT test methods. Sholar et al mentions that if all of the test results compare well, then the lot will be accepted with payment calculated based on the contractor’s test data. If any of the test results do not compare favorably, the verification split samples from the remaining sublots of the lot will be tested only for the asphalt property(s) that did not compare favorably. A comparison will then be made between all of the contractor and verification test results for the asphalt property(s) that did not compare favorably. If there is only one unfavorable comparison, then the lot will be accepted and payment will be based on the contractor’s test results. If there are two or more unfavorable comparisons, then a laboratory identified by the Department will test all of the resolution samples for the asphalt property(s) that did not compare favorably. If all of the resolution test results compare favorably with the contractor’s test results, then the lot will be accepted with payment calculated based on the contractor’s test data. If any of the resolution test results do not compare favorably with the contractor’s test results, then the lot will be accepted with payment calculated based on the resolution test results. Sholar et al indicates that the Florida DOT has developed an Excel spreadsheet (available on the DOT website) that performs all of the required calculations and pay factor determinations. It also generates random numbers to identify sampling points during production. The spreadsheet is password protected to prevent manipulation of tolerances and formula. 1.71.5 Maintenance Practices No information on maintenance practices is provided in this paper. 1.71.6 Rehabilitation Practices No information on rehabilitation practices is provided in this paper 1.71.7 Performance No information on performance is provided in this paper 1.71.8 Structural Design No information on structural design is provided in this paper 1.71.9 Limitations No information on limitation on use of PFC is provided in this paper