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29 chapter three Survey on uSe of Performance SPecificationS for aSPhalt mixtureS introduction In this survey, 90% of the state DOTs (45/50) provided input on their use of performance testing and performance specifica- tions for plant-produced asphalt mixtures. The agency survey questions are presented in Appendix A, along with the entire survey response set. The entire list of agency respondents is provided in Appendix B. There were 14 additional respon- dents, including the District of Columbia DOT, two counties, one city, and 10 Canadian provincial MOTs. Their specific results are referred to in this chapter as other agency responses. BaSiS for accePtance of aSPhalt mixtureS uSing Performance SPecificationS The survey responses to Question 1 showed that the over- whelming majority of respondents reported that in addition to HMA, both WMA [98% of state DOTs (44/45) and 13 other agencies] and asphalt mixtures with RAP [98% of state DOTs (44/45) and 12 other agencies] are used for plant-produced asphalt pavements. The survey results indicated that fewer agencies use asphalt mixtures with RAS [56% of state DOTs (25/45) and three other agencies] and asphalt mixtures with crumb rubber from tires or GTR [36% of state DOTs (16/45) and three other agencies]. Additional mixes used include friction courses that were reported by Arizona DOT and asphalt mixtures with synthetic fibers reported by Pennsylvania DOT. The city of Los Angeles, California, has been design- ing HMA overlays with 50% RAP and has been collecting data on these high RAP projects. Figure 3 shows the survey responses to Question 1 presented geographically. The survey responses to Question 4 revealed the attri- butes that are required by the vast majority of DOTs and other agencies before production of asphalt mixtures of all types including aggregate properties such as angularity, abra- sion resistance and soundness, asphalt binder properties, laboratory air voids, gradation, asphalt content, VMA, and moisture damage determined by the TSR. The most frequent responses included the use of the APA (reported by five state DOTs and one other agency) and considering voids filled with asphalt VFA (voids filled with asphalt), as reported by four DOTs. Other respondents commented on the consider- ation of attributes such as permeability, moisture sensitivity, Hveem stability, and/or the dust-to-asphalt cement ratio. Forty-four percent of state DOTs (20/45) and five other agencies noted in answers to Question 2 that when recycled materials are included in asphalt mixtures, different tests or test approaches are used; a sample of these are highlighted in Table 5. The full set of detailed responses for Question 3 is included in Appendix A. Pennsylvania DOT reported that its test approach changes when SMA or gap-graded mixtures are used. Kansas DOT mentioned that it will be requiring a HWTD test and a TSRST for mixtures using high RAP percentages in the near future. New York DOT requires the AASHTO T 283 test when cer- tain WMA technologies are used. The city of Edmonton reported that it makes adjustments to the binder properties and air voids (in percent of the total mix). For mixtures containing RAS, Edmonton requires the voids in the total mix to be reduced by 0.5% of the voids used in the virgin mix. The responses to Question 7 showed that when using WMA mixtures, Georgia DOT reported that it increases the frequency of samples taken to verify volumetric mix design attributes. Similarly, Pennsylvania DOT increases the frequency of sam- ples tested when using RAP or mixtures with crumb rubber from tires. In response to Question 8, Pennsylvania DOT also reported that it increases the total number of samples taken to verify volumetric mix design attributes when RAP or mixtures with crumb rubber are used. California DOT reported that it increases the total number of samples taken for mixtures containing RAP and RAS. contentS of Performance SPecificationS for aSPhalt mixtureS The survey data from Question 9 showed that the majority of states are either currently using or planning to implement some form of performance specifications, as shown in Table 6. In this context, performance specifications primarily refer to performance-based attributes used for mix design accep- tance and to a lesser extent PRS using volumetric properties with predictive models. The predictive models mentioned by state DOTs and other agencies in responses to Questions 36 and 37 of the survey are presented in Table 7.
30 FIGURE 3 Geographic distribution of state DOT responses to Question 1 on the types of asphalt mixtures produced in each state. : Use of WMA and RAP : No response : Use of WMA, RAP, RAS, GTR : Use of WMA, RAP, GTR : Use of WMA, RAP, RAS : Use of RAP and RAS : Use of RAP, RAS, GTR : Use of WMA Map source: diymaps.net Type of Approach Agency Respondents Use of Blending Charts Alberta, California, Kansas, Maryland, Michigan, North Carolina, Ohio Further Classification of RAP (percentage of RAP, gradation of RAP, etc.) Delaware, Kansas, Maine, Nova Scotia, Oregon, Québec, Wyoming Materials Verification (binder content, percent air voids, specific gravity, asphalt content, etc.) British Columbia, California, Georgia, Idaho, Pennsylvania, Québec, Wyoming Testing (dynamic modulus, HWTD, Texas Overlay Tester, flexural beam fatigue, etc.) Kansas, North Carolina, New Jersey, New York, Ohio, South Dakota, Wisconsin TABLE 5 SuRVEY RESPONSES TO QuESTIONS 2 AND 6 ON TESTS OR TEST APPROACHES FOR RECLAIMED ASPHALT PAVEMENT There were many reasons reported in Question 10 as to why state DOTs are currently using or planning to use per- formance specifications for asphalt mixtures, as indicated in Figure 4. Additional responses included quantifying the quality of the end product, as noted by Louisiana DOTD. In terms of volumetric attributes that are deemed critical to predicting pavement performance in Question 13, 100% of state DOTs that answered this question (44/44) and 13 other agencies reported that density or in-place air voids are one of the most important attributes, followed by asphalt con- tent [82% of state DOTs (36/44) and 11 other agencies], VMA [57% of state DOTs (25/44) and five other agencies], laboratory air voids [55% of state DOTs (24/44) and six other agencies], moisture damage by the TSR [45% of state DOTs (20/44) and nine other agencies], and gradation [39% of state DOTs (17/44) and 10 other agencies]. In other responses to Question 13 regarding performance-based attri- butes, New Jersey, Ohio, and Georgia DOTs all noted that rutting resistance is considered one of the most important
31 Roadway Type and Use of Performance Specifications Currently Using Performance Specifications Planning to Use Performance Specifications No Plans to Use Performance Specifications Interstate Pavements 49% (22/45) 18% (8/45) 33% (15/45) Pavements on Other Arterials (state highway system) 44% (20/45) 22% (10/45) 33% (15/45) Pavements on Local or County Road System 32% (14/45) 17% (7/45) 46% (21/45) TABLE 6 STATE DOT RESPONSES TO QuESTION 9 ON TYPES OF FACILITIES IN WHICH PERFORMANCE SPECIFICATIONS WERE uSED FOR ASPHALT PAVEMENTS Model Type Agencies Simplified Viscoelastic Continuum Damage (S-VECD) Georgia, Louisiana, Maine, Oklahoma, Virginia Fracture energy Colorado, Florida Predictive models based on fatigue, rutting, or other distress types (e.g., MEPDG) California, city of Edmonton, Florida, Georgia, Louisiana, Nebraska, Québec, South Carolina, South Dakota, Utah, Virginia, Wisconsin Quality related standard specification City of Edmonton, Georgia, Louisiana, Maine, Missouri, Pennsylvania, Québec, Saskatchewan Pavement design optimization based on life-cycle cost analysis Georgia, Louisiana, Québec, South Carolina, West Virginia TABLE 7 AGENCY RESPONSES TO QuESTIONS 36 AND 37 RELATED TO THE TYPES OF PREDICTIVE MODELS SuPPORTED BY RESEARCH uNDERWAY attributes, whereas fatigue resistance and smoothness were also noted by a few respondents. Fifty-four percent of state DOTs (21/39) and three other agencies reported in Question 14 that a direct measurement of fatigue is one of the most important performance tests to predict pavement performance, whereas 51% of state DOTs (20/39) and five other agencies reported that a direct measurement of rutting is one of the most important tests. Additional responses included measurement of thermal properties for cracking (five state DOTs), moisture damage or susceptibility testing (two state DOTs), and smoothness or ride quality (two state DOTs). A number of different approaches or sources were reported to be used as the basis for the development of performance specifications, the majority of which are shown in Table 8 from Question 17. Additional responses included Ontario MOTâs implemen- tation based on lessons learned from warranty contracts and on the review and evaluation of historical performance. Kansas DOT reported its use of the AASHTO TSRST test to aid in the development of performance specifications. The types of asphalt mixtures for which the performance parameters are used are summarized in Table A15, as reported by the survey respondents in Question 18, and the responses related to fatigue resistance and moisture resistance for the most common asphalt layers (in this case the standard struc- tural lift, standard overlay lift, and high-performance thin
32 overlay) are shown in Figure 5. The city of Edmonton and Ministry of Highways and Infrastructure of Saskatchewan both responded in Question 18 that the fatigue resistance and moisture resistance of standard structural and overlay lifts, and high-performance thin overlays, were key performance parameters. The Nova Scotia Transportation and Infrastruc- ture Renewal, Ontario MOT, and Ministère des Transports du Québec all responded in Question 18 that the moisture resistance of the standard structural and standard overlay lifts was a key performance parameter. Further analysis of the survey data in Question 19 showed that state DOTs have tested or used performance-based mix- ture design specifications under the following scenarios or project types, as shown in Figure 6. Ohio DOT noted in Question 19 that performance-based mixture design specifications could also be considered when high RAP or RAS mixes are being used. Furthermore, Missouri DOT noted that performance-based mixture design specifica- tions would only be considered with more industry acceptance FIGURE 4 Summary of state DOT responses to Question 10 on the reasons to use performance specifications for asphalt mixtures. 0% 10% 20% 30% 40% 50% 60% 70% Not applicableânot looking into using performance specifications for asphalt To achieve longer service life prior to major maintenance or rehabilitation being required on asphalt pavements To save on maintenance costs over the life of the asphalt pavement To improve performance in terms of asphalt rutting To improve performance in terms of fatigue cracking in asphalt pavements To improve performance in terms of low-temperature cracking in asphalt To improve ride quality of asphalt pavements To level the playing field in terms of industry involvement and encourage better construction product All of the above Other Percentage of state DOT Respondents 12 out of 45 DOTs 31 out of 45 DOTs 27 out of 45 DOTs 21 out of 45 DOTs 28 out of 45 DOTs 23 out of 45 DOTs 23 out of 45 DOTs 26 out of 45 DOTs 12 out of 45 DOTs 14 out of 45 DOTs Responses Fatigue Resistance Thermal Cracking Resistance Durability Moisture Resistance Stiffness Modulus Total DOT Responses Demonstration Project 5 2 3 5 3 6 Pooled Fund Study 1 3 1 1 2 4 Adapted from Another Agencyâs Specifications 1 1 3 3 0 4 Based on FHWA Research 5 5 3 6 2 10 Based on NCHRP Research 5 5 5 10 3 12 Based on Your Agencyâs In- House or Sponsored Research 11 10 9 18 6 20 TABLE 8 STATE DOT RESPONSES TO QuESTION 17 ON THE BASIS FOR IMPLEMENTING PERFORMANCE SPECIFICATIONS
33 and when test methods are both easy to perform and affordable to operate for the contractor. The most common tests used to support performance- based mixture designs reported in Question 20 are shown in Table 9. For the majority of tests performed, the use of an AASHTO or ASTM standard was reported; however, for state DOTs that perform APA testing, seven of the 15 respondents noted that a special agency test method is used in place of an AASHTO or ASTM standard. In addition, Québec MOT reported that it uses the French rutting test in comparison with the APA. In terms of performance tests used for qualification, quality control, or acceptance the attributes reported in Question 21 included fatigue resistance, stiffness modulus, thermal crack- ing resistance, durability properties, and moisture resistance. The most common performance tests reported in Question 21 for predicting fatigue resistance included the flexural beam fatigue test (four of 45 state DOTs and two other agencies) and FIGURE 5 State DOT responses to Question 18 on fatigue resistance and moisture resistance performance parameters for the most commonly-reported asphalt surface layer types. : Fatigue and moisture resistance of SSL and SOL : No response : Moisture resistance of SSL, SOL, HPTO : Fatigue resistance of SSL and SOL : Moisture resistance of SSL : Fatigue resistance of HPTO Moisture resistance of SSL and SOL : Fatigue and moisture resistance of SSL : Moisture resistance of SSL and SOL Legend SSL = standard structural lift SOL = standard overlay lift HPTO = high performance thin overlay Map source: diymaps.net FIGURE 6 Survey state responses to Question 19 on the circumstances for the use of performance-based asphalt mix design specifications. 0% 10% 20% 30% 40% 50% 60% 70% When conducting long-life pavement design When information about the existing pavement conditions under flexible overlays over a concrete pavement are known In a demonstration study When using alternate project delivery methods (i.e., Design-Build, Design-Build hybrid, warranty) All of the above Exclusive/None of the above Other Percentage of state DOT Respondents 27 out of 45 DOTs 19 out of 45 DOTs 26 out of 45 DOTs 22 out of 45 DOTs 11 out of 45 DOTs 10 out of 45 DOTs 14 out of 45 DOTs
34 Performance Test Types Agencies HWTD Test California, city of Edmonton, Colorado, Georgia, Kansas, Louisiana, Montana, New York, Pennsylvania, Québec, Saskatchewan, Texas, Utah, Wisconsin APA Test Alabama, Arkansas, city of Edmonton, Georgia, Idaho, Mississippi, Nebraska, New Jersey, New York, Ohio, Pennsylvania, Québec, South Carolina, South Dakota, Virginia Mixture BBR Test Alabama, city of Edmonton, Colorado, Montana, Nebraska, New Hampshire, Pennsylvania, Québec, Saskatchewan, South Carolina Flow Number Test Using AMPT Colorado, New York, Pennsylvania, South Carolina, South Dakota Dynamic Modulus Test Using AMPT City of Edmonton, Colorado, New York, Pennsylvania, South Carolina, South Dakota Flexural Beam Fatigue Test California, city of Edmonton, New York, Pennsylvania, Québec, Saskatchewan SCB Test Louisiana, South Dakota, Wisconsin RSST Test California, Pennsylvania, Vermont DCT Test Colorado, South Dakota, Wisconsin Overlay Tester New Jersey, New York, Texas TABLE 9 AGENCY RESPONSES TO QuESTION 20 ON MOST COMMON PERFORMANCE TESTS FOR PERFORMANCE-BASED DESIGNS the Texas Overlay Tester (three of 45 state DOTs). The most common tests reported for measuring the stiffness modulus included the Dynamic Modulus test in the Asphalt Mixture Performance Test (AMPT) (three of 45 state DOTs and one other agency), the HWTD test (three of 45 state DOTs), and the APA (two of 45 state DOTs). The most common test reported for predicting thermal cracking resistance was the mixture beam bending rheometer (BBR) (five of 45 state DOTs and three other agencies) and the flexural beam fatigue test used by one other agency. The most common tests reported for measuring the durability properties included the HWTD test (six of 45 state DOTs and one other agency) and the APA (five of 45 state DOTs and two other agencies). Québec MOT reported that it also uses the French rutting test for measuring asphalt mixture durability properties. The most common test reported for predicting moisture resistance was the HWTD test (nine of 45 state DOTs and two other agencies). The survey responses to Question 21 indicated that the HWTD and the APA were the most commonly used performance-based test procedures, with a total of 12 of 45 and 11 of 45 different state DOTs, respectively. One other agency is using the APA for qualification of the mix design, quality control, or acceptance. The city of Edmonton reported that it requires that all SMA mixtures undergo rutting susceptibility testing by the APA procedure dur- ing both mixture design and production; however, it does not currently require this testing on all traditional dense- graded mixtures. The majority of state DOTs (29/44) reported in Ques- tion 22 that they currently do not use independent assurance for performance-based tests. A few respondents noted that performance testing is not used for acceptance, but for test- ing and research purposes only (Florida and Colorado DOTs). The city of Edmonton reported that it operates its own qual- ity assurance (QA) laboratory and Nova Scotia MOT reported that once independent assurance is implemented, the testing would be the responsibility of the contractors. teSt Program imPlementation The survey responses to Question 23 indicated that, of the respondents who use performance mixture design specifica- tions, 29% of state DOTs (12/42) and one other agency use shadow performance mix design testing for data collection
35 FIGURE 7 Summary of responses to Question 34 on the types of performance testing research for PBS that is conducted or sponsored. 0% 10% 20% 30% 40% 50% 60% 70% Fatigue properties Stiffness modulus (i.e., dynamic modulus, flow number, flow time, etc.) Durability properties Thermal cracking Moisture susceptibility Other research underway Not applicable Percentage of state DOT Respondents 10 out of 17 DOTs 10 out of 17 DOTs 8 out of 17 DOTs 10 out of 17 DOTs 10 out of 17 DOTs 1 out of 17 DOTs 0 out of 17 DOTs and use volumetric properties for qualification, quality con- trol (QC), and acceptance. An additional 21% of state DOTs (9/42) and two other agencies are using both volumetric prop- erties and performance design specifications for qualification, QC, and acceptance. Thirty percent of state DOT respondents (13/43) noted in Question 24 that performance testing is completed by the agency at a state laboratory. Contractor performance testing at a commercial laboratory was reported by 12% of the state DOTs (5/43) and two other agencies. Nine percent of state DOTs (4/43) and one agency reported using a testing con- sultant at a commercial laboratory. In most cases, it was reported that the agency was running the performance-based tests; however, some agencies are experimenting with having the contractors purchase the equipment and run the tests as part of their QC program. Twenty-three percent of state DOTs (10/43) and four other agencies indicated that the contractor performs testing for QC while the agency performs the testing for verification or acceptance. Approximately 40% of state DOTs (18/45) and two other agencies indicated in Question 25 that they have the neces- sary equipment for performance testing, while another 27% (12/45) noted that some limited equipment is available. For example, both Oklahoma and South Carolina DOTs reported they are conducting research on the AMPT and expect delivery of the equipment upon completion of the research. Others, such as Georgia, Missouri, and Pennsylva- nia DOTs, indicated that they only have some of the equip- ment presented in the survey. A number of respondents reported in Question 34 that many different performance parameters have been investi- gated with sponsored or internal research in the past, as shown in Figure 7. For example, the city of Edmonton reported it is currently evaluating all of its standard asphalt mixtures by comparing their performance characteristics to determine what properties to test. Nova Scotia MOT reported it is researching past performance of rehabilitation treatments based on visual distresses and working to identify which properties to focus on and the availability of tests. An additional 39% of state DOTs (17/44) and three other agencies noted in Question 33 that they are currently conduct- ing, sponsoring, or planning to conduct or sponsor, research related to performance testing in the future. More detailed information regarding current research, including efforts in Maryland and South Dakota that are assessing the use of models in the AASHTO MEPDG, are reported in Question 35 as shown in Table 10. For example, Rhode Island DOT reported that it is spon- soring research to develop pay adjustment factors for typi- cal AC mixtures used in the state. The pay adjustment factors will be based on pavement life differences predicted using measured material properties and distress models from the QRSS software. The scope of the project includes the evaluation of two typical surface mixtures and a base mix- ture (that contains between 15% and 25% RAP) for non- interstate highways. The project is intended to produce a spreadsheet-based catalog for predicted pavement service lives that can provide Rhode Island DOT materials and field engineers with the necessary information for assessing the quality of asphalt mixtures produced, and potential pay factor adjustment, in advance of (or early on in) construction. Oklahoma DOT reported that it does not use compre- hensive performance specifications; however, it does con- duct certain performance testing on asphalt mixtures. For example, the HWTD rutting test is incorporated into the Oklahoma DOT specifications through agency test method OHD L-55 and the AASHTO T 324 method. In addition, it reported that moisture sensitivity testing is done following the AASHTO T 283 method using one freeze/thaw cycle. Both the rutting and moisture sensitivity tests are required for all asphalt mix designs. Oklahoma DOT reported that it requires the moisture sensitivity testing to be completed every 20,000 tons and the HWTD rutting test to be per- formed on the same samples for information only within
36 Agency Respondent Response Colorado DOT Currently performing AMPT and recently began testing for fracture energy using DCT specimens Georgia DOT AMPT pooled fund study and has sponsored research regarding moisture susceptibility of asphaltic concrete mixtures and best anti-stripping agents research. Maine DOT Performance testing as part of SHRP 2 R07 project Maryland DOT AMPT/MEPDG pooled fund study investigating integration with MEPDG models Minnesota DOT AMPT pooled fund study, as well as a 2013 DCT pilot project. DCT implementation is ongoing. Eleven field projects were sampled in 2014 and the round-robin testing for interlaboratory variability is complete. The DCT specification development for 2016 implementation is underway. Missouri DOT Performance testing research regarding the semicircular bending test (SCB) and the DCT Oklahoma DOT Fatigue testing research Québec MOT (Canada) Dynamic modulus research and complex modulus determination for asphalt mixes South Dakota DOT MEPDG research project on material test characteristics Utah DOT BBR beam slivers for low temperature cracking potential of an asphalt mix. SCB test to balance the mix design or get more asphalt binder into the mix, and to predict cracking potential at intermediate temperatures. Wisconsin DOT Four high RAP asphalt pavement projects in 2014 with analysis of the mixtures using the DCT, SCB, and HWTD tests as required performance tests. West Virginia DOT Beginning some work using the SENB and DENT binder test to correlate with the AMPT and Hamburg tests TABLE 10 SAMPLING OF CuRRENT AGENCY RESEARCH PROJECTS BEING SPONSORED OR CONDuCTED, AS REPORTED IN QuESTION 35 the last year. It reported that the university of Oklahoma is currently conducting sponsored research on the fatigue testing of RAP binders and that Oklahoma DOT expects to purchase the equipment necessary to conduct mixture fatigue testing and dynamic modulus testing. Twenty-three percent of state DOTs (9/39) and two other agencies reported in Question 36 that they pursued pre- dictive models based on rutting, fatigue, or other distress types. A small number of state DOTs and three other agen- cies have pursued other models, such as the S-VECD model (four of 39 DOTs), QRSS (five of 39 DOTs), or pavement design optimization based on life-cycle cost analysis (four of 39 DOTs). In addition to the research information presented in Table 10, additional efforts regarding PBS were reported in Question 37. Pennsylvania DOT reported it is optimizing volumetric prop- erties to improve rutting resistance; Florida DOT reported its efforts to find an appropriate fatigue cracking specifi- cation; Oklahoma DOT reported on its current research to implement an appropriate fatigue cracking test; and Maine DOT noted its efforts to work with industry to implement performance-based mix designs into standard practice. The city of Edmonton reported that it is in the process of review- ing all of its standard specifications and is including industry partners in the process. develoPment of contract ProviSionS for accePtance and Pay factorS for aSPhalt Performance SPecificationS Forty-nine percent of state DOTs (22/45) and four other agencies reported in Question 11 that they are currently using performance specifications (although the survey results appeared to indicate that in many cases these are based
37 primarily on volumetric properties) as a basis for acceptance and/or pay factor adjustments. Both Indiana and Maine DOTs reported that they are in the preliminary stages of implement- ing this effort. Maine DOT noted that the current goal is to first implement the performance-based mix design procedures, then review potential acceptance or pay factor adjustments. Of the 22 states that noted in Question 12 that they are currently using performance specifications, 72% (18/22) and four other agencies indicated that they are using performance specifi- cations as a basis for pay factor adjustments, primarily based on volumetric properties, by utilizing a combined system of both accept/reject and pay adjustments. Only 28% of state DOTs (7/22) reported that they use an accept/reject system only, while another 28% (7/22) use a pay adjustment system only. Indiana DOT and Clark County (Nevada) reported that they are using life-cycle reduction as the basis for pay factor adjustments. The results from performance testing were reported in Question 15 to have had mixed-use purposes for pay fac- tor adjustments at state DOTs. For example, 29% of state DOTs (12/42) and three other agencies have implemented data (primarily from rutting tests such as the HWTD) from performance testing on pay factors for pavement proj- ects of all roadway classes, and an additional 5% of state DOTs (2/42) and two other agencies are using data from performance testing on pay factors for pavement projects only on interstates. Nineteen percent of state DOTs (8/42) and one other agency indicated that they are planning to implement data from performance testing on future pave- ment projects. Finally, 55% of state DOTs (23/42) and six other responding agencies indicated they are not planning to use performance test results as an input for pay factor adjustments. In Question 16, 63% of state DOTs (12/19) and five other agencies that answered this question reported that durability (assumed to mean rutting resistance and resistance to raveling and segregation) and moisture resistance were considered for integration of mixture acceptance and pay factor adjustment. Twelve of 19 state DOTs and three other agencies considered fatigue resistance and stiffness modulus, whereas five of 19 and one other agency considered thermal cracking resistance. In addition, other responses (three of 19 state DOTs) to Ques- tion 16 included consideration of rutting resistance. BenefitS and challengeS of imPlementation of Performance SPecificationS For 36% of the state DOTs (16/44) the required testing time for many of the performance tests was reported in Question 26 to be a challenge to implementing certain tests, as described in Table 11. The survey responses to Question 28 reported that cost is a deciding factor in implementing performance testing for 36% of the state DOTs (16/45) and four other agencies. Thirty- one percent of state DOTs (14/45) and four other agencies noted that they plan to assess the relative costs and benefits of implementing performance testing compared with standard volumetric specifications. Of those that indicated that cost was a deciding factor, several different reasons were reported in Question 29 and are shown in Figure 8. In terms of assessing costs and benefits, nearly all of the 11 state DOTs that responded to Question 31 indicated that HMA (10/11), WMA (9/11), and RAP (10/11) mixes have been included in the assessments. Three other agencies also noted that these mixes are considered. Only 36% of state DOTs (4/11) and two other agencies have considered RAS, while 18% of state DOTs (2/11) have considered asphalt mixes with crumb rubber from tires. New Jersey DOT indicated that they are currently investigating cost and benefit analyses, but that further information is unavailable at this time. Some of the challenges reported by agencies in Ques- tion 38 to implementing performance specifications are shown in Figure 9. The most common response was associated with the hesi- tancy in confidently accepting appropriate performance-based test methods, a concern noted by New Jersey, Tennessee, Missouri, and West Virginia DOTs. utah, Florida, Tennessee, and Missouri DOTs also noted a lack of confidence in full implementation of the available test methods. Reasons Given for Test Turnaround Time as a Deciding Factor Agency Respondent Efficiency in meeting deadlines and production goals Alabama, Florida, Louisiana, Pennsylvania, Utah Limited resources available and issues with testing procedures Montana, Nebraska, New Jersey Avoid delaying the contractor California, Missouri TABLE 11 TEST TuRNAROuND TIME CHALLENGES IN IMPLEMENTING PERFORMANCE TESTING, AS REPORTED IN QuESTION 27
38 FIGURE 9 Issues reported in Question 38 on the challenges of moving toward using performance specifications for the design and acceptance of asphalt mixtures. 0% 10% 20% 30% 40% 50% 60% 70% Cost of equipment and/or testing by Consultant laboratories Delays in project schedule completion Lack of familiarity or confidence in the paving industry Insufficient funds for including the additional test frequencies required Lack of training for agency and industry Gaps in knowledge or insufficient informaton on how to successfully implement the use of performance specifications for asphalt mixtures Lack of evidence that the cost is worth the benefit of implementing a performance-based system Other Not applicable Percentage of state DOT Respondents 25 out of 43 DOTs 15 out of 43 DOTs 18 out of 43 DOTs 14 out of 43 DOTs 21 out of 43 DOTs 29 out of 43 DOTs 17 out of 43 DOTs 12 out of 43 DOTs 5 out of 43 DOTs FIGURE 8 Reasons reported in Question 29 on cost as a deciding factor for implementation of PBS. 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Cost of test equipment Cost of hiring consultant testing lab to conduct performance testing Cost of in-house staff (or allocation of staff time) to run performance tests Cost of increased construction completion time due to awaiting performance test results Other Percentage of state DOT Respondents 16 out of 19 DOTs 12 out of 19 DOTs 15 out of 19 DOTs 15 out of 19 DOTs 3 out of 19 DOTs Summary The survey results indicated that the objectives for using per- formance specifications generally include longer pavement life (in terms of durability), reduced maintenance, and greater resistance to common pavement distresses. The majority of DOTs and other agencies have integrated recycled asphalt materials into their mixture designs. Many of the DOTs and other agencies surveyed are also implementing PBS using one or more performance tests, or are researching the use of PBS for improved durability primarily through rutting or crack- ing resistance. The use of recycled materials (i.e., RAP, RAS, and crumb rubber) has affected or altered DOT approaches to mixture design and qualification and some agencies are inte- grating performance tests into both standard and alternative mixture designs to improve pavement performance. Survey respondents are also researching more advanced mechanis- tic properties (i.e., AMPT, dynamic modulus) as part of the implementation of mechanistic-empirical pavement design methods. Although PBS has been incorporated as a standard practice in only a small number of agencies, its wider imple- mentation appears to be on the horizon and there are a signifi- cant number and variety of research currently underway that address performance testing for mixture design and also for construction acceptance as part of the development of a more advanced mechanistic PBS system for asphalt pavements.
