Use of Recycling Agents in Asphalt Concrete Mixtures (2022)

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29   3.1 Introduction The survey on current practices related to the use of RAs in asphalt mixtures was distrib- uted to state DOTs, the District of Columbia DOT, and CPTAs. Surveys were completed by 92% (47/51) of U.S. DOTs and 73% (8/11) of CPTAs. The survey questions are provided in Appendix A, while Appendix B and Appendix C present the survey results from U.S. DOTs and CPTAs, respectively. The survey responses from state DOTs and CPTAs are discussed in sections that follow. 3.2 State of the Practice Related to the Use of RAM Including RAP and RAS in Asphalt Mixtures All 47 state DOTs that responded to the survey allowed the use of RAM in asphalt mixtures. Use of RAP was allowed by all survey respondents, while 55% (26/47) allowed the use of both RAP and RAS, as shown in Figure 3. All CPTAs that responded to the survey allowed use of RAM in asphalt mixtures. All allowed the use of RAP, but only one also allowed the use of RAS, as shown in Figure 4. Only 13% (6/47) of state DOTs reported that RAs were addressed in their specifications or listed on their APL/QPL, while 32% (15/47) reported that they used RAs for demonstration/ research purposes. Two agencies reported that RAs were addressed in their specifications or on their APL/QPL and used for demonstration/research purposes. A majority of the agencies (28/47) stated that RAs were not allowed in asphalt mixtures with RAM, as shown in Figure 5. For the eight CPTAs, 25% (2/8) reported that RAs were addressed in their specifications or listed on their APL/QPL, while 75% (6/8) stated that RAs were not allowed in asphalt mixtures with RAM, as shown in Figure 6. For the 19 state DOTs reporting that RAs were used in asphalt mixtures with RAM, 15 responded to the question of how they specified RAM in asphalt mixtures. As shown in Figure 7, 13% (2/15) of the respondents reported that they only used total RAM content to specify recycled asphalt amounts in their mixtures, while 40% (6/15) reported that they specified RAP and RAS content separately in asphalt mixtures. Finally, 37% (7/19) of agencies stated that both methods (by total RAM content and by RAP and RAS separately) were used. For the two CPTAs reporting that RAs were used in asphalt mixtures with RAM, only one agency responded to the question, and it reported that both methods (by total RAM content and by RAP and RAS separately) were used to specify the RAM content in asphalt mixtures. C H A P T E R   3 Survey on Practices for Use of Recycling Agents in Asphalt Mixtures

30 Use of Recycling Agents in Asphalt Concrete Mixtures For the 10 agencies (nine state DOTs and one CPTA) reporting that total RAM content was used to specify the RAM content in asphalt mixtures, Table 15 and Table 16 summarize the typi- cal RAM content (in terms of RBR) used in surface and non-surface asphalt mixtures, and the maximum RAM content used in surface and non-surface asphalt mixtures, respectively. Both the typical and maximum RAM content used in surface and non-surface asphalt mixtures were in the 0.2 to 0.3 range for most of the respondent agencies. For the 15 agencies (13 state DOTs and two CPTAs) reporting that the RAP content was speci- ed separately in asphalt mixtures, the number of agencies reporting that the typical RAP content used in surface and non-surface asphalt mixtures, and the maximum RAP content used in sur- face and non-surface asphalt mixtures, are summarized and presented in Table 17 and Table 18, respectively. For most respondent agencies, the typical RAP content used in surface asphalt mix- tures was 0.1–0.3, while the maximum RAP content was above 0.2. e typical RAP content used in non-surface asphalt mixtures was 0.15–0.3, while the maximum RAP content was above 0.2. Note: Number of responses = 47. 21 26 Use of RAP only Use of RAP and RAS Figure 3. RAM usage allowance in asphalt mixtures by responding state DOTs. Note: Number of responses = 8. 7 1 Use of RAP only Use of RAP and RAS Figure 4. RAM usage allowance in asphalt mixtures by responding CPTAs.

Survey on Practices for Use of Recycling Agents in Asphalt Mixtures 31   Note: Number of responses = 47. 4 13 2 28 0 RAs are addressed in the specifications and/or listed on the APL/QPL RAs are used for demo/research purposes RAs are addressed in the specifications and/or listed on the APL/QPL & RAs are used for demo/research purposes Not allowed Number of DOTs 10 20 30 Figure 5. Distribution of responding state DOTs with respect to usage of RAs in asphalt mixtures. Note: Number or responses = 8. 2 0 0 6 0 2 4 6 8 RAs are addressed in the specifications and/or listed on the APL/QPL RAs are used for demo/research purposes RAs are addressed in the specifications and/or listed on the APL/QPL & RAs are used for demo/research purposes Not allowed Number of CPTAs Figure 6. Distribution of responding CPTAs with respect to usage of RAs in asphalt mixtures.

32 Use of Recycling Agents in Asphalt Concrete Mixtures For the 14 agencies (13 state DOTs and one CPTA) reporting that the RAS content was speci- ed separately in asphalt mixtures, the number of agencies reporting the typical RAS content used in surface and non-surface asphalt mixtures, and the maximum RAS content used in sur- face and non-surface asphalt mixtures, are summarized and presented in Table 19 and Table 20, respectively. e typical RAS content used in surface asphalt mixtures for most agencies was below 0.15, while the maximum RAS content was 0.05–0.2. e typical RAS content used in non-surface asphalt mixtures was below 0.15, while the maximum RAS content was above 0.1. Notes: N/A = question not answered; number of responses = 19. 2 6 7 4 By total RAM content By RAP content and RAS content separately Both methods are used N/A Figure 7. Distribution of responding state DOTs that allow use of RAs on specication of RAM content in asphalt mixtures. Typical RAM Content (RBR) Number of DOTs Number of CPTAs Surface Mixture Non-Surface Mixture Surface Mixture Non-Surface Mixture <0.1 0 0 0 0 0.1–0.15 3 0 1 0 0.15–0.2 1 0 0 1 0.2–0.3 5 8 0 0 >0.3 0 0 0 0 Not allowed 0 — 0 — Table 15. Typical RAM contents used in asphalt mixtures by respondent agencies. Maximum RAM Content (RBR) Number of DOTs Number of CPTAs Surface Mixture Non-Surface Mixture Surface Mixture Non-Surface Mixture <0.1 0 0 0 0 0.1–0.15 1 0 0 0 0.15–0.2 1 0 0 1 0.2–0.3 5 5 0 0 >0.3 1 2 1 0 Table 16. Maximum RAM contents used in asphalt mixtures by respondent agencies.

Survey on Practices for Use of Recycling Agents in Asphalt Mixtures 33   Typical RAP Content (RBR) Number of DOTs Number of CPTAs Surface Mixture Non-Surface Mixture Surface Mixture Non-Surface Mixture <0.1 1 1 0 0 0.1–0.15 3 1 0 0 0.15–0.2 3 2 1 2 0.2–0.3 5 7 0 0 >0.3 0 2 0 0 Not allowed 1 — 1 — Table 17. Typical RAP contents used in asphalt mixtures by respondent agencies. Maximum RAP Content (RBR) Number of DOTs Number of CPTAs Surface Mixture Non-Surface Mixture Surface Mixture Non-Surface Mixture <0.1 1 1 0 0 0.1–0.15 1 0 0 0 0.15–0.2 2 0 1 1 0.2–0.3 3 6 0 0 >0.3 5 6 0 1 Table 18. Maximum RAP contents used in asphalt mixtures by respondent agencies. Typical RAS Content (RBR) Number of DOTs Number of CPTAs Surface Mixture Non-Surface Mixture Surface Mixture Non-Surface Mixture <0.05 6 6 1 1 0.05–0.1 0 0 0 0 0.1–0.15 2 2 0 0 0.15–0.2 3 2 0 0 >0.2 0 1 0 0 Not allowed 2 — 0 — Table 19. Typical RAS contents used in asphalt mixtures by respondent agencies. Maximum RAS Content (RBR) Number of DOTs Number of CPTAs Surface Mixture Non-Surface Mixture Surface Mixture Non-Surface Mixture <0.05 3 1 1 1 0.05–0.1 2 2 0 0 0.1–0.15 1 0 0 0 0.15–0.2 3 3 0 0 >0.2 1 2 0 0 Table 20. Maximum RAS contents used in asphalt mixtures by respondent agencies.

34 Use of Recycling Agents in Asphalt Concrete Mixtures 3.3 Experience of RA Use in Asphalt Mixtures For the 19 state DOTs reporting that RAs were used in asphalt mixtures, the number of years that agencies had been using RAs, number of projects using RAs per year, percentage of the total annual tonnage of asphalt mixtures containing RAs, and the number of different RA products that had been used are shown in Figure 8 through Figure 11, respectively. For the two CPTAs reporting that RAs were used in asphalt mixtures, the number of years that agencies had been using RAs, number of projects per year using RAs, percentage of the total annual tonnage of asphalt mixtures containing RAs, and number of different RA products that had been used in asphalt mixtures are shown in Table 21. Notes: N/A = question not answered; number of responses = 19. 1 4 5 3 5 1 0 1 2 3 4 5 6 1 year 2 years 3-5 years >5 years Unsure N/A Number of DOTs Figure 8. Distribution of responding state DOTs with respect to number of years using RAs. Note: Number of responses = 19. 10 0 1 1 1 6 0 2 4 6 8 10 12 <5 5-10 10-30 30-50 >50 Unsure Number of DOTs Figure 9. Distribution of responding state DOTs with respect to number of projects per year using RAs.

Survey on Practices for Use of Recycling Agents in Asphalt Mixtures 35   Notes: N/A = question not answered; number of responses = 19. 8 1 1 0 0 7 2 0 1 2 3 4 5 6 7 8 9 1-5% 5-10% 10-15% 15-20% 20% Unsure N/A Number of DOTs Figure 10. Distribution of responding state DOTs with respect to percentage of total annual tonnage of asphalt mixtures containing RAs. Notes: N/A = question not answered; number of responses = 19. 5 5 1 0 6 2 0 1 2 3 4 5 6 7 <3 3-5 5-10 >10 Unsure N/A Number of DOTs Figure 11. Distribution of responding state DOTs with respect to number of RA products used in asphalt mixtures. Number of Years Using RAs Number of Projects per Year Using RAs Percentage of Total Annual Tonnage of Asphalt Mixtures Contains RAs Number of RA Products Used in Asphalt Mixtures Agency 1 1 <5 1%–5% <3 Agency 2 3–5 <5 1%–5% <3 Table 21. Experience of Use of RAs in asphalt mixtures for responding CPTAs.

36 Use of Recycling Agents in Asphalt Concrete Mixtures Most respondent agencies (both DOTs and CPTAs) had been using RAs for less than 5 years, constructed fewer than five projects constituting less than 5% of their total annual tonnage per year using RAs, and had used fewer than five different RA products. This indicates that the use of RAs is still relatively new, and most agencies generally have little experience with the use of RAs in asphalt mixtures. The different types of RAs used by the 19 state DOTs are summarized in Figure 12. The largest number of respondents to the question, 56% (9/16), indicated that the exact classification type of RA products used in their asphalt mixtures was unknown. For the RA products with known type, most state DOTs (67%; 4/6) reported that they used more than one type of RA in asphalt mixtures, and a majority of the state DOTs (83%; 5/6) used the RA source/chemical component system to classify RA type. Survey results indicated that the tall oil type of RA was more extensively used by agencies than other types. Only one CPTA responded and reported that naphthenic oil was used in asphalt mixtures. Figure 13 summarizes the responses with respect to when the RA is added during mixture production for the 19 state DOTs that used RAs. Pre-blended with binder at the terminal and in-line blending at the plant were the most common processes. Only one CPTA responded, and it reported that the RA was added during hot in-place recycling (HIR). The processes reported in the “other” category are (1) in-line blending when offloading binder from haul unit to storage tank, (2) added during field recycling, (3) pre-blended with binder at plant, and (4) pretreating of RAP/RAS only for research. The number of state DOTs reporting RA usage in surface (wearing) course mixtures and non- surface asphalt mixtures is shown in Figure 14 and Figure 15, respectively. Most (94%; 17/18) respondent agencies reported that the use of RAs was neither specified nor required in asphalt mixtures. Notes: N/A = question not answered; number of responses = 19. 0 0 0 1 0 0 0 3 3 2 3 5 2 9 3 0 2 4 6 8 10 RA0 RA1 RA5 RA25 RA75 RA250 RA500 Paraffinic Oils Aromatic Extracts Naphthenic Oils Triglycerides & Fatty Acids Tall Oils Others Unknown N/A Number of DOTs ASTM D4552 Classifications Source/Chemical Composition Classifications Figure 12. Distribution of responding state DOTs with respect to different types of RA used.

Survey on Practices for Use of Recycling Agents in Asphalt Mixtures 37   Notes: N/A = question not answered; number of responses = 19. 6 7 0 5 3 2 0 1 2 3 4 5 6 7 8 Pre-blended with binder at terminal In-line blending at plant Pretreating of RAP/RAS Other Unknown N/A Number of DOTs Figure 13. Distribution of responding state DOTs with respect to when RAs are added. Notes: N/A = question not answered; number of responses = 19. 1 6 11 1 Use of RA required Use of RA allowed/optional RAs not used N/A Figure 14. Distribution of responding state DOTs with respect to usage of RAs in surface (or wearing) course mixtures. For the two CPTAs that used RAs, only one agency reported that RAs were not used in non- surface asphalt mixtures, but it was allowed/optional in HIR projects with RBR ranges of from 0.85 to 1.00. Figure 16 shows DOT practices for specication of RAs for use in asphalt mixtures for the 19 state DOTs that were using RAs. A majority of agencies (83% of respondents; 15/18) reported that RAs were not listed on their APL/QPL. e processes by which RAs are added to the APL/QPL are summarized in Table 22 for the three DOTs that had RAs on their APL/QPL. e processes falling into the “other” category are summarized in Table 23. Only one CPTA responded, and it reported that RAs were used for experimental or test sections only (mainly HIR projects).

Notes: N/A = question not answered; number of responses = 19. 0 7 11 1 Use of RA required Use of RA allowed/optional RAs not used N/A Figure 15. Distribution of responding state DOTs with respect to usage of RAs in non-surface course mixtures. Notes: N/A = question not answered; number of responses = 19. 3 2 9 4 1 0 2 4 6 8 10 Approved/qualified product list Project by project basis Experimental/test sections only Other N/A Number of DOTs Figure 16. Distribution of responding state DOTs with respect to how RAs are specied for use in asphalt mixtures. RAs are not specified; optional only. For a research section, the material would be part of the project specification. It is referenced in the high-RAP specification. As needed to meet PG binder specifications per M 332, including percent recovery. Table 22. Agencies reporting “other” processes of specifying the use of RA. Meet specified PG and look at delta Tc. Test section is constructed for monitoring field performance; laboratory performance indicators are measured for laboratory evaluation. Based on test results of the final asphalt mixture and satisfactory field performance. Table 23. Process for adding RAs to APL/QPL.

Survey on Practices for Use of Recycling Agents in Asphalt Mixtures 39   3.4 RA Type and Dosage Determination and Verification For the 19 state DOTs using RAs in asphalt mixtures, the entity responsible for determina- tion of RA type and the corresponding methodology are presented in Figure 17 and Figure 18, respectively. The determination processes falling into the “other” category are summarized in Table 24. The RA type was most often determined by the agency. For the agencies that had a formal methodology to specify RA type, the use of binder testing was the primary methodology. Number of DOTs Notes: N/A = question not answered; number of responses = 8. 0 3 1 0 3 1 2 0 1 2 3 4 RA type selection is a function of RBR RA type is determined using binder testing RA type is determined using mixture testing Other Agency does not have methodology to specify RA type Unknown N/A Figure 18. Distribution of responding state DOTs with respect to methodology for determination of RA type. Number of DOTs Notes: N/A = question not answered; number of responses = 19. 7 3 4 0 1 6 1 2 0 2 4 6 8 Agency determined Contractor determined based on agency requirements Contractor determined independently RA determined based on agency requirements RA determined independently Other Unknown N/A Figure 17. Distribution of responding state DOTs with respect to entity for determination of RA Type.

40 Use of Recycling Agents in Asphalt Concrete Mixtures Only one CPTA responded, and it reported that the type of RA was determined by the con- tractor independently. The timing of RA dosage determination, the entity that determined the dosage, and the cor- responding methodology are shown in Figure 19, Figure 20, and Figure 21 respectively. The RA dosage was determined most often during the mix design stage by contractors. For the agencies that had a methodology in place to specify RA dosage, binder and mixture laboratory testing were used most often. Only one CPTA responded, and it reported that dosage of RA was deter- mined based on the binder test (PG grading) during the mix design stage. Table 25 summarizes the testing methods that agencies reported were used for type and dosage determination. The reported timing and methodology for verifying RA dosage for the 19 state DOTs using RAs are presented in Figure 22 and Figure 23, respectively. The verification processes and methods falling into the “other” category are summarized in Table 26 and Table 27, respectively. Approx- imately half of the agencies that responded to this question (8/17) did not verify the dosage of RAs during production. For the agencies that did verify RA dosage, a majority of them (7/9) used plant records. Only one CPTA responded, and it reported that dosage of RA was not verified. Contractor submits product information with mix design for approval. Based on the scenarios for current modifiers. Determined partially by the university research team. Contractors get approved after selecting a product. Determined by contractor and asphalt supplier. Have not determined details. Table 24. Agencies reporting “other” for determination of RA type. Number of DOTs Notes: N/A = question not answered; number of responses = 19. 4 14 1 1 3 0 2 4 6 8 10 12 14 16 Material selection Mix design Production Other N/A (determined in preliminary binder extraction, recovery, and testing phase, prior to mix design evaluation and approval) Figure 19. Distribution of responding state DOTs with respect to timing of RA dosage determination.

Survey on Practices for Use of Recycling Agents in Asphalt Mixtures 41   Notes: N/A = question not answered; number of responses = 19. 3 9 2 0 3 2 1 2 0 2 4 6 8 10 Agency determined Contractor determined based on agency requirements Contractor determined independently RA producer determined based on agency requirements RA producer determined independently Other Unknown N/A Number of DOTs (details TBD; specified a dosage of 2% by weight of virgin binder) Figure 20. Distribution of responding state DOTs with respect to entity for determination of RA dosage. Number of DOTs Note: Number of responses = 19. 1 3 2 1 3 0 1 2 3 4 RA dosage selection is a function of RBR RA dosage is determined using binder testing RA dosage is determined using mixture testing Other Agency does not have dosage methodology specified (specified a dosage of 2% by weight of virgin binder) Figure 21. Distribution of responding state DOTs with respect to methodology for determination of RA dosage. Testing Method Procedure Superpave PG grading AASHTO M 332 MSCR test AASHTO T 350 HWTT AASHTO T 324 SCB Test LADOTD TR 330-14 CT-index ASTM D8225 Table 25. State DOTs reporting testing methods for RA type and dosage determination.

42 Use of Recycling Agents in Asphalt Concrete Mixtures Number of DOTs Notes: N/A = question not answered; number of responses = 19. 5 1 1 4 8 2 0 2 4 6 8 10 Mix design approval Producer quality control Agency quality assurance Other Not verified N/A Figure 22. Distribution of responding state DOTs with respect to point of when RA dosage is veried. Note: Number of responses = 19. 3 2 7 3 By binder testing By mixture testing By plant records Other Figure 23. Distribution of responding state DOTs with respect to methodology for RA dosage verication. Answer based on other modifiers Details TBD Plant records of the in-line blending RA dosage verified on asphalt supplier’s delivery documentation, bill of lading Table 26. State DOTs reporting “other” for how RA dosage is veried. Monitor the amount pumped out of tote during offload of binder from haul unit to binder storage tank Details TBD RA dosage verified on asphalt supplier’s delivery documentation, bill of lading Table 27. State DOTs reporting “other” for methods of RA dosage verication.

Survey on Practices for Use of Recycling Agents in Asphalt Mixtures 43   3.5 QA Aspects for Asphalt Mixtures with RA For the 19 state DOTs that were using RAs, 14 of the 17 responding to this question reported that no changes were made to QA processes for mixtures with RAs; three were unsure if DOT QA processes were changed when RA was used. One of the CPTAs using RAs reported that it was unsure whether there were changes to the QA process, while the other agency reported that both the inspection process and validation/acceptance testing were changed for mixtures that contained RA. 3.6 Performance Evaluation of Asphalt Binder and Mixtures with RA e state of practice with respect to performance evaluation of binders and mixtures with RAs and observed distress for the 19 state DOTs that were using RAs are presented in Fig- ure 24 through Figure 26. Most (59%; 10/17) respondent agencies reported that they evalu- ated the performance of binders and mixtures with RAs. Half (5/10) used more than one method (e.g., testing both binder and mixture) to evaluate performance; only three evaluated the long-term performance of the mixtures with RAs by using laboratory long-term aging conditioning. As shown in Figure 25, the most common methods for evaluating performance were standard Superpave tests on binders, mixture testing on short-term aging (STA) or plant-produced mixtures, and monitoring eld performance. Twenty-seven percent (4/15) of the respondent state DOTs reported that they had observed premature distress for asphalt mixtures with RAs. More than one distress type was reported by three of these four DOTs. The premature distresses for asphalt mixtures with RAs reported include blending, raveling, increased moisture damage, and thermal cracking. For the two CPTAs that were using RAs, one reported that it did not evaluate performance, and the other reported that performance was evaluated by binder testing using standard Superpave tests. No premature distress had been observed by these two CPTAs. Notes: N/A = question not answered; number of responses = 19. 10 6 1 2 Yes No Unsure N/A Figure 24. Distribution of responding state DOTs with respect to whether performance of binders/mixtures with RA was evaluated.

44 Use of Recycling Agents in Asphalt Concrete Mixtures Number of DOTs Note: Number of responses = 19. 5 1 6 3 1 5 1 0 2 4 6 8 Binder testing using standard Superpave tests Binder testing using additional aging/conditioning (e.g., 40 hr PAV, EBBR) Mixture performance testing on STA (or plant produced) mixtures Mixture performance testing on laboratory conditioned mixtures (long term aging) Testing of field core Monitoring of field performance Other (depending on research scope) Figure 25. Distribution of responding state DOTs with respect to methodology for testing of binders/mixtures with RA. Number of DOTs Notes: N/A = question not answered; number of responses = 19. 1 0 2 1 0 0 0 2 0 11 4 0 2 4 6 8 10 12 Bleeding Fatigue cracking Increased moisture susceptibility Raveling Reflective cracking Roughness Rutting and/or shoving Thermal cracking Others No premature distresses or failures have been observed to date N/A Figure 26. Distribution of responding state DOTs with respect to premature distress observed for mixtures with RAs.

Survey on Practices for Use of Recycling Agents in Asphalt Mixtures 45   3.7 Other Applications of RAs Most respondent state DOTs (80%; 37/46) reported that they did not use RAs for applications other than HMA and WMA (Figure 27). Figure 28 shows that other primary applications were HIR and cold in-place recycling (CIR), as well as spray-on applications. e ASTM D4552-20 procedure was mainly used for RA type classication when RAs were used for applications other than HMA and WMA (Figure 30). Half (4/8) of the CPTAs reported that RAs were used for other applications and that these were primarily cold-mix asphalt and HIR, as well as spray-on rejuvenation applications (Figure 29). Naphthenic oils were reported by CPTAs to be used primarily in these applications. Notes: N/A = question not answered; number of responses = 47. 9 37 1 Yes No N/A Figure 27. Distribution of responding state DOTs with respect to whether RAs were used for other applications. Number of DOTs Note: Number of responses = 19. 0 1 7 4 5 1 0 2 4 6 8 Cold mix asphalt Seal coats Hot-in-place recycling Cold-in-place recycling Spray-on rejuvenation application Other (scrub seal) Figure 28. Distribution of responding state DOTs with respect to other applications when using RAs.

46 Use of Recycling Agents in Asphalt Concrete Mixtures Number of CPTAs Note: Number of responses = 4. 2 0 2 0 2 1 0 1 2 3 Cold mix asphalt Seal coats Hot-in-place recycling Cold-in-place recycling Spray-on rejuvenation application Other [Surfacing low-volume TMS (thin membrane structure) roads] Figure 29. Distribution of responding CPTAs with respect to other applications when using RAs. Number of DOTs Note: Number of responses = 9. 1 1 1 3 1 1 1 1 1 0 0 0 3 3 0 1 2 3 4 RA0 RA1 RA5 RA25 RA75 RA250 RA500 Paraffinic Oils Aromatic Extracts Naphthenic Oils Triglycerides & Fatty Acids Tall Oils Others Unknown ASTM D4552 Classifications Source/Chemical Composition Classifications Figure 30. Distribution of responding state DOTs with respect to types of RA used for other applications.

Survey on Practices for Use of Recycling Agents in Asphalt Mixtures 47   3.8 Challenges and Plans for Use of RA For the 47 state DOTs responding to the survey, the reported knowledge gaps or roadblocks for use of RAs, plans for use of RAs, and research related to the use of RAs are summarized in Figure 31, Figure 32, and Figure 33, respectively. e most common challenges for agencies to start or continue using RAs were (1) lack of agency experience in evaluation of asphalt mix- tures with RAs, (2) lack of tests and criteria to approve RAs, and (3) lack of tests and criteria to Note: Number of responses = 47. 10 30 7 19 18 3 30 30 3 16 7 0 10 20 30 40 Cost of RAs relative to expected performance Lack of agency experience in evaluating of asphalt mixtures with RAs Agency inspection process Lack of contractors’ expertise in using RAs Lack of mix design methods and engineering-based design procedures Lack of RA availability Lack of tests and criteria to approve RA Lack of tests and criteria to determine dosage rate and/or performance Poor pavement performance associated with distresses and/or failures Others No significant roadblocks Number of DOTs Figure 31. Distribution of responding state DOTs with respect to knowledge gaps/ roadblocks for use of RAs. Note: Number of responses = 47. 21 7 19 Yes No Unsure Figure 32. Distribution of responding state DOTs with respect to plans for use of RAs in future projects.

48 Use of Recycling Agents in Asphalt Concrete Mixtures determine dosage rate or performance. e knowledge gaps or barriers reported in the “other” category are shown in Table 28. Of the respondent state DOTs, 45% (21/47) reported that they had plans to use RAs in future projects, and 33% (15/46) reported that they sponsored research related to the use of RAs in asphalt mixtures. e primary challenges reported by CPTAs to start or continue using RAs were (1) lack of agency experience in evaluating asphalt mixtures with RAs, (2) agency inspection processes, and (3) lack of tests and criteria to approve RA and to determine RA dosage rate or performance (Figure 34). Of the CPTAs that responded to the survey, 25% (2/8) reported that they had plans to use RAs in future projects (Figure 35). None of the CPTAs reported sponsorship of research related to use of RAs in asphalt mixtures. 3.9 Summary e survey showed that all the state DOTs and CPTAs responding to the survey allowed the use of RAP in asphalt mixtures, with 55% of respondent DOTs and 13% of CPTAs also allowing the use of RAS in asphalt mixtures. For most (75%) of the agencies responding to the survey, the typical RAP content was 0.1–0.3 for surface mixtures and 0.15–0.3 for non-surface mix- tures, while the maximum content was above 0.2 for both surface and non-surface mixtures. Lack of interest from our industry partners Lack of long-term performance data to demonstrate effectiveness Lack of criteria to determine the effectiveness of RAs with respect to long-term performance Lack of ideas/thoughts to initiate the use of RAs Lack of long-term LCCA of mixtures with RAs. The time it takes to perform additional testing when RAs are used Need specs in place to show how to determine dosage Lack of consistency in RAM in general Table 28. State DOTs reporting “other” for knowledge gaps/ roadblocks for use of RAs. Figure 33. Distribution of responding state DOTs with respect to research sponsored related to use of RAs in asphalt mixtures. Notes: N/A = question not answered; number of responses = 47. 15 31 1 Yes No N/A

Survey on Practices for Use of Recycling Agents in Asphalt Mixtures 49   Figure 35. Distribution of responding CPTAs with respect to plans for use of RAs in future projects. Note: Number of responses = 8. 2 15 Yes No Unsure Notes: Number of responses = 8. Comments in the “Others” category were: “Typical HMA have low RAP content and don’t require RA. Limited experience with HIPR. No CIPR projects.” “The benefit of RA is unclear in the local trials and conflicting research results.” “We are typically not using high RAP mixes and don’t require the use of RA.” Figure 34. Distribution of responding CPTAs with respect to knowledge gaps/ roadblocks for use of RAs.

50 Use of Recycling Agents in Asphalt Concrete Mixtures The typical RAS content was below 0.15 for both surface and non-surface mixtures, while the maximum content was 0.05–0.2 for surface mixtures and above 0.1 for non-surface asphalt mixtures. Most of the agencies (60% of state DOTs; 75% of CPTAs) responding to the survey reported that they did not allow the use of RAs in asphalt mixtures. For the state DOTs indicating that RAs were used, the results show that RAs were primarily used for demonstration or research purposes. The majority (94%) of the survey DOTs reported that the use of RAs was neither specified nor required in asphalt mixtures; most of the state DOTs (83%) that were using RAs indicated that RAs were not listed on their APL or QPL. The survey results indicated that the use of RA is still relatively new for the majority of the agencies, and most have limited experience with use of RAs in asphalt mixtures. Approximately 63% of the state DOTs indicated that the exact classification type of RA product(s) used in their asphalt mixtures was unknown. For the RA products with known type, the majority of state DOTs (83%) used the RA source/chemical component system to classify RA type. The tall oil type of RA product was reported to be used more extensively than other types. The survey indicated that the most common processes for introducing RA into mixtures were pre-blending with binder at the terminal and in-line blending at the plant. RA type and dosage were determined primarily by the agency or the contractor during the mix design stage by conducting binder or mixture testing. Approximately half of the state DOTs that were using RAs did not verify the dosage; for those that did verify dosage, the most common method was by using plant records. All state DOTs indicated that no changes were made to QA processes for mixtures with RAs; only one CPTA reported that its validation and acceptance testing during QA processes was different when RAs were used. Most state DOTs (59%) that were using RAs reported that they evaluated performance. The most common methods to evaluate performance were standard Superpave binder tests, mixture testing on STA/plant-produced mixtures, and monitoring field performance. Only three agen- cies reported that they evaluated the long-term performance of the mixtures with RAs by using laboratory long-term aging conditioning. Approximately 26% of respondent DOTs reported that they had observed premature distress of asphalt mixtures with RAs, including bleeding, raveling, increased moisture damage, and thermal cracking. Most state DOTs (80%) reported that RAs were not used for applications other than HMA and WMA. When used for other applications, RAs were primarily used for HIR and CIR, as well as spray-on applications. The ASTM D4552 procedure was typically used for RA type classifica- tion for these applications. The survey indicated that the top three challenges for agencies to start or continue using RAs were (1) lack of agency experience in evaluating of asphalt mixtures with RAs, (2) lack of tests and criteria to approve RAs, and (3) lack of tests and criteria to determine dosage rate or performance.