Construction Guidelines for Cold Central Plant Recycling and Cold In-Place Recycling (2023)

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16 3 REVIEW OF AVAILABLE SPECIFICATIONS A total of 97 agency asphalt pavement recycling specifications were collected. Of this total, twelve local agency specifications were identical to the specification for the state/province in which they were located and were therefore excluded from further consideration. The remaining 85 specifications were summarized for critical elements. Of the 85 specifications, 73 were state/provincial agency specifications or special provisions while 12 were local agency specifications. Sixty-five of the reviewed specifications considered CIR and 20 considered CCPR. Of the 65 CIR specifications, 9 included requirements for both foamed and emulsified asphalt, 41 discussed emulsified asphalt only, 13 discussed foamed asphalt only, and 2 did not specify a specific recycling agent (but stated that the recycling agent must be asphalt binder-based). Of the 20 CCPR specifications 3 included requirements for both foamed and emulsified asphalt, 14 discussed emulsified asphalt only, 2 discussed foamed asphalt only, and 1 did not specify a specific recycling agent (but stated that the recycling agent must be asphalt binder-based). The data and discussion presented below review critical elements relevant to the development of the AASHTO Construction Guide Specification and provide support for the decisions made with regard to the draft specification outline. The data also provide insight into the state of the practice with respect to CR experience and examines CIR and CCPR separately and separates recycling agent type where appropriate. 3.1 Paving Operation A critical element of the paving operation is that of the equipment required. This may include the recycling equipment, compaction equipment, and paving equipment. In many cases specific roller types are mentioned. In 80.4% of the specifications (76 of 85) a pneumatic tire roller was required for compaction. Of those, 43.4% (33 of 76) required a minimum of a 25-ton pneumatic roller. The next roller most frequently referenced is a double drum vibratory roller. Of the reviewed specifications, 78.8% (67 of 85) required a double drum vibratory roller, with 52.2% (35 of 67) requiring a 10-ton minimum. The requirement of a non-vibratory double drum roller or padfoot roller was found in significantly fewer specifications for both CIR and CCPR (padfoot was nonexistent for CCPR). The requirement across all roller types was similar for emulsified asphalt and foamed asphalt specifications, though there were fewer specifications requiring or allowing foamed asphalt than emulsified asphalt. This is likely a byproduct of a much longer history of using emulsified asphalt in CR than foamed asphalt, which is a more recent technology. Figures 3.1 and 3.2 provide the percentage of specifications requiring rollers and roller types for CIR and CCPR respectively.

17 Figure 3.1. Percentage of Specifications Requiring Roller Types for the Construction of Cold In-place Recycled Pavements. Figure 3.2. Percentage of Specifications Requiring Roller Types for the Construction of Cold Central Plant Recycled Pavements. 83% 83% 4% 8% 90% 79% 17% 4% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Pneumatic Vibratory Steel Non-Vibratory Steel Padfoot Foam Emulsion 83% 67% 17% 0% 89% 72% 22% 0% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Pneumatic Vibratory Steel Non-Vibratory Steel Padfoot Foam Emulsion

18 Compaction requirements varied among the reviewed specifications. Seventy-two percent of specifications (61 of 85) required a test strip, of these 67.8% (40 of 59) set the test strip density requirement at the point of refusal while the remaining two specifications mentioned a test strip but were not specific in the method used for determination. For field density, 91.8% (78 of 85) set the field density target at a specific value determined from a method including but not limited to the test strip, field proctor, refusal, or percentage of maximum mix specific gravity (Gmm). Fifty-nine percent (46 of 78) of those that required a field density target used the test strip to establish the field density target. Table 3.1 provides a breakdown of the CR type and recycling agent type and subsequent percentage of specifications requiring a test strip as well as specific mention of test/proof rolling to ensure adequate compaction. Table 3.1. Cold Recycling Technique, Recycling Agent Type, and Percentage of Specifications Requiring Use of Test/Proof Rolling and a Control Strip Process Recycling Agent (No. of specs) Test/Proof Rolling Test Strip CIR (65; 11 Both Foamed & Emulsified Asphalt) Emulsified Asphalt (33 of 52) 6% 63.5% Foamed Asphalt (18 of 24) 0% 75.0% CCPR (20; 4 Both Foamed & Emulsified Asphalt) Emulsified Asphalt (15 of 18) 0% 83.3% Foamed Asphalt (5 of 6) 0% 83.3% Another element of construction that was highlighted is that of smoothness. Because CR mixes typically require surfacing, smoothness is usually specified on the final surface and not the recycled layer. As shown in Table 3.2, a smoothness requirement was found within 78.8% of CIR emulsified asphalt specifications, 66.7% of CIR foamed asphalt specifications, 72.2% of CCPR emulsified asphalt specifications, and 83.3% of CCPR foamed asphalt specifications. Methods identified to achieve smoothness are discussed with the results of the extended interview. Table 3.2. Cold Recycling Technique, Recycling Agent Type, and Percentage of Specifications with a Smoothness Requirement Process Recycling Agent (No. of specs) Smoothness Requirement CIR (65; 11 Both Foam & Emulsion) Emulsified Asphalt (41 of 52) 78.8% Foamed Asphalt (16 of 24) 66.7% CCPR (20; 4 Both Foam & Emulsion) Emulsified Asphalt (13 of 18) 72.2% Foamed Asphalt (5 of 6) 83.3% Weather limitations were found in 90.4% (47 of 52) of CIR emulsified asphalt specifications and 87.5% (21 of 24) of CIR foamed asphalt specifications. Weather limitations were also provided in 88.9% (16 of 18) CCPR emulsified asphalt specifications and 66.7% (4 of 6) CCPR foamed asphalt specifications. Generally, weather limitations included not producing the CR mixture when the RAP is below 50°F or if temperatures are forecasted to drop below 35°F within 48 hours of construction. Some specifications also limited CR use to certain times of the year (i.e., no CR production/placement during specific late-autumn, winter, or early spring months).

19 3.2 Quality Assurance Program Agency specifications require a series of tests to indicate construction quality characteristics as a part of their Quality Assurance (QA) program. While many construction quality characteristics are considered for Quality Control (QC) purposes, some are also included in the Acceptance, and Independent Assurance (IA) programs. For the purposes of this review, the QA construction quality characteristics are presented as a part of the holistic program as opposed to dividing them into QC, acceptance, or IA. Specifications may use the same construction quality characteristics for QC, acceptance, and IA, but also may require them for QC only and the agency may elect to check them as a part of the acceptance process. Specific construction quality characteristics of interest are those that, in the research team’s experience, were considered typical prior to the initiation of this study (e.g., density verification and gradation) and those that are likely less common but not unheard of that may relate to mix or field performance (e.g., indirect tensile tests, dynamic cone penetrometer, Marshall stability, and raveling stability). The results of this analysis are presented visually for CIR and CCPR in Figures 3.3 and 3.4 respectively. For CIR mixtures, 90% of emulsified asphalt and 96% of foamed asphalt specifications required density verification, with 75% and 79% of those, respectively, specifically calling for the use of a nuclear density gauge. In the case of CCPR, 94% of emulsified asphalt and 100% of foamed asphalt specifications required density measurements with 94% of emulsion and 100% of foamed asphalt specifications calling for use of a nuclear density gauge. Gradation checks were required in 75% of emulsified asphalt and 92% of the foamed asphalt mixtures for CIR and 83% of emulsified asphalt and 100% of foamed asphalt mixtures for CCPR mixtures. Specific sieves are discussed in further detail later in this section. It is notable that a higher percentage of foamed asphalt mixes require gradation checks than that of emulsified asphalt mixes. This could be because foamed asphalt mixes rely on the fines content of the mix to help with foamed asphalt dispersion throughout the mixture matrix. There are four additional construction quality characteristics (or methods to measure characteristics) that the research team sees most predominantly in the QA-related portion(s) of specifications: Dynamic Cone Penetrometer, Indirect Tensile Strength, Marshall Stability, and Raveling Stability. As can be seen in Figures 3.3 and 3.4, these tests are employed much less frequently than density and gradation checks. The DCP was used as a quality characteristic for CIR in 2% of emulsified asphalt specifications and 4% of foamed asphalt specifications. It was used for CCPR in 6% of emulsified asphalt specifications and 17% of foamed asphalt specifications. In the case of CIR, ITS is used as a quality characteristic in 8% of emulsified asphalt specifications and 25% of foamed asphalt specifications, whereas Marshall Stability is only checked in emulsified asphalt mix specifications (12%). In the case of CCPR, ITS is used in 11% of emulsified asphalt specifications and 17% of foamed asphalt specifications, and Marshall Stability is checked in 11% of emulsified asphalt and 17% of foamed asphalt specifications. Raveling stability is only checked in emulsified asphalt specifications, 4% of CIR specifications and 6% CCPR specifications. A number of specifications (not shown) did include measurements of strength, just not for pay or acceptance.

20 Figure 3.3. Percentage of Cold In-Place Recycling Construction Specifications for Various Quality Characteristics (DCP = Dynamic Cone Penetrometer; ITS = Indirect Tensile Strength). Figure 3.4. Percentage of Cold Central Plant Recycling Construction Specifications for Various Quality Characteristics (DCP = Dynamic Cone Penetrometer; ITS = Indirect Tensile Strength). 96% 79% 92% 4% 25% 0% 0% 90% 75% 75% 2% 8% 12% 4% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Density Nuclear Gauge Used Gradation DCP ITS Marshall Stability Raveling Stability Pe rc en ta ge o f S pe ci fic at io ns Foam Emulsion 100% 100% 100% 17% 17% 17% 0% 94% 94% 83% 6% 11% 11% 6% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Density Nuclear Gauge Used Gradation DCP ITS Marshall Stability Raveling Stability Pe rc en ta ge o f S pe ci fic at io ns Foam Emulsion

21 There are also cases where pay factors are applied when density and ITS values are included in the QA program. Table 3.3 provides a summary of the frequency in which density or ITS values are included with pay factors for specifications covering CIR and CCPR and by each recycling agent. Generally, however, pay factors were not applied for these two quality characteristics. Table 3.3. Percentage of Specifications Where Density and Indirect Tensile Strength (ITS) Tests Are Included as Pay Factors Pay Factors Cold Recycling Method Recycling Agent Density ITS CIR – 65 (11 both Foamed asphalt and Emulsified asphalt) Emulsified asphalt – 4 of 52 (density) 7.7% 0.0% Foamed asphalt – 4 of 24 (density); 2 of 24 (ITS) 16.7% 8.3% CCPR – 20 (4 both Foamed asphalt and Emulsified asphalt) Emulsified asphalt – 2 of 18 (density) 11.1% 0.0% Foamed asphalt – 3 of 6 (density); 1 of 6 (ITS) 50.0% 16.7% Gradation is another common quality characteristic, occurring in 75% or more of specifications regardless of recycling technique or recycling agent. Eighty-three of 85 specifications required 100% of the CR material to pass through a maximum sieve size. The 1.5-inch sieve was most common in both CR methods. Maximum sieve sizes and frequency of occurrence can be found in Table 3.4. Table 3.4. Percentage of Specifications with Maximum Sieve Size Cold Recycling Method 100% Passing Sieve (inch) Occurrence; Percentage (No.) CIR (64 of 65 specified a 100% passing sieve) 1 9.4% (6) 1.25 28.1% (18) 1.5 48.4% (31) 2 9.4% (6) 3 3.1% (2) Mix Design Basis 1.6% (1) CCPR (19 of 20 specified a 100% passing sieve) 1 26.3% (5) 1.25 15.8% (3) 1.5 57.2% (9) 2 5.3% (1) 3 5.3% (1) Table 3.5 shows the number of sieves referenced in the gradation section for the 64 CIR specifications and 19 CCPR specifications that required gradation. It was most common for CIR to list at least one (32.8%) or two (37.5%) sieves for gradation. There were six specifications that required as many as nine sieves. It was also most common for CCPR to reference at least one sieve (31.6%) or two sieves (21.1%), though three, five, and six sieves was listed 10.5% of the time each.

22 Table 3.5. Percentage of Specifications with Number of Sieves Required Cold Recycling Method Number of Sieves Required Occurrence; Percentage (No.) CIR (64 specifications) 1 32.8% (21) 2 37.5% (24) 3 6.3% (4) 4 4.7% (3) 5 3.1% (2) 6 3.1% (2) 7 1.6% (1) 8 1.6% (1) 9 9.4% (6) CCPR (19 specifications) 1 31.6% (6) 2 21.1% (4) 3 10.5% (2) 4 5.3% (1) 5 10.5% (2) 6 10.5% (2) 7 5.3% (1) 8 0% 9 5.3% (1) 3.3 Measurement and Payment Pay items vary from specification to specification, as shown in Figure 3.5. Of all specifications reviewed, 97.6% (83 of 85) listed the mixture itself as being a pay item. One hundred percent of CCPR specifications listed the CCPR mix as a pay item compared to 97% of CIR specifications. With regard to measurement, 81.2% (69 of 83) specifications measure the mixture in terms of area (square yards or square meters), however, it is important to remember that a majority of specifications reviewed were CIR which is more challenging to measure by weight. The recycling agent is the second most frequently used pay item, appearing in in 69.4% (59 of 85) of all specifications (75% of CCPR specifications and 68% of CIR specifications). Of those specifications that specified recycling agent as a pay item, 67.8% (40 of 59) were based on weight (tons), while 30.5% (18 of 59) used volume (gallons). Of those, 5% (3 of 59) listed gallon or ton, and the remaining 3.3% (2 of 59) used another unit that is not gallons or tons. The active filler was specified as a pay item in 31.8% (27 of 85) of all reviewed specifications, with 81.5% (15 of 59) of those using weight (tons) for measurement. Thirty-five percent of CCPR specifications and 31% of CIR specifications included active filler as a pay item. Corrective aggregate was listed as a pay item in 32.9% (28 of 85) of all specifications and 89.3% (25 of 28) of those used weight (tons) for measurement. Corrective aggregate was found in 40% of CCPR specifications and 31% of CIR specifications as a pay item.

23 Figure 3.5. Percent of Specifications with Pay Items in Cold Central Plant and Cold In-Place Recycled Pavement Construction Specifications (CR = Cold Recycling; CIR = Cold In-Place Recycling; CCPR = Cold Central Plant Recycling). 97% 68% 31% 31% 100% 75% 35% 40% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% CR Mix Recycling Agent Active Filler Corrective Aggregate Pe rc en ta ge o f S pe ci fic at io ns CIR CCPR