Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling (2021) / Chapter Skim
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From page 6... ...
6 The literature review chapter is organized into the following sections: • Project Selection • Pavement Design • Individual Materials • Mix Designs • Construction Processes • Pavement Performance • Economic Benefits • Environmental Benefits Project Selection A well-defined process for identifying projects that are good candidates for CIR and CCPR at the start of the project is key to comparing the economic and environmental factors associated with all options for pavement maintenance and rehabilitation. The most appropriate alternatives for a given project are identified during the project selection phase.
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Literature Review 7 Pavement Distresses CIR and CCPR mitigate or eliminate functional pavement distresses but need a structurally sound, well-drained underlying pavement structure (i.e., minimal structurally related distresses)
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8 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling Aggregates with round shapes or mineralogy that tends to polish under traffic can be recycled into a lower pavement layer, and moisture-sensitive mixes can be amended with an active filler (e.g., lime, Portland cement)
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Literature Review 9 Records Review The existing records are reviewed to determine the existing pavement layers and probable thicknesses, as well as the type, materials, and extent of previous maintenance and preservation activities. Factors that can influence the consistency of the cold recycled RAP mix include the amount of crack sealant, fabric interlayers, material properties in surface treatments, variations in the surface mix [e.g., open-graded friction course, stone matrix asphalt (SMA)
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10 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling tend to have high asphalt binder contents that are polymer or crumb rubber modified (Wagner 2018; Schellhammer 2019)
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Literature Review 11 a visual examination of the cores. The most successful projects ensure that the milling depth is deep enough to remove the cracking.
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12 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling Structural Support Evaluation The load-carrying capability of the unbound pavement layers can be evaluated using a falling weight deflectometer (FWD, ASTM D4694) or a dynamic cone penetrometer (DCP, ASTM D6951)
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Literature Review 13 void content (typically 9% to 17%) and additional materials added to the milled material (e.g., corrective aggregate, recycling agents, fillers)
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14 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling Any load restrictions on roadways leading in and out of the project area need to be checked to avoid any problems with moving heavy recycling equipment in and out of the work area (Schellhammer 2019)
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Literature Review 15 Corrective Aggregate, % Resilient Modulus @ 77°F (25°C) , ksi Limestone RAP Granite RAP Emulsion Foamed Asphalt Emulsion Foamed Asphalt 0% 294 134 ND ND 20% 272 500 319 ND 40% 413 314 407 233 ND = no data.
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16 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling Diefenderfer and Apeagyei (2014) obtained cores from the foamed asphalt CIR and CCPR Virginia DOT I-81 project and measured the resilient modulus at three temperatures.
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Literature Review 17 The dynamic moduli over a range of frequencies and temperatures were reported in several research reports (Table 9)
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18 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling The cold recycled mix dynamic modulus tends to be dependent on the type and amount of recycling agent (Figure 6, Bhavsar 2015)
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Literature Review 19 10 100 1,000 10,000 0 20 40 60 80 100 120 140 Dy na m ic M od ul us , @ 1 H z, k si Temperature, F CIR, Foamed Asphalt, Texas CCPR, Foamed Asphalt, Indiana/Virginia CIR, Emulsion, Lime Slurry, Nevada CIR, 2.5% FA, 2% C, 20% Agg, Poland Surface Mix, Virginia Sources: Indiana/Virginia: Cosenza and Robinson 2019; Nevada: Carvajal 2018; Poland: Buczynski and Iwanski 2018; Texas: Arambula-Mercado et al. 2018; Virginia: Habib 2017.
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20 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling significant differences in the moduli (Figure 7)
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Literature Review 21 Source: Based on Ma 2018. Figure 8.
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22 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling Source: Diefenderfer, personal communication, 2020. Figure 11.
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Literature Review 23 Pavement Design Summary Agencies using the older AASHTO 1993 pavement design methodology employ a wide range of structural layer coefficients. Some dynamic modulus data can be used in the MEPDG pavement design methodology, but data that can be used in cracking and rutting models have not been documented.
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24 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling AASHTO PP 86, ARRA CR201, and ARRA CR202 require that 100% of particles pass the 1-in.
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Literature Review 25 Foamed asphalt cold recycled mixes with finer gradations tend to produce tender mixtures that are susceptible to permanent deformation (i.e., rutting)
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26 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling stabilize the asphalt droplets in the water (i.e., keep the droplets suspended) (Moors 2019)
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Literature Review 27 Influence of Cement on Emulsion Breaking Recent imaging research was used to describe how emulsion droplets coalesce in the presence of both mineral filler and Portland cement (Fang et al.
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28 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling The requirements for the ER are usually from 10 to 20, with 8 to 10 typically set as the minimum. The temperature of the aggregate can influence ER requirements.
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Literature Review 29 from amending the overall gradation; any benefit can be assessed during the mix design and with mix performance testing (Cross et al.
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30 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling recycling process for mix designs. The RAP is crushed and sieved into individual fractions so the required gradations can be batched.
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Literature Review 31 California Department of Transportation (Caltrans) uses three emulsion contents for mix designs that are selected from between 0.5% and 4.0% at increments of either 0.5% or 1%.
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32 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling Foamed Asphalt Contents Cox and Howard (2013) documented 37 instances in 63 documents of foamed asphalt content in CIR mixes (Figure 13)
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Literature Review 33 To prevent over-saturation of the cold recycled mix design specimens, some agencies set the additional water to be used for mix design purposes. Other agencies define a limit on the total liquid content (i.e., additional water plus emulsion)
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34 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling Mixing, Compaction, and Curing Mixing Mixing is accomplished with a standard bucket mixer or laboratory pugmill. The dry RAP is mixed with the additional water, followed by any active fillers such as cement or lime, which is mixed into the RAP.
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Literature Review 35 140°F ± 5.5°F (60°C ± 3°C) to reach a constant mass.
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36 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling volumetrically determined using the mass of the specimen and measurements of the specimen height and diameter (AASHTO T 269, Section 6.2.2, ASTM D3203)
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Literature Review 37 Air Voids.
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38 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling Some Marshall stabilities, both wet and dry, and the retained Marshall strength are reported in the literature (Table 15, Figure 17)
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Literature Review 39 Figure 17. Examples of dry Marshall stabilities for emulsified cold recycled mixes.
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40 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling The use of corrective aggregates can improve the dry and wet tensile strengths (ArambulaMercado et al.
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Literature Review 41 A summary of the indirect tensile strengths for emulsion and foamed asphalt cold recycled mixes reported by various researchers is shown in Table 16. The average indirect tensile strength of emulsion cold recycled mixes is 69 psi; the average for foamed asphalt cold recycled mixes is 46 psi.
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42 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling and tensile strength ratio (TSR) percentages over 70%.
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Literature Review 43 • Reflective cracking – Overlay tester • Rutting – Hamburg loaded wheel rut tester – Asphalt pavement analyzer loaded wheel rut tester – Triaxial testing – Repeated load permanent deformation Cox and Howard (2015) identified eight agencies that require assessment of raveling potential, six that require the evaluation of low-temperature cracking potential, and only one that requires Hamburg rut testing (Table 18)
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44 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling Instrumented Indirect Tensile Strength (AASHTO T322)
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Literature Review 45 compactive effort accentuated the difference between emulsion and foamed asphalt cold recycled mixes. The foamed asphalt mixes have lower FEs compared to emulsion mixes.
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46 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling The researchers noted the CIR mixes tended to crumble during testing in a way that suggests the additional specimen preparation needed for the DCT testing may not be a viable option for testing cold recycled mixes. They noted the DCT test can be used on cores, but it requires special fixtures for testing and several steps for specimen preparation.
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Literature Review 47 Source: Based on Sebaaly et al.
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48 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling index. The cracking index highlights the brittle nature of the cold mixes that contain cement (Figure 23)
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Literature Review 49 The flexibility index is used to rank mixes based on fracture (cracking) potential.
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50 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling VanFrank et al.
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Literature Review 51 was considered the minimum for low loads and traffic volume roadways. The SCB results were compared to a weighted performance index [1 (worst)
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52 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling the mixture stiffness followed by the application of a constant strain until failure. The data from these tests are used as input into advanced mathematical models, such as the linear viscoelastic continuum damage and viscoelastic continuum damage models, with a public domain finite element program, FEP++.
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Literature Review 53 Rutting Pavement rutting resistance performance prediction models are usually based on the general power law relationship: ε = ANp B Where A and B are the intercept and slope, respectively, determined for the steady rate of deformation portion (i.e., secondary flow region) of the log-log deformation per load cycle relationship (Figure 27)
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54 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling mixes. Results show the cold recycled mixes exceed the maximum allowable rut depth of 0.5 in.
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RAP Source No. of Passes to Failure (12.5 mm)
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56 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling Foamed Asphalt Average Flow Number No Confining Pressure, 10 psi Deviator Stress 10 psi Confining Pressure, 70 psi Deviator Stress No Confining Pressure, 70 psi Deviator Stress Field-Mixed, Lab-Compacted CCPR Sieved 66 1,925 -- Not sieved 49 824 -- CIR Sieved 39 772 -- Cores CCPR 2,761 9,158 309 CIR -- - -- - 62 -- -: no data available. Source: Based on Diefenderfer and Apeagyei 2014.
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Literature Review 57 that even a small confining pressure significantly increases the average flow number. The cold recycled mix cores have significantly higher flow numbers than the laboratory-mixed, laboratorycompacted specimens.
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58 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling • Variability in measured permanent deformation was higher for cold recycled mixes than for conventional hot asphalt mixes. Arambula-Mercado et al.
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Literature Review 59 Cantabro Test. The Cantabro test (AASHTO TP 108)
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60 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling Mix Design and Performance Testing Summary Compaction is usually accomplished with a 75 blow Marshall, Superpave gyratory compactor (SGC) using either 30 or 35 gyrations.
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Literature Review 61 cold recycled mixes to resist rutting. Durability testing (i.e., raveling, Cantabro tests)
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62 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling Lombardo (2018) notes that the RAP, rather than the air temperature, needs to be greater than 50°F (10°C)
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Literature Review 63 consistent properties. This is particularly helpful when the RAP comes from both driving lanes and roadway shoulder, or from multiple projects.
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64 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling to transporting a single material, and not contaminated with other materials. A flexible hose connects the nurse truck to the pugmill/recycling unit (FHWA 2019)
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Literature Review 65 the mix design, and ± 0.2% allowances were permitted from the production target. Cross (2012)
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66 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling Equipment calibration can be checked using material quantity volumetrics at the end of each day, certified delivery weigh tickets, or by using the canvas patch test. For foamed asphalt, the system needs to have a sampling valve so the expansion ratio and half-life of the material can be verified.
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Literature Review 67 finish rolling to remove any pneumatic tire impressions. If pneumatic rubber tire rollers tend to shove the mix when used as the breakdown rollers, then one or two passes with a double steel wheel roller can help prevent excessive shoving.
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68 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling In-Place Density Field density can be specified as 97% to 98% of test strip density, field compacted density, or laboratory bulk specific gravity (Cox and Howard 2013)
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Literature Review 69 the morning and compacted in the afternoon had significantly lower voids and higher moduli values than specimens sampled in the afternoon and compacted the next morning. Khosravifar (2012)
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70 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling Delays between mixing the cold recycled materials and testing result in lower densities and strengths than mixes that are compacted shortly after mixing and sampling. Specimens need to be compacted and tested on the same day they are mixed.
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Literature Review 71 Opening to Traffic The cold recycled mix surface is usually fog sealed before the roadway is opened to traffic to seal the new surface. Blotter sand can be used on top of the fog seal to minimize the tracking and raveling of the cold recycled mix.
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72 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling emulsion, one source of RAP, and four levels of Portland cement (0%, 0.3%, 0.6%, and 1%)
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Literature Review 73 were lower after 48 hours compared to the 2-hour results (Figure 30)
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74 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling While the moisture content frequently increased to more than 16% after a rainfall, the CIR layer quickly drained the excess water, usually within 24 hours of the rain stopping. The initial research at the start of the project evaluated the rate of change in moisture content due to temperature changes (Figure 31)
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Literature Review 75 Moisture content changes more rapidly as the temperature increases. Changes in the moisture content slow as the humidity increases.
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76 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling Year County Recycling Agent Peak Stiffness, MN/m Stiffness After Peak, MN/m Days Before Wearing Surface Was Placed 2009 Clinton HFMS-2S 35 at 3 days 30 36 2009 Iowa Foamed asphalt 28 to 30 at 11 days 26 but started to increase again at 23 days 27 2010 Benton Foamed asphalt 18 to 20 at 4 days 12 but started to increase again at 14 days 28 2010 Marshall Foamed asphalt 15 to 17 at 12 days 20 to 22 and continued to increase 28 2010 Delaware (1) Foamed asphalt Consistently 25 to 27 41 2010 Delaware (2)
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Literature Review 77 any loss of stiffness due to rainfall at the early stages of curing. The maximum stiffness readings limit the usefulness of the device to the early stages of strength gain.
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78 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling similarity of the mix stiffnesses. The individual layer differences only begin to emerge when the differences between the individual layer moduli increase.
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Literature Review 79 the miller speed and characteristics define the texture of the milled surface that may need to be used as the driving surface. It is important for recycling equipment to move together.
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80 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling predicted CIR service life of 34 years before the roadway reaches a pavement condition index (PCI) value between 40 and 55.
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Literature Review 81 past Montana DOT documents summarizing information for each project. Table 48 summarizes assessments for 10 of the projects with satisfactory performance for up to 11 years as well as for 3 of the 5 poorly performing projects.
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82 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling The noted problems with tracking would have been eliminated by using blotter sand. One comment noted that CIR may have been a poor choice given the long and extreme winter climate typical in that part of the state.
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Literature Review 83 PASS, and Reflex products. CIR with engineered emulsions has shown mixed performance and service life.
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84 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling y = -0.0589x3 + 1.0378x2 - 5.5726x + 100 R² = 0.3453 0 10 20 30 40 50 60 70 80 90 100 0 5 10 15 20 PC I Years After Construction Source: Based on Sebaaly et al.
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Literature Review 85 21 to 25 years old (Figure 40) , which indicates roadways in good condition at ages of up to 25 years.
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86 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling (50 mm) and the CIR was placed at 5 in.
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Literature Review 87 projects and comparisons are different for each state, when the percent savings is calculated, cold recycled mixes show cost savings from a low of around 20% to more than 60%, depending on the type of wearing surface used on top of the cold recycled mixes. Environmental Benefits Some agencies are beginning to consider both economic and environmental costs and benefits during the design and bidding stages of construction projects.
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88 Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling the number of haul trucks needed, thereby reducing the use of, and emissions from, diesel fuel (Schwartz et al.
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