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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
×
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
×
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
×
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Suggested Citation:"Chapter 3 - Findings." National Academies of Sciences, Engineering, and Medicine. 2011. Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content. Washington, DC: The National Academies Press. doi: 10.17226/14570.
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15 Phase 1—Recycled Polyethylene Resins There are many different types of recycled PE available. One way to classify PE resins based on density is found in Table 2. Notice that at the extremes of density one finds LDPE and HDPE homopolymers. These were the first two types of PE commercially produced. LDPE has the most branch- ing and HDPE has the least. The others are all made by co- polymerizing ethylene gas with other α-olefins, which produces small branches in a controlled manner. The α-olefins are butene, hexene, and octene, which produce 2, 4, and 6 carbon branches, respectively. The density is varied by the amount of α-olefin added. All of these types of PE are available on the recycled-resin market. However, some are certainly more available than others. The main subclasses for recycled PE are post-industrial recycled (PIR) and PCR. There are also several different phys- ical forms one can buy. PIR resins are often sold in their bulk forms or the plastic parts may be ground into chips and sold as regrind. PCR resins are sold as regrind chips, or as a reprocessed resin (repro). Reprocessed resins are chips that have been melted, filtered and pelletized. They are more blended than chips, cleaner from the melt filtration step, and in a better form to feed into an extruder. There were about 50 different recycled polyethylene sup- pliers identified and many were contacted for samples. A list can be found in Appendix B, Section B.8. Post-Industrial Recycled Polyethylene This is a large category that includes scrap from processes such as pipe, sheet, thermoforming, injection molding, blown film, tubing, and more. This includes low density, linear low density, linear medium density, and high density (homo- and co-polymer). The molecular weight also varies from injection molding grade (low molecular weight [LMW], high MI) to thermoforming or blown film (high MW [HMW], low MI). There are certainly resins that would be appropriate for incorporation into pipe available from the PIR market. How- ever, there is a downside. PIR material is sold mainly through brokerage firms and is commonly sold on a lot-to-lot basis. This means that reliable and continuous waste streams are not commonly found. Additionally, it is often in a bulk form and/or co-mingled with different grades of PE. The result is that the PIR material is used mostly in noncritical applications by plastic processors who have the capabilities to accommo- date different grades of PE. Despite the limitations mentioned above, three PIR PE sam- ples were received for evaluation in this study. Two [HDPE and low-density PE (LDPE)] were provided by a re-processor that also produces post-consumer polyethylene. The third sample, medium-density PE (MDPE), was regrind scrap from a manufacturer of geomembranes for landfills. Properties of each of these recycled resins are found in Table 3. Notice that each of these has stress-crack resistance (15% NCTL) higher than most, if not all of, the current AASHTO resins for pipe. They are also much higher in cracking resis- tance than post-consumer HDPE. Therefore, these resins could be useful for enhancing the properties of post-consumer HDPE. They are also much lower in density, which would limit how much could be used in a blend. Notice that the den- sity of the low density material is actually higher than the den- sity of the MDPE. This is due to the high level of inorganic fillers displayed by the percentage ash. In fact, each of the three density values are misrepresented because of fillers in the cases of the HDPE and LDPE and carbon black in the case of the MDPE sample. The density can be calculated from the yield stress through the following relationship: The calculated values for the HDPE, MDPE, and LDPE are 0.943, 0.937, and 0.925 g/cm3, respectively. One can also correct for the carbon black from the MDPE sample because each 1 Yield Stress Density= ( )−81 250 73 500, , C H A P T E R 3 Findings

percentage of carbon black increases the density 0.0044 g/cm3. This also produced a calculated value of 0.937 g/cm3 for MDPE. Post-Consumer Recycled High-Density Polyethylene This is a smaller category, in terms of different resins, that includes primarily recycled bottles and high-strength shop- ping or trash bags. The volume of good recycled bags is low because the bulk density (volume/weight ratio) is low and the high quality bags are usually contaminated with lower quality LDPE bags. Additionally, the volume of plastic bags is shrink- ing because their use is being legislated against in a growing number of communities throughout the United States. The bottles can either be natural or colored. The natural bottles are most often the 1⁄2 to 1 gallon water, juice, or milk jugs. They are made from HDPE homopolymer, which is a resin with high strength and poor stress-crack resistance. The colored bottles include liquid detergent, cleaners, sham- poos, fabric softeners, and others marked with a number “2” recycling code. The resin used in colored bottles is an HDPE co-polymer which is not as strong as the homopolymer but has better cracking resistance. Both the natural and colored HDPE resins are available as regrind (chips) or reprocessed (pellets). The reprocessed pel- lets have the advantage of being melt-filtered during the pel- letizing process. This is essentially one additional purification step. The colored-bottle recycled resin contains a significant amount of natural bottle in it. There is an increasing number of recyclers who are separating the natural bottles from the mixed-color bottles because the natural resin has significantly higher value on the recycled-resin market. The difference can be $0.10 per pound, or more. Most of the samples found during this study came through contact with the Association of Post-Consumer Plastic Re- cyclers (APR). Twenty-two samples of PCR HDPE were received from six member companies of the APR and two nonmembers. The samples included natural regrind (2), natural reprocessed (4), mixed-color regrind (MCRG) (5), MCR (8), and three special 16 Common Name Type (ASTM D1248) Density (g/cm3) LDPE (homopolymer) 0 <0.910 LLDPE (copolymer) 1 0.910–0.925 LMDPE (copolymer) 2 >0.925–0.940 LHDPE (copolymer) 3 >0.940–0.960 HDPE (homopolymer) 4 >0.960 Note: LDDPE = linear low-density polyethylene, LMDPE = linear medium-density polyethylene, LHDPE = linear high-density polyethylene. Resin Type Property HDPE Reprocesse d MDPE Regrind LDPE Reprocesse d Density (g/cm 3 ) 0.970 0.942 0.952 Calculated Density 1 (g/cm 3 ) 0.943 0.937 0.925 Melt Index (g/10 min) 0.32 0.66 0.80 MFR (21.6/2.16kg) 101 46 34 % Volatiles 0.24 — 0.18 % Color 0.28 1.05 0.15 % Ash 3.69 0.05 3.75 Yield Stress (psi) 3143 2631 1686 Break Strain (%) 628 662 727 15% NCTL (h) 104 >800 >300 OIT (min) 18.2 61.4 6.3 1 Calculated from the yield stress. Note: MFR = melt flow rate; “—” = no data available. Table 2. Types of PE. Table 3. PIR resin properties.

blends labeled “mixed color plus” by project personnel. Two of these are MCR with added high molecular-weight (HMW)- HDPE to assist with processing, and to improve properties such as impact strength and stress-crack resistance. The third is a blend of mixed-color PCR HDPE with PIR HDPE. These resins were made into plaques and characterized by a variety of tests. The full test reports for these materials are found in Appendix B, Section B.5. The results were originally generated on plaques made from the “as-received” pellets. Test results indicated that further blending was necessary to obtain homogeneous material for characterization. This is reasonable because single screw production lines are not as well suited for blending as a twin screw. If the recyclers were to improve the mixing on their extruders, the changes could cause more thermal-oxidative degradation to the material. Therefore, the MCRGs and reprocessed materials were further blended and recharacterized. In general, the regrind samples received were melt-blended at least twice and the reprocessed samples were further blended at least one additional time. PCR Natural Resin The average resin properties for post-consumer natural recycled HDPE have been summarized in Table 4. TRI-repro was a blend of the others made in-house as an “average” sam- ple. A milk bottle was also tested for comparison. Observations from the summary table include the following: • The density and melt flow values are higher than typically found for AASHTO pipe resin. AASHTO pipe resins are typically around 0.950 g/cm3 and 0.15 g/10 min. The ash content is low. This demonstrates that recycled natural resin is very clean. • The high yield stress is due to the higher density. Yield stress and density are linearly related. • The percentage strain-at-break was low compared to virgin materials (>500%). This property can be considered a flaw detector, since every break in a tensile test occurs at a flaw. These results indicate that the small amount of particles pres- ent in the recycled result in early breaks. In turn, the flaws can also be initiators of stress cracks in the resultant pipe. • The 15% NCTL times are low, which is a result of the high density and the fact that milk bottle resin is a homopolymer. • The OIT values are indicative of stabilizer concentration, but how much is there cannot be determined without knowing the specific additive package and what the rela- tionship between OIT and concentration is for that specific package. However, the data do indicate that there is some antioxidant protection remaining in the recycled HDPE. The advantage of this recycled resin is that it is clean and strong; the disadvantages include the cost and the poor crack- ing resistance. PCR Mixed-Color Resin Most of the samples obtained fell into the category of PCR mixed-color resin. There were 15 different samples from eight different suppliers. There were five regrind resins and 10 reprocessed resins. And, of the 10 reprocessed resins, three had something else added. Suppliers 2 and 3 sent samples with added HMW PE to improve processing and stress-crack resist- ance. Supplier 5 sent a product with additional PIRHDPE added to improve its properties. Suppliers 1 and 3 sent samples of regrind resins at different times, so the consistency of their products could be examined. The average properties of all the mixed-color resins received are found in Table 5. This table provides a snapshot of the PCR resins available in the first half of 2007. The sample called TRI Repro 1 was a batch prepared in house on the twin screw extruder. All the available mixed-color reprocessed samples were combined to prepare 20 lbs of resin that was basically an average of the samples received. There are a number of important observations from these results: • The density, melt index, and yield stress vary with the amount of milk bottles present in the mixed-color waste stream. The values are probably more consistent in 2010 than in 2007 because more processors are separating the milk bottles due to their increased value over colored bottles. • These resins typically have little color. In this case, all the values were less than 0.4%, except one sample where the manufacturer added 1.3%. • The percentage ash in the products can be reduced by melt filtration through a larger mesh size (smaller openings). This, in turn, will improve the percentage break strain. 17 Resin Type Property TRI Repro Milk Bottle Average Range Density (g/cm 3 ) 0.960 0.958 0.957 ± 0.002 0.955–0.960 Melt Index (g/10 min) 0.79 0.74 0.67 ± 0.1 0.57–0.81 MFR (21.6/2.16kg) 71 75 87 ± 8 76–96 % Ash 0.06 0.04 0.11 ± 0.05 0.05–0.14 Yield Strength (psi) 4523 4316 4402 ± 79 4304–4489 Break Strain (%) 365 114 157 ± 73 75–229 15% NCTL (h) 2.0 5.4 3.7 ± 1.6 1.8–5.7 OIT (min) — 2 3 16.5 ± 7.5 9–27 Note: “—” = no data available. Table 4. Post-consumer natural recycled PE properties.

• The percentage PP reported was typical in 2007. The aver- age is closer to 10% in 2010, due to the popularity of 2X and 3X detergent bottles. The percentage PP by weight can be as high as 30% in the 3X bottles. The caps and spouts are made from PP. • The stress-crack values are typical for these products. Note that the NCLS stress-crack times (F2136) are even lower because the yield stresses are less than 4,000 psi. The NCLS test assumes a 4,000 psi yield stress and loads the samples at 600 psi, which is 15% of 4000. The load as a percentage of the yield stress will increase for resins with yield stresses less than 4,000 psi. For example, a sample with a yield stress of 3,327 will be loaded at 18% of its yield stress during the NCLS test. • The OIT values show that some stabilizers are present, although it is not possible to know what they are from the results. That some stabilization is present, even after repro- cessing, shows that the material is probably not affected by the additional stress of reprocessing. The rather large vari- ability suggests that either some reprocessors are adding stabilizers, or additives are being consumed at different rates by different reprocessors. OIT vs. OITemp This has been a controversial issue for about 5 years now. ASTM D3350 requires the OITemp test to be performed on resins and that a minimum temperature of 220°C be obtained. Other industries, most notably geosynthetics, have used the OIT test for over 15 years to specify HDPE geomembranes. There have been discussions about which one was most appro- priate for different applications and there have also been mis- interpretations about the meaning of the results. In the OIT test (ASTM D3895), a small sample (∼5.0 mg) is maintained at 200°C in a pure oxygen environment until the protective stabilizers are consumed by the oxygen and the sample decomposes exothermally (it basically catches on fire). The time it takes from the addition of oxygen to the onset of oxidation is the OIT. It is known that in well-behaved addi- tive packages, there is a relationship between the OIT value and the amount of additives present in the sample (1, 2). It is also known that the OIT value does not relate to the long- term performance of the material. The test merely shows the oxidation behavior at 200°C, which has little to do with real- time aging at ambient temperatures. However, if one exposes a sample to a condition that consumes additives (oven, chlori- nated water, UV light) then the residual lifetime can be deter- mined by the amount of OIT left after the exposure. This seems to be a reasonable approach. It is known from assessments of old geomembrane liners (3 − TRI, Confidential files) that as the OIT value approaches zero, other changes can be seen such as a reduction in stress-crack resistance or change in melt index, both signs of polymer oxidation. The OITemp test has historically been used on scrapings from the inside walls of thick-walled pipe after manufacturing. The inside wall is exposed to more heat longer and is the first place that will become oxidized during the process if adequate stabilizers are not present. Therefore, when a sample shows an OITemp value less than 220°C, that means it has been degraded during processing. So, it really does not say how good something is, but instead that it has not been made worse. That said, there is a relationship between OIT and OITemp. Figure 14 shows the relationship between OITemp and OIT for 76 data points. The data includes eight PPI-certified virgin corrugated pipe resins, two geomembranes, 21 PCR samples, and 45 points from the Pennsylvania Deep Burial Project (13). These results should settle the controversy. Since the rela- tionship appears to be logarithmic, there will always be a larger change in the OIT value for a given change in the OITemp value. That means the OIT test is more sensitive and can dis- tinguish materials better. Additionally, the OIT test is likely to be more sensitive to long-term antioxidants, while the OITemp is better suited to evaluate process stabilizers, since these are made to be active at higher temperatures. For these reasons, the OIT test will be used in the recommended specifications for the use of recycled resins. The Effects of Contamination The types of foreign matter that may be found in PCR HDPE include labels, paper, cardboard, dirt, aluminum foil, adhesives, and other polymers like PP (from caps), ethylene vinyl alcohol (EVOH), Nylon, PET or polyvinyl chloride 18 Property TRI Repro 1 Average Range Density (g/cm3) 0.960 0.955 ± 0.005 0.946–0.960 Melt Index (g/10 min) 0.54 0.48 ± 0.10 0.37–0.64 MFR (21.6/2.16kg) 83 97 ± 14 75–122 % Color 0.4 0.31 ± 0.32 0–1.3 % Ash 1.2 1.1 ± 0.3 0.4–1.5 % PP 5.7 3.6 ± 1.5 0.8–6.3 Yield Strength (psi) 3,685 3,728 ± 218 3,327–4,037 Break Strain (%) 46 90 ± 81 9–302 15% NCTL (h) 8.8 7.8 ± 2.9 4.5–14.8 OIT (min) 12 13.6 ± 7.2 9–39 Table 5. Post-consumer mixed-color recycled PE properties.

(PVC). There is also a new plastic called poly(lactic acid) (PLA), which is derived from corn and is biodegradable. The recycled HDPE may be contaminated with other grades of PE, like LDPE, which could affect the cracking resistance. Finally, there may be milk and detergent residue, which produce smoke and odors during processing. The foreign particulate matter can be removed during the washing step at the recycler and filtered out during extrusion by either the recycler or pipe manufacturer. However, the re- cyclerswhoproducereprocessed HDPE are more capable of this because some of them already melt filter to 100–120 mesh while the pipe manufacturers generally filter at a mesh size of 80 or below. PP comes from bottle closures (caps) and is found in mixed- color reprocessed HDPE at levels as high as 20%. When pro- cessed, the PP will blend in with sufficient mixing, or be melted and spread out in the final part. This could affect the behavior of the pipe, especially the stress-crack resistance. The HDPE milk bottle resin contains no PP because the caps are made from LDPE. In fact, the recycled natural homopolymer (milk bottle) is much cleaner than the mixed color. The effects of contamination have been investigated three ways. First, samples containing a known size and percentage of angular sand were prepared to see how the sand affected properties such as tensile elongation and stress-crack resis- tance. These results will offer some guidance concerning how much filtration to specify. Secondly, two samples containing MCRG were prepared at three levels of filtration. And, finally, samples containing different amounts of PP were prepared and evaluated. The Effects of Particulates Angular “playground” sand was obtained and sifted with both a 100 mesh and a 120 mesh screen. The sand that passed the 100 mesh, and retained by the 120 mesh was collected. The sand particles ranged in size from 0.0052 to 0.0061 in. From this material, a master batch containing 2.5% sand in Virgin Resin 1 (VR1) was prepared. The 2.5% master batch was diluted with more VR1 to produce samples of about 1.6%, 0.8%, 0.4%, and 0.2% sand. The actual values measured by ash analysis on duplicate samples were 1.61%, 0.79%, 0.41%, and 0.25% respectively. Compression-molded plaques were prepared and the break- ing strain and the BAM stress-crack test were performed on the samples. The BAM test is a stress-crack test without a notch and is described in Appendix A, Section A.3.2. The results are shown in Figures 15 and 16. Notice that this size of sand particle has an extremely strong effect on the break strain, even at a level of 0.25%. The percent- age break strain went from 468% to 148%, or to 32% of the original value. This demonstrates that it’s important to keep the particle size small and the amounts as low as possible. The effect is similar for the BAM stress-crack test results. Sand in the amount of 0.25% reduced the stress-crack resis- tance to 62% of the original value. The Effects of Melt Filtration Two types of samples were prepared for this study. The first was 100% MCRG and the second was 50% MCRG + 50% Virgin MDPE. Each of these was melt filtered at three different 19 y = 11.836Ln(x) + 207.94 R2 = 0.871 225 230 235 240 245 250 255 260 265 270 275 0 20 40 60 80 100 120 140 160 180 OIT (minutes) O IT em p (C ) Figure 14. Comparison between the OITemp and the OIT.

levels. It should also be mentioned that the two sample sets were made with two different batches of MCRG HDPE. The 100% MCRG was blended without filtration and also melt filtered at 100 and 150 mesh. The 50/50 MCRG/MDPE samples were melt filtered at 40, 100, and 150 mesh. The filtration at 40 mesh was to help the material process better by removing larger particles that would cause the melt strand to break. The tensile properties were measured on the two sample types. The percentage strain-at-break was chosen as the best result to follow the effects of blending. Plots of the effects of melt filtration on both types of samples are shown in Fig- ures 17 and 18. Five replicates were tested for the 100% MCRG and 10 were tested for the 50/50 MCRG/MDPE. Both sets of results indicate that melt filtration dramati- cally improves the properties of recycled HDPE and blends containing HDPE. Notice in Figure 18 that the scatter in results gets smaller with better melt filtration. This is important data because tensile specimens always fail at a defect. The plotted results clearly show that melt filtration removes defects. The coefficients of variation (COV) (standard deviation/mean × 100) for the three results were 69%, 30%, and 10% with increas- ing mesh size. A 10% COV is acceptable, even for virgin resins. This is a direct result of fewer larger particles in the samples. The BAM stress-crack test is usually performed at 80°C in a surfactant (Igepal CA720) on a specimen without a notch. It is basically a flaw detector. The results were similar to the tensile results. Longer failure times were associated with higher 20 0 100 200 300 400 500 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 % 100-120 Sand Br ea k St ra in (% ) 0 10 20 30 40 50 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 % 100-120 Mesh Sand BA M F ai lu re T im e (hr s) Figure 15. The effect of sand on the break strain. Figure 16. The effect of sand on the BAM stress-crack resistance.

mesh size. The results for both sets of results are shown in Figures 19 and 20. The tests run on the 100% MCRG were at 70°C. The results of these experiments revealed that the degree of melt filtration is an important parameter for using recycled materials. It appears as if filtration at a mesh size in excess of 100 mesh should be a minimum requirement. However, the results of the BAM test did not show as much improvement in the results with filtration as one might think. The reason for this is found in the next section. The Effect of Silicone Rubber One of the advantages of the BAM test is that the fractured surface can be examined to see where the crack started. Exam- ples are shown in Figures 21 and 22. The clear, rubbery material was identified as silicone rubber by Fourier transform infrared (FTIR) analysis. The IR results are shown in Figure 23. Four different rubbery particles were tested, and they all looked the same. It is not clear where the silicone rubber came 21 y = 0.6014x + 29.214 R2 = 0.984 0 20 40 60 80 100 120 140 0 20 40 60 80 100 120 140 160 Filter Screen Size (Mesh) % B re ak S tra in y = 2.0632x + 158.23 R2 = 0.9937 0 100 200 300 400 500 600 0 20 40 60 80 100 120 140 160 Filter Mesh Size B re ak S tra in (% ) Figure 17. The effect of melt filtration on the percentage break strain of 100% MCRG. Figure 18. The effect of melt filtration on the percentage break strain of 50/50 MCRG/MDPE.

050 100 150 200 250 300 350 400 0 20 40 60 80 100 120 140 160 Filter Mesh Size Fa ilu re T im e (H rs) 0 20 40 60 80 100 120 0 20 40 60 80 100 120 140 160 Filter Mesh Size BA M F ai lu re T im e (hr s) Figure 19. The effect of melt filtration on the BAM failure time of 100% MCRG at 70°C. Figure 20. The effect of melt filtration on the BAM failure time of 50/50 MCRG/MDPE at 80°C. Figure 21. BAM test fracture surfaces for failure times of 11 h (left) and 133 h (right) (unfiltered).

23 CM–1 %T Figure 22. BAM test fracture surfaces for failure times of 12 h (left) and 172 h (right) (100 mesh). Figure 23. Fourier transform infrared (FTIR) spectra for HDPE (top), the rubbery contaminant (middle), and the best library match, silicone rubber.

from, but it is known that the rubber bladder found in the caps of some wide-mouth bottles is made from silicone rubber. Rubber has been seen in ketchup, mustard, jelly, and dessert topping bottles. Unfortunately, the rubber particles are so flexible that they pass through the filter screens. However, it is believed that the particles can be broken up by the screens, so better filtration should produce smaller particles. If this is combined with improvements in stress-crack resistance, then it is believed that the effect of this contaminant can be minimized. The Effect of Polypropylene PP is a contaminant in post-consumer MCRG and re- processed resins that comes from the colored-bottle closures. The recyclers report PP at levels up to 20% by weight. There- fore, it is important to know its effect on the properties of HDPE. There are two obvious ways to measure percentage PP. The first is with the use of FTIR spectroscopy. FTIR is an analyti- cal technique that takes advantage of the fact that different combinations of atoms absorb IR radiation at different fre- quencies. The technique produces a chemical fingerprint of absorption bands of different intensities and at different fre- quencies. This can be used as a quantitative tool because the height of a particular band is directly related to its concentra- tion, assuming the specimen thickness (path length) is a con- stant. With a blend of PE and PP, one can ratio two peaks, each specific to one of the polymers. The ratio of these peaks will be linearly related to the relative concentrations, up to a certain limit that can be determined experimentally. This tech- nique works well for natural resins but becomes more diffi- cult in the presence of colorants, particularly carbon black. These absorb IR radiation and can affect the peak heights and shift the linear portion of a calibration curve. The other measure is with the use of DSC. A DSC measures thermodynamic transitions, like melting or decomposition. This is the method of choice during this study and details of the method can be found in Appendix, Section A.2.6. Samples of VR1 with 2%, 5%, and 10% PP were pre- pared and tested. The properties evaluated were density, melt index (MI), break strain, and two different stress-crack tests (15% NCTL and NCLS). The results are shown in Figures 24 through 27. The density and MI change in a predictable way because this PP has a lower density and a higher MI than VR1. The break strain values reflect the lack of miscibility between HDPE and PP during extrusion. The most interesting results were from the stress-crack tests (Figure 27). Notice that the stress crack resistance actually increased between 2% and 5%, all three times the test was run. The effect is not so great in the NCLS tests as in the 15% NCTL test. The NCLS results are effectively normalized by all the samples being placed under the same applied load. It is clear though, that the stress-crack resistance begins to be compro- mised around 5% PP. Phase 2—Recycled-Resin Blends The results from Phase I of the project showed that recycled HDPE had properties that were below the established limits of AASHTO-approved pipe. Therefore, the percentage of re- cycled material that can be blended with pipe resin will be lim- ited by these properties. Efforts were undertaken to determine 24 y = -0.0005x + 0.9489 R2 = 0.9875 0.943 0.944 0.945 0.946 0.947 0.948 0.949 0.95 0 2 4 6 8 10 12 % Polypropylene D en si ty (g /cc ) Figure 24. The effect of percentage PP on density.

y = 0.0089x + 0.2695 R2 = 0.9804 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0 2 4 6 8 10 12 % Polypropylene M el t I nd ex (g /10 m in) y = -23.388x + 628.65 R2 = 0.8882 0 100 200 300 400 500 600 700 800 0 2 4 6 8 10 12 % Polypropylene B re ak S tra in (% ) 0 2 4 6 8 10 12 % Polypropylene 30 40 50 60 70 80 Fa ilu re T im e (H rs ) 15% NCTL NCLS - 1 NCLS - 2 Figure 25. The effect of percentage PP on MI. Figure 26. The effect of percentage PP on break strain. Figure 27. The effect of percentage PP on the stress-crack resistance.

what those limits were and to also enhance the properties of recycled HDPE by blending it with nonpipe virgin resins such as LLDPE and LMDPE. A secondary but important objective was to determine the relationships between the percentage component in a blend and the resulting blend’s properties. Resins used during the blending study are given in Table 6. A few selected properties of these resins are shown in Table 7. Notice the wide variability in the yield stress and NCTL values. Blends Made with Mixed-Color PCR A total of 29 blends were prepared with the use of Mixed- Color PCR bottle resin. They included VR1 + MCR1 @ 20, 40, 60, and 80%, VR1 + MCRG @ 20, 40, 60, and 80%, VR2 + MCR1 @ 20, 40, 60, and 80%, VR3 + MCR1 @ 20, 40, 60, and 80%, 26 Resin Abbreviation Description Virgin Resin 1 VR1 PPI-certified AASHTO HDPE pipe resin. Virgin Resin 2 VR2 PPI-certified AASHTO HDPE pipe resin. Virgin Resin 3 VR3 PPI-certified AASHTO HDPE pipe resin. Virgin LLDPE LLDPE Commercial linear low-density polyethylene resin from a supplier that makes AASHTO pipe resin. Virgin LMDPE LMDPE Commercial linear medium-density polyethylene resin from a supplier that makes AASHTO pipe resin. Mixed-Color PCR 1 MCR1 Mixed-color post-consumer reprocessed HDPE pellets composed of colored and natural bottles. Mixed-Color PCR 2 MCRG Mixed-color post-consumer regrind HDPE chips composed of colored and natural bottle. Natural PCR NAT Post-consumer reprocessed HDPE pellets made from milk, juice, and water bottles. Natural PCR + 10% LLDPE N10LL Blend of NAT with 10% LLDPE to enhance the properties of the NAT. Natural PCR + 35% LLDPE N35LL Blend of NAT with 35% LLDPE to enhance the properties of the NAT. PIR Low Density PIR-LD Post-industrial low-density polyethylene reprocessed pellets believed to contain mostly film and bags. PIR Medium Density PIR-MD Post-industrial linear medium-density polyethylene regrind chips from the sheet market. PIR High Density PIR-HD Blend of PCR high-density bottles with PIR polyethylene. Resin Density (g/cm 3 ) Yield Stress (psi) Break Strain (% ) 15% NCTL (h) VR1 0.950 3,688 478 45 45.8 2.5 VR2 0.953 3,924 58 639 98 38.5 3 VR3 0.949 3,764 52 647 83 36.2 2.5 LLDPE 0.919 1,616 19 771 94 >1,000 LMDPE 0.934 2,732 24 645 49 >1,000 PCR-MCR1 0.960 3,620 86 62.5 27 7.6 1 PCR-MCRG 0.960 3,527 58 164 30 7.6 1 PCR-NAT 0.960 4,525 42 302 115 2.3 0 PCR-N10LL 0.957 4,037 60 411 191 3.0 0 PCR-N35LL — 3,203 54 655 32 19.5 3 PIR-LD 0.952 1,686 42 727 14 >300 PIR-MD 0.942 2,662 27 692 43 >300 PIR-HD 0.968 3,157 32 684 40 97.5 9 Note: “—” = data not available. 58 Table 6. Component resins for blend preparation. Table 7. Properties of component resins for blending.

MCRG + MDPE @ 25, 50, and 75%, MCR1 + MDPE @ 25, 50, and 75%, MCRG + PIR-MD @ 25, 50, and 75%, 75% MCR1 + 25% PIR-HD, and 50% VR3 + 25% MDPE + 25% MCR1. The effects of recycled content on the yield strength for four blends of virgin pipe resins with mixed-colored PCR are shown in Figure 28. It is fairly clear from these graphs that the yield strength is a linear function with respect to recycled content. That means that a simple mixing equation can be used to approximate the yield strength of a blend. This information will allow one to blend dif- ferent resins to make sure that the resulting blend always stays within the specified yield strength requirements. The correlation is not particularly good, but this is likely caused by the combi- nation of the two blend components not being too far apart in strength and the higher scatter found with recycled materials. Similar plots are shown for the breaking strain in Figure 29. Notice that these are even farther away from the theoretical line, and the scatter in the results is quite high. This is a reflec- tion of the contaminants found in PCR resins and demon- strates the need to control contamination. Plots of the NCTL stress-crack resistance determined at 15% of the yield strength are shown in Figure 30. In this case, the curves are obviously exponential in nature and the match between theoretical and actual is much better. Appendix C, Section C.9 contains summary tables for all the blends made with PCR-MCR, plots of properties versus percentage recycled content, and individual property reports for the 29 blends. Examination of the results reveals that all the properties change in either a linear or an exponential man- ner. More specifically, all the property changes are linear except for the melt flow (both loads) and the stress-crack resistance. This is powerful information because the properties of blends can be predicted based on these relationships. However, some of the inherent scatter found in certain properties makes such predictions unreliable. It is believed, though, that the rela- tionships can be used as a guide for preparing blends with the understanding that actual blend testing will still be required. 27 y = -3.62x + 3934.5 R2 = 0.8439 y = -0.68x + 3688 3000 3200 3400 3600 3800 4000 0 20 40 60 80 100 120 % Recycled Yi el d St re ng th (p si) Theoretical Actual y = -0.65x + 3779 R2 = 0.412 y = -1.44x + 3764 3000 3200 3400 3600 3800 4000 0 20 40 60 80 100 120 % Recycled Yi el d St re ng th (p si) VR3 + MCR VR1 + MCR y = -0.665x + 3564 R2 = 0.2812 y = -1.61x + 3688 3000 3200 3400 3600 3800 4000 0 20 40 60 80 100 120 % Recycled Yi el d St re ng th (p si) VR1 + MCRG y = -3.945x + 3886 R2 = 0.9563 y = -3.04x + 3924 3000 3200 3400 3600 3800 4000 0 20 40 60 80 100 120 % Recycled Yi el d St re ng th (p si ) VR2 + MCR Figure 28. The effect of recycled content on the yield strength of PCR-MCR blends.

The results of the blending and testing with mixed-color PCR HDPE have produced the following findings: 1. The maximum amount of mixed-color PCR that can be blended with one of the pipe resins and meet 24 hours of stress-crack resistance is about 20%. And, since the 15% NCTL is less aggressive that the NCLS test, a conservative number is closer to 15%. 2. At 15% added MCR, all the AASHTO requirements of pipe would be met. 3. The two different batches of mixed-color PCR (MCR1, MCRG) behaved dramatically different. The latter produced much better correlation to theory and had a much higher break strain, showing that there were fewer contaminants in the sample. 4. The difference between the predicted and actual values of percentage strain-at-break might be used to evaluate the level of contamination in the recycled material. 5. Much greater stress-crack resistance may be required to offset the deleterious effects of contamination. 6. The stress-crack resistance can be dramatically improved by the addition of MDPE to the mixed-color PCR. A 50:50 blend would produce a resin with about 200 hours in the 15% NCTL test. The yield stress would be reduced to about 3,250 psi, so this must be kept in balance. 7. The PIR-MD evaluated also improved the resistance to cracking, but not as much as the virgin MD. Blends Made with Natural PCR There were 27 blends made with natural PCR HDPE. They included VR2 + NAT @ 20, 40, 60, and 80%, NAT + LLDPE @ 20, 40, 60, and 80%, NAT + MDPE @ 20, 40, 60, and 80%, VR1 + N10LL @ 20, 40, 60, and 80%, VR2 + N10LL @ 20, 40, 60, and 80%, VR1 + N35LL @ 20, 40, 60, and 80%, 50% NAT + 50% MDPE, 28 y = -1.585x + 246.5 R2 = 0.7001 y = -4.155x + 478 0 100 200 300 400 500 600 700 0 20 40 60 80 100 120 % Recycled B re ak S tr ai n (% ) VR1 + MCR Theoretical Actual y = -3.425x + 551.5 R2 = 0.6076 y = -3.14x + 478 0 100 200 300 400 500 600 700 0 20 40 60 80 100 120 % Recycled B re ak S tr ai n (% ) VR1 + MCRG y = -4.305x + 490 R2 = 0.6047 y = -5.845x + 647 0 100 200 300 400 500 600 700 0 20 40 60 80 100 120 % Recycled B re ak S tr ai n (% ) VR3 + MCR y = -3.655x + 456.5 R2 = 0.9852 y = -5.765x + 639 0 100 200 300 400 500 600 700 0 20 40 60 80 100 120 % Recycled B re ak S tr ai n (% ) VR2 + MCR Figure 29. The effect of recycled content on the break strain of PCR-MCR blends.

65% NAT + 35% PIR-LD, and 50% VR3 + 25% MDPE + 25% NAT. The effect of recycled content on the yield strength for four blends of virgin pipe resins with natural PCR is shown in Figure 31. The N10LL and N35LL are natural PCR with added LLDPE at 10% and 35% by weight. The correlation coefficients for the lines and the agreement between the actual and theoretical are poor. These results are similar to those seen for the mixed-color resin. Once again the correlation between the actual results and the theoretical ones are relatively poor. Similar plots for the breaking strain and the 15% NCTL stress-crack resistance are shown in Figures 32 and 33. The poor correlation in the break strain for the NAT + LLDPE series is easily explained by contaminants. The NAT itself has a COV of 38%, which is carried over into the blends with low amounts of LLDPE. The COVs for 5%, 10%, and 20% LLDPE were 33%, 38%, and 25% respectively. Interest- ingly, the series of NAT with MDPE also has high scatter, but the averages happen to fall in line so it doesn’t present as dra- matically as the NAT + LL results. The COVs for 20% and 40% MDPE were 36% and 28%. These results show a good correlation between the actual and theoretical. This may be due to the fact that the applied loads are based on the yield strengths of the samples. Differ- ences from plaque to plaque, which may contribute to the scat- ter in the yield stress, are minimized by the applied load being 15% of the yield stress. Regardless, these results show a definite exponential relationship between the stress-crack resistance and the recycled content. Appendix C, Section C.10 contains summary tables for the blend series, plots of properties versus percentage recycled, and individual property reports for the 27 blends. The results of the blending and testing with natural PCR- HDPE have produced the following findings: 1. Only about 10% of natural PCR-HDPE can be added to virgin pipe resins and meet a 15% NCTL time of 24 h. 29 y = 37.231e-0.0219x R2 = 0.9941 y = 45.8e-0.018x 0 10 20 30 40 50 60 0 20 40 60 80 100 120 % Recycled N CT L Fa ilu re T im e (hr s) VR1 + MCR Theoretical Actual y = 46.94e-0.0202x R2 = 0.9794 y = 45.8e-0.018x 0 10 20 30 40 50 60 0 20 40 60 80 100 120 % Recycled N CT L Fa ilu re Ti m e (h rs ) VR1 + MCRG y = 55.392e-0.0211x R2 = 0.9647 y = 38.5e-0.0162x y = 36.2e-0.0156x 0 10 20 30 40 50 60 0 20 40 60 80 100 120 % Recycled N CT L Fa ilu re T im e (hr s) VR2 + MCR y = 28.342e-0.0188x R2 = 0.9541 0 10 20 30 40 50 60 0 20 40 60 80 100 120 % Recycled N CT L Fa ilu re T im e (hr s) VR3 + MCR Figure 30. The effect of recycled content on the 15% NCTL on PCR-MCR blends.

However, the yield will be over 4,000 psi, so the NCLS test will be less severe for this blend. That means that the limit might be closer to 15%. 2. Dramatic improvements in stress-crack resistance can be obtained by blending the NAT with either LLDPE or MDPE. A failure time of 50 h in the 15% NCTL test can be obtained with around 45% of added LL and 55% of added MD. 3. Blends between NAT and MDPE are preferred because the yield stress remains higher for the MD blends. For example, the yield stress for 45% LL is around 2,900 psi, while the yield stress for 55% MD is around 3,400 psi. The AASHTO minimum-density requirement for pipe resins is 0.948 g/cm3, which correlates to a yield stress of around 3,500 psi. 4. The addition of only 10% LLDPE does very little to improve the properties of resulting blends. 5. A blend of 50% VR3, 25% NAT and 25% MDPE has prop- erties very close to a PPI-certified pipe resin. Blends Made with PIR-HD A total of 12 blends were prepared with PIR-HDPE. Appen- dix C, Section C.11 contains summary tables for the blend series, plots of properties versus percentage recycled content, and individual property reports for the 12 blends. Tables con- taining correlation coefficients and predicted versus measured properties are found in Tables C-7 and C-8. The blends were VR1 + PIR-HD @ 20, 40, 60, AND 80%, VR2 + PIR-HD @ 20, 40, 60, AND 80%, VR3 + PIR-HD @ 20, 40, 60, AND 80%. This series behaved more predictably. The PIR-HD had 3.9% color + ash but also a high break strain of 720%. The aver- age yield stress of 3,157 psi suggests its true density is around 0.943 g/cm3 and its 15% NCTL time is around 98 h. This is a very good resin for blending because it seems to lack the type of con- tamination that produced the high scatter in the other blends. 30 y = 0.415x + 3905.5 R2 = 0.2146 y = 3.49x + 3688 3200 3400 3600 3800 4000 4200 0 20 40 60 80 100 120 % Recycled Yi el d St re ng th (p si) VR1 + N10LL Theoretical Actual y = -4.835x + 3800 R2 = 0.9761 y = -4.85x + 3688 3000 3200 3400 3600 3800 4000 0 20 40 60 80 100 120 % Recycled Yi el d St re ng th (p si) VR1 + N35LL y = -0.44x + 4062 R2 = 0.0155 y = 1.13x + 3924 3400 3600 3800 4000 4200 4400 0 20 40 60 80 100 120 % Recycled Yi el d St re ng th (p si) VR2 + N10LL y = 3.975x + 4116 R2 = 0.9135 y = 7.62x + 3764 3600 3800 4000 4200 4400 4600 0 20 40 60 80 100 120 % Recycled Yi el d St re ng th (p si) VR3 + N10LL Figure 31. The effect of recycled content on the yield strength of PCR-NAT blends.

The results of blending and testing with PIR-HD have led to the following findings: 1. This PIR resin is apparently void of the contaminants found in PCR bottles that create high scatter in some properties, particularly break strain. 2. A resin with a base density of around 0.943 g/cm3 is an excellent resin for blending because it has a yield stress of around 3,150 psi and stress-crack resistance around 100 h. 3. These test results served to validate the relationships found in the other blends. 4. Blends of virgin resins containing up to 40% PIR-HD had yield stresses around 3,500 psi, break strains above 550%, and 15% NCTL times greater than 40 h. This blend would meet the resin properties found in AASHTO M294 for pipe. A total of 66 blends were prepared and tested to find out how much recycled resin could be used in three PPI-certified resins where the final product would still meet the AASHTO M294 resin requirements for corrugated pipe. It was deter- mined that for simple, two component blends, the maximum amount of PCR-HDPE is around 15%, while a specific PIR-HD obtained could be used in amounts up to 40%. More importantly, it was found that through the relation- ships discovered during this task, other two and three compo- nent blends could be designed and optimized for the specific purpose of maximizing the amount of recycled HDPE used. This information will be invaluable to those developing new blends for improved short- and long-term properties of cor- rugated pipe resins. Contaminants like particles and silicone rubber seemed to affect the relationships in a negative way so the relationships are probably most useful as guidelines; some actual testing will still be required. It also should be stated that much better recycled blends can be made than the ones described in this report. The results herein were limited by the fact that the recycled resins were blended with PPI-certified pipe resins. The virgin resins only had approximately 50 h of NCLS time to begin with. Starting 31 y = 3.04x + 242.5 R2 = 0.8614 y = -0.67x + 478 0 100 200 300 400 500 600 700 0 20 40 60 80 100 120 % Recycled B re ak S tr ai n (% ) VR1 + N10LL VR2 + N10LL Actual Theoretical y = -0.35x + 499.5 R2 = 0.0246 y = -2.28x + 639 0 100 200 300 400 500 600 700 800 0 20 40 60 80 100 120 % Recycled B re ak S tr ai n (% ) y = -2.555x + 553 R2 = 0.8663 y = -3.76x + 647 0 100 200 300 400 500 600 700 800 0 20 40 60 80 100 120 % Recycled B re ak S tr ai n (% ) VR3 + N10LL y = 2.165x + 516 R2 = 0.4525 y = 1.77x + 478 0 100 200 300 400 500 600 700 800 0 20 40 60 80 100 120 % Recycled B re ak S tr ai n (% ) VR1 + N35LL Figure 32. The effect of recycled content on the break strain of PCR-NAT blends.

with similar resins with 100 or 150 h of NCLS time would allow for much more recycled content to be used. Additionally, there are new bi-modal resins with densities that meet M294 requirements and that have thousands of hours of stress-crack resistance. It would be valuable to see the effects of adding these resins to recycled content. Phase 3—Pipe Made from Recycled-Resin Blends Trial Pipe Manufacturing A total of 15 trial pipe samples were prepared at three dif- ferent manufacturing plants, designated Plants A, B. and L. Five, 20-feet-long samples were made from each formulation for a total of 1,500 feet of pipe. The formulations made at the three plants are shown in Table 8. Each of the three plants used the same lots of PCR-MCR and PCR-NAT from a single supplier. Each plant used a different lot of the VR1 and each plant used their own carbon black master batch. The MDPE used was also from the same lot. Each plant made a sample from 100% virgin resin 1 and a 50/20/30 blend of VR1, MDPE, and MCR. Sample L1 was a proprietary pipe resin formulated by the recycled-resin supplier. This was included as a representation of the type of resin that could be supplied by the recycled-resin companies. Short-Term Properties Index Test Results After the 15 sample pipes were manufactured, their prop- erties were measured on compression-molded plaques made from the pipe. All the plaques were made in accordance with ASTM D4703 at a cooling rate of 15°C/min. Complete reports are given for each pipe formulation in Appendix D, Sec- tion D.11. This section will focus on specific properties that may be important for future specifications. A summary of the short-term properties is shown in Table 9. The density of base resins for AASHTO M294 pipe must be between 0.948 and 0.955 g/cm3. This is cell class 4 accord- 32 y = 20.592e-0.0178x R2 = 0.6512 y = 45.8e-0.0273x 0 10 20 30 40 50 60 0 20 40 60 80 100 120 % Recycled N CT L Fa ilu re T im e (hr s) VR1 + N10LL Actual Theoretical y = 29.985e-0.0245x R2 = 0.9712 y = 38.5e-0.0255x y = 36.2e-0.0271x 0 10 20 30 40 50 60 0 20 40 60 80 100 120 % Recycled N CT L Fa ilu re T im e (hr s) VR2 + N10LL y = 31.843e-0.027x R2 = 0.983 0 10 20 30 40 50 60 0 20 40 60 80 100 120 % Recycled N CT L Fa ilu re T im e (hr s) VR3 + N10LL y = 43.269e-0.0093x R2 = 0.9297 y = 45.8e-0.0085x 0 10 20 30 40 50 60 0 20 40 60 80 100 120 % Recycled N CT L Fa ilu re T im e (hr s) VR1 + N35LL Figure 33. The effect of recycled content on the 15% NCTL of PCR-NAT blends.

ing to ASTM D3350. When directly measured, all but four of the samples had densities higher than the upper limit of 0.955 g/cm3. This was caused by the presence of carbon black and particles that are certainly denser than HDPE. However, according to ASTM D3350, these values can be corrected for the percentage carbon black, according to the relationship Dcorr = D − 0.0044C, where C is the percentage carbon black. Density values can also be determined from other material properties, such as the yield stress or flexural modulus. The equation relating density to yield stress is where yield stress is expressed as psi and density as g/cm3. Both values are shown in Table 9. It is believed that the density measured in a gradient density column and corrected for percentage carbon black is inaccurate because of the pres- ence of particles and PP. Their presence will influence the measured value. Also, the direct density measurement might be influenced by the very small size of the test specimen. A piece around 1⁄16 in. × 1⁄16 in. is often the size tested. If this small Yield Stress Density= × −81 250 73 500, , 33 Sample % VR1 % Virgin LMDPE % PCR-MCR % PCR-NAT A1 100 0 A2 85 0 15 0 A3 85 0 0 15 A4 50 20 30 0 A5 40 30 0 30 B1 100 0 0 0 B2 50 20 30 0 B3 20 40 24 16 B4 0 50 50 B5 0 40 36 24 L11 0 0 0 0 L2 50 (VR2) 20 30 0 L3 100 (VR2) 0 0 0 L4 100 0 0 0 L5 50 20 30 0 1Proprietary formulated pipe resin containing about 50% recycled content. SampleProperty A1 A2 A3 A4 A5 B1 B2 B3 B4 B5 L1 L2 L3 L4 L5 Density2 (g/cm3) 0.952 0.943 0.963 0.952 0.948 0.951 0.948 0.948 0.948 0.952 0.950 0.950 0.952 0.946 0.946 Density3 (g/cm3) 0.952 0.951 0.952 0.950 0.948 0.952 0.949 0.945 0.948 0.945 0.949 0.951 0.955 0.955 0.953 Melt Index (g/10 min) 0.12 0.15 0.16 0.19 0.21 0.13 0.22 0.27 0.36 0.34 0.20 0.33 0.36 0.12 0.17 % Carbon Black 1.6 1.4 2.2 0.5 1.5 2.0 2.0 1.9 1.4 1.9 2.1 1.5 1.5 2.5 2.6 % Ash 0.1 0.3 0.2 0.4 0.2 0.0 0.4 0.3 0.1 0.4 0.7 0.4 0.0 0.0 0.3 % PP 0.0 0.7 0.2 1.4 0.3 0.0 1.9 1.7 1.0 2.2 2.5 2.4 0.0 0.0 1.8 Yield Stress (psi) 3851 3775 3863 3710 3623 3865 3638 3251 3523 3311 3631 3751 4079 4145 3922 % Break Strain 183 168 139 241 159 163 343 300 190 351 277 195 252 93 108 OIT (min) 49 39 38 32 96 49 54 93 110 75 13 78 78 70 78 1 All properties measured on compression molded plaques made from the pipe. 2 Measured density corrected for percentage carbon black. 3Density calculated from yield stress. Table 8. Trial pipe formulations. Table 9. Short-term properties for 15 trial pipe samples.1

piece contains a particle or an air bubble, the number could be skewed in either direction. For this reason, it is believed that for a specification of resin blends containing PCR-HDPE, the density is of very limited value. It would be better to simply specify mechanical prop- erties that demonstrate what the density is. Two examples are shown in Table 10. These are the required mechanical property values to ensure that the base resin density was in the range specified by AASHTO M294. Unfortunately, the yield stress and flex- ural modulus values do not fit neatly into cell classes them- selves. Cell class 5 for yield stress is 3,500–4,000 psi, so one could specify a cell class of 5 or higher. If the density were too high, the stress-crack resistance would suffer from too much homopolymer. The cell class 5 for flexural modulus is broad (110,000–160,000) but could be used. A resin too low in flex- ural modulus would also be below the minimum yield stress of 3,500 psi. The MI values were consistent and very close to the theo- retical values, except in a few cases. This suggested that, for the most part, the pipe formulations were made correctly. The percentage carbon black results were a little surprising. Each manufacturer was asked to control the carbon content to 2% to 3%. The results showed that only six samples had the correct amount of carbon black, the others were all less than 2.0%. It should be noted that AASHTO M294 allows from 2% to 5%, so the manufacturers were asked to do something they normally do not do. The percentage ash and percentage PP were both close to the theoretical values with the percentage ash having a linear corre- lation coefficient (R2) of 0.75 and the percentage PP’s was 0.91. The yield stress values showed that all the samples were above 3,500 psi except samples B3 and B5. These two were slightly lower and actually were very close to their calculated values. Either of these could easily be adjusted higher with added virgin pipe resin or recycled PE homopolymer. The percentage strain-at-break values were all much lower than expected. Apparently, the carbon black has a large effect on the break strain. This is one area that should be looked at because, historically, there has been little attention paid to carbon black for corrugated pipe. It is a very important aspect for solid-wall pipe and PE resins used for geomembranes. Specifications for recycled materials could improve the qual- ity of the carbon blacks used simply by setting a high standard for break strain. The OIT values were consistently above 25 min, except for pipe sample L1, which was 13 min. This was a proprietary blend from a single supplier, an example of a fully formulated resin one might obtain from recycled-resin suppliers. In this case, the OIT was below a suggested value of 25 min. The values for the blends chosen for this study varied based on the virgin resin content, because both the HDPE and LLDPE resins were well stabilized. In conclusion, the main findings concerning the short-term properties of the trial pipes were the following: 1. A direct measurement of the density of pipe containing recycled content is of limited value, even when the result is corrected for percentage carbon black. 2. The percentages of carbon black were below 2.0% in nine of 15 samples, which might suggest a lack of control by the corrugated pipe manufacturers. 3. The break strains were significantly lower than predicted on blends without carbon black. This could be caused by poor carbon blending, the quality of the carbon black, or even the quality of the carrier resin in the carbon black concentrate. Stress-Crack Test Results Notched Stress-Crack Tests (NCLS and 15% NCTL). There were two different stress-crack tests performed on the plaques made from the 15 pipe samples. The first was the NCLS test (ASTM F2136), in which each sample is loaded at a constant ligament stress of 600 psi. The 600 psi is a result of taking 15% of 4,000 psi, which is about the yield stress of the PPI-certified resins for corrugated pipe. So, the test basically assumes that most of the samples tested will have a yield stress near 4,000 psi. The NCTL test (ASTM D5397, Appendix A, Section A.3) applies a load based on the actual yield stress of the material tested. Since the yield stresses measured on the 15 pipes ranged from 3,251 to 4,145 psi, many of the samples were not very close to 4,000 psi. Therefore, the NCTL test was also used at an applied stress equal to 15% of the measured yield stress. This means that the applied stresses varied from 488 to 622 psi. Both the NCLS and 15% NCTL results are seen in Figure 34. Notice that the 15% NCTL results are almost always higher than the NCLS. This is due to the fact that most of the yield stresses are less than 4,000 psi, so the 600 psi is a higher load 34 Property Range Equivalent to Density Cell Class 4 (>0.947–0.955 g/cm3) Tensile Yield Stress (psi) 3,500–4,100 Flexural Modulus (psi) 130,000–160,000 Table 10. Mechanical properties related to base resin density.

than 15% of the actual yield stress. Two lines are shown on the graph. The higher one is at 24 h, which is the required NCLS time for virgin blends used to make AASHTO M294 pipe. The lower line is 18 h, which has been suggested for pipe samples made into plaques (14). Three of the samples tested failed to meet the 18 h require- ment. Also, the value for plaques will soon be a minimum of 24 h. Eight of the 15 met 24 h and seven were lower than 24 h. BFF Test. A test has been developed that combines some features from the BAM test with the criteria set in the FL-DOT 100-year durability assessment (3). The test is a stress-crack test without a notch. Whenever there is a critically sized defect present, a crack will initiate at the defect and ultimately cre- ate a running crack through the thickness and width of the test specimen. This test is important for blends containing recycled materials because it is very sensitive to contaminants. It is complimentary to the FL-DOT junction test because it can be performed on the same equipment and is run under the same conditions. The FL-DOT protocol calls for the eval- uation of the junction between the corrugation and the liner with a stress-crack test on a 0.25-in. wide test specimen in D.I. water at 80°C. Samples cut directly from pipe are evaluated under the conditions in Table 11. The results are then used with the RPM model to estimate the service lifetime at 23°C and an applied tensile stress of 500 psi. The specification allows one to terminate the tests if no failures occur under the conditions shown in Table 11 after 110, 430, and 500 h, respectively. The BFF test uses a larger test specimen, namely an ASTM D638 Type I dumbbell. The mold in which the plaques are made for this test has been modified to make the ends of the specimen thicker than the reduced section of the specimen. A drawing of the specimen is shown in Figure 35 and a picture of the head in Figure 36. The main difference in the specimens is the size. The junction specimen is a Type IV and the Fathead is a Type I, as defined by ASTM D638. The Type I has a surface area of 1.12 in.2 while the Type IV has a surface area of 0.32 in.2. Depending on the sample thicknesses, the Type I has 2.5 to 3.5 times the volume of the Type IV. This is important when one is looking for flaws or defects, like small silicone rubber particles. The new specimen is called “Fathead” because the plaque mold was modified to make the heads more than two 35 0 10 20 30 40 50 60 70 A1 A2 A3 A4 A5 B1 B2 B3 B4 B5 L1 L2 L3 L4 L5 Pipe Sample Fa ilu re T im e (h rs ) NCLS 15% NCTL NT NT NT Figure 34. Stress-crack resistance of 15 pipe samples (NT  no test). Temperature (°C) Applied Stress (psi) 80 650 80 450 70 650 Table 11. FL-DOT junction test conditions.

times the thickness of the reduced width section. The use of this test specimen has essentially eliminated grip failures. Figures 37 and 38 show pictures of both the FL-DOT Junc- tion Specimen and the BFF specimen. Tests have been performed on compression molded plaques from each of the 15 trial pipes. Preliminary results are pre- sented in Table 12. Almost all of the samples had average values greater than 100 h. The 3 VR1 samples from each of the 3 plants have COVs of 14%, 19%, and 19%. The three samples of the 50% VR1 + 20% MD + 30% MCR had a COV of 27%, 40%, and 28%. The three samples that only contained natural recycled HDPE had COVs of 14%, 4%, and 21%. These results suggest that the highest variability is in the MCR recycled content. The failure surfaces were examined to determine exactly where the specimens broke. There were five categories used to characterize the fracture face. They were the following: 1. Rubber Particle—a clearly present soft particle. 2. Not Obvious—no visible sign of a crack initiator. 3. Gel—a classic unmelt; harder and darker than a rubber particle. 4. Imperfection—an ambiguous flaw or void. 5. Tiny particle—too small to tell if it’s hard or soft. Examination of fracture faces from the tests reported in Table 12 produced the following breakdown: • Rubber Particle: 48%. • Not Obvious: 28% • Gel: 5%. • Imperfection: 13%. • Tiny Particle: 6%. Rubber particles are involved in at least 48% of the cracks observed. BFF Test Reproducibility. It became clear early on that the BFF test results were influenced by residual surfactants in the exposure bath, reflected in the increasing failure times over time. However, it was also learned that once a bath has been used with surfactants, they are difficult to remove, even after multiple rinsings. The results of repeated BFF tests over time are shown in Table 13. The time period represented was about 18 months. It is clear from the table that baths that have never contained surfactants are preferred for the BFF test. 36 Figure 35. The fathead test specimen. Figure 36. Side view of fathead specimen. Figure 37. Junction specimen.

AASHTO M294 Properties It is useful to see how the trial pipe formulations per- formed as measured by the AASHTO M294 requirements of a cell class of 435400, and the additional requirements of a percentage carbon black between 2% and 5%, a NCLS value on a plaque from the pipe of 18 h, and an OITemp of 220°C. The results for the 15 pipe samples are shown in Table 14. There were six samples that did not meet the density require- ment when the measured density was corrected for carbon black. This is an issue with the contaminants interfering with the accuracy of the test. If one uses the yield stress to calculate the density, only two samples, B3 and B5, do not meet the requirement, and these were designed to be lower in density. There were eight samples that were low in carbon black, but this was a manufacturing mistake that can be easily adjusted. And, finally, there were two samples that did not meet the suggested 10 h of NCLS time on molded plaques from pipe. If one applies the new criteria of 24 h on plaques from pipe, then six of the 15 would not comply. It is clear from these results that more attention needs to be placed on the NCLS test when developing recycled resins for corrugated pipe. There is little doubt that stress-crack resistance is the key property for the successful use of recycled materials in corrugated pipe. Long-Term Properties The results of the short-term tests have shown that it will not be too difficult to make blends with recycled contents over 50% that will meet the property requirements of AASHTO M294. By far, the biggest challenge with recycled materials is controlling and minimizing the effects of contamination. Once more, the effects of contaminants will not be seen in short- term tests, but instead will present themselves through a lim- ited service lifetime of the pipe. This makes an understanding of the long-term properties of the pipe critical to the success- ful use of recycled resins in pipe. Since these are all longer-term tests, not all of the 15 pipe formulations could be evaluated. Therefore, six samples were selected based mainly on the percentage of recycled content and the type of recycled content (colored or natural). The for- mulations selected were as follows: • B1 − 100% VR1. • A2 − 85% VR1 + 15% MCR. • L5 − 50% VR1 + 20% MD + 30% MCR. • A5 − 40% VR1 + 30% MD + 30% NAT. • B3 − 20% VR1 + 40% MD + 24% MCR + 16% NAT. • B5 − 40% MD + 36% MCR + 24% NAT. These formulations vary from 0% to 60% recycled content, and there is one formulation with only natural recycled con- tent. Some of their properties are given in Table 15. The prop- erties were measured on compression-molded plaques from the pipes. This group of formulations is believed to be a good repre- sentation of the recycled pipe formulations that might be used. Notice that A2, L5, and B5 have properties outside of the current M294 requirements for virgin, uncompounded resins (shown in bold in Table 15). Long-Term Tensile Strength by SIM The long-term tensile yield strength (Stage I) was deter- mined by the SIM for TTS. It was used to determine the 50 and 100 year tensile strengths of the six candidate pipe formulations. SIM tests were performed at three levels of stress: 1000 psi, 1500 psi, and 2000 psi. The test specimens were placed under the appropriate load then a series of 10,000 second (166 min) creep rupture tests were performed on the same specimen and separated by 7°C 37 Figure 38. Fathead specimen.

Sample Formulation Failure Time (h) (COV) A1 100% VR1 175 25 (14%) A2 85% VR1 + 15% MCR 157 45 (29%) A3 85% VR1 + 15% NAT 123 17 (14%) A4 50% VR1 + 20% MD + 30% MCR 130 35 (27%) A5 40% VR1 + 30% MD + 30% NAT 245 11 (4%) B1 100% VR1 188 36 (19%) B2 50% VR1 + 20% MD + 30% MCR 155 62 (40%) B3 20% VR1 + 40% MD + 24% MCR + 16% NAT 149 43 (29%) B4 50% MD + 50% NAT 108 23 (21%) B5 40% MD + 36% MCR + 24% NAT 145 29 (20%) L1 Solplast Pipe Resin 56 9 (16%) L2 50% VR2 + 20% MD + 30% MCR 150 35 (23%) L3 100% VR2 147 81 (55%) L4 100% VR1 181 35 (19%) L5 50% VR1 + 20% MD + 30% MCR 190 53 (28%) Time to Failure (h) at 80ºC/650 psi (COV) Sample/ Formulation September 2008 October 2008 October 2009 March 2010 A1 VR1 175 31 (18%) 226 46 (20%) B1 VR1 188 44 (23%) 215 97 (45%) 411 ± 135 (33%) 414 ± 97 (23%) L4 VR1 181 42 (23%) 211 46 (22%) — — A4 VR1+MD+MCR 50/20/30 130 42 (33%) 148 73 (50%) — — B2 VR1+MD+MCR 50/20/30 169 68 (40%) 234 52 (22%) — — L5 VR1+MD+MCR 50/20/30 190 65 (34%) 255 54 (21%) 431 ± 86 (20%) 334 ± 117 (35%) A2 VR1+MCR 85/15 157 ± 56 (36%) — 257 ± 85 (33%) — A5 VR1+MD+NAT 40/30/30 253 ± 14 (6%) — 323 ± 70 (22%) — B3 VR1+MD+MCR+NAT 20/40/24/16 166 ± 36 (22%) — 330 ± 66 (20%) — B5 MD+MCR+NAT 40/36/24 145 ± 35 (24%) — 280 ± 95 (34%) 228 ± 141 (62%) L1 Proprietary 56 ± 9 (16%) — 201 ± 39 (19%) 208 ± 73 (36%) Note: “—” = data not available. Table 12. BFF test results on 15 pipe samples at 80ºC/650 psi in D.I. water. Table 13. Effect of residual surfactant on BFF failure times.

39 Sample Density1 MFI Flexural Modulus Yield Stress % Carbon Black NCLS OITemp M294 4 3 5 4 2–5% >18 hrs >220°C A1 4 4 5 5 1.6 28 257 A2 3 3 5 5 1.4 21 256 A3 5 3 5 5 2.2 <18 257 A4 4 3 5 5 0.5 18 256 A5 4 3 5 5 1.5 29 260 B1 4 4 5 5 2.0 26 253 B2 4 3 5 5 2.0 18 253 B3 3 3 5 4 2.0 30 256 B4 4 3 5 5 1.4 19 257 B5 3 3 5 4 1.9 19 256 L1 4 3 5 5 2.1 <18 240 L2 4 3 5 5 1.5 28 256 L3 4 4 5 6 1.5 39 256 L4 3 3 5 6 2.5 29 254 L5 3 5 5 2.6 26 256 1Measured density corrected for percentage carbon black. Note: MFI = melt flow index. Sample Property B1 A2 L5 A5 B3 B5 Density 1 (g/cm 3 ) 0.951 0.943 0.946 0.948 0.948 0.952 MI (g/10 min) 0.13 0.15 0.17 0.21 0.27 0.34 % Color 2.0 1.4 2.6 1.5 2.0 1.9 % Ash 0.0 0.3 0.3 0.2 0.3 0.4 % PP 0.0 0.7 1.8 0.3 1.7 2.2 Flexural (psi) 148,210 152,607 142,618 140,065 128,361 128,758 Yield (psi) 3,865 3,775 3,922 3,623 3,251 3,311 Break Strain (%) 165 168 108 159 300 351 NCLS (h) 25.5 21.2 25.9 28.6 29.8 19.2 OIT (mib) 49 39 78 96 93 75 BFF Test 2 (h) 411 257 382 323 330 254 1 Corrected for % color 2 At 80ºC and 650 psi of stress. Table 14. AASHTO M294 requirements for 15 trial pipe samples. Table 15. Select index properties of final six candidate formulations.

temperature steps. The test was continued until the specimen yielded. The results from the three loads were analyzed accord- ing to the standard and master creep rupture curves were prepared. The rupture point for each load was defined by the intersection of two tangent lines drawn before and after yielding. The results for Sample B1 (100% VR1) are shown in Fig- ure 39. Tabulated results for the six candidate formulations are shown in Table 16. These predicted values assume that the material will stay basically unchanged over the 50 or 100 years of service life- time. This, of course, is not true; all materials undergo aging effects during service. However, these are the best models cur- rently available and give a good approximation of the time- dependent tensile strength. These results basically suggest that the yield strength of the material will be about 30% of the initial strength after 50 years. So, as long as the applied stress is less than about 1,000 psi, the material will not fail in a duc- tile manner. The long-term tensile strength is largely governed by the short-term strength. Therefore, to ensure a 1,000 psi yield strength after 50 years, the short-term strength should be over 3,500 psi. It would be interesting to compare these results with others obtained through long-term hydrostatic testing, either at room temperature or elevated temperatures to verify that the two methods produce similar results. Long-Term Creep Strain and Modulus by SIM The long-term modulus values on the six final candidate resins were also determined in accordance to ASTM D6992. Initially, the elastic limit of the samples was determined by two short-term (15 min) creep experiments. This is impor- tant for defining when nonreversible creep actually begins. 40 y = -0.0459x + 3.3237 R2 = 0.9527 2.9 3 3.1 3.2 3.3 3.4 0 1 2 3 4 5 6 7 8 Log Time (Hrs) Lo g St re ss (p si) Sample B1 REFERENCE TEMPERATURE - 23°C 1242 psi 1161 psi 1124 psi 100,000 hrs 50 yrs 100 yrs Figure 39. Long-term yield strength of Sample B1. Long Term Tensile Stress (psi) Sample/ Formulation 100,000 h 50 years 100 years B1 100% VR1 1,242 1,161 1,124 A2 85% VR1 + 15% MCR 1,227 1,145 1,108 L5 50% VR1 + 20% MD + 30% MCR 1,184 1,103 1,067 A5 40% VR1 + 30% MD + 30% NAT 1,192 1,105 1,066 B3 20% VR1 + 40% MD + 24% MCR + 16 NAT 1,064 973 934 B5 40% MD + 36% MCR + 24% NAT 1,164 1,082 1,045 Table 16. Long-term tensile stress of six formulations.

Next, the SIM was used to determine the creep properties of the samples when placed under an applied stress of 500 psi. This involves a series of 10,000 second (166 min) creep tests, each done on the same test specimen and separated by 7°C in temperature. In this case, creep curves were generated from 20°C to 83°C. The raw data are then shifted through TTS to generate a master creep curve at a reference tempera- ture (23°C). Creep strain and creep modulus master curves for sample B1 (100% VR1) are shown in Figures 40 and 41, and all of the results are shown in Table 17. The raw data and the master creep curves for these samples are found in Appendix D, Section D.12. These results will be used to evaluate how one would design with recycled formu- lations in the context of Section 12 of the AASHTO LRFD Bridge Design Specifications (15). Long-Term Stress-Crack Resistance The six final candidate formulations and the PCR MCR resin were evaluated by the BFF test under the three sets of conditions 41 0 0.5 1 1.5 2 2.5 3 -4 -3 -2 -1 0 1 2 3 4 5 6 7 LOG TIME (hr) ST RA IN (% ) REFERENCE TEMPERATURE - 23C 100 Yrs 50 Yrs 2.15 % 2.22 %Sample B1 500 psi Stress 0 20000 40000 60000 80000 100000 120000 140000 160000 180000 200000 -3 -2 -1 0 1 2 3 4 5 6 7 8 LOG TIME (hr) CR EE P M O DU LU S (ps i) REFERENCE TEMPERATURE - 23C 100 Yrs 50 Yrs 23,250 psi 22,531 psi Sample B1 500 psi Stress Figure 40. Creep strain master curve for Sample B1. Figure 41. Creep modulus master curve for Sample B1. Creep Strain Creep Modulus Sample 50 year 100 year 50 year 100 year B1 2.15 2.22 23,250 22,531 A2 2.07 2.14 24,160 23,358 L5 2.22 2.30 22,549 21,719 A5 2.19 2.26 22,821 22,091 B3 2.24 2.32 22,300 21,532 B5 2.64 2.72 18,965 18,406 Table 17. Long-term creep strain and creep modulus under 500 psi of stress.

cited in the FDOT protocol. However, the results generated are believed to be unreliable due to the presence of residual sur- factant in the baths. Therefore, there are no reliable service- lifetime estimates for all of the six final candidates. Once the issue with the baths was resolved, the BFF tests were repeated under one set of conditions for eight samples, under two sets of conditions for three samples, and under three sets of conditions for two samples. The results are shown in Table 18. Notice that a new sample was evaluated. This material is a fully formulated pipe blend containing 100% PIR recycled and PCR PE, submitted by a recycled-resin supplier. It repre- sents the possibilities for recycled resins when they are not based on typical virgin corrugated pipe resins. Some of the important properties of this resin are shown in Table 19. The stress-crack resistance for this material was outstand- ing, but the yield stress was a little low, the break strain was poor, and it contained about 0.7% of ash. Melt filtration at 150 mesh reduced the percentage ash to 0.4% and raised the break strain to 225%. This is the type of material that can be developed for use in corrugated pipe. Since there are failure times under three sets of condi- tions for samples B1 and A5, one can make a service-lifetime estimate through bidirectional shifting. The master curves for stress-crack resistance for Samples B1 (100% Virgin) and A5 (30% Recycled) are shown in Figures 42 and 43. These results suggest that the service lifetime under 500 psi of stress will be well above 1,000 years and that even at stresses of 900 psi, the estimated service lifetime is over 100 years. Combined SIM (Stage I) and BFF (Stage II) Service-Lifetime Estimates The SIM test produced information about the long-term tensile strength and the BFF test provided information about the long-term stress-crack resistance. Now, the two results can be combined into one global service-lifetime estimate. This is shown in Figures 44 for Sample B1. This curve shows both the long-term tensile strength that might relate to a buckling failure and the long-term stress- cracking strength. The first thing to keep in mind is these data 42 BFF Failure Time (h) (COV) Sample/Formulation 80ºC/650 psi 80ºC/465 psi 70ºC/650 psi B1 100VR1 411 ± 135 (33%) 1,601 ± 537 (34%) 1,627 ± 680 (42%) A2 85VR1 + 15MCR 257 ± 85 (33%) — — L5 50VR1 + 20MD + 30MCR 431 ± 86 (20%) — — A5 40VR1+ 30MD + 30NAT 323 ± 60 (19%) 1,364 ± 571 (42%) 1,615 ± 644 (40%) B3 20VR1+40MD+24MCR+16NAT 330 ± 66 (20%) — — B5 40MD + 36MCR + 24NAT 280 ± 95 (34%) — — L1 Proprietary Blend – 50% Recycled content 201 ± 39 (19%) — — RPM Proprietary Blend 100% Recycled content 620 ± 376 (61%) 1,480, 4>3,0001 — 1 Four specimens terminated after 3,000 h. Note: “—” = data not available. Property Result Corrected Density 0.948 g/cm 3 Melt Index 0.11 g/10 min % Color 3.9 % Ash 0.7 % PP 4.8 Flexural Modulus 128,606 psi Yield Stress 3,260 psi Break Strain 21% NCLS Stress-crack Resistance 220 ± 54 hrs Table 18. Recent BFF test results. Table 19. Properties of pipe resin containing 100% recycled PE.

were generated on tensile dumbbell specimens with very sim- ple geometry. A pipe is likely to behave differently. Secondly, if these data relate to pipe, they relate to an unconfined pipe. A properly installed pipe would also be a different situation. That said, there is still valuable information contained in the master curves. The curve shows a ductile-to-brittle transition stress of 1,153 psi. This is just above 30% of the material’s initial yield stress. This also means that at applied stresses less than 1,153 psi, the pipe is more likely to crack than to buckle. In fact, as most involved in this project thought, slow crack growth is the key to service lifetime in corrugated pipe, according to these results. The curve also shows that even at the very high service stress of 900 psi, the estimated lifetime is over 100 years. Once more, at a typical operating stress of 500 psi, the service life- time estimate is over 1,500 years. A similar master curve is shown for Sample A5 in Figure 45. Sample B1 y = -0.236x + 4.3928 R² = 0.9835 2.95 3 3.05 3.1 3.15 5.4 5.5 5.6 5.7 5.8 5.9 6 6.1 Lo g St re s s (p s i) Log Failure Time (hrs) 500 psi = 1717 years 100 years = 979 psi BFF Results Shifted to 20C Sample A5 y = -0.2331x + 4.3625 R² = 0.9988 2.950 3.000 3.050 3.100 3.150 5.3 5.4 5.5 5.6 5.7 5.8 5.9 6 6.1 Lo g St re s s (p si) Log Failure Time (hrs) 500 psi = 1563 Years 100 years = 949 psi BFF Results Shifted to 20C Figure 42. BFF stress-cracking master curve at 20ºC for sample B1. Figure 43. BFF stress-cracking master curve at 20ºC for sample A5. 43

Sample A5 contained 30% PCR-NAT, which is basically ground up milk and water jugs. The service-lifetime estimates are similar to 100% virgin. Because of limitations of time and funding, more of the recycled-content-containing pipes were not evaluated. One important aspect here is to define the “long-term strength.” The long-term strength referred to in Section 12 of the LRFD design manual is a long-term yield strength. The results generated during this project suggest that the long- term stress-crack resistance is more important and will limit the lifetime of the pipe. So, it might be more appropriate to determine a long-term stress-crack strength, which is the stress a material can be subjected to without cracking for its ser- vice lifetime. In the two examples above, the 100-year tensile 44 y = -0.0459x + 3.3237 R² = 0.9527 y = -0.236x + 4.3928 R² = 0.9835 2.6 2.7 2.8 2.9 3 3.1 3.2 3.3 3.4 0 1 2 3 4 5 6 7 8 Lo g St re ss (ps i) Log Time (hrs) 50 yrs 100 yrs BFF-POP SIM Sample B1 Shifted to 20C 1153 psi 979 psi y = -0.0471x + 3.3272 R² = 0.9658 y = -0.2331x + 4.3625 R² = 0.9988 2.6 2.7 2.8 2.9 3 3.1 3.2 3.3 3.4 0 1 2 3 4 5 6 7 8 Lo g St re ss (p si ) Log Time (hrs) 50 yrs 100 yrs SIM Sample A5 Shifted to 20C 1116 psi 950 psi BFF-POP Figure 44. Combined master curve for Sample B1 (100% virgin). Figure 45. Combined master curve for Sample A5 (30% recycled).

strengths are 1,124 and 1,067 psi, while the 100 year stress- crack strengths are 979 psi and 950 psi for samples B1 and A5, respectively. The BFF Test for QC There is no question that the successful use of recycled PE depends on the stress-crack resistance of the manufactured pipe. And, because of the inherent variability in recycled resins, each lot should be tested for stress-crack resistance. Therefore, a QC test is needed that will relate to the long-term stress-crack resistance of the pipe, be of a reasonable duration of time, be sensitive to the base resin stress-crack resistance, and be able to determine the effects of contaminants. The BFF test is a good candidate. This test is done on a rel- atively thin plaque made from the pipe. The test specimen is a modified ASTM D638, Type I dumbbell, which has a sur- face area of 7.2 cm2 (1.1 in.2). The thickness is about 1.1 mm (0.045 in.), which means that even a 0.12 mm (0.005 in.) par- ticle will be 11% of the thickness. This ensures that the effects of particles will be determined. The test does not evaluate the actual end product, like the FL-DOT junction test does. How- ever, because of its thickness, larger surface area, and consis- tent stress, the BFF test is the more aggressive test. In fact, results showed that failure times at 80°C/650 psi averaged 2.5 times faster in the BFF test compared to the junction test when 12-inch pipe was tested. The results from four recent, side- by-side tests are shown in Table 20. This comparison is complicated by the fact that nearly all the junction test specimens failed in the liner and not at the junction. The average of these data sets show that the BFF test is at least 1.7 times faster than the junction test. The FL-DOT 100-year service-lifetime protocol calls for the junction test to be run under three sets of conditions and sets minimum time requirements for each condition. These are shown in Table 21. These values were determined with the use of POP factors and the 95% lower confidence interval based on a Student-t distribution. When one applies the Popelar shifts, the 20°C master curve can be generated. This is shown in Figure 46. The master curve shows that a pipe sample under 3.45 MPa (500 psi) of load will not stress crack for 304 years. This shows that the design factor for a 100-year life is 0.33 (307 × 0.33 = 100). This is more conservative than the design factor of 0.50 used for solid wall water pipe. Now, since there is uncertainty regarding the use of recy- cled PE, a very conservative approach would be to use a design factor of 0.10. That would mean that the test results will have to show that the pipe will last for 1,000 years. The master curve for 1,000 years is also shown in Figure 30. The slope of the line is reasonable for the resins used in corrugated pipe. The average slope from PPI (16), Hsuan (17), and this study on 17 data sets was −0.26, with only four values over −0.27. The minimum FL-DOT times to generate the 1,000-year lifetime curve are shown in Table 22. This shows that if a junction specimen lasts 360 h without failure in a 80°C bath under 4.48 MPa (650 psi) of load, it will be estimated to last 1,000 years. Since it has been demonstrated that the BFF test is at least 1.7 times faster than the junction test at 80°C/4.48 MPa (650 psi), it would be conservative to set the requirement for the BFF test at 200 h. Therefore, the proposed minimum aver- age failure time in the single point BFF test for QC is 200 h, or 8.3 days. This is not an ideal time for a QC/quality assur- ance (QA) test, but even longer times are used for HDPE geomembranes. The geomembrane manufacturers perform the test on every railcar of resin and some QA specifications require the test for each batch of resin, or sometimes every 100,000 sq. ft. of material. Additionally, these tests are typi- cally run for 300 or 400 h. A durability test like this one is crit- ical for the successful use of recycled HDPE in corrugated drainage pipe for highway applications. And every lot of recycled-containing resin needs to be tested because of the variable nature of recycled resins. The BFF stress-cracking master curves in Figures 42 and 43 independently support the value of 200 h for a QC test at 45 Sample BFF Time (h) (COV) Junction Time (h) (COV) [liner breaks] Junction/BFF B1 414 ± 97 (23%) 1,076 ± 561 (52%) [4] 2.6 B5 228 ± 141 (62%) 578 ± 224 (39%) [4] 2.6 L1 208 ± 73 (35%) 362 ± 201 (55%) [4] 1.7 L5 334 ± 116 (35%) 1,342 ± 300 (22%) [4] 4.0 Test Conditions Minimum Failure Time 80ºC/4.48 MPa (650 psi) 110 h 80ºC/3.10 MPa (450 psi) 430 h 70ºC/4.48 MPa (650 psi) 500 h Table 20. Comparison between BFF and junction tests at 80ºC/650 psi. Table 21. FL-DOT junction test conditions and minimum failure times.

80°C/650 psi. From the slopes of those lines and shifting back to 80°C, the time that represents 1,000 years of service for both samples is 200 h. Designing Pipe with Recycled Content An evaluation of the existing design methodology out- lined in Section 12 of the AASHTO LRFD Bridge Design Spec- ifications was performed to determine its applicability to pipe manufactured with blends of virgin and recycled HDPE. In particular, the material properties needed to meet M294 required for the AASHTO LRFD design methodology were assessed. The design methodology in Section 12 of the AASHTO LRFD Bridge Design Specifications (and McGrath et al.’s recent recom- mendations in NCHRP Report 631: Updated Test and Design Methods for Thermoplastic Drainage Pipe (13) evaluates local buckling resistance to check the structural capacity of profile wall plastic pipe. The total factored compressive and tensile strains in a pipe wall due to thrust and bending are evaluated to ensure that specified strain limits are not exceeded. Bending strain is also evaluated. The methodology also incorporates a vertical arching factor to account for load relief when the pipe is less stiff than the surrounding backfill. Table 12.12.3.3-1 Mechanical Properties of Thermo- plastics Pipe in AASHTO LRFD Bridge Design Specifications Section 12 sets forth the requirements for the minimum cell class, the initial and 50-year design tensile strength and the ini- tial 50-year modulus of elasticity. Recently, McGrath et al.’s NCHRP Report 631 from project NCHRP Project 04-26, “Thermoplastic Drainage Pipe, Design and Testing” recom- mends 75-year design tensile strength and modulus of elastic- ity requirements as well as service long-term tension strain and factored compression strain limits. Note that the estimated modulus of elasticity values proposed in NCHRP Report 631 for AASHTO LRFD Bridge Design Specifications Section 12 are based on observed field performance of pipe designed with 50-year modulus and relaxation tests on PE pipe in parallel plate tests to estimate 75-year modulus. Values are reported to be reasonably conservative. The material properties studied in this work included the minimum cell class (density, MI, flexural modulus, tensile yield stress), NCLS, NCTL, thermal stability, and oxidation induc- tion time. Long-term properties (50 and 100 years) included creep modulus, creep strain, yield stress, stress-crack stress, service long-term tension strain and factored compressive strain limit. Properties based on parallel plate tests on finished pipe products included pipe stiffness, flattening, environmen- tal stress-cracking resistance (ESCR), and brittleness. The laboratory results demonstrated that pipe can be made with blends of virgin and recycled HDPE to meet AASHTO M294. Three (A5, B1, and L5) of the six final candidate for- 46 y = -0.2695x + 4.4306 R2 = 1 Extended to 1000 yrs y = -0.2694x + 4.5695 2.6 2.7 2.8 2.9 3.0 3.1 3.2 0 1 2 3 4 5 6 7 8 Log Time (hrs) Lo g St re ss (p si) FL-DOT Minimum Failure Times Shifted to 20°C 500 psi 304 yrs 1002 yrs Test Conditions Minimum Failure Time 80ºC/4.48 MPa (650 psi) 360 h 80ºC/3.10 MPa (450 psi) 1,401 h 70ºC/4.48 MPa (650 psi) 1,647 h Figure 46. Master curve from FL-DOT minimum times. Table 22. Minimum times for a 1000-year estimated lifetime.

mulations met the required cell class for AASHTO M294. Pipe A2 met all requirements except for NCLS. Pipe B3 met all requirements except for the density requirement. Pipe B5 met all except for the density and NCLS requirements. Five of the six pipes made from the final candidate formu- lations met the NCHRP Report 631 recommendation for creep modulus and yield stress (long term property requirements). Note that the long-term tests were performed on plaques made from manufactured pipe. This was done to erase all previous stress due to manufacturing to facilitate the comparison of the blended resins without the influence of differences in manu- facturing (such as manufacturing speed). Additional tests should be performed on specimens cut directly from the pipe. Parallel plate tests were performed on the finished pipe prod- uct made from the six final candidate formulations. The results indicate that all six final candidate formulations meet the pipe stiffness requirement of AASHTO M294. For the pipes herein made with blends of virgin and recycled HDPE that have material properties meeting the requirements in Table 12.12.3.3-1, current AASHTO LRFD Section 12 design specifications should apply; however, long-term in-situ load tests and accelerated laboratory tests on finished pipe product embedded in soil are needed to finalize the proposed changes to the AASHTO LRFD design methodology (i.e., structural design equations for thrust, buckling, and bending and resis- tance factors based on field performance data). Proposed Draft Specifications Currently, both AASHTO M252 and M294 have property requirements for both the virgin resins used to make the pipe and the pipe itself. And the National Transportation Prod- uct Evaluation Program (NTPEP) requires the use of a PPI- certified resin, or the testing of each different blend used to make pipe. It is well known that some pipe manufacturers make their own virgin blends, while others prefer to use cer- tified and listed resins. A similar situation would exist if AASHTO allows the use of recycled material containing resins to make pipe. Some manufacturers will prepare their own blends and others will choose to purchase fully compounded pipe resins already con- taining recycled HDPE. For this reason, it is suggested that there should be both required resin properties and required pipe properties in the specifications for M252 and M294 appli- cations allowing recycled HDPE. It is also suggested that the specifications move away from listing cell classification by ASTM D3350. Cell classification is a living standard subject to continuous revisions, which have affected the AASHTO stan- dards in the past. Also, there are tests in the cell classification that may not be necessary in D3350 and tests that are necessary but are not in D3350 (NCLS, OIT). So, instead of a required cell class, the standards could simply have a table of required properties, like is shown in Table 23. Ultimately, all the resin tests should be performed on compression molded plaques from the pipe itself, but resin specifications will allow independent compounders and pipe manufacturers to make appropriate blends and control their properties. Once more, a specification on the recycled material itself will be beneficial to resin compounders and pipe manu- facturers. Therefore, five different specifications are proposed and presented in Appendices E through I. The titles and scopes of each one are shown below. Appendix E—Proposed Draft Standard Specification for PCR MCR High-Density PE Bottles for Use in AASHTO-Approved Corrugated Drainage Pipe 1. Scope 1.1 This specification covers the quality of PCR, MCR, high-density PE bottles for use in AASHTO approved corrugated drainage pipe. 1.2 This specification presents a set of properties to be met for the resin. 1.3 This specification can be used by recycled-resin sup- pliers as part of manufacturing quality control (MQC), or by pipe manufacturers or independent bodies as manufacturing quality assurance (MQA). Appendix F—Proposed Draft Standard for Recycled Content Containing HDPE Resin Formulations for Corrugated Pipe Made to AASHTO Standard M252-Recycled 1. Scope 1.1 This specification covers the quality of HDPE-resin for- mulations containing recycled HDPE that are intended for use in AASHTO M252—Recycled approved cor- rugated drainage pipe for subsurface drainage applica- tions, in sizes 75- to 250-mm diameter (3 to 10 in.). 1.2 The recycled PE may be either post-consumer or post- industrial. 47 Property Requirement Density 0.948-0.955 g/cm 3 MI <0.4 g/10 min % Carbon Black 2%–5% Yield Stress 3,500 psi Flexural Modulus 110,000 psi NCLS Stress Crack >24 h OIT >50 min Table 23. Properties for AASHTO M294 pipe resin (cell class 335500).

1.3 This specification presents a set of properties and test frequencies to be met for the resin. 1.4 This specification can be used by suppliers of resin con- taining recycled PE as part of MQC, or by pipe manu- facturers or independent bodies as MQA. Appendix G—Proposed Draft Standard Specification for Recycled Content Containing HDPE Resin Formulations for Corrugated Pipe Made to AASHTO Standard M294-Recycled 1. Scope 1.1 This specification covers the quality HDPE-resin formu- lations containing recycled HDPE that are intended for use in AASHTO M294–Recycled approved corrugated drainage pipe, in sizes 300- to 1500-mm (12- to 60-in.) diameter. 1.2 The recycled PE may be either post-consumer or post- industrial. 1.3 This specification presents a set of properties and test frequencies to be met for the resin. 1.4 This specification can be used by suppliers of resin con- taining recycled PE as part of MQC, or by pipe manu- facturers or independent bodies as MQA. Appendix H—Proposed Draft Standard Specification for Corrugated Polyethylene Drainage Pipe Containing Recycled Polyethylene, 75- to 250-mm Diameter 1. Scope 1.1 This specification covers the requirements and methods of test for corrugated PE pipe, couplings and fittings for use in subsurface drainage systems, storm sewers, and in surface drainage (culverts), where soil support is given to the pipe’s flexible walls in all applications. 1.2 This standard allows for the use of recycled polyethylene in the pipe, but not in the couplings nor the fittings. 1.3 Nominal sizes of 75 mm to 250 mm are included. 1.4 Material properties, dimensions, pipe stiffness, per- forations, joining systems, and forms of marking are specified. Note 1—When PE pipe is to be used in locations where the ends may be exposed, consideration should be given to combustibility of the PE and the deteriorating effects of prolonged exposure to ultraviolet radiation. 1.5 The following precautionary caveat pertains only to the test method portion, Section 9.3, of this specification. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsi- bility of the user of this standard to establish appropriate safety and health practices and determine the applicabil- ity of regulatory limitations prior to use. Appendix I—Proposed Draft Standard Specification for Corrugated Polyethylene Drainage Pipe Containing Recycled Polyethylene, 300- to 1,500-mm Diameter 1. Scope 1.1 This specification covers the requirements and methods of tests for corrugated PE pipe, couplings, and fittings for use in surface and subsurface drainage applications. 1.1.1 This standard allows for the use of recycled PE in the pipe, but not in the couplings nor the fittings. 1.1.2 Nominal sizes of 300 to 1,500 are included. 1.1.3 Materials, workmanship, dimensions, pipe stiff- ness, slow crack growth resistance, joining sys- tems, brittleness, and forms of markings are specified. 1.2 Corrugated PE pipe is intended for surface and sub- surface drainage applications where soil provides sup- port to its flexible walls. Its major use is to collect or convey drainage water by open gravity flow, as culverts, storm drains, and so forth. Note 2—When PE pipe is to be used in locations where the ends may be exposed, consideration should be given to protection of the exposed portions due to combus- tibility of the PE and the deteriorating effects of pro- longed exposure to ultraviolet radiation. 1.3 This specification does not include requirements for bedding, backfill, or earth cover load. Successful per- formance of this product depends upon proper type of bedding and backfill, and care in installation. The structural design of corrugated PE pipe and the proper installation procedures are given in AASHTO LRFD Bridge Design Specifications, Section 12, and LRFD Bridge Construction Specifications, Section 30, respectively. Upon request of the user or engineer, the manufacturer shall provide profile wall section detail required for a full engineering evaluation. 1.4 The following precautionary caveat pertains only to the test method portion, Section 9.4 of this specification. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsi- bility of the user of this standard to establish appropriate safety and health practices and determine the applicabil- ity of regulatory limitations prior to use. 48

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TRB’s National Cooperative Highway Research Program (NCHRP) Report 696: Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content provides potential specifications for corrugated drainage pipe manufactured with recycled high-density polyethylene (HDPE). The report includes proposed draft specifications for recycled HDPE, formulations of virgin and recycled HDPE, and drainage pipe containing recycled HDPE.

The following three appendixes of NCHRP 696 are available in electronic format only.

Appendix B: Recycled Polyethylene Resins

Appendix C: Recycled-Resin Blends

Appendix D: Pipe Containing Recycled HDPE

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