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1 SUMMARY Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content The corrugated drainage pipe market in the United States consumes in excess of a bil- lion pounds of virgin high-density polyethylene (HDPE) annually. At the same time, mil- lions of pounds of recyclable HDPE are generated each year. Industry-funded research has demonstrated the feasibility of blending recycled and virgin HDPE to manufacture corru- gated drainage pipe. The working hypothesis is that good quality pipe can be manufactured from such blends if critical material properties that affect pipe performance and durability, such as strength and structural properties, density, melt index, environmental stress-crack resistance, and thermal stability, are consistently maintained at specified levels in the blends. At present, AASHTO specifications do not permit the use of recycled HDPE in the pro- duction of corrugated drainage pipe. Research was needed to determine if there were blends of virgin and recycled HDPE that met the current requirements of AASHTO Specifications M252 and M294. Additionally, the long-term performance of pipe made with these blends had to be assessed and specifications were needed to ensure that quality products were made. The objectives of this study were to 1. Determine the availability, properties, and consistency of recycled (HDPE) intended for use in the manufacture of corrugated drainage pipe. 2. Prepare blends of recycled HDPE with virgin corrugated pipe resins and determine the properties of the blends. 3. Select candidate resin formulations containing recycled HDPE and manufacture 12 in. diameter, dual wall, corrugated pipe from the blends. 4. Determine the short- and long-term properties of the blends and evaluate if the currently used design standards can be used for recycled contentcontaining pipe. 5. Prepare specifications and standard test methods for resins and pipe that contain recycled HDPE. The study was divided into three main parts: 1. Recycled polyethylene resins, 2. Blends with recycled and virgin pipe resins, 3. Pipe made from blends containing recycled PE. There were 25 samples of recycled PE obtained for the first part of the study. These in- cluded 22 post-consumer recycled (PCR) and three post-industrial recycled (PIR), and both mixed-color and natural PCR. The results demonstrated that post-consumer, mixed-color, reprocessed HDPE was the best available recycle material available because of its availabil- ity and consistency. PIR PE could be found with superior properties to PCR, but it is not

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2 consistently available. Natural PCR (milk bottles) is consistent, but it is also more expensive than mixed color and is more brittle. Mixed-color PCR (PCR-MCR) resins were favored be- cause there are about a dozen suppliers, the products are more consistent, and there is a trade association dedicated to the production of high quality materials. The resins have good strength properties, but poor stress-crack resistance and contain contaminants that can limit their performance over the long term. The second part of the study included the preparation and testing of 67 different blends. These were all characterized by a variety of tests. Over 700 tests were performed. The results demonstrated that some properties [density, percentage polypropylene, percentage black, percentage ash, oxidative induction time (OIT), and tensile] varied in a linear manner with recycled content. Other properties (melt index, stress-crack resistance) varied exponentially with recycled content. This is important because it allows one to estimate the properties of a blend from the properties of the components. The final part of the study involved the manufacture of 15, 12-in.-diameter pipe samples at three different manufacturing plants. Each plant made five pipe samples, and all three plants made a sample with 100% virgin HDPE and a sample with 30% recycled HDPE for controls. The short-term properties were measured on all 15 samples and long-term dura- bility studies were performed on six candidate blends. The results showed that it is difficult to make blends better than virgin if one simply adds recycled resin to virgin resin. In fact, the results showed that the study was limited by its focus on blending with virgin corrugated pipe resins. Much better properties can be obtained by blending recycled resins with virgin resins lower in density and higher in stress-crack resistance than the virgin pipe resins. It seems clear from the results that pipe made with significant amounts (>50%) of recycled PE can be developed with adequate short-term properties and long-term properties that sug- gest that the pipe will last 50 to 100 years. These results led to the development of five proposed individual product specifications. These included a specification for mixed-color PCR resins intended to be used in formula- tions to make AASHTO M252 or M294 pipe. Two separate specifications for fully formu- lated resins intended for pipe for either M252 or M294 applications. And two specifications for pipe that are to be used in M252 or M294 applications.