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4 CHAPTER 2 Research Approach The approach taken to meet the objectives mentioned in requirements of AASHTO M294. Additionally, some longer- chapter 1 was to divide the project into three distinct phases. term stress-crack tests were performed. And, finally, some These phases were Recycled Resins, Recycled-resin Blends, candidate pipe samples were evaluated for their long-term and Pipe Made from Recycled-resin Blends. creep strength, creep modulus, and stress-crack resistance. Phase 1--Recycled PE Resins Short-Term Properties The purpose of Phase 1 was to determine which types The purpose of short-term tests is to characterize a resin or of recycled PE are available, where these materials can be pipe enough to feel confident that the properties are consistent obtained, and what their properties are. The approach was from lot-to-lot. This is especially important for recycled resins, to collect samples of recycled HDPE, determine what their which are known to be variable. For example, in post-consumer typical properties were, study the effects of some common recycled (PCR) HDPE the percentage of milk bottles mixed in contaminants, and develop test methods to characterize the with colored bottles will change. Since these two types of HDPE materials. The results of this phase of the study allowed the have different properties, the properties of the recycled product assessment of the best kind of recycled PE for use in corru- will change. Short-term tests can reveal these differences in gated drainage pipe. properties. Another use for short-term properties is to control contam- ination. For example, the amounts of particulate matter can Phase 2--Recycled Resin Blends be measured by burning off the polymers and carbon black The purpose of Phase 2 was to determine how the addition and measuring the ash content. The control of contaminants of recycled HDPE would affect the properties of Canadian can also be achieved through mechanical properties. When a Petroleum Products Institute (CPPI)-certified resins and to tensile test is performed, the test specimen will always break at select specific blends for trial corrugated pipe manufacturing. a flaw. Samples with more potential flaws (particles, unblended The approach was to prepare blends of virgin pipe resins that polymers, gels) will break at lower strains. One can therefore contained different types and amounts of recycled HDPE. get an idea about the level and size of contaminants by mea- Once the blends were made, key relationships were developed suring the strain at break. that allowed one to predict the properties of blends so that And finally, the results of some short-term tests can offer optimized formulations could be used in the next phase to a bit of information about the long-term serviceability of the make actual pipe. material. When the flexural modulus or tensile yield stress is measured, one gets a feeling for how the material might respond to stress. Stress-crack tests, like the notched, constant Phase 3--Pipe made from tensile load (NCTL) (ASTM D5397) or notched, constant Recycled-Resin Blends ligament-stress (NCLS) (ASTM F2136) can give an idea of The purpose of this phase of the project was to manufacture the relative stress-crack resistance between materials. These dual wall corrugated drainage pipe out of resin formulations are important for use with recycled materials because the containing recycled HDPE. Once the pipe was made, the particulates and other polymers may promote crack initiation short-term properties were measured and compared with the or growth. And, when one measures the oxidative-induction