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