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1 Proposed AASHTO Structural Design Properties for Corrugated Polypropylene Storm Sewer Pipe 1 2 3 4 5 6 7 Corresponding Author: Brent J. Bass, Simpson Gumpertz & Heger Inc., 41 Seyon St., Building 1, Suite 8 500, Waltham, MA 02453, phone: 781.907.9327, fax: 781.907.9009, [email protected] 9 10 Bill R. VanHoose, Advanced Drainage Systems Inc., 4640 Trueman Blvd. Hilliard, OH 43026, phone: 11 419.424.8367, fax: 419.424.8344, [email protected] 12 13 Timothy J. McGrath, Simpson Gumpertz & Heger Inc., 41 Seyon St., Building 1, Suite 500, Waltham, 14 MA 02453, phone: 781.907.9240, fax: 781.907.9009, [email protected] 15 16 17 18 Submission Date: 1 August 2011 19 Word Count: 4,947 20 Figure Count: 9 21 Table Count: 1 22 Total Equivalent Word Count: 7,447 23 24 TRB 2012 Annual Meeting Paper revised from original submittal.

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Proposed AASHTO Structural Design Properties for Corrugated Polypropylene Storm Sewer Pipe1234567

Corresponding Author: Brent J. Bass, Simpson Gumpertz & Heger Inc., 41 Seyon St., Building 1, Suite8500, Waltham, MA 02453, phone: 781.907.9327, fax: 781.907.9009, [email protected]

10Bill R. VanHoose, Advanced Drainage Systems Inc., 4640 Trueman Blvd. Hilliard, OH 43026, phone:11419.424.8367, fax: 419.424.8344, [email protected]

13Timothy J. McGrath, Simpson Gumpertz & Heger Inc., 41 Seyon St., Building 1, Suite 500, Waltham,14MA 02453, phone: 781.907.9240, fax: 781.907.9009, [email protected]

161718

Submission Date: 1 August 201119Word Count: 4,94720

Figure Count: 921Table Count: 122

Total Equivalent Word Count: 7,4472324

TRB 2012 Annual Meeting Paper revised from original submittal.

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Abstract12

Corrugated polypropylene (PP) storm sewer pipe has been available in the US market since 2007. The3manufacturing process and structural design basis are similar to the more widely used high density4polyethylene (HDPE) pipe; however PP has advantages over HDPE in applications requiring higher5bending resistance and longitudinal beam strength, greater stress crack resistance, and higher operating6temperatures.7

8In 2011, both the American Society for Testing and Materials (ASTM) and the American Association of9State Highway Transportation Officials (AASHTO) adopted corrugated PP pipe material and product10specifications for use in non-pressure surface and sub-surface drainage applications. These standards11include some requirements for PP material properties related to structural design such as minimum initial12modulus and long-term creep modulus, but they do not address all parameters required by AASHTO for13structural design of thermoplastic pipe.14

15This paper presents the test methods and sampling conventions required to arrive at structural design16properties, presents results of these tests on four candidate PP resins commercially available in the US,17and uses these test results as the basis for proposed structural design properties for adoption into the18AASHTO Load and Resistance Factor Bridge Design Specifications for the structural design of PP storm19sewer pipe.20

21

TRB 2012 Annual Meeting Paper revised from original submittal.

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Corrugated high density polyethylene (HDPE) pipe was first commercially introduced in the US in 19671and has gained wide acceptance in surface and subsurface storm water drainage applications. From the2original four inch diameter pipe for agricultural drainage applications to sixty inch diameter corrugated3pipes produced today, profile wall HDPE has proven to be a durable material for use in many markets.4While corrugated HDPE pipes continue to gain acceptance in sewerage and drainage applications, there5remains a need for alternate materials in some applications. For example, applications requiring higher6bending resistance, thermal stability, and/or higher stress crack resistance may be better suited with a7material engineered for this need.8

9The authors began internal research in 2000 to consider polypropylene (PP) as an alternate material for10corrugated pipe production. PP is a material generally offering a higher modulus of elasticity, resulting in11a higher bending resistance and longitudinal beam strength, a higher melt strength, which, under the right12conditions, can allow for higher operating temperatures, and inherently higher stress crack resistance than13HDPE (1). With processing parameters similar to HDPE, PP is readily adaptable to North American14corrugated thermoplastic pipe manufacturing techniques and equipment. In 2007, the first corrugated PP15pipe was commercially sold in the US and has since continued to gain market acceptance in North16America. In 2010 American Society for Testing and Materials (ASTM) specifications were developed for17corrugated PP pipe for use in non-pressure sanitary sewer applications. In 2011, both ASTM and the18American Association of State Highway Transportation Officials (AASHTO) adopted corrugated PP pipe19material and product specifications for use in non-pressure surface and sub-surface drainage applications.20

21While new to the North American pipe market, corrugated polypropylene homo-polymer (PP-h) pipes22have been used in Europe since 1955, with polypropylene block copolymer (PP-b) pipes in use since the23mid to late 1970s (1). PP-b resins, including all candidate resins below, allow for the addition of impact24modifiers, important in thin-walled corrugated pipes which have a higher likelihood of cracking from25impact compared to solid wall thermoplastic pipe.26

27Thermoplastic materials, including HDPE, polyvinyl chloride (PVC), and PP, have duration-dependent28response to external loading. The two main forms of loading for these gravity-fed culvert pipes are short-29term loads (e.g. live loads) and long-term loads (e.g. soil and ground water). Existing AASHTO30thermoplastic pipe design methods for HDPE and PVC culvert pipe in Section 12.12 of the AASHTO31Load and Resistance Factor Design (LRFD) Bridge Design Specifications (AASHTO LRFD, 2), address32the load-duration-dependent response in the service and strength limit states by separating the calculations33into short- and long-term components, then summing the resulting deflections or strains and comparing34the sums to defined deflection or strain limits. Design requirements for the service and strength limit35states include checks for total deflection, thrust (compression in the circumferential direction), buckling,36and combined thrust and bending.37

38Minimum time-dependent material properties and strain limits for the structural design of HDPE and39PVC culvert pipes are found in AASHTO LRFD Table 12.12.3.1-1. The required properties are:40

41 Initial modulus,42

Initial strength,43

Long-term creep modulus,44

Long-term strength,45

Service long-term tension strain limit, and46

TRB 2012 Annual Meeting Paper revised from original submittal.

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Factored long-term compression strain limit.1

There is also a minimum cell classification requirement for different HDPE and PVC resins.2

Previous work by VanHoose and Biesenberger (3) presented a variety of test results on twelve resins3under consideration for PP pipe production and arrived at preliminary recommended structural design4properties addressing some of the AASHTO requirements identified above: initial tensile strength of53,500 psi, initial modulus of elasticity of 175,000 psi, 100 year tensile strength of 1,000 psi, and 100 year6creep modulus of 27,000 psi.7

8The VanHoose and Biesenberger recommendations led to ASTM and AASHTO material and product9standards. The provisional AASHTO material standard for PP Pipe, MP 21-11 (4), includes some10requirements for material properties related to structural design, such as minimum initial modulus and11long-term creep modulus, but it does not address all parameters required by AASHTO LRFD for12structural design of thermoplastic pipe.13

14Based on the VanHoose and Biesenberger recommendations, the twelve resins were reduced to four15candidates which are PP extrusion-grade resins readily available in the US and are referred to here as16Candidate A, B, C, and D resins.17

18This paper builds on the VanHoose and Biesenberger work by presenting the test methods and sampling19conventions required to arrive at structural design properties, presents the results of these tests for the four20candidate resins described above, and uses the test results as the basis for proposed structural design21properties for inclusion in AASHTO LRFD Table 12.12.3.1-1 for corrugated PP storm sewer pipe.22

23CELL CLASSIFICAION24

25Cell class specification alone is not sufficient to fully identify suitable resin properties for pipe26production. Cell classifications for PP pipe resins are not defined in MP 21-11. This specification has27material requirements more tailored to pipe production than the AASHTO standards for HDPE or PVC28pipe which rely on general cell classifications to set many material properties (for example, AASHTO29M 294 for corrugated HDPE (5) or AASHTO M 304 for profile PVC (6)). Thus, for PP storm sewer pipe30resin it is proposed to rely on the requirements of MP 21-11 and not require a minimum cell class.31

32INITIAL PROPERTIES33

34Initial Modulus35

36As described above, the AASTHO thermoplastic pipe design method separates demands into short- and37long-term components. Short-term demands and some failure mode capacities for the service and strength38limit states are evaluated using short-term material properties such as initial modulus and initial strength.39VanHoose and Biesenberger recommended, and AASHTO MP 21-11 requires, the PP resin have a40minimum initial modulus of 175,000 psi and a minimum initial strength of 3,500 psi.41

42Initial modulus is used to determine short-term (live) load deflections and strain demand in AASHTO43LRFD Articles 12.12.2.2 and 12.12.3.10.1c, respectively. It is also used for handling and installation44requirements in terms of the flexibility factor in Article 12.12.3.6 and for global buckling resistance in45Article 12.12.3.10.1e.46

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TRB 2012 Annual Meeting Paper revised from original submittal.

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AASHTO MP 21-11 requires the initial modulus for PP pipes to be determined as the 1% secant flexural1modulus in accordance with ASTM D790 (7), the same method used to determine the initial modulus of2HDPE pipes (AASHTO LRFD Table 12.12.3.3-1).3

4In general, most short term material properties such as flexural modulus are provided for the base virgin5PP resin by the resin supplier on a certificate of analysis (COA). To further validate these results and6account for the effect of additives, colorants, UV inhibitors, and stabilizers, flexural modulus should be7evaluated routinely on specimens made from compounded resin and occasionally verified with specimens8made from the finished product. Specimens from finished pipe are made by grinding up plastic from the9pipe wall and compression molding it into a plaque in accordance with ASTM D4703 (8). Results for10initial modulus testing on ten compounded resin specimens from Candidate A resin are compared in11Figure 1 with the target minimum value.12

13

14

FIGURE 1 Initial modulus test results for Candidate A PP resins.15

The individual test results for this resin were consistent with the manufacturer’s COA 1% minimum16secant flexural modulus of 210,000 psi and meet the recommended initial modulus of 175,000 psi. Each17of the compounded candidate resins tested resulted in a slightly higher flexural modulus compared to the18virgin resin. This may be partly due to an increase in crystallization of the PP molecules from the19colorant, emphasizing the need to evaluate compounded resins.20

21Initial Strength22

23Initial strength is determined from tension tests in accordance with ASTM D638 (9). This property is24important for the pipe’s resistance to stresses from handling, shipping, and installation and is used as a25resin acceptance criterion at the pipe manufacturing plant prior to accepting resin from the supplier. Initial26strength can be used for design in accordance with AASHTO LRFD Article 12.12.3.10.1b if determining27effective area from stub compression test data instead of through theoretical effective area calculations.28

TRB 2012 Annual Meeting Paper revised from original submittal.

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1Ultimate short term tensile strength for the virgin resin can be obtained from the resin supplier’s COA,2but as with initial modulus, it should also determined from the compounded resin including all additives3and stabilizers. Results for initial strength testing on ten compounded specimens of Candidate A resin are4shown in Figure 2.5

6

FIGURE 2 Initial strength test results for Candidate A PP resin.7

Individual test results in Figure 2 were consistent with manufacturer’s COA ultimate tensile strength8value of 4,200 psi. As with flexural modulus, each candidate resin showed a slightly higher value for the9compounded resin when compared to the virgin resin. However the ultimate strains were slightly less than10the value reported in the COA. Due to the relationships between strength, modulus, and ultimate strain,11for a given material strength, if the initial modulus is higher than listed on the COA, the ultimate strain12will be lower. This further emphasizes the need to fully characterize the properties for a particular resin13and not to rely on COA values in design.14

15All test results meet the recommended initial strength value of 3,500 psi proposed by VanHoose and16Biesenberger and required by AASHTO MP 21-11, which is proposed as the design value for initial17strength for PP in AASHTO LRFD Section 12.12.18

19LONG-TERM PROPERTIES20

21One of the most important aspects of designing with thermoplastics is to account for thermoplastic creep22by accurately estimating the material properties for the entire design life of the structure, here 50, 75, or23100 years. Long-term demands and some failure mode capacities are evaluated using long-term material24properties such as long-term modulus of elasticity (here referred to as a creep modulus) and long-term25strength. AASHTO MP 21-11 requires a minimum 75 year modulus of elasticity of 27,000 psi and2675 year strength of 1,000 psi.27

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Creep Modulus12

The long-term thermoplastic creep modulus is used to determine long-term deflections in AASHTO3LRFD Article 12.12.2.2. In the strength limit state, it is used to determine long-term soil load demand on4the pipe through the vertical arching factor in AASHTO LRFD Article 12.12.3.5, long-term strain5demand in Article 12.12.3.10.1c, and the pipe’s resistance to global buckling in Article 12.12.3.10.1e.6Assuming the thermoplastic has adequate stress crack resistance and antioxidant capacity, the material is7undergoing ductile deformation for the majority of its life and has not progressed into the brittle/stress8cracking phase or material degradation phase. Stress cracking would occur under sustained tension; when9the pipe is installed properly, the primary design condition is for axial compression and there is typically10no net tension in the pipe wall, therefore stress cracking should not be a concern.11

12During the ductile deformation phase, thermoplastic creep typically occurs in three stages (Figure 3):13Primary, Secondary, and Tertiary as discussed in Appendix X2 of ASTM D2990 (10). Primary (Stage I)14creep occurs over the initial stages of loading and results in some relaxation of the material, but with the15creep rate decreasing with time. Secondary (Stage II) creep is during the middle stage of loading with the16creep rate reaching a steady state. Tertiary (Stage III) creep occurs when the creep rate increases rapidly17and the material heads toward fracture. Material creep tests are used to determine the material response18during the secondary creep phase, and the resulting material properties are used to design for this19behavior.20

21

FIGURE 3 Typical thermoplastic creep response curve. (Reference: ASTM D 2990)22

Traditionally for HDPE and PVC pipe design there has been no requirement to determine the material’s23actual long-term creep modulus (2, 5, 6). As discussed in the commentary to AASHTO LRFD24Article 12.12.3.3, no product standard for HDPE or PVC pipe requires determination of the actual long-25term properties, however relaxation test data for HDPE and PVC from parallel plate tests performed over26two years shows the modulus of elasticity reduces approximately linearly with the logarithm of time and27that the values in AASHTO LRFD Table 12.12.3.3-1 are reasonably conservative.28

29

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The thermoplastic creep modulus can be determined through a creep modulus test in accordance with1ASTM D2990 for up to 10,000 hours and then extrapolated to 50, 75, or 100 years, with the results able2to be compared to the values in AASHTO LRFD Table 12.12.3.3-1 on a logarithmic time scale. In this3method, a series of at least five tension tests are performed at different stress levels selected in even4increments up to 500 psi, which is the approximate service-level long-term stress magnitude in the pipe5wall.6

7Specimens for creep modulus tests are typically made from virgin resin, however results should be8verified with results from specimens cut from plaques made from compounded pipe wall resin, or taken9directly from the pipe wall where dimensionally practical. As discussed above, a low amount of additives10will typically result in a higher creep modulus than that of virgin resin. For this reason, a more11conservative creep modulus (a lower modulus for long-term creep) will likely be obtained from plaques12made from virgin resin.13

14Once testing is conducted at various stresses or temperatures, the Boltzmann superposition principle (11)15is used to shift data and generate a master curve. Estimations of long-term creep behavior and mechanical16properties for design can then be made.17

18One of the drawbacks of this test is that for evaluation of every new resin, a new 10,000 hour test must be19undertaken at the five different stress levels. If an approved resin is in short supply requiring the use of a20different supplier, the new resin could not be evaluated in less than 10,000 hours, or would have to have21been previously evaluated. Also, this lengthy test cannot be used to reevaluate a resin with simplicity; if a22resin supplier changes blends, there is no efficient method to reevaluate long-term behavior. This leads to23the desire of a more efficient, shorter-term test.24

25In 2003 (12), the geosynthetic community first published ASTM D6992 (13), a standard test method for26determining accelerated tensile rupture and creep behavior of geosynthetic materials. This method uses a27series of constant stress tensile tests at elevated temperatures and superimposes the results to determine28material properties for the product life using time-temperature superposition methods. The test method is29commonly referred to as the SIM test, referring to the stepped isothermal method used for time-30temperature superposition. For pipe, the constant stress is 500 psi, similar to the traditional 10,000 hour31creep test, which is the approximate magnitude of service level stresses expected in buried thermoplastic32pipe. This test method is referenced in AASHTO MP 21-11 and allowed as an alternative to ASTM33D2990, and has been used to qualify material for and in the design of PP thermoplastic stormwater34retention chambers for about ten years in accordance with ASTM F2418 (14).35

36Results from the ASTM D6992 test must be validated with traditional creep test results for a given37material prior to relying on results from the SIM test alone. After validation, the SIM test may be used to38efficiently evaluate the long-term effects of changes in resin or resin blends. This validation work has39been performed on Candidate D resin at a stress level of 500 psi, with the traditional creep test results40(Figure 4a) compared to the SIM test results (Figure 4b).41

42

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1

2

FIGURE 4 Comparison of traditional creep data to SIM test creep data for Candidate D resin.3

Results in Figure 4 show the traditional 10,000 hour creep test had a 10,000 hour creep modulus of about465,000 psi compared to the SIM test results with an average 10,000 hour creep modulus of about562,000 psi for three specimens. This data shows less than 5% difference in results between the two6methods at 10,000 hours thereby validating the SIM test as an acceptable method for predicting ductile7long-term creep behavior of PP pipe resins.8

9SIM tests have been conducted on all four candidate resins with the results shown in Figure 5.10

11

12

FIGURE 5 500 psi SIM test creep modulus results for four candidate resins.13

The minimum creep modulus shown in Figure 5 for 50, 75, and 100 year design lives are 29,224 psi,1428,421 psi, and 27,822 psi, respectively. All data in Figure 5 exceeds the minimum requirements for long-15term creep modulus in AASHTO MP 21-11, and is in line with the 100 year creep modulus of 27,000 psi16proposed by VanHoose and Biesenberger. From the above test data and VanHoose and Biesenberger17recommendations, the proposed minimum creep modulus requirements for the PP thermoplastic pipe18

(a) Traditional 10,000 hr Creep test results. (b) SIM Creep test results.

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design in AASHTO LRFD Section 12.12 are 29,000 psi, 28,000 psi, and 27,000 psi for 50 year, 75 year,1and 100 year design lives, respectively.2

3Long-Term Strength4

5Traditional creep rupture tests and SIM tests can both be used to determine long-term tensile strength.6Long-term strength is used indirectly in the design when estimating the effective area from stub7compression test data, an alternative to the theoretical calculations for effective area, as discussed in8AASHTO LRFD Article 12.12.3.10.1b, and for assurance that the pipe can resist the long-term tensile9stresses present in the pipe wall for the life of the installation.10

11The SIM test can be used to evaluate the thermoplastic’s ultimate tensile strength in two ways: (a) by12developing a rupture envelope for the material by performing SIM tests at a variety of stress levels, or (b)13by performing a constant stress SIM test to show the material would not rupture when subjected to that14stress for the product design life. The former approach would be used to evaluate design properties of15candidate resins while the latter approach would be used as a QA test on resins for production.16

17For the first method, a series of SIM tests are performed at several different stress levels until rupture and18the rupture stress versus time is plotted in a rupture envelope as shown for Candidate A resin in Figure 6.19A similar rupture envelop can be developed using ASTM D2990 where time to rupture for specimens20tested at various stress levels is plotted versus the actual applied stress to develop a master curve. From21the master stress rupture curve, rupture time can be extrapolated at the known design stress.22

23

FIGURE 6 SIM test rupture envelope for Candidate A resin.24

Figure 6 demonstrates that Candidate A resin has 50, 75, and 100 year rupture strengths of 1,172 psi,251,142 psi, and 1,119 psi, respectively.26

27

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A second means of demonstrating long-term strength using the SIM test is to perform a SIM test at a1constant stress level to determine the times to the onset of tertiary creep or rupture under the sustained2stress. If there is no tertiary creep or rupture during the test for the design life of the pipe, the test3demonstrates a rupture strength greater than the test stress at its design life. This method does not arrive at4a specific rupture strength for the resin but can qualify a particular resin as exceeding a minimum rupture5strength. A 1,000 psi SIM test strain versus time curve is shown in Figure 7 for Candidate A resin with a6log-time scale on the x-axis. The results show that the specimen has not experienced tertiary creep7(i.e. there is no rapid increase in strain with time) and the specimen has not ruptured, thus demonstrating8the resin has a rupture strength greater than 1,000 psi for over 100 years. Strains at an estimated 100 years9under a constant stress of 1,000 psi from SIM test rupture envelopes are shown for all four candidate10resins in Table 1.11

12

13

FIGURE 7 PP Candidate A resin 1,000 psi SIM test strain vs. time curve.14

TABLE 1 100-year PP creep strain at 1,000 psi.15

Candidate Resin 100-Year Creep Strain(%)

A 5.50B 6.04C 4.63D 3.57

16The four candidate resins demonstrate greater than 1,000 psi long-term creep strength through SIM17testing. AASHTO MP 21-11 has a required minimum 75 year creep strength of 1,000 psi. VanHoose and18Biesenberger recommended a minimum 100 year creep strength of 1,000 psi. From the requirements of19MP 21-11, work by VanHoose and Biesenberger, and the test results presented here, a minimum long-20term (50 year, 75 year, and 100 year) rupture strength of 1,000 psi is proposed for PP thermoplastic pipe21design in AASHTO LRFD Section 12.12.22

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STRAIN LIMITS12

Service Long-Term Strain Limit34

The SIM test data can be used to determine the service long-term tension strain limit, used in AASHTO5LRFD Article 12.12.3.10.2b for combined thrust plus bending. Since the resin will have a minimum long-6term strength of 1,000 psi, it will be able to undergo at least the magnitude of strain achieved at the design7life during the 1,000 psi SIM test. Figure 7 shows, for example at 50 years, this resin will have the ability8to undergo at least 5.08% strain without rupture under a sustained stress of 1,000 psi, with the strain at an9estimated 100 years still higher without the specimen demonstrating tertiary creep. Using a design factor10of 2 (note that the AASHTO load factor for thermoplastic pipe under earth load is 1.95) gives a service11level long-term tension strain of 2.5% using the 50 year results. This value is proposed for use as the12service long-term tension strain limit for the design of PP pipes in AASHTO LRFD Section 12.12.13

14Factored Compression Strain Limit15

16The factored compression strain limit is used in determining the effective width of individual corrugation17elements in AASHTO LRFD Article 12.12.3.10.1b, and as compressive strain capacity when evaluating18adequacy for thrust in Article 12.12.3.10.1d. It is also used when checking adequacy for combined thrust19and bending for the compression zone of the cross-section in AASHTO LRFD Article 12.12.3.10.2b.20

21National Cooperative Highway Research Project (NCHRP) Report 438 (15) recommended the factored22compression strain limit be determined as the ratio of long-term strength to modulus. For the proposed23minimum long-term strength of 1,000 psi and long-term modulus of 27 ksi above, the compression strain24limit from these minimum values would be 3.7%.25

26More recently, NCHRP Report 631 (16) found that a fixed strain limit for each thermoplastic is more27appropriate than values from test results for individual resins. The recommendations of NCHRP28Report 631 were based on extensive laboratory testing during the development of the Stub Compression29Test, AASHTO T 341-10 (17).30

31In the stub compression test (Figure 8), a specimen taken as a chord of the circumference of the32corrugated pipe is compressed between two load plates at a constant rate of advancement and the load and33displacement (strain) are recorded. The specimen is nominally three corrugation periods in length. The34strain at maximum load can be determined from the data, and the data can also be used to determine the35effective area of the corrugation under compression load in AASHTO LRFD 12.12.3.10.1b instead of the36theoretical calculations for effective area. When evaluating strain at maximum load, machine flexibility37must be accounted for in the results.38

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1

FIGURE 8 Stub compression test.2

Results from stub compression tests on nine specimens of corrugated PP pipe manufactured from3Candidate A and B resins are shown in Figure 9. These results are from four 24 inch diameter pipe4specimens, one 42 inch diameter pipe specimen, and four 48 inch diameter pipe specimens taken from5different circumferential positions around the pipe (0°, 90°, 180°, or 270°). Load is shown in pounds per6length of each specimen along the longitudinal axis of the pipe.7

8

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1

FIGURE 9 Stub compression test load vs. strain plots for nine corrugated PP pipe specimens.2

Strains at maximum load after adjusting for initial specimen seating (toe compensation) and machine3flexibility ranged from 4.4% to 5.1% for the nine specimens, all greater than 3.7% strain calculated from4the minimum long-term strength and modulus. Based on the minimum long-term strength and modulus5values and as demonstrated by stub compression tests, a factored compression strain limit of 3.7% is6proposed for corrugated PP pipe in AASHTO LRFD Section 12.12.7

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CONCLUSION12

The AASHTO LRFD Bridge Design Specifications, Section 12.12, include provisions for the structural3design of thermoplastic culvert pipe. Established minimum values of mechanical properties required for4the structural design of HDPE and PVC pipes are presented in AASHTO LFRD Table 12.12.3.3-1.5

6Corrugated PP culvert pipe has been used in Europe for several decades and has more recently become7available in the United States. The AASHTO Materials Subcommittee recently published a material and8product standard for corrugated PP thermoplastic pipe, AASHTO MP 21-11. This standard has minimum9material requirements for some mechanical properties used in the structural design based on properties10recommended by Vanhoose and Biesenberger; however, the properties presented in AASHTO MP 21-1111do not address all of the mechanical properties required for structural design AASHTO LRFD12Section 12.12.13

14This work presents the test methods and sampling procedures used to determine the mechanical properties15for thermoplastic pipe design, and specifically to arrive at minimum mechanical property requirements for16corrugated PP pipe. These recommended minimum properties for structural design are from test results on17specimens made from four candidate resins readily available in the U.S. for the manufacture of PP pipe.18

19Recommended minimum mechanical properties for corrugated PP pipe in AASHTO LRFD Table2012.12.3.3-1 are as follows:21

22 Service Long-Term Tension Strain Limit, εyt: 2.5%.23

Factored Compression Strain Limit, εyc: 3.7%.24

Minimum Initial Strength and Modulus: 3,500 psi and 175,000 psi, respectively.25

Minimum 50 Year Strength and Modulus: 1,000 psi and 29,000 psi, respectively.26

Minimum 75 Year Strength and Modulus: 1,000 psi and 28,000 psi, respectively.27

Appropriate values for 100 year strength and modulus, where required for 100 year design life, are 1,00028psi and 27,000 psi.29

30In lieu of proposing a minimum cell classification for the resins used in corrugated PP pipe, it is proposed31to rely on the material requirements found in AASHTO MP 21-11 which are more tailored specifically to32pipe resins than traditional cell classifications.33

34

TRB 2012 Annual Meeting Paper revised from original submittal.

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References:12

1. Lars-Eric Janson, Plastics Pipes for Water Supply and Sewage Disposal, 3rd Edition, Lars-Eric3Janson and Borealis - Stockholm 19994

2. AASHTO LRFD Bridge Design Specifications, 5th Edition, Interim 2010. American5Association of State Highway and Transportation Officials, 2010.6

3. VanHoose, B., and J. Biesenberger. Long Term Material Design Properties for Polypropylene7Pipe Grade Resins. Presented at Plastic Pipes XV Conference, Vancouver, CANADA, September82010.9

4. AASHTO MP 21-11. Standard Specification for Corrugated Polypropylene Pipe, 300- to 150010mm (12- to 60-in.) Diameter. American Association of State Highway and Transportation11Officials, 2011.12

5. AASHTO M 294-08. Standard Specification for Corrugated Polyethylene Pipe, 300- to 1500-13mm Diameter. American Association of State Highway and Transportation Officials, 2008.14

6. AASHTO M 304-03 (2007). Standard Specification for Poly(Vinyl Chloride) (PVC) Profile15Wall Drain Pipe and Fittings Based on Controlled Inside Diameter. American Association of16State Highway and Transportation Officials, 2008.17

7. ASTM D 4703-07. Standard Practice for Compression Molding Thermoplastic Materials into18Test Specimens, Plaques, or Sheets. ASTM International, 2007.19

8. ASTM D 790-07. Standard Test Methods for Flexural Properties of Unreinforced and20Reinforeced Plastics and Electrical Insulating Materials. ASTM International, 2007.21

9. ASTM D 638-10. Standard Test Method for Tensile Properties of Plastics. ASTM International,222010.23

10. ASTM D 2990-09. Standard Test Methods for Tensile, Compressive, and Flexural Creep and24Creep Rupture of Plastics. ASTM International, 2009.25

11. Nielsen, L.E. Mechanical Properties of Polymers. Reinhold Publishing Corp., New York, 1962.2612. ASTM D6992 Historical Standard Database. ASTM International.27

http://www1.astm.org/filtrexx40.cgi?-28P+DESIGNATIO+D6992+/usr6/htdocs/astm.org/DATABASE.CART/historicalpick.frm.29Accessed July 22, 2011.30

13. ASTM D 6992-03 (2009). Standard Test Method for Accelerated Tensile Creep and Creep-31Rupture of Geosynthetic Materials Based on Time-Temperature Superposition Using the Stepped32Isothermal Method. ASTM International, 2009.33

14. ASTM F 2418-11. Standard Specification for Polypropylene (PP) Corrugated Wall Stormwater34Collection Chambers. ASTM International, 2011.35

15. McGrath, T. J., and V. E. Sagan. Recommended LRFD Specifications for Plastic Pipe and36Culverts. Report 438, National Cooperative Highway Research Program (NCHRP), 2000.37

16. McGrath, T. J., I. D. Moore, and G. Y. Hsuan. Updated Test and Design Methods for38Thermoplastic Drainage Pipe. Report 631, National Cooperative Highway Research Program39(NCHRP) Report 631, 2010.40

17. AASHTO T 341-10. Standard Method of Test for Determination of Compression Capacity for41Profile Wall Plastic Pipe by Stub Compression Loading. American Association of State Highway42and Transportation Officials, 2010.43

TRB 2012 Annual Meeting Paper revised from original submittal.