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27 strates the feasibility of using estimated compliance values replication of the creep testing procedure at a specific tem- to evaluate the low-temperature properties of asphalt con- perature requires the collection and analysis of data from crete. Additional effort is needed to determine if critical three specimens. Table 19 presents one possible scenario cracking temperatures estimated in this way agree reason- for the factors and levels to be used in ruggedness testing for ably well with those determined using the IDT creep and the AASHTO T322 creep procedure. The factors included in strength test. If positive results are obtained, the approach Table 19 are based in the research team's experience with should be further developed and documented for possible use AASHTO T322 and may require modification as additional in future revisions of the pavement design guide developed data on factors affecting IDT creep tests are published by other in NCHRP Project 1-37A. researchers and practitioners. In addition to the factors and their levels, the ruggedness testing should be conducted over a range of compliances and IMPLEMENTATION include mixtures with a range of nominal maximum aggre- gate sizes. Table 20 presents possible mixture combinations Based on the findings from Phase III of NCHRP Proj- and testing temperatures that may be included in the rugged- ect 9-29, additional efforts to implement AASHTO T322 and ness testing. This design includes four mixture/temperature the compliance and strength predictive equations developed combinations. in Project 9-29 are warranted. Initial plans for these future Ruggedness testing involves a significant level of effort implementation efforts are presented in this section. from the participating laboratories. For the design outline above, each participating laboratory would perform 192 creep AASHTO T322 tests. Assuming that four laboratories participate in the AASHTO T322 creep procedure ruggedness testing experi- Three activities associated with AASHTO T322 should be ment and that all specimens are fabricated at a single location, considered. The first involves the incorporation of the changes the specimen fabrication laboratory will prepare 384 test recommended in Tables 2, 3, and 4 into AASHTO T322. specimens. Rules of thumb for estimating levels of effort These recommendations as well as Appendix A, which docu- are 1.5 hours for each creep test and 2.5 hours per test spec- ments them in detail, have already been forwarded to the task imen for fabrication. Thus a ruggedness testing experiment force responsible for recommending revisions to this test involving 4 laboratories, 2 mixtures, and 2 temperatures will method to AASHTO. require approximately 2,112 person-hours of testing effort. The next logical step in the implementation of AASHTO An additional 400 hours professional time should be bud- T322 is the completion of ruggedness testing for the creep geted for initial planning, coordination, data compilation, testing procedure in AASHTO T322. As outlined below, this data analysis, and reporting. is a substantial effort requiring a significant commitment of The third implementation item associated with AASHTO equipment and resources. Unfortunately, the IDT equipment T322 is future research to better characterize the relationship originally purchased for the Superpave Centers cannot be used between uncorrected IDT strength and corrected IDT strength in the ruggedness testing because of its documented poor per- as determined using the procedure given in AASHTO T322. formance and the lack of technical support for the equipment. This will provide an improved equation for estimating the The ruggedness testing should be performed using properly corrected IDT strength from the uncorrected strength calcu- calibrated servo-hydraulic equipment meeting the revised lated using the maximum load. An additional 16 mixtures AASHTO T322 requirements. There are two options for gain- combined with the 16 mixtures tested in this project should ing access to such equipment. The first is to procure second generation IDT devices specifically for the ruggedness test- ing. The second is to contract with laboratories who currently TABLE 19 Example ruggedness testing factors for AASHTO have the equipment meeting the requirements. T322 creep testing Guidance on the statistical design of a ruggedness testing Factor Low Level High Level program is presented in ASTM C 1067 "Standard Practice Equilibrium temperature X 1 C X + 1 C for Conducting a Ruggedness Screening Program for Test Strain level < 0.025 < 0.05 Methods for Construction Materials." The standard design Specimen air voids 5% 8% tests seven factors that are anticipated to significantly affect the Specimen thickness 40 mm 60 mm Loading strips With neoprene Without neoprene results at two levels. Eight measurements are made using Load application First load Second load predetermined combinations of the seven factors, and the End parallelism < 1.0 < 2.0 entire experiment is replicated within a given laboratory. This results in a total of 16 measurements within each labora- TABLE 20 Example mixture and temperature tory. Ruggedness testing of the creep procedure in AASHTO combinations for AASHTO T322 creep procedure T322 is complicated somewhat by the trimmed mean analy- ruggedness testing sis approach used in this procedure. In the trimmed mean Number Mixture Type Binder Temperature, C approach, data from two sides of three specimens are needed 1 Coarse 9.5 mm PG 76-16 10 and 10 C to develop a single creep compliance curve. Thus, complete 2 Fine 25 mm PG 58-28 0 and 20

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28 provide a very robust data set for the development of an and as possible replacements for the current Level 2 and 3 improved predictive model. The data collected in this effort thermal cracking data input for the pavement design guide can also be used for the development of improved empirical developed in NCHRP Project 1-37A. The major effort for esti- models for estimating tensile strength from volumetric prop- mating creep compliance is the development of methods to erties as discussed below. The level of effort for this testing is predict the binder master curve from limited AASHTO estimated to be approximately 300 person-hours of testing M320 test data. Approximately 240 person-hours of profes- effort and 160 person-hours of professional effort. sional effort should be budgeted for this task. The 16 addi- tional mixtures described above when combined with the 16 Compliance and Strength Predictive Methods tested in this project should provide a very robust data set for comparing estimated and measured creep compliance In addition to work associated with AASHTO T322, future and for developing an improved model for estimating ten- research is needed to further develop and evaluate procedures sile strength from mixture volumetric properties. Approxi- for estimating resistance to low-temperature cracking using mately 220 person-hours of testing effort should be included binder test data and mixture composition through application for conducting creep tests prior to the strength testing of the Hirsch model to determine mixture creep compliance and described in the preceding section. Finally, approximately application of empirical methods to estimate strength. Such 240 person-hours of professional effort should be budgeted approaches would be very useful for general mixture selec- for analyzing this data and the strength data and preparing a tion, mixture design guidance, quality control applications, report documenting the work.