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6 CHAPTER 3 SUMMARY OF TEST METHODS 3.1 DYNAMIC MODULUS mixture was compacted in a Servopac gyratory compactor to a 6-inch diameter by 6.7 inches high. All test specimens were The NCHRP 1-37A Test Method DM-1 (available as sawed and cored to obtain the final 4-inch-diameter by 6- AASHTO TP-62, Determining Dynamic Modulus of Hot- inch-high E* test specimen. Before the E* testing, AASHTO Mix Asphalt Concrete Mixtures) was followed for E* test- T166-93 was followed to measure the bulk specific gravity ing. For each mix, generally two or three replicates were and water absorption of the specimens. All final 4-inch- prepared for testing. For each specimen, E* tests were gen- diameter by 6-inch-high E* test specimens were prepared to erally conducted at 14, 40, 70, 100, and 130F and 25, 10, 5, have the target in-place air voids 0.5 percent. 1, 0.5, and 0.1 Hz loading frequencies. A 60-second rest period was used between each frequency to allow some spec- imen recovery before applying the new loading at the next 3.2 FLOW NUMBER AND FLOW TIME lower frequency. Table 1 presents the E* test conditions. The E* tests were done using a controlled stress mode, Fn and Ft test methods are presented in NCHRP Report which produced strains smaller than 200 micro-strain. This 465. Test methods adapted for the simple performance tester ensured, to the best possible degree, that the response of the developed in NCHRP Project 9-29, "Simple Performance material was linear across the temperature range used in the Tester for Superpave Mix Design," are presented in Appen- study. The dynamic stress levels were 10 to 100 psi for colder dix D of NCHRP Report 513: Simple Performance Tester for temperatures (14F to 70F) and 2 to 10 psi for higher tem- Superpave Mix Design: First-Article Development and Eval- peratures (100F to 130F). All E* tests were conducted in a uation, which is available online at http://gulliver.trb.org/ temperature-controlled chamber capable of holding temper- publications/nchrp/nchrp_rpt_513.pdf. atures from 3.2 to 140F (-16 to 60C). In this research at ASU, repeated load and static creep The axial deformations of the specimens were measured tests, confined and unconfined, were conducted using at least through two spring-loaded linear variable differential trans- two replicate test specimens for each mixture. All tests were ducers (LVDTs) placed vertically on diametrically opposite carried out on cylindrical specimens, 100 mm (4 inches) in sides of the specimen. Parallel brass studs were used to diameter and 150 mm (6 inches) in height. For the repeated secure the LVDTs in place. Two pairs of studs were glued on load tests, a haversine pulse load of 0.1 second and a 0.9 sec- the two opposite cylindrical surfaces of a specimen with each ond dwell (rest time) was applied for a target of 300,000 stud in a horizontal pair being 100 mm (4 inches) apart and cycles. This number was lower if the test specimen failed located approximately the same distance from the top and under tertiary flow before reaching this target level. For the bottom of the specimen. Top and bottom surface friction is a static creep tests, a static constant load was applied until ter- very practical problem for compressive type testing. To elim- tiary flow occurred. inate the possibility of having shear stresses on the specimen An IPC Universal Testing Machine (UTM 25 kN) electro- ends during testing, pairs of rubber membranes, with vacuum pneumatic system was used to load the unconfined specimens. grease within the pairs, were placed on the top and bottom of For confined testing, an IPC UTM 100 kN machine was used. each specimen during testing. Figure 8 is a schematic pre- The machines were equipped to apply necessary confining sentation of the instrumentation of the test samples used in pressure. The load was measured through the load cell; the the dynamic modulus testing. deformations were measured through six spring-loaded All E* test specimens were prepared and the E* tests were LVDTs. Two axial LVDTs were mounted vertically on dia- carried out according to the NCHRP Project 1-37A Test metrically opposed specimen sides. Parallel studs, mounted Method DM-1. Before compaction, the laboratory-blended on the test specimen, placed 100 mm (4 inches) apart, and HMA mixtures were short-term aged in the oven for 4 hours located at the center of the specimen were used to secure the at 275F, according to the AASHTO Test Method AASHTO LVDTs in place. The studs were glued using a commercial PP2, "Standard Practice for Short and Long Term Aging of 5-minute epoxy. An alignment rod with a frictionless bushing Hot Mix Asphalt." Any laboratory-blended or plant-obtained was used to keep the studs aligned at extreme failure

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7 TABLE 1 Test conditions of the dynamic modulus (E*) test Test Temp. Freq. Cycles Rest Period Cycles to (F) (Hz) (Sec) Compute E* 14, 40, 70, 100, 25 200 - 196 to 200 130 10 100 60 196 to 200 (Unless otherwise 5 50 60 96 to 100 specified) 1 20 60 16 to 20 0.5 15 60 11 to 15 0.1 15 60 11 to 15 Figure 9. Vertical and radial LVDTs set-up for an unconfined test. conditions. Figure 9 is a photograph of an actual specimen set up for an unconfined test. For radial deformations, four exter- nally mounted LVDTs aligned on diametrical and perpendic- ular lines were located at the center of the specimen and along opposite specimen sides. The radial LVDTs set-up is also shown in Figure 9. Thin and fully lubricated membranes at the test specimen ends were used to warrant frictionless surface conditions. All tests were conducted within an environmen- tally controlled chamber throughout the testing sequence (i.e., temperature was held constant within the chamber to 1oF throughout the entire test). Figures 10 and 11 show a typical confined test set-up. Figure 10. Confined test set-up. a. Sample Assembly b. Lateral View Figure 11. Test set-up within triaxial cell with mounted Figure 8. Specimen instrumentation of E* testing. radial LVDTs.