National Academies Press: OpenBook

Refining the Simple Performance Tester for Use in Routine Practice (2008)

Chapter: Chaper 3 - Revised Simple Performance Test System

« Previous: Chapter 2 - Abbreviated Dynamic Modulus Master Curve Testing
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Suggested Citation:"Chaper 3 - Revised Simple Performance Test System." National Academies of Sciences, Engineering, and Medicine. 2008. Refining the Simple Performance Tester for Use in Routine Practice. Washington, DC: The National Academies Press. doi: 10.17226/14158.
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Suggested Citation:"Chaper 3 - Revised Simple Performance Test System." National Academies of Sciences, Engineering, and Medicine. 2008. Refining the Simple Performance Tester for Use in Routine Practice. Washington, DC: The National Academies Press. doi: 10.17226/14158.
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Suggested Citation:"Chaper 3 - Revised Simple Performance Test System." National Academies of Sciences, Engineering, and Medicine. 2008. Refining the Simple Performance Tester for Use in Routine Practice. Washington, DC: The National Academies Press. doi: 10.17226/14158.
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Suggested Citation:"Chaper 3 - Revised Simple Performance Test System." National Academies of Sciences, Engineering, and Medicine. 2008. Refining the Simple Performance Tester for Use in Routine Practice. Washington, DC: The National Academies Press. doi: 10.17226/14158.
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Suggested Citation:"Chaper 3 - Revised Simple Performance Test System." National Academies of Sciences, Engineering, and Medicine. 2008. Refining the Simple Performance Tester for Use in Routine Practice. Washington, DC: The National Academies Press. doi: 10.17226/14158.
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Suggested Citation:"Chaper 3 - Revised Simple Performance Test System." National Academies of Sciences, Engineering, and Medicine. 2008. Refining the Simple Performance Tester for Use in Routine Practice. Washington, DC: The National Academies Press. doi: 10.17226/14158.
×
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Suggested Citation:"Chaper 3 - Revised Simple Performance Test System." National Academies of Sciences, Engineering, and Medicine. 2008. Refining the Simple Performance Tester for Use in Routine Practice. Washington, DC: The National Academies Press. doi: 10.17226/14158.
×
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Suggested Citation:"Chaper 3 - Revised Simple Performance Test System." National Academies of Sciences, Engineering, and Medicine. 2008. Refining the Simple Performance Tester for Use in Routine Practice. Washington, DC: The National Academies Press. doi: 10.17226/14158.
×
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Suggested Citation:"Chaper 3 - Revised Simple Performance Test System." National Academies of Sciences, Engineering, and Medicine. 2008. Refining the Simple Performance Tester for Use in Routine Practice. Washington, DC: The National Academies Press. doi: 10.17226/14158.
×
Page 24
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Suggested Citation:"Chaper 3 - Revised Simple Performance Test System." National Academies of Sciences, Engineering, and Medicine. 2008. Refining the Simple Performance Tester for Use in Routine Practice. Washington, DC: The National Academies Press. doi: 10.17226/14158.
×
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Suggested Citation:"Chaper 3 - Revised Simple Performance Test System." National Academies of Sciences, Engineering, and Medicine. 2008. Refining the Simple Performance Tester for Use in Routine Practice. Washington, DC: The National Academies Press. doi: 10.17226/14158.
×
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16 3.1 Revised Simple Performance Test System Equipment Specification Equipment to perform the abbreviated dynamic modulus master curve testing presented in Chapter 2 requires additional low temperature and loading capabilities compared to the SPT developed in Phases I and II. Table 6 compares the require- ments for the SPT developed in Phases I and II, a testing device to produce dynamic modulus master curves using the abbre- viated testing protocol, and a device to produce dynamic mod- ulus master curves using AASHTO TP62. Table 6 also includes an estimate of the cost of each system. The primary differences in the equipment are the temperature range and the required dynamic loading capacity. The substantial difference in the low-temperature range of the environmental chamber is responsible for the increase in the estimated cost of the equip- ment. The increased dynamic loading capacity results in a nominal increase in the estimated cost of the equipment. The equipment specification developed in Phases I and II (10) was revised to specify a device capable of performing the three simple performance tests and developing dynamic modulus master curves using the abbreviated testing proto- col developed during this phase of the project. This specifica- tion was designated as Version 2.0 and is reproduced in Appendix B. It was produced by modifying Version 1.1 of the specification developed in Phase II of the project to include the 39°F temperature control, the increased dynamic load capacity, and the 0.01 Hz load control needed for master curve testing. Version 1.1 of the specification included the improvements identified by the first article evaluation. 3.2 Simple Performance Test System Procurement and Evaluation 3.2.1 Procurement Version 2.0 of the Equipment Specification for the SPT was used to upgrade the first article devices purchased in Phase II of the project to meet the revised requirements for master curve testing and to procure new SPTs. Contracts for upgrade work were negotiated directly with Interlaken Technology Corporation, Inc. and IPC Global. The process used in Phase II of this project to procure the first article equipment was used to procure the new equipment in Phase IV. A request for proposal (RFP) was issued to man- ufacturers who expressed interest in providing equipment under NCHRP Project 9-29. Table 7 lists the manufacturers that provided an RFP package consisting of Version 2.0 of the equipment specification and a copy of the Phase II evaluation report (10). The RFP required the manufacturers to submit a detailed proposal describing the proposed equipment and pro- viding supporting documentation that the proposed equip- ment meets the specification requirements. Additionally, the manufacturers were asked to identify unique features offered in their equipment and to provide a firm fixed price for the equipment delivered to Sterling, VA. Four manufacturers sub- mitted complete proposals in response to the Phase IV RFP: • Interlaken Technology Corporation, • IPC Global, • James Cox and Sons, Inc., and • Medical Device Testing Services, Inc. Cooper Research Technology, Ltd submitted an incom- plete proposal, and Shedworks, Inc. submitted a document describing a more general system capable of performing the tests required by the SPT specification as well as other tests. The four complete proposal were evaluated, and three were selected for award. The following criteria were used in the evaluation, listed in order of importance: 1. Documented ability of the proposed equipment to meet the specification requirements, 2. Unique advantages offered by the proposed equipment, and 3. Cost of the proposed equipment. C H A P T E R 3 Revised Simple Performance Test System

17 Item Simple Performance Test System for Rutting Simple Performance Test System for Rutting and Abbreviated Master Curve Testing AASHTO TP62 Master Curves for Structural Design Temperature Range 20 to 60 oC (68 to 140 oF) 4 to 60 oC (39 to 140 oF) -10 to 60 oC (14 to 140 oF) Temperature Control 0.5 oC ( 1.0 oF) 0.5 oC ( 1.0 oF) 0.5 oC ( 1.0 oF) Dynamic Load Capacity 6 kN (1.3 kips) 12.5 kN (2.8 kips) 22.5 kN (5.0 kips) Loading Rates 0.1 to 25 Hz 0.01 to 10 Hz 0.1 to 25 Hz Confining Pressure YES YES NO Estimated Cost $45,000 $60,000 $100,000 Table 6. Comparison of dynamic modulus testing devices. The equipment proposed by the four manufacturers was similar to the first article devices evaluated in Phase II of the project. All were relatively small, bottom-loading, servo- hydraulic machines with automated testing chambers that serve as a confining pressure cell and temperature control chamber. No manufacturer proposed an alternative to the standard glued gage point system with LVDTs for measuring specimen deformations in the dynamic modulus test. Ver- sion 2.0 of the specification allows alternatives to be consid- ered provided the manufacturer can demonstrate that the alternative produces deformation measurements that are the same as the standard glued gage point system. Interlaken, Cox, and Medical Device Testing proposed equipment with two LVDTs spaced 180° apart on the specimen. IPC Global proposed equipment with three LVDTs spaced 120° apart. Because they were selected as the first article manufacturers in Phase II of the project, the IPC Global and Interlaken pro- posals included specifications and photographs of completed equipment. The Cox and Medical Device Testing proposals included detailed design drawings for the major components of the system. Costs for the proposed equipment ranged from approxi- mately $52,000 to $68,000. Table 8 presents the proposed costs. The Cox and Medical Device Testing proposals indi- cated that the proposed prices included initial development costs of approximately $18,000 and that future production units would cost approximately $50,000. A contract was awarded to IPC Global as the lowest bidder. Considering that one of the overall objectives of NCHRP Project 9-29 is to stimulate the development of commercial equipment, it was decided to award contracts to James Cox and Sons, Inc. and Medical Device Testing Services, Inc. even though they did not provide the lowest prices. Through these two Phase IV contracts and the Phase II first article contracts, seed funding was made available to four equipment manufacturers: IPC Global, Interlaken Technology Corporation, James Cox and Sons, Inc., and Medical Device Testing Services, Inc. Unfor- tunately James Cox and Sons, Inc. was not able to complete Manufacturer Address Phone Contact Cooper Research Technology, Ltd Technical Centre 11 High Holborn Road Codnor Gate Business Park Ripley Derbyshire DE5 3NW ENGLAND 44 (1) 773 512174 Andrew Cooper Interlaken Technology Corporation 8175 Century Boulevard Chaska, MN 55318 (952) 856-4210 Tom Driggers Instron Corporation 825 University Ave. Norwood, MA 02062-2643 (800) 473 7838 Leslie Dixon IPC Global 4 Wadhurst Drive Boronia Vic 3155 Australia 61 (0) 3 9800 2200 Con Sinadinos James Cox and Sons, Inc. 1085 Alpine Way Colfax, CA 95713 (530) 346-8322 James Cox Medical Device Testing Services, Inc. 6121 Baker Road, Suite 101 Minnetonka, MN 55345 (952) 933-1152 Kent Vilendrer MTS Systems Corporation 14000 Technology Drive Eden Prairie, MN 55344 (952) 937-4000 Scott Johnson Shedworks, Inc. 2151 Harvey Mitchell Parkway, S. Suite 320 College Station, TX 77840-5244 (979) 695-8416 Bill Crockford Table 7. Equipment manufacturers receiving Phase IV RFP.

18 Manufacturer Proposed Cost IPC Global $52,136 Interlaken Technology Corporation $62,000 Medical Device Testing Services, Inc $67,500 James Cox and Sons, Inc. $68,000 Table 8. Proposed costs for SPTs. development of their device and at their request, the contract was cancelled. Therefore, new devices were purchased from IPC Global and Medical Device Testing Services in Phase IV of the project. 3.2.2 Upgraded First Article Devices In Phase II of the project, first article devices were pur- chased from Shedworks/IPC Global and Interlaken Technol- ogy Corporation. When these devices were purchased, it was envisioned that the SPT would be used only for fatigue and rutting evaluations at intermediate and high pavement tem- peratures. After the abbreviated dynamic modulus master curve testing procedure was developed, it became apparent that the SPT also could serve as equipment for the develop- ment of dynamic modulus master curves for pavement struc- tural design. Only two modifications were needed to make the first article devices comply with Version 2.0 of the equip- ment specification: expand the low temperature control to 39°F and modify the control software to include 0.01 Hz load- ing. The estimated cost of these upgrades was small relative to the cost of new equipment. Contracts were negotiated with IPC Global and Interlaken Technology Corporation to up- grade the first article equipment to meet Version 2.0 of the equipment specification. 3.2.2.1 Shedworks/IPC Global First Article One of the first article devices evaluated in Phase II of the project was purchased from Shedworks, Inc. The equipment was manufactured by IPC Global and Shedworks represented IPC Global in the United States. Shedworks and IPC Global discontinued their relationship before Phase IV of the proj- ect; therefore, the contract for the first article upgrade was negotiated with IPC Global. The 39°F temperature requirement presented a minor problem for the Shedworks/IPC Global first article device. The refrigeration unit needed to reach this temperature was too large for the first article frame and enclosure. The plan for upgrading this device, therefore, involved removing the elec- tronics, test cell, and hydraulics from the first article and reinstalling them in a new frame and enclosure sized for the new refrigeration unit. The upgrade was estimated to re- quire 4 to 6 weeks to ship the first article to Australia, remove the salvageable components, reassemble the upgraded ma- chine, and return it to the United States. Since the first article was being used extensively by the FHWA Mobile Asphalt Laboratory to demonstrate the SPT, it was decided that the upgrade should not be performed until another unit became available from the project for use in the FHWA Mobile Asphalt Laboratory. The upgrade was delayed several times because the other manufacturers failed to deliver their equip- ment on time. IPC Global eventually offered to replace the Shedworks/IPC Global first article device with a new unit and credit the project approximately 70 percent of the original purchase price of the first article. This offer was accepted and the new unit was installed in the FHWA Mobile Asphalt Lab- oratory on November 15, 2006. The first article will be used by IPC Global for training. 3.2.2.2 Interlaken Technology Corporation First Article The Interlaken first article device did not fully comply with Version 1.1 of the specification. Version 1.1 incorpo- rated several changes that resulted from the first article eval- uation that was completed in Phase II of the project. The test chamber and the deformation measuring system for the dynamic modulus test were the two major elements for the Interlaken first article that were not in compliance with Ver- sion 1.1 of the specification. The test chamber for the Inter- laken first article was a large metal enclosure with a thick site glass that provided only limited view of the specimen and instrumentation during testing. Users of the equipment found this to be a major limitation during testing. The prob- lem was exacerbated by the lack of lighting in the cell. Because of this experience during the first article testing, Version 1.1 of the specification included a requirement that the specimen, platens, and instrumentation must be clearly visible during testing. To comply with this requirement, the test chamber for the Interlaken first article had to be re- placed. Second, the Interlaken first article included a unique extensometer system that was pushed into contact with the specimen by small pneumatic cylinders. This unique defor- mation measuring system was one of the factors leading to the selection of Interlaken to supply a first article device. The first article evaluation revealed that there was some slip between the specimen and the extensometer system. As a result, Version 1.1 of the specification included a standard glued gage point system for specimen deformation meas- urements. To comply with this requirement, Interlaken had to design and install a new specimen deformation meas- uring system. In addition to these major elements, the Interlaken first article also had some unresolved software bugs. Thus, the Interlaken first article upgrade completed in Phase IV addressed the following:

19 Figure 12. Open test chamber for the upgraded Interlaken SPT. 1. Replacement of the test chamber with an acrylic chamber that provided full view of the specimen, instrumentation, and loading platens. 2. Replacement of the original automated extensometer sys- tem with a glued gage point system. This included the design of the gage point system as well as auxiliary equipment to automate gluing of the gage points on the specimen. 3. Replacement of the original temperature control system with a new system designed to allow testing over the tem- perature range of 39 to 140°F. 4. Various software modifications to control temperature, apply 0.01 Hz loading during the dynamic modulus test and to resolve outstanding software bugs. The first article was returned to Interlaken in November, 2003. Interlaken took approximately one year to complete the upgrade work and return the upgraded device to Advanced Asphalt Technology (AAT). The upgraded Interlaken first article is shown in Figure 11. The equipment is fairly large and operates on single phase 230 V power. Compressed air also is required for confined testing. The Interlaken SPT consists of (1) a main wheeled cabinet (63 in. wide by 76 in. high by 31 in. deep) that houses the test chamber, the hydraulic pump, the hydraulic actua- tors, and associated control electronics; (2) a separate stan- dard laboratory bath (16 in. wide by 26 in. high by 17 in. deep) that provides temperature control for the test cell; and (3) a desk top computer for controlling the machine and collecting and analyzing test data. Separate 230 V power sup- plies are needed for the main cabinet and the laboratory bath. The laboratory bath is shown to the left of the test cell in Figure 11; the computer is located to the right of the main cabinet in Figure 11. Figure 12 shows the interior of the test chamber. The heat exchanger and associated fan are located at the back of the test chamber. The test chamber is large, measuring 15 in. diame- ter by 21 in. high. It is raised and lowered by two hydraulic actuators. Two hand switches are provided as a safety feature. Hand contact must be made with both of these switches for the test chamber to close. Strains for the dynamic modulus test are measured by two magnetic LVDT extensometers mounted 180° apart as shown in Figure 13. Each extensometer includes two very flexible springs that allow only vertical movement of the ends. Each extensometer includes a pin that centers the measuring system. When the pin is released, the extensome- ter is activated. To quickly and accurately mount the glued gage points to the specimen, Interlaken designed the gluing apparatus shown in Figure 14. This system has mechanical links that use the weight of the specimen to press the gage points against the specimen at the correct gage length at the center of the specimen. Because several major changes were made during the up- grade of the Interlaken first article, all of the specification Figure 11. Overall view of upgraded Interlaken SPT (main cabinet removed to show system hydraulics).

20 Figure 13. Interlaken specimen mounted extensometer system. compliance tests detailed in Version 2.0 of the specification were performed. Table 9 summarizes the items included in the specification compliance testing. The specification com- pliance testing revealed several deficiencies with the upgraded equipment summarized in Table 10. Most of the deficiencies were related to the control and analysis software. Table 10 also summarizes the changes made to resolve the deficiencies. Substantial effort was expended by both the research team and Interlaken to resolve the deficiencies. All of the deficien- cies were addressed, and the upgraded device was accepted in December, 2006. 3.2.3 Medical Device Testing Services First Article The Medical Device Testing Services (MDTS) first article is shown in Figure 15. The equipment is relatively small. It con- sists of (1) a main wheeled cabinet (26 in. wide by 76 in. high by 24 in. deep) that houses the test chamber, the hydraulic pump, the hydraulic actuator, and associated control elec- tronics; (2) a separate heat exchanger (16 in. wide by 23 in. high by 20 in. deep) that provides temperature control for the test cell; and (3) laptop computer for controlling the machine and collecting and analyzing test data. The heat exchanger is under the laptop computer table in Figure 15. An interesting feature of the MDTS SPT is the hydraulic system operates on 115 V AC power, and the hydraulic pump only operates intermittently, which makes the unit very quiet during oper- ation. The heat exchanger requires single phase 208–230 V AC power. The unit also requires compressed air to raise and lower the test chamber and apply confining pressure. Figure 16 shows the MDTS SPT with the test chamber open, and a specimen inserted for confined testing. The test chamber is relatively small, only 10 in. in diameter by 21 in. high. The reaction posts are located in an awkward position, making installation of the instrumentation on the specimen for dynamic modulus testing difficult. The test cell heat exchangers and associated fans are mounted in the top of the test chamber. The test chamber is insulated; a sight glass and lighting are provided to allow the operator to view the speci- men during testing. The chamber is opened and closed by a manually controlled pneumatic actuator located at the back of the machine as shown in Figure 17. It is locked in the closed position by a manual ring locking mechanism that has posi- tion switches that are interlocked with the pressure and load control. The specimen mounted deformation system consists of two magnetic LVDT extensometers mounted 180° apart as shown in Figure 18. Each extensometer includes two very flexible springs that allow only vertical movement of the ends. Each extensometer includes a pin that centers the measuring system. When the pin is released, the extensometer is acti- vated. These extensometers are similar to those developed by Interlaken. This deformation measuring system is the third system that was developed by MDTS for the SPT. The other two systems did not function properly during the ruggedness testing. To quickly and accurately mount the glued gage points to the specimen, MDTS designed the gluing apparatus shown in Figure 19. This system has pneumatic actuators that press the gage points against the specimen at the correct gage length at the center of the specimen. Figure 14. Interlaken gluing apparatus.

21 Item Specification Section Method Assembled Size 4.4 & 4.6 Measure Specimen and Display Height 4.4 Measure Component Size 4.7 Measure Electrical Requirements 4.5 & 4.6 Documentation and trial Air Supply Requirements 4.8 Documentation and trial Limit Protection 4.9 Documentation and trial Emergency Stop 4.10 Documentation, visual inspection, trial Loading Machine Capacity 5.1 Independent force verification Load Control Capability 5.2 – 5.4 Trial tests on asphalt specimens and manufacturer provided dynamic verification device. Platen Configuration 5.5 Visual Platen Hardness 6.1 Test ASTM E10 Platen Dimensions 6.2 Measure Platen Smoothness 6.3 Measure Load Cell Range 7.1 Load cell data plate Load Accuracy 7.2 Independent force verification Load Resolution 7.3 Independent force verification Configuration of Deflection Measuring System 8.1 Visual Transducer Range 8.2 Independent deflection verification Transducer Resolution 8.3 Independent deflection verification Transducer Accuracy 8.4 Independent deflection verification Load Mechanism Compliance and Bending 8.5 Measure on steel specimens with various degrees of lack of parallelism Configuration of Specimen Deformation Measuring System 9.1 Visual Gauge Length of Specimen Deformation Measuring System 9.1 Measure Transducer Range 9.2 Independent deflection verification Transducer Resolution 9.3 Independent deflection verification Transducer Accuracy 9.4 Independent deflection verification Specimen Deformation System Complexity 9.5 Trial Confining Pressure Range 10.1 & 10.5 Independent pressure verification Confining Pressure Control 10.2 Trial tests on asphalt specimens Confining Pressure System Configuration 10.3 & 10.4 Visual Confining Pressure Resolution and Accuracy 10.5 Independent pressure verification Temperature Sensor 10.6 & 11.4 Independent temperature verification Specimen Installation and Equilibration Time 9.5, 10.7 & 11.3 Trial Environmental Chamber Range and Control 11.1 Independent temperature verification Control System and Software 12 Trial Data Analysis 13 Independent computations on trial test Initial Calibration and Dynamic Performance Verification 14 Certification and independent verification Calibration Mode 14.6 Trial Verification of Normal Operation Procedures and Equipment 15 Review On-line Documentation 16.1 Trial Reference Manual 16.2 Review Table 9. Summary of specification compliance tests.

22 Figure 15. Overall view of MDTS SPT. Figure 16. Open test chamber for the MDTS SPT. Deficiency Solution Slow temperature recovery. Modified the temperature control software to switch control from the test chamber probe to the bath probe when the chamber is opened, then back to the test chamber probe when the chamber is closed. Cooling fluid leaks. Replaced plastic hose clamps with steel band hose clamps. Units for temperature control. Modified software to use both U.S. customary and SI units. Test chamber binding. Lubricated actuator shaft and realign chamber. Test chamber air leaks. Added temporary seal to affected areas. 0.01 Hz loading for dynamic modulus. Modified software to allow user to test at 0.01 Hz loading. Irregular first cycle data during dynamic modulus testing. Modified software to collect additional cycles that are not stored. Only the last 10 cycles are stored and analyzed. Incorrect computation of dynamic modulus data quality statistics. Modified software to correct computations. Poor dynamic load control at high temperatures. Added a tuning algorithm to allow user to develop and store templates with servo-hydraulic gains. Software occasionally crashes when maximum strain is reached during flow number testing. Modified strain limit shut down algorithm. Incomplete documentation. Provide required documentation Table 10. Interlaken deficiencies and solutions. Final design, fabrication, and shop testing of the MDTS SPT required approximately 18 months. MDTS was given authorization to proceed with the machine on February 6, 2004. The machine was delivered on September 14, 2005. Upon delivery, the specification compliance testing summa- rized in Table 9 was performed. The specification compliance testing and the ruggedness testing revealed several deficien- cies with the equipment, which are summarized in Table 11. Most of the deficiencies were related to the control and analy- sis software. Table 11 also summarizes the changes made to

23 Figure 17. Test chamber lift mechanism for the MDTS SPT. Figure 19. MDTS gluing apparatus. resolve the deficiencies. Substantial effort was expended by both the research team and MDTS to resolve the deficiencies. All of the deficiencies were addressed, and the upgraded device was accepted in January, 2007. 3.2.4 IPC Global Production Unit The IPC Global production unit is shown in Figure 20. This unit is very similar to the first article device evaluated in Phase II of the project. The machine is slightly larger than the first article to accommodate the larger refrigeration unit needed for testing at 39ºC and a second acrylic cell was added around the test chamber to provide insulation. IPC Global also made a modification to improve the holders for the LVDTs for the specimen mounted deformation measuring system used in the dynamic modulus test. The IPC Global SPT is relatively small. It consists of (1) a cabinet (44 in. wide by 53 in. high by 25 in. deep) that in- cludes the test chamber, the hydraulic pump and actuator, the heating and refrigeration unit, and associated power and control electronics; and (2) a desktop computer for control- ling the machine and collecting and analyzing test data. The system operates on single phase 208–230 V AC power. Figure 21 shows the IPC Global SPT with the test chamber open and a specimen inserted for unconfined testing. The test chamber is relatively small, only 8.5 in. in diameter by 14 in. high. Since temperature control is provided by conditioned air circulated through the test cell, there are no heat ex- changers inside the test cell to interfere with test specimen in- stallation and instrumentation. The test chamber is opened and closed by pneumatic actuators. Two hand switches are provided as a safety feature. Hand contact must be made with both of these switches for the test chamber to close. The test chamber is insulated by a second acrylic cell that hangs on the Figure 18. MDTS specimen mounted deformation measuring system.

24 Deficiency Solution Specimen mounted deformation measuring system glued contact size exceeded specification. Reduced glued contact size. Moment on glued gage points too high resulting in gage point failure at high temperatures. Revised specimen mounted deformation measuring system by removing LVDT spring and modifying the connection to decrease distance from the specimen. Temperature control is difficult to use to manufacturer supplied offsets. Removed manufacturer supplied offsets. User must develop a table of offsets. Confining pressure control did not function properly in the flow number and flow time tests. Modified the software to properly control the confining pressure during these tests. Auto strain control in the dynamic modulus test does not function correctly. Modified auto strain control algorithm. Incorrect computation of some dynamic modulus data quality statistics Modified the software to correctly compute the data quality statistics. Some data quality statistics not included in dynamic modulus reports. Modified the software to include all data quality statistics in the reports. Raw data, not normalized data, used in the plots in the dynamic modulus reports. Modified the software to use the normalized data in the report plots. Summary report not provided. Modified the software to include the summary report. Strain rate computations for the flow number are shifted forward by one line. Modified the software to correctly report the strain rate Strain not set to zero at the beginning of the flow time test. Modified the software to set the strain to zero at the time specified in the software. Strain rate computations for the flow time are shifted forward by one line. Modified the software to correctly report the strain rate Table 11. MDTS deficiencies and solutions. automated test chamber. The specimen mounted deforma- tion system consists of three spring-loaded LVDTs mounted 120° apart as shown in Figure 22. IPC Global designed a unique holder for the LVDTs that can be used for unconfined and confined testing. Each holder has a stiff spring that grips the glued gage points. The spring was designed to highly com- press the latex membranes to minimize errors during con- fined testing. The ruggedness testing revealed that at high temperatures, creep of the LVDT gauge points can occur, and when this hap- pens, erroneous dynamic modulus data are obtained. The spring force for the IPC Global LVDTs is the highest of the three machines tested, and this machine was the only device to exhibit gauge point creep at the temperatures used in the ruggedness testing. IPC Global designed springs to counter the LVDT spring force and minimize gauge point creep. Figure 23 shows the counter springs on the IPC Global LVDT holders. These counter springs should be used when LVDT gauge point creep is detected in high temperature dynamic modulus tests. Gauge point creep occurred in the ruggedness testing at 95°F when testing specimens made with PG 64-22 binder. To quickly and accurately mount the glued gage points to the specimen, IPC Global designed the gluing apparatus shown in Figure 24. This system has pneumatic actuators that press the gage points against the specimen at the correct gage length at the center of the specimen. It also includes a mem- brane stretcher to assist with membrane installation for confined tests. Final design, fabrication, and shop testing of the IPC Global SPT required approximately 6 months. IPC Global was given authorization to proceed with the machine on February 6, 2004. The machine was delivered on July 29, 2004. Upon delivery, the specification compliance testing summarized in Table 9 was performed. The specification compliance testing revealed a small temperature effect on the LVDTs used in the dynamic modulus testing over the tem- perature range of 39 to 140ºF. IPC Global investigated this problem and determined that the temperature effect was caused by an incorrect excitation frequency being used with the LVDTs. Apparently the LVDT manufacturer provided IPC Global an incorrect optimum excitation frequency. IPC Global subsequently replaced the LVDT conditioners to resolve this problem. The machine was accepted in October, 2004 and delivered to the Turner-Fairbank Highway Research Center, where it has been used extensively on sev- eral research projects.

25 Figure 21. Open test chamber for the IPC Global SPT. Figure 20. Overall view of the IPC Global SPT.

26 Figure 22. IPC Global specimen mounted deformation measuring system. Figure 23. Additional springs to minimize gauge point creep at high temperatures. Figure 24. IPC Global gluing apparatus and membrane stretcher

Next: Chapter 4 - Simple Performance Test Specimen Fabrication System »
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TRB's National Cooperative Highway Research Program (NCHRP) Report 614: Refining the Simple Performance Tester for Use in Routine Practice explores the develop of a practical, economical simple performance tester (SPT) for use in routine hot-mix asphalt (HMA) mix design and in the characterization of HMA materials for pavement structural design with the Mechanistic-Empirical Pavement Design Guide.

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