NCHRP Web Doc 14 Laboratory Determination of Resilient Modulus for Flexible Pavement Design Final Report (1997) / Chapter Skim
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2 Resilient Modulus Testing of Asphalt Concrete
2 Resilient Modulus Testing of Asphalt Concrete
Pages 10-96
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From page 10... ...
Different testing devices and techniques have been used in these studies. All of these efforts have led He American Society for Testing and Materials to standardize the resilient modulus testing method of asphalt concrete (ASTM D 4123-82~.
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From page 14... ...
The Asphalt Institute resilient modulus method was originally developed by Kallas and Shook [131 using cyclic biaxial test results. Their equation was refined by Witczak [141 from an expanded data base which relates dynamic modulus of asphalt concrete with percentage passing the No.
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Due to anisotropy of asphalt concrete, the resultant discrepancy in resilient modulus between diametral testing and biaxial testing can be quite pronounced. Wallace and Monismith [171 carried out tests on an asphaltic concrete core taken from San Diego test road [id.
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A number of different flexural test procedures have been developed to study the resilient and fatigue characteristics of asphalt concrete mixtures including: FIexure tests in which the loads are applied repeatedly or sinusoidally under center-point or third-point load Rotating cantilever beams subjected to sinusoidal loads Trapezoidal cantilever beams subjected to sinusoidal loads or deformations The advantages of the flexure test are [191: (~) it is well known, widespread in use, and readily understood; (2)
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proposed the use of a repeated load indirect tension test (which is called the diametral test) to determine the resilient moduli of asphalt concrete specimens.
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, ~ ~ ~ A, ~ Notes: 1. Diametral tensile stress shown an the atcissa is the werage value from center to edge, i.
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, psi x 105 Figure 7. Comparison of test results between the unconfined compression and indirect tension tests (After Ref (23)
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However, this mechanism will develop a plane of maximum tensile stress along Be horizontal diameter when the loading head moves upward, which violates the theory behind the indirect tensile test. DIAMETRAL RESILIENT MODULUS TESTING DEVICES AND MEASUREMENT SYSTEMS USED IN EXPERIMENT Loading Devices Based upon He previous discussion of testing methods, the diametral test was selected for use in developing a standard test procedure for resilient modulus testing of asphalt concrete.
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· 'e o ~: · c~ of o A: en v: cr.
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From page 22... ...
Since diametral test deformations are extremely small, the use of accurate deformation measurements are critical in the determination of resilient moduli. For example, errors in deformation measurement can be caused by extraneous deformation in the system, rocking of the specimen and unwanted movement of the gages.
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From page 23... ...
Horizontal Deformation Calculation for a Rocking Sample -- When using a stand-alone EVDT measurement device, care should be taken in interpretation of the horizontal deformation data obtained from the EVDTs if rocking is observed from the data. Two distinct cases are possible when rocking occurs: Case I: Sample movement is caused by rocking deformation due to load (see Figure Sa)
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From page 25... ...
This type of system has been extensively used in resilient modulus testing for the measurement of horizontal deformation in the diametral test. The mountable measurement device used in this study consists of an extensometer assembly that can be spring-Ioaded on the horizontal diametral plane of the specimen.
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From page 26... ...
To measure the horizontal deformation accurately, it becomes important to define a horizontal diametral plane, and this plane should be perpendicular to the vertical diametral axes marked on He specimen. It is comparatively easy to mark mutually perpendicular diametral axes on one face of the specimen.
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View of the GEM setup 27
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MARKING EDGE YYINDOW CAN SUDE ON OR ROTAlE ABOUT S~L ROD S~L ROD SCAlE 1'=2' 1~ -1 ~ 1~-______ 1~________ 1~______~ 1p -- _____ ~ 1 ~L 1 1 l I 1 11 1t -- 11 1F-~11 I 1 11 1F -- 11 1F-~11 1 11 1F -- 11 1FJI I 1 11 1F -- 41 1L-~-A1 l ~I _ _ _ =- . _ _ o ~LLc3` L r L~ - 0 5' S~ ROD Front view of the front plate MARKING EDGE~ 0.5.
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: ~< x%~;~;~jj~jj~jjj~j~ A-: :::::: :~:~:~ I; ~~ ~]
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[27] for resilient modulus testing of asphalt concrete specimens.
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denotes the use of an extensometer for measuring horizontal deformation and He use of a EVDT (or EVDTs) for measurement of vertical deformation Or.
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From page 32... ...
Alignment, specimen set-up proc~ures and operation of the system were adjusted until He resilient moduli determined for the synthetic specimens were acceptable when compared to reference values. Resilient Modulus Testing of field Cores Resilient modulus testing was conducted on the asphalt concrete cores obtained from test sections at the Penn State University and supplied by SHRP.
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From page 33... ...
The effect of rest period on the resilient modulus of asphalt concrete has been studied by several researchers [14, 29, 301. At low temperatures and short stress durations the dependency of rest period is not significant, but it is significant for warm temperatures and long stress durations.
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Axis dependency of total MR calculated using ASTM analysis with assumed Poisson's ratio and hor~z. Extensometer data A __2_ ~1_ _ ~, .
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Effect of Poisson's Ratio. Figure 14 clearly demonstrates Me magnitude of difference in the resilient moduli determined using assumed compared to calculated values of Poisson's ratio.
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100 1: >0 Figure 15. Poisson's ratio, calculated using ASTM analysis from extensometer and ram movement data, as a function of temperature 37
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From page 38... ...
results and the core test findings from this study. EVALUATION OF RESILIENT MODULUS TESTING DEVICES USING SYNTHETIC SPECIMENS Testing Program To evaluate different types of loading and measurement devices, synthetic specimens were tested in accordance with SHRP P07 protocol (November 1992)
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From page 39... ...
2 The experimental variables included in Test Series 2 are summarized as follows: Variables Methods Tested Loading Devices: Baladi; MTSIong; MTSshort; and SHRPEGD Measurement Device: Extensometer 3. Specimens: Lucite; Polyethylene; Teflon; and Rubber 4.
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From page 40... ...
The resilient moduli obtained from the SHRP Asphalt Concrete Core Proficiency Sample Program by averaging results from different testing labs serve only as reference values. The average resilient moduli obtained by various labs are' influenced by the type of device used and hence an average value from all labs does not have real meaning.
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Table 4. Summary of test results for synthetic specimens (first set)
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Table 5. - Summary of test results for synthetic specimens (second set)
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RESTP: rest period PREC: level of preconditioning cycles AXIS: Axes of testing (A or B) SECOND SET: DEVICE: the four loading devices chosen for this set SUBSET: Two subsets of tests (hence, two alignments)
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From page 46... ...
DiffHZ: Absolute difference between Horizontal EVDT's DiffVT: Absolute difference between Vertical EVDT's 46 Rubber 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0088 0.0001 0.0001 0.0020
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From page 47... ...
is believed to have occurred due to bad specimen alignment. The low resilient modulus in Table 5 obtained for this setup using the EVDT for horizontal deformation measurement supports this observation, The MTS testing device, which has a thin top plate, showed approx~m$ely the same rotation of the top plate as did He SHRP device with the thicker, heavier top plate.
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Variation of standard deviation/mean absolute difference between horizontal EVDTs for different devices and synthetic specimens - Test Series 48
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From page 49... ...
Variation of mean absolute difference between vertical EVDTs for different devices and synthetic specimens - Test Series Ma 3 25 a' a' := 2 co 1.~ us 1 O5 O ~ , v~ , ~ , ~ 1 MTSlong MTSshort SHRPext SHRPI~dt ~3 Rubber ~ Teflon ~ ~ Lucite ~ Poly Figure 19b. Variation of standard deviation/mean absolute difference between vertical EVDTs for different devices and synthetic specimens - Test Series ~ 49
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Variation of mean absolute difference between vertical EVDTs for different devices and synthetic specimens - Test Series 2 1 0.8 tD A a' ~ O.6 !
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Square root of variance (var-B) /mean MR for Extensometer and LVDT measurement devices: Test Series 1 0.35 0.3 0.25 a' Q 1 5 C]
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From page 52... ...
The Lucite and Poly specimens had resilient moduli in the range typically exhibited by asphalt concrete mixes. The resilient moduli of these two materials are about 200,000 psi and 500,000 psi, respectively.
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r/U _ ~/1 Retsna SHRPLGD | ~ Extensometer LOOT Figure 23. Mean MR values for Poly specimen: Test Series ~ 53
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Mean MR values for Rubber specimen: Test Series ~ 1 ~ 80000 20000 //1 BE hITSbng // MTSs~ l z] Extensometer ~ LVOT Ress~ SHRPLGD Figure 25.
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From page 57... ...
Influence of testing device on mean MR value for Lucite Specimen Test Series 2 25+ 20E +05 8 1.5E+ G c 1.0E+O5 s~ +~ QOE+O . 1 1 MTSlong MTSshort ~/ _ , '_ .
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From page 58... ...
MTSshort r SHRPLGD 1 | ~ subsen subset Figure 30. Influence of testing device on mean MR value for Rubber Specimen: 1 .~ +0~ 1 .2E +05 8 G +04 c a, 4.0E +04 O.OE +00 1 MTSlong MTSshort SHRPLGD Baladi | ~]
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From page 59... ...
The same asphalt concrete specimen was also tested using the MTS loading device, horizontal mountable extensometers, and two EVDTs at the top of the upper loading plate (no gage-point-mounted EVDTs were used)
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or 2 in. gage length in the GPM setup with the SHRP EG devices or M (MTS device with mountable extensometers)
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From page 61... ...
Table 9. Average values from the MTS setup: Test Series 2 Test ID~ ~ pr.as~r ~ pr.as.xv mr.as.xr.c mr.as.xv.c mr.as.~a 1AHLHM ~.0653 0.1 193 358883 682625 1087474 AHHHM ~.0534 0.1392 363007 685813 1039149 ALLH}Jf ~.08~:' 0.0738 349592 639899 1154243 ALH ~-0.0729 0.1009 353872 663652 1109190 1BHLHM 0 0737 0.0945 368739 684893 1165136 1BE~M -0.0679 0.1166 377741 722372 1158769 .
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From page 62... ...
Table ~ I. Standard deviation/average values (coefficient of variation) of five consecutive test cycles from the MTS setup: Test Series 2 ..
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From page 63... ...
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From page 64... ...
Poisson's ratios and the resilient moduli calculated using equations ~ and 9 in Appendix A and deflections from the GPM setup were not realistic. Poisson's ratios varied from negative values to as high as 2.44.
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From page 65... ...
proposed by Roque and ButtIar [28] for the GPM setup is too small to obtain reasonable and consistent values of Poisson's ratio and resilient moduli under repetitive loading.
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From page 67... ...
:~:~:~ :::: Lila ~ ~< ~ ~: , Figure 33. Alignment and setup device for the EXSUM system 67
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For Test Series I, resilient modulus testing was repeated four times with different alignments. The first and last tests were performed using a best effort to align the specimen.
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From page 69... ...
For Test Series 2, even at 41°F, the values using the EXSUM system are all positive compared to negative values obtained using EVDTs mounted at the top of the upper loading plate. Testing at 41°F was performed after testing at 104°F, which might have caused more damage in the specimen and hence the observed higher Poisson's ratio ranging from 0.21 to 0.32.
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Effect of load amplitude on Poisson's ratio (pr.el.xm) obtained from the EXSUM setup using Elastic analysis 70
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From page 71... ...
The resilient moduli values obtained using the measured Poisson's ratios obtained using the EXSUM system were close to those calculated with an assumed Poisson's ratio. The coefficient of variation obtained for both resilient moduli and Poisson's ratio values were small except at low temperatures where rocking is the greatest and the deformations are very small.
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~ Vim Lot ~ Alma (b) Test Series 2 with MTS device ~2 Figure 35.
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From page 73... ...
e ,ct v: of: _ 3 c Be ~5 0 ~i_ _ can .m ~ e _ _ ~_ ~O ~_ ~Be ~.O so c' O He A_ C1)
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From page 74... ...
l (b) Test Series 2 with MTS device Figure 36 Comparison Of MR values - mr.el.x.a (using assumed it)
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From page 75... ...
, obtained from the EXSUM setup using Elastic analysis for Test Series 2 at different temperatures 75
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From page 76... ...
Test Series 2 with MTS device QC) 5 Ace Figure 38.
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From page 78... ...
Coarse 4 4.00 C2 Coarse 1 1 3~75 1 C3 1 Earlier tests indicate a reduction in resilient moduli occurs when the specimen is tested again at a different orientation. Also, the SHRP P07 (November, 1992)
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From page 79... ...
Extensometers were used for the measurement of horizontal deformation, and two EVDTs mounted on the top of the upper loading plate were used for the measurement of the vertical deformation. Seating loads of 10 % of the final load levels were used as suggested in He SHRP P07 (November, 1992)
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From page 80... ...
Table 16. Testing Program, stage || ID, test | Load ~Load | Load ~Rest | sequence | Amplitude| Time | Waveform | Period l | Ll L | H | H | 02 l L| L | H | L 03 | L L | S H | 04 | L ~L | S | L || 05 | L| H | H I H 06 l Ll H | H | L || 07 l I H | S | H 08 | L H | S l 09 | H L | H H 10 l H L | H L 11 l H L | S H 12 l H L | S L 13 l H H | H H 14 l H | H L 15 l H H | S H 16 l H H | S L ~0 .
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From page 81... ...
All six types of specimens (MI, M2, M3, CI, C2, and C3) were tested to study the effect of specimen sue and gradation on the resilient moduli of asphalt concrete CTable 131.
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From page 82... ...
The significant dependency of the resilient modulus on Me wave form makes it important to standardize He load pulse used in resilient modulus testing. Also, comparison of resilient moduli should be avoided where measured using different load pulse shapes.
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From page 83... ...
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From page 84... ...
medium gradation specimen, no trend in the effect of loading period on resilient moduli was observed. For the coarse gradation specimen (type C3)
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From page 85... ...
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From page 86... ...
Also, the resilient moduli decreased suggesting more damage. For 77°F, the number of preconditioning cycles to use was selected to be between the 2nd and 3rd preconditioning levels.
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From page 87... ...
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From page 88... ...
The coefficient of variation in the resilient moduli decreases at higher load amplitudes. Also, the highest load level did not seem to cause any significant damage (based on measured vertical deformation as the tests progressed)
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From page 90... ...
Specimen Gradation. The resilient moduli for coarse gradation specimens (C!
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From page 91... ...
Effect of specimen diameter on MR (mr.el.x.a - obtained from horiz. extensometer deformation using Elastic analysis and assumed By, for Stage 2 tests at 104°F 91
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From page 92... ...
Effect of gradation on MR (mr.el.x.a - obtained from horiz. extensometer deformation using Elastic analysis and assumed it)
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From page 93... ...
MULTI-LAB VALIDATION STUDY The details of the limited, multi-lab validation diametral resilient modulus test can be found in Appendix H The general purpose of this study was to determine, with statistical analysis, the effects of multiple operators, retesting specimens, and assumed versus calculated Poisson's ratio on the resilient moduli determined for identical specimens.
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From page 94... ...
As a result, the resilient moduli obtained from these different methods do not always agree. The repeated load diametral test was concluded to be the most practical, realistic method for evaluating the resilient modulus of asphalt concrete.
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From page 95... ...
At 77 and 104°F the resilient moduli decreased wig increasing number of preconditioning cycles. Based on a study of trends in the coefficient of variation for MR , the following preconditioning levels were Axed at the three deferent test temperatures to make resilient modulus test results more repeatable: 41° F: 77° F: 104° F: 100 cycles 100 cycles 50 cycles A significant difference between resilient moduli and Poisson's ratio is obtained using the SHRP P07 (Nov.
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From page 96... ...
A significant difference exists between resilient moduli and Poisson's ratio values computed using the SHRP PO7 analysis and the elastic analysis used in this study which is similar to the ASTM analysis. The SHRP analysis gives higher values when an assumed Poisson's ratio is used as compared to the elastic analysis with an assumed Poisson's ratio.
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