See discussions, stats, and author profiles for this publication at: https://www.researchgate.

net/publication/270543854

An Assessment of Resilient Modulus Testing: Internal and External Deflection

Measurements

Article  in  Geotechnical Testing Journal · November 2012

DOI: 10.1520/GTJ20120077

CITATIONS READS

7 313

3 authors:

Felipe Camargo Craig H Benson

University of São Paulo University of Virginia
10 PUBLICATIONS   69 CITATIONS    404 PUBLICATIONS   13,779 CITATIONS   

SEE PROFILE SEE PROFILE

Tuncer B. Edil
University of Wisconsin–Madison
368 PUBLICATIONS   9,734 CITATIONS   

SEE PROFILE

Some of the authors of this publication are also working on these related projects:

Multi-sorbent Barrier View project

sustainability of highway construction View project

All content following this page was uploaded by Craig H Benson on 18 May 2018.

The user has requested enhancement of the downloaded file.

 Geotechnical Testing Journal, Vol. 35, No. 6, 2012
Available online at www.astm.org
doi:10.1520/GTJ20120077

Felipe Camargo,1 Craig Benson,2 and Tuncer Edil3

An Assessment of Resilient Modulus Testing:

Internal and External Deflection Measurements

REFERENCE: Camargo, Felipe, Benson, Craig, and Edil, Tuncer, “An Assessment of Resilient Modulus Testing: Internal and External
Deflection Measurements,” Geotechnical Testing Journal, Vol. 35, No. 6, 2012, pp. 1–8, doi:10.1520/GTJ20120077. ISSN 0149-6115.
ABSTRACT: The long-term pavement performance (LTPP) resilient modulus test protocol specifies the use of external linear variable differen-
tial transformers (LVDTs) to measure the material’s response, whereas the Mechanistic-Empirical Pavement Design Guide (MEPDG) requires
input for resilient modulus based on the test results using internal LVDTs. Given this discrepancy of data, the relationship between resilient modu-
lus determined from internal and external measurements was studied for a variety of materials using the NCHRP Project 1- 37A resilient modulus
test protocol and recording deformation data both with internal and external LVDTs. Resilient moduli determined from internal deformation meas-
urements shows to be higher than those from external measurements, whereas the ratio of external to internal resilient modulus decreases with
increasing internal resilient modulus because of an increasing effect of machine compliance as specimens become stiffer. Furthermore, the relation-
ship between internal and external resilient modulus depends on the material type.
KEYWORDS: resilient modulus, machine compliance, internal LVDT, external LVDT

Introduction test results in accordance with NCHRP 1-28A in which internal

LVDTs are used. Using internal LVDTs eliminates the errors
The present state of practice of pavement design in the United resulting from machine compliance and end effects. However, it
States is being transformed based primarily on the findings from also creates discrepancy between the Mr used to develop perform-
research conducted under National Cooperative Highway ance models and Mr measured for future pavement design. There-
Research Program (NCHRP) Project 1- 37A, “Guide for Mecha- fore, there is a need to evaluate the effects of different test
nistic Empirical Design for New and Rehabilitated Pavement protocols on resilient modulus measurements.
Structures” or simply Mechanistic-Empirical Pavement Design In this paper, a direct comparison is made between resilient
Guide (MEPDG). In the MEPDG, a thorough material characteri- modulus determined from internal and external measurements for
zation is a required input to predict the states of stress, strain, and a variety of materials including subgrade soils, natural base aggre-
displacement within the pavement structure when subjected to gate and recycled materials, with and without fly ash stabilization.
external loading. These properties include the material’s elastic or Additional data was obtained from the Minnesota Department of
resilient modulus (E or Mr) and Poisson’s ratio (l). The current Transportation (MnDOT) to cover a wider range of materials,
standard method for determining the resilient modulus of base, with materials ranging from stiff (recycled materials stabilized
subbase, and subgrade materials is described in the National Co- with self-cementing fly ash) to less stiff materials (subgrade soils).
operative Highway Research Program (NCHRP) Project 1- 28A, The main objective is to provide a correlation between internal
“Harmonized Test Methods for Laboratory Determination of and external resilient moduli for a range of materials.
Resilient Modulus for Flexible Pavement Design.”
However, the performance models of pavements in MEPDG
were developed based on the Long-term Pavement Performance
(LTPP) pavement performances and material properties. The
Materials
LTPP Mr test protocol specifies the use of external Linear Vari- The materials that were specifically tested in this investigation are
able Differential Transformers (LVDTs) to measure the material’s described below. The properties of other materials from the litera-
response, whereas the MEPDG required input for Mr based on the ture can be found in the references.

Manuscript received October 30, 2011; accepted for publication June 4, Conventional Base Material
2012; published online September 2012.
1
Civil Engineer, Dynatest Engenharia Ltda., São Paulo, SP, Brazil, 01409- Material meeting the Class 5 specifications for base course in
900, e-mail: felipe.camargo@dynatest.com.br Minnesota (MnDOT 2005) was created by blending pit run gravel
2
Wisconsin Distinguished Professor, Dept. of Civil and Environmental
obtained from Wimme Sand and Gravel (Plover, WI) with crushed
Engineering, Univ. of Wisconsin-Madison, Madison, WI 53706,
e-mail: chbenson@engr.wisc.edu pea gravel obtained from Midwest Decorative Stone and Land-
3
Professor, Dept. of Civil and Environmental Engineering, Univ. of scape Supply (Madison, WI). The pit run gravel was sieved past
Wisconsin-Madison, Madison, WI 53706, e-mail: edil@engr.wisc.edu the 25 mm sieve prior to blending with the pea gravel. The Class

Copyright
Copyright
C 2012 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.
V by ASTM Int'l (all rights reserved); Sat Jan 5 06:32:03 EST 2013 1
Downloaded/printed by
Craig Benson (Unversity of Wisconsin) pursuant to License Agreement. No further reproductions authorized.
2 GEOTECHNICAL TESTING JOURNAL

5 base classifies as poorly graded sand with gravel (SP) according cators of cementing potential (Janz and Johansson 2002; Tastan
to the Unified Soil Classification System (USCS) and A-1-a et al. 2011), are 0.8 and 0.4, respectively.
according to the AASHTO Classification System (AASHTO). Recycled materials were blended using two different fly ash
Particle size distribution curves for the Class 5 base are shown in contents (10 % and 15 %) and three curing times (7, 28, and 56 d).
Fig. 1.
Methods
Recycled Materials
The RPM and Class 5 base materials classify as Type I material in
The recycled pavement material (RPM) was obtained from a road- NCHRP 1-28A, which requires a specimen 150 mm in diameter
way reconstruction project in southwestern Madison, WI, near the and 305 mm in height for resilient modulus testing (NCHRP
intersection of Muir Field Rd. and Carnwood Rd. The RPM was a 2004). For consistency, all specimens were prepared to these
blend of pulverized asphalt and limestone base layer (approxi- dimensions even though smaller specimens could have been used
mately equal parts) created by removing and pulverizing the exist- for RSG. Specimens were compacted in six lifts of equal mass
ing pavement. The RPM had asphalt content of 4.6 %, as and thickness using a split mold 150 mm in diameter. All materi-
determined by the procedure in ASTM D6307 (2005), and classi- als were compacted to 100 % of maximum standard Proctor den-
fies as well-graded gravel or silty gravel (GW-GM) according to sity at optimum water content. Specimens were compacted to
the USCS and A-1-a according to the AASHTO. A particle size within 1 % of the target dry density and 0.5 % of target moisture
distribution for the RPM is shown in Fig. 1. The RPM was content (NCHRP 2004). Similar methods were employed for base
screened with a 25-mm sieve prior to testing. materials prepared with and without fly ash. Unstabilized base
A road surface gravel (RSG) sample was created by blending course aggregates were prepared in a split mold placed directly on
Class 5 base with washed limestone fines obtained from Rose- the bottom plate of the resilient modulus test cell. A latex mem-
nbaum Crushing and Excavating (Stoughton, WI). The Class 5 brane was placed inside the split mold and stretched on the inside
base was screened past the 19-mm sieve prior to blending with the surface of the mold. After attaching the top cap, a small vacuum
limestone fines. The RSG meets the AASHTO gradation require- was applied to the specimens before removing the split mold until
ments for surface course materials, as outlined in AASHTO the first cell pressure was applied.
M147, and classifies as silty sand (SM) according to USCS and Resilient modulus test specimens were instrumented with both
A-1-b according to the AASHTO. A particle size distribution for internal and external linear variable displacement transducers
the RSG is shown in Fig. 1. (LVDTs). Internal LVDTs were mounted on clamps around the
specimen and membrane (see Fig. 2), whereas external LVDTs
Fly Ash were mounted on the plunger outside the chamber and rested on
the cover plate (Fig. 3). Internal LVDTs were placed at quarter
Fly ash was obtained from Columbia Power Plant Unit No. 2 in points of the specimen to measure deformations over half the
Portage, WI, where sub-bituminous coal is burned in pulverized length of the specimen, whereas external LVDTs measured defor-
boilers. The fly ash is collected using electrostatic precipitators. mations of the entire specimen length.
Columbia fly ash is a self-cementing fly ash that classifies as Resilient modulus testing was performed in accordance with
Class C according to ASTM C618. The CaO  SiO2 and the NCHRP 1-28A protocol (NCHRP 2004). All base materials
CaO  (SiO2 þ Al2O3) ratios for Columbia fly ash, which are indi- were tested under Procedure Ia, which applies to base and subbase
materials. All resilient modulus tests were conducted with both in-
ternal and external LVDTs for comparison. Clamps for the inter-
nal LVDTs were built in accordance with NCHRP 1-28A
specifications, having 152 mm (6 in.) in diameter, weighing less

FIG. 1—Particle size distributions for Class 5 base, RPM, and RSG. FIG. 2—Internal LVDT clamps mounted on a resilient modulus specimen.

Copyright by ASTM Int'l (all rights reserved); Sat Jan 5 06:32:03 EST 2013
Downloaded/printed by
Craig Benson (Unversity of Wisconsin) pursuant to License Agreement. No further reproductions authorized.
 CAMARGO ET AL. ON AN ASSESSMENT OF RESILIENT MODULUS 3

FIG. 4—Sample results for a resilient modulus test (load sequence 1–5 for an
FIG. 3—External LVDTs mounted on a resilient modulus specimen. RPM sample).

than 2.4 N (0.55 lb), having a spring force of 44.5 N (10.0 lb), and materials without fly ash and from 4.0 to 18.3 for the recycled
using two pairs of 12-mm rods to position the clamps in a horizon- materials stabilized with fly ash (Table 1).
tal plane in the correct location on the specimen (i.e., quarter Jardine et al. (1984) first emphasized the significance of meas-
points along the specimen height). Both the external and internal uring axial strains locally. Others have shown that internal resil-
LVDTs had a measurement range of 65 mm for specimens with- ient modulus measurements are higher because displacement
out fly ash and 61.5 mm for specimens with fly ash. The former measurements for external LVDT readings are affected by several
had an accuracy of 0.005 mm, whereas the latter had an accuracy external sources of error, such as bedding errors, sample end
of 0.0015 mm. effects, and machine compliance (Goto et al. 1991; Tatsuoka et al.
An MTS Systems Model 244.12 servo-hydraulic machine was 1994; Bejarano et al. 2003; Boudreau and Wang 2003; Ping et al.
used for top-loading the specimens with a loading pulse having a 2003). System compliance may be defined as the deflection of the
0.1 s duration followed by a rest period of 0.9 s. loading sequen- resilient modulus equipment parts, such as the load cell, top cap,
ces, confining and deviator stresses, and data acquisition were and piston.
controlled by a PC equipped with Labview 8.5 software. Barksdale et al. (1997) evaluated the variability and reliability
Resilient moduli (Mr) from the last five cycles of each test of three different displacement measuring techniques for deter-
sequence were averaged to obtain the resilient modulus for each mining the resilient modulus: two external LVDTs, two or three
load sequence. The resilient modulus data were fit to the power LVDTs from the top platen to bottom platen, and LVDTs located
function proposed by Moosazedh and Witczak (1981). A sum- on clamps at [1=4] points. Two 152-mm (6-in.) diameter by 305-
mary resilient modulus (SRM) was also computed, as suggested
in Section 10.3.3.9 of NCHRP 1-28A. The summary resilient TABLE 1—Summary resilient modulus for base materials with and without fly
modulus of a given material is simply the resilient modulus at a ash.
given state of stress (the state of stress expected for that material Fly ash Curing Internal External SRM INT=
in the field). The advantage of reporting a SRM is that a standard, Materials content (%) time (d) SRM (MPa) SRM (MPa) SRM EXT
single value for the resilient behavior of the material is determined
Class 5 base 0 – 174 236 1.4
and can be used for comparing two or more materials. For base
RPM 0 – 220 309 1.4
materials, the SRM corresponds to the resilient modulus at a bulk
10 7 443 1753 4.0
stress of 208 kPa.
28 537 2702 5.0
56 533 2947 5.5
15 7 625 4477 7.2
Results and Analyses 28 658 6816 10.4
RSG 0 – 179 212 1.2
The summary resilient moduli (SRM) computed from internal
10 7 507 5785 11.4
LVDT measurements are higher than those for external LVDT
28 582 7219 12.4
measurements for all resilient modulus tests. A sample graph
56 614 8183 13.3
shows the typical internal and external resilient moduli from
15 7 536 10118 18.9
sequences 1–5 for a RPM sample (Fig. 4). The ratio of internal to
28 667 12189 18.3
external SRM ranged from 1.2 to 1.4 for the base and recycled

Copyright by ASTM Int'l (all rights reserved); Sat Jan 5 06:32:03 EST 2013
Downloaded/printed by
Craig Benson (Unversity of Wisconsin) pursuant to License Agreement. No further reproductions authorized.
4 GEOTECHNICAL TESTING JOURNAL

mm (12-in) high synthetic elastometer specimens: one having low for the blasting sand, whereas the recommended ratio for silty
resilient modulus (54 MPa) and the other having relatively high clay was approximately 1.12. The ratio of internal to external
resilient modulus (350 MPa) were used. LVDTs were also rigidly SRM for the recycled materials stabilized with fly ash was signifi-
attached to each specimen for eliminating system compliance de- cantly higher than the ratios for materials without fly ash (ranging
formation as well as the potential for slip and vibration associated from 4.0 to 18.3). The ratio of internal to external SRM also
with the clamps. increases with increasing stiffness (Fig. 5). Additional data from
Both Anova and Duncańs multiple range tests showed there Kootstra (2009) and Bozyurt (2011) were obtained for comparison
exists statistical differences at the 95 % confidence level for the and are included in Fig. 5. Bozyurt calculated the ratio of internal
mean resilient modulus determined by each measuring technique. to external SRM for recycled asphalt pavement (RAP) and
Furthermore, the test showed that at 95 % confidence level the recycled asphalt concrete (RCA) obtained from different sources
resilient moduli measured using the rigidly mounted LVDTs are in the United States, whereas Kootstra (2009) determined the ratio
statistically different from the resilient moduli using the clamp of internal to external SRM for the RSG and RPM previously
mounted LVDTs at the same location for both the low and high described, each blended with 4 % cement (CS-RSG and CS-
stiffness synthetic specimens. RPM) as well as with 10 % cement kiln dust (RSG, 10 % CKD
Taking the rigidly mounted LVDTs as reference, the internal and RPM, 10 % CKD). The latter yielded moduli in excess of
clamp mounted LVDTs resulted in a better average resilient mod- 2000 MPa, in some cases, with more variability.
ulus (-6 % error) than those for the externally mounted LVDTs The increase in ratio with increasing stiffness is attributed to an
(-14 % error) for the stiffer specimen. On the other hand, the increase in overestimation of the displacement as the material
externally mounted LVDTs resulted in a better average resilient becomes stiffer (i.e., lower displacements), increasing the differ-
modulus (2.5 % error) than those for the internal clamp mounted ence between external and internal displacement measurements.
LVDTs (-6 % error) for the low stiffness specimen. The contrast- These results are consisted with the results obtained by Barksdale
ing results were attributed to the fact that low stiffness specimens et al. (1997) for high synthetic elastometer specimens, where
undergo a large amount of deformation for a given stress com- externally mounted LVDTs performed poorly for the stiff speci-
pared to a stiff specimen, with system compliance deformations men. Bejarano et al. (2003) also report higher Mr from internal
becoming less important in the measuring of the resilient modulus readings, with an increase of Mr for increasing stiffness because
when compared to these large deformations. The system compli- of the greater influence of machine compliance (Bejarano et al.
ance deformations for the stiff specimens; on the other hand, 2003). The measurement accuracy also decreases for very stiff
become important because they can be on the same order of the materials at low deviator stresses as the displacements become so
small deformations occurring in stiff specimens. As a result, the small they are at the limit of the LVDT’s accuracy, resulting in
external LVDTs show more error for the stiffer specimen. more variability of the data.
Puppala (2008) summarized the resilient moduli information
available in the literature collected from various state DOTs in an Base Materials
extensive study for the National Cooperative Highway Research
Program (NCHRP). The majority of the studies conducted resil- Additional resilient moduli computed from internal and external
ient modulus testing using either internal or external LVDT meas- LVDT measurements were obtained from the Minnesota Depart-
urements, showing certain variations in the resilient moduli ment of Transportation (MnDOT) database (Chadbourn 2007) for
measurements. In general, research studies conducted using both
internal and external LVDT measurements system yielded higher
resilient moduli for internal measurements when compared to
external measurements. The higher internally measured resilient
moduli were attributed to displacements measurements free from
system compliance errors.
The resilient modulus results for base and recycled materials
without fly ash are similar to those found by Mohammad et al.
(1994), Ping and Ge (1996), and Ping et al. (2003). Ping and Ge
(1996) conducted resilient modulus tests on lime rock, a weath-
ered limestone base material commonly used in Florida, instru-
mented with internal and external LVDTs. The ratio of internal to
external resilient moduli calculated from the data reported ranges
from 0.85 to 1.48. Ping et al. (2003) conducted resilient modulus
tests on granular soils (A-3 and A-2-4) instrumented with internal
and external LVDTs. The ratio of internal to external resilient
moduli ranged from 1.19 to 1.35 for A-3 soils, whereas the ratio
ranged from 1.14 to 1.30 for A-2-4 soils. Mohammad et al. (1994)
showed the influence of LVDTs location on the resilient modulus
FIG. 5—Ratio of internal to external SRM versus internal SRM for Class 5
of a blasting sand (A-3) and a silty clay (A-7). The recommended base, RAP, RCA, and RPM and RSG with and without fly ash, CKD, and
ratio of internal to external resilient moduli ranged from 1.5 to 1.6 cement stabilization.

Copyright by ASTM Int'l (all rights reserved); Sat Jan 5 06:32:03 EST 2013
Downloaded/printed by
Craig Benson (Unversity of Wisconsin) pursuant to License Agreement. No further reproductions authorized.
 CAMARGO ET AL. ON AN ASSESSMENT OF RESILIENT MODULUS 5

FIG. 6—Ratio of internal to external Mr versus internal Mr for base materials (a), and boxplot of ratio of internal to external Mr versus internal Mr for base materi-
als (b).

comparison with the data collected in this study. The procedures a. A p-value lower than a indicates the slope is statistically differ-
used and the data collected in the University of Wisconsin tests ent from zero and the internal resilient modulus is dependent of
were reviewed and confirmed by MnDOT as suitable for their the external resilient modulus. A significance level of a ¼ 0.05,
database requirements. Thus, the data used in this study from vari- the significance level commonly used in hypothesis testing (Ber-
ous sources meet similar quality control and are suitable for com- thouex and Brown 2002), was used.
parison. The ratio of internal to external Mr was computed for all The corresponding p-value for Eq 1 is <.0001. Thus, we reject
cycles during resilient modulus testing, except those from the the null hypothesis and conclude that there was a positive signifi-
loading phase (Sequence 0). The ratio of internal to external Mr as cant relationship between internal and external resilient moduli.
a function of internal Mr for base aggregate and recycled materials The same statistical analysis was performed for the remaining
without fly ash is shown in Fig. 6 along with the corresponding equations.
boxplot.
The Class 5 base, RPM, RSG, MnROAD Class 6, and Subgrade Materials
MnROAD RPM in Fig. 6 are materials tested at the University of
Wisconsin-Madison (UW). The MnROAD Class 6 base and RPM Resilient modulus data for subgrade materials instrumented with
in Fig. 6 were obtained from a research project at the MnROAD both internal and external LVDTs were also obtained from the
facility in Minnesota (Camargo et al. 2009). The Class 6 material MnDOT database (Chadbourn 2007) and from a previous Univer-
is a crushed aggregate conforming to Minnesota’s Class 6 specifi- sity of Wisconsin-Madison (UW) study (Sawangsuriya et al.
cations (MnDOT 2005), and the RPM is a recycled material con- 2009). The ratio of internal to external resilient moduli as a func-
taining 50 % RAP. These tests were conducted at MnDOT tion of internal Mr for subgrade materials is shown in Fig. 8.
(MnDOT base, RPM, and reclaimed concrete). MnDOT base
materials include gravels, granite, and taconite tailings. The
MnDOT RPMs consist of base materials (Class 5, Class 6, and
taconite tailings) having RAP contents of 30, 50, and 70 %.
There is no apparent trend in the data (Fig. 6(a)). The boxplot
shows that the majority of the ratios ranging are between 1.0 and
2.2, with a median ratio of 1.5 for all base and recycled materials
(Fig. 6(b)).
The relationship between internal (Mr INT) and external resil-
ient moduli (Mr EXT) for base aggregate and recycled materials is
shown in Fig. 7. This relationship can be described by
Mr INT ¼ 1:5Mr EXT (1)
2
Equation 1 has R ¼ 0.85 (p-value <0.001). This slope of Eq 1
equals the median Mr ratio shown in the boxplot in Fig. 6(b).
A linear regression analysis was performed to determine if a
statistically significant relationship existed between the internal
and external resilient moduli. In this analysis, the probability of
falsely rejecting the null hypothesis (slope is zero), referred to as
the p-value, is determined and compared to the significance level, FIG. 7—Internal versus external Mr for base materials.

Copyright by ASTM Int'l (all rights reserved); Sat Jan 5 06:32:03 EST 2013
Downloaded/printed by
Craig Benson (Unversity of Wisconsin) pursuant to License Agreement. No further reproductions authorized.
6 GEOTECHNICAL TESTING JOURNAL

FIG. 8—Ratio of internal to external Mr versus internal Mr for subgrade FIG. 10—Ratio of internal to external Mr versus internal Mr for recycled mate-
materials. rials stabilized with fly ash.

MnDOT subgrade materials include soils such as clay, clay

loam, loam, loamy sand, sandy clay loam, sandy loam, silty clay, which has R2 ¼ 0.86 (p-value <0.0001).
and silty loam. UW subgrade materials include four subgrade soils
from Minnesota classified as ML, CL, and CH according to the Recycled Materials Stabilized with Fly Ash
Unified Soil Classification System. The ratio of internal to external resilient moduli as a function of
The ratio of internal to external resilient moduli for subgrade internal Mr for recycled materials stabilized with fly ash is shown
materials increases approximately linearly with increasing internal in Fig. 10. The ratio increases with increasing internal Mr, ranging
Mr, ranging from 1 to 10. This relationship can be described by from 2 to 25. An approximate linear relationship exists between
Mr INT the ratio of internal to external Mr and internal Mr for the recycled
¼ 0:007Mr INT þ 1:05 (2)
Mr EXT materials stabilized with fly ash:
which has R2 ¼ 0.87 (p-value <0.001). Mr INT
¼ 0:0014Mr INT þ 1:195 (4)
The relationship between internal and external Mr for subgrade Mr EXT
materials is shown in Fig. 9. The relationship between internal which has R2 ¼ 0.76 (p-value <0.001).
and external can be described by the power function: The relationship between internal and external Mr for recycled
Mr INT ¼ 0:172ðMr EXT Þ1:627 (3) materials stabilized with fly ash is shown in Fig. 11. There is no

FIG. 11—Internal versus external Mr for recycled materials stabilized with fly

FIG. 9—Internal versus external Mr for subgrade materials. ash.

Copyright by ASTM Int'l (all rights reserved); Sat Jan 5 06:32:03 EST 2013
Downloaded/printed by
Craig Benson (Unversity of Wisconsin) pursuant to License Agreement. No further reproductions authorized.
 CAMARGO ET AL. ON AN ASSESSMENT OF RESILIENT MODULUS 7

increasing effect of machine compliance relative to increas-

ing specimen stiffness.
• The relationship between internal and external resilient
modulus depends on material type.
• Different relationships are provided for unstabilized natural
or recycled base course materials, fly ash stabilized recycled
base course materials, and natural subgrade soils. Statistical
analysis indicated that all relationships are highly significant
(p-values <0.0001).
This difference in resilient moduli depending on test procedure
is important to know as the modulus determined from external
deflection measurements is used in calibrating field performance
based on the Long-term Pavement Performance (LTPP) of high-
ways whereas the design agencies are moving to adopt the new
Mechanical-Empirical Pavement Design Guide, which requires
use of modulus based on internal deflection measurements.
FIG. 12—Ratio of external to internal Mr versus internal Mr for a range of Whereas the difference is less than 50 % for unbound materials
materials. and subgrade soils, it is significantly higher for stiff stabilized
materials.
apparent trend in internal to external Mr for these materials. The
recycled materials stabilized with fly ash have significantly higher
Acknowledgments
stiffness than those without fly ash, which results in less accurate
external deformation measurements because of a higher machine This study was sponsored by the Minnesota Local Roads
compliance effect. This behavior is also observed in Fig. 10, where Research Board (LRRB), the Combustion Byproducts Recycling
a larger scatter exists when the internal Mr exceeds 6000 MPa. Consortium (CBRC), and the Recycled Materials Resource Center
The ratio of external to internal Mr for a range of materials (RMRC). Thanks to the Minnesota Department of Transportation
(fine-grained soils, crushed natural aggregates, recycled materials, for collaborating with this study. The findings in this report are
and recycled materials stabilized with fly ash) is shown in Fig. 12. solely those of the authors. Endorsement by LRRB, CBRC,
The concrete in Fig. 12 refers to the results for concrete specimens MnDOT, or RMRC is not implied and should not be assumed.
also tested for calibration purposes. To be consistent with the
other data in Fig. 12, the data for fine-grained materials were lim-
ited to measurements on 150-mm diameter. The ratio of external
References
to internal Mr decreases with increasing internal Mr. This trend is Applied Research Associates (ARA), 2004, “Guide for Mechanistic-
attributed to the increasing effect of machine compliance as the Empirical Design on New and Rehabilitated Pavement
specimen becomes stiffer, which increases the difference between Structures,” NCHRP project 1-37A, National Cooperative High-
internal and external Mr and therefore decreases the ratio of exter- way Research Program, Washington, D.C.
nal to internal Mr. ASTM D6307, 2005, “Standard Test Method for Asphalt Content
of Hot-Mix Asphalt by Ignition Method,” Annual Book of
ASTM Standards, Vol. 04.03, ASTM International, West Con-
shohocken, PA.
Conclusions Barksdale, R., Alba, G., Khosla, N., Kim, R., Lambe, P., and Rah-
This study presented the results of a direct comparison between man, M. S., 1997, “Laboratory Determination of Resilient
resilient moduli determined from internal and external deflection Modulus for Flexible Pavement Design,” NCHRP Project
measurements for a range of granular base course materials 1–28, National Cooperative Highway Research Program,
including both natural and recycled aggregates. In addition, data Washington, D.C.
Bejarano, M., Heath, A., and Harvey, J., 2003, “A Low-cost
from other sources at the University of Wisconsin-Madison and
High-performance Alternative for Controlling a Servo-
the Minnesota Department of Transportation, including a variety hydraulic System for Triaxial Resilient Modulus Apparatus,”
of subgrade soils, were used to investigate the correlations Resilient Modulus Testing for Pavement Components, ASTM
between resilient modulus determined from the internal and exter- STP 1437, G. Durham, W. Marr, and W. De Groff, Eds.,
nal deflection measurements. The tests in the database followed ASTM International, West Conshohocken, PA, pp. 129–140.
the same procedures albeit different operators. The following con- Berthouex, P. and Brown, L., 2002, Statistics for Environmental
clusions can be drawn: Engineers, 2nd ed., CRC Press, Boca Raton, FL.
Boudreau, R. and Wang, J., 2003, “Resilient Modulus Test–
• Resilient moduli determined from internal deflection meas- Triaxial Cell Interaction,” Resilient Modulus Testing for Pave-
urements are higher than those from external measurements. ment Components, ASTM STP 1437, G. Durham, W. Marr, and
• The ratio of internal to external resilient modulus increases W. De Groff, Eds., ASTM International, West Conshohocken,
with increasing internal resilient modulus because of the PA, pp. 176–188.

Copyright by ASTM Int'l (all rights reserved); Sat Jan 5 06:32:03 EST 2013
Downloaded/printed by
Craig Benson (Unversity of Wisconsin) pursuant to License Agreement. No further reproductions authorized.
8 GEOTECHNICAL TESTING JOURNAL

Bozyurt, O., 2011, “Behavior of Recycled Asphalt Pavement and tation Research Record 810, TRB, National Research Council,
Recycled Concrete Aggregate as Unbound Rd. Materials,” Washington, D.C., pp. 10–17.
M.S. thesis, University of Wisconsin-Madison. Madison, WI. NCHRP, 2004, “Harmonized Test Methods for Laboratory Deter-
Camargo, F., Wen, H., Edil, T., and Patton, R., 2009, “Laboratory mination of Resilient Modulus for Flexible Pavement Design,”
Evaluation of Sustainable Materials at MnROAD,” 88th An- National Cooperative Highway Research Program Research
nual Meeting, Transportation Research Board, Washington, Results Digest, Transportation Research Board, Washington,
D.C. D.C., Vol. 285, pp. 1–48.
Chadbourn, B., 2007, MN Department of Transportation Pave- Ping, W. and Ge, L., 1996, “Evaluation of Resilient Modulus of
ment Section, St. Paul, MN (personal communication). Cemented Limerock Base Materials in Florida,” Transporta-
Goto, S., Tatsuoka, F., Shibuya, S., Kim, Y., and Sato, T., 1991, tion Research Record 1546, TRB, National Research Council,
“A Simple Gauge for Local Small Strain Measurements in the Washington, D.C., pp. 1–12.
Laboratory,” Soils Found., Vol. 31, No. 1, pp. 169–180. Ping, W., Xiong, W., and Yang, Z., 2003, “Implementing Resil-
Janz, M. and Johansson, S.-E., 2002, “The Function of Different ient Modulus Test for Design of Pavement Structures in Flori-
Binding Agents in Deep Stabilization,” Report 9, Swedish da,” Report FL=DOT=RMC=BC-352–6 (F), Florida
Deep Stabilization Research Centre, Linkoping, Sweden. Department of Transportation, Tallahassee, FL.
Jardine, R., Symes, M., and Burland, J., 1984, “The Measurement Puppala, A. J., 2008, “Estimating Stiffness of Subgrade and
of Soil Stiffness in the Triaxial Apparatus,” Geotechnique, Unbound Materials for Pavement Design,” NCHRP Synthesis
Vol. 34, No. 3, pp. 323–340. 382, Transportation Research Board, Washington, D.C.
Kootstra, B., 2009, “Large Scale Model Experiments of Recycled Sawanguriya, A., Edil, T. B., and Benson, C. H., 2009, “Effect of
Base Course Materials Stabilized with Cement Kiln Dust,” Suction on Resilient Modulus of Compacted Fine-Grained
M.S. thesis, University of Wisconsin-Madison, Madison, WI. Subgrade Soils,” Transportation Research Record 2101, TRB,
MnDOT, 2005, “Standard Specifications for Construction,” Min- National Research Council, Washington, D.C., pp. 82–87.
nesota Department of Transportation, St. Paul, MN. Tastan, E. O., Edil, T. B., Benson, C. H., and Aydilek, A. H.,
Mohammad, L. N., Puppala, A. J., and Alavilli, P., 1994, 2011, “Stabilization of Organic Soils with Fly Ash,” J. Geo-
“Influence of Testing Procedure and LVDTs Location on tech. Geoenviron. Eng., Vol. 137, No. 9, pp. 819–833.
Resilient Modulus of Soils,” Transportation Research Record Tatsuoka, F., Teachavorasinskun, S., Dong, J., Kohata, Y., and
1462, TRB, National Research Council, Washington, D.C., pp. Sato, T., 1994, “Importance of Measuring Local Strains in
91–101. Cyclic Triaxial Tests on Granular Materials,” ASTM Special
Moosazedh, J. and Witczak, M., 1981, “Prediction of Subgrade Technical Publication 1213, ASTM International, West Con-
Moduli for Soil that Exhibits Nonlinear Behavior,” Transpor- shohocken, PA, pp. 288–302.

Copyright by ASTM Int'l (all rights reserved); Sat Jan 5 06:32:03 EST 2013
Downloaded/printed by
Craig Benson (Unversity of Wisconsin) pursuant to License Agreement. No further reproductions authorized.
Erratum

Erratum GTJ20120077, An Assessment of Resilient Modulus Testing: Internal and

External Deflection Measurements, Felipe Camargo, Craig Benson, and Tuncer Edil,
published online September, 2012 and included in Geotechnical Testing Journal
(GTJ), Volume 35, Issue 6, November, 2012, pp. 1–8.

TABLE 1—Summary resilient modulus for base materials with and without fly ash.

Fly Ash Content Curing Time External SRM Internal SRM SRMINT/SRMEXT
Materials (%) (d) (MPa) (MPa)

Class 5 base 0 – 174 236 1.4

0 – 220 309 1.4
7 443 1753 4.0
10 28 537 2702 5.0
RPM
56 533 2947 5.5
7 625 4477 7.2
15
28 658 6816 10.4
0 – 179 212 1.2
7 507 5785 11.4
RSG 10 28 582 7219 12.4
56 614 8183 13.3
7 536 10118 18.9
15
28 667 12189 18.3

Copyright
Copyright©by
2012 by ASTM
ASTM Int'l (allInternational, 100 Sat
rights reserved); BarrJan
Harbor Drive,EST
5 06:32:03 PO Box
2013C700, West Conshohocken, PA 19428-2959. i
Downloaded/printed by
Craig Benson (Unversity of Wisconsin) pursuant to License Agreement. No further reproductions authorized.
View publication stats