Development of a Hollow Cylinder Tensile Tester
To Obtain Mechanical Properties of Bituminous Paving Mixtures
by
William G. Buttlar, Ph.D., P,E.
Assistant Professor
Department of Civil and Environmental Engineering
UniverSity of Illinois at Urbana-Champaign
205 North Mathev.rs Avenue
1212 Newmark Laboratory
Urbana,l l 61801
Ph, (2 I7) 333·5966
Fax, (217) 333·1924
[email protected]
Ghazi G. A1-Khateeb, M.S.C.E.
Graduate Research Assistant
Department of Civil and Environmental Engineering
University of Illinois at Urbana-Champaign
1208 Newmark Laboratory
Urbana, IL 6180 I
Diyar Bozkurt, M.S .C. E.
Graduate Research Assistant
Department of Civil and Environmental Engineering
University of Illinois at Urbana-Champaign
1208 Newmark Laboratory
Urbana, IL 6180 1
Submitted for Publication in the
Journal of the Association of Asphalt Paving Technologists
December 9, 1998
Buttlar, AI-Khateeb, and Bozkurt
Abstract
A new hollow cylinder tensile test (HCT) device was de\'eloped. which can be used 10
obtain fundamental properties of asphaltic paving mixtures, such as creep compliance, tensile
strength, and dynamic modulus, at low and intermediate temperatures. The device was
originally developed to be a compact, portable, and operationally simple surrogate test to
obtain similar properties as the Superpave Indirect Tensile Tester (JOT), but is capable of
obtaining properties at both low and intermediate pavement service temperatures. The
device produces strain in an asphalt cylinder by appl~'i ng pressure to the inner cylinder \\'all .
causing tensile or 'hoop' stress to develop in the cylinder The load system is also used to
measure specimen deformation, which makes specimen preparation and device operation \'et\'
simple.
Three·dimensional finit~ element analyses were conducted to model practical test
conditions in the HCf, including effects of eccentrically cored test specimens. A series of
simple formulas are presented, which allow stresses and strains to be accurately determined
from test measurements, based upon finite element results and the elastic·viscoelastic
correspondence principle, Formulas for tensile strength and creep compliance are presented,
the lauer of which requires that creep tests are conducted in the linear viscoelastic range.
Preliminary tests have been conducted using a prototype HCf, which have ShOlI11
very promising results. A reference material was measured to within one percent of expected
modulus, and tests on asphalt concrete have produced very reasonable properties.
Measurement resolution, even for very stiff materials, has be~n found to be exceptionally
good. This is due to the large gage area of HCf spedmens, e.g.. the cylindrical cavity wall. A
comprehenSive validation program is now needed to verify the accuracy and repeatability of
the HCT.
Key Words: Hollow Cylinder, HCT, SupelJl3ve JOT, Creep Compliance. Tensile Strength, Dynamic
Modulus, Resilient Modulus, Asphah Mixture, Asphah Concrete, Tensile Test, Thermal Cracking
Introduction
Mechanical testing of asphaltic paving mixtures has long been recognized as a vital
step in mixture deSign, production control. and forensic investigation of this most important
construction material. Over the past several decades. there has been movement away from
devices that measure empirical binder and mixture properties (penetration, stability and now,
etc.) and an increased emphasis on devices that obtain fundamental material properties. such
as dynamic modulus, creep compliance, and tensile strength. Fundamental material
properties, combined with mechanics·based pavement response and distress models. can be
calibrated to pavement performance with far fewer observations than empirical test results.
and can handle changes in traffic, materials, and production techniques with little or no
model re-calibration.
Increases in traffic volume, vehicle loads, tire pressures, and tire stiffnesses, have
resulted in the need to reevaluate the types of mixtures that are appropriate for present and
future transportation faci lities. More than ever, mixture design must lead to materials that
are stable enough to resist rulting under severe loading and heat in summer months, yet
BlIlllar, Al-Khaleeb, and Bozkurt
durable enough to resist fatigue, thermal, and block cracking during cooler months. The
responsibility for the proper design of tomorrow's mixtures will fall largely on the shoulders
of the contracting industry. The Supt'rpave mixture design SYStem offers the contractor a
volumetric mix design system plus advanced performance tests and modds to help meet this
challenge. The tests originally selected to suppon. the performance based. prediction modds
were the Superpave Shear Tester (SST) and Superpave Indirect Tension Tester {101l The
SST collects mechanical properties at high and intermediate service temperatures for use in
rutting and fatigue prediction models, while the JOT collects low-temperature mechanical
propenies for thermal cracking performance prediction. These testS have proven to be
excellent research tools, and in some instances, have been employed to enhance Superpave
volumetric mix designs for recent paving projttt.s in the United States. To meet the needs of
the paving industry, every e(fon mUSt be made to obtain the required properties in the
simplest manner, and using compact, portable equipment whenever poisible.
Because of the modularity of the Superpave performance prediction system, it may be
possible to develop surrogate tests, which will yidd the required properties for the Superpave
prediction models using simpler, more portable devices. Care must be taken; however, to
ensure that the surrogate device produces suitably acrurate and repeatable measures of the
desired property, for the 1e-.'eJ of design reliability sought. A Hollow Cylinder Tensile Tester
is presented in this paper, which appears to have promise as a surrogate test for the lOT in
asphalt mixture design . The device also appears to have other useful measurement
capabilities related to asphalt mixture design and analysis.
ObjectiVes
The objectives of this paper m :
1. To describe potential benefits of the hollow cylinder tensile teSt arrangement
2. To describe theoretical analyses conducted (0 evaluate the feasibility of a thickwalled Hollow Cylindtr Tensile Tester (Her) to obtain tensile propenies of
asphaltiC paving mixtures
3. To describe initial design concepts for a hollow cylinder tensile test device, critical
design issues, and the need for three-dimtnsional finite element analysis when test
conditions depan from assumed conditions for closed·form solutions
-l . To present results of fin ite element Msed sensitivity analyses, including Stress,
strain. and defleclion fi elds when closed·form solutions are not applicable
5. To describe the developmem of a suaightforward procedure for converting teSt
measurements into accurate, fundamental material propenies, which utiliu finite
element results
6 To briefl~' summarizt ongoing developments on a prototype HCT, to present
prdiminary leSI results, and to outline plannffi testing and validation effons
Buttlar, AI-Khateeb, and Bozkurt
S<ope
This study is focussed on the development of a thick-walled hollow cylinder device to
obtain tensile propenies of brittle materials, such as asphalt concrete. The loading
arrangement considered is that of internal (cavity) pressure only, with uncapped,
unrestrained cylinder ends.
Hollow Cylinder Testi ng
Previous Studies
A review of the literature revealed that the hollow-cvlinder test mode has never been
specifically used to dmrmine the tensile properties of asphalt concrete. The literature is
replete with applications involving the hollow-cylinder testing of granular materials. mostly to
delermine compressive, shear and torsional properties (Saada {1988J, Hight et al. [1983]).
The hollow cylinder test mode is viewed favorably by geotechnical researchers because of its
ability to produce fundamental material properties, while giving the versatility to manipulate
principle stress orientation by controlling axial and torsional loads. along with inner and
outer pressure.
The application most closely related to the proposed research was reported by Alavi
and Monismith (1994 ). In their study. hollow cylinders having 114.3 mm (4.5-inch) and
88.9 mm (3.5-inch) outer and inner radii, respectively, were tested in compression along the
axis of symmetry. The scope of their research, however, was aimed at determining shear and
compressive properties of asphalt concrete at moderate and high in-service temperatures (4.
25, and 40 C) . Crockford (1983). also used hollow cylindrical specimens to determine shear
and compressive properties of asphalt mixtures.
Proposed Application: Hollow Cylinder Tensile Tester (HCT)
Modulus, creep compliance, and smngth under tension are key fundamental
propenies used in bituminous pavement design and in mixture design . This paper describes
the use of a thick-walled pressure cylinder arrangement (figure I) for measuring these
propenies on asphaltic concrete sp«imens. Constitutive equations aTe available for both
thin-walled and thick-walled cylinders (Timosh ~nko and Woinowsky-Krieger [1959 J), where
Lhin·walled cylinders are generally regarded as those having inner and outcr radii differing by
no more than ten percent. In the case of asphaltic paving mixtures. the use of thick-walled
cylinders is necessary, since aggregate-size-to-wall-thickness ratio can affect test results. For
the purposes of obtaining tensile propenies. the only applied stress that will be considered
hereafter is internal (cavity) pressure. Cylinders with uncapped ends were studied. since
capping ends complicates test procedures and requires larger pressures to induce desired
tensile stresses.
Advantages of Hollow Cylinder Test Mode fo r Obtaining Tensile Properties
There are several methods for inducing and measuring tensile propenies of materials
in the laboratory, including: direct tension, indirect tension (figure 2), beam testing, and
Vertical Stress
Radial Stress
Circumferential
(Hoop) Stress
Applied Pressure
10 Hollow Cavity
a
•• ,"":-f--;'"
"
•
-..
"
:·'-..: ..I --~--':
•
•
•
•
~
~
Figure 1. Schematic and Stress Defin itions for Hollow
Cylinder Tensile Test Specimen
Burtlar, Al-Khateeb, and Bozkurt
Figure 2. The SUPERPAVE Indirect Tensile Test (l OT)
hollow cylinder testing (figure I). In ~am testing. it is difficult to derive a fundamental
measure of tensile suength because of neutral axis shifting and stress redistribution after the
initiation of tensile fractu~. Also. for compatibility with Superpave. it is most desirablt to
utilize 150-mm diameter by 115-mm tall cylindrical specimens as obtained from the gyratory
compactor, which limits maximum possible specimen dimensions for direct tension testing. A
similar restriction occurs for direct tension testing.
Figure 3 compares the relative advantages and disadvantages of dirtct tension, indi rw
tension, and hollow cylinder tensile testing. Oirtct ttnsion has the advantage of ~ing the
only mode with a pure tensile stress state, but has several disadvantages. One dassic probltm
is the difficulty in gripping and testing brittle materials in ttnsion, as suess concentrations
often result in failures near damping points (grips). End platens are sometimes used;
how~r , specimen preparation then involves gluing tht platens to the specimen with careful
alignment, which is time-ronsuming. Indirect tension has many advantages, induding; direct
utilization of cylindrical specimtns, simple application of compressive loads through loading
strips. and good accuracy if surface-mounted transducm and three-dimensional correction
factors art used, as in the Superpave lOT (Buular and Roque [1994]) . Potential
disadvantages of the IDT include the size and lack of portability of the test device.
One of the advantages of the HCf is the long gage length in the direction of tensile
response, which is along the inner diameter of the C)~indrical hoop (e.g., tangential). Tension
is induced uniformly around the entire circumference of the cylinder (figure 1), giving a -gage
length" of approximately 3DO-mm around the inner wall for a standard 150·mm diameter
specim«l with a lDO-mm diameter cavity. Another advantagt of the Her is the mechanical
advantage afforded by applying load through pressurizing the inner cavity. By -pushing from
the inside" and by utilizing a simple pressure intensifier. there is no need for load (rame
Test
Direct Tension Test
Indirect Tensile
Hollow Cylinder
IOn
Te.t lion
Ten.it, Test IHen
J-
/l~
/'
•m
•m
al
Schematic
diagram
(possible
location of
maximum
tensile stress
is donoted bV
point "m1
Stless state
at point Mm"
(plotted on
Mohr's circle)
l oad , P
,
,
r-..... ,.~m
/"~"-~-i"
'-
'\
a
a,
t8 p
( 1,\ a-
a
-p
-6'IIP) \ 2'IIP)
Potential
Advantages
, Pure tensHe state
• Accurate, it test
performed carefully
•
•
thin paving lifts
•
•
Potential
Dis·
advantages
Can use cylindrical
specimens
Accurate
Can test
specimens from
•
Identifies first
failure of specimen
during strength les\
IE1
2.6 p
0.8 p
-2'IIP)
,
pre~sure, p
,
( I 1\
~
....:./
Internal
4'1~
a,n
I(
t ... t A': t
"y
Applied Stress, 01
"
~y
•
Can use cylindrical
specimens
•
Simple, portable
•
device is possible
large measurement
'ffi'
Requifes beamor bar
•
....m."
Dlfficu~
10 gnp
Equipment not
specimen &1d ensure •
aligned loads
• Silort gage leflgth
Specimefl
•
preparatKlfl\ime
consumil'lg
"""'"
Effects of usng only
outer portion of
gyrato.'y spectmen
needs study
• Wall thickness effects
fleeds study
Figure 3. Comparison of Tensile Test Modes
Buttlar, Al·Khateeb, and Bozkurt
apparatus. Based upon developments with a current prototype (described in detail later) . it
appears HCf apparatus can be assembled that weighs less than 1.33 kN (300 Ibn ·
Another advantage of the HCf is the lack of stress concentration at the point of load
application. Unlike direct and indirect tensile tesling. which results in stress concentrations
at load platens, the HCf involves the application of a uniform internal pressure to induce
tension. This may have advantages in obtaining properties at test temperatures abovt' 0 C.
and for testing of ct'rtain polymer.modified mixtures. For instance, soft or highly ductile
mixtures can fail in compression and sht'ar in the IDT rather than in tension, denott'd by y.
shaped shear failure regions near load strips.
Finally, specimen preparation for HCf testing is uncomplicated , involving only coring
of the central cavity in the case of cylindrical specimens, or l'....O coring operations in the case
of laboratory compacted slabs or field specimens. Hence, the HCf is envisioned to be a
small, portable, and operationally simple test device, capable of measuring fundamental
mixture properties. Some potential disadvantages related to the hollow cylinder tensile test
arrangement are also listed in figure 3, which include wall-thick.ness·to·partic!e ratio and
tfft'cts of non-homogeneity of gyratory-compacted specimens. These issues will be discussed
at length in a later section.
Theoretical Analysis of the HCT
Theoretical analyses were performed to assess the feasibility of a thick·walled cylinder
test for the determination of cretp, modulus, and strength properties of asphalt concrete.
The following issues were investigated, all of which are interrelated:
I. The optimum wall thickness for hollow cylinder specimens
2. The resulting stress distribution across the waH
3. The amount of internal pressure required to rupture asphalt concrete specimens
Assuming all specimens have ouler diameters of 150-mm and 3450 kPa (500 psi )
tensile strength, the required inlernally applied breaking pressure was estimated to be no
greater than 2070 kPa (300 psi). depending on wall thickness (lable I ). This pressure can
easily be achieved through compressed gasses or by using a small piston to compress a volume
of fluid.
Table i . Breaking Pressure VI. Wall Thickness for 150-mm Diameter Specimen
Wall Thickness,
mm
38.1
31.8
25.4
19.1
12.7
Required Internal
Pressure, kPa (psi)
2070 (300)
1697 (246)
1325 (192)
966(140)
621 (90)
Note. Based Upoo Tangential BreaklTlg Strengl/l 01
Asphall Concrete of 3450 kPa (500 psi)
Buttlar, Al-Khateeb, and Bozkurt
Breaking pressures and stress distributions were computed using constitutive
equations for thick-walled cylinders (Timosnenko and WOinowsky-Krieger [1959j), givt'n by
equations I and 2:
(I )
(2)
Where:
p = Internally-applied pressure
cr, = Tangential (hoop) stress, which is tensile
cr, = Radial suess, which is compressive
All other quantities are as defined in figure 1.
A second concern was that me change in tangential (hoop) stress across the thick wall
should be minimized to the extent possible. Figure 4 shows the tangential (hoop) stress
distribution across the specimen wall as a function of wall thicknt'ss. Note that tensilt'
sut'sse. are highest at the inner wal!. Based upon this analYSiS, a 25.4-mm (I-inch) wall
thickness would give an outer walVinner wall tangential stress ratio of 0.63. This wall
thickness st'ems to strike a reasonable balance between the relative advantages and
disadvantages of using thin- or thick-walled specimens. Thick. walls are advantageous for
increasing the wall thickness-to-maximum aggregate size ratio. Thin walls favor unifonn
stress distributions, accurate tensile strength determination, higher deformations (and thus
improved signal-to-noise ratiOS), and lower required pressum to fail spC(imens.
Development of a Prototype HoUow Cylinder Tensile Tester
Two possible test configurations for the Hollow Cylinder Tensile Tester (HCf) art'
shown in figures 5 and 6. A spool-shaped metal "intensifier" is the hean of the HCf
apparatus and serves three main purposes: I) to reduce the amount of fluid that will undergo
bulk compression; 2) to house the loading pistOn, and; 3) to intensity (amplify) pressure.
The arrangement in figure 6 appem to be superior to that of figure 5, sinet' pressurization
along the entire height of {he inner wall leads to more uniform stress Slates. However, the
preliminary teSI results reponed herein were collected using the first prototype HCT
developed, which is described by figure S. In any case, since available closed-form solutions
require both full-height loading and concentric coring of the inner cavity, finite element
analYSis were conducted to obtain accurate measures of stress, strain, and deflection when
these conditions are not met..1S described in the next section.
Pressure is t'asily monitored using a pressure transducer located anywhere in the flui d
on Ihe specimen ·sidt'· of the piston. as shown in figures 5 and 6. In this way, applied
pressure and rhus tensile Stress are monitored independent of friction in the loading piston.
A fl exible membrane is used to keep the pressurizing fluid from penetrating voids in and
Inner wall for specimen with 11 .5 mm walilhicl\ness
•
Applied cavily
pressure =
2070 kPa
Axis of symmetry
11500
Outer wall for all cases
10000
~
~
••
g
~
8500
7000
;;
"••
•
>-•
5500
Q
4000
2500
1000
lR"t.iD":f:" "~"~f;:'f 'f:" ~' "~'~ "~f;i;"~ ,w~;'f1~~~~~~~~;;;~
35
45
55
65
Radial Distance from Axis of Symmetry (mm)
Figure 4: Tangential (Hoop) Stresses Distribution Across Wall
of Hollow Cylinder Specimens of Various Wall Thickness
75
150 mm
100mm
Section A·A'
n .
Pressure
Intensifter ~--J..
Possible
LVDl
Arrangement
for Poission's
Ratio Determination
Flexible Membrane
-4---- Piston
Figure 5. Cross-Sectional View of Original Her Prototype Arrangement:
Partially . Loaded Inner Cavity Wall
Pressure
Transducer
Rigid Cylindrical
Intensifier
T
Possible
LVDT
Arrangement
for Poission's
Ratio Determination
Flexible Membrane
Cylindrical Specimen
'Dimensions X and Y can be varied to allow range of possible cylinder heights
Figure 6. Cross-Sectional View of Proposed Modified HCT Prototype Arrangement:
Fully-Loaded Inner Cavity Wall
ButtJar, Al·Khaleeb. and Bozkurt
around the specimen. and to contain the fluid after specimen rupture occurs in a strength
le~1
To measure propeTlies such as creep compliance. dynamic modulus. and resilient
modulus of asphalt concrete sperimen. it is necessary to measure specimen deformations in
response to the applied pressure. Originally. it was assumed that an externally mounted
chain tyPf: extensometer would be the most con\.'enient measure of circumferential expansion.
H o\\"~·t'r. since tensile suesses are largest on the inner wall, a method to measure inner
curcumfercnlial expansion was sought This was eventually accomplished by measuring the
change in cavit}' expansion . which was quantified by monitoring fluid movement in the inner
ca,·ily A flu id was selw.ed as the pressurizing medium to reduCt' volume changes associated
\Iith bulk compression under ten pressures.
A piston is driven inside the intensifier to compress the fluid and induce pressure
loading. Since the area of the piston is known. the movement of the piston can be monitored
to measure the extension of the hollow cylinder under pressure loading. Of course, one must
be able to subtract out any pinon movement due to bulk fluid compression and compression
of the membrane. fittings. etc.. to arrive at an accurate result. This can be accomplished by
first measuring the piston movement as a function of cavity pressure for a very rigid cylinder.
such as a steel cylinder with very thick walls.
Based upon these considerations. a protot)~ Hollow Cylinder Tensile Tester was
constructed. as displayed in figu re 7. A detailed description of the prototype device is
beyond the scope of this paper. However, some of the key features of the HCT prototype
afe:
• It is much simpler to induce tension by ~ pushing from the inside.- For example,
faili ng a specimen with 3450 kPa (500 psi) tensile strength in the HCT requires
that about 1.50 kN (337 Ibf) be applied to the piston in the intensifier. [n the
lOT, applying the same tensile stress takes over 4 1.8 kN (9400 lb£).
• The HCf only requires a standard pressure transducer and a Single. standard
linear voltage differential transducer (LVDT) to take all necessary measurements
to determine creep compliance. tensile strength, resilient modulus. etc.
• The final HCf device is expeae:d to weigh less than 1.33 kN (300 Ibf).
The hollow cylinder asphalt mixture specimen shown in figure 7 was produced by
coring a standard gyratory compacted specimen using a portable coring rig (figure 8) with a
I01.6·mm (4'inch) outer diammr core barrel. A description of preliminary test resulLS is
presented in a later 5e{:tion.
PltJnned Equipment FetJtuns
A servo·hydraulic system will be used to drive: the piston, with a control system
capable of dosed loop control on either piston movtment or fluid pressure. A post failure
restraint cylinder will sunound the outer diameter of the asphalt specimen, to prevent large
0IXnings in the ~sp h.all cylindef after loading .to failure. ~ heating/cooling ~stem ~Il also be
employed to malntam consunt temperature In the speomen and test deVIce dunng testing.
A f1uid·based bath system is being considered, due to the good temperature stability and
accuracy offered by these systems.
The HCT devil"t' (like the JOT device) will be capable of running creep and strength
tesls on asphalt mixtures to determine the material properties needed for the SUPERPAVE
Figure 7a : Intensifier Unit on HCT
Attached
Figure 7c: HCT With Specimen In Place, Figure 7d: HCT With Specimen In Place,
After Strength Test
Before Strength Test
Figure 7: Prototype Hollow Cylinder Tensile Tester
Figure B. Coring Rig With Two-Dimensional Centering Capabilities for
Producing HCT Specimens
Bunlar. AI-Khaleeb. and Bozkurt
thermal cracking model. A creep test involves the sudden application of a constant pressure
in the cavity of a hollow cylinder specimen for a specified period of time and the
measurement of resulting specimen deformation. Material properties such as creep
complianct, which is required by SU PERPAVE, can De: obtained from this test. A strength
test involves the application of a uniformly increasing piston displacement on the specimen
until rupture occurs. Because of the excellent dynamiC control characteristics of fluid-based
loading S)'Slems, it will also be possible to measure dynamic modulus and resilient modulus
with the Her. These tests will involve dosed·loop pressure control of the desired stress
pulse, and recording the resuhing piston displactment so that specimen main response can
be obuined, and the approprim modulus be determined.
Three-Dimensional Finite Element Modeling
Three·dimenSional finite element modeling was condumd to evaluate deflection,
mm, and strain fields for instances where specimen and test configurations deviated from
dosed-form solution assumptions. These deviations include:
• Wall thicknm: Assumed to be uniform around cylinder, but in practice some
eccentricity will occur due pranicallimitations in coring equipment
• Pressure on inner cavity Assumed to be applied (l\Ier full height of specimen, but
if a panial-loading arrangement such as described by figure 5 is used, finite
element analysis will be needed
Description of Modtl
Gyratory-sized hollow cylinder specimens were modeled, with outer diameters of
150 mm, and specimen heights of 112 , II S, and 118 mm. Three different load cases were
used, where pressure was applied across the region representing the middle 90, 95, and 100
!'trcent of total specimen height. Cavitr !!ccenuicities were modeled using O-mm, S.08·mm
(0.2·inch). and 10.1 6-mm (OA-inch) differences betw!!en maximum and minimum wall
thidn!!sses. Finite element modeling was conducted using ABAQUSl"looI. For modeling
concentrically-cored speci mens, axisymmetric modeling was conducted. However, for the
Casl! of eccentrically cored specimens, three-dim!!nsional models were necessary, as shown in
figure 9. In this case, symmetry was taken advantage of in the y- and z-rlirections. Thus, t.he
half-circle, half·height model uses onlr IHth as many elements as would be necessary to
model the entire ~..,.lind(r.
For thrl'c.'·dimensionaJ modeling, 20·noded quadratiC brick elements were employed.
Originally, 8·noded isoparametric brick elements were used; however, inadequate acrurae),
was achieved wllh Ihe element Illesh used. Rath!!r than regenerate the original mesh, the
more complic31c.'d 20·noded quadratic bri.:k elements were substituted and satisfactory
results were al:htewd. Element aspect ratios (largest to smallest dimensionsl were
predommantly less than 2: 1; e.~cqJl in areas where suess gradients were low, where maximum
as!'tct ratios of about -1 .1 were pemlined Two-degree·of.frcedom rollt'r supportS were
supplied al ea(h nodt' along plants of symmetry In addition. nodes at the center of the inner
cavity wall were fi~cd mil'll.' x-Jirwion 10 pr!.'\'ent rigid bod~' mo\'ement. Poi sson's ratio was
taken as 0.30 for the model runs reponed herein.
20·Noded
Isoparametric
Brick Elements
Figure 9. Finite Element Mesh and Typical Stress Contour,
Zero Cavity Eccentricity
100~/.
Loading,
Buttlar, Al-Khateeb, and Bozkurt
!mults qJ Finiu Eltmtnl Ana[ysis
Figure 10 illustrates the effect of eccentric cavity location on hoop stresses in the
hollow tylinder. Obviously, a 10.1 6-mm (0.4 inch) wall thick.ness differential (between
maximum and minimum thickness) is not acceptable, as a maximum to minimum hdbp stress
ratio of about 2:I results. Fortunate.ly, with a simple centering attachmwt as shown in
figure 8, one should be able to core specimens routinely with under 5.08-mm (0.2 inch) wall
thickness diffmntial. which will yield maximum to minimum hoop stress ratios no larger
than 1.24 to 1. Although correction factors based upon finite element results will be
presented, careful coring will reduce the magnitude of the correction factor to be applied.
Figures I Ithrough 14 illustrate the effects of partially loaded inner walls, which OCctJr
when using test conditions such as those described by figure 5. For this analysis, concentric
coring was assumed and axisymmetriC fi nite element modeling was employed. Axisymmetric
modeling is much more efficient than three-dimensional (solid) modding and allo ....'td more
mesh refinement to be utilized. Three load cases, which are <kscribed by fi gure I I, are
presented. Complete inner wall loading (100% loaded) and partial loading (90% loaded)
were considered. For the partially loaded cylinder, the unloaded region was assumed to be
identical at the top and bottom of the test specimen, as in the arrangement shown in figure 5.
Two analysis cases are presented for partially·loaded cylinders: sudden and gradual transition
from full to zero pressure, as illustrated in figure II .
As ex~ed, figure 12 illustrates that partial loading results in a cuMd inner wall
afler deformation, due to the restraint caused by the unloaded tylinder ends. However, the
suess discontinuity associated with partial loading has a more pronounced effect on tensile
and shear messes, as sho.....n in figu res 13 .and 14. By examining shear messes in figure 14, it
is apparent that the sudden transition from full 10 zero pressure results in a stress condition
indicatl\'e of double·shear in the materi al near the transition. This shear response resembles
that of material being extruded through an orifice. In the case of the partially loaded hollow
cylinder, however, the double shear is being caused by the sharp stress gradient on one side,
and by the constraint of the material in the unloaded, ring-shaped portion of the cylinder on
the other side.
Shear and hoop stress magnitudes are lower in the more realistic case of gradual
pressure reduction, as shown in figures 13 and 14. In summary, this analysis illustrates that
although deflections are lower near cylinder ends for partiaJl)'·loaded cylinders, suess
conctntrations result m less reduction in hoop suess than would be expected. This analySIS
also shows the advantage of the load system shown in figure 6, which pro\1des for 100·
percent loadmg of the lOner 9'hndcr wal!. and thus. no Stress lQnCentrallon
Fin ite Element-Based Su ess and Strain Correction FaCtors
The followmg relationships were derived so thai measurements of volume change and
applied pressure could be accumely com'erted into maximum hoop sum and strain. based
upon 3·0 finile element stress and stram fields. These results, in rum , can be used 10 obtam
fundamental propertH.'S such as creep l:omphance, tensile strength, etc. The fol!olling
procedure and relationships were developed.
<
c
<
E
E
<D
~
.;
~
"
<i
"
E
E
'"o
"
.,;
E
E
o
o
o
§
•
(I!dlll SS8JIS dOOH
57.5
E
E
50
•i
•,
•,,
<
•
J
'0
~ ..... ......
:1o
•
j
•,,•
~
;;•
I""':I
30
Center
Lfne'"
20
. . }+-..
jI /
J ..... ......
t ......
........- ~ .....
I
57.5 mm
I
I
Vi.It:::---':::17'~
LU"--:>
10
o
o
100
50
150
200
250
300
Pressure Ipsi)
-
100% loaded
-+- 90% loaded. Sudden Pressure Removal
-+- 90% loaded, Gradual Pressure Removal
Figure 11. Applied Cavity Pressures for Axisvmmetric
Finite Element Modeling, Three Cases
350
575
E
E
•;
•,
J
,•
50
40
~:~ .....
0
;(
•
",
JO
1
1
;
••,
0
••,•
,
;•
Center
line
20
1
I
· r,mm
.....af-...... . . It <:---: . ...
1
1
~' T/~
.... .:-::-L>- "
10
0
o
o
0.02
0.04
006
0.06
0.1
0.12
0.1<1
Radial Denection (mm)
100% loaded
-+- 90% l oaded, Sudden Pressure Removal
-+- 90% loaded, Gradual Pressure Removal
Figure 12. Radial Deneclion for Axisymmetric Finite
Element Modeling, Three Cases
57.5,-- - -- - - - - - - - - . 1
50
E
g
,•
J
S"
,
•
40
~ ..... ......
30
0
I
I
E
!
•,
0
"•0
"
"
Center
LIne'"
20
57.5 mm
.....
...... 1.I
I
t/ I
'-oJ •.••• ......
......... ~ ......
I
I
1
1,..."'
1/ t-lI
. . ...-::::L _~ . . .
10
oL-______________________
o
1000
2000
3000
4000
Tangentlal Stress (kPa)
-
100% loaded
-+- 90% Loaded, Sudden Pressure Removal
......... 90% loaded, Gradual Pressure Removal
Figure 13. Hoop Stress
~~~
5000
6000
57 .5r;:::;::;;;:;;;:;:::~;;:=.:::;:::::;::::;;;::=.:~:;::=;:,-+=:
100 % loaded Case has Zero Shear Stress I ...
E
i
,,•
,·••
u
"
~ "'"
,
30
E
1,
,,• "
•
"
"
, 'r,mm
.. ...
,
I '- t / 1
.....
I..----..I " ..
ll;;e"
I ....... ~ "t.. I
Center
,
""17"
~-<L-"~
oL-----____________________
.."
.,,,
·300
~------~
o
Shu ' SlrHl (kP'1
100% l oaded
-+- 90% loaded, Sudden Pressure Removal
-+- 90% loaded, Gradual Pressure Removal
Figure 14. Shear Stress
,so
BunJar, AI·Khaleeb, and Bozkun
Ta nKlntial (Hoop) Stress ConvlTSioll Fat1.ors
The conversion faclOrs for tangential st ressts are dttermined based on the maximum
(critical) tangential stress results obtained from the finite element analysis (FEA) at the mid·
height of the hollow cylinder inner wall, and the internal pressure used for analysis 2070 kPa
(300 psi). Where ttcentricity exists. the critical hoop stress occurs at the thinner side of the
hollow cylinder. The conversion factors for hoop stress, based upon finite element load cases
with various combinations specimen heights. cavity eccentricities, and percent inner wall
loading are determined by:
F = (J', •• __
•
P
(3)
Where:
F.,
Hoop stress conversion factor for given FEA load case
Critical {maximum) tangential {hoop) mess for given FEA load case
p '" Applied cavity pressure
Ow "... 1
The dosed form solution for hoop Stress conversion factor for the cavity wall can be
applied in case of no eccentricily and for 100 % loading. By seuing r=a in Equation I and
combining with Equation 3. we obtain:
b! +a !
-,
F"":-b
' ,
(4)
Where:
F.... '" Conversion factor for hoop stresses. based upon doscd·form
solution (100 perctnt loading of cavity wall, no coring eccentricit~')
a '" Inner radius of hollow (ylinder
b
Outer radius of hollow ("\'Jinder
TanGential (Hoop) Strains
The com'erslon factors of tangenlial mains are determined based upon the strains
obtained from the F£:\. again at the nllJdle of the hollow cylinder. and the change in ca\'It~·
volume und~r pressure as shown in equation \3).
(S)
8Ulllar, AI-Khateeb, and Bozkurt
Wher~ ,
F" = Conversion factor for tangential strains for gi\"en FEA load case
t, ""'Kal ::: Critical tangential strain for given FEA load case
:.\ V = Change in volume calculated ba~ on FfA nodal deflection re5ulLS and
equation 6
(6)
Where:
V(; •• I = Volume of the inner cavin' after deformation
V,...".. ::: Volume of the inner ca\'itv lx-fore deformation
Volumes were found by determining crms-sectional areas at each row of elements
throughout the height of the cylinder. based upon nodal coordinates before and after loading.
The cros.s sections were then used to detennine volume using the equation for a frustum cone
for each pair of adfacent cross-sectional areas.
The coll\'ersion factor for tangential strain based upon the dosed fonn solution, f"".
lI'as obtained by manipulating dasticity equations for thick-walled cylinders (Timoshenko
and Woinowsky' Krieger [1959J:
F.. ::
2
I
ITH,D,
(7)
Where:
Fete ::: Conversion factor for hoop strain. based upon dosed-form
solUlion (100 percent loading of cavity, no coring eccentricity)
Equation 7 can also be applied in the case of zero mentricity and 100 % loading of inner
wall.
Table 2 summarizes the HO' conversion factors for ungential stress, while table 3
summarizes HCT conversion factors for tangential strain. A comparison betwetn the
conversion factors from FEA and those from the closed-form solutions. for the case of 100%
loading of inner wall and zero eccentricity is summarized in table 4. The convmion factors
based upon FEA and dosed-form solution are nearly identical. ali should be expected. One
can gain an appreciation for the magnitude of correction factors for cases of partially loaded
inner walls. and eccentrically cored cavities. by comparing the factors of tables 2 and 3. to the
corresponding dosed-form conversion factors in table 4.
Table 2: HCT Convers ion Factors for Hoop Stresses, Fot (kPalkPa)
Height (mm)
Eccentri-
D,
(mml
112
115
116
%loaded
95
90
100
% loaded
%loaded
ci~
~t (mm)lll
100
95
90
100
95
90
0.00
2.658 2.608 2.548 2.658 2.616 2.5&\ 2.658 2.6201 2.578
102.6
5.08
3.1 43 3.108 3057 3.143 3.118 3.076 3.143 3.127 3 094
10.16
3990 3.987 3.957 3.990 4.000 3.980 3.993 4.010 4.003
~'olfference between maximum and minimum wall thickness for eccenlncally-cored speCJmens
Table 3: HCT Conversion Factors for Tangential Strains , Fu (1'10·/ lImml)
Hei hi (mm)
Eccentri-
D,
(mml
,,~
112
116
115
~1 (mm)I'1
% loaded
% loaded
% loaded
100
95
90
100
95
90
100
95
90
0.00
5.396 5995 5578 5.255 5.848 5.424 5.122 5.708 6276
5.127 6.833 7.523 5.968 6.664 7.342 5.815 6.503 7169
102.6
5.08
10.16
7064 7.899 8.714 6.882 7.701 8.498 6.708 7.512 8.291
Difference between maximum and minimum walllhtekness for eccenlncally-cored s~mens
"'
Table 4: Comparison of HCT Conversion Factors: Finite Element Analysis Versus
Closed·Form Solution, ~I = 0.0 mm (no eccentricity), 100% loaded
D,
(mml
l11
t.1 = 0 0 mm
(no eccentricity)
arid 100%
l oaded
Hei hi (mm)
115
112
FEA
ClosedForm
FEA
Closed·
Form
118
FEA
Closed·
Foon
ConverSIOn
Faclor For
5257
5.396
5398
5255
5 122
5124
Tangential
1
Strains (1"10. )
1025
ConversIOn
Faclor For
2658
2659
2658
2659
2658
2659
Tangential
Stresses
( Difference between maximum and minimum walllhickness for eccentncally-cored spectmens
"
ButtJar, AJ-Khaleeb. and Bozkurt
Use of Convers ion Factors
Obtililring Crup Cornpliana
Now (hal the conversion factors for hoop (tangential) stresses and tangemial strains
have been delermined, accurale measures of creep compliance, correctw for actual test
conditions, can ea5i1v be determined, This approach assumes test ml:3surements were
obtained in the linear viscoe:laSlic range of mamial response. In mep testing of asphalt
mixtures, this c~n generally Ix accomplished by testing at 0 C and below, and by keeping
tensile strains in the 5p«imen below 500 microStTains (conservati\'ely) at all times, Thl:
correspondencl: principle allows one to convl:rt elasticity solutions, including finite element
results, to viscoelastic solulion, if malerial response is ml:asured in the linear range.
Based upon measurw pressure and volume change from the Her, one can determine
the stms at the center of the cylinder's inner wall, a" as:
(J , '" F,. • p_
(8)
.-
(9)
{;, = F " oV
Where:
P..... , :: Measured pressure in fluid inside intensifier (kPa)
6. V..... :: Measured volume change in specimen due to cavity expansion (mml)
Fa, and F&, arl: determined from tables 2 and 3. respectively.
Creep complianct can then
Hook's Law:
~
D(,) =
determined using the follov.ing equation. based upon
&,
(J , - p(J,
= ----'&~,-:(J, +J1 " P
Where:
O(t)
Creep compliance (kPa")
I.l '" Poisson's ratio = 0.30 (assumed)
a, '" Radial stress = -p (kPa)
( 10)
Bunlar, AI·Kha!eeb, and 80zkurt
Tensile Strength
Tensil~
sHength can also bt: dmrmined using the conversion factors developed as
follows:
S,
::p~
'F..
(I I)
Where:
Pi........ :: lnu:rnal pressure recorded at lime of specimen failure
Sensitivity to Poisson 'f Ratio
For the HCf, deflection, and hence modulus or compliance measurements are
affected by Poisson's ralio, while tensile strength is independent Poisson's ratio. Sensitivity
analyses revealed that a maximum error in me.1sured modulus or compliance of about 5% \\;11
occur by simply assuming a v.1lue of 0.3 for Poisson's T.1tio in the HCT. Alternativel),.
additional transducm can be added to the HCf to enable direct measurement of Poisson's
ratio (ligure 5), The principle is that since Poisson's dfect causes the height of the cylinder
to decrease when pressure is applied to the inner cavity, measurements of chang~ in specimen
height could be used to determine the Poisson's ratio of the material being tested. The
measured Poisson's ratio could then be used in equation 10 in lieu of an assumed I'alue,
although correction fa ctors F~ and F" would be needed for values of Poisson's ratio other
than 0.3.
Preliminary Test Result s
PreliminalY tests have been performed using the prOtOtype HCT del'ice to determine
the accurac)' of the device in measuring the strains and deflections, and to inveStIgate the
feasibility of the HCf mode for determini ng the tenSl[e properties of asphalt concrete
mixtures at low temperatures. Calibration spelimens of Aluminum and Delrin plastiC were
fabricated to lest Ihe prolOt)'pt: unit using specimens of varied rigIdity, or 20.7 and 2.i ) CPa
(3,000,000 psi and 400,000 psi), respectil'ely (figure 15). t\ re sistance·t~'Pe strain gage was
mounted on the outside of the aluminum C\'linder \0 check measured \'ersus theoretical
strain. The results of lhe firsl testS run on th~ prOtOI ~'pt HCf were quile good, as
summarized in labl~ 5. The predlftion of strain on an aluminum l.yhnder, and the prediction
of the modulus ot' el a sll~'lty of a l)e[rin plastiC ~-:-'1inder we r~ bolh \\;thin 1% of the t:xpt(led
n:sult.
Bunlar, AI-Khatetb_ and BozkuJt
Figure 15. Hollow Cylinder Tensile Tester Prototype Along
With Aluminum and Oelrin Plastic Calibration Cylinders
Table 5. Preliminary Test Results
Material
Delrin Plastic
Aluminum
Test Description
Estimate Modulus
of Delrin Hollow
Cylinder
Estimate Strain on
Outer Wall of
Aluminum Hollow
Cylinder
Expected Resull
E =2.76 GPa
(Manufacturer
Reported Value)
, =379.6
microslrains
(closed-form
solulion)
Measured Result
E - 2.75 GPa
380
microstrains
I: -
Prtliminary Tat 0" Asphall Mixtun Spedmm
A preliminary low-temperature test has now been performed on a dense-graded Illinois
surface mixture with an AC-20 binder. The results of creep testing al -25 C are presented in
figure 16. Under an applied pressure of 379 kPa (55 psi), which corresponds to a tensile
stress of 993 kPa (144 psi) (equation 8). approximately 4.06 microns (160 microinches) of
deOroion were obtained in the 45·second test (using measured volume change due to
cylinder expansion during testing). At 10 seconds loading time, about 5.16 microns (13 1
160
];
f
..
e
r-=====:::~::1
Appned T.nslle Stress '" 993 kPa (144 psi)
120
.!!
E
o
80
f
;;
!
•o
--
40
~
o~------------------------------~
10
20
30
40
o
Time (sec)
Figure 16. Preliminary Creep Test Result with the Prototype HeT for Dense-Graded
Surface Course Mixture at -25 C
Buttlar. Al·Khateeb. and Bozkun
microinches) of denection occurred , which corresponds to a creep compliance (equation 9) of
019 GPa ] (8.16 . 10 1 psi]). or 8.4 GPa (1.23"100 psi) stiffness modulus. which is very
rtasonablt for this material at this temperature. Despite the rather crude naturt of the
prototype HCT at the time of this testing. the crtep curvt obtained was extrtmely dean and
stable Tht L\'OT signal stability and resolution is a direct result of the advantage of
measuring cavity expansion to obtain ci rcumferential strain. Even with thtse very small
strains 4.06 microns (160 microinches). the cavity expansion was about 0.26 mm l
{O.016in'1. which corrt sponds \0 a piston movement of 0.28 mm (0.011 inches). A
movement of this magnitude can be measured with ease \\;th a slandard lVo T.
Due \0 the crudt temperature control system used in this early prototype (endosed
chamber cooled with dr;.' ice). a testing delay caused the system to warm up. such that
strength tests were performed when temperature equillibrium was restored at -16 C. The
internal cavity pressure was ramped until the specimen ruptured at 938 kPa (1 36 psi), which
corresponds to a tensile strtngth of 2442 kPa (354 psi) using equation 10. Again. this value
is very reasonable for this material at this tI:mperature Tensile strengths usually vary from
about 1725 to 3450 kPa (250 to 500 psi). in the range of -10 to -20 C.
Al though the test results to date on reference materials and asphalt mixtures look very
promising, obviously much more testing is needed to validate the accuracy and repeatability
of the HCT.
Key Issues to Resolve through Additional Testing
Panicle Siu·to·WaIlThickntJs Ratio
The wall thickness of HCT specimens in the prototype arrangement is 25.4 mm. It
could be argued that the wall thickness to maximum aggregate (stone) diameter ratio is too
small , and could l~ad to inaccuracies. For unbound aggregate masses, a specimen size to
maximum particle diameter ratio of approximately fiv~ is desired. as a rule of thumb (Height
et al. [1 983)). Obviously. there is no way to satisfy this criterion if tensile properties are to
be obtained from a gyratory·sized specimen, regardless of the test method ustd. However,
the extent to which this rule of thumb appHu to bound aggregate materials. such as asphalt
concrete is not well understood. ~ mentioned earlier. the HCT has an excellent gage length.
to· maximum particle size ratio in the dirtttion of measurement (around the hoop on the
inner cavity wall). since the inner ci rcumference of the sptcimen is over 300·mm in length.
One way to resolve this issue is through testing of mixtures with varying maximum
aggregate size in the HCT. [n addition, sptcimens of varying wall thiclrness could be tested
in the HCT to ~ dentify minimum wall thiclrness requirements for various types of mixtures.
Properties measured on identical mixtures using the lOT and direct tension ttsting mode
could be used as an additional basis of comparison.
Effects of Density Gradients and Broken Particles in Gyratory Compacted Spttimens
Since the HCT specimens represent th~ outer 25-mm ring of a gyratory specimen,
significant density gradients in the specimen could affect the measured properties, depending
Buttlar, Al-Khatccb, and Bolkun
upon mixture composition and compactive effon . Harvey et al. (! 994) and Shashidhar
(! 998) have shown that density gradients in gyratory-compacted specimens can be
significant. The effects of aggregate orientation and aggregate crushing, particularly near the
outer portion of the specimen, where aggregates are in contact with the steel gyratory mold,
should also be investigated. It is envisioned that mixtures with larger andlOT weaker
aggregates, including fl at and elongated aggregates, will show the most pronounced effects.
Testing should be conducted on cylinders obtained from gyratory specimens and those
cored from slabs to assess the magnitude of theSt effects. ill a control case, !DT tests should
be performed on a similar set of specimens. Conlrol tests are necessary to quantify the
magnitude of differences that exist simply becauSt slab and gyratory compaction do not yield
identical specimens, regardless of the physical test they will be used in. Also deserving
investigation is the feaSibility of *double coring" gyratory specimens, to discard the oUlermost
ring of material , if deemed necessary. A slightly smaller inner diameter could then be used to
maintain adequate wall thickness.
It should be recognized, however, that maximum hoop mess occurs at the inner wall
of the HCT specimen, which is gradually reduced to sixty-three percent of this value on the
outer wall (figure 4) . Thus, material closer to the inner wall of the cylinder, which is less
likely to have been altered by edge effects in gyratory compaction, governs a larger portion of
the material response.
Tensile Strength Determination
One advantage of the four deflection transducers required in the !DT is the ability to
identify "first failure " of the specimen, which is in turn uStd to determine the true tensile
strength of the mixture (Bultlar et al. [1996]). The peak value of vertical minus horizontal
deflection was found 10 be a good indicalOr of fi rst failure in the lOT, and occurs, on average,
at about eighty percen! of the ultimate load 10 complmly fail the specimen. It is unknOlITI
whether or not the onStt of failure will be dearly evident from the deflection measurement
(piston movement and hence change in cavity volume ) obtained in the proposed HCf
arrangement (figures 5 through 7). However, it is suspected that the difference in load at
fi rst failure and ultimale load \\~11 be fairly small in the HCT, since tensile suesses are fairly
uniform across the wall of the C\'Hnder. Future studies should include the use of crack
detection gages al various locations on the inner and OUlcT walls of HCT speci mens \0 stud~'
this issue in more detail.
Other Potential Modes and Appl ications of the HCT
In addition \0 creep compliance an..! tensile strength. the HCT should be capable of
obtaining other usdul asphah concrete propmies, including POisson's ratio, resilient
modulus, and dynamiCmodulus. Funhermore, use of the HCf 10 obtain measures of fatigue
resistance, fracture toughness, and moisture sensitil'it~' of asphalt mixtures will be
investigated. Olher materials that (oulJ potentially be tested in the HCT mode include:
Portland cement concrete, mortal>, ceramics, polymers, asphalt binders, asphalt mastics, and
cohesive soils. For heterogeneous materials or nl.llaial s lI"ith small particks, smaller test
specimens could be used.
Buttlar, AI·Khatecb, and B07.kUrt
The simplicity, versatility, and portability of the HCT suggests that the device has
merit for use in quality controVquality assurance of hm·mix asphalt construction. Tensile
strength, modulus. andlor compliance could be measured on as·produced or as·constructed
materials at periodic intervals. This would ensure that any changes that occur in production,
induding changes in properties of malerials, proportioning, etc., would not Significantly alter
these important fundamental mixture properties. Tests could be performed on cylinders from
gvratory·compacted spe<:imens, which are normally produced for control of volumetric
plOperties. or from cores obtained from the compacted pavement In the case of field cores.
it would be necessary to use the HCf arrangement shown in figure 6. This arrangement
allows the tesung of shorter cylinciers, such as would be needed to characteriu a single
p.m ng lift.
Summary and Conclusions
A new hollow cylinder tensile test (HCT) device was developed, which can be used to
obtain fundamental tensile properties of brittle materials such as asphaltic paving mixtures.
These propmies include creep compliance, tensile strength, and dynamic modulus, at low
and intermediate temperatures. The theoretical and experimental results obtained can be
summarized as follows:
I. The hollow cylinder test mode provides a favorable method for imparting tensile
stresses to brittle materials, such as asphalt concrete, with minimum stress
concentrations.
2. The HCf takes average properties over the entire inner wall of the specimen,
which is over 4()() mm long in circumference and 115 mm high for standard
gyratory-siztd specimens (about 460 square centimeters) . This offers excdlent
resolutio!! and gage length-to-partide size ratio in tht direction of measurement
(along the inner wall of tht cylinder).
3. Finite elemtnt·based conversion factors were presented, which allow stresses and
maim to be accurately determined from test mtasurements. Test arrangements
with partially loaded cavity walls andlor tests performed on eccentric.ally-cored.
specimens require tht use of the finite elemtnt formulas presented.
4. A second LVOT can be added to the HCT to directly measure Poisson's ratio:
however, the added complexity does not appear to be justified for most
applications. On the other hand. hoop stress, and hence, tensile strength is
independent of Poisson's ratio.
5. Preliminary teslS have verified the accuracy of the HCf modt using calibration
cylinders of known properties. Tests on asphalt concrete spedmens have given
promising results, but much more experimentation is needed to validate accuracy
and precision of the HCf device.
Based upon tht rtsults of this study, the following conclusions can be drawn:
Bunlar, Al-Khateeb, and Bozkurt
I. The HCf has many potential advantages for obtaining fundamental proptrties of
bnuie matenals, such as asphalt concrete, and funher development and validation
of test results should be pursued.
2. The Her appears to have the Simplicity, versatility, and portability to be used for
routine measurements of modulus and strength. Thus, the Her has potential
application as a supplement to volumetric mixture design, such as Superpave
level I mix design.
3. The simplicity, versatility, and portability of the HCf suggests that the device has
ment for use in quality controVquality assurance of hot·mix asphalt construction.
Acknowledgements
The authors would like 10 acknowledge the Significant contributions of Mr. Tom
8rovold and Mr. Jim Adams ill the design, asstmbly, and preliminary testing of the protOtype
hollow cylinder tensile tester. Without their expertise and dedication, this work would nOl
have been possible.
References
Alavi , S. H., and C. L Monismith, "orne and Temptrature Dependent Propenies of Asphalt
Concrete Mixes Tested as Hollow Cylinders and Subjected to Dynamic Axial and Shear
wads", Journal of Iht Assodatlilll oj Asphalt Pavmg TechllDWgists, Vol. 63, pp. 152-181 , 199-1.
Buttlar, W. G. and R. Roque, "Experimental Development and Evaluation of the New SHRl)
Measurement and Analysis System for Indirect Tensile Testing of Asphalt MiX"tures at Low
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National Academy Press, Washington, D. c., pp. 163-171 , 1994.
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Hight. O. W. A. Gens. and M. I. S~'mes . ~The Ot'velopment of a New Hollow Cylinder
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33. pp 355·383. [983.
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MPerformance Models and Validation of Test Results·, FIIlIII Ripon Iil Strategic Highway
Rtlt~r{h Progrll/lr. Asphalt Proiect A·OO5. Repon SHRP·t\·357. National Academy of Sciences.
\\"a ~hi nglOn . 0
1993.
c..
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