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EXPERIMENTAL STUDY ON STRUCTURAL RESPONSE OF RIGID PAVEMENTS
UNDER MOVING TRUCK LOAD
M. Y. Darestani, David P. Thambiratnam and A. Nataatmadja,
Department of Urban Design, Queensland University of Technology,
Australia Daksh Baweja, Rinker Australia, Australia
ABSTRACT
The structural adequacy of a rigid pavement can normally be
predicted based on its structural response to the applied loads.
While considerable knowledge of pavement behaviour under static
loads is available word-wide, only very limited number of studies
have been carried out in the past to determine the effect of
dynamic loads on rigid pavement deteriorations. Hence, opinions
differ as to which type of load (static or dynamic) results in
greater values of base deflection or flexural stress.
In the present study, a rigid pavement test section consisting
of two jointed reinforced concrete pavements and two jointed plain
(unreinforced) concrete pavements was constructed and tested under
both quasi-static and dynamic truck loads. Truck load was allowed
to wander at predetermined locations on top of the instrumented
pavement. Nominal speeds from 5 km/h to 55 km/h were used in the
study. Various devices including strain gauges, displacement
transducers, vertical accelerometers and thermocouples were
installed at different depths along the test section. A total of
5184 time history responses of the test section were recorded.
Results indicate the importance of dynamic analysis in rigid
pavement design.
INTRODUCTION
The serviceability and longevity of rigid pavement constructions
depend on the rate of pavement deterioration which is a function of
factors such as material properties, climatic effects and vehicular
load characteristics. As the main reason behind deterioration and
delamination processes, cracks can be considered as a tensile
failure in concrete pavements. Cracks can occur at any location
within the pavement where tensile stresses exceed the concrete
flexural strength. Tensile stresses are induced in a rigid pavement
due to bending action of concrete base under vehicular as well as
climatic forces. The pavement response to these loads can be
individually calculated and be then superimposed to determine the
total value of stresses or deflections provided that the pavement
materials exhibit an elastic behaviour. While current rigid
pavement design procedures are well established, questions still
remain as to the accuracy of the assumptions used.
Most recent rigid pavement design guides have been based on
empirical-mechanistic approaches. Field data derived from the
American Association of State Highway and Transportation Officials
research (AASHTO, 1962) have been widely used in the empirical part
of design procedures. While the mechanistic part of design guides
provides required information on calculation of the critical
stresses and deflections in pavements, the empirical part specifies
possible failure modes of pavements under applied loads. The
predominant failure modes in many rigid pavements are faulting and
fatigue cracking (Roesler et al., 2000). However, the most critical
failure mode in AASHTO (1962) test sections was erosion of subbase
or subgrade materials
Vehicular loads have been assumed as static loads in rigid
pavement design guidelines because dynamic analyses and
experimental tests on rigid pavement in the past showed that
dynamic loads has no effect on pavement responses. For instance,
AASHTO (1962) showed that an increase in vehicle speed from 3.2 to
95.6 km/h decreases the value of pavement
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responses by about 29 per cent. However, recent analytical
studies of rigid pavements under dynamic loads (Bhatti and Stoner
1998, Liu and Gazis 1999) indicated that significant effects of
dynamic loads were observed when surface roughness was taken into
account. Furthermore, Izquierdo et al. (2002) found that velocity
can noticeably change the value of base deflections or stresses of
a plain concrete pavement resting on a subbase with low stiffness
under very heavy truck loads.
Analytical dynamic analysis of Jointed Plain (unreinforced)
Concrete Pavement (JPCP) and Jointed Reinforced Concrete Pavement
(JRCP) under different moving axle group loads (Darestani et al.,
2006) indicates vehicle speed has a significant effect on pavement
responses even when a smooth surface is considered. Furthermore,
diagonal, corner, and transverse cracking may be addressed by
consideration of vehicle speed. However, no recent experimental
test on rigid pavement dynamic responses has been conducted to
demonstrate the effect of heavy vehicle velocity on rigid pavement
damage.
In order to address the aforementioned problems, a fully
instrumented rigid pavement test section consisted two concrete
bases namely, JPCP and JRCP was constructed and tested under either
quasi-static or dynamic truck loads. This paper describes the test
procedure and presents some significant outcomes of the test.
PROJECT DESCRIPTION
An experimental work on rigid pavement performance under dynamic
truck loading has been conducted by Queensland University of
Technology (QUT) and a major Australian concrete producer, Rinker
Australia, at Rinker sand quarry in Oxley Creek, southwest of
Brisbane. This location was selected since a weighbridge is
available to provide data on truck loads, number and type of axle
groups which can be recorded for long term pavement performance
monitoring. Furthermore, geotechnical information on subgrade
properties including soil classification, soil profile and texture,
bulk density, the Atterberg limits, and CBR, which had been derived
from surface and depth explorations of the site in 2001, is
available in Readymix archive at Milton Branch.
The test section has 32 m length, 5.1 m width and 250 mm
thickness. It consists of two JPCP and two JRCP which have been
constructed over 150 mm concrete subbase resting on a stiff
subgrade (CBR = 14%). The widths and lengths of the concrete bases
are 3.6 m and 4.6 m for JPCP and 3.6 m and 10 m for JRCP,
respectively. The concrete subbase (32.5 x 5.5 m) was constructed
on top of a sand layer with maximum aggregate size of 3 mm. The
thickness of the sand layer was about 15 mm. The sand layer was
placed on the subgrade layer to firstly create a separation between
subbase and subgrade and secondly, to develop a level platform for
subbase. The subbase was left to shrink for one week before
constructing the concrete bases and shoulder.
Figure 1 shows the layout of the test section. An additional
JPCP section (1.4 m x 3.6 m) is placed at each longitudinal end of
the test section to restrain the free transverse edges and simulate
the conditions of a long stretch of pavement.
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Figure 1: Layout of the test section
A mesh reinforcement layer of round bar with a diameter of 9 mm
was used in the JRCPs. Two vertical locations of reinforcement
namely close to top surface layer of the concrete base (50 mm deep
from top surface layer) and close to bottom surface layer of the
concrete base (200 mm deep from top surface layer) were considered
in this study to determine the effects of reinforcement location on
the pavement responses and consequently the damage progress.
Voids (250 mm L x 150 mm W x 250 mm H) were formed by inserting
expanded polystyrene blocks at the intersection between the
transverse and the longitudinal joints along the confined edge of
the pavement to install linear displacement sensors. Steel sections
(25 mm x 25 mm x 3 mm), 1500 mm long each, were driven into the
subgrade as appropriate and used as mounting poles of the
displacement sensors. Only 350 mm of the total length of these
steel poles protruded above the subgrade surface layer. Note that
the centre of the mounting pole’s cross section was located 20 mm
away from free edge and at the centre of void formed along the
confined edge.
Shoukry et al. (2002) mentioned that the contact stress between
loaded round dowels and concrete can be quite high Although round
dowels are the most widely used in pavements, research elsewhere
showed that different shaped dowels such as flat plates and oval
dowel bars can increase the bearing area without increasing the
cost or mass of the dowel bar. Therefore, flat plate dowels that
are widely used for slabs on ground were employed for this study.
With the use of flat plate dowels, the effect of dowel locations
within the concrete base can be studied.
Each transverse joint was dowelled by eight flat plate dowels
(300 mm x 50 mm x 6 mm). Since one side of the dowel was coated by
a PVC sleeve, longitudinal movements of the concrete bases on both
sides of the transverse joint were not restrained. Dowels were
vertically positioned at three different depths to determine the
effects of dowel positions on load transfer efficiency (LTE) of
joints and pavement performance. The locations of the dowels
(measured from the top of the concrete base) were 55 mm, 125 mm (at
mid-depth) and 200 mm (see Figure 1).
One of longitudinal edges of the test section was confined by a
shoulder. Hence, round tie bars (12 mm Ø, 1000 mm long) were
positioned at middle depth of longitudinal joints. Four tie bars
were used in each JPCP and eight in each JRCP.
To minimise the effect of drying shrinkage and differential
temperature gradients in concrete pavements, a friction reducer
layer may be placed between concrete base and subbase.
Consequently, bonded, unbonded, and partially bonded boundary
conditions between concrete base and subbase may be created
depending on the value of the friction coefficient between these
layers.
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Most analytical research conduced in the past was based on fully
bonded or fully unbonded boundary condition between concrete base
and subbase (Heath and Roesler, 1999). The use of debonding
materials usually results in partially unbonded boundary condition
between concrete base and subbase (Zhang and Li, 2001). Note that
fully unbonded conditions could only be achieved by using a double
layer of polyethylene sheets (Tarr et al., 1999). In contrast, Yu
et al. (1998) stated that friction between concrete base and
subbase is sufficient to produce bonded behaviour even if
polyethylene sheets are placed between them. In reality, only
devices such as anchor or shear stud can create a fully bonded
boundary condition.
As structural responses of concrete pavements to vehicular load
are highly affected by boundary condition between concrete base and
subbase (Tarr et al., 1999), half of the test section incorporated
a single layer polyethylene sheet between the base and subbase (see
Figure 1) to determine the effects of debonding on the dynamic
responses of the test pavement.
Evaporation retardant was poured at top surface of the concrete
base during levelling to protect the concrete bases against plastic
shrinkage. The results of a concrete pavement analysis by the
Authors (Darestani et al. 2006) showed the importance of dynamic
analysis even when a smooth surface is considered. To verify these
results, the concrete surface was subsequently floated by a power
trowel. Note that an increase in pavement roughness will result in
higher induced dynamic responses (Bhatti and Stoner, 1998; Liu and
Gazis,1999).
Zollinger et al. (1994) indicated that early-age sawing methods
with sawing depths less than 0.25d (d=slab depth), should provide
better crack control than conventional methods with depths of 0.25d
or 0.33d. Sawing sooner with early-age saws can take advantage of
larger changes in the concrete's surface moisture content or
surface temperature, which has been shown to induce cracking
(Okamoto et al., 1994). Therefore, transverse joints were prepared
using soft sawing method three hours after initial set. The width
and depth of the saw cuts were 10 mm and 50 mm, respectively. The
width of the sawcut joints allowed easy installation of
instrumentation wires across the test section.
An unreinforced shoulder with 1.5 m width and 250 mm thickness
was poured about 15 hours after constructing the concrete bases. It
contains five dowelled transverse joints. Four flat plate steel
dowels were installed at each transverse joint. Dowel dimensions
are similar to those used in the concrete bases. Due to problems
with the concrete saw, transverse joints of shoulder were saw-cut
36 hours after initial set.
INSTRUMENTATIONS
A total of 120 electrical gauges including 120Ω electrical
strain gauges (ESGs), linear displacement transducers (LDTs) and
strain gauge based vertical accelerometers have been used to
investigate the structural response of the test pavement under
either static or dynamic loads.
Since recent research (Choubane and Tia 1995, Health and Roesler
1999) showed a strong interrelationship between temperature
gradients and damage potential of concrete base, four thermocouples
were evenly installed at different depth within the concrete bases.
Recording of temperature gradients was started 24 hours after
initial set.
Two types of ESGs, namely embedded and standard (glued to
surface layer of structure), have been used. Embedded strain gauges
should be fully covered by concrete to accurately measure the
induced strains in the concrete. Hence, they were installed at a
depth of 225 mm from the top of the concrete base using a rebar
chair. The locations of the strain gauges are shown in Figure 2
while those of the LDTs and accelerometers are shown in Figure 3.
Note that none of LTDs was installed close to the first and the
last transverse joints or in the additional JPCP sections (1.4 m x
3.6 m, see Fig. 1) as load transfer efficiency of these transverse
joints may be affected by the dimensions of these additional
sections.
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An eDaQ dynamic data acquisition system with 48 channels
including 16 specific channels for strain gauges and 32 general
purpose inputs was used to record time history responses of each
individual instrumented point of the test section. InField analysis
software developed by Monash University was utilised for data
processing. Since the eDaQ data acquisition system only has 48
channels, three different recording setups were utilised. Each
setup utilised 32 switchable channels and 16 dedicated channels.
Half of switchable channels were always connected to 10 ESGs and 6
LDTs to provide benchmark readings.
Figure 2: Locations of strain gauges
MATERIAL PROPERTIES
The subgrade soil was a silty clay loam with a compacted bulk
density of 2.18 t/m3 (AS1141.4). The maximum dry density of the
soil was 1.86 t/m3. Particle size distribution (AS1141.12) showed
that 70.7 per cent of aggregate was finer than 0.075 mm. Liquid
limit, plastic limit and plasticity indices of the fines were 22.8,
14 and 8.8 per cent, respectively. Subgrade CBR was 14 per cent.
The average 28-day concrete compressive and flexural strengths were
7.3MPa and 1.55MPa for the subbase, 50.5MPa and 5.45MPa for the
bases and 38.5MPa and 4.1MPa for the shoulder, respectively.
Figure 3: Locations of linear displacement sensors and vertical
accelerometers
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VISUAL MONITORING OF THE TEST SECTION
The test section was closely monitored for the first 28 days
after casting the concrete base. The first top-down crack occurred
within 2 days after casting at the middle of JRCP where mesh
reinforcement layer had been positioned close to top surface layer
of the base (Fig. 4). Two random surface cracks of about 150 mm
long were also noticed in the same concrete base at the same time.
It should be noted that this part of the test section did not have
a debonding layer between concrete base and subbase. All the above
mentioned cracks were very fine hairline cracks. Other bases showed
no cracks. Crazing cracks were observed in all concrete bases one
week after initial concrete set suggesting inadequate curing or
ineffective evaporation retardant. Apart from being unsightly,
these cracks do not affect the structural integrity of the
concrete.
Two shrinkage top-down transverse cracks were initiated close to
transverse joints in the shoulder (see Figure 4) within 36 hours
after casting. It should be noted that transverse joints in the
shoulder were sawed after the cracks had appeared. Another
transverse crack occurred 2 weeks after casting in the depth of
shoulder and at the middle length of it where shoulder has 10 m
long and had a partially bonded interface between base and subbase.
During this period, two small diagonal cracks (100 mm long) were
also initiated in the concrete bases close to the transverse
joints. No additional visible cracks were noticed in the concrete
bases or shoulder during the first 28 days. However, the width of
one of the transverse cracks in the shoulder increased by about 2
mm (see Figure 4). In the long run, the crack widening may decrease
the load transfer efficiency of transverse joint in the shoulder
due to the possible corrosion of dowels and may also result in
joint faulting.
Figure 4: Locations of cracks in the test section
As mentioned earlier, the subbase was left to shrink for one
week before constructing the concrete bases and shoulder. Hence,
several transverse, longitudinal and diagonal cracks were initiated
and propagated in it due to environmental forces.
TRUCK CHARACTERISTICS, MOVEMENT AND SPEED
A semi-trailer truck with a gross weight of 477.3 kN was used to
apply traffic load in one direction. Truck contains three different
axle groups namely Single Axle Single Tyre (SAST), Tandem Axle Dual
Tyre (TADT) and Triple Axle Dual Tyre (TRDT) of 60.6 kN, 206.2 kN
and 210.5 kN respectively. Tyre inflation pressure in all tyres was
set to be 750 kPa.
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Figure 5: Tyre and axle group configurations
Exact measurement of tyre contact area could be done using
methods such as the multiple overlay technique (Sharma and Pandey,
1996). However, for simplicity, in this study the contact area was
determined by measuring the size of imprint left by the tyre on top
of the base after spraying paint around the tyre. Information on
truck configuration and tyre pavement contact area are shown in
Figure 5.
Three longitudinal coloured lines were drawn at different
locations on top of the concrete bases to help driver maintain the
truck movement at a certain distance from the longitudinal joints.
These include a red line close to the free longitudinal edge of the
pavement, a blue line close to the confined longitudinal joints of
the test section and a yellow line between them to symmetrically
apply the truck loading on both sides of the centre line of the
test section. The truck was driven along the aforementioned lines
at various nominal speeds including 5, 20, 35 and 55 km/h. Higher
speeds could not be achieved in this study as they would need a
longer acceleration distance. Pavement time history responses under
moving truck load were recorded thrice for each individual speed
and position of the applied load to accurately determine the
structural responses of the test section. In total, 5184 time
history responses of the test section were recorded. Real truck
speeds for each individual channel were finally calculated based on
the configurations and distance between axle groups and pavement
time history responses.
RESULTS AND DISCUSSION
Differential temperature gradients and loss of moisture content
through the depth of the concrete base may affect the pavement
response. However, since the variation in ambient temperature
during the tests was small (less than 1ºC), pavement curling can be
assumed to remain constant in the analysis. Nevertheless, a finite
element analysis may help to develop a better understanding on the
effects of the aforementioned factors on the dynamic response of
concrete pavements. This analysis is currently being done by the
Authors of the current paper and the results will be published
elsewhere.
InField analysis software was used to develop time history
responses of the concrete bases, JPCP and JRCP, under moving truck
load for different locations within the test section. Results were
then redrawn to appropriate scales using Microsoft Excel for
comparison. The dynamic amplification (DA), which is defined as
(Dynamic response / Static response)-1) ×100, was then calculated
for each individual channel. Whilst DA varies with truck speed,
only the maximum and the minimum captured DA are presented and
discussed in this paper. Results can be summarized as follows:
Concrete base deflection
A comparison between base deflections at the corner and at the
mid-length of free edge was firstly done for results validation as
corner deflection was expected to be greater than other
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deflections. Furthermore, for subsequent validation processes,
it was also expected that base deflections along a free edge would
be higher than the corresponding deflections along a confined edge.
Result shows that base deflection decreases from the corner of free
edge towards mid-span and confined edge. Base deflection at the
corner is about 60 per cent greater than those at the middle of the
free edge.
Concrete base deflection is strongly affected by truck speed so
that dynamic amplification varies between 55 per cent and 313 per
cent depending on the base type, interface between base and subbase
and location of measurement. Greater dynamic amplifications occur
along the confined longitudinal edge of the test section though the
base deflection values of these points are relatively lower than
those along the free longitudinal edge. Figure 6 as an example of
the current study outputs shows time history base deflections for
different speeds at the corner of free longitudinal edge (DL7, see
Figure 5) in JPCP. The critical truck speed (which creates maximum
base deflection) depends on several factors such as the location of
measurement and the type of concrete base. Hence, medium speed in
some cases results in greater base deflection (Figure 7).
Figure 6: Time history deflection responses for different speeds
at DL7
Vertical location of reinforcement layer also affects base
deflection responses. Results of the current study show that base
deflections in JRCP where reinforcement was located close to the
top of the concrete base is about twice the values from other JRCP
where reinforcement was located close to bottom of the concrete
base (Figure 8).
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Figure 7: Time history deflection responses for different speeds
at DR13
Study of dowel performance under moving truck load indicates
that load transfer devices at transverse joints exhibit a stiffer
behaviour under dynamic load (higher speed) than quasi-static load
(lower speed). In other words, the value of load transfer
efficiency (LTE% = (deflection of unloaded slab / deflection of
loaded slab) ×100) of transverse joints under dynamic load is
slightly greater than static load. Results also indicate that the
value of LTE in transverse joints under truck loads is not constant
and depends on type of axle groups, the applied load and truck
speed (Fig. 9).
Figure 8: Time history deflection responses in JRCP for
different reinforcement locations
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Figure 9: Time history deflection responses at transverse joint
(truck speed 49 km/h)
A comparison between time histories of base deflections at the
corner of the confined edge (Figure 10) shows the importance of
dowel position in depth of concrete base. The base deflection under
TADT and TRDT significantly decreases when dowels are positioned at
the mid-depth of the concrete base. On the other hand, with dowels
placed close to the top of the concrete base, lower base deflection
results under SAST loading. Hence, for the flat dowels used in this
work, the best dowel location would be at, if not slightly above,
the middle of the concrete base depth. As mentioned earlier, none
of the LTDs was installed close to the first and the last
transverse joints or in those JPCP having 1.4 m length (see Figure
3).
.
Figure 10: Comparison between dowel positions based on critical
speed
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Induced tensile stresses
Tensile stresses are also affected by truck speed. Dynamic
amplification of tensile stresses varies between -10.8 and +108.9
per cent. A small number of recorded stress time histories shows a
decrease in the magnitude of tensile stresses when truck speed
increases. Most time history stress responses suggest a need to
consider dynamic loading in rigid pavement design. Figure 11 is an
example of recorded stress time history where dynamic loads result
in greater stress values than static loads.
Figure 11: Time history stress responses in JRCP at TCL12 for
different truck speeds
Although dynamic amplification shows the significance of dynamic
analysis, it does not mean that the location where tensile stress
is greater than of other locations has a greater dynamic
amplification. For instance, the maximum dynamic amplification at
TCL12 (Figure 11) is about 3½ times more than the maximum dynamic
amplification at TCL8 (Figure 12), however, the maximum tensile
stress for each individual speed at TCL8 is relatively greater than
those at TCL12. Further observations can be made when the location
of TCL12 and TCL8 are taken into account (see Figure 2). Both
strain gauges, TCL12 and TCL8, were installed close to transverse
joints, in the same distance from free edge and at top surface
layer of the JRCP where reinforcement has been located close to the
bottom of the base. Boundary conditions between base and subbase
for both points were similar. However, dowels were located close to
the top of the concrete base for TCL12 and at the mid-depth of the
concrete base for TCL8. A comparison between maximum induced
tensile stresses at TCL12 and TCL8 for each individual speed
indicates that tensile stresses at transverse joints increase by
87.5, 9.4, 45.1 and 6.1 per cent with truck speeds (real truck
speeds) of 5 (4.8), 20 (16.5), 35 (32.2) and 55 (44.3) km/h,
respectively, when dowels are located at the mid-depth of the
concrete base.
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Figure 12: Time history stress responses in JRCP at TCL8 for
different truck speeds
Tensile stresses in both JRCPs are greater than those in JPCP.
While the difference in panel lengths may have contributed to the
results (the length of uncracked concrete base panel in JRCP is
about twice the length of concrete base panel in JPCP), the
reinforcement may also have some effects. Note that no crack was
observed in JPCP and JRCP where reinforcement was positioned close
to the bottom surface layer of the concrete base. Commonly, the
recommended position of the longitudinal steel is between 1/3 and
1/2 of the depth of the base as measured from the surface. However,
effects of reinforcement location on pavement dynamic tensile
stresses in the current study are still unclear at this stage as
analyses of time history responses have not lead to a specific
conclusion.
Vertical acceleration in concrete bases
Results of the current study indicate that vertical acceleration
in rigid pavements depends on the distance between transverse
joints, boundary conditions between base and subbase, provision of
shoulder or adjacent traffic lane, and traffic wander. An increase
in length of concrete base panel or the use of bonded interface
between base and subbase can increase the vertical base
acceleration. This acceleration also increases when the moving load
is applied close to free longitudinal edge of the pavement.
Provision of shoulder or adjacent traffic lane decreases the
vertical acceleration in the concrete bases.
Results of the current study indicate that the absolute concrete
base vertical acceleration varies between 0.001 g and 0.62 g, in
proportion with the nominal truck speed ranging between 5 km/h and
55 km/h. It is known that acceleration and speed of structural
deflection induce dynamic forces in a structure. This dynamic force
may increase or decrease at the certain time depending on the
magnitudes of acceleration and speed. Consequently, at certain
location, the tensile stress in this experimental rigid pavement
may either increase or decrease due to the dynamic loading effect.
Understandably, slab curling and warping can affect these results.
Further study will therefore be carried out on these factors by
means of finite element techniques.
CONCLUSION
A fully instrumented rigid pavement test section including JPCP
and JRCP was constructed and tested under quasi-static and dynamic
truck loading. Information on the test section, instrumentation
layout, material properties and truck characteristics were
described.
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Pavement performance under environmental conditions was studied
during the first 28 days after casting. Truck loading was
subsequently applied at different location of the pavement. Time
history responses were recorded for nominal truck speeds between 5
km/h to 55 km/h.
Investigation of the recorded time history responses of the test
section indicates the importance of dynamic analysis in pavement
design. Results also indicate that dowel position can strongly
influenced the pavement responses. Furthermore, the base deflection
in JRCP decreases when reinforcement was located close to bottom
surface layer of the concrete base. Further studies are needed to
determine effects of reinforcement position on induced dynamic
stresses of the pavement.
Since variation in subgrade property, differential temperature
gradients and loss of moisture contents within the concrete base
may influence the dynamic responses of the concrete pavement,
finite element analysis approaches shall be carried out to address
the effects of these parameters on dynamic responses of concrete
pavements. This work is currently in progress and the results will
be subsequently published.
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ACKNOWLEDGEMENTS
The original work of this study was sponsored by the Queensland
University of Technology (QUT), Australia, and Rinker Australia,
under R&D project RD835. Thanks are expressed to Glenn Carson
(Rinker) for the assistance in project planning and execution and
to Arthur Powell (QUT) for his contributions in instrumenting the
test section.
AUTHOR BIOGRAPHIES
M.Y. Darestani - PhD Student, School of Urban Development,
Queensland University of Technology
David P. Thambiratnam – Professor, School of Urban Development,
Queensland University of Technology
A. Nataatmadja – Senior Lecturer, School of Urban Development,
Queensland University of Technology
Daksh Baweja – Principal Engineer, Rinker Australia
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