Experimental Investigation of PCC Incorporating RAP
International Journal of Concrete Structures and Materials
Experimental Investigation of PCC Incorporating RAP
Sawssen El Euch Ben Said
Saloua El Euch Khay
Rehabilitation and repair of flexible pavements produce huge amounts of reclaimed asphalt pavement (RAP) material. Using RAP in the formulation of portland cement concrete (PCC) is a technique that is part of a sustainable development approach since it reduces on the consumption of new aggregates and reuses a material that is considered as waste. This paper describes the semi-adiabatic calorimetry test performed on a concrete mix incorporating RAP material as aggregate. Results showed that the cement hydration process is not affected by the presence of asphalt coated on the surface of RAP material. Classical tests (compressive strength, flexural and indirect-tensile strengths, elastic modulus, and free-shrinkage) were also performed on PCC mixes incorporating different percentages of RAP. It was found that as the percentage of RAP increases, the PCC mechanical properties decrease. This is mainly attributed to the presence of voids in the transition zone between the asphalt-coated aggregates and the hydrated cement paste as confirmed by scanning-electron microscope images. Unrestrained shrinkage testing showed statistically insignificant change in shrinkage strain with RAP content. The strength and shrinkage results lead to conclude that as much as 40% of RAP could be incorporated into the formulation of PCC and achieve properties that are acceptable for the construction of rigid pavements.
portland cement; recycled asphalt pavement; heat of hydration; semi-adiabatic; shrinkage; rigid pavements; sustainability
The incorporation of recycled aggregates, obtained from
the rehabilitation and demolition of old infrastructure
(buildings, pavements, and bridges), into the formulation of
PCC has become an essential practice for sustainable
development. Several studies around the world have been
particularly interested in the use of recycled concrete
(Choi et al. 2016; Yehia et al. 2015;
McNeil and Kang 2013)
(Okafor 2010; Kolias
1996; El Euch Ben Sa¨ıd et al. 2014; Roberts et al. 1996;
Sommer 1994; Topcu and Isikdag 2009; Delwar et al. 1997;
Huang et al. 2006; Hossiney et al. 2010; Brand and Al-Qadi
2012; Li et al. 1998; Hassan et al. 2000; Al-Oraimi et al.
2009; Mahmoud et al. 2013; Bermel 2011; Mathias et al.
2004; Abdel-Mohti et al. 2016; Hossiney et al. 2010; Brito
and Saikia 2013)
for the production of new PCC. In fact,
using RCA and RAP material in the formulation of PCC
permits not only to value a material that is considered as
solid waste in many parts of the world, but also to limit the
usage of quarry products leading to preserving natural
aggregate resources and energy. For example, it is estimated
that the embodied energy (defined as the total energy
required to produce and install a material during all stages of
the life cycle) and the embodied carbon (defined as the
quantity of released CO2 during a material’s life cycle) of
limestone aggregates are 250 MJ t-1 and 12 kg t-1,
. Therefore, replacing limestone
aggregates with RAP would reduce the embodied energy
and carbon of the formulated PCC. Moreover, depletion of
materials in existing quarries and difficulties in opening new
ones, given the limited availability of natural deposits,
impose researchers in the area of construction materials to
find new sources of supply. In this context and in order to
minimize the use of natural aggregate resources in the
country, several studies in Tunisia have focused on using
abundant local materials in the road sector. For instance,
dune sand, crushed quarry sand, and sea-dredged sediments
were incorporated in the formulation of sand concrete
Euch Khay et al. 2010a, b, 2011; Ben Othmen et al. 2013)
and RAP material were tested for usage in the formulation of
(El Euch Ben Sa¨ıd et al. 2014)
and PCC (object of this paper).
2. Research Background
Because of repair, rehabilitation, and reconstruction of
deteriorated pavements with hot-mix asphalt wearing
surfaces, a large amount of RAP material is generated annually
from the milling process. Since stocks of RAP have negative
effects on the environment, several studies were undergone
to reuse this material in new construction projects, mainly in
the formulation of new hot-mix asphalt
(Roberts et al. 1996)
Another possible use of RAP, especially in countries with
no or little resources of asphalt and good provisions of
portland cement, is in the formulation of PCC. Several
research efforts have focused on studying the influence of
the introduction of RAP on the mechanical resistance of
PCC: compressive, flexural, and indirect tensile strengths
(Okafor 2010; Kolias 1996; Sommer 1994; Delwar et al.
1997; Huang et al. 2006; Hossiney et al. 2010; Brand and
Al-Qadi 2012; Li et al. 1998; Hassan et al. 2000; Al-Oraimi
et al. 2009; Mahmoud et al. 2013; Bermel 2011; Mathias
et al. 2004; Abdel-Mohti et al. 2016)
. All published results
assert that the strength of PCC decreases with an increase in
the incorporated percentage of RAP, but with no thorough
explanation of the reasons behind this decrease. The same
trend was also found for the PCC elastic modulus
1994; Delwar et al. 1997; Huang et al. 2006; Hossiney et al.
2010; Brand and Al-Qadi 2012; Al-Oraimi et al. 2009;
Mahmoud et al. 2013; Mathias et al. 2004)
. On the other
hand, results on the effects of RAP on PCC free shrinkage
are controversial. In fact, some researchers claim that the
incorporation of RAP has no effect on PCC shrinkage
(Sommer 1994; Brand and Al-Qadi 2012)
claim that RAP tends to reduce shrinkage of PCC
et al. 2010)
, another group reported inconclusive results
(Hossiney et al. 2010)
, and some researchers found that RAP
increases shrinkage of PCC
(Abdel-Mohti et al. 2016; Brito
and Saikia 2013)
. In addition, a small number of researchers
investigated whether the fine or coarse portion of RAP has
more negative effects on PCC strength properties. Results on
this context were also discordant; with a study showing that
replacing only the coarse portion has less negative effect
than replacing both portions (coarse and fine)
(Hassan et al.
, while another study claims that replacing the fine
portion with its equivalent RAP material results in better
(Huang et al. 2006)
The originality of the work described in this paper is the
study of the hydration kinetics of PCC containing RAP. In
fact, to the authors’ best knowledge, no research team
evaluated the influence of asphalt present in RAP on the
cement hydration process. For that purpose, semi-adiabatic
calorimetry tests were performed. In addition, PCC
incorporating local materials and different percentages of RAP
were tested to validate the use of such material in the
construction of rigid pavements.
All PCC mixes made for this study were composed of
local materials (RAP, fine and coarse aggregates, portland
cement, and water) with no mineral or chemical admixtures.
Portland cement from a local plant was used and is classified
as CEM I-42.5 according to Tunisia specification NT-47.01
. This cement has a specified 28-day
compressive strength of 40 MPa, a specified 2-day compressive
strength of 10 MPa, and a specific gravity of 3.10.
According to its manufacturer, the percentages per mass of
its main constituents are: 54.4% of tricalcium silicates (C3S),
18.6% of dicalcium silicates (C2S), 11.4% of tricalcium
aluminates (C3A), and 9% of tetracalcium aluminoferrite
(C4AF). The new aggregates (fine and coarse) were obtained
from a local limestone quarry, while potable water was used
for mixing. A 20-mm maximum aggregate size was used for
all produced mixes. RAP material was obtained from the
milling process of a national highway. The pavement was
14-years old prior to milling; the asphalt content of the
material, as obtained from extraction tests, was about 5%;
while the penetration grade of the asphalt was 35/50. The
RAP material was used in its milled state with no processing
(fracture of particles or taking out of binder) performed. To
study the effects of RAP gradation on PCC performance,
three different size classes of RAP were used: 0/20, 0/4 (fine
portion) and 4/20 (coarse portion). The coarse and fine
portion of the RAP were obtained after careful sieving
through a 4 mm sieve of the 0/20 RAP. The gradation
notation d/D means that at least 95% of the material passes
the D sieve and is retained in the d sieve (d and D are
expressed in mm). The gradations of the three classes of
RAP are shown in Fig. 1. The main properties of RAP, fine
and coarse aggregates were studied and are displayed in
4. Laboratory Testing Program
The laboratory experimental program had three major
objectives: to examine whether or not asphalt, coated on RAP,
affects PCC hydration process, to quantify the effect of RAP
content on mechanical and shrinkage properties of PCC, and
to determine, for the same RAP content, which replaced
portion (fine or coarse) has more negative effects on PCC
properties. Once the second objective is achieved, it is easy to
define the threshold RAP content under which PCC containing
RAP can be used for constructing rigid pavements. A 28-day
compressive strength of 20 MPa and an indirect tensile
strength of 2 MPa, as suggested by the French specification,
NFP 98-170, for constructing rigid pavements for class 2
, were used in this study to find the
threshold RAP content. Figure 2 shows the performed tests on
all the mixes: semi-adiabatic calorimetry, compressive
strength test with its initial low-stress portion used to calculate
the elastic modulus, the indirect tensile strength test, the
3-point bending test, and the free-shrinkage test.
The tests of compressive and indirect tensile strengths were
performed on cylindrical specimens 16 cm in diameter by
32 cm in length, while the 3-point bending and free-shrinkage
tests were performed on prismatic beams 7 cm 9 7 cm 9
28 cm in dimension. Since shrinkage of concrete is
significantly affected by the conditions before and after setting, all
specimens were prepared and kept, once the moulds were
removed, in standard conditions (ambient temperature of
20 ± 2 C and relative humidity of 50 ± 2%). Length
measurements were performed by means of a retractometer
equipped with a dial gauge that has a sensitivity of 1 m. For
each mix and for each test, three specimens were evaluated.
In total eight PCC mixes were prepared for this study. The
mixes were labelled as F (for formula) followed by a number
(0, 20, 40, 60, 80, and 100) that represents the used
percentage of 0/20 RAP in the mix. These percentages represent
the volume of used RAP with respect to the total volume of
aggregates (fine and coarse). Mix F0 composed of 100%
new aggregates served as a control mix. Another letter (S or
G) was added after the number for two mixes (F40S and
F40G) to specify whether the used RAP is graded as 0/4 (S
for sand) or 4/20 (G for gravel). All mixes were designed
based on the granular packing mo
del as proposed by De
). The final proportioning of all mixes made
for this study, is shown in Table 2. For all mixes, the cement
content was kept constant at 330 kg m-3 (a typical cement
content for concrete used in the construction of rigid
pavements) and the w/c ratio was kept at 0.6. The slump of the
achieved mixes was between 5 cm to 6 cm, indicating a
plastic concrete that could be placed using conventional
slipform paving techniques. The laboratory tests were
carried out on all studied mixes (a total of eight as shown by
Table 1) with the exception of the semi-adiabatic calorimetry
test where only the two extreme formulations were examined
(F0 and F100). Three replicates were evaluated at each
testing date for all tests and for all mixes.
5. Semi-adiabatic Calorimetry Testing
In order to verify if asphalt, coated on RAP, affects or not
PCC hydration process, semi-adiabatic calorimetry testing
was performed on two mixes, F0 and F100. It is a known
fact that the chemical reactions involved in portland cement
hydration are all exothermic; that is they liberate heat. The
heat of hydration depends on the cement type and the w/c
ratio. Since mixes F0 and F100 have the same cement type
and w/c ratio, it is expected that they liberate the same heat
Fig. 2 Performed laboratory tests: a semi-adiabatic calorimeter device, b compressive strength and elastic modulus, c
indirecttensile strength, d 3-point flexural strength, e free-shrinkage.
at the same rate during hydration, unless the asphalt present
in mix F100 affect this hydration reactions.
The Langavant-type semi-adiabatic calorimeter (shown in
Fig. 2a) was used in this study to calculate the heat released
from samples taken right after batching F0 and F100 mixes.
Each sample was placed inside an 800 cm3 capacity tinplate
cylindrical container, which is placed by itself inside the
calorimeter. The latter is a silvered Pyrex glass cylindrical
container with a hemispherical bottom. For every
calorimeter, a thermocouple was placed inside the PCC
sample in order to measure temperature development over
time. Temperature measurements were taken at successive
intervals over a seven-day period. The ambient temperature
around the calorimeters was set constant at 20 C.
The hydration of cement paste in PCC is a
thermo-activated process, which development could be modelled using
an Arrhenius type equation (Eq. 1) as proposed by
dt ¼ A~ðnÞ eð R TÞ
where n is the degree of hydration, A˜(n) is the normalized
chemical affinity (s-1), Ea is the activation energy (J mol-1),
R is the perfect gas constant (8.314 J mol-1 K-1), and T is
the absolute temperature (K). The semi-adiabatic test has
been simulated in detail elsewhere
(Briaut et al. 2010)
therefore, only the key equations needed to interpret the
results are presented hereafter. The quantity of heat released
during hydration at time t (Q(t)) can be written under
adiabatic conditions as shown by Eq. 2a, or under semi-adiabatic
conditions as shown by Eq. 2b.
QðtÞ ¼ Cc
QðtÞ ¼ Ct
ða þ b
where Cc is the concrete heat capacity (J 9 C-1), Tad(t) is
the concrete temperature at time t under adiabatic conditions,
Tc(0) is the concrete temperature at time 0 under adiabatic
conditions, Ct is the total heat capacity (concrete plus
calorimeter), h(t) is the measured concrete temperature at
time t, h(0) is the measured concrete temperature at time 0,
a (W 9 C-1) and b (W 9 C-2) are the calorimeter heat
loss coefficients. The total heat capacity can be calculated as
presented by Eq. 3.
Ct ¼ Cc þ n ¼ ðCci
mci þ Ca
ma þ Cw
mwÞ þ l
where Cci, Ca, and Cw are the specific heat capacities
(J 9 kg-19 C-1) of cement, aggregates, and water,
respectively; mci, ma, and mw are the mass (kg) of cement,
aggregates, and water, respectively, and l is the heat
capacity of the calorimeter.
From the mix design and the reported calorimeter property
(l), Ct could be easily calculated using Eq. 3. Then, using
the measured concrete temperature during the test, the
quantity of heat released during hydration could be easily
calculated using Eq. 2b. Once Q(t) is determined, the
temperature under adiabatic condition could be deduced from
Eq. 2a as shown by Eq. 4.
The degree of hydration as a function of time could, then,
be calculated from the adiabatic temperature as shown by
nðtÞ ¼ n1
where n? is calculated using model proposed by
, shown by Eq. 6.
100 150 200 250 300 350 400 450 500
Fig. 5 Degree of hydration development for mixes F0 and
adiabatic temperature stabilized at 65 and 61 C For mixes
F0, and F100, respectively. Figure 5 shows the degree of
hydration development for both mixes. The curves follow
the exact same trend, which indicates that the hydration
process is similar for both mixes. These results prove that
asphalt, coated on RAP, does not alter the cement paste
hydration process and therefore PCC incorporating RAP
could be used for the construction of rigid pavement if its
mechanical and shrinkage properties are adequate for such
application. These properties were therefore tested in the lab
and the results are presented hereafter.
6. Effect of RAP Content on Properties
In order to quantify the effect of RAP content on PCC
properties, mixes F0, F20, F40, F60, F80, and F100 were
tested for their compressive strength, indirect tensile and
flexural strengths, modulus of elasticity, and free shrinkage
6.1 Testing Results
Figure 6 shows the results of the compressive strength as
well as density for all tested mixes at 7, 14, and 28 days of
age. It is noted that both properties decrease as RAP content
increases. For all tested mixes, the compressive strength after
7 days of age is approximately equal to 75% of that reached
after 28 days. The average 28-day compressive strength of
the control mix is 30.1 MPa, while that of F100 is 11.4 MPa,
representing a decrease of about 62%. It is also noticed that
only mixes F0, F20 and F40 reached the 20-MPa required
compressive strength for concrete to be used in the
construction of rigid pavement.
The 28-day indirect tensile and flexural strength results are
shown in Fig. 7. These two properties also decrease as the
RAP content increases. However, the decrease is not as
pronounced as that for compressive strength. In fact, the
average indirect tensile strength of mix F0 is 3.1 MPa and
that for F100 is 1.7 MPa, representing a decrease of about
45%. Also, the average flexural strength of mix F0 is
4.8 MPa, while that of mix F100 is 2.5 MPa, representing a
decrease of about 48%. For all tested mixes, the indirect
tensile strength and the flexural strength represent about
10–15 and 16–22% of the average 28-day compressive
strength, respectively. In addition, except for mix F100, the
28-day indirect tensile strength of 2 MPa was achieved by
all the mixes.
Figure 8 shows the results of the calculated modulus of
elasticity, which is a fundamental pavement design
parameter. The modulus is calculated using the slope of the secant
line at about 40% of the ultimate strength (secant modulus of
elasticity). The elastic modulus decreased from a value of 31
GPa for mix F0 to only 14.5 GPa for mix F100. This means
that the introduction of RAP in PCC reduces its rigidity,
which is an interesting result for pavement design purposes
as will be explained hereafter.
F0 F20 F40 F60 F75 F100
Figure 9 shows the average shrinkage strain development
over time for all tested mixes. It is clear that all curves follow
the same trend, indicating that RAP does not have a
significant effect on this property. The average 90-day
shrinkage strain did not exceed a value of 420 lm m-1 for all
mixes. Mix F100 showed the largest average strain,
418 lm m-1, after 90 days of age, which is higher by only
13% with respect to mix F0 that exhibited the lowest average
shrinkage strain, 370 lm m-1, during the same period.
6.2 Results’ Interpretation
Figure 10 shows the variations of the different studied
PCC mechanical resistances as a function of RAP content.
The figure shows also the exponential regression curves that
fit the data. For the compressive strength data, an
exponential regression curve fits much better the measurements
than a linear line in terms of the coefficient of determination
(0.996 vs. 0.979) and mainly the standard error (0.7 MPa vs.
1.6 MPa). For the indirect tensile strength and flexural
strength, the exponential regression is not very different
from the linear one, but the former was selected to keep the
same type of equation for all properties. The incorporation of
RAP into PCC leads to a drop of the compressive strength,
indirect tensile strength, and flexural strength as shown by
Eqs. 7, 8, and 9, respectively.
where fc0(T or R) is the 28-day compressive strength of the
mix (indirect tensile strength or flexural strength), fc00(R0 or
T0) is the 28-day compressive (indirect tensile strength or
flexural strength) of the mix with zero RAP content, and
%RAP is the percentage RAP in the mix. This finding is
expected since the presence of asphalt on the surface area of
coarse and fine aggregates negatively affects the strength of
the interfacial zones contained in hardened PCC and mainly
the zone between the cement paste and coarse aggregates
and the interfaces between the various phases that make up
the cement paste. For instance, the bond strength of the
interfacial zone between coarse aggregate and cement paste
depends on the former surface characteristics (mainly its
roughness) and on chemical bonding depending on the
minerals found in the aggregates. In fact, the presence of
fc0 ¼ fc00
T ¼ T0
R ¼ R0
e 0:01 %RAP
e 0:006 %RAP
e 0:006 %RAP
RAP content (%)
asphalt on the surface of coarse aggregates reduces their
roughness and inherent any chemical bonding that might
have occurred between the minerals contained in the
aggregates and the cement paste. This was confirmed by
images obtained from scanning electron microscope (SEM)
on mix F100, as shown by Fig. 11. The figure clearly shows
the presence of a void at the interface between the cement
paste and RAP. Looking at Eqs. 7–9, it is also noted that the
rate of decrease in the compressive strength is much higher
than that of the indirect tensile and flexural strengths (the
exponential component is 0.01 for compressive strength and
only 0.006 for indirect and flexural strengths).
As presented (Fig. 8) and discussed earlier, the
incorporation of RAP considerably decreases the modulus of
elasticity of PCC. This finding is also expected since, as
Mehta and Monteiro (1993)
, the transition zone
serves as a bridge between the aggregates and the cement
paste. Even if these two later phases have high stiffness, the
stiffness of the composite could be low because of the voids
and microcracks present in the transition zone which do not
permit stress transfer. With PCC incorporating RAP, in
addition to the voids and microcracks present in the
transition zone, another soft material (asphalt) is added, which will
reduce more the stiffness of the composite. This reduction of
stiffness is of great importance in rigid pavement design.
Indeed, since the modulus of elasticity decreases, the
horizontal tensile stress at the bottom of the concrete slab
induced by truck loading will decrease if linear elastic
properties of materials are used as is the case in all pavement
design procedures worldwide. For instance, Fig. 12 presents
the calculated horizontal tensile stress at the bottom centre of
a concrete slab induced by a standard 65-kN dual tires with a
contact pressure of 662 kPa, placed at the top centre of the
slab. The hypothetical rigid pavement is composed of a
20-cm-thick concrete slab with elastic modulus ranging from
14 to 30 GPa, placed on top of a granular base layer with a
modulus of 400 MPa, placed on top of a subgrade with a
modulus of 100 MPa. The horizontal tensile stress at the
bottom of the slab induced from the considered truck loading
(no moisture or temperature differential in the concrete slab
were considered in this example), which is a critical design
variable in rigid pavements, decreases from 1.5 to 1.2 MPa,
when the modulus decreases from 30 to 14 GPa. The
example is shown to illustrate that reducing the concrete
modulus would decrease the flexural stress in the concrete
slab. Only a load in the center was used for the example, but
the main result (decrease in stress with a decrease in concrete
modulus) would be obtained for other load locations (corner
or edge). This decrease in the calculated horizontal stress at
the bottom of the slab comes to compensate for the decrease
in the flexural strength of PCC incorporating RAP.
In terms of shrinkage behaviour (Fig. 9), PCC containing
RAP does not differ from that without it. To confirm this
finding statistically, an analysis of variance (ANOVA) was
performed on the results of the 90-day shrinkage strain for
all mixes. The obtained p value of 0.27 indicates that there is
no statistical evidence that the mean 90-day shrinkage strain
is different between the tested PCC mixes at a level of
significance of 0.95. Since shrinkage is mainly a paste property
and the paste volume is similar for all eight tested concrete
mixes (same cement content and same w/c ratio), the main
shrinkage behaviour is expected to be similar for all the
mixes. However, in concrete, the aggregates have a
restraining effect on the shrinkage that takes place within the
hydrated cement paste. Since RAP has lower modulus than
quarried new aggregates, concrete mixes made with RAP are
expected to exhibit slightly more shrinkage strain. This is
exactly what was found, but the increase in the shrinkage
strain (a maximum of 13% between F0 and F100) was found
The strength and shrinkage results lead to conclude that as
much as 40% of RAP could be incorporated into the
formulation of PCC (mix F40) and achieve properties that are
acceptable for the construction of rigid pavements. This mix
was retained to evaluate which portion of RAP (fine or
coarse) has more negative effects on PCC mechanical
properties as presented in the next section.
PCC Modulus of elasticity (GPa)
Fig. 12 Calculated horizontal tensile stress at the bottom of
concrete slab as a function of modulus of elasticity.
Fig. 13 Compressive strength as a function of age for mixes
F40, F40S, and F40G.
7. Effects of RAP Gradation (Fine or Coarse)
on PCC Properties
In order to evaluate the effect of RAP gradation (fine or
coarse) on PCC properties, two additional mixes were
formulated based on mix F40. RAP (graded as 0/20) was
carefully sieved over a 4 mm sieve to make two piles of 0/4
and 4/20 graded RAP materials. As shown by Table 2, Mix
F40S was proportioned using only 0/4 RAP, while mix
F40G was proportioned using only 4/20 RAP. The same
mass quantity of RAP was used for all three mixes (F40,
F40S, and F40G) to be able to compare between them.
Figure 13 shows the average compressive strength after 7,
14, and 28 days of age for the three studied mixes. At all
ages, mix F40G had the highest compressive strength
followed by mix F40, then mix F40S. For instance, after
28 days of age, mix F40S achieved an average of only
19.5 MPa while mix F40G achieved an average of
23.6 MPa, which is about 21% higher than mix F40S. The
same trend was observed for the indirect tensile and flexural
strengths (Fig. 14). On the other hand, no differences were
Strength type Flexural
found in the calculated modulus of elasticity between the
three mixes. Figure 15 shows the shrinkage strain
development over time for the three studied mixes. The three curves
are very similar with a difference after 90 days of age not
Figure 16 shows the percentage difference in compressive,
indirect tensile, and flexural strength for mixes F40S and
F40G with respect to those obtained for mix F40. The
figure shows that replacing only the coarse aggregate by its
equivalent RAP would have better effects than replacing
both coarse and fine aggregates with their corresponding
RAP material. For instance, an increase by 14% is achieved
for the compressive strength and by 11% for the indirect
tensile and flexural strengths. On the other hand, replacing
just the fine aggregate by RAP would have worse effects
than replacing both coarse and fine aggregates with their
corresponding RAP material (a decrease of about 6 to 7% in
the mechanical resistance properties). These results could be
explained by the fact that the surface area of fine RAP coated
with asphalt is higher than that of coarse RAP which leads to
an increase in the weakest links represented by the transition
8. Summary and Conclusions
In a context of sustainable development, using RAP,
considered as waste in many countries around the world, in
the formulation of PCC reduces the use of natural aggregate
resources. For that reason, an experimental laboratory study
was performed on several PCC mixes incorporating different
percentages of RAP to determine their mechanical
behaviour. The results of the various performed tests lead to the
Asphalt, coated on RAP, does not affect portland cement
An increase in RAP content is associated with a decrease
in PCC mechanical properties due to the fact that asphalt
present in RAP negatively affects the strength of the
PCC interfacial zones.
The negative effect of RAP is more pronounced for
compressive strength than for indirect-tensile and flexural
strengths. In fact, the interfacial zones are already weak in
tension than in compression and therefore the asphalt
negative effect is more perceptible in compression.
An incorporation of up to 40% RAP will produce PCC
with good quality to be used for constructing rigid
pavements. No extra thickness for the concrete slab is
needed since the modulus of elasticity of PCC
incorporating RAP decreases leading to smaller induced tensile
stresses at the bottom of the slab, which compensates for
the reduced flexural strength.
RAP in PCC does not affect its shrinkage behaviour
For the same RAP content, replacing only the fine
portion of aggregates with its equivalent RAP has more
negative effects than replacing both fine and coarse or
only the coarse portion of aggregates.
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