1. INTRODUCTION
⌅During
renovation and maintenance works on highways, old road pavements are
scraped from the road surface with machines called milling cutters, and
they are broken into certain sizes with the help of these machines and
stored as waste material in municipal construction sites or empty lands (11.
Debbarma S, Ransinchung RN. 2020. Achieving sustainability in roller
compacted concrete pavement mixes using reclaimed asphalt pavement
aggregates – state of the art review. J Clean Prod. 287:125078. https://doi.org/10.1016/j.jclepro.2020.125078.
). Due to the high amount of these waste materials, they cause environmental pollution (22.
Saboo N, Nirmal Prasad A, Sukhija M, Chaudhary M, Chandrappa AK. 2020.
Effect of the use of recycled asphalt pavement (RAP). Aggregates on the
performance of pervious paver blocks (PPB). Constr Build Mater.
262:120581. https://doi.org/10.1016/j.conbuildmat.2020.120581.
). The availability of waste generated during production means not only an industrial gain but also an environmental problem (33.
Ray Chaudhuri A, Hashimoto Y, Herrador R. 2012. Topoisomerase I
poisoning results in PARP-mediated replication fork reversal. Nat Struct
Mol Biol. 19:417–423. https://doi.org/10.1038/nsmb.2258.
).
For this reason, alternatives that can be found in the evaluation of
asphalt wastes will not only provide resources for the country’s
economy, but also will eliminate the environmental polluting feature of
these wastes to a large extent (44. Oikonomou ND. 2005. Recycled concrete aggregates. Cem Concr Compos. 27(2):315–318. https://doi.org/10.1016/j.cemconcomp.2004.02.020.
).
As a result of using waste asphalt cracks in concrete instead of
natural aggregate, environmental pollution can be prevented and a great
contribution can be made to the national economy (55.
Huang B, Shu X, Li G. 2013. Laboratory investigation of Portland cement
concrete containing recycled asphalt pavements. Cem Concr Res.
35(10):2008–2013. https://doi.org/10.1016/j.cemconres.2005.05.002
, 66.
Decker D. 1997. State of the practice for use of RAP in hot mix
asphalt. J. Assoc. Inf. Sci. Technol. 66:704-722. Retrieved from https://trid.trb.org/View/1163622.
).
Considering that road construction and widening works are increasing
day by day in almost all countries of the world, it is inevitable that
the aggregate requirement will increase accordingly (77.
Jahanbakhsh H, Karimi MM, Naseri H, Nejad FM. 2019. Sustainable asphalt
concrete containing high reclaimed asphalt pavements and recycling
agents: performance assessment cost analysis and environmental impact.
J. Clean. Prod. 244:118837. https://doi.org/10.1016/j.jclepro.2019.118837.
).
The cost of concrete will decrease, as the use of waste asphalt
fractures in concrete as aggregate has the effect of reducing natural
aggregate consumption and transportation costs. The fact that the water
absorption capacity of waste asphalt fractures, which is a bituminous
material, is lower than that of natural aggregate, reduces the water
requirement in fresh concrete and increases the workability. Moreover,
when various studies are examined, it is seen that the toughness of the
hardened concrete increases and the formation of cracks decreases (8-108.
Adesina A, Das S. 2021. Sustainable utilization of recycled asphalt as
aggregates in engineered cementitious composites. Constr. Build. Mater.
283:122727. https://doi.org/10.1016/j.conbuildmat.2021.122727.
9.
Hossiney N, Sepuri HK, Mohan M, Arjun HR, Govindaraju S, Chyne JM.
2019. Alkali-activated concrete paver blocks made with recycled asphalt
pavement (RAP). aggregates. Case Stud. Constr. Mater. 12:e00322. https://doi.org/10.1016/j.cscm.2019.e00322.
10.
Ma Y, Hu W, Polaczyk PA, Han B, Xiao R, Zhang M, Huang B. 2020.
Rheological and aging characteristics of the recycled asphalt binders
with different rejuvenator incorporation methods. J. Clean. Prod.
262:121249. https://doi.org/10.1016/j.jclepro.2020.121249.
). Erdem et al. (1111.
Erdem S, Blankson MA. 2014. Environmental performance and mechanical
analysis of concrete containing recycled asphalt pavement (RAP). and
waste precast concrete as aggregate. J. Hazard. Mater. 264:403–410. https://doi.org/10.1016/j.jhazmat.2013.11.040.
)
In their study, they investigated the use of 100% recycled aggregates
in concrete and its effect on mechanical strength. They used concrete
waste aggregate and RAP obtained from precast elements as waste
aggregate. They stated that the use of 100% is not suitable for
concrete, causing structural problems. According to İbrahim et al. (1212.
Ibrahim A, Mahmoud E, Khodair Y, Patibandla VC. 2014. Fresh mechanical
and durability characteristics of self-consolidating concrete
incorporating recycled asphalt pavements. J. Mater. Civ. Eng. 26(4):668–675. https://doi.org/10.1061/(ASCE)MT.1943-5533.0000832.
)
using RAP in self-compacting concrete, they investigated fresh,
mechanical and durability properties. After examining all experimental
results, they suggested that RAP should not be used more than 25% in
self-compacting concrete. Zaumanis et al. (1313.
Zaumanis M, Arraigada M, Poulikakos LD. 2020. 100% recycled
high-modulus asphalt concrete mixture design and validation using
vehicle simulator. Construct. Build. Mater. 260:119891. https://doi.org/10.1016/j.conbuildmat.2020.119891.
)
analyzed rutting resistance and fatigue performance of high modulus
asphalt concrete with 100% RAP dosage. It was stated that high modulus
asphalt concrete prepared with 100% RAP content could not fully meet the
performance index requirements and it behaved inferior resistance to
crack propagation compared with the traditional high modulus asphalt
concrete. Yang et al. (1414.
Yang C, Wu S, Cui P, Amirkhanian S, Zhao Z, Wang F, Zhang L, Wei M,
Zhou X, Xie J. 2022. Performance characterization and enhancement
mechanism of recycled asphalt mixtures involving high RAP content and
steel slag. J. Clean. Prod. 336:130484. https://doi.org/10.1016/j.jclepro.2022.130484
)
Recycled asphalt mixtures containing RAP 50%, 60% and 70% RAP and steel
slag were prepared and their road performances were characterized.
Their results indicate that incorporating steel slag in recycled asphalt
mixtures with 70% RAP content reveals a desirable performances index in
contrast to basalt. Asphalt fractures are waste materials that occur
during the renovation and maintenance of roads, it has been seen from
the studies in the literature that it is possible to reuse these
materials on flexible and rigid pavements. Cracks can be seen in the
concrete slab under the stresses caused by the temperature and humidity
difference and traffic loads on concrete roads, which are a rigid
pavement. In order to prevent these cracks, the joints that make the
concrete road into free slabs should be made at certain and appropriate
intervals. In addition, these cracks can be minimized and concrete
tensile strength can be increased by placing steel wires close to the
surface or by placing mesh reinforcements close to the surface. It is
seen as a great advantage that the concrete road is the only pavement
type that accepts steel reinforcement among the road types. Another
method to prevent crack formation in concrete roads is to increase
concrete toughness by using various materials with higher deformation
capacity instead of aggregate. This situation was examined in detail in
the study, and the effects of using waste asphalt fractures instead of
aggregate on the formation of cracks in concrete were investigated (1515.
Topcu İB, Isıkdağ B. 2006. Atık asfalt kırıklarının agrega olarak beton
yollarda değerlendirilmesi. ACE 2006, 7th International Congress in
Civil Engineering. Yıldız Technical University, İstanbul, Turkey. TCMB
Cimento ve Beton Dunyas 11:72-85.
, 1616.
Bittencourt SV, da Silva Magalhães M, da Nóbrega Tavares ME. 2021.
Mechanical behavior and water infiltration of pervious concrete
incorporating recycled asphalt pavement aggregate. Case Stud. Constr.
Mater. 14:e00473. https://doi.org/10.1016/j.cscm.2020.e00473
). It is stated in the specifications that the amount of cement in concrete road construction should be at least 350 kg/m3.
In addition, the amount of alkali in the cement and the reactivity of
the aggregate to be used should be considered against the possibility of
alkali-silica reaction, and the necessary standard tests should be done
beforehand. For Concrete Pavement, the concrete must be of at least C
30/37 class and its flexural strength must be at least 4.0 MPa. It is
recommended that the water/cement ratio should not exceed 0.45 (15-1715.
Topcu İB, Isıkdağ B. 2006. Atık asfalt kırıklarının agrega olarak beton
yollarda değerlendirilmesi. ACE 2006, 7th International Congress in
Civil Engineering. Yıldız Technical University, İstanbul, Turkey. TCMB
Cimento ve Beton Dunyas 11:72-85.
16. Bittencourt SV, da Silva
Magalhães M, da Nóbrega Tavares ME. 2021. Mechanical behavior and water
infiltration of pervious concrete incorporating recycled asphalt
pavement aggregate. Case Stud. Constr. Mater. 14:e00473. https://doi.org/10.1016/j.cscm.2020.e00473
17.
Rezende LR, Silveira LR, Araújo WL, Luz MP. 2014. Reuse of fine quarry
wastes in pavement: Case study in Brazil. J. Mater. Civ. Eng. 26(8):1-9. https://doi.org/10.1061/(ASCE)MT.1943-5533.0000997
).
From the literature review, it was seen that most of the research is focused on the evaluation of RAP in concrete as a recycling material in terms of physical or mechanical properties. However, durability properties were not taken into consideration. Therefore, the novelty of this study is to investigate in detail whether recycled asphalt aggregate (RAP) obtained by scraping old asphalt can be used in concrete road construction. For this purpose, RAP was used instead of crushed stone aggregate used in concrete road construction. In all concrete mixes, the dose was kept constant as 350 kg/m3 and the water/cement ratio of 0.45. Recycled asphalt pavement aggregates (RAP) supplied from Afyonkarahisar asphalt construction site were added to the concrete mixtures by replacing the total of crushed sand and crushed stone-I used in the concrete at the rates of 25%, 50% and 100%. The fresh slump and air contents of the concrete samples were determined. The mechanical properties of compressive and splitting strength, physical properties of water absorption, porosity, ultrasonic pulse velocity and electrical resistivity were determined. Reinforced corrosion and acid effect were examined as durability properties, and finally, microstructure properties were examined with SEM and XRD analyzes.
2. MATERIALS USED
⌅As cement, CEM I 42.5 cement in accordance with TS EN 197-I (1818. TS EN 197-1. 2012. Cement-Stage 1: General cements–component. Turkish Standard Institute Ankara Turkey.
)
standard was used. Three different sizes of limestone-based aggregate
were used as aggregate: 0-6 crushed sand, 6-12 mm crushed stone-I and
12-22 mm crushed stone-II. The specific gravity of the aggregates was
determined as 2.65 gr/cm3 for crushed sand, 2.70 for crushed
stone-I and 2.72 for crushed stone-II Recycled asphalt pavement
aggregates (RAP), supplied from Afyonkarahisar asphalt construction
site, were added to the concrete mixtures by changing the weight of the
total crushed sand and crushed stone-I used in the concrete at the rates
of 25%, 50% and 100%. RAP view is given in Figure 1. The specific gravity of RAP was determined as 2.6 gr/cm3.
Concrete mixtures prepared in the concrete mixer in the laboratory were
produced with 350 doses and a water/cement ratio of 0.45. A
hyperplasticizer additive was used at the rate of 1% by weight of
cement.
3. APPLIED EXPERIMENTS
⌅Following the concrete production, the fresh workability and air content of concretes containing RAP were determined. Compressive strength, splitting tensile strength, electrical resistivity value, accelerated corrosion test of hardened concretes were subjected to corrosion resistance, water absorption and porosity percentage, acid resistance, ultrasonic pulse rate and SEM analyzes were determined. All experiments were carried out at laboratory ambient temperature. Each experiment is applied to 3 samples and the average is given in the results section. As a result of these comprehensive tests, if the RAP ratio exceeds 25%, it has been observed that concrete roads are risky in terms of both mechanical and durability properties.
The slump value of fresh concrete in accordance with the TS EN 12350-2 (1919. TS EN 12350-2. 2019. Testing fresh concrete - Part 2: Slump test.
) standard, and the percentages of air contents according to the TS EN 12350-7 (2020. TS EN 12350-7. 2019. Testing fresh concrete - Part 7: Air content - Pressure Methods.
)
standard were determined for workability. The concrete placed in the
molds was removed from the mold after 24 hours and cured in water for up
to 3, 7 and 28 days under standard conditions. After the curing
process, the compressive strengths of 150x150x150 mm concretes for 3, 7
and 28 days were determined according to TS EN 12390-3 (2121. TS EN 12390-3. 2021. Testing hardened concrete - Part 3: Compressive strength of test specimens.
), and the split tensile strengths were determined according to TS EN 12390-6 (2222. TS EN 12390-6. 2010. Testing hardened concrete - Part 6: Tensile splitting strength of test specimens.
).
Instead of tensile test and flexural test, the tensile strength of the
produced concrete was determined by splitting tensile strength.
Concretes
reaching final strength after completing the 28-day curing period were
subjected to physical property and durability tests. Porosity and water
absorption, which are the basic physical properties of concrete, were
determined using standard TS EN 12390-7 (2323. TS EN 12390-7. 2010. Testing hardened concrete - Part 7: Density of hardened concrete TSE Ankara.
) test methods.
Electrical resistivity values were measured according to ASTM C 1760 (2424. ASTM C 1760. 2012. Standard test method for bulk electrical conductivity of hardened concrete. West Conshohocken (PA): ASTM.
)
with the help of resistivity meter using the two-plate method on
100x100x100 mm. The resistance meter measures 0.1, 0.12, 1, 10 and 100
kHz in alternating current. The purpose of determining the electrical
resistivity at different frequencies is to determine the resistivity
value that can be obtained depending on the measurement frequency. In
other words, the frequency value chosen during the determination of the
resistivity values of the materials directly affects the results. The
electrical resistivity values of the mortars whose resistance values (δ)
were measured were also determined by the Equation [1]:
Where:
δ: Electrical resistive (kΩ∙m)
R: resistance (kΩ)
A: Sample area (cm2)
L: Sample length (m)
The Ultrasonic pulse velocity (UPV) test was carried out with the linear method in accordance with TS EN 12504-4 (2525. TS EN 12504-4. 2021. Testing concrete in structures - Part 4: Determination of ultrasonic pulse velocity.
)
on 100x100x100 mm. The probes of the device that sends ultrasonic sound
waves are placed on the concrete surface and time is given for the
sound wave to pass from one surface to the other in the concrete. The
measure of the concrete sample between the probes is the path length of
this sound wave, using the distance and duration of the sound, the speed
of sound was determined. UPV gives information about the strength of
concrete and the number of voids in it. The fuller the concrete, the
higher the speed of sound.
In order to determine the acid resistance of concretes, 3 different solutions with 0.5, 1M and 1.5M concentrations were prepared by using H2SO4 (sulfuric acid). Concretes reaching final strength were weighed and placed in acid solutions and exposed to acid for 14 days. At the end of 14 days, the weights of the concretes removed from the acid solution were measured and their weight losses were determined. The detected weight losses were calculated as a percentage. The samples were in size of 100x100x100 mm.
The accelerated corrosion test was used to examine the corrosion performance of the reinforcement bar in the concrete. In order to apply the accelerated corrosion test, Ø12 mm diameter reinforcement was placed in the mold center of the Ø100/200 mm cylindrical concretes, leaving equal rust in all directions. This experimental setup consists of a power source with direct current capacity, a plastic container with 4% concentrated NaCl solution and two stainless steel plates, and a test sample. The reinforced concrete sample was placed in a container with 4% NaCl solution. A reinforcement bar (working electrode) is connected to the positive pole of the direct current (DC) source, which applies a constant 50 volts voltage to the system, and plates (counter electrode) are connected to the negative pole. In this circuit, the reinforcement bar is the anode, the plates the cathode, and the NaCl solution is the electrolyte (Figure 2). The current values of the samples under voltage, the corrosion initiation times, the temperature of the brine solution and the weight losses in the reinforcement after the test were determined.
4. RESULTS AND DISCUSSIONS
⌅In
terms of durability of road concretes, they should contain as little
hydrated water as possible. Therefore, this situation has a direct
impact on machinability. Workability can also be increased with the use
of some chemical additives. The slump values of concretes containing
RAP at certain rates are presented in Figure 3.
While the slump values of the control series were 60 mm, the
workability of the concretes increased with the use of RAP and 75 mm
slump was obtained in the concretes using 100% RAP. As the surfaces of
RAP aggregates are covered with bitumen, frictions between the other
components in the concrete and among themselves are relatively reduced,
which increases the workability by enabling the concrete to move more
easily. The percentages of air content of concrete samples containing
RAP are given in Figure 4.
It is seen that the air content decreases with the increase in the rap
rate. The air content decreased to 2% in the reference concrete and 1.8%
in the concrete where the RAP ratio was 100%. The decrease in
compressive strength and apparent density have the same trend with
increasing air content in concrete mixes (2626.
Dąbrowski M, Glinicki MA, Dziedzic K, Antolik A. 2019. Validation of
sequential pressure method for evaluation of the content of microvoids
in air entrained concrete. Constr. Build. Mater. 227:116633. https://doi.org/10.1016/j.conbuildmat.2019.08.014.
).
The compressive strengths of concretes containing RAP in certain proportions are presented in Figure 5.
When the 7 and 28-day strengths of the concretes are examined, the
strength development in all series is approximately the same. However,
the compressive strengths of 7- and 28-day-old concretes started to
decrease as the RAP ratio increased. The adhesive cement matrix and RAP
in the concrete was relatively weak due to asphalt residue, thus, the
effect of the crushing age was more moderate (2727.
Poon CS, Azhar S, Anson M, Wong YL. 2001. Comparison of the strength
and durability performance of normal- and high-strength pozzolanic
concretes at elevated temperatures. Cem. Concr. Res. 31(9):1291-1300. https://doi.org/10.1016/S0008-8846(01)00580-4.
, 2828.
Nagataki S, Gokce A, Saeki T, Hisada M. 2004. Assessment of recycling
process induced damage sensitivity of recycled concrete aggregates. Cem.
Concr. Res. 34(6):965-971. https://doi.org/10.1016/j.cemconres.2003.11.008.
).
Compared to the 28-day control concrete, the strength loss in concretes
with 25, 50 and 100 percent RAP is 26%, 36% and 59%, respectively. It
is recommended that the concrete to be used in road construction should
have a cube compressive strength of at least 37 MPa for 28 days.
Accordingly, the 28-day concrete strength of the series containing 25%
RAP is 41.6 MPa, while the compressive strength of the concretes
containing 50% RAP is 35.7 MPa. Therefore, RAP ratio of 25%-50% can be
used in road concrete in terms of compressive strength. In terms of
splitting strength, concretes containing RAP showed similar properties
to compressive strength (Figure 6).
The split tensile strength of concretes using fully RAP is 1.85 MPa,
while the split tensile strength of control concretes is 3.7 MPa. This
criterion is also met with the use of RAP between 25% and 50% in road
concrete, which is recommended to be at least 2 MPa in terms of
splitting tensile strength.
The electrical resistivity values of concretes containing certain proportions of RAP are given in Figure 7.
With the increase of the frequency value, the electrical resistivity
values decreased. As is known, frequency is the number of revolutions
per second of an alternating current (AC) signal (2929.
Uygunoğlu T, Topçu İB, Şimşek B, Çınar E. 2018. Kendiliğinden yerleşen
harçların elektriksel özdirenci üzerine mineral katkıların etkisi.
Süleyman Demirel Üniversitesi Fen Bilimleri Enstitüsü Derg.
22(2):986-992. Retrieved from https://dergipark.org.tr/tr/pub/sdufenbed/issue/38975/456430.
).
In cement-based systems, electrical conductivity occurs due to ion
transfer in porous solutions and ion transfer accelerates with
increasing frequency. Therefore, the resistance decreases with
increasing frequency. The electrical resistivity value was determined as
0.43 kΩ.m at a frequency of 0.1 kHz and 0.30 kΩ.m at a frequency of 100
kHz in concrete with a RAP ratio of 0%. In concrete where 100% RAP is
used, it is determined as 19.65 kΩ.m at 0.1 kHz frequency and 0.70 kΩ.m
at 100 kHz frequency. The electrical resistivity values decreased with
the increase of RAP content.
Current data obtained from accelerated corrosion test are given in Figure 8, solution temperatures in Figure 9 and corrosion initiation times in Figure 10.
When we examine the flow data, the highest current value was observed
in the concrete where 25% of RAP was used, and the lowest current value
was observed in the concrete where RAP was used 100%. In this type of
test methods, the high current drawn during the test shows that the
corrosion event will be faster (3030.
He SJ, Wang Z, Hu J, Zhu JB, Wei LP, Chen Z. 2018. Formation of
superhydrophobic micronanostructured iron oxide for corrosion protection
of N80 steel. Mater. Design. 160:84–94. https://doi.org/10.1016/j.matdes.2018.09.002.
).
When we examined the solution temperatures, it was seen that it was
directly proportional to the current data. The solution temperature
increases with the increase in the current drawn by the sample. Starting
from the current values, the points where the temperature started to
increase were determined as the corrosion initiation times. When the
corrosion initiation times were examined, it was determined as 6320,
7160, 8960 and 10280 minutes, respectively, in cases where 0, 25, 50 and
100% RAP ratios were used. It is the concrete sample in which corrosion
first started, 0% of RAP was used, while 100% of RAP was used last. It
has been observed that with the increase of the RAP ratio, the corrosion
initiation times increased, and the use of RAP increased the corrosion
resistance of the concrete. Corrosion initiation times were found to be
inversely proportional to current densities (3131.
Uygunoğlu T, Topçu İ.B, Çınar E, Eryeşil Ö. 2021. Yüzeysel su yalıtımlı
betonların bazı durabilite özeliklerinin araştırılması. El-Cezerî Fen
ve Mühendislik Dergisi. 7(3):1245-1257. https://doi.org/10.31202/ecjse.742967
). Corrosion initiation times increased with decreasing current density. Concrete appearances after corrosion given in Figure 8 also show that RAP reduces corrosion resistance. While there was a high
rate of rust stains in the sample with 0% RAP ratio, it was observed
that the concrete containing 100% RAP had less rust stains.
The correlation between corrosion times and electrical resistivity values of concretes containing RAP is given in Figure 11. Correlation R2 value between corrosion time and electrical resistivity was determined
as 0.9973. This shows that there is a strong correlation. Since
reinforcement corrosion is an electrochemical process, there are studies
that electrical resistance is used as a parameter that provides
information about this process, and it is used in the development of
service life models (3232.
Nguyen AQ, Klyz G, Derby F, Balayssac JP. 2018. Assessment of the
electrochemical stateos steel in water saturated concrete by resistivity
measurement. Constr. Build. Mater. 171:455–466. https://doi.org/10.1016/j.conbuildmat.2018.01.155
, 3333.
Chen CT, Chang JJ, Yeih W. 2014. The effects of specimen parameters on
the resistivity of concrete. Constr. Build. Mater. 71:35–43. https://doi.org/10.1016/j.conbuildmat.2014.08.009
).
The electrical resistivity values and the accelerated corrosion test
results showed parallelism. The higher the electrical resistivity, the
less ion mobility that will occur in the concrete, which reduces the
corrosion rate.
The weight losses in the reinforcements as a result of the accelerated corrosion test are given in Figure 12. While the weight loss is 8.03% in concrete with a RAP ratio of 0%, it was determined as 6.71%, 4.45% and 2.46%, respectively, in the case of 25%, 50% and 100% use of RAP ratio. A 5.56% reduction in weight loss occurred with the use of 100% RAP ratio. It was observed that with the increase of RAP ratio, concretes showed higher protection against reinforcement corrosion. The polymer-based bitumen layer decreased the ion mobility and increased the electrical resistivity of the concretes, as well as increased the corrosion resistance.
The water absorption and porosity values of concretes containing RAP are given in Figure 13.
It was observed that the water absorption and porosity percentages
increased with the increase in the RAP ratio. In the case of using 0%,
25%, 50% and 100% RAP ratio, the porosity values were determined as
5.40%, 5.94%, 6.0% and 6.17%, respectively. In the case of using 0%,
25%, 50% and 100% RAP ratio, the water absorption values were determined
as 2.20%, 2.49%, 2.52% and 2.68%, respectively. In the study conducted
by Abraham and Ransinchung (3434.
Abraham SM, Ransinchung GDRN. 2018. Influence of RAP aggregates on
strength durability and porosity of cement mortar. Constr. Build. Mater.
189:1105–1112. https://doi.org/10.1016/j.conbuildmat.2018.09.069
)
they observed that when the RAP ratio is 25%, the porosity and water
absorption value are close to the reference concrete, while it increases
too much when the RAP ratio rises to 50% and 100%. The increase in void
content of RAP mixtures was attributed to the increase in porosity in
the interfacial transition zone of RAP mixtures compared to mixtures
with natural aggregates (3535.
Brand AS, Roesler JR. 2017. Bonding in cementitious materials with
asphalt-coated particles: Part I – The interfacial transition zone.
Constr. Build. Mater. 130:171–181. https://doi.org/10.1016/j.conbuildmat.2016.10.019
).
Weight losses of concretes containing RAP under the effect of acid are given in Figure 14.
With the increase in the RAP ratio, the weight losses due to the acid
effect decreased. During the contact of the concrete with the acidic
environment, calcium ions are separated from the calcium-containing
phases in the hardened cement paste, that is, the calcium silicates that
emerge as a result of hydration to form the calcium salt, resulting in a
significant decrease in mechanical strength and durability performance (3636.
Fan YF, Hu ZQ, Luan HY. 2012. Deterioration of tensile behavior of
concreteexposed to artificial acid rain environment. Interact.
Multiscale Mech. 5(1):41–56. Retrieved from https://www.techno-press.org/samplejournal/pdf/imm0501004.pdf.
).
As the use of RAP increases the void ratio, the void ratio in the
concrete increases and the penetration of acid into the concrete
accelerates. This increased the damage caused by the acid with the
increase of the RAP ratio, causing an increase in weight losses (3737.
Wongkvanklom A, Posi P, Kampala A, Kaewngao T, Chindaprasirt P. 2021.
Beneficial utilization of recycled asphaltic concrete aggregate in high
calcium fly ash geopolymer concrete. Case Stud. Constr. Mater.
15:e00615. https://doi.org/10.1016/j.cscm.2021.e00615.
).
An increase in weight loss was observed as the molarity of the acid
increased. With the acid molarity, the aggressiveness of the acid also
increases and the concretes are damaged more. Although increases in acid
damage were observed with the increase of RAP ratio, it was observed
that when 25% was used, it gave results close to the sample without RAP.
While the weight loss in 0.5 M sulfuric acid is 3% in concretes with 0%
RAP content, the weight loss reaches 17% with an increase in acid
molarity of 1.5M. While the weight loss in 0.5M sulfuric acid is 18% in
concretes with 100% RAP content, the weight loss reaches 42% with an
increase in acid molarity of 1.5M. In concretes where 0% RAP was used,
if the acid molarity increased from 0.5 to 1.5, there was an average of 6
times increase in weight losses. On the other hand, if the acid
molarity increased from 0.5 to 1.5 in concretes where 100% RAP was used,
there was an average of 2 times increase in weight losses.
Ultrasound
transmission velocity (UPV) is one of the measurement methods used to
estimate the void structure of materials such as concrete, and it is
thought that with an increase in this value, it becomes a fuller and
denser material, and as a result, its strength will be higher (3838.
Yasar E, Erdogan Y, Kılıç A. 2004. Effect of limestone aggregate type
and water cement ratio on concrete strength. Mater. Lett. 58(5):772-777. https://doi.org/10.1016/j.matlet.2003.06.004
, 3939.
Çınar E, Dündar B, Uygunoğlu T. 2020. Investigation on high-temperature
effect of recycled concrete aggregate on mortars. Mat. Int.
2(2):236-241. Retrieved from https://materials.international/wp-content/uploads/2020/05/2668572822236241.pdf.
). UPV measurements of concretes containing different ratios of RAP were made at 3, 7 and 28 days and the results are given in Figure 15.
With the advancement of concrete age, hydration products increase and
fill the voids. For this reason, an increase in UPV values was observed
as the age of concrete increased. It can be thought that the voids in
the concrete increase slightly with the RAP ratio. The speed of sound
decreased with the increase of the void ratio. Using the RAP rate of 0%,
25%, 50% and 100%, the UPV values were measured as 4.52, 4.40, 4.34 and
4.22 km/h, respectively. In addition, it was concluded that the
bitumen-coated aggregates prevent the transmission of sound, therefore
the sound transmission speed decreases (4040.
Abdalfattah IA, Mogawer WS, Stuart K. 2021. Quantification of the
degree of blending in hot-mix asphalt (HMA) with reclaimed asphalt
pavement (RAP) using energy dispersive X-ray spectroscopy (EDX)
analysis. J. Clean. Prod. 294:126261. https://doi.org/10.1016/j.jclepro.2021.126261.
). Because polymeric materials such as bitumen are in the group of materials that reduce the transmission of sound.
SEM images and XRD analyzes of concretes containing RAP are given in Figure 16.
When the SEM image is examined, bitumen coated asphalt surfaces are
seen. It is clearly seen that the bitumen coated parts have a smooth
surface on the aggregate surface (4141. Ryu JS. 2002. An Experimental study on the effect of recycled aggregate on concrete roperties. Mag. Concr. Res. 54(1):7-12. https://doi.org/10.1680/macr.2002.54.1.7.
, 4242.
Al-Mufti RL, Fried AN. 2017. Improving the strength properties of
recycled asphalt aggregate concrete. Constr. Build. Mater. 149:45–52. https://doi.org/10.1016/j.conbuildmat.2017.05.056.
).
The asphalt coating of the aggregate surface provides the concrete with
more workable but weaker adhesion with the cement matrix compared to
the reference concrete. As a result of XRD, elemental analysis in the
form of surface scanning was obtained. In element analysis, it was
observed that all components, especially CaO, decreased between 150-300
nm. Since there is a bitumen layer on the aggregate surface in the
mentioned range, the components occurring in the concrete have
decreased. The polymeric bitumen on the aggregate surface reduces the
conductivity in the concrete, thus significantly reducing corrosion.
5. CONCLUSIONS
⌅In this study, the use of waste asphalt fractures in concrete road construction, instead of crushed stone in certain proportions, was investigated, especially in terms of strength. As a result of the findings, the following conclusions were drawn:
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Thanks to the bitumen coated aggregate surfaces, it has been observed that they increase the workability compared to the crushed stone concrete with the same low water/cement ratio. It was observed that there was a decrease in air.
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The fact that the aggregate surfaces are covered with bitumen weakens the aggregate-cement adherence, resulting in a decrease in compressive and splitting strengths.
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It has been observed that the electrical resistivity values increase with the increase in frequency. A high increase in electrical resistivity values was observed with the increase of RAP ratio.
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In all the results obtained from the accelerated corrosion test, it was observed that the increase in the RAP ratio increased the corrosion resistance.
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Since corrosion is an electro-chemical reaction, it has been observed that it is directly related to the electrical resistivity value in the concrete. The correlation coefficient R2 value was determined as 0.9973 and showed a strong relationship.
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An increase was observed in RAP content, water absorption and porosity values. It has been stated that the polymeric bitumen layer on the aggregate surface reduces the adherence in concrete. The high porous structure formed by the RAP content has reduced the acid resistance of the concrete.
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Polymeric materials such as bitumen are in the material group that reduces the transmission of sound, and since the aggregates are covered with this material, they cause a decrease in the ultrasound transmission rate in the concrete.
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In SEM analysis, the bitumen layer on the aggregate surface is clearly visible. The asphalt coating of the aggregate surface provides the concrete with more workable but weaker adhesion with the cement matrix compared to the reference concrete.
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As a result of XRD, when the bitumen coated aggregate surface was examined, a decrease in concrete components was observed. The polymeric bitumen on the aggregate surface reduces the conductivity in the concrete, thus significantly reducing corrosion.
The transportation of materials on the renewed roads is among the important factors in increasing the cost. From a financial point of view, one of the most important factors increasing road construction costs is the transportation of aggregate to the construction site. The distances between the material source and the construction site impose an additional burden on construction costs. After RAP is crushed to the desired dimensions, it can be utilized in mobile concrete batching plants located close to the construction site and can reduce the transportation cost required for natural aggregates. As a result, it was concluded that it provides up to 50% of the limit values recommended in the specifications in terms of pressure and splitting strength, and therefore it can be used in concrete road construction. While obtaining RAP, it should be kept in mind that the behavior may change depending on the bitumen content and the aggregate origin in the RAP, and it is recommended to determine the optimum ratios with preliminary experiments before using them. It is recommended to be used on reinforced concrete roads that will be exposed to adverse environmental conditions with its high corrosion resistance, thanks to its anti-corrosion feature.