Nativa, Sinop, v. 11, n. 2, p. 283-291, 2023.
Pesquisas Agrárias e Ambientais
DOI: https://doi.org/10.31413/nativa.v11i2.15566
ISSN: 2318-7670
Rheological investigation of asphalt binder modified with soybean oil sludge
Osires de Medeiros MELO NETO1* , Lara Pereira Tavares MENDES1,
Milena Cristina Rocha de SOUZA1, Albaniza Maria da Silva LOPES1,
Mateus Valdevino de SIQUEIRA1, Evando Lucio Candido da COSTA2, José Lucas da Silva CASTRO2,
Ben Hur Andrade de Medeiros NÓBREGA2
1Federal University of Campina Grande, Campina Grande, PB, Brazil.
2State University of Paraíba, Araruna, PB, Brazil.
*E-mail: osiresdemedeiros@gmail.com
Submitted on 05/18/2023; Accepted on 08/18/2023; Published on 08/22/2023.
ABSTRACT: The utilization of alternative materials to asphalt binder in pavement aims to diminish the
consumption of natural resources and energy, and in some cases, enhance pavement performance. This study
thus examined the effects on physical and rheological properties of asphalt binder with 50/70 penetration,
modified by soybean oil sludge at percentages of 1%, 3%, 5%, 7%, and 9% by binder weight. This modification
was aimed at reducing viscosity for application in recycled asphalt mixtures. The asphalt binder was assessed
through rotational viscosity tests, Performance Grade (PG), and Multiple Stress Creep Recovery in natura
sludge and post-drying process. Results indicated that adding sludge led to increased viscosity in the asphalt
binder. The modifier also couldn't lower the PG temperature of the pure binder. The modified binders
exhibited greater susceptibility to permanent deformation, except for adding in natura sludge at 9% content.
Consequently, soybean oil sludge didn't act as a viscosity-reducing material and thus didn't exhibit a rejuvenating
effect for use in recycled asphalt mixtures.
Keywords: recycled mixtures; rejuvenating agent; viscosity; waste.
Investigação reológica do ligante asfáltico modificado com a borra do óleo de soja
RESUMO: A utilização de materiais alternativos ao ligante asfáltico na pavimentação tem por finalidade reduzir
o consumo de recursos naturais, de energia e, em alguns casos, melhorar o desempenho do pavimento. Assim,
este trabalho investigou os efeitos nas propriedades físicas e reológicas do ligante asfáltico com penetração
50/70 modificado pela borra do óleo de soja nos teores de 1%, 3%, 5%, 7% e 9% por peso do ligante,
empregada como o objetivo de reduzir a viscosidade para o uso em misturas asfálticas recicladas. O ligante
asfáltico foi avaliado por meio de testes de viscosidade rotacional, performance grade (PG) e Multiple Stress Creep
Recovery, modificado com a borra in natura e após processo de secagem. Os resultados apontaram que a adição
da borra gerou um ganho de viscosidade ao ligante asfáltico. O modificador também não foi capaz de reduzir a
temperatura de PG do ligante puro. Os ligantes modificados se apresentaram mais suscetíveis à deformação
permanente, com exceção da adição da borra in natura no teor de 9%. Assim, a borra de óleo de soja não se
configurou como um material redutor de viscosidade, e com isso, não demonstrou um efeito rejuvenescedor
para uso em misturas asfálticas recicladas.
Palavras-chave: agente rejuvenescedor; misturas recicladas; viscosidade; resíduos.
1. INTRODUCTION
In Brazil, approximately 95% of paved roads rely on
asphalt coating. According to Zhang et al. (2018), the asphalt
mixture is the predominant material for road surface layers
globally. The key ingredient in producing this mixture is
asphalt binder, a viscoelastic binder derived from petroleum.
As Benachio et al. (2020) highlighted, road pavements
consume around 30% of natural resources and contribute to
25% of construction industry-generated solid waste. This
waste typically ends up in landfills.
Flexible pavements require maintenance, preservation,
and reconstruction over their lifespan. During
reconstruction, material from the asphalt surface layer is
termed Reclaimed Asphalt Pavement (RAP). RAP has
significant recycling potential, offering reduced
environmental impact and costs when used as aggregate,
leading to substantial reductions in Greenhouse Gas (GHG)
emissions and energy consumption related to the pavement
sector (AURANGZEB et al., 2014). Consequently, reusing
RAP is crucial for formulating new asphalt mixtures (SILVA
et al., 2012).
When incorporating RAP into asphalt mixtures at high
levels exceeding 30%, the use of Rejuvenating Agents (RA)
becomes necessary. These agents soften the rigid binder,
offsetting RAP's inherent stiffness. The utilization of
rejuvenating agents, termed bio-oils, sourced from organic
plant materials and plant oil residues, has garnered attention
among modern researchers. These modifiers have
demonstrated notable outcomes, particularly restoring
asphalt binder properties, including enhanced crack
resistance and reduced binder viscosity (SANTOS;
FAXINA, 2019).
Rheological investigation of asphalt binder modified with soybean oil sludge
Nativa, Sinop, v. 11, n. 2, p. 283-291, 2023.
284
These endeavors aim to introduce alternative materials to
asphalt binders, reducing natural resource consumption,
lowering energy usage, and, in some cases, improving
pavement performance (PORTUGAL, 2016). In this
context, Zargar et al. (2012) explored using residual cooking
oil to rejuvenate aged asphalt binder. The authors observed a
progressive decrease in complex shear modulus for the
analyzed samples (virgin, aged, and rejuvenated binder with
1%, 2%, 3%, 4%, and 5% modifiers) as temperature
increased from 30°C to 80°C. Additionally, the aged binder
displayed a lower phase angle than virgin asphalt binder,
increasing with the addition of residual cooking oil. The
rheological and chemical analysis led the authors to conclude
that residual cooking oil acts as a rejuvenator for aged
binders, offering an environmentally and economically viable
solution for waste reuse.
The literature features studies employing post-consumer
residual cooking oil as a rejuvenating agent (SUN et al., 2017;
LI et al., 2021; YAN et al., 2021). Melo Neto et al. (2022a)
explored the use of fatty acid from soybean oil sludge, the
residue after acidulation with hydrochloric acid. The authors
indicated a rejuvenating effect on aged asphalt binders,
although the production process requires appropriate
treatment for the generated acidic water.
This research, therefore, investigated the application of in
natura soybean oil sludge, without acidulation, as a viscosity-
reducing agent for asphalt binder. Addressing the gaps in
knowledge regarding the use of industrial soybean oil refining
process residues as rejuvenating agents, this study examined
the impact of adding in natura soybean oil sludge, both
before and after oven-drying, on the rheological behavior of
50/70 penetration-grade asphalt binder at 1%, 3%, 5%, 7%,
and 9% content levels by binder weight.
Recycling this residue, a byproduct of the neutralization
process in soybean oil production, as a modifying agent for
asphalt binder, benefits from its rich content of saponified
fatty acids, cost-effectiveness, and wide availability in
soybean oil and biodiesel industries, presenting itself as a
sustainable raw material choice for reducing asphalt binder
viscosity (SEIDEL; HADDOCK, 2014).
2. EXPERIMENTAL PROGRAM
The procedures implemented in this study adhered to the
guidelines outlined by the American Society for Testing and
Materials (ASTM) and the American Oil Chemists Society
(AOCS). Each test was conducted in triplicate, and the
average of the results for each test was provided.
2.1. Materials
The asphalt binder used in this study was supplied by
Cordilheira Company, located in Campina Grande - PB. This
binder was classified as a penetration grade of 50/70 with a
maximum performance grade (PG) temperature of 64°C,
representing the predominant binder type used in the
Northeast region of Brazil. All tests conducted for the
unmodified binder (AB) were also carried out on asphalt
binder samples modified with soybean oil sludge.
Various characterization tests were conducted, including
penetration, softening point, rotational viscosity, and
performance grade (PG) assessments. These tests were
performed on both virgin and aged binder samples through
the Rolling Thin-Film Oven (RTFO) short-term aging
process. Viscosity evaluations were executed using a
Brookfield viscometer, while rheological analyses were
carried out using a Dynamic Shear Rheometer (DSR) from
the Discovery Hybrid Rheometer (DHR-1) series. The
asphalt binder characterization outcomes are summarized in
Table 1.
Table 1. Binder characterization.
Tabela 1. Caracterização do ligante.
Tests
Conducted Results (AB)
Standards
Utilized
Penetration 0.1
mm (100g, 5s at
25ºC)
58.00
ASTM D5/D5M
(2020)
Softening Point
(ºC) 52.00
ASTM D36/D36M
– 14 (2020)
Rotational
Viscosity (cP)
135ºC
401.00
150ºC – 198.00
177ºC – 72.75
ASTM
D4402/D4402M
(2015)
Maximum PG
Temperature (°C) 64.00
ASTM D6373
(2021)
RTFO (Rolling Thin-Film Oven)
ASTM D2872
(2019)
Rotational
Viscosity (cP)
135ºC
557.50
150ºC – 269.00
177ºC – 94.00
ASTM
D4402/D4402M
(2015)
Maximum PG
Temperature (°C) 64.00
ASTM D6373
(2021)
Multiple Stress
Creep Recovery
(MSCR)
Jnr at 0.1 kPa
–
3.40
Jnr at 3.2 kPa – 5.30
% Recovery at 0.1
kPa – 5.03
% Recovery at 3.2
kPa – 0.37
ASTM D7405
(2020)
For the rejuvenating agent, soybean oil sludge from
IMCOPA company located in Paraná was employed. The
characteristic properties of this material were determined
using tests specified by the American Oil Chemists Society
(AOCS) and methodologies outlined by Da Fré (2009) and
Araújo (2016), as detailed in Table 2.
Table 2. Characterization of soybean oil sludge.
Tabela 2. Caracterização da borra de óleo de soja.
Tests
Conducted Results
Standards
Utilized
Free fatty acids in oleic
acid (%) 0.68 AOCS Ca 5a-40 (2017)
Total fatty acids
content (%) 41.59 AOCS G 3-53 (2017)
Oxidized fatty acids
content (%) 1.22 AOCS G 3-53 (2017)
Unsaponifiable matter
content (%) 0.87 AOCS Ca 6a-40 (2017)
Neutral oil content (%)
12.44
AOCS G5
-
40 (2017)
pH at 25°C
9.96
AOCS G
7
-
56 (2017)
Moisture and volatile
content (%) 41.85 AOCS Ca 2c-25 (2017)
Based on the data presented in Table 2, the total content
of fatty acids was determined to be 41.59%, which falls within
the range of 35% to 50%, as stipulated by Swern (1982).
Notably, the moisture content of the material exceeded 40%,
a feature that could impact the outcomes of binder
modification. The pH test conducted at 25°C indicated that
the material exhibits a basic or alkaline nature, as evidenced
by its pH value exceeding 7.
Melo Neto et al.
Nativa, Sinop, v. 11, n. 2, p. 283-291, 2023.
285
2.2. Methods
2.2.1. Drying of soybean oil sludge
As indicated in Table 2, the soybean oil sludge displayed
a notable moisture content of 41.85%, constituting nearly
half the total sludge added to the binder. This prompted the
consideration that the inclusion of 1% sludge into the binder
would effectively mean adding 0.58% actual sludge content,
with the remaining 0.42% accounting for the moisture
present in the sludge. In response, a drying protocol was
implemented, as outlined in Figure 1, facilitating the
examination of the behavior of the binder modified with
both in natura and dried sludge.
This protocol was executed at the Pavement Engineering
Laboratory (LEP) of the Federal University of Campina
Grande (UFCG) over a span of 72 hours (3 days). Initially,
two samples were weighed, positioned on aluminum foil, and
subjected to drying in an oven set at a temperature of 65°C.
After 17 hours, the samples underwent another weighing
process. This weighing procedure was repeated at 40, 43, 65,
68, and 72 hours. The protocol concluded after 72 hours of
drying, during which approximately 35% of the moisture
content was extracted from the soybean oil sludge samples.
Considering the boiling point of water at 100°C, exceeding
the temperature employed in the protocol, a more extended
duration would be necessary to eliminate moisture from the
soybean oil sludge entirely. As such, the practical
implementation of this material as a modifying agent for
asphalt binder within large-scale asphalt mixture production
is logistically unviable. The samples displayed the subsequent
masses during the various weighings (Table 3).
Figure 1. Soybean oil sludge drying process.
Figura 1. Processo de secagem da borra de óleo de soja.
2.2.2. Modification of asphalt binder
For the study, percentages of 1%, 3%, 5%, 7%, and 9%
of soybean oil sludge based on asphalt binder weight were
examined, falling within the modifier range established by He
et al. (2017). The FISATOM model 722D mechanical shaker
was employed for the mixing process (modifier + binder).
Initially, the binder was heated to 135°C for 90 minutes to
achieve fluidity. Following preheating, the material was
transferred to a Becker flask and positioned on the
mechanical shaker at a rotation speed of 600 rpm to ensure
thorough mixture homogeneity. As the temperature reached
140°C, the additives were added separately based on the pure
binder weight, and the rotation speed was increased to 1000
rpm for 30 minutes for the 1%, 3%, 5%, 7%, and 9%
contents. This technique was adopted based on studies by
Faxina (2006), Souza (2012), and Melo Neto (2022). Table 4
presents the descriptions of the samples and their respective
nomenclatures.
Table 3. Nomenclature of samples used in the research.
Tabela 3. Nomenclatura das amostras utilizadas na pesquisa.
Drying period Sample 1 (g) Sample 2 (g)
Without drying 288.76 288.18
17 hours
245.35
245.70
40 hours 214.11 216.19
43 hours 210.91 212.94
65 hours 194.33 196.79
68 hours
192.54
194.96
72 hours 190.59 193.03
Table 4. Nomenclature of samples used in the research.
Tabela 4. Nomenclatura das amostras utilizadas na pesquisa.
Samples
Nomenclatures
Penetration
-
grade 50/70 asphalt binder
AB
AB + 1% in natura soybean oil
sludge
1% SS
AB + 3% in natura soybean oil sludge
3% SS
AB + 5% in natura soybean oil sludge
5% SS
AB + 7% in natura soybean oil sludge
7% SS
AB + 9% in natura soybean oil sludge
9% SS
AB + 1% dried soybean oil sludge
1% DSS
AB + 3% dried
soybean oil sludge
3% DSS
AB + 5% dried soybean oil sludge
5% DSS
AB + 7% dried soybean oil sludge
7% DSS
AB + 9% dried soybean oil sludge
9% DSS
2.2.3. Test procedures
The modified asphalt binders were characterized at the
Pavement Engineering Laboratory (LEP) of the Federal
University of Campina Grande (UFCG). The samples
underwent testing before and after the Rolling Thin Film
Oven (RTFO) aging procedure (ASTM D2872, 2019)
without any treatment and after the drying process.
Rotational viscosity analyses (ASTM D4402, 2015)
involved placing the samples within a controlled-temperature
container with a rotating rod set at a specified speed. The
force needed to overcome the resistance posed by the
binder's viscosity was determined based on the recorded
rotation during the test.
For the Performance Grade (PG) test (ASTM D6373,
2021), the parameter G*/senδ was examined. The initial
temperature was set at 46°C, with subsequent increments to
temperatures of 52°C, 58°C, and 64°C. The maximum test
temperature corresponded to the point of binder failure.
The Multiple Stress Creep Recovery (MSCR) test (ASTM
D7405, 2020) was conducted at the PG temperatures of the
asphalt binder. The goal was to compare pure binder samples
with modified binder samples. This test assesses that lower
Jnr values at 3.2 kPa indicate more viscous binders, while
higher values suggest more fluid materials.
Rheological investigation of asphalt binder modified with soybean oil sludge
Nativa, Sinop, v. 11, n. 2, p. 283-291, 2023.
286
3. RESULTS
This section presents the outcomes obtained from the
physical and rheological characterization of the asphalt
binders modified in natura soybean oil sludge and after the
drying procedure to eliminate moisture.
3.1. Rotational Viscosity
Table 5 displays the findings of the rotational viscosity
assessment for the pure binders (AB) and binders altered
with in natura soybean oil sludge (SS). The procedure
adhered to the ASTM D4402 (2015) standard and aimed to
ascertain the binder's viscosity and consistency.
Table 6 illustrates the viscosity outcomes for the pure
binders and binders that underwent modification with dried
soybean oil sludge (DSS).
Table 5. Results of the rotational viscosity test within natura sludge.
Tabela 5. Resultados do teste de viscosidade rotacional com borra
in natura.
Tests
Before
RTFO
Rotational Viscosity (cP)
ºC 135.00 150.00 177.00
AB 401.00 198.00 72.75
1%SS 397.50 194.00 71.25
3%SS 356.25 181.50 69.50
5%SS 354.30 182.50 680.00
7%SS 428.75 211.00 104.75
9%SS 446.25 182.50 72.25
Limits ≥274.00 ≥112.00
57.00 at
285.00
Tests
After
RTFO
Rotational Viscosity (cP)
ºC 135.00 150.00 177.00
AB 548.00 269.00 94.00
1%SS 553.75 264.50 91.75
3%SS 496.25 240.50 85.25
5%SS 563.75 268.50 98.25
7%SS 558.75 272.00 103.25
9%SS 593.75 286.50 99.50
Limits ≥55.00 NA NA
NA = Not Applicable. NA = Não Aplicável.
Table 6. Results of the rotational viscosity test with dried sludge.
Tabela 6. Resultados do teste de viscosidade rotacional com borra
seca.
Tests
Before
RTFO
Rotational Viscosity (cP)
ºC 135.00 150.00 177.00
AB 404.43 200.34 72.24
1%DSS 398.53 193.65 71.06
3%DSS 457.50 201.27 74.17
5%DSS 674.57 248.47 119.61
7%DSS 879.34 251.52 115.16
9%DSS 401.00 198.00 73.00
Limites ≥274.00 ≥112.00
57.00 at
285.00
Tests
After
RTFO
Rotational Viscosity (cP)
ºC 135.00 150.00 177.00
AB 535.00 257.00 89.50
1%DSS 518.48 249.24 88.82
3%DSS 584.55 278.74 98.32
5%DSS 705.53 326.60 114.25
7%DSS 974.50 418.78 155.42
9%DSS 548.00 269.00 94.00
Limites ≥55.00 NA NA
NA = Not Applicable. NA = Não Aplicável.
For both pre and post RTFO conditions, only the binder
containing 1% sludge exhibited viscosity values lower than
those of the pure asphalt binder. As the additive content
increased, viscosity also increased. These findings differ from
those obtained with the asphalt binder modified with
soybean oil sludge fatty acid. Melo Neto (2022) reported a
linear decrease in asphalt binder viscosity with increasing
fatty acid content.
3.2. Performance Grade (PG)
In the performance grade tests, the values corresponding
to the minimum PG temperatures were excluded due to the
negligible likelihood of negative temperatures in tropical
countries like Brazil. Figures 2 and 3 illustrate the variations
in the G*/Sinδ parameter values across temperatures ranging
from 46°C to 64°C. These figures pertain to the asphalt
binders modified with in natura and dried soybean oil sludge,
respectively, before and after the short-term aging process.
Figure 2. G*/Sinδ parameter versus temperature before and after
short-term aging RTFO for binders modified with in natura sludge.
Figura 2. Parâmetro G*/Senδ versus temperatura antes e após o
envelhecimento a curto prazo RTFO para os ligantes modificados
com a borra in natura.
Figure 3. G*/Sinδ parameter versus temperature before and after
short-term aging RTFO for binders modified with dried sludge.
Figura 3. Parâmetro G*/Senδ versus temperatura antes e após o
envelhecimento a curto prazo RTFO para os ligantes modificados
com a borra seca.
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
G*/Sinδ
46 ºC 52ºC 58ºC 64ºC
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
G*/Sinδ
46 ºC 52 ºC 58 ºC 64 ºC
Melo Neto et al.
Nativa, Sinop, v. 11, n. 2, p. 283-291, 2023.
287
From the information depicted in Figures 2 and 3, it is
evident that the G*/Sinδ parameter of the pure binders, both
pre and post RTFO, exceeded those attained with the
addition of soybean oil sludge under both considered
conditions and lower temperatures (46°C and 52°C). At the
temperature of 64°C, before the short-term aging process,
the asphalt binder modified with in natura sludge at contents
of 7% and 9% exhibited values surpassing those of the pure
binder. The latter recorded a value of 1.53, while the former
marked 1.87 and 1.88, respectively.
Regarding the binder amended with dried sludge, at the
temperature of 64°C, binders containing percentages
exceeding 3% displayed G*/Sinδ values surpassing the pure
binder before RTFO. Figures 4 and 5 provide a graphical
representation of the PG and continuous PG values for the
pure asphalt binders and those modified with in natura
soybean oil sludge, encompassing conditions before and after
the short-term aging RTFO procedure.
Figure 4. Performance Grade of pure asphalt binders and binders
modified with in natura soybean oil sludge before and after short-
term aging RTFO.
Figura 4. Grau de desempenho dos ligantes asfálticos puro e
modificados com a borra do óleo de soja in natura antes e após o
envelhecimento a curto prazo RTFO.
Figure 5. Continuous Performance Grade of pure asphalt binders
and binders modified with in natura soybean oil sludge before and
after short-term aging RTFO.
Figura 5. PG contínuo dos ligantes asfálticos puro e modificados
com a borra do óleo de soja in natura antes e após o envelhecimento
a curto prazo RTFO.
A discernible pattern emerges after thoroughly examining
the outcomes depicted in Figure 4. The asphalt binder,
subject to modification with 3% SS and 5% SS, exhibits a
notable reduction in PG temperature post-aging, resulting in
a shift from 64°C to 58°C. This shift signifies an increased
susceptibility to oxidative effects, which, in turn, contributes
to reduced deformability and enhanced rigidity at elevated
temperatures. The specimen treated with 7% SS showcases a
similar PG temperature shift following RTFO, marking a
decrease of one interval, corresponding to a 6°C range, and
descending from 70°C to 64°C. Conversely, the 9% SS
sample demonstrates a more pronounced reduction,
spanning two intervals and descending from 70°C to 58°C.
Figures 6 and 7 graphically depict the PG and continuous
PG values of the unmodified pure asphalt binders and those
that underwent modification by incorporating dried soybean
oil sludge. These graphical representations encompass
conditions before and after the short-term aging RTFO
procedure, providing a comprehensive visual overview of the
evolving performance of the binder.
Figure 6. Performance Grade of pure asphalt binders and binders
modified with dried soybean oil sludge before and after short-term
aging RTFO.
Figura 6. Grau de desempenho dos ligantes asfálticos puro e
modificados com a borra do óleo de soja seca antes e após o
envelhecimento a curto prazo RTFO.
Figure 7. Continuous Performance Grade of pure asphalt binders
and binders modified with dried soybean oil sludge before and after
short-term aging RTFO.
Figura 7. PG contínuo dos ligantes asfálticos puro e modificados
com a borra do óleo de soja seca antes e após o envelhecimento a
curto prazo RTFO.
Continuing the analysis concerning Figure 6, it becomes
evident that including dried soybean oil sludge leads to
consistent PG values when employing 1% DSS (64°C).
Nonetheless, upon the incorporation of 3% sludge, there is a
discernible reduction in PG temperature after the short-term
aging RTFO assessment. Notably, the sample treated with
5% DSS displays an intriguing pattern, indicating an elevation
in PG value pre-RTFO from 64°C to 70°C, encompassing a
AB 1%SS 3%SS 5%SS 7%SS 9%SS
Before RTFO 64.00 64.00 64.00 64.00 70.00 70.00
After RTFO 64.00 64.00 58.00 58.00 64.00 58.00
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
PG (ºC)
AB 1%SS 3%SS 5%SS 7%SS 9%SS
Before RTFO 67.00 66.00 64.00 64.00 70.00 71.70
After RTFO 65.00 65.00 63.00 63.00 64.40 63.70
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
Continuous PG (°C)
AB 1%DSS 3%DSS 5%DSS 7%DSS 9%DSS
Before RTFO 64.00 64.00 64.00 70.00 70.00 76.00
After RTFO 64.00 64.00 58.00 58.00 64.00 64.00
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
PG (°C)
AB 1%DSS 3%DSS 5%DSS 7%DSS 9%DSS
Before RTFO 67.00 66.60 69.10 70.80 74.00 77.00
After RTFO 65.00 65.00 61.40 63.70 67.70 66.20
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
Continuous PG (°C)
Rheological investigation of asphalt binder modified with soybean oil sludge
Nativa, Sinop, v. 11, n. 2, p. 283-291, 2023.
288
6°C range. In cases involving the application of natural
soybean oil sludge, an intriguing discrepancy at the 5%
threshold emerges: the pre-RTFO value is 64°C for the 5%SS
sample, whereas it registers at 70°C for the 5%DSS sample.
This discrepancy suggests a more notable increase in asphalt
binder stiffness with sludge utilization post the drying
procedure. These findings bolster the observations from the
rotational viscosity tests, reiterating that the drying process
insignificantly interferes with soybean oil sludge's efficacy as
a viscosity-reducing agent in asphalt binder.
Turning attention to the 7%DSS and 9%DSS samples,
there surfaces an elevated PG before RTFO. Following the
aging examination, both the 7%DSS and 9%DSS samples
manifest a reduction in continuous PG temperature,
recording reductions of 6.3°C and 10.8°C, respectively. This
comprehensive analysis intimates that introducing soybean
oil sludge yields negligible effects on the PG value when
juxtaposed against the unadulterated binder sample.
Table 7 shows the temperature deviations prior to and
post RTFO between PG and continuous PG values for the
specimens under scrutiny. Notably, the transition from PG
to continuous PG spans a spectrum of 0 to 5°C, findings that
parallel the investigation by Melo Neto et al. (2022b)
involving the analysis of the physical-rheological dynamics of
asphalt binders modified with refined cotton oil. Their study
echoes similar temperature variations, with the authors
emphasizing that the amplitude of 6°C in PG variation also
translates to the determination of lower performance grades
than the authentic ones.
Table 7. Variation of PG and Continuous PG temperatures in
asphalt binder samples.
Tabela 7. Variação das temperaturas de PG e PG contínuo nas
amostras dos ligantes asfálticos.
Samples Before RTFO After RTFO
AB (°C) 3.00 1.00
(%) 4.69 1.56
1%SS (°C) 2.00 1.00
(%) 3.13 1.56
3%SS (°C) 0.00 5.00
(%) 0.00 8.62
5%SS (°C) 0.00 5.00
(%) 0.00 8.62
7%SS (°C) 0.00 0.40
(%) 0.00 0.63
9%SS (°C) 1.70 5.70
(%) 2.43 9.83
Samples Before RTFO After RTFO
AB (°C) 3.00 1.00
(%) 4.69 1.56
1%DSS (°C) 2.60 1.00
(%) 4.06 1.56
3%DSS (°C) 5.10 3.40
(%) 7.97 5.86
5%DSS (°C) 0.80 5.70
(%) 1.14 9.83
7%DSS (°C) 4.00 3.70
(%) 5.71 5.78
9%DSS (°C) 1.00 2.20
(%) 1.32 3.44
As depicted in Table 7, a notable observation emerges,
underscoring the 7%SS sample for exhibiting the most
minimal variance in both PG and continuous PG values. This
finding designates it as the most indicative and faithful
representation within the analyzed set. Remarkably, the PG
classification value for this specific sample closely aligns with
its actual failure point, signifying its heightened accuracy and
reliability.
3.3. Multiple Stress Creep Recovery (MSCR)
The multiple stress creep and recovery test serves as a
valuable tool for assessing critical parameters such as
recovery percentage (%R), non-recoverable compliance (Jnr),
and the percentage difference between non-recoverable
compliances (Jnr, diff). These metrics provide insights into
elasticity, susceptibility to permanent deformation
accumulation, and sensitivity to increased stress levels. The
test facilitates the determination of suitable traffic levels for
the binder and its recovery behavior under the applied
stresses corresponding to the chosen levels. Notably, higher
Jnr values indicate a heightened susceptibility to permanent
deformations.
Figures 8 and 9 impeccably portray the test outcomes
conducted at the asphalt binder's maximum PG temperature
(64°C) and its elastic recovery concerning binders modified
with in-nature soybean oil sludge, respectively.
Figure 8. Non-recoverable compliances of pure and soybean oil
sludge-modified binders.
Figura 8. Compliâncias não recuperáveis dos ligantes puro e
modificados com a borra de óleo de soja in natura.
Figure 9. Elastic recovery at 0.1 kPa and 3.2 kPa for pure and
soybean oil sludge-modified binders.
Figura 9. Recuperação elástica a 0.1 kPa e 3.2 kPa para os ligantes
puro e modificados com a borra de óleo de soja in natura.
According to AASHTO M320 (2021), a relationship can
be established between the values obtained for Jnr at 3.2 kPa
and the traffic grade to which the binder belongs. This
classification is shown in Table 8. Based on the values
obtained for Jnr at 3.2 kPa, binders with 1%, 3%, and 5% can
AB 1%SS 3%SS 5%SS 7%SS 9%SS
0.1 kPa 3.40 3.90 1.89 2.15 3.82 3.66
3.2 kPa 3.83 4.21 2.27 2.30 5.28 5.49
Jnr, diff (%) 12.68 8.01 20.91 6.63 38.17 50.13
0.00
100.00
200.00
300.00
400.00
500.00
600.00
700.00
800.00
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
Non-recoverable
Compliance - Jnr ((kPa-1)
0.1 kPa 3.2 kPa Jnr, diff (%)
AB 1%SS 3%SS 5%SS 7%SS 9%SS
0.1 kPa 5.03 1.93 9.34 3.03 6.74 15.18
3.2 kPa 0.37 0.27 1.50 0.90 1.09 1.10
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
Recovery Percentage (%)
0.1 kPa 3.2 kPa
Melo Neto et al.
Nativa, Sinop, v. 11, n. 2, p. 283-291, 2023.
289
be classified for standard traffic use. However, the additions
of 7%SS and 9%SS had Jnr values above the specified limit,
making them unsuitable for highway use.
Table 8. Classification of traffic level based on Jnr values.
Tabela 8. Classificação do nível de tráfego com base nos valores de
Jnr.
Property Jnr (kPa)
Traffic Type Traffic level
Jnr up to 3.2
kPa at
maximum PG
temperature
2.0
-
4.0
Standard
< 10
million
1.0
-
2.0
Heavy
> 10
million
0.5
-
1.0
Very Heavy
> 30
million
0.0 - 0.5
Extremely
Heavy > 100 million
When analyzing the recovery percentage, as shown in
Figure 9, it can be observed that the highest (%R) values are
for the additions of 3%SS, 7%SS, and 9%SS, with values
above those of the pure binder, both for Jnr at 0.1 kPa and
Jnr at 3.2 kPa. Figures 10 and 11 present the Jnr test data
conducted at the maximum PG temperature of the asphalt
binder (64°C) and the elastic recovery for binders modified
with dried soybean oil sludge.
Figure 10. Non-recoverable compliances of pure binders and
binders modified with dried soybean oil sludge.
Figura 10. Compliâncias não recuperáveis dos ligantes puro e
modificados com a borra de óleo de soja seca.
Figure 11. Elastic recovery at 0.1 kPa and 3.2 kPa for pure binders
and binders modified with dried soybean oil sludge.
Figura 11. Recuperação elástica a 0.1 kPa e 3.2 kPa para os ligantes
puro e modificados com a borra de óleo de soja seca.
According to Figure 10, it can be observed that with the
incorporation of dried soybean oil sludge at 1%, 3%, and 5%,
the values of Jnr at 3.2 kPa tend to increase.
Regarding the percentages of 7%DSS and 9%DSS, a
decrease in the value of Jnr at 3.2 kPa is noticeable compared
to the previous percentages. This behavior was unexpected
due to the stiffness gain observed in the rotational viscosity
and PG tests for these additions.
4. DISCUSSION
4.1. Rotational Viscosity
Based on the results presented in Table 5, a reduction in
asphalt binder viscosity was observed for additions of up to
5% soybean oil sludge (SS), particularly at the lower test
temperatures, consistent with the findings reported by Melo
Neto et al. (2022a). However, 7% and 9% increased viscosity
compared to the pure asphalt binder before the short-term
aging procedure (RTFO). Following the RTFO test, only the
3% addition exhibited lower viscosity than the pure binder at
all three temperatures. Overall, all percentages yielded results
within the limits stipulated by the standard.
In the case of binders modified with dry soybean oil
sludge, the viscosity increased with higher additive
percentages. The study aimed to establish soybean oil sludge
as a potential viscosity reducer, and the test results indicate
that adding up to 5% raw sludge ensures this reduction.
However, samples with dry sludge suggest that values lower
than 1% can achieve this viscosity reduction. Given that raw
sludge contains a notable moisture content, the effective
added amount of soybean oil sludge is lower than the actual
quantity employed.
According to Silva et al. (2022), as viscosity decreases
relative to the pure binder, the action of the modifying agent
will consequently influence compaction and mixing
temperatures, which are linked to the workability of the
binder.
4.2. Performance Grade (PG)
The results presented in Figures 2 and 3 allowed us to
ascertain that following the addition of crude soybean oil
sludge (in natura) and dried sludge, as well as when subjected
to higher temperatures, there is increased development of
stiffness in the asphalt binder. For lower temperatures, these
findings indicate that incorporating the modifier contributes
to reducing the stiffness of the binders. Furthermore, it's
noteworthy that for both crude and dried sludge, there was
an increase in the G*/Senδ parameter with short-term aging,
albeit consistently maintaining values lower than those of the
pure sample. This phenomenon arises from the samples
becoming stiffer after RTFO, with parameters around twice
as high as those obtained before the procedure, a behavior
also observed in the studies by Portugal (2016) and Melo
Neto et al. (2022b).
It's worth noting that in the case of adding dried sludge,
the fact that this parameter is lower than that of the pure
binder diverges from the values obtained in the viscosity
tests. This suggests that there may have been incomplete
homogeneity in the mixture, leading to non-representative
results, or that this modifying agent may behave as a viscosity
reducer under low temperatures.
An increase was observed regarding the PG values for the
binders modified with both crude and dried sludge, as
presented in Figures 4 and 6. This increase could be
attributed to the high moisture content present in the
material (approximately 40%). As the amount of sludge
added to the asphalt binder increases, the water content also
AB 1%
DSS
3%
DSS
5%
DSS
7%
DSS
9%
DSS
0.1 kPa 3.40 3.82 4.22 4.02 1.93 0.53
3.2 kPa 3.83 4.10 4.59 4.99 4.37 4.37
Jnr, diff (%) 12.68 7.21 8.87 24.21 125.94 721.54
0.00
100.00
200.00
300.00
400.00
500.00
600.00
700.00
800.00
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
Non-recoverable
Compliance - Jnr ((kPa-1)
0.1 kPa 3.2 kPa Jnr, diff (%)
AB 1%DSS 3%DSS 5%DSS 7%DSS 9%DSS
0.1 kPa 5.03 1.62 0.96 6.18 33.53 73.95
3.2 kPa 0.37 0.28 0.30 0.58 3.13 3.40
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
Recovery Percentage (%)
0.1 kPa 3.2 kPa
Rheological investigation of asphalt binder modified with soybean oil sludge
Nativa, Sinop, v. 11, n. 2, p. 283-291, 2023.
290
increases, which could have oxidized the asphalt binder and
increased its stiffness.
4.3. Multiple Stress Creep Recovery (MSCR)
Regarding the samples of modified binder derived from
crude sludge, based on the Jnr values presented in Figure 8,
it can be observed that when applying stress levels of 0.1 kPa
and 3.2 kPa, the binders modified with 3%SS and 5%SS
exhibited the lowest values of non-recoverable compliance
compared to the other modified binders. These values were
also lower than those obtained for the binder without
additives. The reduction of this parameter indicates a less
fluid binder and, thus, a lower susceptibility to permanent
deformation, which contradicts the rotational viscosity test
results indicating a reduction in material stiffness. The
samples 7%SS and 9%SS had Jnr values at 3.2 kPa above the
specified norm, rendering them unsuitable for use, according
to AASHTO M320 (2021). High Jnr values at 3.2 kPa indicate
a more fluid asphalt binder and, consequently, a binder more
susceptible to permanent deformation.
As for the differential Jnr values (Jnr diff), it can be
observed that for all tested samples, the Jnr diff values were
below the limit of 75%, indicating that the samples are
suitable for use at this temperature range.
Regarding the percentage of recovery shown in Figure 9, as
mentioned by Mendonça et al. (2022), the Multiple Stress
Creep Recovery (MSCR) percentage can identify and quantify
the effect of the additive in the binder. Based on this, it is
noted that the additions of 3%SS, 7%SS, and 9%SS
significantly influence the elastic characteristics of the binder
under high traffic levels.
As for the binders modified with dry sludge, according to
Figure 10, it was observed that for additions of 1%, 3%, and
5%, the Jnr values at 3.2 kPa tend to increase. This indicates
that adding material at these percentages to the pure binder
increases its stiffness and reduces its susceptibility to
permanent deformation.
However, it is important to note that these results are for
a temperature of 64°C above the RTFO-aged PG
temperature obtained for these samples (58°C). This might
have led to oxidation and increased consistency. These
inconsistent values could result from a lack of chemical
interaction between the asphalt binder and the dry soybean
oil sludge. This absence of interaction prevents a
homogeneous mixture from forming, rendering the samples
unrepresentative and invalidating the data or the material's
use in pavement applications.
In terms of the percentages of 7%DSS and 9%DSS, a
decrease in the value of Jnr at 3.2 kPa was observed, a
behavior unexpected due to the stiffness gain observed in
rotational viscosity and PG tests for these additions.
Concerning their recovery percentages, these samples are
classified as inadequate due to having values significantly
above 75%, as shown in Figure 11.
5. FINAL CONSIDERATIONS
Based on the obtained results, it can be concluded that
using soybean oil sludge as a viscosity-reducing agent is not
viable. The modified samples exhibited higher stiffness than
the pure binder. The PG temperatures before the aging
process were higher than the reference values, but after aging,
the found values were equal to or lower than the reference
values. Thus, the modifier was not effective in reducing the
PG temperature.
In the case of raw soybean oil sludge, adding this modifier
reduced susceptibility to permanent deformation at the 9%
level. Concerning this material, it was noted that the high
moisture content present in the soybean oil sludge could have
contributed to the oxidation process of the asphalt binder
during modification and short-term aging, resulting in
increased stiffness.
Such uncertainties led to analyzing the binder modified
with dried soybean oil sludge. The results showed that
additions of up to 5% provided viscosity values equivalent to
those of the pure binder. In comparison, percentages above
7% increased the stiffness of the asphalt binder. Like the raw
sludge, the dried sludge did not reduce the PG temperature,
rendering it unsuitable as a rejuvenating agent for recycled
asphalt mixtures.
Furthermore, removing moisture from the soybean oil
sludge samples increased the materials' sensitivity to elevated
stress levels, making the modified binder more susceptible to
deformation under increased load, as demonstrated in the
MSCR test. Thus, the hypothesis that removing moisture
from the sludge would improve its performance in the
asphalt binder was disregarded.
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Author Contributions: O.M.M.N. - conceptualization,
methodology, investigation, data curation, writing - original draft,
writing - review and editing; L.P.T.M.; M.C.R.S.; A.M.S.L.; M.V.S.;
E.L.C.C.; J.L.S.C.; B.H.A.M.N. - methodology, investigation, data
curation, writing - original draft.
Funding: Not applicable.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement (Ethics Committee of the area):
Not applicable.
Data Availability Statement (how the data can be made
available): Study data can be obtained by request to the
corresponding author or the first author, via e-mail. It is not
available on the website as the research project is still under
development.
Conflicts of Interest: The author affirms that she has no financial
or personal affiliations that could unduly affect or skew the paper's
content.