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TRANSCRIPT
2018 Test and Measurement Conference
From Crude Oil to Application: A Low Temperature and Aging Nexus
Approach to Material Memory
Speaker / Author: Keith D. Nare
Co-author: Shanganyane P. Hlangothi
Centre for Rubber Science and Technology
Nelson Mandela University
PO Box 77000, Summerstrand, Port Elizabeth, 6031, South Africa
e-mail: [email protected]
Phone: 041 504 2380 Fax: 041 504 2574
Abstract
Creep and deflection associated with thermal changes gradually develops as temperature
drops and can be simulated using a thermoelectric bending beam rheometer. Fundamentals of
the elementary beam theory and the elastic-viscoelastic correspondence principle give the
basis for understanding time dependent flexural-creep behavior of bitumen. Being a by-
product of crude oil distillation at refineries, the effects of origin and refining technology play
a critical role in understanding chemistry related to material memory and fingerprint.
Spanning across a variety of neat and modified binders, material exposure to low temperature
and age state is important in predicting in-service and longevity behavior of the road. In
accordance to South African proposed framework on performance related specifications in
practice, studies performed on the bending beam rheometer highlight the low temperature and
aging nexus as related to material memory. Understanding inherent material signatures helps
in better decision making leading to informed choices and major cost savings in the life cycle
of your road. The thermal history of the binder in addition to cycles of short term and long
term aging contributes to the changes over time from source to application of the parent
binder. In essence, binder rheology depicted in free shifted stiffness isotherms plots together
with parameters such as aging indices and critical temperatures are used in the study to
understand changes in the material with aging and relaxation processes based on binder
composition. The basis of establishing a fingerprint using the bending beam rheometer is to
aid in identifying the source of the parent binder in either unknown or modified binders; thus
enabling binder traceability and contributes to the performance grading of the binders. Neat
20/30, 50/70, 70/100 as well as crumb rubber, styrene butadiene styrene and ethylene vinyl
acetate modified binders were used in this study.
1. Introduction
Bitumen quality affects its performance as a road construction material. Variability in
fractional composition stems from changes associated with processing and crude sources [1].
According to media [2] and technical reports [3], 45% of South Africa’s crude oil comes
from Saudi Arabia, a further 23% from Nigeria, 18% from Angola, 4% from Ghana, with the
trade-off of 10% from other sources. Although world politics can shift the demand and
supply of crude oil, operating capacity at local refineries (currently at a maximum average of
80%) also affects its import. Nonetheless, since fractional composition is dependent on the
crude source, the fingerprint and memory of the bitumen by-product is also unique to the
crude oil type, with capacity and refining technology adding onto the variation.
Peer-reviewed manuscriptTest and Measurement 2018 Conference and Workshop
2018 Test and Measurement Conference
Dating back to the early 90s, Anderson et al. [4] introduced the bending beam rheometer
(BBR) as part of the Strategic Highway Research Program (SHRP) for stress controlled direct
measurement of the bitumen at the lowest pavement temperature [5]. The BBR has been used
since to generate bitumen, modified bitumen and asphalt data and their inferences on creep
stiffness (S) and creep rate (m) as related to performance criterion [6]. In the interest of
characterisation it would be misleading to have a materials chemistry blind approach to the
source, modifier and thermal history of the bitumen under analysis. South Africa has recently
introduced performance grade (PG) bitumen testing and protocols with emphasis on grading
based on the age state of the binder; harnessing both an empirical testing basis coupled with a
transition to performance related testing. The use of the BBR [7] in PG testing is on residue
exposed to short and long term aging via the rolling thin film oven test [8] and the pressure
aging vessel [9] respectively.
The BBR finds its applications in municipal waste modified bitumen [10], crumb rubber
modified bitumen [11], fracture and moisture damage characteristics of 70/100 bitumen with
loadings of warm mix additives [12] and polyethylene wax modified bitumen [13]. In
addition, it can be used to measure bitumen emulsion PG grading of the material associated
with poly-phosphoric acid induced physical hardening [14], as well as its effect on aged
asphalt concrete [19]. Compared to other instrumentation approaches, BBR can be used as an
alternative to both the bending beam creep tests for asphalt mixtures [15] and the dynamic
shear rheometer (DSR) with 4mm parallel plates [16]. With regard to thermal analysis, BBR
can be an alternative to differential scanning calorimetry (DSC) in determining low
temperature properties and glass transition temperature of bitumen [17]. For example, BBR
was used in determining the engineering behaviour of bitumen loaded with mineral filler [18]
as well as low temperature properties of styrene butadience styrene (SBS) polymer modified
bitumen [20], amongst many others.
Marasteanu et al. [21] reported that critical temperature and limiting temperature from the S
and m values of the BBR are considerably affected by physical hardening. For determining
the single event cracking temperature directly from the BBR, Shenoy [22] proposed a
procedure which uses pavement thermal stresses from the BBR binder stiffness data to
calculate two asymptotic thermal stresses build up rates which directly identifies the cracking
temperature. In essence the BBR becomes a stand-alone device for low temperature binder
specification determination. Understanding bituminous binders relaxation properties at low
temperatures has led to advanced techniques for master curve development from the BBR.
Rowe et al. [23] identified that the discrete spectrum fit is the best method for fitting a master
curve, however with limitations of non-extrapolation beyond the range over which data is
collected. In the early 2000s, the Christensen-Anderson-Sharrock method was given as the
best functional from for fitting BBR data owing to the lowest root mean square errors and the
least bias in the test results [23].
Marasteanu and Anderson [24] discarded the use of pseudo black diagrams with BBR data
because of errors in calculating m-values associated with the use of polynomial
approximation. The c-coefficient can be used as a quick check of BBR data on the basis of
the fact that the slope of the m-values decreases as the test temperature decreases. ∆Tc
parameter is age dependent and indicates the tendency of either S-controlled or m-controlled
binders with preference for the former as they generally have better relaxation properties
leading to better performance [25]. Christensen et al. [26] proposed that the R-value
(rheological index) is linked to binder behaviour related to fatigue resistance, chemical
composition and the degree of oxidative aging. This was depicted in the shape and skewness
2018 Test and Measurement Conference
of the spectrum. King et al. [27] and Rowe et al. [28] reinforced the R-value as an aging
function highlighting whether aging trends would translate to mixture properties as evidenced
by the shape of relaxation spectra and the ability to relax stress.
In this study, thermo-rheological properties of neat and polymer-modified binders sourced
from different refineries in South Africa were analysed. The binders used were short and
long-term aged through the rolling thing film oven test, modified rolling thin oven test and
pressure aging vessel [29].
2. Materials and methods
2.1 Materials
The particular selected seal and asphalt binders for the study consisted of 9 samples namely:
20/30, 50/70, 70/100, S-E1, S-E2, A-E1, A-E2, A-P1 and NCRT (New Crumb Rubber
Technology). Governing the selection was the inclusion of most seal and asphalt binders
commonly used in different parts of the country. The following is a background to the binders
and where they were sourced:
Neat binders:
20/30, Acoustex, Eastern Cape, parent binder sourced from Sapref refinery.
50/70, Much Asphalt, Gauteng, parent binder sourced from Natref refinery.
70/100, Much Asphalt, Western Cape, parent binder sourced from Chevron refinery.
Styrene butadiene styrene modified binders:
S-E1, Colas, Eastern Cape, parent binder sourced from Chevron refinery.
S-E2, Colas, Eastern Cape, parent binder sourced from Sapref refinery.
A-E1, Much Asphalt, Eastern Cape, parent binder sourced from Chevron refinery.
A-E2, Much Asphalt, Eastern Cape, parent binder sourced from Chevron refinery.
Ethylene vinyl acetate modified binder:
A-P1 from Colas in the Eastern Cape, parent binder sourced from Chevron refinery.
Crumb rubber modified binder:
NCRT from Tosas in Bloemfontein, parent binder sourced from Sapref refinery.
2.2 Methods
The aging conditioning and the rheological testing were conducted at the Nelson Mandela
University bitumen laboratory and at the SANRAL Technical Excellence Academy
laboratories in the Eastern Cape, respectively. Specific instrumentation, methods and
procedures are given as follows:
2.2.1 Instrumentation
The instruments used in the study include:
Rolling Thin Film Oven (RTFO);
Pressure Aging Vessel (PAV) and Vacuum Degassing Oven (VDO); and
Thermoelectric Bending Beam Rheometer (BBR).
2018 Test and Measurement Conference
2.2.2 Experimental design
The thought process behind the experimental design included the goals of the testing
procedure and the sample preparation. The steps taken to test and age the binders are given in
the flow chart shown in Figure 1.
Figure 1: Experimental design flow chart to depict the regime of testing for the nine binders.
2.2.3 Goal of the testing procedure
The main objective was the thermorheological analysis of low temperature and aging nexus
of the nine binders. Progression in the binder age state as simulated by short term and long
term aging and rheological behaviour at low temperatures was paramount for further
inferences. The binder fingerprint would assist in revealing the nature of the material memory
associated with the origin and additive nature relating to the chemistry of the related changes
because of the aging regime. The binder thermal history and material memory were evaluated
in the following ways:
Low temperature aging indices approach to changes from a neat binder, RTFO and
PAV aged binders.
The S and m approach to binder analysis through BBR experimental data.
2.2.4 Sample preparation
All neat and modified bitumen samples were varied across different suppliers in the country.
In the interest of minimizing the thermal history of binders, samples were heated prior the full
regime of testing with neat, modified and NCRT binders heated at 160 ºC, 170
ºC and 180
ºC
respectively. The regime of heating was conducted for 1 hour followed by sample
homogenising using a laboratory mixer fitted with a dual helical impeller prior use in the
testing. The BBR beam preparation was conducted in aluminium moulds according to ASTM
standard [7]. Samples were then cooled to approximately -5ºC for 1 minute and demoulded.
After demoulding, the sample beam was immersed in a constant temperature methanol bath
and kept at each test temperature for 30 minutes.
2.3 Aging of binders
Age hardening affects durability of bituminous binders. It is manifested as an increase in
stiffness reflected in viscosity measurements and is highly dependent on temperature, time
and thickness of bitumen film. Characteristics of aging is either physical and/or exudative
20/30 50/70 70/100 S-E2S-E1 A-E2A-E1 NCRTA-P1
BBR RTFO BBR
PAV
neat binder RTFO binder
VDO
PAV binder
2018 Test and Measurement Conference
hardening due to loss of volatile components and oxidation during construction (short term)
and in-field after construction (long term). As a result, extended heating procedures are
performed to correlate accelerated laboratory aging with field performance. In this study, the
aging of binders was done in the RTFO and PAV. The RTFO was for the short term aging
whereas the PAV was for the long term aging. Residue from the RTFO was used in the PAV
and after the PAV aging, the residue was taken to the Vacuum Degassing Oven after which
the sample was ready to be tested in the BBR.
2.3.1 Rolling Thin Film Oven
Introduced as a significant modification of the Thin Film Oven Test (TFOT), the RTFO test
involved placing bitumen in glass jars and rotating 1.25 mm thin films relative to the TFOT
3.2 mm films to simulate bitumen hardening. The method adopted in this study was the one
developed by the California Division of Highways, where about 35 g of neat bitumen was
placed in vertically rotating shelf while blowing hot air into each sample bottle at its lowest
travel position. The amount of hardening in RTFOT correlates with conventional batch
mixer. For the modified binders, the Modified Rolling Thin Film Oven Test (RTFOTM) was
developed by Bahia as an improvement for highly viscous binders failing to roll inside the
glass bottles and overcome binders rolling out of the bottles. This method is identical to the
RTFOT except that a set of 127 mm long by 6.4 mm diameter steel rods was placed inside
brass containers. Steel rods create the shearing forces to spread the binder into thin films and
help in overcoming the problem of aging high binder viscosity. [8,29,30].
2.3.2 Pressure Aging Vessel
The Pressure Aging Vessel test was developed by the SHRP-A-002A research team to
simulate the long term, in-service oxidative aging. In this method, the RTFOT/RTFOTM
conditioning comes first, followed by oxidation of residue in the PAV. The process involves
placing about 50 g of sample in 140 mm diameter pan, 3.2 mm binder film, with air
pressurized to 2±0.1 MPa for 20 h at temperatures between 90 and 110 ˚C [30]. The residue
from the PAV was heated at 170 ºC prior degassing in the Vacuum Degassing Oven (VDO)
for 30 minutes to remove entrapped air. If not degassed, entrapped air bubbles may cause
premature breaking in the Direct Tension Test [9,30].
2.3.3 Bending Beam Rheometer
The Bending Beam Rheometer was introduced as a binder test in the Strategic Highway
Research Program. It has been incorporated in the performance grade specification to
determine binder stiffness at 60 seconds and the slope of stiffness curve, log time versus log
stiffness, gives the m-value. In essence its development was to overcome testing problems
common with other methods when testing stiff binder at low temperatures [23]. The binder
tests were carried out on different temperatures ranging from 0 ºC to -24 ºC with -6 ºC
increments representing the low temperature binder grade [22]. A constant load of 100 g was
applied to the rectangular beam sample supported by stainless steel rounds and the deflection
at the centre point was measured continuously. Creep stiffness (S) and creep rate (m) were
measured at different loading times spanning from 8 to 240 seconds [17]. The final result is
the performance grade limiting temperature determined from stiffness and m-value,
representing the slope of stiffness versus time curve in a double logarithm plot. Both values
are determined for the time loading at 60 seconds [7,15].
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2.4 Data analyses
The proposed hypothesis of the study was based on the assumption that as binder ages, low
temperature relaxation properties disintegrate more rapidly than stiffness. The decline in the
m-value shows that the binder flow ability is limited to heat distress accumulating in the mix.
Validation of the hypothesis through binder testing is reflected in BBR critical temperature
for m-value deteriorating faster than the critical temperature for stiffness during PAV aging.
BBR test data from samples conditioned in the RTFOT and PAV were used for generation of
free shifted stiffness isotherms in Microsoft Excel. Numerical stability within the constraints
of testing was the basis used for the selection of test data used in the analysis. The approach
to use isotherms of stiffness, S(t) was taken and applied to obtain multiple BBR isotherms. In
the process, it obtained shift factors where stiffness data at six loading times between 8 and
240 s for every test temperature was shifted horizontally on the log time scale. This formed a
smooth reasonable overlap, which according to Gordon and Shaw’s method can be used to
obtain free-shifted stiffness isotherms for all binders at a particular reference temperature.
The temperature dependency of the shift factors was modelled using Arrhenius equation [23].
2.5 Research constraints and areas of growth
The availability of the RTFOT, PAV and BBR was at a separate testing facility to the
institution given the scarcity of such instrumentation in the Eastern Cape and the
country at large.
The cleaning of the BBR aluminium moulds posed a huge challenge with stubborn
residual solvent that remained even after cleaning. A final flush clean with acetone
helped in the process.
Unavailability of the RHEA Software to convert the BBR data to G* using the
Hopkins and Hamming method limited the application of black space plots and master
curve development. The sole focus was the BBR, though if available it would have
been great to use merged DSR data to construct master curves.
BBR data was difficult to obtain for neat binders, hence the need to test RTFOT and
PAV conditioned samples to track the changes in aging prior conditioning.
Grease on the mylar strips if not prepared well in the beam demoulding stage would
give skew dimension to the beam which would lead to erroneous results.
The use of the probe thermometer was inevitable so as to compare the actual temperature
of the bath relative to what is being recorded on the software as well, given that one has
to calibrate at every test temperature.
The importance of a temperature controlled room especially in summer where the
heat/water unit would not flange down to allow for reaching the desired low temperature.
Adhering to the limit of all the testing to be done within 4 hours of preparation was very
important for the reliability of results.
Importance of shutting down the machine properly to avoid solvent rise and emphasis on
the shutting down temperature to avoid solvent level engulfing the load cell.
3. Results and Discussions
3.1 Free shifting isotherms
The development of Gordon and Shaw free-shifting isotherms was based on the similarity in
reference temperature to match the temperature dependency of the shift factors across all
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samples regardless of the binder. The RTFOT and PAV aged binders under the regime of low
temperature testing had reference temperatures -12ºC (20/30, A-E2 and A-P1), -18 ºC (50/70,
70/100, S-E1, S-E2 and A-E2) and -24 ºC (NCRT). Figures 2, 3 and 4 depict the free shifting
isotherms for all the binders used in the study.
Figure 2: Modified Gordon and Shaw free shifting isotherms for 20/30, A-E2 and A-P1
binders.
At reference temperature -12 ºC, 20/30 was more susceptible to aging relative to A-E2 and A-
P1. Given that 20/30 is a neat binder, at low temperatures the effects of short and long term
aging tend to proliferate more as opposed to the other two binders. The A-P1 binder was not
far off from the 20/30 binder. Given the nature of the EVA plastomer additive, the
disintegration of the plastomeric backbone at accelerated conditions could have led to the
increased aging tendency to be more inclined towards the 20/30 binder. A 3D rigid network is
generally formed for plastomers in bitumen, with ethylene and vinyl acetate moieties
breaking down. The interaction with the oxidized bitumen molecules after PAV aging affects
binder homogeneity, hence remaining unstable during aging. Ultimately, this renders more
parent bitumen hardening and minimal participation of plastomer in the bitumen aging
mechanism. The bitumen rich phase of the modified binder is what is exposed more to the
effects of short and long term aging in the case of the A-P1. EVA as a bitumen modifier is
known to have limited improvement in low-temperature properties due to its significantly
high glass transition temperature which is strongly dependent on vinyl acetate content and
elastic recovery owing to its plastomeric nature. A further low melting temperature of the
ethylene domains in the EVA disintegrates on shearing through preparation [31,32]. Of all
the three binders, at a particular reference temperature, the SBS modified A-E2 showed the
least susceptibility to aging at low temperatures as shown in Figure 2.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 1 2 3 4 5 6
log
S (
MP
a)
log reduced time (s) Tref -12˚C
20/30
20/30
20/30
A-E2
A-E2
A-E2
A-P1
A-P1
A-P1
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Figure 3: Modified Gordon and Shaw free shifting isotherms for 50/70, 70/100, S-E1, S-E2
and A-E1 binders.
Figure 3 shows the Gordon and Shaw free shifting isotherms at a reference temperature of -
18 ºC. The source of neat bitumen could have played a huge role in the aging susceptibility
of 50/70 relative to 70/100. Unique to the parent binder would be the chemistry associated
with the loss in volatiles associated with distribution of SARA fractions in the bitumen. 50/70
is found to be more prone to aging and indeed reflected in its low temperature behaviour in
the modified Gordon and Shaw free shifting isotherms in Figure 3. The aging resistance is
improved by modification, which is evident in the S-E1, S-E2 and A-E1. SBS is elastomeric
in nature and confers the modified bitumen improved low temperature relaxation properties
based on the loading of SBS, which is subject to temperature sensitivity for the different SBS
modified binders. The distinction amongst the three SBS modified binders is based on
different applications for seals and asphalt, thus the possibly of additives associated with
asphalt leading to the most aging resistance at the reference temperature. S-E1 and S-E2
binders are prone to less thermal degradation during the chip seal spraying process, with A-
E1 binders subjected to thin film oxidation in the coating drum and when paving in the hot
mix applications. Hence severity in degradation is prevalent in A-E1 binders during
manufacture and application.
In the case of NCRT, the nature of the additive played a huge role due to the composite
nature of crumb rubber and loadings of warm mix FT wax used in the modification of
bitumen. Figure 4 shows the modified Gordon and Shaw free shifting isotherms for NCRT
binder. Kim and Lee [34] reported that rubber can be used to improve the cracking resistance
of asphalt binders modified with wax. Fazaeli et al. [35] showed that among all additives,
Sasobit and crumb rubber combination exhibited the best performance at low and
intermediate temperatures. The authors reported that crumb rubber provided an elastomeric
backbone for the modified binder with increased elasticity. In addition, the compositional
variations in crumb rubber from a highly engineered passenger or truck tyre would bring up
the dynamic of carbon black, which is an antioxidant and is effective in crack resistance in
the low temperatures. The resistance to aging at low temperatures can be associated with
modification of bitumen with crumb rubber and FT wax. Specific technical requirements at
low temperatures should lead to binder formulation for the particular engineering application.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 1 2 3 4 5 6
log
S (
MP
a)
log reduced time (s) Tref -18˚C
50/70
50/70
50/70
70/100
70/100
70/100
S-E1
S-E1
S-E1
S-E2
S-E2
S-E2
A-E1
A-E1
A-E1
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3.2 Limiting temperatures and ∆Tc
Figure 4: Modified Gordon and Shaw free shifting isotherms for NCRT binder.
Baumgardner et al. [36] suggests that at temperatures close to or below the glass transition
temperature (Tg), a reversible effect with heating occurs where mixture beams decrease in
stiffness with time at a constant temperature. Lu and Isacsson [33] proposed that Tg
determined using BBR limiting temperatures is greatly dependent on source and grade of
bitumen. A decrease in Tg is noted on polymer modification with negative influence on the
limiting temperatures. Lu and Isacsson [37] reported that SBS modification causes a
reduction in the Tg with Masson et al. [38] indicating that relative to the polystyrene moiety,
the polybutadiene moiety has good interaction with bitumen, which improves miscibility. Anderson et al. [4] described the isothermal aging at low temperatures as a metastable
structural state near or below Tg as a slow and time dependent structural relaxation process
driven by the bias in internal energy leading to changes in material properties.
Modulated Differential Scanning Calorimetry (MDSC) studies [39,40], in the reversing heat
flow curve, revealed two Tgs in bitumen. The first transition at -20 ºC was attributed to the
SARA fraction of maltenes and the other in the temperature range of 53 ºC and 70 ºC was
assigned to asphaltenes. The inclusion of S and m parameters in determining the difference
between the continuous grading for the m-value and stiffness (Ts-Tm,) goes back to the SHRP
validation report which upon plotting BBR stiffness vs the m-value showed that neither
parameter was solely responsible for the rejection of the binders [28]. Table 1 summarises the
performance grade limiting temperatures and ∆Tc for the 9 binders used in this study. The
performance grade limiting temperatures include the stiffness limiting temperature at S(60s)
= 300 MPa, -10 ºC; whereas the m-value limiting temperature is at m(60s) = 0.3 min, 10 ºC.
Implications of long term aging to low temperature performance of the binders as related to
material characteristics gives a better understanding of how the different binders behave
under such conditions.
Most of the binders in Table 2 were found to be m-controlled binders. Given similar stiffness
levels, increased m-values led to faster development of thermal stresses. In the performance
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 1 2 3 4 5 6
log
S (
MP
a)
log reduced time (s) Tref -24˚C
NCRT
NCRT
NCRT
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grade criterion for reasonable low temperature climates, elevated m-value binders have been
found to perform better due to more relaxation occurring in the extended period of time [41].
The approach of looking at the m-value in that regard is by virtue of being the rate of change
of stiffness that is associated with inherent relaxation properties of the binders.
Table 1: Representation of the limiting temperatures and ∆Tc for the 9 binders used in the
study according to [25].
Binder Type
Limiting Temperature (-10 ºC) Ts-Tm
S(60s) m(60s) ∆Tc
20/30 Neat -17.3 -17.2 -0.1
50/70 Neat -22.8 -22.4 -0.4
70/100 Neat -25.7 -24.0 -1.7
S-E1 Elastomer -27.9 -24.1 -3.8
S-E2 Elastomer -26.9 -19.0 -7.9
A-E1 Elastomer -28.6 -23.4 -5.2
A-E2 Elastomer -22.3 -19.0 -3.3
A-P1 Plastomer -19.5 -16.7 -2.8
NCRT Elastomer* -33.3 -26.2 -7.1 *NCRT contains loadings of FT wax which introduces a plastomeric component to the binder
The criterion for obtaining ∆Tc involves the use of two adjacent specification grading
temperatures with limits that one value passes and the other fails the requirement for both S
and m-value.
According to the South African performance grade specification, the ∆Tc should be less than -
5 ºC. However, values greater than -5 ºC were obtained for S-E2 and NCRT as a result of
failure in both m-values when calculating the limiting temperature for m. A-E2 also failed
owing to failing in the stiffness value to meet the pass criteria. However, A-E1 has a value of
-3.3 ºC, which is a pass value even though the stiffness value did not meet the criterion. The
rest of the binders did conform to the pass fail criteria for both the S and m-value from the
BBR data. Critical temperature and limiting temperature from the BBR S and m-values are
mainly affected by physical hardening; hence proper sample preparation was critical because
testing in the BBR contributes to the results of the creep test.
3.3 Aging Indices
Aging indices are taken to be an arbitrary measurement of material changes that take place
from the neat, short and long term aged binders. The expected trend would be an increase in
stiffness as a result of each conditioning stage which reflects in the percentage change in
aging. Figure 5 shows the percentage change in aging for 8 of the binders with change
depicted from RTFOT to PAV. The values of the aging indices used for the percentage
change in aging were performed at -12ºC which for the NCRT sample was above the
temperature at which the RTFO and PAV aged temperature was measured.
The A-E1 and A-E2 binders showed the least susceptibility in aging behaviour at the test
temperature, with the former showing no changes in aging and the latter showing a negative
percentage change in aging with RTFO and PAV conditioning. The A-P1 showed the most
susceptibility to effects of changes from the short term to the long term aging heavily
reflected in the 74% incremental change in aging. S-E2 showed the second most
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susceptibility with move from short term to long term aging at 64%. The percentage change
in aging from short term to long term aging at low temperatures was to depict the nature of
the effects of binder changes when moving from workability to an in-service approach in
general when considering performance parameters. The integrity of the modifier moieties,
loss of material memory and finger print could have contributed to the behaviour of the
binders shown in Figure 5.
Figure 5: Percentage change in aging from RTFO to PAV aged binders reflecting effects of
aging conditioning on the binders.
4. Conclusion
The nexus to low temperature and accelerated laboratory aging based on the unique binder
finger-print and memory led to the following summary of conclusions and recommendations:
The source of binder, type of modifier and thermal history plays a pivotal role in low
temperature rheological properties measured at different stages of short term and long
term aging.
The contribution of stiffness and rate of change in stiffness is critical in the low
temperature rheology approach to effects of aging at different isothermal temperatures
The S > 300 MPa and m > 0.300 criterion in calculation of ∆Tc impacts on the -5 ºC
limit for the performance grade specifications which was the case for S-E2 and
NCRT.
Tracking low temperature incremental aging changes through aging indices and
percentage change in aging reflects aging susceptibility in the binders.
The BBR can be used as a stand-alone instrument to measure low temperature
performance of neat, RTFO and PAV aged binders.
Recommended for further study would be the merged BBR and DSR data for master curve
development and black space plots. The inclusion of MDSC data is to highlight the
importance of thermal history and modification on the Tg and its effects on SARA fractions in
the binder.
29
2228
77
0
-35
12
64
-60
-40
-20
0
20
40
60
80
100
(20/30) (50/70) (70/100) (A-P1) (A-E1) (A-E2) (S-E1) (S-E2)
Percentage Change
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5. References
1. M. Paliukaite, A. Vaitkus and A. Zofka, “Evaluation of bitumen fractional composition
depending on the crude oil type and production technology”, The 9th
International
Conference of Environmental Engineering, Vilnius, Lithuania, 22-23 May 2014, pages
1 to 8
2. SA dependence on petrol imports growing - https://www.fin24.com/Economy/SA-
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2018 Test and Measurement Conference
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2018 Test and Measurement Conference
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2018 Test and Measurement Conference
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