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Article

Effect of Weak Zones on Resilience of Sustainable Surface Course Mixtures of Fresh-Reclaimed Asphalt Pavement

by
Syed Iqrar Hussain
1,2,
Ammad Hassan Khan
1,*,
Zia ur Rehman
1,
Wasim Abbas
3,
Safeer Abbas
3,
Abdeliazim Mustafa Mohamed
4,
Dina Mohamed Fathi
5 and
Mubashir Aziz
6,7
1
Department of Transportation Engineering and Management, University of Engineering and Technology, Lahore 54890, Pakistan
2
Punjab Mass Transit Authority, Lahore 54600, Pakistan
3
Department of Civil Engineering, University of Engineering and Technology, Lahore 54890, Pakistan
4
Department of Civil Engineering, Prince Sattam Bin Abdul Aziz University, Alkharj 16273, Saudi Arabia
5
Department of Structure Engineering and Construction Management, Future University, Cairo 11835, Egypt
6
Department of Civil and Environmental Engineering, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
7
Interdisciplinary Research Center for Construction and Building Materials, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
*
Author to whom correspondence should be addressed.
Sustainability 2022, 14(16), 9966; https://doi.org/10.3390/su14169966
Submission received: 10 March 2022 / Revised: 5 July 2022 / Accepted: 6 July 2022 / Published: 12 August 2022
(This article belongs to the Special Issue Sustainable Road Construction)
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Abstract

:
The use of reclaimed asphalt pavement (RAP) is necessary for sustainable and cost-effective road infrastructure construction. This research investigates the effect of the area of weak zones (WZ) on the resilient modulus (MRT) of mixtures of fresh asphalt with 20% RAP. Experimentation on fresh asphalt–RAP mixtures comprising Superpave (SP-A, SP-B) and Asphalt Institute (MS-2) gradations with 20/30, 40/50, 60/70 and 80/100 penetration grade binders was carried out. WZ were determined based on the analysis of magnified digital images of asphalt specimens obtained using optical microscopy. This study demonstrates that the 20/30 grade binder caused an increase in the MRT at 25 °C up to 1.8, 2.9 and 9.2 times for a 0.1 s load duration, and 2.4, 3.0 and 9.7 times for a 0.3 s load duration. In contrast, improvement at 40 °C was observed to be up to 1.9, 3.1 and 9.7 times for a 0.1 s load duration, and 1.9, 3.0 and 12.4 times for a 0.3 s load duration in comparison with 40/50, 60/70 and 80/100 grade binders, respectively. Experimental data were validated by factorial analysis. Power trendline equations were also developed between MRT and WZ to explain the effect of gravel particle orientation on the sustainable resilience of surface course mixtures.

1. Introduction

Reclaimed asphalt pavement (RAP) is frequently used in fresh asphalt, worldwide, to create cost-effective pavements [1]. Resilient modulus (MRT) is the key parameter for the design of asphalt pavements. Asphalt mixture is a viscoelastic material which shows resilient behavior during cyclic loadings [2]. Several factors affect the resilient modulus (MRT) of asphalt mixture, i.e., binder grade, temperature, loading pulse duration, loading pulse shape, moisture, indirect tensile strength, aggregate geometry, etc. [3,4,5,6,7]. The performance of asphalt mixtures depends upon the characteristics of the binder and aggregate. The gradation of constituent particles is significant, as voids between the larger particles are filled by smaller particles in the case of well-graded asphalt mixtures for the provision of grain to binder contact [8].
The characterization of RAP is vital for its optimum use, as the gradation of the RAP aggregate and old RAP binder is found to be different between roads of variable ages [9]. In the USA, the rate of re-use of asphalt is reaching up to 99%, whereas the average rate of re-cycling is up to 20%, as it reduces gas emissions by 35% and cost by 70% [10,11]. The characteristics of a sustainable binder fall between those of the old RAP binder and the fresh binder, whereas the mixing of fresh asphalt and RAP is important to achieve the desired properties of fresh asphalt–RAP mixtures [12].
MRT, calculated on the basis of recoverable strain, is used to characterize the mechanical response of the pavement to applied cyclic (traffic) loadings. In the laboratory, the MRT is usually measured by applying a haversine waveform for an applied loading time (duration) and rest period [13,14,15]. Indirect tensile strength (ITS) is the most commonly repeated load test to measure the resilient modulus of asphalt mixtures because of its simplicity and easy application [16].
High-modulus asphalt mixtures are prepared with hard-grade binder (e.g., 10/20, 20/30). These mixtures exhibit higher values of MRT than those obtained from mixtures prepared with conventional grade binders (40/50, 60/70 or 80/100). The use of high-modulus asphalt mixtures can reduce maintenance costs and pavement distress (rutting and fatigue) caused by ever-increasing heavy traffic loads [17,18,19,20,21,22,23,24]. The dynamic moduli of asphalt mixtures comprising hard binder 13/22 increased the rutting resistance two times and the fatigue resistance five to ten times as compared with conventional binder mixtures such as 40/50, 60/70, 100/150 and 150/200, and also reduced the shear displacement [25,26].
Hard-grade binder (20/30) increased MRT by 29%, 102% and 63% for temperatures of 20, 40 and 60 °C, respectively, compared to the mixtures with conventional binder (40/50) [27,28,29,30]. The moduli of asphalt concrete mixtures with hard-grade asphalt binder (20/30) are 18% higher than that of the polymer-modified asphalt binder [31].
An increase in loading duration reduces the MRT and produces more damage in comparison with a shorter loading time at the 25 and 40 °C test temperatures. This is because less time is taken by the mixtures to recover from the deformation [32,33,34]. The MRT values at the same temperature decreased from about 20 to 45%, with an increase in pulse width from 150 to 450 ms. An increase in loading duration of up to two times may cause the resilient modulus to decrease to about 44.47%, 43.15% and 41.3% for 19 mm, 25 mm and 37.5 mm nominal aggregate sizes, respectively [35].
The resilience of asphalt mixtures is a function of the gradation of aggregate particle shapes [36]. The most common internationally recognized, well-graded aggregate gradation curves (Asphalt Institute (MS-2), Superpave (SP-B, SP-A)) used in asphalt mixtures show different packing patterns (orientation and distribution), resulting in variable resilient moduli (MRT). The images of asphalt mixtures obtained from microscopy may be used to study the surface distress initiated due to the orientation and distribution of gravel particles. Two more popular procedures of microscopy—i.e., Scanning Electron Microscopy (SEM) at micro to nano magnification levels and optical microscopy at macro to micro magnification levels—can be used for the identification of the surface distress of asphalt mixtures. The analysis of asphalt mixture surface images at macro to micro magnification levels through optical microscopy can be used for the determination of the weak zones (WZ) in the packing/compaction. Notable studies about the zones of cracking in asphalt mixtures are limited [36] to date, and not enough studies on this novel topic are available. The application of IDT tests for the study of cracks and the initiation of cracks on the different zones of specimens are also documented [36] in the literature.
Furthermore, few studies are seen in the literature on the cumulative effect of binder grade and RAP on resilient moduli (MRT) for commonly used 20/30, 40/50, 60/70 and 80/100 grade binders involving SP-A, SP-B and MS-2 gradations.
The main objectives of this study were:
  • To determine the resilient modulus (MRT) of asphalt mixtures prepared with 20/30, 40/50, 60/70 and 80/100 grade binders for surface course gradations (such as SP-A, SP-B and MS-2) of fresh asphalt aggregate and 20% reclaimed asphalt pavement (RAP) mixture at different temperatures and load durations.
  • To conduct image analysis to view the orientation of aggregate particles of fresh asphalt and RAP for the determination of weak zones.
  • To compare the areas of weak zones and MRT.

2. Materials and Methods

For aggregates with a nominal aggregate size, as per the grain size distribution guidelines of the Strategic Highway Research Program (SHRP), Superpave was used. Superpave was labelled as SP-A, SP-B and MS-2. Aggregate characterization for surface course mixtures was carried out in the laboratory using different tests, i.e., Los Angeles abrasion [37], sand equivalent [38], flakiness and elongation [39], water absorption [40], and soundness [41].
RAP was taken from sections of flexible pavement undergoing expansion after five years of construction. The sources of the RAP aggregates were the same as the sources of fresh/virgin aggregates used in this research. At the time of construction, the aggregate gradation of RAP was SP-B with 40/50 grade asphalt binder (4.5% optimum asphalt content). Aggregate gradation and asphalt binder extraction were carried out in the laboratory for the RAP sample. Aged binder was found at 3.0% by weight in the RAP. The aggregate gradation was also observed to be comparable with the SP-B specification limits.
From the RAP, the sample of aged binder was recovered by a distillation procedure for laboratory characterization, i.e., penetration, softening point [42], ductility [43], and fire and flashpoint [44]. Both hard (20/30 penetration grade) and conventional (40/50, 60/70, 80/100 penetration grades) asphalt binders were also characterized in the laboratory by these tests.
RAP was added at a level of 20% by weight to each asphalt mixture. The gradation limit requirements of SP-A, SP-B and MS-2, as per the specifications, were achieved in the laboratory during the preparation of RAP–asphalt mixtures. For each gradation (SP-B, SP-A, MS-2), four separate samples corresponding to asphalt binder grades, 20/30, 40/50, 60/70 and 80/100, were prepared. RAP was mixed with virgin aggregates and asphalt binders in a mechanical mixer at temperatures of 160 °C. The optimum asphalt content of the mixtures was determined using the Marshall mix design.
Test specimens used for performing the indirect tensile strength (IDT) and resilient modulus tests (MRT) were prepared by a gyratory compactor in accordance with the Superpave standards [45]. A total of 205 gyrations were applied to each sample in the compactor to simulate thirty million equivalent single axle loads (ESAL) for a typical design life period of 20 years. Replicates of three samples each were made for IDT and MRT evaluation against each testing condition.
The IDT [45] and MRT [46] tests were carried out on a Servo-Hydraulic Universal Testing Machine with a loading capacity of up to 25 kN (UTM-25). MRT tests were carried out at temperatures of 25 °C and 40 °C with a haversine waveform at load durations of 100 ms, 300 ms and 900 ms as a rest period (loading frequency of 1 Hz). The tensile stress level of 15% of IDT was used as the peak loading stress. The seating stress was kept at 4% of the peak loading stress. The data acquired from the UTM-25 software were used for necessary output variable display/recording (compressive loading, recoverable horizontal deformation, and loading cycles).
Preconditioning was carried out on each asphalt mixture sample through 100 loading cycles for each test scheme. After the preconditioning cycles, values for compressive loading and recoverable horizontal deformation were recorded for the next five loading cycles, and the resilient modulus was determined as a mean of the last five readings as per the following formula [46]:
M R T = P c y c l i c × ( μ + 0.2734 ) δ h × t
where MRT is the resilient modulus (MPa), Pcyclic is the repeated compressive load (N), μ is Poisson’s ratio assumed as 0.35, δ h is the recoverable horizontal deformation (mm) and t is the thickness of the specimen (mm).
The significance of resilient modulus experimental results was determined using an analysis of variance (ANOVA) test. Minitab-18 was used for this purpose. Nominal maximum aggregate size (A), temperature (B) and load pulse duration (C) were the factors considered in the factorial analysis. Influential analysis was used for the diagnostic checking of the outliers in the data in order to predict its health.
The Olympus STM6 Optical microscope (Figure 1) was used to view high-resolution images of asphalt mixture samples at three magnifications, 5×, 10× and 20×.
An optical microscope was used to view the detailed surface structure regarding aggregate particles weak zones in asphalt mixture specimens [47,48,49,50]. The effects of change in aggregate weak zones on resilient moduli need to be recognized. The importance of the weak zones is due to the heterogeneity of the asphalt mixture’s coarse and fine aggregate composition. The gravel particle orientation affects physical and resilience performance of asphalt mixtures [51,52,53,54,55,56]. An attempt was made to plot the WZ against resilient modulus to study possible regression. In this study, the term weak zones (WZ) refers to the area on the surface of asphalt mix from which shear cracks are expected to propagate in straight or semi-straight paths. The area of the WZ primarily comprises binder and small aggregate particles. The area occupied by binder in asphalt mixes shows viscoelastic behavior. The area comprising small aggregate particles coated with binder shows a low grain-to-grain contact force. The area composed of large aggregate particles coated with binder exhibits a high grain-to-grain resistance force. In weak zones, the slippage is due to the flow of bitumen and the movement of small particles, which hang in binder under traffic loading and environmental changes. The direct physical determination of the WZ from the core/block samples of the asphalt mixes is cumbersome. However, determining the WZ can be carried out easily from the image analysis of asphalt mix cores. Contour lines can be drawn on the image of the asphalt mix cores, highlighting the WZ. The traversing knob of the planimeter can then be used for the determination of the area of the WZ from the image of the core. The percentage of WZ for a core sample was determined by [2]:
Weak zone (%) = (Area of weak zone from the core image/Total area of core) 100
where total area of core = (π/4) (core diameter)2
An analysis was carried out on all the asphalt mixture images obtained from optical microscopy, for the determination of the area of weak zones (WZ). Magnified images, along with a planimeter, served this purpose.

3. Results and Discussions

Figure 2 shows aggregate gradation plots along with control points and a restricted zone of particle sizes as per AASHTO MP-2.
The SP-A and SP-B gradations fulfill the Superpave criteria, while the MS-2 gradation passes slightly within the restricted zone. Well-graded compositions of aggregates were observed in all the three gradations.
The detailed engineering properties of the qualitative testing of virgin aggregates are summarized in Table 1.
The engineering properties of aggregates summarized in Table 1 fall well within the acceptable range for aggregate properties to be used in asphalt mixtures, as recommended by the Superpave Strategic Highway Research Program (SHRP).
Table 2 summarizes the properties of the asphalt binders utilized in this study.
Table 2 shows that the binders fall within the acceptable limits of AASHTO M20 for use as binders in asphalt mixtures.
Figure 3 shows the typical load cycles observed in the resilient modulus testing of asphalt mixtures, i.e., MS-2, SP-B, and SP-A with 20/30 penetration-grade asphalt binder.
In Figure 3, the variations in load cycle are observed more in portion “a”, particularly at the peak before 0.1 s in all three asphalt mixtures. After 0.1 s in portion “b”, the variation in load cycle for all the three mixes is comparable. Portion “a” in Figure 3 is further expanded in Figure 4 to closely compare the change in the trend of load and unload cycles.
It is evident from Figure 4 that all three mixtures show similar patterns, but of different magnitudes during loading and unloading cycles. Various early research studies showed the pattern of loading and unloading cycles for conventional asphalt mixtures prepared with 40/50, 60/70 and 80/100 grade asphalt binders. For high-modulus asphalt mixtures prepared with 20/30 grade binders and RAP, the patterns of loading and unloading cycles obtained in resilient modulus tests were not available in the literature. Therefore, the obtained patterns are shown in Figure 3 and Figure 4.
Presented in Figure 5 are the typical deformation curves corresponding to the loads applied to MS-2, SP-B and SP-A mixtures with 20/30 grade asphalt binder.
It is evident from Figure 5 that deformation curves show similar trends with different magnitudes in all asphalt mixtures. The loading portion, unloading portion, displacement peak and recovery portion of deformation curves of high-modulus asphalt mixtures are introduced in the literature for asphalt mixtures with RAP through Figure 5.
Figure 6 and Figure 7 present the resilient modulus comparison for all asphalt mixtures at 25 °C and 40 °C testing temperatures, respectively.
It can be seen in both Figure 6 and Figure 7 that the resilient modulus of SP-B gradation with 20/30 asphalt binder and RAP is observed at its maximum at 0.1 and 0.3 s load cycles and 25 °C and 40 °C testing temperatures, respectively. In addition to the variables listed in Equation (2) (above), the resilient modulus is also sensitive to temperature, loading cycle frequency, etc. The design of the experiments was conducted at 95 % confidence intervals, with a significance level of α = 0.05. Table 3 represents the analysis of variance (ANOVA) of the data, including main effects and 2-way and 3-way interaction effects for three defined factors, A, B and C.
A higher value of F or lower value of P represent the significance of the factor, as shown in Table 3. Degree of freedom (DF) shows that a total of three main and three interacting factors explain the variation. The temperature (C), as a factor, has the largest F-value, reflecting its importance to the resilient modulus. Table 3 shows that all three individual factors (A, B, C) have a p-value of 0.0001, which shows that these factors are significant. All 2-way interactions have a significant effect on the resilient modulus, except for nominal maximum aggregate size A * load pulse duration (B), for which p is 0.425 > 0.05 (α), showing that this interaction is not significant. Similarly, the 3-way interaction of factors is also insignificant for the resilient modulus of surface course mixtures, having a p-value of 0.929 > 0.05 (α).
Figure 8 shows the typical asphalt mixture images taken from the optical microscope at normal, inverted and threshold positions. The images were captured with a digital camera before the resilient modulus test, while the inverted and threshold images were treated using PineTools filters. The inverted images show the typical distribution of aggregates within the compacted mixtures, while the threshold images show the spread of mastic asphalt binder within the mixtures. The size and orientation of gravel are the main factors affecting the deformation of asphalt mixtures, as observed from these images.
Figure 8 shows that small size particles are distributed all over the SP-A specimen, with a smaller number of large particles; whereas, in the case of SP-B, there is a higher quantity of larger size particles and there are fewer small particles to fill the voids between large particles. It is clear from Figure 8, that, for SP-B, small and large particles are distributed in all portions of the specimen, and the spaces between large particles are properly filled with small particles. Hence, the high resistance between particles of SP-B presents increased resilience in tested specimens.
The size of the gravel and intermediate weak zones can be determined from the analysis of these images, as shown in Figure 9. Planimeter and optical microscope software can help in marking the orientation/contours of the weak zones on the images. The cumulative area of the weak zones in an image when compared with the total area of the image can give us the area of weak zones in a sample. Figure 9 shows the typical normal and magnified view of zones identified around the gravel particles of MS-2, SP-B and SP-A. Red lines shows the boundaries of weak zones on the images and the blue lines show weak planes on the surface.
In this study, images of different asphalt mixtures labelled MS-2, SP-B and SP-A were analyzed. It is evident from Figure 9 that the size of weak zones (WZ) is presented in increasing order for the SP-B, MS-2 and SP-A specimens. WZ fall in the order of SP-B < MS-2 < SP-A, which validates the evaluated resilient modulus (MRT) of SP-B, MS-2 and SP-A and infers that SP-B is more resistive and offers higher values of resilient modulus. Hence, the image analysis should be used for the selection of gradation to indicate weak zones and weak shear planes and to then identify the specimens of higher resilient modulus.
It was observed that a relation exists between the resilient modulus and the area of weak zones (WZ). As the area of the WZ decreases, the resilient modulus of asphalt mixtures increases. This may be is due to the increase in grain-to-grain contact between gravel particles. MRT was found to be related to the WZ of the asphalt specimens at 0.1 s and 0.3 s load durations for temperatures of 25 °C and 40 °C for fresh asphalt aggregate and 20% reclaimed asphalt pavement (RAP).
Figure 10, Figure 11, Figure 12 and Figure 13 present the MRT versus WZ data.
It is observed that MRT decreases with the increase in WZ for 20/30, 40/50, 60/70 and 80/100 grade binders involving MS-2, SP-B and SP-A gradations for 0.1 s and 0.3 s load durations at both 25 °C and 40 °C. In all three gradations used, i.e., SP-B, MS-2 and SP-A, the MRT values are observed at their maximum with 20/30 grade binders for a 0.1 s load duration at 25 °C, followed by mixes prepared with the same gradations, load duration and temperature, using 40/50, 60/70 and 80/100 binder grades.
The SP-B gradation blended with 20/30 grade binder for 0.1 s load duration at 25 °C, exhibits higher values of the MRT than the MS-2 and SP-A gradations prepared with 20–30 grade binder for a 0.1 s load duration at 25 °C. Similar trends, but lower MRT values, are observed at a load duration of 0.3 s at 25 °C. Minimum WZ are also observed in SP-B mixes with 20–30 binder for a 0.1 s load duration at 25 °C, reflecting better packing and compaction of the aggregates than in the MS-2 and SP-A gradations blended with 20/30 binders at a load duration of 0.1 s. Typical ranges of WZ are observed in all mixes under adopted testing conditions, i.e., SP-B from 16 to 26%, MS-2 from 34 to 47% and SP-A from 66 to 78%, respectively. It is observed that the ranges of the WZ in different mixes remained comparable with the changes in load duration (0.1 and 0.3 s) and temperature (25 and 40 °C). A uniform trend is observed in all mixes in the typical range of WZ, with the change in binder grades from 20/30 to 40/50 to 60/70 to 80/100, respectively. Hence, WZ are more governed by aggregate and RAP gradation type than the binder grade type. It is also observable that MRT is in the order of 20/30 > 40/50 > 60/70 > 80/100 grade binders, and gradations show MRT in the order SP-B > MS-2 > SP-A.

4. Conclusions

This research involved experimentation on fresh asphalt and 20% RAP mixtures comprising Superpave gradations (SP-A, SP-B) and Asphalt Institute gradation (MS-2) for the determination of the resilient modulus (MRT) and the image analysis of asphalt mixtures. Based on the results of this study, the following conclusions can be drawn:
  • This study shows that the 20/30 grade binder enhanced the MRT up to 1.8, 2.9 and 9.2 times for a 0.1 s load duration and 2.4, 3.0 and 9.7 times for a 0.3 s load duration at 25 °C, whereas a rise in MRT was observed to enhance the MRT 1.9, 3.1 and 9.7 times for 0.1 s load duration and 1.9, 3.0 and 12.4 times for 0.3 s load duration at 40 °C, when compared with 40/50, 60/70 and 80/100 binder grades, respectively. Hence, this study presents the selection of a sustainable grade of binder to achieve a high resilience in roads.
  • MRT was observed to decrease, in order, for different grades such as 20/30 > 40/50 > 60/70 > 80/100, and for different gradations in the order SP-B > MS-2 > SP-A. The SP-B showed the highest resilient modulus and maximum sustainability potential. Experimental results were validated by factorial analyses and found the data in good health.
  • Images of asphalt mixture specimens can be used to measure the area of weak zones (WZ) for the reasonable prediction of resilient modulus of sustainable surface course road mixtures.
  • Area of weak zones (WZ) in asphalt mixes is controlled more by aggregate RAP gradations than the asphalt binder grade.
  • Resilient modulus (MRT) decreases with the increase in the area of weak zones (WZ) for 20/30, 40/50, 60/70 and 80/100 binder grades involving MS-2, SP-B and SP-A gradations for 0.1 s and 0.3 s load durations at both 25 °C and 40 °C.
The prediction of the resilient modulus of asphalt mixes can be made using the area of weak zones (WZ). WZ may be used by pavement experts for the determination of distresses and its possible future propagation patterns in the asphalt mixes. These findings can lead towards sustainable road construction utilizing reclaimed asphalt pavement (RAP).
The observations in the above conclusions need to be further explored through more rigorous image analyses.

Author Contributions

Conceptualization, S.I.H. and A.H.K.; methodology, S.I.H., A.H.K., Z.u.R.; validation, S.I.H., A.H.K., W.A. and S.A.; formal analysis, S.I.H., A.H.K., Z.u.R., W.A., S.A., A.M.M., D.M.F. and M.A.; investigation, S.I.H., A.H.K., Z.u.R.; resources, A.H.K. and Z.u.R.; data curation, S.I.H., A.H.K., Z.u.R.; writing—original draft preparation, S.I.H.; writing—review and editing, A.H.K., Z.u.R., M.A.; visualization, S.I.H., A.H.K., Z.u.R.; supervision, A.H.K., Z.u.R.; project administration, A.H.K., Z.u.R.; funding acquisition, A.H.K. and Z.u.R. All authors have read and agreed to the published version of the manuscript.

Funding

Higher Education Commission of Pakistan (HEC) NRPU 9639.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Olympus STM6 Optical microscope used in image analysis experimentation.
Figure 1. Olympus STM6 Optical microscope used in image analysis experimentation.
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Figure 2. Grain size analysis curves of aggregates.
Figure 2. Grain size analysis curves of aggregates.
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Figure 3. Typical loading cycles used in resilient modulus evaluation with 20/30 grade binder.
Figure 3. Typical loading cycles used in resilient modulus evaluation with 20/30 grade binder.
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Figure 4. Detailed view of loading cycles in portion “a”.
Figure 4. Detailed view of loading cycles in portion “a”.
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Figure 5. Typical deformation curves of the last cycle with 20/30 grade binder.
Figure 5. Typical deformation curves of the last cycle with 20/30 grade binder.
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Figure 6. Comparison of the resilient modulus of different asphalt mixtures at 25 °C.
Figure 6. Comparison of the resilient modulus of different asphalt mixtures at 25 °C.
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Figure 7. Comparison of the resilient modulus of different asphalt mixtures at 40 °C.
Figure 7. Comparison of the resilient modulus of different asphalt mixtures at 40 °C.
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Figure 8. Typical optical microscope images of asphalt mixtures at different microscopic positions.
Figure 8. Typical optical microscope images of asphalt mixtures at different microscopic positions.
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Figure 9. Normal and magnified optical microscope images of different asphalt mixtures used for the determination of the area of weak resistive zones (WZ).
Figure 9. Normal and magnified optical microscope images of different asphalt mixtures used for the determination of the area of weak resistive zones (WZ).
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Figure 10. MRT versus area of WZ for at 0.1 s duration and 25 °C.
Figure 10. MRT versus area of WZ for at 0.1 s duration and 25 °C.
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Figure 11. MRT versus area of WZ at 0.3 s duration and 25 °C.
Figure 11. MRT versus area of WZ at 0.3 s duration and 25 °C.
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Figure 12. MRT versus area of WZ at 0.1 s duration and 40 °C.
Figure 12. MRT versus area of WZ at 0.1 s duration and 40 °C.
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Figure 13. MRT versus area of WZ at 0.3 s duration and 40 °C.
Figure 13. MRT versus area of WZ at 0.3 s duration and 40 °C.
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Table
Table 1. Summary of the engineering properties of the virgin aggregates used.
Table 1. Summary of the engineering properties of the virgin aggregates used.
Aggregate PropertyTest Results *
LA Abrasion loss (%)17.9
Sand Equivalent (%)70
Flakiness (%)8
Elongation (%)6
Water Absorption (%)0.96
Bulk Density (kg/m3)1533
Sodium Sulphate Soundness (%)—Coarse4.3
Sodium Sulphate Soundness (%)—Fine3.6
* Average of three replicates.
Table
Table 2. Summary of the asphalt binder’s properties.
Table 2. Summary of the asphalt binder’s properties.
Type of TestRAP Binder *20/30 *40/50 *60/70 *80/100 *
Penetration at 25 °C, 0.1 mm37254465.285
Softening point (°C)5458.251.647.546
Ductility at 25 °C (cm)6518126.7134144
Flashpoint (°C)295300335329252
* Average of three replicates.
Table
Table 3. ANOVA summary of factorial analysis.
Table 3. ANOVA summary of factorial analysis.
SourceDFAdj SSAdj MSF-Valuep-Value
Model71,425,598,363203,656,909851.770.0001
Linear31,325,354,497441,784,8321847.70.0001
A118,222,30018,222,30076.210.0001
B11,046,392,6041,046,392,6044376.390.0001
C1260,739,593260,739,5931090.510.0001
2-Way Interactions370,416,61423,472,20598.170.0001
AB14,976,8324,976,83220.810.0001
AC1154,422154,4220.650.425
BC165,285,36065,285,360273.050.0001
3-Way Interactions1193219320.010.929
ABC1193219320.010.929
Error5212,433,172239,099
Total591,438,031,535
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Hussain, S.I.; Khan, A.H.; Rehman, Z.u.; Abbas, W.; Abbas, S.; Mohamed, A.M.; Fathi, D.M.; Aziz, M. Effect of Weak Zones on Resilience of Sustainable Surface Course Mixtures of Fresh-Reclaimed Asphalt Pavement. Sustainability 2022, 14, 9966. https://doi.org/10.3390/su14169966

AMA Style

Hussain SI, Khan AH, Rehman Zu, Abbas W, Abbas S, Mohamed AM, Fathi DM, Aziz M. Effect of Weak Zones on Resilience of Sustainable Surface Course Mixtures of Fresh-Reclaimed Asphalt Pavement. Sustainability. 2022; 14(16):9966. https://doi.org/10.3390/su14169966

Chicago/Turabian Style

Hussain, Syed Iqrar, Ammad Hassan Khan, Zia ur Rehman, Wasim Abbas, Safeer Abbas, Abdeliazim Mustafa Mohamed, Dina Mohamed Fathi, and Mubashir Aziz. 2022. "Effect of Weak Zones on Resilience of Sustainable Surface Course Mixtures of Fresh-Reclaimed Asphalt Pavement" Sustainability 14, no. 16: 9966. https://doi.org/10.3390/su14169966

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