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Background:
Systematic Review

Fatigue Resistance of RAP-Modified Asphalt Mixes Versus Conventional Mixes Using the Indirect Tensile Test: A Systematic Review

by
Giuseppe Loprencipe
*,
Laura Moretti
and
Mario Saltaren Daniel
*
Department of Civil, Constructional and Environmental Engineering, Sapienza University of Rome, Via Eudossiana 18, 00184 Rome, Italy
*
Authors to whom correspondence should be addressed.
Designs 2025, 9(5), 104; https://doi.org/10.3390/designs9050104
Submission received: 17 July 2025 / Revised: 22 August 2025 / Accepted: 25 August 2025 / Published: 1 September 2025
(This article belongs to the Special Issue Sustainable Construction: Innovations in Design, Engineering, and the Circular Economy)
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Abstract

The use of Reclaimed Asphalt Pavement (RAP) in asphalt mixtures offers environmental and economic advantages by reducing reliance on virgin aggregates and minimizing construction waste. However, the aged binder in RAP increases mixture stiffness, which can compromise fatigue resistance. This systematic review evaluates the influence of RAP content on fatigue performance compared to conventional mixtures, with a focus on the Indirect Tensile Test (IDT) as the primary assessment method. Following the parameters of Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, five studies published between 2014 and 2024 were identified through searches in Web of Science, ScienceDirect, ASCE, and Scopus. Study quality was assessed using the Cochrane Risk of Bias tool. The results indicate that although RAP enhances rutting resistance, higher contents (>30%) often lead to reduced fatigue performance due to binder hardening and reduced mixture flexibility. The incorporation of rejuvenators—such as heavy paraffinic extracts—and modifiers, including high-modulus agents, polymers, and epoxy binders, can partially restore aged binder properties and improve performance. Sustainable innovations, such as lignin-based industrial by-products and warm-mix asphalt technologies, show promise in balancing mechanical performance with reduced environmental impact. Variability in material sources, modification strategies, and test protocols limits direct comparability among studies, underscoring the need for standardized evaluation frameworks. Overall, this review highlights that optimizing RAP content and selecting effective rejuvenation or modification strategies are essential for achieving durable, cost-effective, and environmentally responsible asphalt pavements. Future research should integrate advanced laboratory methods with performance-based design to enable high RAP utilization without compromising fatigue resistance.

1. Introduction

The increasing global emphasis on sustainability and efficient resource utilization in road construction has driven greater adoption of Reclaimed Asphalt Pavement (RAP) [1]. This material, sourced from recycled asphalt layers, enables the reuse of aged pavement materials while providing notable environmental and economic benefits [2,3]. Over the past decade, incorporating RAP into traditional bituminous mixtures has attracted significant interest for its ability to reduce the construction costs and environmental impacts [4,5] of road pavements. This interest has intensified in response to growing vehicular traffic and harsher weather conditions that challenge pavement performance and durability [6,7]. From an environmental perspective, RAP use contributes to waste minimization by promoting material reuse [5], reduces the need for landfill disposal through increased recycling [4,8], and lowers greenhouse gas emissions associated with virgin material production [9]. These advantages align with international sustainability objectives and address the technical challenge of meeting or exceeding the mechanical performance of conventional materials [1,10].
In pavement engineering, meeting these dual objectives requires designing mixtures that not only satisfy structural and functional requirements but also perform reliably under defined service conditions [11,12]. Within this context, RAP is a purposeful design component [13,14], integrated using modern approaches that strike a balance between durability, fatigue resistance, and environmental impact [15,16]. This perspective positions RAP as part of an intentional, performance-driven design process, rather than a direct replacement for virgin materials [17,18].
However, mixtures with high RAP content often display increased stiffness and reduced fatigue resistance [19,20,21,22]. Such mechanical shortcomings can shorten pavement service life by accelerating cracking and fatigue damage [23]. Therefore, it is essential to evaluate the mechanical performance of RAP-containing mixtures by varying RAP proportions using reliable and standardized testing methods. Among these, the Indirect Tensile Test (IDT) is widely recognized for fatigue evaluation due to its standardized procedure, reproducibility, and relevance [24]. Its frequent use in studies involving RAP-containing mixtures strengthens this review, as it allows for methodological consistency and reliable cross-study comparisons [25]. Although the IDT does not fully replicate the stress states of in-service pavements [26], it provides valuable insights into rheological behavior and critical mechanical thresholds [16]. In the scientific literature, recent studies suggest that RAP improves rutting resistance [27,28]; however, the higher stiffness of aged bitumen can diminish mixture flexibility and potentially reduce fatigue life [29,30].
To address these drawbacks, several modification strategies have been explored. These include incorporating high-modulus agents to improve structural stiffness [22,31], applying rejuvenators (e.g., oils and low-viscosity compounds) to restore binder properties [32,33,34], and adding advanced modifiers (e.g., polymers and nanomaterials) to improve cohesion and adhesion within the mixture [35,36,37,38]. Moreover, the use of industrial by-products and secondary raw materials in RAP-based mixtures is a promising approach to improve fatigue resistance and structural stability [39,40]. These innovations aim to balance the often-conflicting goals of sustainability and mechanical performance, enabling RAP-based asphalt mixtures to match or surpass conventional alternatives. Despite the notable progress, there remains a lack of comprehensive comparative studies that address the following key questions:
(1)
How does RAP content influence the fatigue behavior of asphalt mixtures when evaluated using the IDT?
(2)
How do RAP content and modification strategies interact to affect the mechanical performance of asphalt innovative mixtures compared to conventional ones?
(3)
How can technological enhancements be leveraged to optimize RAP performance, thereby guiding the design of durable, cost-effective, and environmentally responsible pavements?

2. Methods

A systematic literature review was conducted to evaluate the influence of RAP content on fatigue resistance [41], with performance assessed via the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol [42], ensuring transparency, replicability, and methodological rigor to identify, screen, and evaluate eligible scientific articles. Studies were included based on predefined criteria for thematic relevance and methodological quality, enabling the identification of research trends, gaps, and the validity of experimental approaches [43]. The search was performed in four major databases widely used in civil and pavement engineering: ASCE Library, ScienceDirect, Scopus, and Web of Science (WoS). The search strategy used the Boolean string (“Reclaimed Asphalt Pavement” OR “RAP”) AND (“Fatigue Resistance”) AND (“Indirect Tensile Test”). The search was limited to English-language papers published between 2014 and 2024 to capture recent advancements in RAP technology. Eligible studies were systematically classified by research objectives, methods, and outcomes, facilitating a robust synthesis of findings. Publication frequency has shown a marked increase from 2017 onward (Figure 1).
The selected studies underwent a five-stage review process: identification, validation, extraction, comparison, and synthesis. Post-extraction, consensus validation was applied to detect patterns, inconsistencies, and methodological commonalities, excluding non-compliant studies. Study quality and reliability were evaluated through dual independent assessments based on criteria adapted from the Cochrane Handbook [44,45]. Discrepancies were resolved using the Kappa Free-Marginal Multirater Coefficient (Kfree) [46], requiring a minimum agreement of 75% (classified as “substantial”, Kfree = 0.61–0.80) for inclusion.
Keyword co-occurrence analysis was conducted using VOSviewer (v1.6.20). Three main thematic clusters emerged (Figure 2):
Materials and Mechanical Strength (red cluster) includes the keywords “aggregate”, “cracking”, and “resistance”.
Pavement Performance and Deterioration (blue cluster) includes “fatigue”, “rutting”, and “performance”.
Binder Properties and Sustainability (green cluster) includes “binder”, “moisture susceptibility”, and “rejuvenator”.
The co-occurrence analysis identified RAP as a central term linking all three thematic clusters. The keyword “rejuvenator” also showed strong cross-cluster connections, reflecting its key role in improving RAP performance by restoring or modifying aged binder properties.
The initial database search retrieved 134 articles (Figure 3). After duplicate removal, 126 unique studies remained. In the first screening stage, 91 were excluded for not meeting the inclusion criteria. The second stage involved full-text assessment of 33 articles for methodological rigor, topic relevance, and alignment with the review scope. Twenty-eight were excluded for inadequate quality or insufficient focus on RAP content and fatigue resistance evaluated using IDT. The final selection comprised five original research studies that satisfied all criteria.
Following article selection, study quality and bias risk were evaluated using a modified Cochrane Risk of Bias Tool [45], adapted for experimental research in asphalt materials. The assessment covered five domains: selection (clarity and representativeness of the inclusion criteria), implementation (accuracy of the test method and condition descriptions), detection (control of external factors such as climate and traffic), wear (transparent handling of missing data), and reporting (completeness of outcome reporting).
Two reviewers conducted independent evaluations, resolving disagreements through discussion. Bias classification was based on the highest risk level across domains, rating studies as Low Risk (1), Some Concerns (2), or High Risk (3) (Table 1).
Table 2 summarizes the concordance between the reviewers’ overall risk of bias ratings. Each cell indicates the number of studies assigned to a given combination of reviewer judgments, with perfect agreement represented along the diagonal. All five studies underwent evaluation. The interrater reliability results are shown in Table 3.
Interrater agreement beyond chance was quantified using the Cohen’s kappa (Table 3). The coefficient was Kfree = 1, indicating perfect agreement. This result demonstrates excellent consistency between the reviewers and supports the reliability of the bias assessments, confirming the inclusion of all five studies in this review.

3. Results

Table 4 synthesizes the most relevant information about the materials, methodologies, instrumentation, and key findings of the selected studies.
Based on Table 4, the following sections focus on the main findings.
Notable results have been reported on the fatigue resistance of RAP-containing asphalt mixtures [47]. Florida IDT energy ratio testing at 10 °C showed that 100% RAP mixtures rejuvenated with a low dosage (7.9%) of RA1—a rejuvenating agent derived from distilled paraffin extract— exhibited substantially higher cracking resistance than virgin mixtures. Compared with virgin asphalt, summarizing the adhesive aging conditions and how they influenced the characteristics of the binder using oven aging [47], the strength increased by approximately 75% after the loose mixture was subjected to short-term aging (STA) for 1 hour at 165 °C, by 160% after the compacted mixture underwent long-term aging (LTA) for 5 days at 85 °C, and by 55% after long-term aging (LTA) for 10 days at 85 °C. This improvement is attributed to the rejuvenator’s ability to restore the ductility and flexibility of aged binders, thereby delaying the onset of cracking.
Although rutting resistance is not a measure of fatigue performance, it reflects structural integrity. In [20], high-temperature performance was evaluated using the WTT at 60 °C, comparing virgin and recycled epoxy asphalt mixtures. The recycled epoxy asphalt mixture demonstrated 67% greater rutting resistance than the traditional mix (Figure 4).
In [20], IDT was performed on virgin and recycled epoxy asphalt mixtures before and after a freeze–thaw cycle (Figure 5) to evaluate moisture sensitivity. No significant difference in IDT strength was observed. The virgin epoxy asphalt mixture shows an approximate decrease of 3%, whereas the recycled epoxy asphalt mixture shows an approximate increase of 4%.
The recycled epoxy asphalt mixture exhibited lower fatigue performance than the control mixture (Figure 6).
Performance comparisons indicate that epoxy resin components have the potential to enable effective recycling of mixtures containing 100% RAP.
In [48], an industrial lignin-rich by-product was assessed as a partial replacement for asphalt emulsions in pavement applications. IDT results showed that incorporating 5.0% of this by-product at the optimal residual binder content (i.e., 3%) improved performance. Specifically, the TSR value was 1.35% higher than the control mixture (Table 5). However, high substitution levels of 10%, 15%, and 20% led to substantial reductions in TSR, falling below the 85% specification limit [52]. At these levels, TSR decreased by 35.19%, 21.61%, and 27.65%, respectively.
The WTT results showed that, in areas where air temperatures range between 30 and 35 °C, the mixture incorporating 5% of the by-product had higher resistance to rutting than the control (Figure 7).
In [21], the performance of Hot Mix Asphalt (HMA) containing 100% RAP and no rejuvenators was compared to a control HMA with raw materials. The WTT results showed that, according to the specifications of the PG-3 for HMA surface course type AC 16 surf S [53], the RAP-based mixture exhibited higher rutting resistance than the control (Table 6).
Additionally, an immersion-based IDT test, performed in accordance with [54], was carried out to assess water sensitivity [21]. The results indicated that both the control and the high-RAP HMA mixtures exhibited satisfactory resistance to moisture-induced damage (Table 7).
However, the control mixture exhibited 53% longer fatigue life compared to the high-RAP HMA without rejuvenators (Figure 8).
Similarly, ref. [22] investigated the characteristics of high-modulus recycled asphalt modified with high-modulus additives, comparing its performance to a conventional recycled asphalt. Wheel load tests indicated that, for standard AC20 mixtures, the dynamic stability of high-modulus asphalt, whether containing RAP or not, increased with higher RAP content. Specifically, raising the RAP content from 0% to 60% enhanced dynamic stability by roughly 330%, from about 400 cycles/mm to more than 1700 cycles/mm. The stiffening effect of the aged bitumen in RAP can justify this trend because it boosts mixture rigidity and rutting resistance.
For high-modulus mixtures, the AC20-A (4.3% asphalt content with high-modulus agents), achieved the greatest stability values: approximately 6800 cycles/mm at 0% RAP and over 9500 cycles/mm at 60% RAP, reflecting a 40% increase. The AC20-B mixture containing 4.5% asphalt raised from about 6000 cycles/mm at 0% RAP to 8600 cycles/mm at 60% RAP. At the 60% RAP content, the standard AC20 mixture achieved about 1700 cycles/mm, whereas the AC20-A and AC20-B attained between 8600 and 9500 cycles/mm, respectively. This represents 5–6 times increased rutting resistance compared with the standard mixture (Figure 9). The threshold values used by [22] were aligned with the minimum dynamic stability limits generally recognized in the literature [55].
According to [22], the Marshall Strength Ratio (Figure 10a) and TSR (Figure 10b) of both conventional and high-modulus recycled asphalt mixtures decreased as the RAP content increased. This behavior indicated that higher RAP content causes greater moisture susceptibility and reduces mechanical performance.
Four-point bending beam tests performed at 250 με, 350 με, 450με, and 550 με strain levels showed that the fatigue life of conventional AC20, high-modulus AC20-A, and high-modulus AC20-B mixtures decreases with increasing RAP content. As RAP levels rise, the fatigue life gap between the AC20 and the AC20-A narrows. This trend is attributed to the ability of high-modulus additives to improve asphalt binder adhesion, thereby mitigating some of the detrimental effects associated with RAP. A comparison between AC20-A and AC20-B revealed that increased bitumen content further extends service life. This benefit was evident when RAP content exceeded 30%, suggesting that additional binder enhances adhesion and mixture flexibility (Figure 11).
Table 8 synthesizes the RAP content, rejuvenator dosage, and fatigue resistance outcomes reported in the included studies.

4. Discussion and Conclusions

A systematic literature review was conducted to examine the influence of RAP content on asphalt fatigue resistance as measured using the Indirect Tensile Test [26]. Although RAP improves sustainability in asphalt production, excessive use can increase brittleness and susceptibility to fatigue cracking under repeated loads [56,57,58] and reduce asphalt viscosity [20,59,60,61]. Current pavement design practices aim to maximize recycled content without compromising established performance standards [13,16,62]. Following PRISMA guidelines, five relevant studies were identified to address three key questions. However, inter-study variability in aging protocols, IDT procedures (e.g., Florida IDT [49], European standard [54]), and testing conditions, as well as potential publication bias and the lack of field validation compared to laboratory-based tests, limited statistical comparability. The included studies also encompassed a wide range of binders, modifiers, RAP contents, and rejuvenators, and these materials and mix design differences may further influence performance outcomes and complicate direct comparisons across studies.
Regarding the first question, multiple studies report that high RAP levels (>30%) often reduce fatigue resistance [22,63,64,65]. Although RAP increases mixture stiffness—e.g., high-RAP HWMA without rejuvenators can exhibit a resilient modulus 46% greater than the control mixture [21]—this comes at the expense of fatigue life. For instance, at an initial strain of 200 µε, control mixtures can last 275% longer than high-RAP HWMA; at 300 µε, the difference rises to 477% [21], consistent with other findings [20,46]. Dynamic modulus tests confirm that stiffness gains limit deformation capacity under cyclic loading [22,48]. Complementary four-point bending tests show fatigue life reductions of 15–20% as RAP content rises from 0% to 60% [22]. Similarly, trabecular fatigue testing on recycled epoxy asphalt mixtures found fatigue lives ~45% shorter than virgin epoxy asphalt at all stress ratios [20].
For the second question, combining RAP with rejuvenators or modifiers substantially improves mechanical performance, narrowing the gap with conventional mixtures [22,47,63,66,67,68,69]. Rejuvenators—such as heavy paraffinic extracts—can restore binder flexibility, improving cracking and fatigue resistance [47,48,70] by reducing stiffness [65,71]. Using ≥5% rejuvenator when RAP content exceeds 40% is recommended. Modifiers such as high-modulus agents [68,69] also enhance fatigue resistance while reducing rutting and moisture susceptibility [20,21]. Epoxy-modified 100% RAP mixes achieved 67% higher rutting resistance, but 45% lower fatigue life compared to virgin epoxy asphalt [20]. Notably, rejuvenated binders can achieve up to 29% more fatigue cycles to failure than untreated RAP binders [72,73]. Rejuvenator performance varies. Heavy paraffinic oils with high aromatic content show strong effects at 4.3–28.6% dosage, whereas semi-solid re-refined products require 6.2–67.0% [74]. Slow-aging rejuvenators have been shown to extend service life by up to 30% [46].
The third question explored technological innovations for optimizing RAP use. Warm-mix asphalt (HWMA) can lower production emissions by 25–50% while maintaining performance [75]. The incorporation of lignin-rich industrial by-products offers a sustainable alternative to commercial additives, improving stiffness, rutting resistance, and moisture performance at substitution rates as low as 5% by mass [48]. Such approaches support the valorization of industrial waste while enhancing RAP mixture performance, including in warm and semi-warm applications [75,76].
In summary, the beneficial effects of mixtures with high RAP content (up to 100%) [20,21,47,48] are more consistently observed in warm climates [21,48], where the increased stiffness of the aged binder contributed to improved rutting resistance and a dynamic modulus. These effects are further enhanced by the incorporation of rejuvenators or modifiers (e.g., RA1 at 7.9% [47], epoxy asphalt at 25% [20], lignin by-product at 5% [48], or high-modulus agents at 0.3% [22]). Although improvements in stiffness and rutting resistance can be considered generalizable trends across studies [20,22,47], the performance outcomes related to fatigue resistance, cracking, and moisture susceptibility remain highly dependent on the specific type and dosage of additives, as well as the mix design parameters. Consequently, findings in these domains should be regarded as more context-specific [20,21,47,48].
A limitation of this review is that only five studies were ultimately included. This restriction stems from the specific objectives of the research and the strict search and selection criteria applied to ensure methodological consistency. Nevertheless, the small number of studies highlights a gap in the scientific literature, as few investigations have examined the fatigue resistance of RAP-modified asphalt mixtures compared to conventional ones using the indirect tensile test.
Future advances are likely to focus on higher RAP incorporation, with tailored designs using optimized blends of modifiers and rejuvenators for specific traffic and climate conditions. Although IDTs are valuable tools for evaluating cracking and rutting resistance, more advanced methodologies (e.g., four-point bending, dynamic modulus testing, and accelerated aging protocols) should be used to replicate field conditions. Research should also pursue integrated design frameworks considering binder aging, additive synergy, and life-cycle performance [77], supported by multi-scale testing and numerical modeling. Combining industrial by-products with modern mixing technologies offers a pathway toward durable, resource-efficient, and environmentally responsible pavements.

Author Contributions

Conceptualization, M.S.D. and G.L.; methodology, M.S.D.; software, M.S.D.; formal analysis, M.S.D.; investigation, M.S.D.; data curation, M.S.D. and G.L.; writing—original draft preparation, M.S.D.; writing—review and editing, M.S.D., L.M. and G.L.; visualization, M.S.D.; supervision, G.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

This article includes the data presented in this study.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
RAPReclaimed Asphalt Pavement
AC20asphalt concrete with a 20 mm aggregate size
IDTIndirect Tensile Test
WTTWheel Tracking Test or Hamburg Wheel Test
HMAHot Mix Asphalt
TSRTensile Strength Ratio
HWMAHot–Warm Mix Asphalt
KfreeKappa Free-Marginal Multirater Coefficient

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Designs 09 00104 g001
Figure 1. Yearly publication distribution across databases.
Figure 1. Yearly publication distribution across databases.
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Figure 2. VOS viewer network visualization.
Figure 2. VOS viewer network visualization.
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Figure 3. PRISMA diagram of the study search and selection process in the systematic review.
Figure 3. PRISMA diagram of the study search and selection process in the systematic review.
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Figure 4. Dynamic stability—adapted from [20] with permission from Elsevier. License number: 6072011489584, Copyright Clearance Center.
Figure 4. Dynamic stability—adapted from [20] with permission from Elsevier. License number: 6072011489584, Copyright Clearance Center.
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Figure 5. IDT strength—adapted from [20] with permission from Elsevier. License number: 6072011489584, Copyright Clearance Center.
Figure 5. IDT strength—adapted from [20] with permission from Elsevier. License number: 6072011489584, Copyright Clearance Center.
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Figure 6. Loading cycle results—adapted from [20] with permission from Elsevier. License number: 6072011489584, Copyright Clearance Center.
Figure 6. Loading cycle results—adapted from [20] with permission from Elsevier. License number: 6072011489584, Copyright Clearance Center.
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Figure 7. Hamburg wheel tracking test results—adapted from [48] with permission from Elsevier. License number: 6072030425481, Copyright Clearance Center.
Figure 7. Hamburg wheel tracking test results—adapted from [48] with permission from Elsevier. License number: 6072030425481, Copyright Clearance Center.
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Figure 8. Fatigue life results—reproduced from [21], under a CC BY 4.0 license.
Figure 8. Fatigue life results—reproduced from [21], under a CC BY 4.0 license.
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Designs 09 00104 g009
Figure 9. Test results from wheel loading tests: (a) conventional asphalt mixtures; (b) high-modulus asphalt mixtures—adapted from [22] with permission from Elsevier. License number: 6072040116678, Copyright Clearance Center.
Figure 9. Test results from wheel loading tests: (a) conventional asphalt mixtures; (b) high-modulus asphalt mixtures—adapted from [22] with permission from Elsevier. License number: 6072040116678, Copyright Clearance Center.
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Figure 10. Test results for moisture susceptibility: (a) Marshall strength ratio using the Marshall test; (b) tensile strength ratio using the IDT test—adapted from [22] with permission from Elsevier. License number: 6072040116678, Copyright Clearance Center.
Figure 10. Test results for moisture susceptibility: (a) Marshall strength ratio using the Marshall test; (b) tensile strength ratio using the IDT test—adapted from [22] with permission from Elsevier. License number: 6072040116678, Copyright Clearance Center.
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Designs 09 00104 g011aDesigns 09 00104 g011b
Figure 11. Fatigue life results at different testing strains: (a) 250 µε; (b) 350 µε; (c) 450 µε; (d) 550 µε—adapted from [22] with permission from Elsevier. License number: 6072040116678, Copyright Clearance Center.
Figure 11. Fatigue life results at different testing strains: (a) 250 µε; (b) 350 µε; (c) 450 µε; (d) 550 µε—adapted from [22] with permission from Elsevier. License number: 6072040116678, Copyright Clearance Center.
Designs 09 00104 g011aDesigns 09 00104 g011b
Table 1. Assessment of study quality and risk of bias.
Table 1. Assessment of study quality and risk of bias.
Refs.ReviewerSelectionImplementationDetectionWearReportingOverall, for Author
[47]1111111
2111111
[20]1111122
2111111
[48]1112112
2112112
[21]1111111
2111111
[22]1111111
2111111
Table 2. Comparison of results between evaluators.
Table 2. Comparison of results between evaluators.
Overall 1/Overall 2Low Risk of BiasSome ConcernsHigh Risk of BiasOverall
Low risk of bias2103
Some concerns2002
High risk of bias0000
Overall4102
Table 3. Results of Kappa Free-Marginal Multirater Coefficient.
Table 3. Results of Kappa Free-Marginal Multirater Coefficient.
IndexValue
Proportion of observed agreement1
Proportion of agreement expected by chance3500
Kfree1
Table 4. Synthesis of the selected studies.
Table 4. Synthesis of the selected studies.
Refs.MaterialsMethods and TestsResults
[47]1. Virgin asphalt binder
2. Virgin limestone aggregates
3. RAP
4. Rejuvenators: heavy paraffinic distilled solvent extract (RA1), petroleum neutral distillate (RA2), re-refined used oils (RA3), pine oil (RA4), bio-rejuvenator, oil base, and fluid (RA5)		1. The staged extraction technique was used for the extraction of the asphalt binder in each rejuvenated RAP mixture.
2. Mixtures compliant with AASHTO R 35 [12] and Florida DOT Standard Specifications for Road and Bridge Construction [49].
3. Loaded-Wheel Tracking Test
4. Florida Indirect Tensile Test		A recycled mixture with a 6 °C higher High Temperature Performance Grade showed improved rutting and moisture resistance after aging compared to the conventional mix. In 100% RAP mixtures with minimal rejuvenator, rut depth was unaffected by homogeneity index or aging. Both conventional and RAP mixtures exhibited satisfactory crack resistance. The RA1 mix showed the best crack performance.
[20]1. Virgin asphalt
2. Epoxy resins and curing agent
3. RAP
4. Virgin aggregate		1. Marshall Method
2. Wheel Tracking Test (WTT)
3. Trabecular Bending Test
4. Freeze–Thaw Test
5. Trabecular Fatigue Test
6. Indirect Tensile Test (IDT)
7. Semi-Circular Bending (SCB)		The recycled epoxy asphalt mixture outperformed the conventional one in rutting resistance, whereas crack resistance and moisture susceptibility were similar to both conventional and 100% RAP mixes. Epoxy components influenced crack resistance more than the aged binder. Despite lower fatigue resistance, epoxy asphalt can be recycled with 100% RAP.
[48]1. RAP
2. Bitumen emulsion: C67B2 MBC Ecotemp
3. By-product containing lignin
4. Asphalt mixture		1. Indirect Tensile Strength (ITSW and ITSD). Tensile Strength Ratio (TSR)
2. Resilient Modulus Test
3. Uniaxial Confined Test
3. Hamburg Wheel Tracking Test
4. Cántabro Test
5. Penetration Test according to [50]
6. Ring And Ball Test		In hot–warm mix asphalt (HWMA), replacing 5% of the material with industrial by-products containing lignin enhanced water resistance and deformation capacity. The optimized mix outperforms the control in terms of its mechanical properties.
[21]1. Natural aggregates
2. RAP
3. Bitumen Emulsion		1. Indirect Tensile Strength (ITS) and Tensile Strength Ratio (TSR)
2. Resilience Modulus Test
3. Wheel Tracking Test
4. Indirect Tensile Fatigue Test (ITFT)
5. Penetration test according to [50]
6. Ring And Ball Test according to [51]		The high RAP HWMA demonstrated superior resistance in warm climates, contributing to energy and raw material savings. However, its increased stiffness resulted in reduced fatigue life.
[22]1. Neat asphalt
2. RAP
2. Limestone aggregates
3. Mineral fillers
4. High-modulus agent		1. Simple Performance Tester
2. Wheel Loading Test
3. Indirect Tensile Test
4. Marshall Test
5. Three-Point Beam Bending Test
6. Four-Point Beam Bending Test		RAP combined with high-modulus agents increases dynamic modulus and stability but decreases resistance to thermal and fatigue cracking. High-modulus agents improve moisture resistance, mitigating RAP’s negative effects. Combined with additional binders, they enhance mixture strength and stability.
Table 5. Water resistance—adapted from [48] with permission from Elsevier. License number: 6072030425481, Copyright Clearance Center.
Table 5. Water resistance—adapted from [48] with permission from Elsevier. License number: 6072030425481, Copyright Clearance Center.
By-Product Content (% of the Dry Mass of the Residue)ITSD (MPa)ITSW (MPa)TSR (%)
AverageStandard DeviationAverageStandard Deviation
02.0270.0961.8020.07688.90
52.2290.2482.0680.23690.08
102.4100.1251.3890.10457.62
151.9640.1781.3690.16569.69
202.15702391.3870.27864.32
Table 6. Wheel tracking test results—adapted from [21] under a CC BY 4.0 license.
Table 6. Wheel tracking test results—adapted from [21] under a CC BY 4.0 license.
Parameter (Unit)Control HMAHigh-RAP HMA
Rut depth, d10,000 (mm)1.810.89
PRDair (%)3.011.49
WTSair (mm/103 cycle)0.090.04
Table 7. Moisture damage resistance—adapted from [21] under a CC BY 4.0 license.
Table 7. Moisture damage resistance—adapted from [21] under a CC BY 4.0 license.
Residual Binder Provided by the Bitumen Emulsion (%)Total Residual Binder (%)Va (%)TSR (%)
1.506.216.1-
2.006.685.6087.69
2.507.165.068.87
2.757.403.976.59
3.007.643.788.84
Table 8. RAP content, rejuvenator dosage, and fatigue resistance.
Table 8. RAP content, rejuvenator dosage, and fatigue resistance.
Refs.RAP ContentRejuvenator DosageFatigue Resistance
[47]100% RAPFive commercially available rejuvenators were evaluated; RA1 was the best.The R1 mixture (100% recycled RAP with 7.9% RA1) showed the best cracking performance compared to the virgin mixture.
[20]100% RAPEpoxy resin components were 25% of the total weight of the asphalt binder (including virgin asphalt and RAP asphalt).The fatigue performance of the recycled epoxy asphalt mixture was inferior to the virgin epoxy asphalt mixture.
[48]100% RAPAn industrial by-product rich in lignin was used as a substitute for the bituminous emulsion at 0% (control), 5%, 10%, 15%, and 20% by weight.The optimal percentage of rejuvenators to improve fatigue resistance was 5%.
[21]100% RAP and 0% RAP (control) were comparedNo rejuvenators.The control mixture fatigue life was much longer than the high-RAP HWMA without rejuvenators.
[22]From 20% to 60% RAP percentageLow molecular weight synthetic polyolefin polymers were used for high-modulus mixtures.The fatigue life of conventional high-modulus mixtures decreases with increasing RAP content.
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Loprencipe, G.; Moretti, L.; Saltaren Daniel, M. Fatigue Resistance of RAP-Modified Asphalt Mixes Versus Conventional Mixes Using the Indirect Tensile Test: A Systematic Review. Designs 2025, 9, 104. https://doi.org/10.3390/designs9050104

AMA Style

Loprencipe G, Moretti L, Saltaren Daniel M. Fatigue Resistance of RAP-Modified Asphalt Mixes Versus Conventional Mixes Using the Indirect Tensile Test: A Systematic Review. Designs. 2025; 9(5):104. https://doi.org/10.3390/designs9050104

Chicago/Turabian Style

Loprencipe, Giuseppe, Laura Moretti, and Mario Saltaren Daniel. 2025. "Fatigue Resistance of RAP-Modified Asphalt Mixes Versus Conventional Mixes Using the Indirect Tensile Test: A Systematic Review" Designs 9, no. 5: 104. https://doi.org/10.3390/designs9050104

APA Style

Loprencipe, G., Moretti, L., & Saltaren Daniel, M. (2025). Fatigue Resistance of RAP-Modified Asphalt Mixes Versus Conventional Mixes Using the Indirect Tensile Test: A Systematic Review. Designs, 9(5), 104. https://doi.org/10.3390/designs9050104

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