Sustainable asphalt concrete containing RAP and RCA: volumetrics, mechanical properties, and economic analysis

ABSTRACT

The pavement maintenance field produces a large amount of waste materials, primarily composed of reclaimed asphalt pavement (RAP) and recycled concrete aggregate (RCA), and considering the shortage of natural materials in pavement engineering, the production of sustainable asphalt mixtures to reduce the demand for natural materials become a topical issue. To this end, this study aims to assess the feasibility of utilizing RAP and RCA for the production of sustainable asphalt mixtures. Seven schemes of asphalt mixtures were designed, containing varying proportions of RAP at 20% and 30%, and RCA at 15%, 25%, and 35%, as well as a control scheme with natural materials. A battery of tests, such as Marshall stability, rutting, freeze-thaw splitting, low-temperature bending, and fatigue cracking performance tests, were conducted to evaluate the optimum asphalt content (OAC) and the durability properties of sustainable asphalt mixtures. In addition, the significance of the effect of RAP and RCA was analyzed using the ANOVA method, and the economic benefits of sustainable asphalt mixtures were analyzed. The results show that the OAC of sustainable asphalt mixtures escalates with higher proportions of RAP and RCA. The high-temperature stability, moisture stability, and fatigue performance of sustainable asphalt mixtures can be improved by adding RAP and RCA, albeit with a slight reduction in low-temperature cracking resistance. RCA emerges as a significant factor influencing the mechanical properties of sustainable asphalt mixtures, while RAP primarily impacts low-temperature cracking resistance. The utilization of RAP and RCA yields cost reductions in asphalt mixture production, leading to substantial economic benefits.

Keywords:
Reclaimed asphalt pavement (RAP); Recycled concrete aggregate (RCA); Mechanical properties; ANOVA method; Economic benefits

1. INTRODUCTION

In the era of striving for carbon neutrality, the issue of how to reduce carbon emissions has become one of the most significant concerns in the world [¹]. Road construction and maintenance in the transportation industry is one of the most important industries that generate carbon emissions, as it uses a large amount of non-renewable resources. Therefore, how to reduce carbon emissions in the field of road construction and maintenance has become a hot issue for builders, researchers, and other pertinent parties. The transportation industry is capable of using hundreds of millions of tons of natural materials and generating large amounts of solid waste each year [²]. For instance, in road maintenance projects, various waste materials are produced [³, ⁴], including reclaimed asphalt pavement (RAP), recycled concrete aggregates (RCA), cement-stabilized base layers, glass granules, and other byproducts, depending on the pavement type. However, the recycling of these waste materials can replace some of the natural materials, which not only solves the problem of land and water pollution caused by waste disposal but also reduces the demand for natural materials and material costs. Therefore, investigating the recycling of waste materials generated during road maintenance processes represents a valuable research field.

RAP is typically derived from the original asphalt pavement using cold milling technology, which contains aged asphalt and aggregates, and is characterized by the agglomeration of RAP particles and aggregate crushing [⁵]. Currently, RAP is commonly utilized in the creation of recycled asphalt mixtures through plant mixing hot recycling technology to realize its high-value utilization. Previous studies have shown that blending RAP with asphalt mixtures can improve the economic efficiency of the asphalt mixtures [⁶]. In addition, the recycled asphalt mixture containing a minor proportion of RAP not exceeding 30% can be capable of performing similarly to conventional hot mix asphalt mixture, with some performance that may be better. Incorporating RAP into the asphalt mixture can improve rutting resistance [⁷, ⁸], extend fatigue life [⁹, ¹⁰], and reduce the moisture susceptibility of recycled asphalt mixtures [¹¹]. However, the low-temperature cracking resistance of recycled asphalt mixtures tends to decrease, primarily due to the aging of asphalt in RAP [¹²]. Moreover, when the RAP proportion is high, the percentage of aged asphalt within the recycled asphalt mixture proportionally increases, which will notably impact the mechanical properties of the recycled asphalt mixture, the resistance to rutting of recycled asphalt mixture will be improved, but the stability under wet conditions, resistance to low-temperature cracking, and resistance to fatigue aging are apt to decline. Hence, to mitigate the influence of aged asphalt in RAP on the mechanical properties of recycled asphalt mixtures, scholars have advocated for several strategies [¹³, ¹⁴], including the use of high-performance rejuvenators, fibers, and polymer modifiers, et al.

While incorporating RAP can enhance the economic benefits of recycled asphalt mixtures, it’s essential to highlight that the proportion of RAP utilized profoundly influences mechanical performance. RCA, in contrast, lacks aged asphalt on its surface and is another waste product generated during pavement maintenance. Therefore, combining RCA with RAP can mitigate the influence of higher aged asphalt content on the mechanical performance of asphalt mixture, and this approach facilitates a higher replacement percentage of new aggregates, resulting in sustainable asphalt mixtures that will have a more significant economic benefit. Based on past reports [¹⁵], the reuse and recycling of Reclaimed Asphalt Pavement (RAP) and Recycled Concrete Aggregate (RCA) in asphalt pavement are subject to constraints. Incorporation of RAP and RCA into asphalt pavement will encounter significant engineering obstacles and variability in mechanical properties and durability, primarily due to the influence of cement residues on the external surface of RCA and the aged asphalt content in RAP [¹⁶, ¹⁷] In addition, the properties of asphalt mixtures are subject to fluctuations contingent upon the amount of RAP and RCA utilized, thus making the use of RAP and RCA in asphalt mixtures challenging.

Previous studies [¹⁸, ¹⁹, ²⁰] have shown that the variations in the proportion of RAP and RCA utilized in sustainable asphalt mixtures exert notable impacts on volumetric indices and stability. The optimal asphalt content of sustainable asphalt mixtures rises in proportion to the increase in the quantity of RAP and RCA. Notably, the properties of sustainable asphalt mixtures with the proportions of RAP and RCA not exceeding 50% are similar to those of conventional hot mix asphalt mixtures. In addition, it was found that the rough texture and porous structure of RCA surfaces promote interlocking within the asphalt mixture, thereby enhancing stability and reducing flowability. Similarly, the aged asphalt mastic on the RAP surface will have a higher stiffness and is also willing to cause an increase in the stability of sustainable asphalt mixtures [¹⁴]. These research findings demonstrate the feasibility of incorporating RAP and RCA to produce sustainable asphalt mixtures. However, there are fewer studies have investigated the synergistic effects of RAP with RCA and the influence of proportion variation on the properties of sustainable asphalt mixtures [²¹, ²²].

This study investigated the variation of volumetric indices and mechanical properties of sustainable asphalt mixtures with different RAP and RCA proportions. The impact of the change of RAP and RCA proportion on the optimal asphalt content of sustainable asphalt mixtures was analyzed. Furthermore, the performance characteristics of sustainable asphalt mixtures under the optimal asphalt content, including thermal stability at elevated temperatures, resistance to low-temperature cracking, hydrological stability, and fatigue resistance, were assessed. Furthermore, The significance of the influence of RAP and RCA on the optimal asphalt content and mechanical properties was calculated by using analysis of variance (ANOVA). Finally, the economic benefits of sustainable asphalt mixtures were analyzed. The study can provide ideas for the material composition design of sustainable asphalt mixtures. The flow diagram is shown in Figure 1.

Figure 1
Flow diagram of research methodology used in this study.

2. MATERIALS AND METHODS

2.1. Raw materials

The materials utilized in this study encompass RAP, RCA, new aggregates, mineral powder, rejuvenators, and 70# matrix asphalt. The RAP were sourced from the Sanming section of the Fuzhou-Yinchuan Expressway located in Fujian Province and were sorted into three size categories (0–6 mm, 6–12 mm, and 12–16 mm) utilizing milling, crushing, and screening techniques, as illustrated in Figure 2. Separation of asphalt and aggregate within RAP was achieved through an extraction method, the asphalt content of the three RAPs was 9.02%, 3.37%, and 2.34%, sequentially, and the aggregate gradation test results for RAP are depicted in Figure 3, while the performance indicators are tabulated in Table 1. RCA, derived from dismantled cement concrete pavement, was sorted into different size fractions (9.5–13.2 mm, 13.2–16 mm, 16–19 mm, and 19–26.5 mm) via water washing and screening methods, as delineated in Figure 4. Both new aggregates and mineral powder are sourced from limestone. The properties test results for RCA, new aggregates, and mineral powder are tabulated in Table 2. The performance indicators for the rejuvenator and the matrix asphalt are illustrated in Table 3 and Table 4, sequentially.

Figure 2
RAP after crushing and screening.

Figure 3
Aggregate gradation test results in RAP.

Table 1
Performance indicators of RAP.

MATERIAL TYPE	INDICATORS	TEST RESULTS
RAP	Moisture content, %	0.72
	Sand equivalent, %	88.7
Asphalt in RAP	Penetration, 25℃, 0.1 mm	30.4
	Softening point, ℃	63.8
	Ductility, 15 ℃, cm	13.1
Coarse aggregate	Crushing value, %	8.9
	Flakiness and elongation particles, %	12.3
Fine aggregate	Angularity	31.9

Figure 4
RCA after crushing and screening.

Table 2
Performance indicators of new aggregates and RCA.

AGGREGATE TYPE	TEST ITEMS	TEST RESULTS	REQUIREMENTS
Coarse aggregate	Specific gravity	2.693	≥ 2.5
	Flakiness and elongation particles, %	12.5	≤ 18
	Crushing value, %	10.9	≤ 28
	Water absorption, %	0.43	≤ 3.0
Fine aggregate	Specific gravity	2.652	≥ 2.5
	Sand equivalent, %	70.3	≥ 60
Filler	Specific gravity	2.584	≥ 2.5
RCA	Specific gravity	2.321	–
	Flakiness and elongation particles, %	17.8	–
	Crushing value, %	26.4	–
	Water absorption, %	5.53	–

Table 3
Performance indicators of rejuvenator.

TEST ITEMS	TEST RESULTS
Physical form	Pale yellow solution
Density, 25 ℃, g/cm3	0.825
Viscosity, 20 ℃, Pa·s	0.6~0.8

Table 4
Performance indicators of 70# matrix asphalt.

TEST ITEMS		TEST RESULTS	REQUIREMENTS
Penetration, 25 ℃, 0.1 mm		69.5	60–80
Softening point, ℃		49.3	≥ 45
Ductility, 15 ℃, cm		>100	≥ 100
RTFOT	Penetration ratio, 25 ℃, %	86.4	≥ 61
	Residual ductility, 15 °C, cm	45.2	≥ 15
	Mass loss, %	−0.1	± 0.8

2.2. Experimental schematic design

The AC-20 asphalt mixture was formulated, and the gradation of the asphalt mixture was determined based on engineering research results, as depicted in Figure 5. The designed composition of the sustainable asphalt mixture includes varying percentages of RAP and RCA, seven experimental schemes were devised, as depicted in Figure 6. In Figure 6, V denotes that all aggregates in the asphalt mixture are new materials, while R20C15 indicates that the sustainable asphalt mixture comprises 20% RAP and 15% RCA. This numbering convention is consistent across other schemes.

Figure 5
Gradation design of sustainable asphalt mixture.

Figure 6
Experimental scheme.

Employing a rejuvenator to restore the performance of aged asphalt within RAP. Recycled asphalt binders were prepared with rejuvenator dosages of 0%, 3%, and 6% by weight of the aged asphalt. The penetration of each binder was tested at 25 °C. The results showed that the binder with a 3% rejuvenator dosage achieved a penetration value within the typical range of virgin asphalt. Therefore, a 3% dosage by weight of the aged asphalt was selected as the optimal rejuvenator content for this study. The designated asphalt content for the various experimental schemes was 3.8%, 4.2%, 4.6%, 5.0%, and 5.4%, respectively.

During the preparation process of the sustainable asphalt mixture, the RAP was heated to 130 °C, with a heating duration not exceeding 2 hours to prevent secondary aging of the aged bitumen in RAP [²³]. The new aggregate, RCA, and 70# matrix asphalt were subjected to a heating process at temperatures of 170 °C, 170 °C, and 150 °C, sequentially. The mixing temperature of the sustainable asphalt mixture was set at 155 °C, while the compaction temperature was 150 °C. Throughout the mixing process of the sustainable asphalt mixture, RAP is first mixed with the rejuvenator, followed by the addition of 70# matrix asphalt, new aggregate, and RCA, and finally, the inclusion of mineral powder.

2.3. Experimental methods

The asphalt mixtures, prepared according to different experimental schemes, undergo Marshall testing to assess the Marshall and volumetric properties. Additionally, following the Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering (JTG E20-2011) [²⁴], a battery of tests including rutting, freeze-thaw splitting, low-temperature bending, fatigue cracking performance tests were conducted to evaluate the high-temperature stability, hydrological stability, resistance to low-temperature cracking, and fatigue performance of the asphalt mixture.

2.3.1. Marshall test

In the Marshall test, the molded specimens are cylindrical, with a diameter of 100 mm and a height of 63.5 mm. The bulk volume relative density of the specimens was determined using the basket method and the theoretical maximum relative density test method for asphalt mixtures, enabling the calculation of the air voids, Voids in Mineral Aggregate (VMA), Voids Filled with Asphalt (VFA) of specimens. The Marshall stability and flow value indicators were tested through the Marshall stability test. The abovementioned indicators were Marshall and volumetric properties. In addition, to different experimental schemes and asphalt content, four Marshall specimens were molded, and the average of the test results obtained from these four specimens was utilized to represent the final results.

2.3.2. Rutting test

The specimens for the rutting test are rectangular, with dimensions of 300 mm in length, 300 mm in width, and 50 mm in height. Different experimental schemes produce three rutting specimens, with testing conducted at a temperature of 60 °C. The high-temperature stability of the asphalt mixture is evaluated using the dynamic stability index, as determined by Equation (1).

(1) $$DS=\frac{(t_2-t_1)\times N}{d_2-d_1}\times C_1\times C_2$$

where, DS represents dynamic stability, cycles/mm; d₁ denotes the deformation of the specimen at time t₁, mm; d₂ represents the deformation of the specimen at time t₂, mm; C₁ and C₂ denote specimen coefficients, typically set to 1.0; N indicates the rolling speed, typically set to 42 cycles per minute.

2.3.3. Freeze-thaw splitting test

The freeze-thaw splitting test assesses the moisture stability of asphalt mixtures. Marshall specimens were employed for this test, with four specimens tested before and after freeze-thaw cycles, respectively. Equation (2) was utilized to calculate the ratio of splitting tensile strength before and after freeze-thaw cycles, providing an assessment of the moisture stability of the asphalt mixture.

(2) $$TSR=\frac{R_{\text{T-con}}}{R_{\text{T-uncon}}}\times 100\%$$

(3) $$R_T=\frac{0.006287\times p_T}{h}$$

where, TSR denotes the freeze-thaw splitting tensile strength ratio, %; R_T-con represents the tensile strength of conditioned specimens subjected to vacuum at 0.9 MPa for 15 minutes, followed by storage in a refrigerator at −18 °C for 16 hours, immersion in a 60 °C bath for 24 hours, and ultimately, tensile strength testing after 2 hours in a water bath at 25 °C, MPa; R_T-uncon indicates the tensile strength of unconditioned specimens immersed in a water bath at 25 °C for 2 hours, MPa; R_T represents the splitting tensile strength, MPa; P_T represents the maximum value of the load, N; h represents the height of the specimen, mm.

2.3.4. Low temperature bending test

The low-temperature bending test was utilized to assess the crack resistance performance of asphalt mixtures under low-temperature conditions. Specimens were prepared by cutting rutting test specimens to dimensions of 250 mm in length, 30 mm in width, and 35 mm in height for low-temperature bending tests. Each group of tests consists of 5 specimens. Experimental testing was conducted at −10 °C in accordance with the Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering (JTG E20-2011), with a spacing of 200 mm between the test supports and a loading speed of 50 mm/min. Before experimental testing, specimens are conditioned at −10 °C for 6 hours to guarantee the temperature in the specimen is consistent with the test temperature. The maximum flexural tensile strain index, as calculated in Equation (4), was utilized to characterize the low-temperature crack resistance properties of asphalt mixtures.

(4) $${\epsilon }_B=\frac{6\times h\times d}{L^2}$$

where, ε_B represents the maximum flexural tensile strain of the specimen at fail, με; L represents the span of the specimen, typically 200 mm; h represents the height of the specimen, typically 35 mm; d represents the mid-span deflection observed at the time of specimen failure, mm.

2.3.5. Fatigue cracking performance test

The fatigue cracking performance of asphalt mixtures was evaluated by a semicircular bending fatigue test. The semicircular bending specimen of different test schemes featured a diameter of 100 mm, a thickness of 50 mm, and a center slit depth of 15 mm. The fatigue cracking performance of the semi-circular specimen was tested by using the UTM-100, with a span of 80 mm between pivot points, and a test temperature of 25 °C. The test was conducted in fixed stress ratio mode with a stress ratio of 0.3 and a loading frequency of 10 Hz, and 3 specimens were tested in different test schemes. The resulting curve, illustrating the relationship between cyclic load number and displacement, is presented in Figure 7, and the quantity of cyclic loads corresponding to the complete destruction of the specimen was the fatigue life of the asphalt mixture, represented by N_f.

Figure 7
Fatigue cracking resistance (a) Laboratory testing using UTM-100, and (b) Typical fatigue cycle number versus displacement curves.

3. RESULTS AND DISCUSSION

3.1. Marshall and volumetric properties

The volumetric and Marshall properties for specimens with varying asphalt contents under different experimental schemes are represented in Figure 8.

Figure 8
Volumetric and Marshall properties (a) bulk volume relative density, (b) air voids, (c) VMA, (d) VFA, (e) Marshall stability, and (f) flow.

As depicted in Figure 8(a), the bulk volume relative density of asphalt mixtures under various experimental schemes exhibits an increasing trend with the increase in asphalt content. This trend was ascribed to the lower specific gravity of RCA in comparison to new aggregates. Consequently, higher RCA content results in a decrease in the bulk volumetric relative density of sustainable asphalt mixtures. Furthermore, under equivalent RCA contents, changes in RAP content have a relatively minor effect on the alteration of bulk volume relative density in sustainable asphalt mixtures. This result is based on a qualitative analysis and should be supplemented with statistical analysis to accurately assess the impact of RAP.

As depicted in Figure 8(b), the air voids of sustainable asphalt mixtures across various experimental schemes decrease with increasing asphalt content. Notably, the air voids of the V scheme, comprising entirely new aggregates, remain at the lowest level across different asphalt contents. Furthermore, at constant RAP content, an upward trend in sustainable asphalt mixture air voids was observed with increasing RCA content under the same asphalt content. Additionally, when the RCA content was the same, sustainable asphalt mixtures with higher RAP content exhibited elevated air voids at the same asphalt contents. The higher the RAP and RCA proportion in sustainable asphalt mixtures, the higher the asphalt content will be required under the same air void requirements. Thus, under the same asphalt content, the proportion of RAP and RCA used in sustainable asphalt mixtures will affect the test results of the air voids.

Figure 8(c) shows that the VMA of sustainable asphalt mixture across various experimental schemes initially decreases and then increases with the increase of asphalt content. Notably, the VMA of sustainable asphalt mixture incorporating RAP and RCA was lower compared to that of the V scheme. Moreover, when the RAP content was the same, an escalation in RCA content within sustainable asphalt mixtures led to an increase in VMA. Similarly, at equivalent RCA content, the VMA of sustainable asphalt mixtures with 30% RAP content surpasses that of asphalt mixtures with 20% RAP content.

Figure 8(d) illustrates that the VFA of sustainable asphalt mixtures across different experimental schemes increases with rising asphalt content. Notably, compared to the experimental scheme incorporating RAP and RCA, the VFA of the V scheme was the highest at different asphalt contents. Moreover, when the RAP content was the same, the higher the RCA content, the smaller the VFA in sustainable asphalt mixtures under the same asphalt content. Similarly, at equivalent RCA content, elevated RAP content results in diminished VFA of sustainable asphalt mixture at identical asphalt content levels. These observations underscore the significant impact of RAP and RCA proportions on VFA variation in asphalt mixtures.

Figure 8(e) indicates that the Marshall stability of sustainable asphalt mixtures across different experimental schemes exhibits a decreasing trend with increasing asphalt content. For asphalt content not exceeding 4.2%, the addition of RAP and RCA to the asphalt mixture, compared to the V scheme, may result in either an increase or decrease in Marshall stability. However, when the asphalt content surpasses 4.6%, incorporating RAP and RCA tends to improve the Marshall stability of the asphalt mixture relative to the V scheme. Notably, within the designated asphalt content interval, the Marshall stability of sustainable asphalt mixtures under various test schemes exceeds 8 kN.

Figure 8(f) depicts that the flow values of sustainable asphalt mixtures across various experimental schemes demonstrate an increasing trend with rising asphalt content. However, at equivalent asphalt content, the flow value of sustainable asphalt mixtures does not exhibit a clear pattern with variations in RAP and RCA proportions.

As indicated by the test results of volumetric and Marshall properties, variations in the proportion of RCA and RAP utilized in sustainable asphalt mixtures significantly affect the outcomes of volumetric and Marshall properties. To investigate the influence of RCA and RAP on the volumetric and Marshall properties, ANOVA analysis was conducted [²⁵], and the results are presented in Table 5. As can be seen, the P-value of Air voids, VFA, Marshall stability, and Flow is more than 0.05. It can be deduced that the impact of RAP and RCA on the Air voids, VFA, Marshall stability, and Flow are not significant. Notwithstanding, the P-value of Bulk volume relative density and VMA are lower than 0.05, and the influences of RAP and RCA are statistically significant.

Table 5
ANOVA analysis of the volumetric and Marshall properties of sustainable asphalt mixtures.

PROPERTIES	ANOVA TEST RESULTS	ADJ. MS	F-VALUE	P-VALUE
	FACTOR
Bulk volume relative density	RAP	0.012	8.911	0.001
	RCA	0.018	38.497	0.000
Air voids	RAP	4.446	0.967	0.391
	RCA	7.062	1.623	0.204
VMA	RAP	1.244	8.571	0.001
	RCA	0.728	4.558	0.009
VFA	RAP	277.884	1.223	0.308
	RCA	400.631	1.875	0.154
Marshall stability	RAP	4.531	1.544	0.229
	RCA	7.261	2.774	0.058
Flow	RAP	0.044	0.141	0.869
	RCA	0.014	0.043	0.988

Utilizing the test results of Marshall and volumetric properties, the optimal asphalt content (OAC) of asphalt mixtures for different experimental schemes was calculated based on the Technical Specifications for Construction of Highway Asphalt Pavements (JTG F40-2017) [²⁶], and the results of the OAC are depicted in Figure 9. It is evident from Figure 9 that the addition of either RAP or RCA leads to an increment in the OAC of the sustainable asphalt mixture. Specifically, the increase in the OAC for R20C15, R20C25, R20C35, R30C15, R30C25, and R30C35 is 1.9%, 6.5%, 11.4%, 4.1%, 10.4%, and 14.5%, respectively, compared to the V scheme. Moreover, the rise in OAC induced by RCA exceeds that of RAP at equivalent addition ratios of RAP and RCA. Upon analysis, previous studies [²⁷, ²⁸, ²⁹] have shown that during the hot mixing process, the aging asphalt on the surface of RAP can not be entirely separated and interact with the new aggregate and virgin asphalt. Consequently, a disparity arises between the asphalt contained in RAP and the effective asphalt, leading to an elevation in the OAC of sustainable asphalt mixtures containing RAP. Furthermore, the surface morphology of RCA significantly differs from that of new aggregates. Notably, the minute voids on the surface of RCA outnumber those present in new aggregates, resulting in higher water absorption by RCA compared to new aggregate. This characteristic facilitates the absorption of asphalt into the voids, consequently elevating the OAC of sustainable asphalt mixtures containing RCA. In addition, the air voids test results for V, R20C15, R20C25, R20C35, R30C15, R30C25, and R30C35 schemes under the optimal asphalt content were 4.7%, 4.4%, 4.6%, 4.8%, 4.5%, 4.8%, and 5.0%, respectively. It can be seen that the difference in air voids between the different test schemes at the optimum asphalt content was small.

Figure 9
Calculation results of optimal asphalt content for different experimental schemes.

3.2. Mechanical properties

3.2.1. Rutting resistance

Due to the combined influences of traffic loads, materials, and other factors, rutting has emerged as a significant factor affecting the durability of asphalt pavements [²], necessitating asphalt mixtures with robust rutting resistance to load-induced deformation. According to the design experimental scheme, the dynamic stability results of different experimental schemes under the OAC at 60 °C test temperature are illustrated in Figure 10.

Figure 10
Dynamic stability test results.

As illustrated in Figure 10, the addition of RAP and RCA enhances the dynamic stability of sustainable asphalt mixtures and improves the load-deformation resistance of asphalt mixtures. Compared with the addition of new aggregate alone in scheme V, the growth rates of dynamic stability of R20C15, R20C25, R20C35, R30C15, R30C25, and R30C35 are 19.8%, 47.3%, 54.5%, 35.1%, 61.7%, and 72.0%, respectively. The dynamic stability increased by 22.9% and 29.0% with a 25% and 35% RCA proportion, respectively, compared to a 15% RCA proportion for a sustainable asphalt mixture containing 20% RAP. Similarly, the increase in dynamic stability of sustainable asphalt mixtures with a 25% and 35% RCA proportion over 15% under 30% RAP content was 19.7% and 27.3%, respectively. The dynamic stability of sustainable asphalt mixtures increased by 12.8%, 9.8%, and 11.3% with a 30% RAP compared to a 20% RAP at 15%, 25%, and 35% RCA proportions, respectively. These results indicate that the increase in dynamic stability of sustainable asphalt mixtures induced by RAP was lower than that achieved with RCA. The observed improvements in dynamic stability with increasing RCA and RAP contents can be attributed to multiple interacting factors. Firstly, the residual cement mortar attached to RCA particles tends to increase surface roughness and angularity, which enhances interlock within the aggregate structure and improves resistance to permanent deformation. Secondly, the presence of aged asphalt in RAP increases the overall stiffness of the binder matrix, contributing to higher rutting resistance. In addition, the dynamic stability test results of different test schemes are higher than the JTG F40-2017 specification of not less than 800 cycles/mm, indicating that the rutting resistance of the designed sustainable asphalt mixture meets the requirements.

To assess the significance of the impact of RAP and RCA on the dynamic stability of sustainable asphalt mixtures, the ANOVA analysis was conducted, and the results are presented in Table 6. As evident from Table 6, statistically, the influence of RCA proportion variation on the dynamic stability of sustainable asphalt mixtures surpasses that of RAP. Furthermore, as indicated by the P-value calculation result, the P-value of RCA is approximately equal to 0.05. This indicates a potential influence of RCA on improving rutting resistance, though the result narrowly misses the conventional threshold for statistical significance (p < 0.05). The observed trend suggests that increasing RCA content may contribute to higher dynamic stability, possibly due to enhanced aggregate interlock or the stiffening effect of residual mortar. Further investigation with a larger sample size may help confirm this trend.

Table 6
ANOVA analysis of the dynamic stability of sustainable asphalt mixtures.

PROPERTIES	ANOVA TEST RESULTS	ADJ. MS	F-VALUE	P-VALUE
	FACTOR
Dynamic stability	RAP	359345.5	3.416	0.136
	RCA	342506.4	9.180	0.051

3.2.2. Moisture stability

Asphalt pavement is vulnerable to various forms of water erosion, including solid, liquid, and gaseous infiltration, which can lead to pavement deterioration. Consequently, asphalt mixtures must exhibit robust resistance to water-induced damage. The freeze-thaw splitting test was employed to assess the moisture stability of asphalt mixtures with optimal asphalt content across different test schemes, and the results are presented in Figure 11.

Figure 11
Test results of splitting tensile strength and splitting tensile strength ratio.

As presented in Figure 11, the splitting tensile strength of sustainable asphalt mixtures containing 30% RCA content before freeze-thaw was lower than that of the V scheme; conversely, this trend reverses for RCA proportions of 15% and 25%, respectively. Furthermore, the freeze-thaw split tensile strength of sustainable asphalt mixtures with the inclusion of both RAP and RCA exceeds that of the V scheme. The TSR of sustainable asphalt mixtures containing RAP and RCA exhibited an upward trend compared to Scheme V. Specifically, the TSR of sustainable asphalt mixtures with a 35% RCA content increased notably across different RAP proportions. These observations demonstrate that the incorporation of RAP and RCA enhances the moisture stability of sustainable asphalt mixes. The results can be attributed to several contributing factors. First, the aged asphalt present in RAP typically exhibits higher stiffness and enhanced resistance to moisture compared to virgin binders, which improves the overall durability of the mixture. Second, RCA particles often retain residual cement mortar on their surfaces, which can enhance the bonding between the aggregate and asphalt binder due to increased surface roughness and potential chemical interaction. Additionally, the higher optimum asphalt content required for mixtures containing RCA ensures that more binder is available to fully coat the aggregates and fill internal voids, thereby offering better protection against moisture intrusion. In addition, the TSR test results for the different test schemes are higher than 70%, meeting the JTG F40-2017 requirement of not less than 70%.

ANOVA analysis was employed to examine the influence of RAP and RCA on the TSR of sustainable asphalt mixtures, and the results are summarized in Table 7. It can be seen that RCA has a statistically significant effect on the moisture stability of sustainable asphalt mixtures, whereas RAP shows no significant effect. Further investigation demonstrates that higher RCA proportions correlate with a notable increase in the optimal asphalt content of sustainable asphalt mixtures, leading to an increase in free asphalt within the asphalt mixtures, consequently enhancing the moisture of sustainable asphalt mixtures [³⁰].

Table 7
ANOVA analysis of the TSR of sustainable asphalt mixtures.

PROPERTIES	ANOVA TEST RESULTS	ADJ. MS	F-VALUE	P-VALUE
	FACTOR
TSR	RAP	11.107	0.311	0.749
	RCA	52.919	25.202	0.013

3.2.3. Low-temperature crack resistance

In the low-temperature climate region, the low-temperature cracking resistance of asphalt pavement significantly impacts its durability. The outcomes of the low-temperature bending and tensile strain tests for the different test schemes at −10 °C are present in Figure 12.

Figure 12
Test results of maximum bending and tensile strain of sustainable asphalt mixture.

As depicted in Figure 12, the maximum flexural tensile strains of sustainable asphalt mixtures incorporating RAP and RCA were lower compared to the V scheme, which exhibits a maximum flexural tensile strain of 2045 × 10⁻⁶ με, meeting the JTG F40-2017 specification requirement of not less than 2000 × 10⁻⁶ με. However, the maximum flexural tensile strains of sustainable asphalt mixtures with RAP and RCA additions fall within the range of 1940 × 10⁻⁶–1970 × 10⁻⁶ με, and the differences in the maximum flexural tensile strains between the different schemes were small. It is hypothesized that the incorporation of RAP reduces the maximum flexural tensile in sustainable asphalt mixtures, primarily due to the effects of aging asphalt present in RAP [³¹, ³², ³³]. Moreover, considering that the asphalt content increases with the addition of RAP and RCA in different schemes, the air voids remain relatively consistent among different schemes at optimal asphalt content, which may be the main reason for the limited variation in maximum flexural tensile strains of sustainable asphalt mixtures across different RAP and RCA additions [³⁴, ³⁵].

The results of ANOVA calculations of RAP and RCA on the maximum flexural tensile strains of sustainable asphalt mixtures are presented in Table 8. It can be seen that the P-values associated with RAP and RCA are below 0.05, signifying their statistically significant impact on the maximum flexural tensile strains of sustainable asphalt mixtures, i.e., incorporating RAP and RCA into asphalt mixtures will affect the low-temperature cracking resistance.

Table 8
ANOVA analysis of the maximum flexural tensile strains of sustainable asphalt mixtures.

PROPERTIES	ANOVA TEST RESULTS	ADJ. MS	F-VALUE	P-VALUE
	FACTOR
Maximum flexural tensile strains	RAP	3643.922	36.989	0.003
	RCA	2461.152	24.740	0.013

3.2.4. Fatigue performance

The fatigue life test results of sustainable asphalt mixtures at 0.3 stress ratio for different test schemes at 25 °C are shown in Figure 13. As depicted in Figure 13, the fatigue life of sustainable asphalt mixtures varies with different proportions of RAP and RCA. The fatigue life growth rate of R20C15, R20C25, R20C35, R30C15, R30C25, and R30C35 schemes were −5.7%, 18.9%, 22.4%, −9.3%, 15.4%, and 17.6%, respectively, as compared to V scheme. Notably, the fatigue life of R20C15 and R30C15 schemes was lower than that of the V scheme, indicating that the use of RAP will reduce the fatigue life of sustainable asphalt mixtures. This reduction was primarily affected by the properties of the aged asphalt in the RAP, which reduces the anti-fatigue properties of aged asphalt and thus leads to a diminution in the performance of sustainable asphalt mixtures containing RAP. However, the fatigue life of sustainable asphalt mixtures with 20% and 30% RAP proportions showed a smaller reduction in fatigue life than the V scheme, which is mainly due to the lower proportion of aged asphalt contained in sustainable asphalt mixtures. In addition, the fatigue life of sustainable asphalt mixtures with the same RAP proportion shows an increasing trend with the increase of RCA content, which is mainly because the increase of RCA content also causes an increase in the optimal asphalt content of sustainable asphalt mixtures, and the higher the asphalt content, the higher the fatigue life of asphalt mixtures. Previous studies [³⁶, ³⁷, ³⁸] show that RCA particles typically have a rougher surface texture and residual mortar, which may enhance mechanical interlock within the mixture, helping to delay crack initiation and propagation. Due to the more porous nature of RCA, it can absorb some of the asphalt binder and gradually release it under repeated loading, providing a form of internal healing that may contribute to improved fatigue resistance. Additionally, the heterogeneous composition of RCA may alter the crack path, leading to more tortuous and energy-dissipating propagation routes, which could also enhance fatigue performance. Consequently, the fatigue life of sustainable asphalt mixtures containing RAP or RCA can be improved by increasing the asphalt content of the asphalt mixture [³⁹].

Figure 13
Fatigue life test results of sustainable asphalt mixtures.

The results of the ANOVA calculations assessing the influence of RAP and RCA on the fatigue life of sustainable asphalt mixtures are exhibited in Table 9. As demonstrated in Table 9, the P-value associated with RAP exceeds 0.05, while that of RCA is below 0.05. This discrepancy indicates that the effect of RAP on the fatigue life of sustainable asphalt mixtures is statistically insignificant, whereas the effect of RCA is significant. These findings align closely with the results illustrated in Figure 13.

Table 9
ANOVA analysis of the fatigue life of sustainable asphalt mixtures.

PROPERTIES	ANOVA TEST RESULTS	ADJ. MS	F-VALUE	P-VALUE
	FACTOR
Fatigue life	RAP	24783.667	0.234	0.801
	RCA	153853.000	41.369	0.006

3.2.5. Mechanical properties analysis

The mechanical properties of sustainable asphalt mixtures, including high-temperature stability, moisture stability, low-temperature crack resistance, and fatigue properties, are shown in Figure 14 via radar plots. The optimal asphalt content (OAC) of sustainable asphalt mixtures increases with the increase of RAP and RCA proportion. Moreover, the dynamic stability (DS) of sustainable asphalt mixes at optimal asphalt content demonstrates an augmented trend with increased RAP and RCA proportion. The differences in freeze-thaw split tensile strength ratios (TSR) of sustainable asphalt mixtures at optimum asphalt content are negligible, with the R30C35 scheme exhibiting the highest moisture stability. Notably, the maximum flexural tensile strains (ε_B) of sustainable asphalt mixtures under optimum asphalt content remain consistent across different schemes. The fatigue life (Nf) of sustainable asphalt mixtures at optimal asphalt content generally exhibits an upward trend, except for the R20C15 and R30C15 schemes. These findings suggest that the mechanical properties of sustainable asphalt mixtures, enhanced through the addition of RAP and RCA, surpass those of conventional hot-mix asphalt mixtures, affirming the feasibility of producing sustainable asphalt mixtures by using RAP and RCA that meet asphalt mixture performance requirements.

Figure 14
Test results of mechanical performance of sustainable asphalt mixtures.

3.3. Economic analysis

3.3.1. Calculations for economic analysis of asphalt mixtures

Economic benefits play a significant role in determining the material composition of sustainable asphalt mixtures. While changes in the proportions of RAP and RCA have a minimal impact on the mechanical properties of sustainable asphalt mixtures, and even improved the mechanical properties relative to the conventional hot-mix asphalt mixtures. However, higher RAP and RCA contents lead to an increased optimal asphalt content for sustainable asphalt mixtures, thereby affecting the economic benefit of asphalt mixtures. Consequently, it is imperative to conduct an economic analysis of sustainable asphalt mixtures. In this study, sustainable asphalt mixtures were produced using a conventional production process, and the production cost can be calculated using Equation (5).

(5) $$C_s={\displaystyle {\sum }_{i=1}^n{c}_i\times }{w}_i\times C_p+C_T+C_o$$

where, C_s represents the total cost of sustainable asphalt mixture, USD/Ton; c_i denotes the production cost of the i materials that consist of the asphalt mixture, e.g., new aggregate, RAP, RCA, asphalt production, USD/Ton; w_i denotes the mass of material i in the asphalt mixture, USD/Ton; C_P denotes the cost of plant producing the asphalt mixture, USD/Ton; C_T represents the cost of transporting the different materials, USD/Ton; C_O denotes the other cost of producing the asphalt mixture, e.g., RAP and RCA processing, USD/Ton.

Considering the cost components of producing asphalt mixtures, only material costs, production costs, and processing costs of RAP and RCA are considered in this study. In this case, both RAP and RCA were recycled materials, there is no production cost with raw materials, and only RAP and RCA processing costs were considered, with the assumption that the processing costs for both materials were equivalent. Additionally, the cost of new aggregate and virgin asphalt was not considered transportation costs in this study. Based on previous studies [⁴⁰, ⁴¹], the unit costs for each material, RAP, and RCA material processing are summarized in Table 10.

Table 10
The unit costs for each material, RAP and RCA material processing [⁴⁰, ⁴¹].

EXPENSE POSITION	COST (USD/TON)
New aggregate production	19.8
Virgin asphalt production	704.0
RAP processing	3.3
RCA processing	3.3
Plant production	12

3.3.2. Results of economic analysis

The total costs of the different sustainable asphalt mixtures were calculated by considering the differences in the material composition of the asphalt mixes, as shown in Figure 15. As seen in Figure 15, the utilization of RAP and RCA markedly reduces the costs associated with new aggregate and virgin asphalt production, while the costs of RAP and RCA processing constitute a lower percentage of the total costs of the asphalt mixtures, resulting in a downward trend in total production costs for sustainable asphalt mixtures. Compared to the asphalt mixes employing exclusively new aggregates and new asphalt (V scheme), the total cost reductions for the R20C15, R20C25, R20C35, R30C15, R30C25, and R30C35 schemes were 20.0%, 20.5%, 20.8%, 27.5%, 27.1%, and 27.8%, respectively. Notably, the change in RAP proportion was the primary factor that caused the reduction in the total production cost of sustainable asphalt mixtures, while changes in RCA proportion exhibited negligible impact on total production cost, primarily due to its increase in the cost of virgin asphalt. In addition, it is essential to acknowledge that the transportation and purchase costs for RAP and RCA were not factored into this study, which would reduce the economic benefits of sustainable asphalt mixtures if these costs were substantial. In summary, for regions with a shortage of new aggregates, sustainable asphalt mixtures can fully realize their economic benefits when transportation distances for RAP and RCA are minimized and purchase costs are minimized.

Figure 15
The production cost of the different sustainable asphalt mixtures.

4. CONCLUSION

This study aims to assess the feasibility of using RAP and RCA to produce sustainable asphalt mixtures. To achieve the mentioned objective, the AC-20 asphalt mixture was designed, the optimal asphalt content of sustainable asphalt mixtures with varying RAP and RCA proportions was analyzed, the mechanical properties of sustainable asphalt mixtures were evaluated, and the economic analysis was conducted. As indicated by the research findings, the following conclusions can be drawn:

1. There is a tendency for the air voids of sustainable asphalt mixtures, under the same asphalt content, to increase with the addition of RAP and RCA. As the content of RAP and RCA in sustainable asphalt mixtures increases, the optimal asphalt content of the sustainable asphalt mixtures tends to increase. In addition, the variation in air void among sustainable asphalt mixtures with different RAP and RCA contents at the optimum asphalt content was small, ranging from 4.4% to 5.0%.

2. Relative to the conventional hot mix asphalt mixtures produced with new aggregates and virgin asphalt, the sustainable asphalt mixtures containing RAP and RCA showed several notable improvements. The sustainable asphalt mixtures exhibit enhanced high-temperature stability and moisture resistance, and a smaller difference in low-temperature cracking resistance. Furthermore, the fatigue performance of sustainable asphalt mixtures is generally heightened, although exceptions are observed in schemes such as R20C15 and R30C15.

3. The ANOVA findings indicate that the proportion of RCA notably influences the mechanical properties of sustainable asphalt mixtures. Conversely, the proportion of RAP demonstrates a significant impact solely on low-temperature cracking resistance. The results are essentially caused by changes in the optimal asphalt content due to RCA and the effect of aged asphalt in the RAP.

4. The addition of RAP and RCA to asphalt mixtures can reduce production costs and contribute to the significant economic benefits for sustainable asphalt mixtures. Notably, RAP is the primary factor affecting the economic benefits of sustainable asphalt mixtures, while the RCA does not exert a significant impact on economic benefits.

5. ACKNOWLEDGMENTS

The Science and Technology Research and Development Project of Xinjiang Transportation Investment Group Co., Ltd. (XJJTZKX-FWCG-202411-0737); The Science and Technology Project of the Xinjiang Uygur Autonomous Region Transportation Industry in 2024 (2024-ZD-002); Tianshan Leading Talents in Scientific and Technological Innovation (2022TSYCLJ0045); National Natural Science Foundation of China (52268068).

• Funding
  The Science and Technology Research and Development Project of Xinjiang Transportation Investment Group Co., Ltd. (XJJTZKX-FWCG-202411-0737); The Science and Technology Project of the Xinjiang Uygur Autonomous Region Transportation Industry in 2024 (2024-ZD-002); Tianshan Leading Talents in Scientific and Technological Innovation (2022TSYCLJ0045); National Natural Science Foundation of China (52268068).

6. BIBLIOGRAPHY

• ^[1] YAO, Y., YANG, J., GAO, J., et al., “RAP chunks produced in cold milling operation of asphalt pavement: evaluation, mechanism, and engineering investigation in China”, Journal of Traffic and Transportation Engineering, v. 11, n. 5, pp. 972–1000, 2024. doi: http://doi.org/10.1016/j.jtte.2024.03.004.
  » https://doi.org/10.1016/j.jtte.2024.03.004
• ^[2] RIKAMBURA, V., M’TULATIA, M., WAWERU, S., “Investigation of the effect of cement kiln dust-rice husk ash composite fillers on volumetrics and durability properties of recycled hot-mix asphalt”, International Journal of Civil Engineering, v. 11, n. 3, pp. 94–106, 2024. doi: http://doi.org/10.14445/23488352/IJCE-V11I3P108.
  » https://doi.org/10.14445/23488352/IJCE-V11I3P108
• ^[3] BARADARAN, M.S., QAZANFARI, R., BARADARAN, S., “Study of soil reinforcement in the east of Mashhad using glass granule”, Materials Research Express, v. 10, n. 5, pp. 055202, 2023. doi: http://doi.org/10.1088/2053-1591/acd5af.
  » https://doi.org/10.1088/2053-1591/acd5af
• ^[4] BAZOOBANDI, P., MOUSAVI, S.R., KARIMI, F., et al., “Cracking resistance of crumb rubber modified green asphalt mixtures, using calcium carbonate nanoparticles and two by-product wax-based warm mix additives”, Construction & Building Materials, v. 424, pp. 135848, 2024. doi: http://doi.org/10.1016/j.conbuildmat.2024.135848.
  » https://doi.org/10.1016/j.conbuildmat.2024.135848
• ^[5] YANG, J., TAO, W., GAO, J., et al., “Measurement of particle agglomeration and aggregate breakdown of reclaimed asphalt pavement”, Construction & Building Materials, v. 296, pp. 123681, 2021. doi: http://doi.org/10.1016/j.conbuildmat.2021.123681.
  » https://doi.org/10.1016/j.conbuildmat.2021.123681
• ^[6] KASEER, F., MARTIN, A.E., ARÁMBULA-MERCADO, E., “Use of recycling agents in asphalt mixtures with high recycled materials contents in the United States: a literature review”, Construction & Building Materials, v. 211, pp. 974–987, 2019. doi: http://doi.org/10.1016/j.conbuildmat.2019.03.286.
  » https://doi.org/10.1016/j.conbuildmat.2019.03.286
• ^[7] SUZUKI, K., VASCONCELOS, K., KLINSKY, L.M., et al., “Evaluation of recycled asphalt mixtures with different RAP contents and the effect of recycling agent”, Road Materials and Pavement Design, v. 25, suppl. 1, pp. 124–136, 2023. doi: http://doi.org/10.1080/14680629.2023.2191739.
  » https://doi.org/10.1080/14680629.2023.2191739
• ^[8] PRECIADO, J., GULZAR, S., CASTORENA, C., et al., “Performance assessment of high reclaimed asphalt pavement asphalt mixtures with recycling agents”, Transportation Research Record: Journal of the Transportation Research Board, v. 2678, n. 10, pp. 1205–1220, 2024. doi: http://doi.org/10.1177/03611981241236483.
  » https://doi.org/10.1177/03611981241236483
• ^[9] SHI, B., DONG, Q., CHEN, X., et al., “A comprehensive review on the fatigue resistance of recycled asphalt materials: Influential factors, correlations and improvements”, Construction & Building Materials, v. 384, pp. 131435, 2023. doi: http://doi.org/10.1016/j.conbuildmat.2023.131435.
  » https://doi.org/10.1016/j.conbuildmat.2023.131435
• ^[10] XUE, Y., LIU, C., QU, J., et al., “Research on pavement performance of recycled asphalt mixture based on separation technology of asphalt and aggregate in RAP”, Construction & Building Materials, v. 393, pp. 132103, 2023. doi: http://doi.org/10.1016/j.conbuildmat.2023.132103.
  » https://doi.org/10.1016/j.conbuildmat.2023.132103
• ^[11] SAPKOTA, K., YAGHOUBI, E., WASANTHA, P.L.P., et al., “Mechanical characteristics and durability of HMA made of recycled aggregates”, Sustainability, v. 15, n. 6, pp. 5594, 2023. doi: http://doi.org/10.3390/su15065594.
  » https://doi.org/10.3390/su15065594
• ^[12] WU, J., REN, H., JIN, A., “Low-temperature fracture resistance of plant-mixed heat recycled asphalt mixture based on SCB”, Materials Research Express, v. 10, n. 11, pp. 115101, 2023. doi: http://doi.org/10.1088/2053-1591/ad05f2.
  » https://doi.org/10.1088/2053-1591/ad05f2
• ^[13] CAO, Z., YU, J., YI, J., et al., “Investigation of road performances of rejuvenated styrene-butadiene-styrene modified asphalt mixture”, Case Studies in Construction Materials, v. 18, pp. e02181, 2023. doi: http://doi.org/10.1016/j.cscm.2023.e02181.
  » https://doi.org/10.1016/j.cscm.2023.e02181
• ^[14] BARADARAN, S., RAHIMI, J., AMERI, M., et al., “Mechanical performance of asphalt mixture containing eco-friendly additive by recycling PET”, Case Studies in Construction Materials, v. 20, pp. e02740, 2024. doi: http://doi.org/10.1016/j.cscm.2023.e02740.
  » https://doi.org/10.1016/j.cscm.2023.e02740
• ^[15] ALBAYATI, A., MOSAWE, H.A., SUKHIJA, M., et al., “Appraising the synergistic use of recycled asphalt pavement and recycled concrete aggregate for the production of sustainable asphalt concrete”, Case Studies in Construction Materials, v. 19, pp. e02237, 2023. doi: http://doi.org/10.1016/j.cscm.2023.e02237.
  » https://doi.org/10.1016/j.cscm.2023.e02237
• ^[16] SHU, X., HUANG, B., VUKOSAVLJEVIC, D., “Laboratory evaluation of fatigue characteristics of recycled asphalt mixture”, Construction & Building Materials, v. 22, n. 7, pp. 1323–1330, 2008. doi: http://doi.org/10.1016/j.conbuildmat.2007.04.019.
  » https://doi.org/10.1016/j.conbuildmat.2007.04.019
• ^[17] DE JUAN, M.S., GUTIÉRREZ, P.A., “Study on the influence of attached mortar content on the properties of recycled concrete aggregate”, Construction & Building Materials, v. 23, n. 2, pp. 872–877, 2009. doi: http://doi.org/10.1016/j.conbuildmat.2008.04.012.
  » https://doi.org/10.1016/j.conbuildmat.2008.04.012
• ^[18] FOURNIER, J.M., ÁLVAREZ, D.A., AENLLE, A.A., et al., “Combining Reclaimed Asphalt Pavement (RAP) and Recycled Concrete Aggregate (RCA) from Cuba to obtain a coarse aggregate fraction”, Sustainability, v. 12, n. 13, pp. 5356, 2020. doi: http://doi.org/10.3390/su12135356.
  » https://doi.org/10.3390/su12135356
• ^[19] PUROHIT, S., PANDA, M., CHATTARAJ, U., “Use of reclaimed asphalt pavement and recycled concrete aggregate for bituminous paving mixes: a simple approach”, Journal of Materials in Civil Engineering, v. 33, n. 1, pp. 04020395, 2021. doi: http://doi.org/10.1061/(ASCE)MT.1943-5533.0003480.
  » https://doi.org/10.1061/(ASCE)MT.1943-5533.0003480
• ^[20] NASER, M., ABDEL-JABER, M., AL-SHAMAYLEH, R., et al., “Evaluating the effects of using reclaimed asphalt pavement and recycled concrete aggregate on the behavior of hot mix asphalts”, Transportation Engineering, v. 10, pp. 100140, 2022. doi: http://doi.org/10.1016/j.treng.2022.100140.
  » https://doi.org/10.1016/j.treng.2022.100140
• ^[21] XU, X., LUO, Y., SREERAM, A., et al., “Potential use of recycled concrete aggregate (RCA) for sustainable asphalt pavements of the future: a state-of-the-art review”, Journal of Cleaner Production, v. 344, pp. 130893, 2022. doi: http://doi.org/10.1016/j.jclepro.2022.130893.
  » https://doi.org/10.1016/j.jclepro.2022.130893
• ^[22] XU, X., CHEN, G., WU, Q., et al., “Chemical upcycling of waste PET into sustainable asphalt pavement containing recycled concrete aggregates: Insight into moisture-induced damage”, Construction & Building Materials, v. 360, pp. 129632, 2022. doi: http://doi.org/10.1016/j.conbuildmat.2022.129632.
  » https://doi.org/10.1016/j.conbuildmat.2022.129632
• ^[23] YAO, Y., GAO, J., YANG, J., et al., “Sustainable asphalt concrete containing RAP and coal gangue aggregate: performance, costs, and environmental impact”, Journal of Renewable Materials, v. 10, n. 8, pp. 2263–2285, 2022. doi: http://doi.org/10.32604/jrm.2022.018911.
  » https://doi.org/10.32604/jrm.2022.018911
• ^[24] RESEARCH INSTITUTE OF HIGHWAY MINISTRY OF TRANSPORT, JTG E20-2011, Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering, China, China Communications Press, 2011.
• ^[25] JAHANBAKHSH, H., KARIMI, M.M., NASERI, H., et al., “Sustainable asphalt concrete containing high reclaimed asphalt pavements and recycling agents: performance assessment, cost analysis, and environmental impact”, Journal of Cleaner Production, v. 244, pp. 118837, 2020. doi: http://doi.org/10.1016/j.jclepro.2019.118837.
  » https://doi.org/10.1016/j.jclepro.2019.118837
• ^[26] RESEARCH INSTITUTE OF HIGHWAY MINISTRY OF TRANSPORT, JTG F40-2017, Technical Specifications for Construction of Highway Asphalt Pavements, China, China Communications Press, 2017.
• ^[27] LI, M., LIU, L., HUANG, W., et al., “Study on the mixing process improvement for hot recycled asphalt mixture”, Construction & Building Materials, v. 365, pp. 130068, 2023. doi: http://doi.org/10.1016/j.conbuildmat.2022.130068.
  » https://doi.org/10.1016/j.conbuildmat.2022.130068
• ^[28] WU, Q., WU, S., SUN, X., et al., “Improvement of RAP binder mobilization and blending efficiency using microwave induction”, Journal of Materials in Civil Engineering, v. 35, n. 10, pp. 04023348, 2023. doi: http://doi.org/10.1061/JMCEE7.MTENG-15836.
  » https://doi.org/10.1061/JMCEE7.MTENG-15836
• ^[29] GAO, J., YAO, Y., YANG, J., et al., “Migration behavior of reclaimed asphalt pavement mastic during hot mixing”, Journal of Cleaner Production, v. 376, pp. 134123, 2022. doi: http://doi.org/10.1016/j.jclepro.2022.134123.
  » https://doi.org/10.1016/j.jclepro.2022.134123
• ^[30] ZHANG, D., YU, P., LIU, Z., et al., “Influence of acidity and alkalinity of water environments on the water stability of asphalt mixture: Phase I - molecular dynamics simulation”, Construction & Building Materials, v. 411, pp. 134466, 2024. doi: http://doi.org/10.1016/j.conbuildmat.2023.134466.
  » https://doi.org/10.1016/j.conbuildmat.2023.134466
• ^[31] CUI, Y., CHEN, Q., LI, M., et al., “Study on low temperature crack resistance of warm-mixed recycled SBS modified asphalt mixtures”, Construction & Building Materials, v. 409, pp. 134120, 2023. doi: http://doi.org/10.1016/j.conbuildmat.2023.134120.
  » https://doi.org/10.1016/j.conbuildmat.2023.134120
• ^[32] HUGENER, M., WANG, D., FALCHETTO, A.C., et al., “Recommendation of RILEM TC 264 RAP on the evaluation of asphalt recycling agents for hot mix asphalt”, Materials and Structures, v. 55, n. 2, pp. 31, 2022. doi: http://doi.org/10.1617/s11527-021-01837-0.
  » https://doi.org/10.1617/s11527-021-01837-0
• ^[33] GAO, J., YAO, Y., HUANG, J., et al., “Effect of hot mixing duration on blending, performance, and environmental impact of central plant recycled asphalt mixture”, Buildings, v. 12, n. 7, pp. 1057, 2022. doi: http://doi.org/10.3390/buildings12071057.
  » https://doi.org/10.3390/buildings12071057
• ^[34] MONIRI, A., ZIARI, H., ALIHA, M.R.M., et al., “Laboratory study of the effect of oil-based recycling agents on high RAP asphalt mixtures”, The International Journal of Pavement Engineering, v. 22, n. 11, pp. 1423–1434, 2019. doi: http://doi.org/10.1080/10298436.2019.1696461.
  » https://doi.org/10.1080/10298436.2019.1696461
• ^[35] BARADARAN, S., ALIHA, M.R.M., “Mode I and Mode II fracture assessment of green asphalt pavements containing plastic waste and RAP at low and intermediate temperature”, Results in Engineering, v. 25, pp. 103734, 2025. doi: http://doi.org/10.1016/j.rineng.2024.103734.
  » https://doi.org/10.1016/j.rineng.2024.103734
• ^[36] BURITATUM, A., SUDDEEPONG, A., HORPIBULSUK, S., et al., “Improved performance of asphalt concretes using bottom ash as an alternative aggregate”, Sustainability, v. 14, n. 12, pp. 7033, 2022. doi: http://doi.org/10.3390/su14127033.
  » https://doi.org/10.3390/su14127033
• ^[37] HOY, M., SAMRANDEE, V., SAMRANDEE, W., et al., “Evaluation of asphalt pavement maintenance using recycled asphalt pavement with asphalt binders”, Construction & Building Materials, v. 406, pp. 133425, 2023. doi: http://doi.org/10.1016/j.conbuildmat.2023.133425.
  » https://doi.org/10.1016/j.conbuildmat.2023.133425
• ^[38] TAKAIKAEW, T., HOY, M., HORPIBULSUK, S., et al., “Performance improvement of asphalt concretes using fiber reinforcement”, Heliyon, v. 7, n. 5, pp. e07015, 2021. doi: http://doi.org/10.1016/j.heliyon.2021.e07015. PubMed PMID: 34041388.
  » https://doi.org/10.1016/j.heliyon.2021.e07015
• ^[39] BARADARAN, S., ALIHA, M.R.M., MALEKI, A., et al., “Fracture properties of asphalt mixtures containing high content of reclaimed asphalt pavement (RAP) and eco-friendly PET additive at low temperature”, Construction & Building Materials, v. 449, pp. 138426, 2024. doi: http://doi.org/10.1016/j.conbuildmat.2024.138426.
  » https://doi.org/10.1016/j.conbuildmat.2024.138426
• ^[40] ZAUMANIS, M., MALLICK, R.B., FRANK, R., “100% recycled hot mix asphalt: a review and analysis”, Resources, Conservation and Recycling, v. 92, pp. 230–245, 2014. doi: http://doi.org/10.1016/j.resconrec.2014.07.007.
  » https://doi.org/10.1016/j.resconrec.2014.07.007
• ^[41] YANG, R., KANG, S., OZER, H., et al., “Environmental and economic analyses of recycled asphalt concrete mixtures based on material production and potential performance”, Resources, Conservation and Recycling, v. 104, pp. 141–151, 2015. doi: http://doi.org/10.1016/j.resconrec.2015.08.014.
  » https://doi.org/10.1016/j.resconrec.2015.08.014

Publication Dates

• Publication in this collection
  25 July 2025
• Date of issue
  2025

History

• Received
  19 Feb 2025
• Accepted
  06 June 2025