Yi Yong, Jiang Yingjun, Tian Tian, Zhang Yu, Fan Jiangtao, Bai Chenfan, Deng Changqing. 2024: Investigation of indoor and field tests on asphalt pavement with inverted asphalt layers based on the vertical vibration compaction method. Journal of Road Engineering, 4(4): 478-478. DOI: 10.1016/j.jreng.2024.01.007
Citation:
Yi Yong, Jiang Yingjun, Tian Tian, Zhang Yu, Fan Jiangtao, Bai Chenfan, Deng Changqing. 2024: Investigation of indoor and field tests on asphalt pavement with inverted asphalt layers based on the vertical vibration compaction method. Journal of Road Engineering, 4(4): 478-478. DOI: 10.1016/j.jreng.2024.01.007
Yi Yong, Jiang Yingjun, Tian Tian, Zhang Yu, Fan Jiangtao, Bai Chenfan, Deng Changqing. 2024: Investigation of indoor and field tests on asphalt pavement with inverted asphalt layers based on the vertical vibration compaction method. Journal of Road Engineering, 4(4): 478-478. DOI: 10.1016/j.jreng.2024.01.007
Citation:
Yi Yong, Jiang Yingjun, Tian Tian, Zhang Yu, Fan Jiangtao, Bai Chenfan, Deng Changqing. 2024: Investigation of indoor and field tests on asphalt pavement with inverted asphalt layers based on the vertical vibration compaction method. Journal of Road Engineering, 4(4): 478-478. DOI: 10.1016/j.jreng.2024.01.007
Yi Yong: Dr. Yong Yi earned his PhD degree in the School of Highway at Chang'an University. He is an assistant professor in School of Civil and Architectural Engineering at Yangtze Normal University. He mainly engaged in the research of long-life asphalt pavement structure, new pavement materials and heat reflective coatings. He has published more than 30 SCI/EI academic papers
Jiang Yingjun: Yingjun Jiang is a professor of road engineering in the School of Highway at Chang'an University. Engaged in road engineering teaching and scientific research, focusing on major theoretical and practical research on super-large particle size long-life pavement technology, key technologies for long-life roadbeds in special areas, and so on. He has won 3 first prizes, 9 second prizes, and 9 third prizes at the provincial and ministerial level for scientific and technological progress. More than 180 papers have been published in core journals, more than 50 invention patents have been authorized, and 5 monographs have been published
Dr. Tian Tian earned her PhD degree in the School of Highway at Chang'an University. She mainly engaged in the research of long-life asphalt pavement structure and new pavement materials. She has published more than 20 academic papers
Zhang Yu: Yu Zhang is a PhD candidate of Chang'an University, mainly focuses on research on comprehensive utilization technology of solid waste, design and construction of crack resistant and durable cement stabilized crushed stone base, and structural design of long-life asphalt pavement. He has published more than ten academic papers, including 9 SCI/EI papers
Fan Jiangtao: Dr. Jiangtao Fan earned his PhD degree in the School of Highway at Chang'an University. He mainly engaged in the research of key technologies for long life of subgrade in special areas and key technologies for treatment of large-thickness collapsible loess subgrade of intercity railway. He has published more than 20 academic papers
Bai Chenfan: Chenfan Bai, a PhD candidate at Chang'an University, is dedicated to road engineering research. His work primarily involves the asphalt pavement structure design, pavement functional material development, and construction technologies for subgrade in specialized regions. He has published over ten academic papers, including 4 in SCI/EI papers
Deng Changqing: Dr. Changqing Deng earned his PhD degree in the School of Highway at Chang'an University. He is an assistant professor in College of Urban and Rural Construction at Shaoyang University. His research interests are in asphalt pavement structures and materials. He has published more than 30 academic papers and won two provincial and ministerial-level scientific and technological progress awards
An inverted asphalt pavement is created by reversing the sequence of the lower and middle layers in a conventional asphalt pavement. The lower layer is composed of material with larger particle size and lower asphalt content, which improves its ability to withstand deformation caused by rutting. On the other hand, the middle surface has a higher asphalt content, specifically designed to resist fatigue cracking. This paper examines the mechanical response of two pavement structures and investigates the potential of two measures, inverted asphalt pavement and asphalt mixture design by vertical vibration compaction method (VVCM), in reducing stresses and stress levels in asphalt pavements. Additionally, a large thickness rutting and fatigue test method was developed to study the rutting resistance and fatigue life of the pavement structures, and to construct rutting deformation and fatigue life prediction models. Finally, test sections were paved to verify the feasibility of the inverted pavement and VVCM materials. The findings show that inverted pavement and VVCM materials have a minimal impact on pavement stress, but can reduce pavement shear and tensile stress levels by up to 18%–25%. Furthermore, inverted pavement and VVCM materials have positive effects on improving the rutting resistance and fatigue life of asphalt pavements.
Semi-rigid asphalt pavement is the predominant type of pavement structure used for high-grade highways in China, accounting for approximately 95% (Sha et al., 2022). A typical semi-rigid asphalt pavement consists of a 4 cm upper layer, 6 cm middle layer, 8 cm lower layer, and a 40–56 cm cement-stabilized macadam base layer. The primary types of damage that affect asphalt pavements are rutting deformation and fatigue cracking (Chen et al., 2021). Previous studies on damage to semi-rigid-base asphalt pavements have shown that rutting deformation mainly occurs in the middle layer, where the maximum shear stress is concentrated (Qian et al., 2019), while fatigue cracking initiates at the base of the lower layer, where the maximum tensile stress is observed (Cheng et al., 2022; Ge et al., 2023; Sudarsanan and Kim, 2022). To address these issues, various methods have been employed to reduce pavement structural stress and enhance the mechanical strength of the materials (Jiang et al., 2018; Liang et al., 2012). Structural adjustments, such as controlling the thickness of the asphalt layer and modifying the base layer, have been implemented (Jiang et al., 2020a, 2021). Material improvements, such as using high modulus middle layer materials and increasing the asphalt film thickness of the lower layer, have also been utilized to enhance the performance of asphalt pavements (Jiang et al., 2020b; Li et al., 2018; Ren and Yin, 2022). However, it is important to note that while these methods offer significant advantages in enhancing pavement performance, they also lead to increased project costs. Therefore, it is crucial to improve the service performance of asphalt pavements without incurring additional costs.
The middle layer of asphalt pavement experiences high shear stress, leading to rutting deformation as the primary issue (Jiang et al., 2021). Typically, AC-20 asphalt mixture, which consists of SBS modified asphalt with an asphalt content of 4.2%, is used as the filling material for this layer. On the other hand, the lower layer of asphalt pavement deals with significant tensile stress, resulting in fatigue cracking as the main problem. AC-25 asphalt mixture, composed of matrix asphalt with an asphalt content of 3.3%, is commonly employed for this layer (Deng et al., 2020). It is worth noting that the middle layer asphalt mixture has smaller particle size and higher asphalt content. Previous studies have shown that larger aggregate particle size and lower asphalt content in the mixture contribute to reduced rutting deformation in the asphalt pavement (Pouranian and Haddock, 2018). Therefore, it seems that the lower layer asphalt mixture may be more suitable for paving the middle layer. Similarly, higher asphalt content leads to greater fatigue life of the asphalt pavement, indicating that middle layer asphalt mixtures could be more appropriate for the lower layer (Ren and Yin, 2022). By inverting the middle and lower layers, it might be possible to achieve a pavement with improved rutting and fatigue properties at no additional cost. In this scenario, the middle layer, which experiences deformation due to rutting, can benefit from asphalt mixtures with larger particle size and lower asphalt content, enhancing resistance to rutting deformation (Petkevicius et al., 2010). Conversely, the lower layer can have a higher asphalt content with smaller particles, which is advantageous for combating fatigue cracking, the primary issue in that layer. It is important to note that previous research by Bulevicius et al. (2014), Du et al. (2012), and Petkevicius et al. (2010) has emphasized the significance of the middle and lower layers in an asphalt pavement, with the middle layer being prone to rutting deformation and the lower layer being the site where fatigue cracking initiates.
In recent studies, it has been found that the performance of asphalt pavement is greatly influenced by the quality of construction (Sha et al., 2022). To achieve better rutting and fatigue properties, it is crucial to have small initial voids and a homogeneous mixture. In China, the Marshall method is commonly used to design asphalt mixtures. However, due to the increased tonnage of rolling equipment, there is a weak correlation between the Marshall specimens and the actual asphalt pavement after rolling (Deng et al., 2021). Considering the current construction equipment, it may not be necessary to grind the asphalt mixture to the densest chamber in order to achieve pavement compaction exceeding 98% of the Marshall density (Jiang et al., 2018). This could potentially explain the early damage observed in asphalt pavements. To enhance the correlation between laboratory specimens and field core samples, a research group utilized the vertical vibratory compaction method (VVCM) for asphalt mixture design. They developed vertical vibratory compaction equipment (VVCE) that mimics the pavement rolling process and offers greater compaction work. Notably, published papers have demonstrated a correlation exceeding 90% between VVCM and field core samples (Xue et al., 2022). Thus, utilizing VVCM in asphalt mixture design may play a significant role in improving the quality of asphalt pavement construction.
Recent studies have shown the advantages of using inverted asphalt layers to prevent rutting deformation in asphalt pavements. However, most of the research conducted so far has relied on numerical simulations, and the test results have not been validated. Additionally, there is a lack of experimental methodology for testing the rutting and fatigue performances of asphalt pavements with an inverted asphalt layer. Therefore, this paper aims to analyze the differences in mechanical responses between an asphalt pavement with an inverted asphalt layer and a traditional asphalt pavement. To achieve this, full-thickness rutting and fatigue tests are conducted on the asphalt pavement after inverting the asphalt layer. These tests aim to investigate the rutting deformation and fatigue life properties of the pavement. The results obtained from the tests are then verified through theoretical analyses and further tests. Finally, the paper explores the impact of different design methods, such as the Marshall method and the VVCM, on the performance of asphalt pavements.
2.
Materials
2.1
Asphalts
A styrene-butadiene-styrene- (SBS) (I-C) modified asphalt (Zhejiang Yinji Petrochemical Co., Ltd., Zhejiang, China) was used for the upper layer asphalt mixture and the sticky layer oil, and an A-level 70# matrix asphalt (China Petroleum and Chemical Corporation) was used for the middle and lower layers. The technical indicators for asphalt were measured according to the standard test methodology for bitumen and bituminous mixtures specified in JTG E20-2011 (RIOH, 2011), and the results are provided in Table 1.
This study used basalt gravel (Jinhua Pan'an Stone Material Factory) as a coarse aggregate for the upper asphalt mixture and limestone gravel (Jinhua Pan'an Stone Material Factory) as the coarse aggregate for the middle and lower asphalt mixtures. Limestone was selected as the fine aggregate. The main technical indicators for the aggregates were tested in accordance with those specified for highway engineering in JTG E42-2005 (RIOH, 2005), and the results are presented in Table 2, Table 3.
Table
2.
Main technical properties of coarse aggregates.
This study used AC-13, AC-20, and AC-25 asphalt mixtures as the materials for the upper, middle, and lower layers, respectively. Fig. 1 shows the gradation of these asphalt mixtures.
Figure
1.
The gradation of AC-13, AC-20 and AC-25 asphalt mixtures.
The design process of asphalt mixtures involves the use of both the Marshall test method and the vertical vibratory compaction method (VVCM). The asphalt mixture was designed according to the Marshall method as outlined in JTG E20-2011 (RIOH, 2011). To simulate a vibratory roller, a customized vertical vibratory compaction equipment (VVCE) was utilized, as shown in Fig. 2(a). The VVCE is composed of three main parts: the control system, vibration system, and hydraulic power equipment. The control system is responsible for regulating the working frequency and vibration time of the equipment. The vibration system, which includes the frame, on-board system, off-board system, shaker, and indenter, is the crucial component of the VVCE. The hydraulic power system consists of a splitter box and a motor. The shaker's core component is the eccentric block, depicted in Fig. 2(b). The two symmetrically arranged eccentric blocks ensure that only vertical force is generated by the instrument, while canceling out the horizontal force to maintain the stability of the VVCE and achieve effective compaction. The working frequency is set at 38 Hz, with a vibration time of 65 s (Jiang et al., 2018).
Figure
2.
Structure and working principle of VVCE. (a) VVCE. (b) Symmetrical eccentric block.
3.2
Physical and mechanical properties of asphalt mixtures
The physical and mechanical properties of asphalt mixtures designed by Marshell and VVCM methods are shown in Table 4, Table 5, Table 6. In the tables, OAC, VV, VMA, and VFA represent the best oil-stone ratio, void ratio, mineral clearance ratio, and asphalt mixture saturation, respectively. DS, RD, εB, TSR, and MS0 represent the dynamic stability, rut depth, lowtemperature failure strain, and freeze-thaw split ratio residual stability, respectively.
Table
4.
The volume parameters of asphalt mixtures designed by different methods.
The rutting performance of the pavement structure was evaluated using a self-developed large thickness rutting test system (Fig. 3). To simulate the actual rutting deformation of the pavement as closely as possible and test the overall resistance of the asphalt layer, we utilized self-made equipment for molding large-thickness rutting specimens (Fig. 3(c)) and conducting the rutting tests (Fig. 3(d)). Our self-developed test system allows rutting tests to be performed on specimens with a thickness ranging from 50 to 200 mm. Compared to traditional rutting test systems, our system offers increased range of motion for the wheel mill and improved clearance. The large thickness rutting test equipment also allows for adjustment of the load size, typically ranging from 0.5 to 1.3 MPa. The rutting test specimens were formed by layering and rolling. Sticky-layer oil was sprayed between the layers, and the upper layer was formed after the lower layer had cooled. The fabrication process of the specimen is shown in Fig. 3(a) and (b).The anti-rutting performance of the asphalt pavement structure was determined based on the rutting depth (RD) obtained from the rutting test, which was conducted following the guidelines of JTG E20-2011 (RIOH, 2011). The loads applied were 0.7 and 1.2 MPa, respectively, at an experimental temperature of 60 ℃. The holding time was 8 h (Jiang et al., 2020b), and the loading time was 10 h. Six parallel specimens were tested for the rutting test, and the coefficient of variation of the test results was less than 15%.
Figure
3.
The self-developed large thickness rutting test system. (a) Lower layer moulding. (b) Large thickness rutting specimens. (c) Rutting specimens moulding equipment. (d) Rutting test equipment.
A fatigue test was conducted using an MTS testing machine (Fig. 4(a) and (b)) in which a concentrated load was applied in the middle of the test specimen until breakage occurred. The span (the support spacing) of the fatigue test sample was 200 mm, the load frequency was 10 Hz, and the test temperature was 10 ℃. A sine wave load was applied at maximum loads (Pmax) of 30, 50, and 70 kN. The cyclic characteristic value was R = 0.1, the minimum load was 0.1 Pmax. The number of parallel specimens for fatigue test was 6. A fatigue test specimens measuring 300 mm (length) × 180 mm (width) was cut from the rutting test specimens (Fig. 4(c)).
Figure
4.
The fatigue test. (a) MTS testing machine. (b) The loading method. (c) Beam specimen for fatigue test.
4.1
Asphalt pavement structure with an inverted asphalt layer
4.1.1
Asphalt pavement structure
This study examined the mechanical responses of two pavement structures commonly used in China (Fig. 5). The first structure, referred to as X-M, consisted of an asphalt pavement with a semi-rigid base using Marshall-designed asphalt surface material. The second structure, referred to as X-V, followed the VVTM design.
Figure
5.
Asphalt pavement structure. (a) Semi-rigid base asphalt pavement (SP). (b) Semi-rigid base asphalt pavement with inverted asphalt layer (SPI).
BISAR 3.0 software is based on the elastic layered system theory and is widely used for analysing the mechanical responses of asphalt pavements; therefore, it was used for that purpose in this study (Li et al., 2020). The calculated load was a double-circle uniformly distributed vertical load. The interlayer contact states between the asphalt–cement-stabilised macadam layers was defined as partly continuous. The contact state between the other layers is defined as completely continuous. The stresses of the asphalt pavement under a load condition of 0.7 MPa was given in Fig. 6. The stress levels of the asphalt pavement was given in Table 8. The stress level is the ratio of the structural stress of the pavement to the mechanical strength of the pavement material.
Figure
6.
The stresses of the asphalt pavement. (a) Relationship between tensile stress and depth. (b) Tensile stress at the bottom of the asphalt layer. (c) Tensile stress at the bottom of the base. (d) Relationship between shear stress and depth. (e) Maximum shear stress of the middle layer. (f) Maximum shear stress of the upper layer.
The results presented in Fig. 6 demonstrate the beneficial effect of both measures, namely the inverted pavement structure and VVCM design asphalt mixture, in reducing pavement stress. In Fig. 6(a), it can be observed that the change in pavement tensile stress is negligible. However, Fig. 6(b) and (c) reveal that the inverted pavement structure and VVCM design asphalt mixture can respectively reduce the tensile stress at the bottom of the asphalt layer by approximately 2%–3% and 1%. The maximum reduction in tensile stress amounts to approximately 0.004 MPa. Moreover, Fig. 6(d) indicates that the change in pavement shear stress is minimal. Nevertheless, Fig. 6(e) and (f) demonstrate that the inverted pavement structure and VVCM design asphalt mixtures can respectively decrease the maximum shear stress in the mid-surface layer by approximately 2%–3%. The maximum reducible shear stress is approximately 0.01 MPa. Despite the reduction in stresses achieved by these measures, it should be noted that the extent of reduction is quite limited. This limitation may be attributed to the similarity in modulus of the asphalt mixtures in the middle and lower layers, which implies that the difference in pavement stresses is also expected to be small.
The study presented in Table 8 demonstrates that the inverted pavement structure effectively reduces the stress level of the pavement. Specifically, the shear stress levels of the middle and lower layers of the SPI-M pavement are 0.269 and 0.196, respectively, whereas the shear stress levels of the inverted pavement SPI-M are only 0.236 and 0.193. This reduction in shear stress can be attributed to the use of AC-25 asphalt mixture in the middle layer of the SPI-M pavement, which exhibits superior shear strength. The findings from Fig. 6 further support these results, indicating a small difference in shear stresses between SP-M and SPI-M pavements, with the middle layer of the SPI-M pavement experiencing lower shear stress. This reduction in shear stress is crucial for enhancing the pavement's resistance to rutting deformation, as previous studies have highlighted the significance of shear stress in the middle layer in relation to pavement rutting deformation (Li et al., 2015). Moreover, a comparison between SPI-M and SPI-V pavements reveals that the shear stress level in SPI-V pavements is reduced by 18%. This reduction can be attributed to the asphalt mixtures designed for VVCM, which exhibit higher densities and greater shear strengths, as supported by existing literature (Deng et al., 2021). Notably, the maximum shear stress level in SPI-V pavements can be reduced to less than 0.2. In terms of tensile stress, the inverted pavement structure proves beneficial in reducing the tensile stress level at the bottom of the asphalt layer, while having little to no effect on reducing the tensile stress level at the bottom of the base layer. Specifically, SPI-M pavements exhibit lower tensile stress levels at the bottom of the asphalt layer compared to SP-M pavements, possibly due to the use of AC-20 in the lower layer, which offers better tensile strength. This improvement is valuable in mitigating cracking issues in asphalt pavements. Furthermore, SPI-V pavements demonstrate the minimum tensile stress level, thanks to the superior tensile strength of the asphalt mixture designed by VVCM (Deng et al., 2021).
5.
The pavement performances of asphalt pavement
5.1
The rutting depth of asphalt pavement
5.1.1
Factors affecting rutting depth
Table 9 below shows the RD data of different asphalt pavement structures. The RDs of the pavement structure under loading cycles of 2550 and 25, 500 are presented in Fig. 7.
Figure
7.
RD of asphalt pavement structure. (a) Load acting times = 2550. (b) Load acting times = 25,500.
According to Table 9 and Fig. 7, the inclusion of an inverted asphalt layer improves the anti-rutting performance of the asphalt pavement. The loading level and design method of the asphalt mixture also have a significant impact on its anti-rutting performance. Compared to traditional asphalt pavements, the anti-rutting performance of inverted-layer asphalt pavement can be improved by over 12%. Specifically, during the initial loading stage (2550 loading cycles), the anti-rutting performance of asphalt pavement with the inverted asphalt layer can improve by approximately 20%. Loading parameters play a crucial role in the anti-rutting performance of asphalt pavements, as increasing the load from 0.7 to 1.2 MPa increases RD by 58%. Moreover, the use of VVCM in asphalt mixture design has a positive influence on this performance. By including an inverted asphalt layer structure and using VVTM materials, a 40% reduction in RD can be achieved. This reduction is attributed to the decrease in shear stress level in the middle layer (Table 8). In comparison to SP-M pavement, SPI-V pavement can reduce shear stress levels by 29%.
Table
9.
The RDs of different asphalt pavement structures.
Load (MPa)
Pavement structure
RD of pavement with the following load acting times (mm)
As is evident in Fig. 8, an increase in the number of loads corresponds to similar curves in the shape of the rut development curve on different road surfaces. Up to 2250 loading cycles, there was a sharp increase in the RD of the pavement structure; however, when the number of cycles exceeded 2550, the increase in the RD of the pavement structure gradually slowed (according to the number of loading cycles) until it stabilized.
As there was only a slight increase in RD above 25, 500 loading cycles, the RD is assumed to have a limit value (RDmax), which is represented in the two boundary conditions in Eq. (1). Consequently, a rutting prediction equation (Eq. (2)) can be established in accordance with the boundary conditions of Eqs. (1), (2). Table 10 and Fig. 9 present the regression coefficients after fitting and the fitted curve, respectively.
where RD0 and RD∞ are the corresponding road RD (in mm) when the number of loading cycles is 0, N is number of loading cycles (times), ∞, RDmax, and ξ are regression coefficients.
According to the information in Table 10 and Fig. 9, the correlation coefficient of the rutting prediction equation is R2 > 0.98. This confirms the accuracy of the prediction equation in calculating the law for the development of rutting in a pavement's structure. Additionally, the RDmax value of the asphalt pavement with an inverted asphalt layer is about 16% lower than that of the traditional pavement structure.
5.2
The fatigue life of asphalt pavement
5.2.1
Fatigue test results
Table 11 presents the fatigue lives of the fatigue test specimens.
Table
11.
Fatigue lives of the fatigue test specimens.
It can be seen from Table 11 that the fatigue lives of asphalt pavements are positively influenced by the inclusion of inverted asphalt layers and the use of VVCM materials. However, the data presented in Table 11 are discrete. The Weibull distribution forms the basis for analyzing theoretical reliability and fatigue life; its ability to reflect the effects of design parameters means that it is used frequently in fatigue life analyses (Deng et al., 2020; Xue and Jiang, 2017).
5.2.2
Weibull fatigue equation
Assuming that the equivalent fatigue life (N>) obeys the Weibull distribution, the failure probability (P) should satisfy Eq. (3). Then, Eq. (3) can be transformed into Eq. (4), as follows.
P=F(ˉN)=1−e−¯Nmt0ˉN≥1,m>0,t0>0
(3)
lnln11−P=mlnˉN−lnt0
(4)
where m is the shape parameter, t0 is the scale parameter, and ˉN=N1−R.
As presented in Table 12, the regression coefficients m, lnt0, and R2 were obtained by substituting the data in the table into Eq. (4). A good correlation between the Weibull distribution and the fatigue life (R2 > 0.9) is evident in Table 12. The substitution of m and lnt0 obtained from the Weibull distribution test into Eq. (4) produces the equivalent fatigue life of pavement structures with different failure probabilities, as presented in Table 13.
Table
12.
Results of test data examined by the Weibull distribution.
It is assumed that the relationship between the fatigue life (N) and the load (Pmax) is linear on the double logarithmic coordinate (Eq. (5)) in which a and b are regression coefficients. The fatigue curve under different failure probabilities can be obtained by fitting the data in Table 13 with Eq. (5) (Fig. 10).
The intercept of the fatigue equation curve on the ordinate axis is denoted by 'a' in Eq. (5). A higher value of 'a' indicates better fatigue performance of the asphalt pavement. On the other hand, 'b' represents the slope of the fatigue equation curve. A lower value of 'b' suggests better fatigue performance of the asphalt pavement. In Fig. 10, there is little variation observed in the 'b' values of the pavement structures. Among them, SPI-V exhibits the highest 'a' value, indicating a longer fatigue life in the structural layers of the pavement after the inverted asphalt layer. This longer fatigue life can be attributed to the reduction in the tensile stress level at the bottom of the asphalt layer, as shown in Table 8. Specifically, SPI-V pavement shows a 39% reduction in tensile stress levels compared to SP-M pavement.
6.
Evaluation of asphalt pavement structure with inverted asphalt layer
6.1
Theoretical verification of the inverted asphalt pavement
Table 9 and Fig. 8 display the RDs of various pavement structures, indicating that the anti-deformation ability of the asphalt pavement is enhanced after the inverted asphalt layer is applied. This finding aligns with the results of theoretical calculations (refer to Table 7, Table 8) and can be attributed to the reduction in shear stress levels in the asphalt pavement. The internal shear stress of the asphalt pavement with the inverted asphalt layer is lower compared to a traditional asphalt pavement under the same load and temperature conditions, while the shear strength remains the same. Consequently, the road surface experiences reduced shear deformation, which is consistent with the findings of Li et al. (2011) and Sha et al. (2020).Based on the fatigue life data presented in Table 11 and Fig. 10, it can be observed that the asphalt pavement with the inverted asphalt layer exhibits the longest fatigue life. This indicates improved durability and a longer service life for this pavement type in terms of mechanical response. This can be attributed to the lower internal tensile stress levels in the asphalt pavement with the inverted asphalt layer (Table 7, Table 8) compared to the traditional asphalt pavement. Under repeated loading, the asphalt pavement with the inverted asphalt layer operates under lower stress levels. As fatigue life of asphalt pavements is closely related to stress levels, the asphalt pavement with the inverted asphalt layer demonstrates a longer fatigue life, which is consistent with the findings reported by Sha et al. (2020).
6.2
The construction process of field test sections
To verify the performance of inverted pavements, a test section was paved on National Highway G330 in Zhejiang, China. The lengths of SP-M, SPI-M, SP-V, and SPI-V pavements were 300, 250, 290, and 300 m, respectively. The structure of the pavements is shown in Fig. 11(a). The asphalt mixtures used in the test section were consistent with the indoor tests. The construction process of the test section is shown in Fig. 11(b)–(e). Tracked asphalt mixture paving equipment was used for asphalt pavement paving. The screed of the paving equipment had a vibration frequency of 37 Hz, an amplitude of 0.4–0.8 mm, and a paving speed of 2–5 m/min. Rubber-wheel compaction equipment and double-steel-wheel vibratory compaction equipment were used for asphalt pavement compaction. The asphalt pavement compaction process was divided into three stages. In the first stage, rubber wheel compaction equipment is used. The asphalt mixture is rolled and compacted by the rubber wheel compaction equipment, reassembling the particles and embedding small particle size particles into the skeleton of large particle size particles to form a stronger skeleton compact structure.The second stage uses double steel wheel vibratory compaction equipment to ensure the compaction of the asphalt pavement and eliminate the wheel tracks left by the rubber wheel compaction equipment in the first stage. Compaction continues until the desired degree is achieved. The third stage uses rubber wheel compaction equipment to eliminate small cracks. The asphalt pavement compaction process is shown in Table 14.The field core samples of the pavement after compaction are shown in Fig. 11(f).
Figure
11.
The structure and construction process of the test section. (a) Pavement structures. (b) Paving process. (c) First stage of compaction process. (d) Second stage of compaction process. (e) Third stage of compaction process. (f) The field core samples of the pavement after compaction.
According to Fig. 12, there was no significant difference between the compaction of the asphalt pavement after the inverted asphalt layer and that of the traditional asphalt pavement. The use of VVCM materials caused a reduction in the pass rate of the flatness of the asphalt pavement and the inverted asphalt layer; however, this difference is relatively small compared with the traditional asphalt pavement.
After the inversion of the asphalt layer, better results can be achieved without changing the original construction process. The data in Table 15 reveal that reductions of 12% and 11% were realized in the surface deflection value of the asphalt pavement after the inverted asphalt layer using Marshall materials and VVCM materials, respectively. These results indicate that the stiffness of the asphalt pavement after the inverted asphalt layer was improved.
7.
Conclusions
This study combined theoretical calculations, laboratory experiments, and field tests to investigate the performance of asphalt pavements with inverted asphalt layers. This is beneficial for reducing road rutting deformation and prolonging the service life of the road surface. At the same time, the pavement maintenance cost is reduced without increasing the construction cost. The following conclusions can be drawn.
(1) The pavement structure shear and tensile stresses were slightly reduced, within 2%, after inverting the middle and lower layers. However, the reduction in maximum shear stress levels for the middle layer was about 18%. The reduction to the tensile stress level at the bottom of the asphalt layer was about 25%.
(2) The application of VVCM-designed asphalt mixtures has a beneficial effect on pavement stress reduction. Compared to SPI-M pavements, the maximum shear stress level in the middle layer of SPI-V pavements can be reduced by 18% and the tensile stress level at the bottom of the asphalt layer can be reduced by 19%.
(3) A rutting test was used to assess the anti-deformation abilities of different pavement structures, and an RD prediction model was established. It was confirmed that the asphalt pavement with an inverted asphalt layer is more resistant to deformation by over 12% compared with the other types. A correlation higher than 0.98 was identified between the results of the RD prediction model and the laboratory tests, which indicates good prediction ability.
(4) Fatigue tests were conducted to assess the fatigue lives of different pavement structures. The data were analysed using the Weibull distribution, which produced a correlation greater than 0.9, and a fatigue life equation was established. Consequently, the asphalt pavement with the inverted asphalt layer was found to have an enhanced fatigue life.
(5) The field test section was paved to verify the feasibility of inverted pavement and VVCM on National Highway 330. The SPI-V pavement had the smallest road surface rebound deflection of 9.0 (0.01 mm).
Acknowledgments
This research was supported by Shaanxi Province Innovation Capacity Support Program (2022TD-06), Transportation Industry Key Science and Technology Projects (2021-MS1-011), the Science and Technology Project of the Shaanxi Provincial Department of Transportation (20-02K), the Scientific Project from Henan Provincial Communication (2021-2-8). The authors gratefully acknowledge all the financial support.
HIGHLIGHTS
● The mechanical response of the asphalt pavement with the inverted asphalt layer and the traditional pavement were analyzed.
● The high-temperature deformation and fatigue performance of asphalt pavements with inverted asphalt layers have been studied.
● The field and theoretical analysis were used to verify the asphalt pavement performance of the inverted asphalt layer.
Declaration of competing interest
The authors do not have any conflict of interest with other entities or researchers.
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