1.

INTRODUCTION

After China officially proposed the “dual carbon” goal, “carbon peaking” and “carbon neutrality” have become hot topics of concern for all sectors of society. For the transportation industry, meeting the transportation development aspirations brought about by comprehensive modernization and people living a better life, while balancing the hard constraints of the “dual carbon” goals, is a huge challenge for the entire industry. Achieving sustainable development through the promotion of low-carbon and green transformation within the transportation industry is a vital issue that needs to be addressed throughout the industry^1-4.

Currently, research on the reasonable structure of asphalt pavement in China mainly focuses on the structural combination and material selection of the base layer⁵. Thickness per structural layer and the materials used in the asphalt surface layer of the paved test road pavement structure are relatively fixed. There is relatively little research on the reasonable combination and material selection of the asphalt surface course structure^6,7. In addition, the use time of the test road in various provinces is still short, and various structural characteristics have not been demonstrated. It remains to be tested over time which structure is more reasonable and durable⁸.

On the premise of meeting the performance requirements of road use, designing a reasonable thickness of road structure as much as possible, fully leveraging the advantages of layer position, and seeking potential alternative solutions for raw materials to alleviate the pain points of scarce high-quality raw materials and high mining energy consumption is an effective way to achieve the urgent requirements of the current dual carbon goal. This article focuses on the rational design of pavement structure and conducts an analysis of economic and durable countermeasures for asphalt pavement, in order to achieve technological breakthroughs in low-carbon construction.

2.

PAVEMENT STRUCTURE AND PARAMETER SELECTION

Clarifying the tasks to be undertaken by each structural layer, fully leveraging the functional advantages of each layer, and ensuring or even extending the service life, are a manifestation of achieving carbon emission and energy consumption reduction in the design phase⁹.

The pavement structure fully considers the actual traffic conditions and durability requirements of China, while drawing on the design experience of typical asphalt pavement construnctions of semi-rigid base^10,11. The values of compressive rebound modulus of asphalt mixture and cement stabilized crushed stone refer to the “Design Specification for Highway Asphalt Pavement”, and the values of Poisson’s ratio refer to previous studies such as the SHARP plan. The specific pavement structure and material parameters are listed in Table 1 ^12-14.

Table 1.

Pavement design and material attributes.

The pavement structure computation employs BISAR3.0 software, a product of the shell working group, grounded in the principles of elastic layered system theory. This approach posits that all material layers, except the soil subgrade, have constrained thicknesses and are considered both homogeneous and isotropic, with each layer extending infinitely laterally. In a semi-rigid base asphalt pavement, the peak shear stress and maximum tensile stress are located at the midpoint of the wheel track.

3.

THE INFLUENCE OF CHANGES IN SUB BASE PARAMETERS ON THE STRESS OF PAVEMENT SYSTEM

Gradually, as the modulus of the underbase layer E5 increases from 800 to 2000 MPa, the variation laws of the maximum shear stress (MSS) in the pavement structure and the maximum tensile stress at the bottom of the base layer (BBL) were calculated and obtained (Figures 1 and 2).

Figure 1.

The variation law of maximum shear stress with E₅.

Figure 2.

The variation law of tensile stress of BBL with E₅.

With the increase of sub base modulus, the MSS in the structural content and the MTS of BBL both increase, with the increase in tensile stress of BBL being more significant. As the thickness of the base layer increases, the value of MSS slightly increases, while the tensile stress of BBL gradually decreases. Based on the consideration of the most unfavorable combination of corresponding stresses, when calculating the MSS value in the following text, the modulus of the underbase layer is the compressive modulus, which is taken as 1200 MPa. When analyzing the tensile stress of BBL, the flexural modulus is taken, with a value of 2000 MPa. During the calculation process in the following text, the thickness of the base layer remains unchanged and remains at 20 cm.

4.

THE INFLUENCE OF CHANGES IN BASE LAYER PARAMETERS ON THE STRESS OF PAVEMENT SYSTEM

The calculation of the tensile stress at the bottom of the sub base layer (BSBL) is performed, taking into account two factors pertaining to the changes in the base layer’s parameters: the modulus E4, which has been increased from 1000 MPa to 10000 MPa, and the thickness of the base layer h4, which has been augmented from 30 cm to 40 cm. The results of this calculation are subsequently presented in Figure 3.

Figure 3.

The variation law of tensile stress in sub base layer with E₄ and h₄.

As the modulus of the base layer E4 increases, the tensile stress of BSBL gradually increases (Figure 3). However, there are negatively correlated between the thickness of the base layer h4 and the tensile stress of BSBL (Figure 3). In the context of pavement structure design, it is advisable to reduce the modulus of the base layer while increasing its thickness. This adjustment serves to mitigate potential bending and tensile stresses within the base layer, thereby offering enhanced protection against cracking induced by fatigue.

5.

THE STRESS OF THE PAVEMENT STRUCTURE SYSTEM IS INFLUENCED BY THE ASPHALT CONCRETE SURFACE LAYER.

5.1

The variation law of maximum shear stress

(1) The influence of lower surface modulus variation on maximum shear stress

With the modulus of the middle layer being fixed at 1000 MPa, 2000 MPa, and 3000 MPa respectively, the modulus E3 of the lower layer is incremented from 1000 MPa to 4000 MPa to compute the MSS value at the corresponding location, resulting in the stress distribution pattern depicted in Figure 4.

Figure 4.

The MSS changes with the modulus of the underlying layer.

From the results, it can be seen that under different moduli of the middle layer, the trend of the MSS values with the change of the lower layer modulus is the same. That is, with the increase of the lower layer modulus, the MSS value gradually increases. Therefore, the increase of the lower layer modulus is unfavorable for the stress of the middle layer, increasing the possibility of shear failure and rutting in the middle layer.

(2) Analysis of the influence of middle layer on maximum shear stress

The maximum shear stress MSS variation law was calculated, where the thickness of the lower layer was selected to vary as 6 cm, 8 cm, and 10 cm, respectively. Additionally, the modulus of the middle layer underwent a gradual increase from 1000 MPa to 2000 MPa, while its thickness also gradually increased from 4 cm to 12 cm. These calculations are presented in Figures 5 and 6.

Figure 5.

The law of MSS changing with the middle surface modulus.

Figure 6.

The variation law of MSS with the thickness of the middle surface layer.

According to the analysis of the results, it can be concluded that under different thicknesses of the lower layer, the variation pattern of MSS with the modulus of the middle layer is the same, that is, as the modulus of the middle layer increases, the MSS value gradually decreases. Under different thicknesses of the lower layer, the variation pattern of MSS with the thickness of the middle layer is the same. That is, as the thickness of the middle layer increases, the MSS value initially rises before it starts to decline. Moreover, when the thickness of the middle layer is 8 cm, the corresponding maximum shear stress value is the smallest.

5.2

Analysis of the variation law of tensile stress at the bottom of asphalt concrete surface layer (BACSL)

(1) The influence of changes in the modulus of the middle surface layer on the tensile stress of BACSL

The modulus of the lower layer was selected as 1000 MPa, 2000 MPa, and 3000 MPa, respectively. The modulus of the middle layer gradually increased from 1000 MPa to 4000 MPa, and the variation law of the tensile stress of BACSL was calculated (Figure 7).

Figure 7.

The variation law of MSS with the thickness of the middle surface layer.

When the modulus of the lower layer is different, the trend of the tensile stress of BACSL is the same. With the increase of the modulus of the middle layer, the trend of the tensile stress of BACSL is relatively gentle. Therefore, the change of the modulus of the middle layer has no significant impact on the tensile strength of the lower layer.

(2) Analysis of the influence of lower layer parameter changes on the tensile stress of BACSL

The thickness of the middle layer was selected as 6 cm, 8 cm, and 10 cm, respectively. The modulus of the lower layer gradually increased from 1000 MPa to 4000 MPa, and the thickness of the lower layer gradually increased from 4 cm to 12 cm. The variation law of the tensile stress of BACSL was calculated, and the result were shown in Figures 8 and 9.

Figure 8.

The variation of tensile stress at the bottom of the surface layer with the modulus of the lower layer.

Figure 9.

The variation law of tensile stress at the bottom of the surface layer with the thickness of the lower layer.

According to the results, it can be observed that the trend of the calculation results obtained by setting different middle layer thickness is consistent. The larger the lower layer modulus, the greater the corresponding tensile stress of BACSL. Increasing the thickness of the lower layer will help reduce the tensile stress of BACSL.

6.

CONCLUSION