1. Introduction
The rapid growth of highway traffic volume, the continuous increase in super-heavy loads, and the complex and bad traffic environment lead to higher requirements for asphalt concrete pavement. According to statistics, more than 80% of the maintenance and repair of asphalt pavement is caused by the permanent deformation of pavement rutting [
1]. Compared with other pavement performance issues, the rutting disease of asphalt pavement is the most harmful [
2]. In order to improve the rutting resistance of asphalt concrete pavement, in the selection of raw materials, in addition to selecting the ore aggregate with hard stone, wear resistance, no impurities, no weathering and good particle shape, we should also select a high-performance asphalt with a high softening point, high consistency and good temperature stability, which can maintain sufficient viscosity under high-temperature conditions and ensure that the mixture has good low-temperature cracking resistance in a low-temperature environment.
In recent years, the application research direction of improving the high-temperature performance of asphalt mixture is mainly reflected in the selection of asphalt, such as styrene-butadiene-styrene block copolymer (SBS) modified asphalt, natural rock asphalt-modified asphalt [
3], low-grade hard asphalt [
4,
5,
6], plus anti-rutting agent or high-modulus agent [
7,
8,
9,
10,
11]. However, in engineering application, it is found that a single-modified asphalt, such as SBS-modified asphalt, cannot meet the increasing high-temperature performance requirements [
12]. The asphalt modified with pure natural rock asphalt significantly improves the high-temperature performance, but reduces the low-temperature performance to almost the same extent [
13]. Low-grade hard asphalt improves the high-temperature performance of the mixture, but also significantly reduces the low-temperature performance, and the low-temperature cracking of the pavement is serious [
14,
15]. The cost of adding high-modulus agent or anti-rutting agent is high, which increases the difficulty of mixing and the probability of inaccurate measurement. Therefore, considering both performance and cost factors, natural rock asphalt and SBS modifier were used to modify the matrix asphalt, so as to obtain a composite-modified asphalt with low price and high road performance, and apply it to the construction of expressway.
Rock asphalt is a kind of natural asphalt. It has the advantages of high nitrogen content, good durability and good compatibility with base asphalt. The preparation process and application process are simple. It is commonly used in the modification of asphalt and asphalt mixture. It can significantly improve the high-temperature stability and shear strength of asphalt pavement, reduce rutting deformation and prolong the service life of pavement. SBS polymer modifier can significantly improve the temperature sensitivity, stability, durability, adhesion and aging resistance of asphalt. It has been found [
16,
17,
18,
19,
20] that the composite modification of asphalt with rock asphalt and SBS modifier can significantly improve the viscosity and softening point of asphalt binder, and improve the high-temperature stability and water stability of asphalt mixture. For example, Bulgis et al. [
21] studied the influence of Buton rock asphalt particles on the compressive stress-strain behavior of asphalt mixture. The results showed that the compressive strength of the mixture mixed with butun rock asphalt is higher than that of the mixture without modifier, and the number of cracks is fewer. Suaryana [
22] studied the performance of Buton rock asphalt in Stone Mastic Asphalt (SMA) pavement and the results showed that the addition of Buton rock asphalt can improve the road performance of SMA mixture. Li et al. [
23] used dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests to study the rheological properties of asphalt modified by rock asphalt and found that the addition of rock asphalt can increase the strength of asphalt materials and reduce the low-temperature relaxation potential of asphalt mixture. Compared with the performance before and after long-term aging, rock asphalt can slow down the aging rate of asphalt mixture. Huang et al. [
24] have systematically studied the high-temperature performance, water stability and fatigue resistance of rock asphalt-modified asphalt mixture by using sk70#, Zhonghai 70# asphalt as matrix asphalt and Qingchuan rock asphalt, North American rock asphalt and star rock asphalt as modifiers. The research shows that the high-temperature resistance, water stability and fatigue resistance of rock asphalt-modified asphalt mixtures have been improved to varying degrees. Li et al. [
25] have compared and analyzed the road performance of matrix asphalt mixture, BRA rock asphalt mixture and SBS-modified asphalt mixture. The research shows that BRA rock asphalt can significantly improve the deformation resistance, water loss resistance, low-temperature crack resistance and fatigue resistance of asphalt mixtures. According to the above research and the application of rock asphalt, so far, compared with Qingchuan rock asphalt and Buton rock asphalt, the composite modification technology of North American rock asphalt and SBS has not been reported and has not been widely used. The research on North American rock asphalt is mostly in the indoor test stage. Therefore, according to the current situation, this paper studies and evaluates the road performance of rock asphalt and SBS composite modified asphalt. It provides a theoretical basis for the large-scale application of North American rock asphalt in highway construction.
4. Conclusions
Based on the limited testing results, the following conclusion can be drawn.
(1) The composite modification of SBS and North American rock asphalt can effectively improve the high-temperature resistance and reduce the temperature sensitivity of 50# matrix asphalt, but it has no obvious improvement on the low-temperature performance. It is found that the reasonable content of SBS and rock asphalt can better reflect the thermal storage stability of composite-modified asphalt. The preferred ternary blending system containing 4~6 wt.% SBS and 6~8 wt.% rock asphalt is obtained by performance analysis.
(2) When the content of SBS modifier is 4%~6% and the content of rock asphalt is not less than 6%, the performance indicators of modified asphalt meet the requirements of DB 37/T 3564-2019 and EN14023 specifications for high-modulus asphalt. The test results meet the requirements of GB/T 36143-2018 specification for high-modulus asphalt mixtures.
(3) This study shows that the 50# matrix asphalt can be enhanced in its traditional performance, thermal storage stability and rheological properties using common modifiers. Moreover, the ternary blending system containing SBS and rock asphalt can achieve good performance, indicating their potential to reduce construction costs in road engineering.