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Low-Temperature Cracking and Improvement Methods for Asphalt Pavement in Cold Regions: A Review

Rui Ma

¹,

Yiming Li

^2,*

Peifeng Cheng

¹,

Xiule Chen

¹ and

Aoting Cheng

School of Civil and Transportation Engineering, Northeast Forestry University (NEFU), Harbin 150040, China

Long Jian Road and Bridge Co., Ltd., Harbin 150001, China

Author to whom correspondence should be addressed.

Buildings 2024, 14(12), 3802; https://doi.org/10.3390/buildings14123802

Submission received: 28 October 2024 / Revised: 13 November 2024 / Accepted: 21 November 2024 / Published: 28 November 2024

(This article belongs to the Section Building Materials, and Repair & Renovation)

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Abstract

The advantages of asphalt pavement in terms of driving comfort, construction efficiency, and ease of maintenance have established it as the predominant choice for high-grade pavements at present. However, being highly sensitive to temperature and stress, asphalt performance is significantly influenced by external environmental conditions and loading, making it susceptible to various distress phenomena. Particularly in high-latitude regions, asphalt pavement cracking severely limits asphalt pavement’s functional performance and service lifespan under cold climatic conditions. To enhance the low-temperature cracking resistance of asphalt pavement in cold regions, tools such as VOS viewer 1.6.20 and Connected Papers were utilized to systematically organize, analyze, and summarize relevant research from the past 40 years. The results reveal that temperature shrinkage cracks and thermal fatigue cracks represent the primary forms of asphalt pavement distress in these regions. Cracking in asphalt pavement in cold regions is primarily influenced by structural design, pavement materials, construction technology, and climatic conditions. Among these factors, surface layer stiffness, base layer type, and the rate of temperature decrease exert the most significant impact on cracking resistance, collectively accounting for approximately 45.4% of all cracking-related factors. The low-temperature performance of asphalt pavement can be effectively improved through several strategies, including adopting full-thickness asphalt pavement with a skeleton-dense structure or reduced average particle size, incorporating functional layers, appropriately increasing the thickness of the upper layer and the compaction temperature of the lower layer, utilizing continuous surface layer construction techniques, and applying advanced materials. High-performance modifiers such as SBR and SBS, nanomaterials with good low-temperature performance, and warm mixing processes designed for cold regions have proven particularly effective. Among various improvement methods, asphalt modification has demonstrated superior effectiveness in enhancing the deformation capacity of asphalt and its mixtures, significantly boosting the low-temperature performance of asphalt pavements. Asphalt modification accounts for approximately 50% of the improvement methods evaluated in this study, with an average improvement in low-temperature performance reaching up to 143%. This paper provides valuable insights into the underlying causes of cracking distress in asphalt pavements in cold regions and offers essential guidance for improving the service quality of such pavements in these challenging environments.

Keywords:

low-temperature cracking in cold regions; pavement structure; asphalt modification; nanotechnology; warm mix asphalt

1. Introduction

Asphalt pavement is the preferred choice of high-grade pavement in the world because of its excellent performance, easy maintenance, and comfortable driving. In the United States, asphalt pavement makes up approximately 92–94% of the total pavement, while in Europe, it exceeds 90%, and in Japan, it surpasses 95%. Currently, asphalt pavement has become the main form of high-grade highways in China. By the end of 2023, the total length of highways in China reached 5.441 million kilometers, with 183.6 thousand kilometers of asphalt roads [1], ranking first in the world. The proportion of asphalt pavement exceeds 90%. However, as a temperature-sensitive material, asphalt’s performance is greatly influenced by ambient temperature [2], making it susceptible to rutting at high temperatures, as well as cracking, potholes, and spalling at low temperatures. Cracking damage to pavement is more pronounced in cold regions with low average annual temperatures, large daily temperature fluctuations, and intense freeze–thaw cycles. According to statistics, most of China belongs to the alpine region, and the cold region is 417.1 × 10⁴ km², accounting for about 43.5% of the land area (Figure 1) [3]; most of the cold regions are located in the west (Qinghai, Tibet, Xinjiang), northeast (Inner Mongolia, Heilongjiang, Jilin), and other economically underdeveloped areas with large transportation demand, which also leads to the frequent cracking of asphalt pavement, increased maintenance repair costs, and seriously restricting the economic development of cold regions. For example, in a study of asphalt pavement in the cold regions of the Qinghai–Tibet Plateau, the incidence rates of deformation and surface damage are 18.9% and 0.23%, respectively. The incidence of low-temperature cracking is as high as 21.6% [4], accounting for 37.5% of the total distress ratio (Figure 2) [5], making it a major factor affecting and restricting the serviceability of pavement. Pavement cracking can be attributed to changes in the viscoelastic properties of the asphalt mixture in cold environments, as well as the aging effects induced by external environmental factors during use. When asphalt is influenced by temperature load, there will be repeated contraction and tensile action, which changes the stress state within the pavement structure. When coupled with the use of processing, the pavement will be affected by the external environmental impact of the aging phenomenon so that the asphalt hardness increases, the modulus of strength increases, and the low-temperature creep relaxation of the mixture declines, which leads to the tensile stress experienced by the pavement structure exceeding the tensile limit strength and cracking phenomenon. The occurrence of pavement cracking not only disrupts the continuity of the pavement but also creates infiltration paths for surface water and impurities. Under the action of freeze–thaw cycles, they will erode the base layer, resulting in secondary distress such as frost heave, thaw settlement, frost boiling, and potholes. This greatly affects the driving safety and service level of roads and shortens the service life of roads. Therefore, the prevention and treatment of low-temperature cracking is the key to improving the service quality of asphalt pavement in cold regions.

In summary, the purpose of this paper is to summarize and discuss the types and causes of the low-temperature cracking of asphalt pavement in cold regions, analyze the main factors and proportions of asphalt cracking in cold regions, and propose evaluation methods and evaluation indicators suitable for the low-temperature performance of asphalt pavement in cold regions. Finally, the advanced research results are summarized from three aspects, road structure, modifier type, and technical process, and reasonable measures are put forward to improve the low-temperature crack resistance of asphalt and asphalt mixtures, to provide a reference for improving the service condition of asphalt pavement in cold regions.

2. Methods

The index database Web of Science (http://www.webofknowledge.com/ (accessed on 10 September 2024)) was used to search the database literature with the keywords of “cold region road distress”, “low-temperature crack of asphalt pavements”, and “low-temperature crack improvement methods” from 1 January 1985 to 1 August 2024, and a total of 3440 high-quality peer-reviewed papers were retrieved. According to Figure 3, the number of relevant studies is increasing year by year, which shows that relevant research has received more attention. In addition, using the VOS viewer (VOS viewer 1.6.20) literature visualization tool, the term threshold was set to 25, and the correlation degree was 60%, and the terms of the text data were co-occurrence-mapped (Figure 4 and Figure 5). This study found that “low-temperature performance”, “crack”, and “stress” appeared as many as 1081, 769 and 621 times, respectively, while “modifier”, “pavement structure”, and “warm mix process” as related improvement methods in the literature database had related factors of 3.69, 2.41, and 2.03.

The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) approach was used to gather data for this systematic review during the literature screening phase. This methodology is commonly used in systematic reviews as it provides a clear outline of the procedures for identifying, filtering, including, and excluding the relevant literature, thereby enhancing the accuracy and precision of the review process. Targeted keywords were employed to refine research papers under the inclusion and exclusion standards illustrated in Figure 6. Using the method of PRISMA technology, 1465 studies related to reviews were finally obtained.

3. Results and Discussion

3.1. Types and Causes of Cracks

The cracking of asphalt pavement in cold regions can be classified into three types: temperature type, aging type, and load type. The temperature type is characterized by temperature shrinkage cracks and thermal fatigue cracks, which mainly occur in cold regions where the average temperature of the coldest month is below 3.0 °C, the average temperature exceeds 10 °C for fewer than five months, and the average annual temperature is ≤5 °C [6]. However, temperature shrinkage cracks are primarily caused by a single extreme low temperature or a significant temperature drop, leading to rapid crack formation, whereas fatigue cracks are induced by frequent temperature fluctuations and prolonged exposure. The aging type is classified into physical hardening, chemical aging, and microbial aging, with physical hardening caused by low temperatures being the primary factor for early asphalt cracking. Load-type cracks are mainly caused by the deviation between the prediction of road traffic volume and the actual development, construction quality defects, overload behavior, etc., which occur less frequently and are not discussed separately.

3.1.1. Temperature Shrinkage Cracks

Temperature shrinkage cracks typically occur when asphalt pavement is subjected to rapid temperature fluctuations, causing material contraction and thermal stress in the surface layer, which exceeds the material’s ultimate tensile strength, leading to cracking [7]. Asphalt, as a viscoelastic material, has certain stress relaxation characteristics, and the thermal stress generated by temperature changes can be effectively relaxed. However, in cold regions with large short-term temperature fluctuations, prolonged low-temperature conditions lead to an increase in the stiffness modulus of the asphalt mixture and a significant decrease in its relaxation capacity [8], resulting in the rapid accumulation of thermal stress that exceeds the permissible stress range, causing cracking damage. The formation of thermal stress is primarily influenced by the cooling amplitude and the position of the structural layer. For example, in the Tibet Plateau [9], the greater the cooling amplitude during the same period, the higher the stress imposed on the pavement. When the temperature is reduced by 15 °C in one hour, the maximum temperature stress of the pavement can reach 3.33 MPa (Figure 7a). At the same cooling amplitude, the thermal stress of each structural layer decreases with the depth, and the temperature stress increases linearly. The thermal stress of the asphalt surface layer is the largest, and the stress increases by 53% compared with the structural layer of 14 cm depth (Figure 7b).

3.1.2. Thermal Fatigue Cracks

Thermal fatigue cracking is another major form of cracking in pavements in cold regions. Repeated temperature fluctuations cause thermal stresses, which reduce the ultimate tensile strain of the mixture [10]. The low-temperature environment further increases asphalt stiffness, and the faster the cooling rate, the greater the shrinkage strain of the mixture [11]. This inhibits the material’s ability to relax stress, leading to the continued accumulation of thermal stresses and the onset of fatigue damage [12,13].

The causes of thermal fatigue cracking can be summarized into two cases: surface fatigue cracking and subgrade shrinkage cracking. Research shows that the temperature difference between day and night can reach more than 25 °C in the Qinghai–Tibet area, and in this area, the structure is affected by a tensile stress of 0.1~1.55 MPa from 20:00 to 10:00 and is affected by an extrusion stress of 0.1~0.6 MPa from 12:00 to 16:00; the maximum tensile stress of the pavement appears at 6:00 (Figure 8a,b), and the pavement undergoes the repeated action of temperature stress throughout the day to cause the fatigue cracking of the surface layer. At the same time, the pavement in the cold region is also affected by the periodicity of the freeze–thaw cycle throughout the year (Figure 8c). From November to January of the next year, the frost heave of the pavement produces a large vertical deformation of 2.5~5 cm, and from March to May, the thawing and sinking of the pavement back to the initial elevation can be observed [14]. The synergistic effect of the day and night temperature difference and freeze–thaw cycle greatly reduces the fatigue life of asphalt pavement.

3.1.3. Reflection Cracks

Semi-rigid and flexible base structures are commonly employed in high-grade highways and municipal roads across China. However, low temperatures can cause material shrinkage in the pavement base or lower layers, which, through interlayer stress transfer, leads to reflective cracking in the asphalt surface layer (Figure 9). As a result, the reflection cracks of asphalt pavement in cold regions are more prevalent than those in non-cold areas [15], and the frequency of occurrence increases with the decrease in annual average temperature. Reflective cracking mechanisms can be categorized into three main types [16]: ➀ A semi-rigid base is directly laid on the asphalt surface layer; due to the temperature shrinkage or drying shrinkage effect of the base, the cracks in the base layer expand upward to the surface layer. ➁ In an asphalt pavement with cracks on the new asphalt surface, the old surface cracks due to the uneven force exerted to produce reflective cracks. ➂ In a reconstruction project, the asphalt surface layer is paved on the cement concrete pavement, and the original cement slab surface joints and crack positions are prone to cracking.

Temperature shrinkage cracks and reflection cracks are similar in form, and both belong to transverse cracks, but by observing the propagation direction of cracks through coring, it is found that Top-Down cracks [17] with a large top crack width that developed from top to bottom belong to temperature shrinkage cracks, while reflection cracks are often Down-Top cracks with a large bottom crack width that developed from bottom to top.

3.1.4. Aging Cracks

The main causes of aging cracks are physical hardening, chemical aging, and microbial aging, among which physical hardening has the greatest impact in cold regions. Asphalt binders are mainly composed of the crystalline part of the chain alkane structure (wax). The physical hardening that occurs at low temperatures (e.g., wax crystallization, asphaltene structuring or gelation, volume relaxation) is a significant cause of the early cracking of asphalt. Hesp et al. [18,19] found through field research on the road surface of 46 districts/sections in Ontario, Canada, that a binder treated at low temperature for 24 h will be separated from the coarse aggregate interface, or cracks and micro-cracks will appear, the mixture will be damaged after low-temperature treatment for more than 72 h, and the stress relaxation of the material cannot effectively offset the physical hardening effect; this phenomenon can be explained by the crystalline phase transition in asphalt aging, as described by the “Avrami Theory” [20]. Structural cracking occurs progressively under low-temperature conditions. Józef et al. [21] found that the hardness of AC and SAM increased by 11~17% after low-temperature (−20 °C) treatment for 120 h; the initial stiffness of SAM increased slower; after 5–16 days of low-temperature storage, the physical hardening rate (PHR) was larger than that of AC (Figure 10A); and the difference in physical hardening between AC and SAM was mainly attributed to the difference in gradation, void ratio, and asphalt binder.

Asphalt is composed of four parts of a saturated fraction, aromatic fraction, gum, and asphaltene. Under the influence of temperature and radiation changes, the asphalt material oxidation reaction is intense; the asphalt content of the aromatic fraction gradually decreases; gum and asphaltene and other polar components account for an increase in the proportion of the viscous rise in plastic reduction in the mixture (Figure 10B); and the pavement hardens and becomes brittle when subject to stress that is difficult to dissipate [22]. Microorganisms first use lightweight asphalt as a nutrient source to be propagated on the surface to form pits; the smooth surface is gradually roughened with microbial degradation; needle-like structures clearly appear after 30 d of degradation (Figure 10C); the continuity of the asphalt surface is disrupted; the adhesion between mixtures decreases [23]; and cracks are generated.

3.2. Influencing Factors

The low-temperature cracking of asphalt pavement in cold regions can be summarized into four categories of influencing factors: structural design, road materials, technical process, and the climate of the environment. Among these factors, surface layer stiffness, basement layer type, and cooling rate have the greatest influence on the low-temperature cracking of pavement, accounting for about 45.4% of the total cracking factors.

3.2.1. Structural Design

(1) Surface layer: The thickness and stiffness of the surface layer significantly impact cracking behavior. Dong et al. [24] analyzed 339 samples from 46 LTPP sections in nine cold regions of the United States and Canada (Figure 11). They found that when the surface layer thickness was less than 4.8 cm, the risk of cracking increased from 24% to 48%. When surface stiffness decreased from above 300 MPa to 100 MPa, the cracking probability dropped from 42.45% to 21.84%. Surface stiffness [25] exhibits the most significant influence on the low-temperature cracking of asphalt pavements, contributing approximately 17.3% (Figure 12).

(2) Basement layer: Rigid base layers are heavy, consumable, costly to construct, and are prone to vehicle wear and tear and passenger discomfort. The low modulus subgrade of flexible pavements generates large underlayment tensile strains, top compressive strains, and bending subsidence and is prone to cracking and deformation when the pavement shear stress is high [26]. The semi-rigid basement layer exhibits excellent stability, minimal compressive strain at the base top, high stiffness, superior fatigue-resistant hydro-stability, and a strong capacity for structural load diffusion. However, the reflective cracks caused by the shrinkage of the base material are difficult to avoid [27], and the type of base filler has a significant impact on the low-temperature performance of the structure.

(3) Soil subgrade: The larger the soil particles in a road subgrade, the worse the low-temperature performance of the pavement structure. The asphalt creep stiffness of a sand subgrade is 10.1% lower than that of a silty clay subgrade, and the asphalt creep stiffness of a silty clay subgrade is 17.3% lower than that of a clay subgrade [28]. The low-temperature performance of highways with the same temperature and grade is in the following order: clay > silty clay > sand.

(4) Traffic: A larger amount of annual average daily traffic (AADT), long-term heavy load on pavement, actual road traffic conditions exceeding the design expectations, and high pavement roughness with uneven load distribution [29,30] can damage road life, but AADT has a lesser impact, and the cracking level of the most favorable and unfavorable conditions (Figure 11) varies from 29.90% to 21.25%.

(5) Road age: With the increase in road service life, the physical hardening, microbial aging, and chemical aging of asphalt [12,31] make the flexibility of asphalt mixtures gradually decline; the integrally stiffness of the structure increases, but the strength decreases, and the deterioration of pavement performance gradually increases.

3.2.2. Road Materials

(1) Grade: Grade represents asphalt’s viscoelastic properties. The lower the grade of matrix asphalt is, the better the high-temperature performance is, and the worse the low-temperature performance [32]: SBS > 90 # > 70 # > 50 #. The order of the low-temperature performance of modified asphalt is as follows: SBS110 # > SBS / SBR90 # > SBR110 # > SBS90 #.

(2) Modifiers: The study of SHRP [33] showed that asphalt and mineral powder affected rutting and fatigue at rates of 29% and 52%, with a maximum effect on cracking of 87%. The order of the low-temperature cracking resistance of mixtures under the same conditions is as follows [34,35]: SBR asphalt mixtures > SBR/SBS asphalt mixtures > SBS asphalt mixtures > crumb rubber-modified asphalt mixture > resin-modified asphalt mixtures > matrix asphalt mixtures. Modifiers optimize the low-temperature crack resistance of asphalt and mixtures by physically modifying asphalt to produce a stable structure with interlayers and interlocks within asphalt or by chemically modifying asphalt to produce esterification, cyclisation, and grafting reactions to cross-link the phases to form a spatial mesh structure [36]. Composite modification can further enhance low-temperature performance while optimizing high-temperature, fatigue, water damage, and storage stability [37].

(3) Preparation parameters: Sometimes, the dosage of the modifier is too small, the modification is not sufficient, and the crack resistance of the system is insufficient. If the dosage is too high, the original stable state will be destroyed, and the excess modifier is wrapped in the outer layer of the structure in a free state to hinder the reaction process. Zhang et al. [38] found that the low-temperature performance of 3% SBS-modified asphalt was significantly improved with the increase in rubber powder dosage, and the low-temperature performance was unchanged after the dosage was higher than 10%. Development time, mixing rate, shear, preparation temperature, and other conventional preparation parameters will affect the low-temperature performance of asphalt [39]. Li et al. [40] concluded from the range analysis of orthogonal tests that the best low-temperature performance of DRP/SBS was obtained by adding SBS to matrix asphalt at 175 °C with mixing for 10 min, followed by adding DPR and shearing at 5000 rpm for 50 min.

(4) Nanomaterials: The incorporation of nanoparticles facilitates nano-scale dispersion within the binder, enhancing phase compatibility and significantly improving crack resistance [41]. Tang et al. [42] found that nanoparticles have a small size, no paired atoms on the surface, and strong binding ability with polymers, which can improve the low-temperature performance of composite asphalt. Morea et al. [43] found that nanofibers act as a bridge and transfer stress in cracks, effectively inhibiting the displacement of aggregates under load and slowing down the crack propagation inside asphalt mixtures.

(5) Gradation composition: The asphalt–aggregate ratio affects the shrinkage and flexibility of a mixture [44]. The nominal maximum particle size significantly affects the bending strain energy density of a mixture. Mixtures with smaller nominal maximum particle sizes exhibit superior low-temperature bending strength [45]. The ranking of low-temperature performance is SMA-13 > AC-13 > AC-16 > AC-20. Alkaline aggregates offer more stable adhesion for the surface layer, while acidic aggregates require the addition of anti-stripping agents to enhance adhesion. The skeleton-dense structure adopts discontinuous dense gradation, the skeleton is formed by an appropriate amount of coarse aggregate, and fine aggregate fills the skeleton gap form; the mixture then has high cohesion and internal friction resistance, good stability, and excellent high- and low-temperature performance [45,46].

3.2.3. Process Technology

(1) Production processing: According to the production and processing technology, petroleum asphalt can be divided into straight-run asphalt, solvent de-oiled asphalt, oxidized asphalt, blended asphalt, and modified asphalt. Among these types of asphalt, the low-temperature performance of straight-run asphalt and blended asphalt is poor, the low-temperature performance of oxidized asphalt is better than that of straight-run asphalt, and the low-temperature performance of rubber-modified asphalt is the best [47].

(2) Mixing process: The warm mix asphalt process between a hot mix and cold mix reduces the mixing viscosity of a mixture through the rheological principle; the essence is to solve the problem of asphalt workability. The mixing and compaction temperature of the same type of hot mix asphalt mixture can be reduced to 20~40 °C, and a reasonable warm mix process can improve the low-temperature performance of pavement in cold regions [48,49].

(3) Paving and compaction process: The discontinuous layered paving of asphalt pavement will prolong the construction time, the temperature loss of thin layers is faster in the low-temperature environment of cold regions, and it is easy for the environment to be polluted by dust during this interval, which leads to a difference in the material modulus between layers and the lack of adhesion between layers. At the same time, with the increase in surface compaction temperature and times within a reasonable range, the low-temperature crack resistance of pavement will gradually improve [50].

3.2.4. Climatic Environment

(1) Climatic temperature: The road surface temperature was significantly correlated with air temperature (Figure 13A): air temperature and asphalt concrete temperature increased rapidly from 5:00 onwards over the following 7 h, with a peak at 12:00–14:00, followed by a gradual decline reaching a low-temperature period the following day at 3:00–5:00, which can be approximated by using a temperature gradient diagram to calculate the road surface temperature [51]. Zhang et al. [28] found that for every 1 °C decrease in ambient temperature, the creep stiffness of asphalt decreases by an average of 44.97 MPa, and for the temperature intervals −35.4~−36.3 °C, −36.3~−38.3 °C, and −38.3~−43.4 °C, the creep stiffness of asphalt decreases by an average of 1.27%, 1.16%, and 0.91% for every 0.1 °C decrease in ambient temperature, but with a decrease in temperature, the creep strength of the reduction rate will gradually decrease [52].

(2) Latitude and altitude: High-latitude areas have lower average annual temperatures and longer durations of low temperatures, and the frost heave distress of road structures is frequent [53]. High-altitude regions experience lower temperatures and intense solar radiation. Pavements in these cold regions are more susceptible to ultraviolet aging (Figure 13B), which significantly reduces the flexural and tensile strength of an asphalt mixture [54].

(3) Freeze–thaw cycling: The average annual freeze–thaw cycles in the cold region of Qinghai–Tibet occur more than 120 times (even more than 200 times in extreme cases). As the number of freeze–thaw cycles increases, the internal fracture stress (Figure 13C), strain energy density, and bending stiffness modulus [55,56] of the pavement material decrease, causing pavement fatigue and temperature shrinkage cracks.

Figure 13. Influencing factors. (A) a. Daily average temperature T_max-T_min temperature gradient diagram. b. Temperature gradient calculation of highest and lowest temperature of road surface [51]. (B) Flexural tensile strength of asphalt mixture after ultraviolet aging [54]. (C) Freeze–thaw cycles in fracture stress test results [55].

3.3. Evaluating Indicators

(1) Fraser brittle point: This is one of the earliest tests for evaluating the low-temperature mechanical properties of asphalt. A thin steel sheet coated with asphalt film is placed in a test tube, and the temperature is controlled to decrease it at a rate of 1 °C/min; the temperature at which the film cracks for the first time is used as the Fragile Brittle Point (FBP) [57,58,59]. However, due to the obvious influence of the cooling rate, specimen preparation, and asphaltene viscosity, the test repeatability is poor and has not been widely used in the United States and Canada.

(2) Temperature sensitivity index: The Penetration Index (PI) [60,61,62] and Penetration Viscosity Numbers (PVNs) are two indexes used [63,64]. The PI value is too high to show cementitious properties, asphalt durability, and crack resistance performance deterioration, while the PI value is too low to increase temperature sensitivity, and it shows obvious brittleness under low-temperature conditions, so it is recommended that the PI value be in the range of −1.0~+1.0.

The PVN proposed in 1976 based on 25 °C penetration and 135 or 60 °C viscosity is used more in North America and Canada. A higher PVN value indicates a lower temperature sensitivity of asphalt. Based on tests conducted on Road 219 in Pennsylvania, the PVN temperature sensitivity classification is summarized in Table 1 [65].

(3) SHRP test: The bending beam rheological test (BBR) [66] and direct tensile test (DTT) [67] specified by AASHTO Standard are the main test methods for binder cracking. The specification requires that the tensile strain of −46~0 °C DTT should not be less than 1%; SHRP believes that there is a good correlation between the DTT breaking strain and the breaking temperature of the mixture thermal stress test. The BBR test (60 s) stipulates that the creep stiffness modulus S ≤ 300 MPa, and the creep rate m ≥ 0.3; there are limitations in evaluating the low-temperature performance of asphalt only by a single S or m index, and it is more comprehensive to evaluate the low-temperature performance by both.

The extended bending beam rheometer (EBBR) test based on the BBR test was listed as AASHTO Standard [68] in 2016. The EBBR test stipulates two curing temperatures (PG + 10, 20 °C), three curing times (1, 24, 72 h), and two test temperatures (PG + 10, 16 °C). Considering the grade loss of the low-temperature physical hardening of asphalt, the discrimination of the low-temperature performance of asphalt is more accurate [69].

The Burgers model based on viscoelastic theory (Figure 14a) can effectively characterize mechanical behaviors such as creep recovery and stress relaxation [70]. Yang et al. [71] combined the creep equation of the Burgers model to fit the creep compliance and loading time curve (Figure 14b). A correlation coefficient of 0.99795 is widely utilized to assess the low-temperature rheological properties of asphalt.

(4) Glass transition temperature: An asphalt mixture is a typical thermo-rheological viscoelastic material, which will undergo a transition from the elastic state in the high-temperature section to the glassy state in the low-temperature section [72]; the temperature range that causes the transformation of physical parameters is called the glass transition temperature T_g. The ideal state of an asphalt mixture is that T_g is less than its minimum service temperature, and the lower the value is, the better the low-temperature crack resistance of the mixture is [73]. Studies have shown that (Figure 14c) the correlation coefficient r between the bending failure strain ε of an asphalt mixture and asphalt T_gb and the asphalt mixture T_gm is 0.926 and 0.975, indicating that T_g can better describe the low-temperature performance of asphalt and mixtures.

(5) Low-temperature ductility: In 1988, FHWA proposed to the U.S. Department of Transportation that the low-temperature crack of asphalt pavement increases with the presence of wax; therefore, it is recommended to increase the 4 °C ductility in the AASHTOstandard; when the tensile speed is 1 cm/min, the requirements for AC-2.5, AC-5, AC-10, and AC-20 are greater than 50, 25, 15, and 5 cm, respectively. The Hungarian asphalt grading system BTA verified the reliability of 4 °C low-temperature ductility. Romanian asphalt standard STAS stipulates [74] that the penetration grades D80/120, D120/180, and D180/200 of asphalt at 0 °C ductility should not be less than 1.5 cm, 5 cm, or 8 cm.

(6) Toughness ratio: The fitting correlation between the toughness ratio R_T/V and the m value of the BBR test is 0.9476 [75,76], which is suitable for high-grade modified asphalt. The R_T/V value in the permafrost region should not be less than 4.5, and the greater the R_T/V, the better the low-temperature resistance to the cracking performance of asphalt.

(7) Semi-circular bend test: Based on the basic shape of the load–displacement curve obtained from the SCB test, Yang et al. [77] found that the two cracking indexes of slope before peak (S_bp) and fracture energy (G_f) are suitable for evaluating the low-temperature crack resistance of asphalt mortar, with a higher S_bp indicating that the asphalt mortar is harder and a higher G_f indicating that the asphalt mortar has better crack resistance.

(8) Low-temperature viscosity: Tan et al. [78,79] proposed a three-stage low-temperature rheological constitutive relationship of asphalt through a self-developed three-plate skateboard rheometer (Figure 14d). The slope of the asymptote on both sides of the pseudoplastic fluid was used to represent the zero-shear viscosity η₀ and the infinite shear viscosity η_∞. The comprehensive flow curves of −10, 0, and 10 °C (Table 2) were fitted by the Levenberg–Marquardt (L-M) damping variable step regression method, and the correlation coefficient was high, and the effect was good. It was found that the low-temperature viscosity and viscosity–temperature index (dynamic load) at 0 °C were in line with the actual situation of the road surface and can evaluate the low-temperature performance of asphalt.

(9) Thermal stress restrained specimen test: There are differences in the four evaluation indexes of the TSRST. According to Meng and Tan et al. [80,81], the gray correlation coefficient between fracture temperature and bending strain energy is the largest, which can be used as the main index to evaluate the low-temperature crack resistance of an asphalt mixture. The turning point temperature can also be used as a reference index, and slope and freezing stress can characterize the low-temperature crack resistance to a certain extent, but they need comprehensive analysis.

(10) Double-Edge-Notched Tension test and limiting phase angle temperatures: The Double-Edge-Notched Tension (DENT) test is an improved ductility test that provides the essential work of failure W_e and the plastic work of failure term βW_p and can obtain the crack tip opening displacement (CTOD), which can effectively reflect the failure relationship between coarse aggregate particles in service pavement. The temperature at which the phase angle reaches the critical values of 45°, 27°, and 28° has been proven to be related to the cracking level of the pavement; however, Hesp et al. [82] proposed a limit of a 30° phase angle temperature (T_30°) (Figure 14e,f), which has a higher correlation with the limit expansion BBR temperature after three days of cold adjustment (R² = 0.90~0.96).

Figure 14. Evaluation method. (a) Burgers model [71]. (b) Creep model fitting [71]. (c) Relationship curve between T_g of asphalt and asphalt mixture and flexural failure strain ε of mixture [73]. (d) Three-plate skateboard viscometer [79]. (e) Correlation between limiting phase angle temperature and BBR [82]. (f) Correlation between limiting phase angle temperature and EBBR [82].

3.4. Improving Methods

3.4.1. Pavement Structure

The pavement structure type and construction technology significantly influence the low-temperature performance of asphalt pavements. A reasonable design of the surface layer, base layer, and functional layer can effectively absorb interlayer stress, disperse load, and inhibit cracking development, thus improving the low-temperature crack resistance and bearing performance of pavement.

(1) Surface layer

Traditional asphalt pavement relies on discontinuous paving and compaction techniques. The prolonged construction intervals between layers, coupled with the thin layer thickness, accelerate temperature loss. Additionally, the process is prone to dust contamination, leading to reduced interlayer adhesion. Consequently, the road structure becomes disconnected and lacks overall integrity, making it highly susceptible to pavement cracking, delamination, slippage, and other forms of damage under heavy loads [83]. The continuous construction of the base and asphalt layers (CCBA) [84]: An anti-cracking agent (50 ± 5% calcium sulfate, 50 ± 5% lime powder, 0.5% lanthanum chloride) is added to the cement-stabilized base material; after the base is compacted, the asphalt surface layer is paved before the initial setting; the road is compacted and cooled; and it can be opened to traffic for more than 3 days (base strength is greater than 2.5 MPa). The construction equipment is arranged in sequence, as shown in Figure 15a, and the material transfer scheme is as shown in Figure 15b. Vehicles are not allowed to drive on the newly laid subgrade when the lateral transport of materials is permitted, which effectively suppresses subgrade cracking and enhances interlayer bonding as compared with the conventional construction technique (CCT).

Zhang et al. [85] studied asphalt pavement of continuous and discontinuous paving compaction technology under different conditions (room temperature, low temperature, freeze–thaw) (Figure 16): Under the same grading conditions, the flexural tensile strength of continuous paving specimens is significantly better than that of discontinuous paving specimens. Under different conditions, the flexural tensile strength of continuous paving specimens is better than that of discontinuous paving specimens. Under low-temperature conditions, the continuous paving compaction has the most obvious improvement in flexural tensile strength. The low-temperature performance of the AC13/AC16 and AC16/AC20 specimens is increased by 24% and 27%, respectively. The low-temperature performance is also affected by the gradation type; among the mixtures, the low-temperature performance of the mixture with a smaller nominal maximum particle size is better than that of the mixture with a large particle size. The low-temperature performance of the AC13/AC16 specimens is better than that of the AC16/AC20 specimens.

Gong et al. [86] analyzed the effects of compaction degree, compaction temperature, asphalt film thickness, and load on interlayer bonding and mechanical response. From Figure 17a, the pavement is susceptible to cracking under tensile stress, so the trailing edge of the wheel track is a high-incidence location for slipping cracks during the interlayer adhesion failure state. Increasing the number of compaction times can reduce the maximum principal stress of asphalt pavement and inhibit the generation of cracks; when the number of compaction times of the lower layer is 50, the interlayer adhesion has the best crack resistance. It can be seen from Figure 17b that as the compaction temperature of the lower layer of asphalt increases, the maximum principal stress in the tensile zone and the compression zone decreases, which is attributed to the fact that a higher compaction temperature can effectively improve the pavement modulus and improve its crack resistance. With an increase in horizontal braking force, the maximum principal stress dispersion at the same compaction temperature increases, indicating that when the horizontal braking force is high, the crack resistance of the pavement is greatly affected by the compaction temperature of the lower layer. From Figure 17c, with an increase in the thickness of the upper layer, the absolute value of the maximum principal stress of the pavement decreases; thickening the asphalt surface layer can effectively weaken the load transfer, improve the pavement modulus, and effectively improve its crack resistance. The influencing factors were evaluated, and the order of influencing factors on the crack of the asphalt surface layer was as follows: lower compaction times > horizontal braking force > lower compaction temperature > upper asphalt thickness.

(2) Base layer

The pavement base structure is primarily categorized into a semi-rigid base, composite base, full-depth base, and inverted base (Figure 18), each of which has a significant impact on the crack resistance of asphalt pavements. Qiu et al. [87] conducted a field study on the 213 Lang Chuan National Highway in the cold region of the northwestern Sichuan Plateau, taking the typical semi-rigid structure (I) as a comparison. A composite structure (II), full-depth structure (III), and inverted structure (IV, V) were designed. The cracking of each pavement structure during service is shown in Table 3:

The crack distress of semi-rigid base asphalt pavement (I) in a cold area is more frequent than that in a general area, and the average crack distance (I, II) is about 1.5 m. Type IV and type V sub-base cracking is more serious; the crack rate is 5~6 times that of other sections; and the type Ⅳ cracking rate is only about 50% of that of type I and type II, which shows that reducing cement dosage can effectively reduce the pavement base shrinkage cracking rate, and at the same time, inhibiting the upward expansion of the cracks in the semi-rigid sub-base also has a certain effect. There is no crack phenomenon in the asphalt surface layer after type III and type V adopt a flexible base, indicating that the flexible structure with reasonable design has sufficient flexibility and effectively suppresses the reflective crack of the asphalt surface layer.

The inverted asphalt pavement (V) also effectively solves the problem of reflective cracks by reducing the cement dosage of the graded crushed stone base. However, the thickness of the surface layer needs to be appropriately increased to improve the integral bearing capacity of the structure, and the thickness of the cement-stabilized base increases from 10 cm to 15 cm. The tensile stress at the bottom of the plate is reduced by 50%, and the tensile stress at the bottom of the plate is reduced by 30% from 15 cm to 20 cm. Increasing the thickness of the base layer is an important measure to improve the bearing capacity of the pavement. At the same time, the large temperature difference in the cold region changes the mechanical response state of the road structure and vehicle load; therefore, appropriate design standards should be selected from the temperature state, rather than overemphasizing the bearing capacity of the structure and deliberately increasing the strength of the base.

(3) Functional layer

The functional layer is a structural layer positioned between the sub-base and soil base or between additional surface layers. It enhances the overall performance of the road structure by improving interlayer bonding [88]. The functional layer exhibits high elasticity and flexibility, effectively absorbing and diffusing stresses while reducing peak structural stresses. The functional layer [89] effectively absorbs base cracking stresses, slows crack propagation, and deflects cracks in the upper layers (Figure 19). When placed within the semi-rigid base layer, the functional layer effectively absorbs interlayer stresses and suppresses reflective cracking; it is suitable for high-grade highways and composite pavements with asphalt overlays. The discrete element model is established by a two-dimensional particle flow program [90]; it is found that the vertical contact force, velocity, and displacement of the particles at the bottom of the open-graded large-size asphalt gravel mixture (such as OLSM-25) with a stress-absorbing layer are smaller than those of the control group. Through finite element analysis and an indoor impermeability test [89,91], when the thickness of the stress-absorbing layer is 1~2.5 cm, the design porosity of the mixture is 1.0~2.5%, and the modulus is 400~600 MPa, so the crack resistance of the asphalt pavement is better. The tensile stress σ_X, equivalent stress σ_Mises, and maximum shear stress τ_Max of the surface layer decrease by 31.7%, 29.2%, and 25.7%, respectively.

3.4.2. Modification Technique

It is generally believed that 80% of the low-temperature performance of asphalt mixtures is determined by the low-temperature performance of asphalt [92]. Therefore, in practical engineering applications, the low-temperature crack resistance of a mixture is generally improved by improving the low-temperature performance of asphalt.

(1) Rubber category

Styrene butadiene rubber (SBR) is a widely used rubber product. When added to asphalt as a modifier, it forms a highly elastic network structure that significantly enhances the low-temperature crack resistance of asphalt. Zhang et al. [92] demonstrated using the Burgers model that the stress relaxation and creep recovery of SBR-modified asphalt mixtures outperform those of unmodified asphalt. Che et al. [93] found that SBR also had a significant effect on improving the low-temperature performance of aged asphalt, which was attributed to the good dispersion of SBR modification on asphalt elasticity recovery and binders. Zhao D et al. [94] found that increasing SBR content within the range of 5~10% (Figure 20 and Figure 21) enhanced the high- and low-temperature performance of modified asphalt both before and after aging. However, Yang et al. [95] noted that at an SBR content of 8%, uneven dispersion, and particle agglomeration caused significant two-phase separation. They concluded that an SBR content of 4~6% is optimal, reducing the S value by 41% and increasing the m value by 32% based on stability and other performance indicators. Overall, the use of SBR results in a significant improvement in the performance of asphalt pavement and is cheap, which is suitable for asphalt pavement in cold regions.

Natural rubber (NR) is a renewable natural polymer material. It is considered that the optimum content is 4~6% [96], which can significantly improve the low-temperature crack resistance and storage stability of asphalt. Wen et al. [97] found that NR significantly improved the high-temperature rutting resistance, low-temperature crack resistance, and fatigue resistance of modified asphalt. When the content of NR was 5% (Figure 22), the low-temperature PG grade increased by 6 °C, and the interlocking structure between NR and asphalt showed a good crack resistance structure. Liu et al. [98] optimized the preparation process of Vulcanized Natural Rubber-Modified Asphalt Binder (VNRMB), ensuring the full vulcanization of the NR modifier with asphalt to form a three-dimensional polymer network, which significantly enhanced the binder’s rutting and cracking resistance. It is recommended to apply VNRMB in the middle or bottom layers of asphalt pavement in cold regions to enhance low-temperature cracking resistance.

Chloroprene rubber (CR) is widely used in the asphalt modification process. Duan et al. [99] found that 18% CR-modified asphalt has excellent low-temperature crack resistance. Jian et al. [100] conducted low-temperature bending and creep tests under different salt solutions and freeze–thaw cycles; it was found that the low-temperature crack resistance of the warm mix CR asphalt mixture was better than that from the hot mix process, and the use of 12% CR in the northern cold region could effectively improve the most serious ice and salt damage of an asphalt road (8%). Li et al. [101] found that the S/m value of CR asphalt after aging was significantly better than that of SBS. Wang and Song et al. [102,103] applied CR to the cold region of Xinjiang and found that modified asphalt still met the specification requirements of the creep rate m value being greater than 0.3 and the creep stiffness s value being less than 300 MPa under the condition of −30 °C, and the high-temperature performance and fatigue performance were excellent.

Yeh et al. [104] showed that using an ethylene propylene diene monomer (EPDM) improved the low-temperature crack resistance of asphalt through an indirect creep test; meanwhile, Haibin et al. [105,106] decided to add graphene to EPDM to prepare a heat transfer layer and developed a new type of asphalt road active de-icing material in a cold region.

(2) Thermoplastic elastomer category

Styrene-butadiene-styrene (SBS) is a multi-metallographic block copolymer composed of different block segments, rubber segments, and plastic segments in series. Under the premise of full expansion with an asphalt matrix, the comprehensive modification effect of star SBS is better than that of linear SBS. The C-C unsaturated bond of SBS is cross-linked with asphalt, and the grafting reaction forms a network structure (such as SBS-modified F300 asphalt (Figure 23)) to make the asphalt have excellent low-temperature crack resistance [107]. Li et al. [108] found that when the high content of SBS was in the range of 10~15%, modified asphalt changed from the “interpenetrating network” structure to the “island” structure with the increase in content. The saturated hydrocarbons in asphalt caused SBS to completely swell, the number of particles per unit volume increased, the distance between them shortened, and the interaction between the polymers increased. The SBS particles overlapped and fused with each other to form a network structure to limit the two-phase separation, and the low-temperature performance was improved. At the same time, in the face of the huge difference in molecular weight between low-content SBS and asphalt, the system is unstable, and the low-temperature performance deteriorates. Ren et al. [109] prepared SBS-modified emulsified asphalt with 0.13~3% emulsifier, and Chen et al. [110] compounded 2~4% rubber oil to supplement the loss of asphaltene to improve storage stability and low-temperature performance. Qiu et al. [36] proposed that the modified asphalt mixture prepared by 3% SBR and 3% SBS has excellent road performance, which provides an option for the prevention and treatment of the low-temperature cracking, aging, and water damage of asphalt roads in cold regions [111].

Compared with SBS, styrene-ethylene-butylene-styrene (SEBS) has better compatibility and stability between polymers due to the absence of double bonds on thermal degradation. A greater improvement in the 5 °C ductility of modified asphalt is shown by 4.5% SEBS [112]. With the increase in SEBS content (Figure 24), the low-temperature performance is continuously improved under the optimum asphalt–aggregate ratio (4.9%). When the SEBS content is less than 4%, the maximum tensile strain of the mixture at low temperature increases slowly; after the content is greater than 4%, the low-temperature performance is improved rapidly, and the low-temperature performance of 8% SEBS can be improved by 11% [113]. The research of Zhang et al. [114] shows that 7.5% SEBS-modified asphalt has the best proportion of 4.6% in a cold patch asphalt mixture, and the low-temperature crack resistance is increased by 15.7%.

As a specialized modifier for porous drainage asphalt pavement, TAFPACK-Super (TPS) absorbs light components by swelling with asphalt, thereby increasing the asphalt content. At the micro level, TPS is uniformly dispersed in asphalt, forming a stable, interconnected network structure that enhances the high- and low-temperature performance, fatigue resistance, and water damage resistance of asphalt mixtures. Zhang et al. [115] found that the flexural strain energy of the mixture reached its peak (0.21) when the TPS content was 12% and the oil–stone ratio was 4.9%. Chen et al. [116] reported that at 5 °C, ductility gradually increased when the TPS content was below 8% but decreased initially and then increased when the TPS content exceeded 8%. The optimal TPS content is recommended to be 14~16%, as this provides the best low-temperature crack resistance. Additionally, TPS-modified asphalt exhibits superior resistance to ultraviolet oxygen aging, outperforming SBS-modified asphalt in both long-term and short-term thermal oxygen aging (Figure 25).

(3) Mineral category

Diatomite is a commonly used mineral asphalt modifier (Figure 26a). Tian et al. [117] found that the performance of modified asphalt is better when the content of diatomite is 14%: the heat capacity value is increased by 1.3 times, the strain energy density at 0~20 °C is increased by about 13%, the fracture temperature is −27.4 °C, the particle distribution is more uniform, the porous structure increases the specific surface area, and the low-temperature crack resistance of the asphalt mixture is effectively improved.

The obvious interlaminar structure (Figure 26b) in the physical blending of montmorillonite (MMT) and asphalt improves the low-temperature crack resistance of the mixture. The comprehensive modification effect of organic montmorillonite (OMMT) is better than that of MMT, and 1~3% OMMT improves the low-temperature toughness of asphalt greatly [118].

The tourmaline outer shell wall had a lamellar structure; the shell surface pores and asphalt come into full contact and release negative ions (Figure 26c). When enhancing the bonding material between the adsorption and tensile strength and doping 17% of the asphalt mixture, flexural tensile strength increased dramatically, and when doping 20% of SBS-modified asphalt, flexural tensile strength increased by 7.8%. Wang et al. [119] found that a tourmaline-modified asphalt mixing temperature of 160~170 °C and compaction temperature of 145~155 °C provided the best high- and low-temperature performance.

Basalt fiber forms a fiber network structure in the asphalt mixture, and load deformation can better transfer and disperse stress (Figure 26d) and make the aggregate and asphalt combine closely with better integrity. Li et al. [120] found that the optimum content of basalt fiber was 0.3~0.4%, and the strain and strain energy density of the mixture at −20 °C increased by 23% and 50% on average. The low-temperature failure type will change from brittle failure to flexible failure. Basalt fiber has good low-temperature crack resistance and adaptability and is suitable for applications in the cold regions of Inner Mongolia.

(4) Composite modification

The composite modification process can further improve the low-temperature performance of asphalt and mixtures while making up for the shortcomings of water loss resistance, aging resistance, and storage stability in conventional modification.

Polyphosphate (PPA) reacts with hydroxyl and imine groups in asphalt, which improves the elastic modulus and deformation toughness of the system and greatly improves the high-temperature performance and fatigue life of modified asphalt. When the content of PPA is less than 1%, it can form a spatial network with SBR to improve the low-temperature performance [121], but when it is mixed with SBS, it will lead to the deterioration of the low-temperature crack resistance of asphalt. It is determined that 4%SBS/3%SBR-modified asphalt and the AC-16 asphalt binder have the best high- and low-temperature performance, aging resistance, and water damage resistance [36,122,123], which are suitable for cold regions such as the Qinghai–Tibet Plateau. Microfiber (MCF) [124] has the advantages of high strength, low density, and few defects. The composite modification of asphalt according to a specific ratio (0.8%MCF/5%SBS/2%SBR or 0.8%MCF/6%SBS) can improve the binding energy of the binder and enhance the adhesion between aggregates and the self-healing ability of micro-cracks. XH-type HVA high-viscosity additive and asphalt form an overlapping fiber network [125], and SBR is added to absorb oil and SBS molecules to form a molecular chain with cross-linking points; due to the reduction in the constrained deformation of the cross-linking points and the physical winding reaction, the drawing diameter of the asphalt becomes larger, which improves the crack resistance of asphalt. Polyurethane (TPU) [126] can effectively reduce the segregation phenomenon of SBR-modified asphalt and significantly enhance the low-temperature crack resistance, external load resistance, deformation recovery, and integral stability of SBR-modified asphalt. The reactive ternary polymer modifier (RET), combined with SBR, can break up the large volume of asphaltene clusters [127], and the colloid changes from the solution–gel type to the gel type; the dispersion of micro-asphaltene in the soft component is improved, thus forming a stable network; the number of bee-shaped structures in the phase diagram increases significantly; and the area of resin between the mass and saturates and aromatics increases, thereby improving low-temperature crack resistance. DTDM/DOP/SBS composite-modified asphalt has a stable polymer network structure [128], and the polar groups are closely combined with asphalt macromolecules, which further improves the high- and low-temperature performance of SBS. At the same time, the cross-linking agent (DTDM) molecule and plasticizer (DOP) molecule effectively prevent the reaction of oxygen-containing functional groups so that the composite asphalt has excellent anti-aging ability. TB rubber powder undergoes desulfurization and decomposition under high-temperature conditions [38,129] and rapidly fuses with asphalt to effectively improve low-temperature performance, but the high-temperature performance is not good, which can be solved by compounding SBS. The cost of traditional graphene is high, and a system with poor compatibility with matrix asphalt is unstable. Polyvinylpyrrolidone (PVP) [130] is used to treat graphene to obtain modified graphene (PVP-G); after compounding it with SBS, the elastic component and stiffness modulus of asphalt are enhanced, and the enhancement effect on the low-temperature fracture resistance of the binder is greater than the sum of the linear superposition of the two. With the increase in polyurethane (WPU) content, the low-temperature performance of SBS-modified asphalt is gradually improved, but a content that is too high (>15%) will lead to the excessive agglomeration of internal particles and affect storage stability [131]. Waste edible oil (WCO, about 80% of which is less than 400 g/mol) is added to the light component of asphalt; the ethylene-vinyl acetate copolymer (EVA) and SBS cross-linked AFM imaging shows a uniform “honeycomb” system [132]; crack resistance is enhanced; and PG classification is increased from −12 °C to −18 °C. The temperature difference between day and night in the alpine region is large, and the ultraviolet radiation is strong, which means that the unsaturated double bond of SBS asphalt is easy to destroy and would cause a large degree of aging. The addition of naphthenic oil (KN4009) and ultraviolet absorber (UV-531) can effectively inhibit the double bond damage [133] while increasing the light component content to improve the low-temperature performance. When elemental sulfur (S) is added to SBS-modified asphalt, its “island” morphology is transformed into a uniform and continuous two-phase structure to undergo a vulcanization reaction and form a stable network [134]. The United States is rich in soybean production, accounting for one-third of the world. Soybean derivatives and S can effectively improve the elasticity of polymer systems [135]. Plastic recycled polyethylene (LDPE) and ethylene-vinyl acetate copolymer (EVA) can improve the flexibility of the mixture, but when the EVA content exceeds 8%, the 5 °C toughness area decreases, resulting in a decrease in fracture energy [136]. The specific parameters are shown in Table 4.

(5) Nanotechnology

In 1994, the American Society for Materials Research formally proposed the concept of nanomaterial engineering; in 2006, the Nanocem organization made a report on “From nanocem to nanobit” and put forward the application concept of the use of nano-modification technology for asphalt binders. The small size effect and surface effect of nanoparticles can lead to the realization of the nano-scale dispersion and construction of asphalt systems, which can effectively improve the low-temperature performance of asphalt and realize the optimization of pavement performance in cold regions.

The particle size, content, preparation time, temperature, and other factors of nanomaterials [137] influence the low-temperature performance of nano-modified asphalt. With the increase in nano titanium dioxide (TiO₂) content, the ductility of asphalt increases slowly, while the low-temperature performance of nano zinc oxide (ZnO)-modified asphalt increases first and then decreases, and the low-temperature performance is the best when the content is 4% (Figure 27a). With an increase in mixing time, the low-temperature performance of nano-rectorite (REC)- and montmorillonite (MMT)-modified asphalt decreases proportionally, while the low-temperature performance of SBS/nano-ZnO-modified asphalt increases logarithmically, and that of nano-TiO₂/nano-CaCO₃-modified asphalt decreases first and then increases, and when the mixing time is 50 min, the low-temperature ductility is the best (Figure 27b). With an increase in preparation temperature, the low-temperature performance of nano-REC- and nano-MMT-modified asphalt gradually decreases, but nano-TiO₂/nano-CaCO₃ asphalt is basically unaffected. When the preparation temperature is 170 °C, the low-temperature ductility of nano-ZnO- and nano-MMT-modified asphalt is the best (Figure 27c).

The difference in the particle size of nanomaterials will also significantly affect the low-temperature performance of modified asphalt; the difference in the dispersion, compatibility, and microstructure of the blends may be the main reason for these differences. A comparison of the stiffness of nano-silicon carbide (SiC)-modified asphalt with varying particle sizes reveals that particle sizes below 20 μm have no effect on the low-temperature crack resistance of asphalt. When the particle size reaches 20 μm, the low-temperature performance deteriorates, but crack resistance gradually improves as the particle size increases beyond this point (Figure 28a). A comparison of SBS/nano-ZnO-modified asphalt with varying proportions and particle sizes reveals that the low-temperature performance of asphalt improves gradually within the particle size range of 2~80 μm but declines progressively as particle size increases from 80 to 350 μm (Figure 28b).

Because of the different nanomaterials used, the preparation process of nano-modified asphalt is also different. The preparation parameters of some nano-processes with better low-temperature performance are shown in Table 5: Nano-ZnO has a large surface area, less defects, more unpaired atoms, and stable van der Waals force between particles, and the quantum tunneling effect and surface effect of nanoparticles can be brought into play [138], which effectively reduces the temperature sensitivity of asphalt, improves the viscosity of asphalt, and improves the low-temperature performance of the mixture. Nano-CaCO₃ is mainly wrapped with asphalt by physical modification through high-speed shearing, and the compatibility is greatly improved; at the same time, the hydroxyl group reacts with the surface-activated nanoparticles to increase the interfacial binding energy, thus forming a dense and stable system [139,140]. Nano-SiO₂-modified asphalt does not present interface delamination [141,142] under an electron microscope. Due to the small size of SiO₂ and the expansion of the specific surface area, the particles have high adsorption and produce a network structure, while the existence of nano-SiO₂ produces stress concentration so that the surrounding micro-cracks appear to absorb the stress–energy of asphalt so that asphalt shows good low-temperature performance and temperature sensitivity. Nano-TiO₂ can reduce the surface free energy of asphalt and promote the uniform dispersion of polymers. Under a halogen lamp microscope, TiO₂ is dark brown and has poor light transmittance; thus, it can effectively shield ultraviolet radiation, has good anti-aging performance, and is suitable for application in high-altitude and strong-radiation areas [143]. The Yang Shi modulus of carbon nanotubes (CNTs) is 1000 GPa, and the tensile strength can reach 150 GPa. The microscopic morphology has a clear aggregation trend and is interconnected to increase the low-temperature crack resistance of the binder, and especially for the polymer system, the improvement in low-temperature performance is more obvious [144,145]. Nano-paper cellulose (NPC) and wood-derived nano-cellulose (WDC) asphalt binders with large aspect ratios and good networks can effectively improve the critical fracture temperature of asphalt at low temperature. The best choice to improve fatigue and low-temperature performance is 1.0%WDC, while 0.5%NPC can produce more carbonyl functional groups for long-term aging, and its low-temperature performance is better than that of the WDC binder [146]. It should be noted that OMMT, MMT, and Al₂O₃ have adverse effects on the low-temperature performance of matrix asphalt, which can be improved by composite modification with SBS and SBR.

Table 5. Nano-process parameter table.

Nanomaterial	Content/%	Temperature/°C	Speed/rpm	Time/min	Test	Result	Document
ZnO	4.0	165	4000	10	−10 °C low-temperature bend test	Bending strength increased by 13%; maximum bending strain increased by 17%	[138]
ZnO	4.0	165	7500	30	−10 °C low-temperature bend test		[138]
CaCO₃	4.0	160	4500	40	−12, −18, −24 °C BBR test	S value average decreased by 27%; m value average increased by 8%	[139]
SiO₂	5.0	160	5500	20	−12, −18, −24 °C BBR test	S value average decreased by 60%; m value average increased by 17%	[141]
TiO₂	1.0	170	8000	30 ± 5	−6, −12, −18 °C BBR test	S value average decreased by 13%; m value average increased by 6%	[143]
CNT	1.0	160 ± 1	4000	60	−12 °C DTT test	Elongation at break increased by 50%; tensile strength increased by 61%	[144]
NPC	0.5	room temperature	8000	30	−6, −12, −18 °C BBR test	S value average decreased by 28%; m value average increased by 8%	[146]
WDC	1.0	room temperature	500		−6, −12, −18 °C BBR test	S value average decreased by 49%; m value average increased by 19%	[146]

3.4.3. Warm Mix Technology

Between 1998 and 2001, Shell (UK) and Veidekke (Norway) first introduced warm mix asphalt (WMA) technology. In 2003, the American Asphalt Pavement Association (NAPA) focused on further research and successfully paved roads with WMA the following year. Since then, WMA has been widely used worldwide for over 20 years. According to the European Pavement Association (EAPA), the temperature of warm mix asphalt is 20~40 °C lower than that of the equivalent hot mix, with a difference of 20~30 °C domestically and internationally. This reduction in temperature effectively lowers construction temperatures, decreases greenhouse gas emissions, and promotes global energy conservation and emission reductions. However, most current studies on warm mix additives suggest that they compromise the low-temperature performance of asphalt, which may hinder the development of warm mix technology in cold regions. Based on relevant research by domestic and international scholars (Table 6), this paper presents several specific warm mix strategies aimed at improving the low-temperature performance of asphalt and mixtures, providing a reference for a further exploration of warm mix technology in cold regions.

(1) Organic viscosity reduction technology

By enhancing the dispersion of asphalt colloid molecules and increasing the fluidity of a mixture, an organic viscosity reducer can effectively reduce the temperature range required for low-temperature paving in cold regions, thereby improving the overall quality of road construction in these areas. The warm mix agent EC-120 is a long-chain aliphatic polymer that absorbs heat and melts within the temperature range of 102 to 113 °C. As dosage increases, enthalpy also increases, resulting in a more pronounced viscosity reduction effect [147], which facilitates better cross-linking between the binder and the aggregate. Zhang and Wu et al. [147,148] found that when the optimum dosage was 3.0%, the EC-120 warm mix agent and binder were connected to form a stable multi-grid structure at 135~145 °C; the low-temperature asphalt mixture before and after PAV aging was significantly improved. At the same time, Tian and Xiang et al. [149,150] also pointed out that the EC-120 warm mix process also significantly improved the strength and toughness of the pavement. The optimum content of Kaomax is 2%. Afshar et al. [151,152] found that the Kaomax warm mix process significantly improved the low-temperature performance of asphalt mixtures, and the high-temperature rutting resistance, elastic modulus, and indirect tensile strength were increased by about 7%, 13%, and 9%, respectively. At the same time, 0.06% Para-fiber was recommended; the deformation resistance and fatigue life of the mixture were increased by 16.8% and 11.7%, respectively; and the low-temperature crack resistance was further increased by about 20%, which was attributed to the fact that Para-fiber can reduce the internal stress of the mixture, stabilizing the internal structure to improve crack resistance. However, it should be noted that Kaomax may reduce the water resistance of the pavement, and a combination with CaCO₃ provides an effective solution [153]. The WMA-1 warm mixing process involves mixing 6% PP char and 6% wax with asphalt at 160 °C and 120 °C for 10 and 20 min, respectively, at 200 rpm. The modifier and asphalt are uniformly dispersed at lower temperatures, resulting in a softer binder grade, which enhances the compaction performance compared to HMA [154]. Additionally, the adequate adhesion of the colloid to the aggregate improves the low-temperature performance by 19%. Wang et al. [155] investigated the WMA-2 warm mix process, using 60% Gabbro, 40% re-recycled RAP, 3.6% 160/220 binder, and 0.2% Sasobit to prepare the asphalt mixture at 135 °C. The recycled asphalt mixture exhibited the best low-temperature and fatigue resistance when compared to other experimental groups and the original HMA.

(2) Surface active technology

The active warm mix agent is mainly composed of an emulsifier, surfactant, anti-stripping agent, and other components. Through the action of surface-activated molecules on the micro-interface of the aggregate and asphalt, the interface friction is reduced to reduce the mixing and compaction temperature, and the integral performance of pavement in cold regions is improved. The lipophilic tail of the Evotherm DAT molecule gathers the hydrophilic head to diverge to form a spherical micelle. After warm mixing, the micelle reverses to form a special film structure of lubrication, which improves the encapsulation of asphalt to an aggregate. Qin et al. [156] found that the fatigue strength and low-temperature crack resistance of the Evotherm DAT mixture increased by 60% and 5% on average. Guo et al. [157] considered the large seasonal temperature difference in cold regions and the repeated freeze–thaw damage caused by the pore water seepage of asphalt pavement; therefore, by conducting five freeze–thaw splitting tests, they showed that the Evotherm DAT process could effectively improve the durability and water resistance of pavement in cold regions, and the low-temperature crack resistance increased by 25%. The mechanism of Evotherm 3G is similar to that of Evotherm DAT. The SCD test shows that the low-temperature performance is improved by 33% [158]. According to the surface free energy theory of Li et al. [159], the freeze–thaw splitting strength ratio of short-term aging at 146 °C for 8 h is taken as the main evaluation index of WMA water stability, and the improvement effect of the 3G type on the low-temperature performance of asphalt mixtures is better than that of the DAT type. Rediset is a multifunctional WMA additive based on aliphatic amine surfactants and polyethylene. Hamzah et al. [160] reviewed many studies and found that the recommended dosage of the Rediset warm mix process is 1.0~3.0%, and when the compaction temperature is about 130 °C, it can effectively reduce the creep rate of various asphalt types (SBS, SBR, etc.), increase the stiffness, improve the Fraser brittle point and PG low-temperature grade, and has a higher tensile strength ratio than the corresponding HMA. WMA improves the crack resistance of RAP mixtures at a large strain level. Cecabase RT is one of the most popular liquid warm mix agents, and the recommended dosage is 0.2~0.5%; compared with other warm mix agents, it has lower C-O tensile absorbance and is not oxidized easily, which contributes significantly to the low-temperature performance of long-term aging asphalt [161]. The new warm mix agents ZYF-1 and SYDK developed by Zhang’s team [162] and Wang’s team [163] are also worthy of attention. The ZYF-1 warm mix process can greatly improve the low-temperature performance of asphalt. Compared with Sasobit and Aspha-min, ZYF-1 inflicts the least damage to the water stability of the mixture, but the improvement in high-temperature performance is weak. The SYDK warm mixing process can significantly improve the low-temperature performance of 60-mesh crumb rubber-modified asphalt, but it will cause deterioration to the low-temperature performance of mixed mesh crumb rubber-modified asphalt.

(3) Foaming technology and other categories

Aspha-min is an ultra-fine sodium aluminosilicate mineral that contains a significant amount of crystalline water. By releasing this crystalline water, this enhances the workability of the mixture, promotes the foaming of viscosity-reducing asphalt, and improves the compaction quality of the pavement, ultimately enhancing low-temperature performance. However, the release of water also makes the charge redistribution more complicated, which damages the water stability of the mixture [164,165]. To meet the application requirements of warm mix additives in low-temperature and sensitive cold regions, Luo’s team developed a new silicon-based quaternary ammonium salt three-component warm mix additive siligate [166,167], which is different from those in the three conventional categories. The silane coupling layer isolates the asphalt molecules from each other, reduces the viscosity of asphalt, and improves the low-temperature toughness of asphalt. After determining the optimum mixing and compaction temperature through the viscosity–temperature curve of the asphalt binder, the low-temperature stress r(n) and the critical cracking temperature T_cr were obtained based on the creep compliance J(t). The influence of siligate on the low-temperature performance of various types of asphalt was as follows: SBS + 6%siligate > SBS > SBS + 0.8%Evotherm M1 > SBS + 3%Sasobit. Siligate improved the low-temperature performance of SBS-modified asphalt by about 10%, which provided a new idea for improving the low-temperature cracking of asphalt pavement in cold regions.

Table 6. Warm mix asphalt process parameter table.

Type	Warm Mix Technology	Dosage/%	Warm Mix Temperature/°C	Compaction Temperature/°C	Test	Result	Conclusion	Document
Organic viscosity reduction technology	EC-120	3.0	140.0		−20 °C BBR test	After PAV aging, S value decreased by 8%, and m value increased by 7%	Improved low-temperature performance, toughness of asphalt, and crack resistance of binder after long-term aging; water stability has little effect	[147]
	EC-120	3.0	143.1	130.3	−10 °C low-temperature bend test	Bending failure strain increased by 14%		[148]
	Kaowax	2.0	130.0	118.0	SCB test	Max load P_max increased by 40%; fracture energy G_f increased by 122%. FI value increased by 40%; j_c is within the acceptable range; fracture resistance CRI value increased by 23%	Medium- and low-temperature crack resistance is obviously improved	[151]
	WMa-1	12.0	PP char 160	30 °C lower than HWA	−12, −18, −24 °C BBR test TSRST	S value average decreased by 48%, m value average increased by 19%, fracture temperature T_F average decreased by 19%, and fracture strength σ_cry increased by 15%	Improved crack resistance and rutting resistance	[154]
	WMa-1	12.0	wax 120	30 °C lower than HWA	−12, −18, −24 °C BBR test TSRST		Improved crack resistance and rutting resistance	[154]
	WMA-2	3.8	135		TSRST	T_F reduced by 17%	Excellent low-temperature crack resistance and fatigue resistance	[155]
Surface active technology	Evotherm DAT		30 °C lower than HMA	115	SCB test	Tensile strength ratio increased by 4.3%	Low-temperature crack resistance, fatigue resistance, and water stability improved	[156]
	Evotherm DAT	5.3	135	125	Freeze–thaw splitting test	Splitting strength of 5 freeze–thaw cycles was 51% higher than that of TSR, an increase of 25%		[157]
	Evotherm 3G	0.5	138	127	−12 °C SCB test	G_f increased by 33%	Low-temperature crack resistance is improved, and water stability improvement effect is better than that of DAT type	[158]
	Rediset	1.0~3.0	30 °C lower than HMA	110~140	−12, −18 °C BBR test FBP test	S value average decreased by 15%, m value average increased by 25%, and FBP and low-temperature PG rating both decreased	Low-temperature performance and fatigue resistance are improved	[160]
	Cecabase RT	0.3	120	130	−6, −12, −18 °C BBR test	After PAV aging, S value average decreased by 8%, and m value average increased by 8%	Low-temperature performance after long-term aging is improved	[161]
	ZYF-1	4.0	154	144	−12, −18 °C BBR test 5, 10 °C ductility tests	S value of SK90 # asphalt and SBS asphalt average decreased by 53% and 26%, m value average increased by 19% and 15%, and ductility of SK90 # asphalt and SBS asphalt increased by more than 21% and 19%, respectively	Significantly improves low-temperature performance, with minimal impact on high-temperature performance and water stability	[162]
	SYDK	0.6	100~120		−12, −18, −24, −30 °C BBR test	S value average decreased by 27%, and m value average increased by 38%	Low-temperature performance of 60-mesh rubber powder-modified asphalt is improved	[163]
Foaming technology	Aspha-Min	0.3	153.1	139.2	−10 °C low-temperature bend test	Bending failure strain increased by 5.3%	Improved low-temperature performance of asphalt and mixture, decreased water stability	[164]
Foaming technology	Aspha-Min	0.3~0.5	10~30 °C lower than HMA	20~30 °C lower than HWA	10 °C ductility tests	Ductility increased by 9.2%		[165]
Miscellaneous	Siligate	6.0	176	164	BBR test	PG classification 82–22; critical cracking low T_cr increased by 10%	Improved low-temperature crack resistance and fatigue resistance	[166,167]

Based on a statistical analysis of the research literature on improving the low-temperature performance of asphalt pavements in cold regions from 1984 to 2024, improvement measures can be broadly categorized into three categories (Figure 29a): pavement structure, asphalt modification, and technical processes. More than 50% of research focuses on improving the low-temperature crack resistance of asphalt pavements through asphalt modification. In contrast, newer technologies, such as the warm mixing and continuous paving processes, were developed later and require further investigation. Although these technologies constitute a smaller proportion of the literature, they have a significant impact. To further evaluate the improvement in low-temperature performance in various types of asphalt, the creep-rate-to-stiffness ratio (m/S value) from the BBR test is used as the evaluation index. The results show that composite modification leads to an average improvement of approximately 143%. However, the interquartile range (IQR) of the improvement effects is large, indicating significant variation between the different modification schemes. Overall, SBR- and SBS-modified asphalts exhibit excellent low-temperature performance. The improvement effect of nanotechnology averages 83.5%, with Nano-SiO₂ demonstrating superior modification effects compared to other nanomaterials. The improvement effect of the warm mixing process is relatively stable at 65.0%, and it can be further optimized as the warm mixing process evolves in cold regions (Figure 29b).

4. Conclusions

Low-temperature cracking is the primary distress in asphalt pavements within cold regions, accounting for approximately 37.5% of all pavement distresses. Among these distresses, temperature shrinkage cracks and thermal fatigue cracks caused by temperature fluctuations and freeze–thaw cycles are the most prevalent. Reflective cracks, indirectly induced by base layer shrinkage under low temperatures, are the next most common. The thermal oxygen aging and ultraviolet aging of asphalt pavements mainly occur in the surface layer. Additionally, the physical hardening phenomenon caused by long-term low-temperature exposure significantly affects the overall crack resistance of the pavement, making it a critical factor contributing to early cracking in cold regions. However, in actual engineering construction, the physical hardening effect is often overlooked or deliberately avoided, resulting in the inability to accurately characterize the material’s true performance. At present, there is ongoing debate regarding the causes of physical hardening and how to accurately evaluate the degree of the hardening reaction. Furthermore, research focused on binders that inhibit hardening remains scarce.
The main factors influencing the low-temperature cracking of asphalt pavement in cold regions can be classified into four categories: structural design, road materials, technical process, and the climate of the environment. Moreover, surface stiffness, base type, and cooling rate are the most critical influencing factors, collectively accounting for approximately 45.4% of all cracking factors. Surface stiffness is primarily affected by pavement materials and gradation composition, whereas traffic volume has little effect on pavement cracking. Clay subgrades with finer particles, asphalt mixtures with smaller nominal maximum particle sizes, and dense skeleton structures within a reasonable range exhibit better cohesion and internal friction resistance and superior low-temperature crack resistance.
BBR, EBBR, DTT, T_g, SCB, DENT, FBP, TSRST, T_δ=30°, R_T/V, 0 °C viscosity, 4 or 5 °C ductility, PI, PVN, etc., can be used to evaluate the low-temperature performance of asphalt. At present, the BBR test and DTT, as the main evaluation methods of the low-temperature performance of asphalt binders, can characterize the low-temperature performance of asphalt to a certain extent, but they ignore the influence of hardening behavior on asphalt performance caused by long-term low temperature. The EBBR test considering the physical hardening of asphalt at low temperature is more effective to supplement it. CTOD can effectively reflect the failure relationship between coarse aggregate particles in service pavement; R_T/V is suitable for evaluating the low-temperature performance of high-grade modified asphalt. The accuracy of T_δ=30° for pavement cracking evaluation is higher than that of T_{δ=45°,27°,28°}. It is important to note that the S and m values from the BBR test, as well as the turning point temperature, slope, and freezing stress from the TSRST, should be considered together, as a single index alone cannot provide an accurate evaluation of low-temperature performance. The viscosity at 0 °C, ductility at 4 °C, and the FBP are sensitive to external factors, thus requiring further research.
Appropriately increasing the compaction temperature of the lower layer and the thickness of the upper layer; adopting CCBA technology and a full-depth pavement structure or the inverted structure of reducing the cement dosage of the base layer and increasing the thickness of the surface layer; and setting up a high-flexibility functional layer can all effectively improve the crack resistance of asphalt pavement. However, the optimal compaction temperature and frequency range for continuous pavement construction remain unclear. Meanwhile, the climate of the environment and ultraviolet radiation in each cold region are different, so the asphalt structure crack resistance design focuses on different aspects, and it is necessary to study the appropriate pavement structure in combination with the actual situation.
Modification is the current mainstream improvement method for low-temperature cracking; it has a significant effect on the improvement in the low-temperature performance of asphalt, with an average improvement of 143%. The combination of various modifiers can further optimize the performance of asphalt and has a good development prospect. In addition, the warm mixing process of asphalt mixtures can also improve the low temperature of pavement to a certain extent, and it follows the concept of green development, so its application in cold-area pavement deserves more in-depth research. However, despite its excellent low-temperature performance, the SBR modifier has not been widely adopted in cold regions. This is primarily because global warming has led to rising summer temperatures in cold regions, and the high-temperature performance of SBR-modified asphalt is insufficient, causing frequent rutting distress. The development and improvement of high-performance modifiers tailored for cold regions represent a key focus of current research.

Currently, the occurrence of cracking distress in asphalt pavements in cold regions is frequent across various countries, with the types and causes of cracking in these regions differing significantly from those in non-cold regions. Cracking in cold-region pavements was traditionally attributed solely to extreme climatic conditions and ultraviolet radiation. However, with the continuous advancement of pavement research in cold regions in recent years, several previously overlooked factors, such as the low-temperature physical hardening of asphalt, have gradually gained attention. Meanwhile, research on improving the structure, processes, materials, and modifiers to enhance the low-temperature performance of pavements in cold regions remains insufficient. Exploring more effective methods for improving pavement performance under the guiding principles of green and sustainable development is a critical area for future research.

Author Contributions

Conceptualization, Y.L. and P.C.; methodology, Y.L. and R.M.; software, R.M. and A.C.; validation, Y.L. and X.C.; formal analysis, Y.L.; investigation, R.M. and A.C.; data curation, R.M. and A.C.; resources, Y.L.; writing—original draft preparation, R.M. and A.C.; writing—review and editing, Y.L. and P.C.; visualization, Y.L. and R.M.; supervision, Y.L.; project administration, Y.L. and X.C.; funding acquisition, Y.L. and P.C. All authors have read and agreed to the published version of the manuscript.

Funding

Independent research and development project of Longjian Road and Bridge Co., Ltd.: 230000100004258240011; Science and Technology Program of Department of Transportation Heilongjiang Province: HJK2024B003; Fundamental Research Funds for the Central Universities: 2572022BJ01.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

Author Yiming Li was employed by the company Long Jian Road and Bridge Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Figure 1. Distribution of cold regions in China (Alberts projection) [2].

Figure 2. The proportion of asphalt pavement distress in cold regions.

Figure 3. Literature growth diagram.

Figure 4. VOS viewer density view.

Figure 5. VOS viewer relational view.

Figure 6. A PRISMA flow chart of the literature review.

Figure 7. Temperature shrinkage cracks [9]. (a) A thermal stress curve of pavement with different cooling amplitudes throughout the day. (b) The maximum thermal stresses in the structural layers of pavements at different cooling rates.

Figure 8. Thermal fatigue cracks. (a) Daily variation in thermal stress on pavement structure [9]. (b) Daily variation in thermal stress at different depths [9]. (c) Vertical deformation curves of pavements throughout year [14].

Figure 9. Reflection cracking mechanism.

Figure 10. Aging cracks. (A) Physical hardening ratio of AC and SMA at −20 °C [21]. (B) Changes in asphalt components [22]. (C) Microstructure of asphalt degraded by pseudomonas aeruginosa at different times ((a) undegraded control group; (b) degradation for 15 days; (c) degradation for 30 days; (d) degradation for 45 days) [23].

Figure 11. Factor radar chart [24].

Figure 12. Proportion diagram of influencing factors [25].

Figure 15. Continuous construction machinery scheme [84]. (a) Construction equipment layout. (b) Material transfer scheme.

Figure 16. Comparison of different paving compaction processes [85].

Figure 17. The influence of the continuous paving and compaction process (the red circle is a local enlarged image) [86]. (a) The corresponding relationship between the times of lower layer compaction and the maximum principal stress. (b) The corresponding relationship between the lower layer compaction temperature and the maximum principal stress. (c) The relationship between the thickness of the upper layer and the maximum principal stress (different braking conditions).

Figure 18. Pavement structure.

Figure 19. Principle of stress-absorbing layer improvement [89].

Figure 20. A 400× fluorescence micrograph ((a) 2% SBR-modified asphalt; (b) 4% SBR-modified asphalt; (c) 6% SBR-modified asphalt; (d) 8% SBR-modified asphalt) [95].

Figure 21. Low-temperature performance of 2, 4, 6, and 8% SBR-modified asphalt ((a) stiffness modulus S value; (b) creep rate m value) [95].

Figure 22. NR-modified binder with 100× magnification [96].

Figure 23. Fluorescence micrograph of SBS-modified high-permeability asphalt (F300) [107].

Figure 24. Maximum bending strain of best oil–stone ratio of SEBS at low temperature [113].

Figure 25. Ductility change curve of TPS with different dosages [116].

Figure 26. Microstructure diagram. (a) SEM diagram of diatomite [117]. (b) OMMT through-layer structure [118]. (c) SEM diagram of tourmaline lamellar structure [119]. (d) SEM diagram of basalt fiber [120].

Figure 27. Influencing factors of nano-process. (a) Ductility and nano-modifier content. (b) Effect of preparation time on ductility. (c) Effect of temperature on ductility [137].

Figure 28. Creep stiffness of different nanomaterial particle sizes [137]. (a) Effect of nano-SiC particle size on stiffness. (b) Effect of nano-ZnO particle size on stiffness.

Figure 29. Analysis of improvement methods. (a) Proportion of types of low-temperature performance improvement methods. (b) Comparison of improvement effects.

Table 1. PVN temperature sensitivity classification of asphalt materials.

PVN	−1.5~−1.0	−1.0~−0.5	−0.5~0
Level	C	B	A
Asphalt temperature sensitivity classification	high	middle	low
Suitable place	light-traffic road	medium-traffic road	heavily trafficked road

Table 2. Pseudoplastic fluid regression results.

Temperature/°C	Shear Stress τ₀/Pa	Shear Rate γ₀/l/s	Composite Fluidity C	Correlation Coefficient
−10	2501.38	1.656 × 10⁻⁸	0.411	0.925
0	668.99	3.406 × 10⁻⁷	0.476	0.918
10	80.49	5.149 × 10⁻⁶	0.514	0.893

Table 3. Cracks of different pavement structures.

Structure	Evaluating Indicator	I	II	III	IV	V
Upper surface		4 cm AC-13 SBR-modified asphalt mixture
Bottom surface		5 cm AC-20 Common asphalt mixture
Pavement base		22.5 cm 5% Cement-stabilized macadam	2.5 cm AC-5 Stress-absorbing layer	22.5 cm ATB-30 asphalt-stabilized macadam	22.5 cm Graded gravel (mixed with 2% cement)	22.5 cm Graded broken stone
Pavement base		22.5 cm 5% Cement-stabilized macadam	20 cm 5% Cement-stabilized macadam	22.5 cm ATB-30 asphalt-stabilized macadam	22.5 cm Graded gravel (mixed with 2% cement)	22.5 cm Graded broken stone
Pavement sub-base		22.5 cm 4% Cement-stabilized macadam
Soil layer		300.0 cm Improved soil base (completely continuous with sub-base)
Surface	Number of cracks/strips	11	1	0	3	0
	Average crack distance/m	27.3	300.0	0.0	100.0	0.0
	Cracking rate/m·km⁻²	3.05	0.30	0.00	0.85	0.00
Base	Number of cracks/strips	195	202	0	71	0
	Average crack distance/m	1.5	1.5	0.0	4.2	0.0
	Cracking rate/m·km⁻²	110.00	136.00	0.00	55.15	0.00
Sub-base	Number of cracks/strips	5	2	6	29	25
	Average crack distance/m	60.0	150.0	50.0	10.3	12.0
	Cracking rate/m·km⁻²	2.60	1.75	3.05	17.05	15.70

Table 4. Composite modification parameter table.

Asphalt	Modifier			Dosage			Shear Temperature	Shear Rate	Time	Experiment	Compared with Uncompounded Modified Asphalt/Mixture	Document
Asphalt	I	II	III	①%	②%	③%	°C	rpm	min	Experiment	Compared with Uncompounded Modified Asphalt/Mixture	Document
China PG64-22 asphalt	SBR	PPA		2.5	0.75		155	4000	60	SCB test	Peak load P, tensile strength R, fracture energy density FED, and fracture strain tolerance FST increased by 3.5%, 3.5%, 167%, and 158%, respectively	[121]
Panjin 90 # asphalt		SBS		3.0~4.0	3.0		165	3000	20	5 °C ductility Beam bend test −12, −18, −24 °C BBR test	Ductility was 283 mm, bending strain was 4900 με, and S value decreased by 59%	[36,122,123]
Qinhuangdao 70 # asphalt			MCF	2.0	5.0	0.8	180	4000	60	−12, −18, −24 °C BBR test −10 °C low-temperature bend test	S value average reduced by 21%, m value average increased by 3%, and failure strain of mixture increased by 25%	[124]
Lent 70 # asphalt			HVA	2.0	5.0	10.0	SBS SBR160	3000 ± 200	30	−12, −18, −24 °C BBR test	S value decreased by 64%, and m value increased by 89%	[125]
Lent 70 # asphalt			HVA	2.0	5.0	10.0	HVA 170 ± 10	5000 ± 200	30	−12, −18, −24 °C BBR test	S value decreased by 64%, and m value increased by 89%	[125]
Kunlun brand A-70 # asphalt		TPU		3.5	10.0		140	SBR 1000	10	−12 °C BBR test	S value decreased by 44%, and m value increased by 9%	[126]
Kunlun brand A-70 # asphalt		TPU		3.5	10.0		140	TPU 4000	60	−12 °C BBR test	S value decreased by 44%, and m value increased by 9%	[126]
Dongming AH-70 # asphalt		RET		3.5	1.5		175~180	3500~4000	30	−12, −18, −24 °C BBR test	S value average decreased by 61%, and m value average increased by 18%	[127]
Qinhuangdao 70 # asphalt	SBS	MCF		6.0	0.8		180	4000	60	−12, −18, −24 °C BBR test −10 °C low-temperature bend test	S value average reduced by 23%, m was basically unchanged, and failure strain of mixture increased by 14%	[124]
90 # asphalt		DTDM	DOP	4.0	3.0	1.0	175	4500	50	−12, −18, −24 °C BBR test	S value average decreased by 56% and 50% before and after aging, and m value average increased by 45% and 47% before and after aging	[128]
Aesop 70 # asphalt		TB		3.0	20.0		175		60	BBR test SCB test	Low-temperature classification of PG was −29.8 °C, low-temperature stress curve decreased, and J_c value fitted by strain energy density U increased by 246%	[38,129]
Karamay A-70 asphalt		PVP-G		4.0	1.5		170	1500	15	5 °C ductility test −18 °C BBR test −10 °C low-temperature bend test	Increase in ductility and maximum yield strength by 32% and 91%, decrease in S value by 15% and 14% before and after aging, increase in m value by 8% and 8% before and after aging, and increase in flexural tensile strength and bending strain by 35% and 46%	[130]
South Korea SK asphalt		WPU		4.0	15.0		SBS 175	3000	60	−12, −18, −24 °C BBR test	S value average decreased by 29%, and m value average increased by 14%	[131]
South Korea SK asphalt		WPU		4.0	15.0		WPU 180	3000	60	−12, −18, −24 °C BBR test		[131]
80/100 asphalt		EVA	WCO	3.5	5.5	10.0	170	5000	SBS 40	5 °C ductility −12, −18, −24 °C BBR test	Ductility increased by 1068%, S value average decreased by 60%, and m value average increased by 27%	[132]
									EVA 60
									WCO 30
Yueyang SBS791		KN4009 (naphthenoid oil)	UV-531 (ultraviolet absorber)		1.4	1.0	165	5000	60	5 °C ductility Beam bending failure test	Ductility increased by 117.6%, equivalent brittle point decreased by 80%, bending stiffness modulus decreased by 9.61%, and maximum bending strain increased by 11.20%	[133]
Tahe 100 # asphalt		S		4.0	0.15		180~200		120~180	−12, −18, −24 °C BBR test	S value average decreased by 43%, and m value average increased by 20%	[134]
Vacuum Tower Distillation Bottoms (VTBs)			soybean-derived additive	2.0	0.2	12.0	SBS/S 180	3000	90	−18, −24 °C BBR test	S value average decreased by 45%, and m value average increased by 77%	[135]
Vacuum Tower Distillation Bottoms (VTBs)			soybean-derived additive	2.0	0.2	12.0	soybean-derived additive 140	2000	720	−18, −24 °C BBR test		[135]
70 # asphalt	EVA	LDPE		8.0	2.0		185 ± 5	4000	60	−12, −18 °C BBR test	S value average decreased by 47%, and m value average increased by 12%	[136]

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Ma, R.; Li, Y.; Cheng, P.; Chen, X.; Cheng, A. Low-Temperature Cracking and Improvement Methods for Asphalt Pavement in Cold Regions: A Review. Buildings 2024, 14, 3802. https://doi.org/10.3390/buildings14123802

AMA Style

Ma R, Li Y, Cheng P, Chen X, Cheng A. Low-Temperature Cracking and Improvement Methods for Asphalt Pavement in Cold Regions: A Review. Buildings. 2024; 14(12):3802. https://doi.org/10.3390/buildings14123802

Chicago/Turabian Style

Ma, Rui, Yiming Li, Peifeng Cheng, Xiule Chen, and Aoting Cheng. 2024. "Low-Temperature Cracking and Improvement Methods for Asphalt Pavement in Cold Regions: A Review" Buildings 14, no. 12: 3802. https://doi.org/10.3390/buildings14123802

APA Style

Ma, R., Li, Y., Cheng, P., Chen, X., & Cheng, A. (2024). Low-Temperature Cracking and Improvement Methods for Asphalt Pavement in Cold Regions: A Review. Buildings, 14(12), 3802. https://doi.org/10.3390/buildings14123802

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