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The development of asphalt mortar design methods is a prerequisite for cross-scale prediction from asphalt mortar scale to asphalt concrete scale. Existing studies have given some asphalt mortar design methods. However, these studies have not explored the impact of different maximum aggregate sizes of asphalt mortar on the cross-scale prediction results, nor have they judged the rationality of mortar design methods. In order to find the appropriate maximum particle size of asphalt mortar and develop an asphalt mortar design method that is suitable for predicting the mechanical behaviour of asphalt concrete, in this study, two commonly used particle sizes (2.36 and 1.18 mm) were selected as the maximum aggregate size of asphalt mortar, and an asphalt mortar design method, including the assumption of boundary particle size, was proposed. Then, utilising cross-scale simulation, the maximum aggregate size of asphalt mortar was compared and selected, and the rationality of the proposed asphalt mortar design method was verified. The results indicate that asphalt mortar with a maximum aggregate size of 1.18 mm is more suitable for predicting the mechanical behaviour of AC-13C, AC-20C, and AC-25C asphalt concrete. The design method of asphalt mortar containing the assumption of boundary particle size is reasonable. [ABSTRACT FROM AUTHOR]

The effect of different filler types on the properties of asphalt mortar before and after water saturation was studied by laboratory tests. Under both dry and water-saturated circumstances, four alternative fillers, limestone powder, hydrated lime, PO42.5 cement, and brake pad powder, are used, evaluated, and compared. The study methodology included characterizing the micromorphology, while X-ray diffraction imaging analysis and scanning electron microscopy were used to determine the chemical composition of the asphalt mortar following water saturation. To quantify the effects of moisture on the bonding mechanisms, surface energy concepts were employed to compute the surface free energy parameters of the asphalt mortar made with different filler materials. Dynamic shear rheometry was employed in the investigation to describe the rheological characteristics of the asphalt mortar as a function of filler under different water saturation conditions. The bonding strength of the asphalt mortars with various fillers was then quantitatively measured using pullout tests to account for the coupling effects of moisture and temperature. The findings of the laboratory tests generally showed that the asphalt mortar's effectiveness declined following moisture conditioning and saturation in water. However, hydrated lime, brake pad powder, and cement showed promise in strengthening the bonding of fillers and asphalt, with hydrated lime being superior. Likewise, the asphalt mortar's ability to tolerate moisture and resist water damage was also generally improved by hydrated lime. [ABSTRACT FROM AUTHOR]

Asphalt mortar is a mixture of asphalt mastic and fine aggregates (<2.36 mm) in asphalt concrete. Accurately predicting the complex modulus of asphalt mortar is essential to further estimating asphalt concrete's viscoelastic properties. However, existing analytical and numerical mesomechanical models generally underestimate the dynamic moduli of asphalt mortar and overestimate its phase angles, especially at high temperatures and low frequencies, because the solidifying reinforcement mechanisms are not considered. Also, the commonly used mesoscale division method for asphalt mortar, which takes asphalt mastic as the matrix phase, may lead to computational inefficiencies due to the presence of numerous fine aggregates. To address these issues, this study proposed a coarse asphalt mastic-based three-dimensional (3D) mesostructure model of asphalt mortar considering a conjunctive shell mechanism of interface transition zones (ITZs). A new mesoscale division method was proposed for asphalt mortar, which defines the coarse mastic incorporating the aggregates smaller than 0.6 mm as the matrix phase. A conjunctive shell mechanism of ITZs was proposed to account for the solidifying reinforcement effect due to the overlapped ITZs of closely adjacent aggregates. The results indicate that the overlapped ITZs led to the formation of the agglomeration networks of aggregates. The introduction of conjunctive shell mechanism of ITZs enabled accurate prediction of the complex modulus of asphalt mortar even at low frequencies and high temperatures and revealed the solidifying behaviors of asphalt mortar. The computational efficiency was substantially improved by introducing the coarse mastic matrix. [ABSTRACT FROM AUTHOR]

As the demand for sustainable and environmentally friendly road construction materials increases, corn stalk fiber modified with NaOH is a promising candidate due to its renewable and eco-friendly nature. This study employs an orthogonal experimental design to optimize the investigation of multiple factors (corn stalk fiber length, content, and modifier concentration) in the experiments, ensuring that the effects of different factors on the high and low temperature performance of asphalt binder can be independently estimated. Dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests were conducted. The bonding between fiber and asphalt was analyzed by infrared spectroscopy, and the action mechanism of fiber in asphalt was revealed from a microscopic perspective by scanning electron microscopy and fluorescence microscopy. Evidently, the concentration of modifier is the main factor affecting the rheological properties of fiber asphalt mortar. Considering the influence of various factors on the rheological properties of modified corn stalk fiber asphalt mortar, the optimal modifier concentration is 7%, the fiber length is 6mm, and the content is 1.5%. After adding modified corn stalk fiber, the asphalt mortar did not produce new characteristic peaks, and the fiber and asphalt were mainly bonded by physical action. The large surface roughness of the modified corn stalk fiber determines its good adsorption capacity, which is conducive to increasing the bonding force of the asphalt. Fibers with a large aspect ratio are easy to bridge with each other, restraining the expansion of cracks and thus enhancing the crack resistance of the mortar. [ABSTRACT FROM AUTHOR]

In this study, the feasibility of using bamboo bark fibers as modifiers to enhance asphalt mortar performance was investigated. Bamboo bark fibers were modified with NaOH, KH570 silane coupling agent, and nano-SiO2, and their preparation methods were established. The modified fibers were assessed for their oil absorption, thermal stability, and hydrophobicity. The asphalt mortar was evaluated for three key indicators: rutting resistance, deformation resistance, and durability at high temperatures. The microscopic morphology and modification mechanisms of the fibers were also studied. The results showed that modification with NaOH increased fiber porosity and surface roughness, while KH570 and its hydrolysis products enabled nano-SiO2 grafting onto the fibers, improving their adsorption to asphalt. The NaOH-KH570-nano-SiO2 ternary-composite-modified bamboo bark fiber (NKSBF) demonstrated superior hydrophobicity, oil absorption, and thermal stability at the asphalt mixing temperature. Among the modified fibers, asphalt mortar containing 3% NKSBF showed the best performance based on three key indicators, increased the shear strength by 96.4% and the softening point by 7.1% compared to the base asphalt, and increased the ductility by 1% compared to lignin fiber asphalt mortar. The incorporation of 3% bamboo bark fibers improved the rutting resistance, deformation resistance, and durability of short-term-aged asphalt mortar, with NKSBF showing the most significant improvement. [ABSTRACT FROM AUTHOR]

The size of the representative volume element (RVE) for the two-dimensional (2D) random aggregate numerical model of asphalt mortar in a non-destructive state, which directly affects the time required to simulate the linear viscoelastic behavior from asphalt mastic to asphalt mortar. However, in the existing literature, limited research has been conducted on the size determination of the numerical model RVE for asphalt mortar. To provide a recommended size for the typical 2D random aggregate numerical model RVE of asphalt mortar in a nondestructive state, this paper first applies the virtual specimen manufacturing method of asphalt concrete 2D random aggregate to asphalt mortar. Then, it generates numerical model RVEs of asphalt mortar with different maximum particle sizes, after which geometric and numerical analyses are conducted on these models. Finally, based on the geometric and numerical analysis results, the recommended minimum sizes of RVE for the 2D asphalt mortar numerical model are provided. [ABSTRACT FROM AUTHOR]

The direct action of salt on asphalt materials has received limited research despite the abundance of studies on salt erosion and its effects on the moisture stability of asphalt concrete. This study aimed to investigate the effects of chloride salt on the rheology of asphalt and erosion mechanisms. Microscopic properties of asphalt mortar were analyzed through scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR), and the erosion degree of salt in asphalt mortar was evaluated based on three major indexes. Rheological properties of asphalt mortar were determined through temperature sweep and multiple stress creep and recovery (MSCR) tests, while the modified water-boiling test was conducted to evaluate the adhesion of asphalt mortar. Results showed that as salinity increases, the agglomerate phenomenon tends to occur in asphalt mortar, leading to physical aging effects on its basic properties. Meanwhile, chloride salt modified asphalt concrete is prone to cracking at low temperatures and has reduced durability at high temperatures, making it unsuitable for standard load or heavy traffic pavement requirements of PG64 modified asphalt. Furthermore, the presence of chloride in asphalt mortar was not conducive to its adhesion. [ABSTRACT FROM AUTHOR]

The objective of this study is to unravel the modification mechanism of a coupling agent on the water sensitivity of phosphogypsum asphalt mortar. The adhesion process of phosphogypsum asphalt mastic modified with three kinds of coupling agents (KH-550, KH-570, and CS-101) and raw phosphogypsum to the aggregate minerals was simulated based on the molecular dynamics software, Materials Studio 2020, and the water film layer was considered along the simulation. When the three coupling agents were added, the interfacial adhesion work gradually increased with the increase of modified phosphogypsum dosage, and the trends of each model were relatively similar. With the increase of simulation time, the mean square displacement of water molecules of the three interfacial models showed different trends, and the increasing trend rank was unmodified phosphogypsum > KH-550 > KH-570 > CS-101. The diffusion coefficient of the water molecular layer of asphalt mastic modified with CS-101 coupling agent in phosphogypsum shows a significant decrease with the increase of CS-101-modified phosphogypsum (more than 5% mass ratio to asphalt). Compared to raw phosphogypsum asphalt mortar, the addition of coupling agents can significantly limit the diffusion of water molecules and effectively improve the interfacial adhesion work, in which CS-101 coupling agent has the best effect, followed by KH-570 and KH-550. [ABSTRACT FROM AUTHOR]

To understand the effects of filler-asphalt ratio on different properties of lignin and polyester fiber reinforced shape memory polyurethane (SMPU)/styrene butadiene styrene (SBS) composite modified asphalt mortar (PSAM), as well as to reveal the reinforcing and toughening mechanisms of lignin and polyester fibers on PSAM, SMPU, SBS and mineral powder were first utilized to prepare PSAM. Then the conventional, rheological and anticracking properties of lignin fiber reinforced PSAM (LFAM) and polyester fiber reinforced PSAM (PFAM) at different filler-asphalt ratios were characterized. Test results indicate that the shear strength, deformation resistance and viscosity are increased after adding 0.8wt% lignin fiber or polyester fiber and increasing the filler-asphalt ratio from 0.8 to 1.2. The optimal filler-asphalt ratio of 1.0 is proposed after comprehensive performance assessments of PSAM. Polyester fiber shows a better reinforcing effect than lignin fiber, but its improvement in the thermal stability of PSAM is not significant at high temperatures. Additionally, the complex modulus, storage modulus, loss modulus and rutting resistance factor of PSAM are improved after adding lignin fiber and polyester fiber, as well as show an increasing trend as the filler-asphalt ratio is raised, but the phase angle is gradually decreased. Further, the increase of elastic components in PSAM effectively enhances the anti-deformation ability of PSAM at high temperatures, and polyester fiber more obviously improves the high-temperature deformation resistance of PSAM than lignin fiber. Finally, the anti-cracking performance of PFAM and LFAM at low temperatures is reduced by 74.2% and 46.7%, respectively, as the filler-asphalt ratio is raised from 0.8 to 1.2. The low-temperature anti-cracking performance of LFAM is lower than that of PFAM at the same filler-asphalt ratio, even lower than that of PSA. Compared with lignin fiber, the anti-cracking performance and deformation resistance of PSAM at low temperature is more greatly enhanced by polyester fiber. [ABSTRACT FROM AUTHOR]

The performance of an asphalt mixture is significantly affected by the properties of its asphalt mortar, which consists of an asphalt binder, mineral fillers, fine aggregates and air voids. The aim of this work was to evaluate the correlations between the high-temperature performance of an asphalt mixture and the rheological properties of its corresponding asphalt mortar. The multisequence repeated loading (MSRL) test was used to estimate the high-temperature performance of the asphalt mixture. Six different gradations, AC-13, SMA-13, SUP-13, AC-20, SUP-20 and AC-25, and two styrene–butadiene–styrene (SBS)-modified asphalt binders were considered and used to prepare the asphalt mixture specimens. The gradations and asphalt types of asphalt mortars were consistent with their asphalt mixtures. A modified multiple-stress creep–recovery (MSCR) test was proposed for evaluating the rheological properties of asphalt mortar with a dynamic shear rheometer (DSR). Based on the basic form of the Hirsh model, a multiple regression model was established, and its coefficient of determination (R-square) was 0.96. The rheological response of the asphalt mortar presented great correlation with the high-temperature behaviour of the asphalt mixture. In addition, the MSCR indicators (nonrecoverable compliance and percent recovery) obtained at 12.8 kPa creep stress represented the rheological status of asphalt mortar in asphalt mixture well. Therefore, the mechanical behaviours of asphalt mixture at high temperature could be accurately predicted by the MSCR indicators of asphalt mortar and its coarse aggregate parameters. [ABSTRACT FROM AUTHOR]

Matrix and SBS modified asphalt mortar were prepared by replacing mineral powder with cement under different filler-asphalt ratios. The variation laws of ductility, softening point, penetration, cone penetration, and Brookfield rotational viscosity of the two kinds of pastes with filler-asphalt ratio were studied. The shear strength of the two kinds of asphalt mortar was calculated. And the viscosity-temperature curve was established. The best filler-asphalt ratio was recommended. The results show that the addition of cement and the increase of filler-asphalt ratio will reduce the ductility, penetration, and cone penetration of asphalt mortar, while improve the softening point, shear strength, and viscosity. In a specific range of filler-asphalt ratios, cement can improve the high-temperature performance of asphalt mortar without significant impact on the low-temperature performance. [ABSTRACT FROM AUTHOR]

Moisture damage is one of the undesired distresses occurring in flexible asphalt pavements, mostly through water intrusion that weakens and ultimately degrades the asphalt mortar-aggregate interfacial bond. One method to mitigate this distress is using anti-stripping or anti-spalling filler materials that, however, require a systematic quantification of their interfacial bonding potential and moisture tolerance properties prior to wide-scale field use. With this background, this study was conducted to comparatively evaluate and quantitatively characterize the moisture sensitivity and water damage resistance of the interfacial bonding between the asphalt mortar and aggregate fillers. Using an in-house custom developed water-temperature coupling setup, numerous laboratory pull-out tests were carried out on the asphalt mortar with four different filler materials, namely limestone mineral powder, cement, slaked (hydrated) lime, and waste brake pad powder, respectively. In the study, the effects of moisture wet-curing conditions, temperature, and filler types were comparatively evaluated to quantify the water damage resistance of the asphalt mortar-aggregate filler interface. For interfacial microscopic characterization, the Image-Pro Plus software, 3-D digital imaging, and scanning electron microscope (SEM) were jointly used to measure the spalling rate and the surface micromorphology of the asphalt mortar and aggregate filler before and after water saturation, respectively. In general, the pull-out tensile force exhibited a decreasing response trend with more water damage and interfacial bonding decay as the moisture wet-curing temperature and time were increased. Overall, the results indicated superiority for slaked (hydrated) lime over the other filler materials with respect to enhancing and optimizing the asphalt mortar-aggregate interfacial bonding strength, moisture tolerance, and water damage resistance, respectively—with limestone mineral powder being the poorest performer. [ABSTRACT FROM AUTHOR]

This study introduced phosphogypsum coupled with steel slag powder to prepare the phosphogypsum based filler (PF) for asphalt mixture. Penetration, penetration index, softening point, ductility, equivalent softening point, moisture stability of asphalt mortars with different steel slag powder content, filler-asphalt ratio, and PF content were studied. Mechanical properties of PF based asphalt mortar (P-AM) were then analyzed to determine the optimum steel slag content in PF. Overall desirability method was used to determine the optimum replacement ratio of PF content in limestone filler. Rheological properties of P-AM were also analyzed through dynamic shear rheometer. Volumetric performance, high-temperature performance, low-temperature performance, and moisture stability tests were carried out on PF based AC-20 asphalt mixture. Results showed that P-AM presented the optimum performance when the content of steel slag powder was 23% by mass of phosphogypsum. Fatigue and rutting factor of asphalt mortar were enhanced by PF. The optimum PF content in replacing limestone filler was 75% through overall desirability evaluation. PF developed the high-temperature performance and moisture stability of asphalt mixture. Additionally, volumetric and low-temperature performance were not significantly affected by PF. It is suggested that using PF which is based on phosphogypsum as a filler of asphalt mixture to partially replace traditional limestone filler was adequate. [ABSTRACT FROM AUTHOR]

Utilizing agricultural waste rice straw as fiber and filler in asphalt pavement is a win-win strategy for environmental protection and cost reduction. This study investigated the properties of asphalt binder and asphalt mortar with rice straw fiber or filler and elucidated the interaction mechanism between asphalt binder and rice straw products. The results revealed that adding rice straw fiber decreased the penetration by over 30 % while increasing the softening point by more than 13 % and the viscosity of the asphalt binder. The addition of 8 % rice straw fiber or 50 % filler improved the complex modulus and Superpave rutting parameter G */sin δ of both asphalt binder and asphalt mortar through DSR tests. Additionally, BBR test results indicated that the creep stiffness of asphalt binder and asphalt mortar initially decreased by over 10 % and then increased by 5–50 % with higher rice straw fiber or filler content, a trend that contrasted with the behavior of the m-value. Molecular models of asphalt binder and rice straw products were established based on molecular dynamics to evaluate the diffusion characteristics of asphalt binder. It revealed that higher temperatures enhanced the diffusion of asphalt binder on cellulose surfaces. And it has a greater adsorption effect on asphalt binder at the amorphous region of cellulose compared with that at the crystalline region. • Adequate addition of rice straw products improves G * and G */sin δ of asphalt binder. • Rice straw products can enhance the low-temperature properties of asphalt binder. • Higher temperatures promoted the diffusion of asphalt binder on cellulose surface. • The amorphous region of cellulose exhibited a greater adsorption. [ABSTRACT FROM AUTHOR]

The severe agglomeration of Reclaimed Asphalt Pavement (RAP) particles not only leads to high gradation variability during recycling, but also impedes the miscibility between new-old binders. This phenomenon imposes significant limitations on maximizing the utilization of RAP with high content and value. This paper first realized the effective separation of asphalt milling material by the self-developed RAP refined processing equipment to obtain coarse RAP with low binder content and fine RAP with high binder content. The fine RAP with high binder content underwent a deep rejuvenation process, and the recovery efficiency of the asphalt mortar was evaluated by CT scanning test, microscope observation test, and dynamic shear rheology test. Moreover, to investigate the strength formation characteristics of recycled asphalt mixtures with high RAP content, specific tests including wheel tracking test, three-point bending test, Hamburg Wheel Tracking test, dynamic modulus test, and two-point bending fatigue test, were conducted. By using the refined processing equipment, the asphalt film on the RAP can be precisely removed, thereby addressing the issue of aged binder agglomeration. In the coarse RAP with low binder content, the binder content was reduced to 1.48 %, allowing it to be used as a direct substitute for new aggregate, whereas the binder content of fine RAP exceeded 10 %. It was found that the direct incorporation of unrefined RAP enhanced the high-temperature stability and dynamic modulus of recycled asphalt mixture, but impacted their low-temperature cracking resistance, moisture stability, and fatigue performance. After refined processing and differentiated recycling design, the agglomeration of aged binder was reduced and the miscibility of new-old binders was improved, effectively enhancing the comprehensive performance of the recycled asphalt mixture. It should be noted that the mixing homogeneity and miscibility decrease as the RAP content exceeds 75 %, resulting in the reduction of moisture stability, cracking resistance, and fatigue performance of recycled asphalt mixture. • Reclaimed Asphalt Pavement is a waste product generated during pavement maintenance and causing serious environmental problems. • This paper employed the self-developed RAP refined disposal equipment by using coarse RAP aggregate self-grinding and fine RAP aggregate self-spraying grinding technology, which realized the separation of aged binder and aggregate. • It was concluded that using refined disposal RAP materials and differentiated regeneration process, 75 % of RAP content can be recycled and reused in recycled asphalt mixtures. [ABSTRACT FROM AUTHOR]

To confirm the feasibility of waste incineration fly ash applied in asphalt pavement materials, the waste fly ash from the waste incineration station in Dongguan (DG-FA) and Guangzhou (GZ-FA) were selected as mineral filler replacing limestone powder (LF) to prepare asphalt mortar. The physical properties, chemical composition, and thermal characteristics of FA were analyzed. The effect of FA on the physical properties and rheological properties of asphalt binder was investigated systematically. The micromorphology of FA asphalt mortar was characterized. Finally, the blocking effect of asphalt binder on the leaching of toxic elements from FA was evaluated through XRF test. The results showed that the granular composition of FA particles was similar to that of LF. Furthermore, compared to LF, the specific surface area and the pore structure of FA were more developed, and the high active amorphous material was higher. Adding FA to asphalt mortar and increasing replacing amount improved its high-temperature rutting resistance as well as its ability to adhere to asphalt, while the low-temperature crack resistance was decreased. Further, the asphalt binder provided the good shielding effect against the migration of heavy metals in FA. While the leaching concentration of Pb element slightly exceeded the hazardous waste leaching standard (GB5085.3–2007), the remaining elements met the standard requirements. Overall, FA improved asphalt mortar performance, and the asphalt had a good curing and stabilizing effect on the toxic elements in fly ash, indicating that FA could be used as a filler in asphalt pavements. [ABSTRACT FROM AUTHOR]

Many research studies have been conducted on the ultraviolet (UV) ageing performance of asphalt and asphalt mixture, but the superposition relationship between the loading time–temperature and the aggravation of UV ageing degree is still lacking. In this research, the dynamic modulus of styrene butadiene styrene (SBS) polymer-modified asphalt mortar, under different UV intensities, UV ageing time and loading temperatures, was obtained by the dynamic modulus sweep test at different temperatures. The results showed that the dynamic modulus decreases with the increase of temperature, and increases with the increase of UV ageing time and intensity. To further evaluate the UV ageing of asphalt mortar, the time–temperature superposition has been expanded to incorporate the UV ageing time and intensity, and the dynamic modulus curves of asphalt mortar under different UV ageing time or intensities and temperatures were constructed through superposition shift equations. The results showed that the reduced UV ageing time or intensity increases with the decrease of test temperature. Based on the superposition relationship of time–temperature–UV ageing degree (radiation time and intensity), the comprehensive shift factor functions were determined. These superposition equations conducted in this research provided meaningful predictions for different UV ageing time and intensity conditions. [ABSTRACT FROM AUTHOR]

The distribution characteristics of asphalt and cement mortar play a crucial role in determining the cracking resistance of semi-flexible pavements (SFP). In this study, digital image processing technology was utilized to quantify the thickness distribution of asphalt and cement mortar within SFP, and a parallel line segmentation method was employed to characterize the random distribution of mortar thickness (RDMT) of asphalt and cement mortar. Variance, coefficient of variation (COV), and interquartile range were proposed to characterize RDMT, examining the effects of air voids (AV) content, nominal maximum aggregate size (NMAS), and compaction method on RDMT, and its variation along the specimen height. Semi-circular bending test was conducted to evaluated the cracking resistance of SFP, exploring the relationship between RDMT and cracking resistance. Results indicate that parallel line segmentation method with 36 parts and 25 parts is recommended to characterize the RDMT of asphalt and cement mortar, respectively. An increase in AV content led to a higher RDMT for asphalt mortar but a lower RDMT for cement mortar. Conversely, as NMAS increased, the average thickness of asphalt and cement mortar increased, while the RDMT of asphalt mortar decreased and that of cement mortar increased. RDMT of asphalt and cement mortar is higher under Superpave gyration compaction method compared to the Marshall compaction method. Additionally, RDMT increased from the top to the bottom of the specimen height. Based on the RDMT, a random distribution index (RDI) was proposed, which exhibited a strong linear relationship with the cracking resistance of SFP. When the RDI decreased by 44.4 %, the corresponding cracking resistance of SFP increased by 84.0 %. Improving the distribution of asphalt and cement mortar could enhance the cracking resistance of SFP. • RDMT of asphalt and cement mortar in semi-flexible pavement was characterized. • Effects of AV content, NMAS, and compaction method on the RDMT of asphalt and cement mortar were investigated. • Relationships between cracking resistance of SFP and RDMT of asphalt and cement mortar were firstly investigated. [ABSTRACT FROM AUTHOR]

• Combining indoor experiments and numerical simulation results, the macro-fracture behavior and meso -fracture process of the asphalt mortar is revealed from macroscopic and mesoscopic perspectives. • Revealing the influence of crack deflection angle and crack length on the loading characteristics of cracks and facture behavior. • The fracture mode and the stress field at the crack tip is identified by using the FISH programming subroutine. Asphalt mortar is the base material used in asphalt concrete, and its mechanical properties directly affect those of the prepared asphalt concrete. An analysis of the loading response characteristics of cracks in asphalt mortar under low-temperature conditions can help reveal the interaction effect of multiple cracks in asphalt concrete and the influence mechanism of aggregates on the crack propagation and evolution behaviors. In this study, various forms of pre-cracks were generated in asphalt mortar specimens using the water jet cutting technology. Combined with the discrete element method (DEM), an indirect tensile (IDT) test and a virtual IDT test were conducted to analyze the effects of the crack deflection angle (β) and crack length (r) on the crack propagation behavior from macro- and meso -perspectives. The main results showed that: (1) Changes in the crack shape parameters (β and r) not only induced multiple branch cracks in the asphalt mortar but also led to the development of II Mode fractures; (2) With the increase in the crack shape parameters, the low-temperature crack resistance of the asphalt mortar decreased, with β having a greater effect on the crack propagation behavior than r ; (3) At the mesoscale, with the increase in the crack shape parameters, there was a gradual transformation of the fracture mode from I Mode to II Mode, and the crack propagation process accelerated, resulting in a significant decrease in the low-temperature crack resistance at the macroscale. The research results establish a theoretical foundation for revealing the characteristics of multi-crack propagation in asphalt concrete under environmental influences, and offer technical support for pavement crack repair and maintenance. [ABSTRACT FROM AUTHOR]

Basalt fiber has been shown to significantly improve the performance of asphalt mixtures and extend the lifespan of roads. However, more research is needed to investigate the characteristic parameters of basalt fiber when used in asphalt mortar and asphalt mixture. In order to enhance the reinforcing effect of basalt fiber on asphalt mixture and understand how it works, this study examines the properties of asphalt mortar mixed with basalt fiber with different characteristic parameters. Nine types of basalt fibers with varying characteristic parameters were selected for this work, including three lengths (3 mm, 6 mm, 12 mm) and three diameters (7 μm, 16 μm, 25 μm). The properties of asphalt mortar mixed with basalt fiber with different characteristic parameters were tested. High-temperature properties were characterized using the ZSV and MSCR tests; medium-temperature properties were characterized using the LAS test; low-temperature properties were characterized using the BBR and direct tensile tests. In addition, the effects of fiber characteristics on the viscosity, structural integrity and interfacial properties of asphalt mortar were analyzed through the bond strength test, Rigden porosity test and fiber monofilament drawing test. The results demonstrate that basalt fiber can improve high-temperature properties significantly in asphalt mortar while being greatly influenced by its characteristic parameters. Specifically, fibers with a length of 6 mm and a diameter of 7 μm exhibit superior reinforcement effects. Fatigue life results indicate that basalt fiber enhances fatigue resistance in asphalt mortar as well; furthermore, the influence exerted by fiber characteristic parameters aligns consistently with that observed for high-temperature performance. Although the BBR test results indicate that fiber incorporation has minimal impact on its enhancement, the direct tensile test results demonstrate a significant improvement in the toughness of asphalt mortar due to fiber reinforcement. The addition of basalt fiber enhances the bond strength of asphalt mortar. According to Einstein viscosity formula, the viscosity of asphalt mortar decreases with shorter fiber lengths and larger diameters. Incorporating basalt fiber can enhance the proportion and strength of structural asphalt in asphalt mortar. When comparing fibers with equal diameter or length, an increase in either parameter initially improves the strength of structural asphalt but eventually leads to a decline. Results from monofilament fiber drawing tests and theoretical critical embedding length confirm that a 6 mm fiber length is most beneficial for enhancing the performance of asphalt mortar. Basalt fiber exhibits significant potential for improving various properties of asphalt mortar and provides a favorable reference for optimizing the selection of basalt fiber. [Display omitted] • The synergistic effect and mechanism of basalt fiber (BF) and asphalt mortar with different characteristic parameters were studied. • The properties of basalt fiber and asphalt mortar with different characteristic parameters under multiple temperature fields are comprehensively characterized. • Einstein viscosity, structural asphalt and interfacial properties were used to study the effects of fiber characteristic parameters on the properties of asphalt mortar. • Basalt fiber, especially fiber with reasonable characteristic parameters, is the key to further improving the performance of asphalt mortar. [ABSTRACT FROM AUTHOR]

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The use of steel slag powder instead of filler to prepare asphalt mortar was beneficial to realize the effective utilization of steel slag and improve the performance of asphalt concrete. Nevertheless, the anti-aging properties of steel-slag powder–asphalt mortar need to be further enhanced. This study used antioxidants and UV absorbers in steel-slag powder–asphalt mortar to simultaneously improve its thermal-oxidation and UV-aging properties. The dosage of modifier was optimized by second-generation non-inferior sorting genetic algorithm. Fourier-Transform Infrared Spectroscopy, a dynamic shear rheometer and the heavy-metal-ion-leaching test were used to evaluate the characteristic functional groups, rheological properties and heavy-metal-toxicity characteristics of the steel-slag-powder-modified asphalt mortar, respectively. The results showed that there was a significant correlation between the amount of modifier and G*, δ, and the softening point. When the first peak appeared for G*, δ, and the softening point, the corresponding dosages of x1 were 2.15%, 1.0%, and 1.1%, respectively, while the corresponding dosage of x2 were 0.25%, 0.76%, and 0.38%, respectively. The optimal value of the modifier dosage x1 was 1.2% and x2 was 0.5% after weighing by the NSGA-II algorithm. The asphalt had a certain physical solid-sealing effect on the release of heavy-metal ions in the steel-slag powder. In addition, the asphalt structure was changed under the synergistic effect of oxygen and ultraviolet rays. Therefore, the risk of leaching heavy-metal ions was increased with the inferior asphalt-coating performance on the steel-slag powder. [ABSTRACT FROM AUTHOR]

Asphalt mortar is a typical temperature-sensitive material that plays a crucial role in the performance of asphalt mixture. This study evaluates the high- and low-temperature performance of asphalt mortar based on the dynamic mechanical analysis (DMA) method. Temperature-sweep tests of asphalt mortars were conducted using the DMA method under fixed strain level, frequency, and heating rate conditions. The dynamic mechanical response curves, characteristic temperature, and other indices were obtained and used to investigate the high- and low-temperature performance of asphalt mortar. The results showed that the phase transition temperatures T1, T0, and Tg can be used to evaluate the low-temperature performance of asphalt mortar. Additionally, they had a good linear relationship, and the evaluation results were consistent. Meanwhile, T2, E60, and tan(δ)max indicators can effectively evaluate the high-temperature performance of asphalt mortar. Asphalt plays a key role in the performance of asphalt mortar. Mortars with neat asphalt A70 and modified asphalt AR had the worst and best high- and low-temperature performances, respectively. Furthermore, the finer gradation improved the low-temperature performance of asphalt mortar, while the coarser gradation improved the high-temperature properties of modified asphalt mortars but had the opposite effect on neat asphalt A70. [ABSTRACT FROM AUTHOR]

This article presents a new methodology of analysis based on a fast-running experimental procedure to characterise the mechanical response of asphalt mortars in terms of stiffness, ductility, and fatigue resistance. This was achieved using the DMA (Dynamic Mechanical Analyser) three-point bending configuration. The study was carried out by considering the employment of different types of fillers such cement and CaCO3 and different types of binders such as conventional asphalt binder (B35/50) or modifided polymer-modified bitumen (PMB 25/55–65). From the results of this study, the filler was found to have a greater influence on the stiffness and ductility of the asphalt material, while bitumen had a higher effect on the fatigue life of the asphalt mortar. Fatigue life was observed to increase with the use of a polymer-modified binder, while a lower degree of permanent deformation and higher bearing capacity achieved by the use of cement instead of calcium carbonate as active fillers. [ABSTRACT FROM AUTHOR]

The mechanical performance of asphalt mixtures with high air void content – like Permeable Friction Courses (PFC) – is significantly affected by climate-related processes. Previous studies have demonstrated that ravelling (i.e. the loss of aggregates from the surface of the PFC) is related to the quality of the stone-on-stone contacts within the microstructure of these mixtures. Since the material located at these contacts is asphalt mortar, the durability of the mixtures strongly depends on the mechanical properties of this phase. This paper evaluates, for the first time, the coupled effects of ageing and moisture on the mechanical and fracture properties of the asphalt mortar of a typical PFC. The climatic conditioning processes included short and long-term ageing and dry-wet-dry moisture vapour cycles. The linear viscoelastic and fracture properties of the PFC mortar specimens were characterised using Dynamic Mechanical Analyser (DMA) and Semi-Circular Bending (SCB) tests. The results showed that ageing impacted the dynamic modulus of the mortar, while moisture had a negligible effect on this property. Also, the coupled effects of long-term ageing and moisture cycles reduced the fracture energy and other fracture parameters of the mortar between 2 and 10 times with respect to the short-term ageing condition in dry state. [ABSTRACT FROM AUTHOR]

The film thickness of asphalt mortar, which is a mix of binder and fine mineral aggregates, has been considered as an important indicator for assessing the durability of asphalt mixture. This study proposes a novel method to characterise distribution of mortar film thickness in asphalt mixture through image processing techniques. Four asphalt mixtures with unmodified and modified binders were produced at various compaction temperatures in the laboratory. Their internal images were scanned and analysed. The values of mortar film thickness along the boundary of each aggregate in the scanned image were measured. And their mean value (Tm) and standard deviation (SDt) were calculated for characterising the distribution of mortar film thickness. The results indicate that both binder modification and compaction temperature have significant effects on the mortar film distribution. Furthermore, the proposed parameters were employed for understanding the correlation between the mortar film thickness and mixture cracking resistance. The flexibility index of short-term and long-term aged mixtures were measured and correlated with the mortar film parameters. The findings show that asphalt mixture with a lower mortar film thickness and a wider distribution is more sensitive to oxidative aging, which may result in a dramatic decrease of mixture's resistance to cracking. [ABSTRACT FROM AUTHOR]

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This paper uses the Saturation Ageing Tensile Stiffness (SATS) conditioning to evaluate the combined effects of moisture and oxidative ageing on the rheological characteristics of the Fine Aggregate Matrix (FAM) portion of various Foamed Bitumen Mixtures (FBMs) in combination with Reclaimed Asphalt Pavement (RAP) material produced at 90, 120 and 160°C (i.e. half-warm, warm and hot processes, respectively). A reference fine Hot Mix Asphalt (HMA) with RAP – no foamed bitumen – was also manufactured. Their rheological properties were determined through Dynamic Mechanical Analysis (DMA) tests on specimens tested in their unconditioned and after SATS conditioning states. Rheology of the recovered binders of all FAM mixes before and after SATS conditioning was also studied, and rheological parameters were used to link their long-term performance in terms of cracking susceptibility. The results showed an overall increase in the stiffness of the fine mixtures after the conditioning process, mainly due to oxidation of the bitumen. Although the half-warm and warm fine RAP-FBMs exhibited the highest increase in their complex shear modulus after SATS conditioning, rheological analysis of their corresponding binders indicated that their long-term performance in terms of cracking susceptibility might be superior to those of the hot RAP-FBM, and the HMA-RAP fine mixtures. [ABSTRACT FROM AUTHOR]

• Performing temperature sweep test to generate master curves for viscoelastic properties of bitumen. • Optimizing the number of frequencies and temperatures to develop master curves of asphalt mortar and mixture. • Reducing the time and cost of dynamic modulus test without missing the accuracy of master curves. This study aimed to assess the feasibility of substituting temperature sweep tests for frequency sweep tests and explore the potential of utilizing fewer temperatures and frequencies in dynamic modulus tests to formulate viscoelastic properties master curves. The results indicated that master curves derived from temperature sweep tests mirrored the trends and values obtained from frequency sweep tests, presenting a viable alternative for constructing viscoelastic properties master curves of bitumen. Furthermore, models fitted to dynamic modulus test results at three temperatures and three frequencies exhibited comparable primary parameters, values, and trends to those derived from the complete dataset. The model fitted on reduced data demonstrated robust performance with correlation and R-squared values exceeding 0.95. Considering a marginal increase of about 5% in Residual Standard Error (RSE) values when using the reduced dataset, generating master curves with fewer test results underscored the feasibility and reliability of the original master curves. [ABSTRACT FROM AUTHOR]

Encapsulated rejuvenators based on sunflower oil and alginate biopolymer have recently gained attention to promote self-healing in asphalt mixtures. However, the complex interaction between these millimetre-size capsules and the asphalt mortar and the potential early release of the rejuvenator from the capsules could compromise the mechanical performance of the asphalt composite. This study evaluates the effect of an optimised alginate capsule design with sunflower oil on the rheological properties of short-term aged (STA) and long-term aged (LTA) asphalt mortars. A total of 15 capsule designs were synthesised by the vibrating jet technique and based on five oil-in-water (O/W) emulsions varying their biopolymer:oil (B:O) mass ratio (1:1, 1:3, 1:5, 1:7, and 1:9) and three CaCl 2 solutions (2%wt., 5%wt., and 8%wt. of deionised water). Morphological, physical, thermal, and mechanical properties of each capsule were statistically evaluated to select the optimal design. The selected capsule was incorporated to STA and LTA cylindrical asphalt mortars to evaluate their rheological properties, through the dynamic shear modulus, using the Dynamic Mechanical Analysis (DMA) test and their susceptibility to permanent deformation using a modified Multi-Stress Creep Recovery (MSCR) test. The main results showed that the capsules had sizes between 1.12 and 1.64 mm with regular spherical morphology. The optimum capsule design was that with a B:O ratio of 1:7 and 5%wt. of CaCl 2 , which presented a size of 1.54 mm, high encapsulation efficiency and thermal/mechanical stability. The addition of the optimised capsule design to STA and LTA mortars resulted in i) a softening effect, significatively reducing the dynamic shear modulus at lower temperatures, and ii) no significant impact on the susceptibility to permanent deformations. [Display omitted] • Millimetre-size capsules based on sunflower oil and alginate were synthesised. • A thermally and mechanically stable capsule design was added into asphalt mortars. • Dynamic mechanical analysis of aged asphalt mortars with capsules was performed. • Capsules promote a softening effect in aged asphalt mortars at lower temperatures. • Capsules have no impact in permanent deformation on short-term aged asphalt mortars. [ABSTRACT FROM AUTHOR]

Since asphalt mortar is highly heterogeneous and occurs as an interfacial bonding material between the asphalt-binder and aggregate, it is very important to have a detailed and adequate understanding of its mechanical properties at a multi-scale (micro and macro) level analysis. In this study, the fundamental properties of the asphalt mortar were evaluated and quantified using molecular dynamic simulations. The tensile strength, stress-separation responses, and adhesive-bonding strength were numerically measured and characterised from a micro perspective. Other mechanical properties such as the complex modulus, low-temperature stiffness modulus, hardness, and elastic modulus were also experimentally measured to verify the dynamic simulations and modelling results. In comparison to the macro experimental test results, it was found that the micro-simulated results were superior in terms of characterising the mechanical properties of the asphalt mortar. Whilst the tensile strength, adhesive-bond strength, and hardness of the asphalt mortar changed significantly as a function of aging, the stress-separation responses and elastic modulus were hardly affected. Overall, the study findings indicated that multi-scale characterisation of the mechanical properties of asphalt mortar is a potentially promising methodology for quantitatively evaluating and understanding the mechanical properties. [ABSTRACT FROM AUTHOR]

Featured Application: This study was about a new test instrument to test and evaluate the bonding ability between basalt fiber bundles and the asphalt mortar. It could be used as a verification tool to exam the quality of the basalt fibers which are going to be used in the road construction. Because different manufacturers use their own coupling agents to modify the basalt fibers and have different characteristics of the manufacturing process, this could result in the differences of the quality of basalt fiber product. The test results of this instrument might also be adopted in other studies, e.g., to predict the properties of basalt fiber reinforced asphalt composite materials, etc. The bonding ability between basalt fiber bundle and asphalt mortar has a great influence on the properties of basalt fiber reinforced asphalt mixtures, yet the studies about the bonding between them is very limited. In this paper, a new test instrument called fiber-asphalt pulling machine and a new index called the nominal bonding stress (NBS) were designed and adopted to test and reveal the bonding between basalt fiber bundle and asphalt mortar. The procedures and rationality analysis of this new experiment was specified in this paper. In order to verify the reliability of the NBS index, the NBS values derived from this new test method and the rheological property indexes values of asphalt mortar under different powder–cement ratios were adopted to analyze the correlation between them. Two kinds of basalt fibers produced by two different manufacturers were adopted to conduct the parallel experiment. The results show that the nominal bonding stress between basalt fiber and asphalt mortar derived from this new test has a great correlation with the rheological properties of asphalt mortar, which also proves the credibility of this new test method and the NBS index. [ABSTRACT FROM AUTHOR]

In view of the disadvantage that coal waste powder(CWP) can reduce the crack resistance of asphalt mortar at low temperature, silane coupling agent KH-550 was used to modify coal waste powder. The surface characteristics and modification mechanism of silane coupling agent modified coal waste powder were characterized by using Scanning Electronic Microscopy (SEM). Five kinds of silane coupling agent modified coal waste powder asphalt mortar with content 0%, 0.5%, 1.0%, 1.5%, 2.0% and limestone(LS) powder asphalt mortar were prepared under different filler-asphalt ratios, respectively. The effects and mechanism of silane coupling agent modified coal waste powder on the pavement performance of asphalt mortar and asphalt mixture was studied by the dynamic shear rheological test(DSR), low temperature bending beam rheological test (BBR), Brookfield viscosity test, adhesion test, Fourier Transform Infrared Spectroscopy (FTIR), rutting test, bending test at low temperature, immersion Marshall test and freeze-thaw split test. The results showed that the optimal proportion of KH-550 is 1.5% of CWP mass and CWP modified by silane coupling agent can greatly enhance high temperature performance, low temperature performance and adhesion of the asphalt mortar. Furthermore, CWP modified by silane coupling agent can significantly improve rutting resistance, low temperature crack resistance and water damage resistance of asphalt mixture. [ABSTRACT FROM AUTHOR]

It has long been recognized that fine aggregate (FA) plays a crucial role in the performance of asphalt mixture, especially for the viscoelastic behavior. In this research, 13 types of FA (1 natural sand, 5 stone chips, and 7 machine-made sands) were selected for investigation. Three indirect indicators (uncompact void content test, flow time test, and standard test method for index of aggregate particle shape and texture ASTM D3398) and three types of direct indicators (form, angularity, and texture) were employed to evaluate the geometric characteristics of FA and conduct comprehensive studies on the indicator system. Meanwhile, the effects of FA geometrical properties on the viscoelastic behavior of asphalt mortar were investigated. The results show that only the form indicator ratio of equivalent ellipse axis (E) and angularity indicator surface parameter (SP) can effectively distinguish different types of fine aggregates. The correlation analysis reveals that the parameters of the four elements in the Burgers model are negatively related to the form index (E) but positively related to the angularity index (SP), while the parameter retardation time ( τ r ) exhibits the opposite. This indicates that the use of less flat-elongated and more angular FA can increase both the overall stiffness and elastic component of asphalt mortar. [ABSTRACT FROM AUTHOR]

• Adding fly ash and increasing the replaced amount could significantly improve the high-temperature rutting resistance and resistance to unrecoverable deformation of asphalt mortar, but the low-temperature performance was weakened. • Segregation had no discernible effect on fly ash-asphalt mortar's heavy metal dissolution concentration, and the mortar's storage stability was excellent. • Before and after segregation, the stabilization effect of asphalt on heavy metal leaching from fly ash was excellent, but the effect decreased with the increase of fly ash replaced amount. • When the replaced amount of fly ash was 25%-50%, the overall efficacy of fly ash-asphalt mortar was optimal. Fly ash from diverse sources had various physical and chemical properties, resulting in different modified asphalt properties. Therefore, this paper aimed to investigate the interaction between fly ash and asphalt from different sources and the performance of fly ash-asphalt mortar and further sought the best-replaced amount of fly ash. The fillers included limestone, Dongguan fly ash, and Guangzhou fly ash. First, the filler's physical and chemical properties and microstructure were evaluated. Secondly, asphalt mortar was prepared according to the replaced amount (0%, 25%, 50%, 75%, 100%) and powder binder ratio (0.7). Then, the basic performance test, micro test, high-temperature rheological test, and low-temperature rheological test were conducted on asphalt mortar to investigate the interaction between fly ash and asphalt, as well as the high-temperature performance, elastic recovery ability, and low-temperature crack resistance of asphalt mortar. Finally, the segregation and heavy metal leaching of fly ash-asphalt mortar (FA-AM) were evaluated by the segregation and ICP test. The results indicate that fly ash had a small particle size, a rugged surface, well-developed porosity, abundant mineral components including potassium salt, sodium salt, and calcium carbonate, strong interaction with bitumen, and excellent compatibility. Adding fly ash and increasing the replacement amount improved the high-temperature performance of asphalt and enhanced the elastic recovery ability, but the low-temperature performance was weakened. The enhancement of Dongguan fly ash's high-temperature performance was more significant, while the low-temperature performance of Guangzhou fly ash was marginally superior to that of Dongguan fly ash. However, there was no discernible difference between the two types of fly ash in terms of elastic recovery ability. Segregation had no noticeable effect on the heavy metal absorption concentration of FA-AM, and the storage stability was excellent. Asphalt had the best stabilization effect on Zn, Cu, and Pb in FA-AM (Dongguan) and Pb and Cr in FA-AM (Guangzhou). The recommended replacement amount of Dongguan fly ash and Guangzhou fly ash was 25%∼50%. [ABSTRACT FROM AUTHOR]

• A device and a method were developed for testing the workability of asphalt mixtures, respectively; • The viscosity and rheological properties of asphaltic mortar with different powder-binder ratios are discussed. • The influence of the viscosity and rheological properties of the asphalt mortar on the workability of the asphalt mixture was analyzed. In order to understand the flow characteristics of asphalt mixture in the composition of materials, the influence of the viscoelastic properties of asphalt mortar on asphalt mixture workability was investigated. In this study, an asphalt mixture workability test device was developed and the corresponding evaluation index was proposed. Analysis of the basic and rheological properties of asphalt mortar for different filler-asphalt ratios and asphalt compositions, and evaluated the corresponding asphalt mixture workability. Finally, the distribution uniformities of asphalt mortar, aggregate and pore structure in compacted asphalt mixture were analyzed according to digital image processing techniques. The obtained experimental results showed that asphalt mixture workability was closely related to asphalt mortar viscoelastic properties. Also, rheological indices such as viscosity, complex shear modulus G*, phase angle δ and rutting factor G*/sinδ of asphalt mortar were to be highly correlated with workability index. As the viscosity of asphalt mortar was increased, workability index was also enhanced. In addition, lower asphalt mixture workability resulted in poorer uniformity of material distribution. [ABSTRACT FROM AUTHOR]

• Laboratory long-term oven aging of asphalt mortar at 85 °C for 72 h indicates a significant increase in the carbonyl and sulfoxide indices. • Dynamic compressive strength and impact toughness of asphalt mortar are both enhanced with the increase in the strain rate and temperature. • Dynamic failure characteristics of asphalt mortar are strongly affected by the strain rate and temperature. • An increase in the temperature produces a better gradation of the fragments at higher strain rates regardless of the aging state. Asphalt pavement structures are subjected to impact loading during the milling process. This study aims to investigate the dynamic behavior of asphalt mortar under high strain rates ranging from 281.7 to 830.3 s−1 through the Split Hopkinson Pressure Bar (SHPB) experiments. The effects of temperature and long-term oven aging on the dynamic properties of asphalt mortar under impact loading were statistically analyzed. The results indicated that the dynamic strength and the impact toughness are both enhanced with the increase in the strain rate and temperature. Laboratory oven aging of asphalt mortar at 85 °C for 72 h indicates a significant increase in the carbonyl and sulfoxide indices, a decrease in compressive strength, and rising in elastic modulus. The failure patterns show a strong correlation with the strain rates. An increase in the temperature produces a better gradation of the fragments at higher strain rates regardless of the aging state. [ABSTRACT FROM AUTHOR]

The effects and influence mechanisms of different filler-to-bitumen ratios on the low-temperature cohesive strength of asphalt mortar were studied using quantitative testing technology. Two control variables, namely filler-to-bitumen ratio (the quality of the mineral filler/quality of asphalt) and temperature, were selected for this experiment. The first variable was divided into six groups. The cohesive strength of each group was then measured under different low-temperature conditions. Results show that the optimization of filler-to-bitumen ratio was related to the cohesive strength of the asphalt matrix, which was in turn associated with the change on the surface between the asphalt matrix and the strength of the mineral power fillers generated from asphalt embrittlement. Therefore, the optimal filler-to-bitumen ratio should be determined by the local low-temperature conditions. Moreover, the cohesive strength of the asphalt matrix, its embrittlement state and the contact surface strength effect of asphalt filler should be comprehensively considered in determining the optimal filler-to-bitumen ratio. [ABSTRACT FROM AUTHOR]