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• The compaction process of asphalt mixture was simulated in the laboratory. • The migration and rotation characteristics of aggregate particle was analyzed during asphalt mixture compaction. • The development of surface texture was explored during asphalt mixture compaction. • The compaction mechanism of asphalt mixture was discussed in combination with the Stribeck curve. Pavement performance is not only affected by materials and production but also by compaction quality. This paper investigates the migration and rotation law of coarse aggregate during asphalt mixture compaction using the statistical means based on 2D image analysis. The variation of surface texture during compaction was extracted by laser scanner, and its anti-sliding performance was tested. The compaction mechanism was then discussed in combination with the Stribeck curve. The results show that mixtures with different gradations required different compaction energy during compaction, the AC-13 mixture was easier to compacted than the SMA-13. The aggregate contact developed rapidly in the early compaction stage in the horizontal direction but increased gradually in the vertical direction. With the compaction, the radial angle of the aggregate tended to be consistent in the horizontal direction and the major axis of the aggregate approached to the horizontal axis in the vertical direction. At the same time, the aggregates on the surface of the mixture were embedded with each other with compaction, and the surface structure gradually decreased. Combined with the aggregate contact, asphalt mortar viscosity and the Stribeck curve theory, the compaction process of asphalt mixture could be divided into pre-mixed lubrication dominated by asphalt lubrication and post-mixed lubrication dominated by aggregate contact. The research results offer a reliable basis for studying the compaction mechanism and improving the construction quality control of the asphalt pavement. [ABSTRACT FROM AUTHOR]

For the preventive maintenance engineering of special pavements such as ultra-thin friction courses and bridge deck pavements, the performance requirements of the utilized high-viscosity asphalt, including the resistance to permanent deformation, cracking ability, durability, and recyclability, are becoming increasingly stringent. In this study, based on the click reaction principle of carbon-carbon double (C C) bond, hydroxyl-terminated polybutadiene (HTPB) and isophorone diisocyanate (IPDI) were selected as the raw materials to synthesize thermoplastic polyurethane (TPU), and then 4,4'-disulfanediyldiphenol (DSDDP) was introduced as the chain extender to design a high-viscosity thermoplastic polyurethane modified asphalt (PUA). Subsequently, the mechanical and rheological properties of PUA under different types of chain extenders and polyurethane (PU) contents were tested, and the microstructure and modification mechanism were investigated at multiple scales. The results indicated that after the introduction of DSDDP, the basic physical properties and viscosity of PUA were greatly enhanced, the fluidity was significantly reduced, and excellent deformation and cracking resistance were achieved at various temperatures. The microscopic tests revealed that the viscosity enhancement effect mainly originated from the click reaction between the disulfide (S-S) bonds in DSDDP and the C C bonds on the soft segments of PU, which can further crosslink the linear PU molecular chain and form a dense spatial network structure to restrict the flow of macromolecules. The dynamic exchange of some S-S bonds facilitates the repetitive opening of the PUA network structure at high temperatures, so the PUA still exhibits thermoplasticity at high temperatures, which verifies the feasibility of the proposed design. Moreover, the addition of DSDDP reduced the degree of microphase separation of PUA, so the designed PUA can effectively adapt to various temperature environments. Overall, the findings of this study can boost the application of this novel PUA in the thin surface layers of high-performance pavements. [Display omitted] • The click reaction principle is applied to polyurethane modified asphalt (PUA) system. • Formed carbon-sulfur bonds provide PUA with high viscosity and excellent mechanical properties. • The PUA has a thermoplastic three-dimensional network structure that is partially reversible. • The designed PUA is a suitable material for high-performance pavement surface thin layer. [ABSTRACT FROM AUTHOR]

[Display omitted] • A CR/polyurethane modified asphalt sealant was prepared by the in-situ polymerization method. • The high and low temperature rheological properties of sealant were all excellent. • The PU phase was uniformly dispersed in asphalt quantified by fluorescence images. • The sealant has achieved great effects in the treatment of pavement cracks on site. Under the long-term effect of loads and climate conditions, various diseases can appear on the surface of asphalt pavement, causing deterioration in its performance. To address the pavement surface cracks during service, the present study developed a crumb rubber/polyurethane (CR/PU) compound as the modified asphalt sealant with excellent properties. The optimal material proportion, ensuring the best asphalt compatibility was selected to meet the requirements of standard hot-poured sealants for pavement. Additionally, the fineness and content of CR were determined. The research investigated rheological properties, aging performance, microstructure, and modification mechanism of the CR/PU sealant was then applied in an engineering project to evaluate its effectiveness in treating pavement cracks, and suitable construction techniques were summarized. The results revealed that the in-situ polymerization method is an appropriate approach for preparing the CR/PU sealant, demonstrating good high-temperature deformation resistance and low-temperature crack resistance, indicating synergistic interactions between CR and PU. Among various compositions, the sealant with 30 %PU and 15 %CR content exhibited the best thermal oxygen and UV aging properties. Microscopic tests indicated that CR was physically blended with asphalt, while PU underwent chemical modification and formed a cross-linked network structure with asphalt, resulting in CR dispersion around it, enhancing the thermal stability of the system. Furthermore, the test section displayed an ideal crack treatment effect, demonstrating the sealant's excellent sealing, durability, and watertight capacity. [ABSTRACT FROM AUTHOR]

• Quantitative determination for SBS content of aged modified asphalt by FTIR and potentiometric titration tests. • The rheological properties were investigated after TFOT and long-term aging of modified asphalt. • The actual SBS content versus the rheological indexes of aged modified asphalt can be well-fitted. The content of styrene–butadiene–styrene (SBS) modifier has a significant influence on the physical and chemical characteristics of asphalt. However, determining the SBS content in SBS modified asphalt (SBS MA) after aging remains a challenge. To facilitate the understanding of the relationship between physical properties and SBS content, the Fourier transform infrared (FTIR) and potentiometric titration test were utilized to detect SBS content of aged binders. In this paper, radial and linear SBS were incorporated into asphalt binders at three levels, and their rheological properties were investigated after thin film oven aging (TFOT) and long-term aging. Furthermore, the actual SBS content versus the rheological index at different aging stages was investigated. The results showed that both I C=C and Na 2 S 2 O 3 titration volume highly correlated with SBS content (R2 > 0.99), and there was only a slight difference between the actual content of SBS determined by the two methods. The fatigue resistance, high-temperature elastic, and low-temperature cracking characteristics of asphalt were weakened after aging, due to SBS degradation, especially in the early stage. In addition, the resistance to deformation, elastic recovery, anti-fatigue properties of radial SBS MA were superior to that of linear SBS MA at the same SBS content, while the low-temperature cracking performance demonstrated an opposite trend. The actual SBS content versus the rheological indexes after aging can be well-fitted by a nonlinear equation. Therefore, FTIR and potentiometric titration tests can effectively predict SBS content and analyze the aging degree of SBS MA. [ABSTRACT FROM AUTHOR]

• CN pcf promotes the majority of coarse aggregates to form a well-embedded skeleton. • Optimum contents of dominant structure and disturbing aggregates were determined. • Correlation of CN pcf with contact zones (CZ) can describe internal structural features. • Mann-Whitney U test verified stability of the dominant skeleton with the appropriate level of CN pcf for resisting permanent rutting. Optimizing asphalt mix design at the indoor stage is of significant importance for enhancing the rutting resistance of asphalt mixture, which is affected by its structural characteristics. In this work, the coordination number of particle contact force (CN pcf) was proposed as an indicator to represent contact characteristics of skeleton structure aggregates in asphalt mixture. Nine asphalt mixtures with different gradations were designed, and the relationship of CN pcf with the number of aggregate contact zones (CZ) was established by combining rutting tests and digital image processing technique (DIP). The Mann-Whitney U test was implemented to analyze the distribution properties of inter-particle contacts before and after the rutting test. In addition, the resistance to the further expansion of rutting was analyzed. The results revealed a significant positive correlation (PCCs = 0.843, R 2 = 0.711) between CN pcf and CZ. The content of coarse aggregates in the dominant structure did not exhibit monotonic related to anti-rutting performance of the asphalt mixture. Therefore, an optimum aggregate content of 57% was utilized. The Mann-Whitney U test revealed that the mesoscale skeleton structure of the asphalt mixes before and after rutting exhibited excellent stability. This study further indicated the applicability of combining CN pcf to adjust the mix design to enhance the rutting resistance of asphalt mixture and to prevent rutting expansion in flexible pavement. [ABSTRACT FROM AUTHOR]

• Early hydration kinetics model of IC materials with different absorption behavior was studied. • Effect of IC materials on microstructure and hydration products of cement paste was investigated. • The hydration degree and rate of cement can be promoted by increasing the dosage of composite microgel. • Hydration characteristics are in good agreement with the hydration kinetic model. Internal curing with superabsorbent polymer (SAP) has potential effect on the early deformation and hydration of cementitious material. However, there are few studies on the hydration kinetics and hydration characteristics of internal curing cementitious material. Here, the effects of microgel, composite microgel and commercial SAP with different dosage and absorption behaviors on the hydration characteristics of cement paste were studied by the hydration model proposed by Krstulović-Dabić and hydration heat. Results showed that the hydration reaction of paste containing internal curing materials increased as function of the dosage. When nano-silica(NS) incorporated into microgel, 24.5% and 5.6% increase in value of exothermic peak and cumulative heat were observed for paste. The hydration kinetic model showed that the composite microgel promoted the crystal growth and phase boundary reaction process, thus extending the transition point to the diffusion process. For commercial SAP with premature desorption behavior, the hydration rate of cement paste decreases and the appearance of conversion point at each process is delayed. Hydration characteristics are in good agreement with the kinetic model, suggesting that portlandite consumed by pozzolanic reaction promoted the development of hydration reaction and further refined the microstructure of paste. [ABSTRACT FROM AUTHOR]

• 5 kinds of WAL for steel bridge pavement have been prepared based on self-stratification behavior between the acrylic resin and epoxy resin. • WAL demonstrates excellent adhesive strength, mechanical performance, impermeability and UV durability. • The self-stratification mechanism was discussed based on surface energy theory and micro characterization. In view of the shortcomings of the existing steel bridge deck waterproof adhesive layer (WAL), such as poor durability, high construction cost and long construction period, a new preparation method of waterproof coating with self-stratification effect is proposed. In this paper, poly butyl acrylate-methyl methacrylate–styrene block copolymer with lower glass transition temperature was synthesized by free radical solution polymerization, and 5 kinds of self-stratification coatings were obtained by mixing it with epoxy resin at different mass ratios. The glass transition temperature, thermal stability and chemical composition of acrylic resin were characterized by DSC, TGA, and FT-IR. The self-stratification behavior of the coatings was confirmed by FT-IR, SEM, and water contact angle test. The basic performance and road performance of above self-stratifying waterproof coatings were tested according to specific standards. The results show that these coatings exhibit excellent heat resistance, low temperature flexibility and mechanical properties, namely, average tensile strength can reach 6 MPa, the elongation at break can reach 108 %. Furthermore, the coatings also present extraordinary pull-out strength of 9.51 MPa and excellent water impermeability. Moreover, the tensile strength and elongation at break of the self-stratifying waterproof coatings after UV aging test decreased by 7.3 % and 5.2 %, respectively, indicating that above coating have excellent durability. Therefore, the performance of the coating prepared in this paper fully meets the requirements of the road and bridge waterproof coating standards. The optimum mixing ratio of acrylic resin and epoxy resin is recommended as 3:7 based on their performance. Finally, self-stratifying mechanism of coatings was proposed based on the surface energy theory, which provides theoretical support for the design and preparation of the steel bridge deck WAL. [ABSTRACT FROM AUTHOR]

• The internal meso structure of AC compacted using six different compaction methods was analyzed. • The distribution characteristics of asphalt binder and aggregate of compacted AC by six different compaction methods were obtained. • The relationship between aggregate contact points, aggregate freedom degree and mechanical performance of AC was established. • The AC compacted by roller and SGC in the laboratory could effectively simulate the compaction state on site. The difference between asphalt concrete (AC) compacted in the laboratory and the field significantly influences its gradation design and performance evaluation accuracy. In this research, the effect of the laboratory compaction and field compaction on AC characteristics were compared using the characteristic indexes of surface texture, internal structure, asphalt binder distribution, aggregate distribution, compressive resilience modulus, and the crack resistance index (CRI). Six different compaction methods for AC specimens were studied, and five different types of laboratory compaction equipment were used, namely the Marshall compactor, Steel segmented roller compactor (SSRC), Superpave gyratory compactor (SGC), shear box compactor (SBC), and roller. The results showed that a uniform texture of AC surface was created with vibration and kneading. The aggregate contact distribution of specimens compacted by SGC, SBC, and roller was similar to field compaction as an inverse "bathtub" shape. The aggregate rotation angle of AC compacted by SGC, SBC, and roller showed higher randomness. The coarse aggregate of specimens degraded after Marshall compaction. The fine aggregate coated with more asphalt binder being moved towards the middle height of the specimen, resulting in higher asphalt binder content in the middle layer during the compaction of SGC and SBC. The specimens compacted with SGC and SBC had better mechanical properties, especially in the middle layer of the specimen. The increase of aggregate contact points improved the mechanical properties of the mixture. The free movement of aggregates was helpful for slippage of aggregates and promoted the filling of voids with asphalt mastic to make the skeleton structure more compact. Correlation analysis showed that SGC and the roller could better reproduce the field compaction state. [ABSTRACT FROM AUTHOR]

• PP fiber and nano-TiO 2 modification improves the road performances of PMM. • The optimum ratio of PP fiber and nano-TiO 2 in PMM has been determined. • The PMM showed excellent photocatalytic exhaust degradation capacity. • The PMM significantly reduces the energy consumption and greenhouse gas emissions. To purify severe air pollution in traffic-intensive urban areas and tunnels, an innovative type of photocatalytic micro-surfacing mixture (PMM) was designed, which was enhanced by polypropylene (PP) fiber and nano-TiO 2. In this work, the road performance of sixteen PMMs with the different contents of PP and nano-TiO 2 were evaluated by wet-track abrasion test, wheel rutting deformation test and low-temperature splitting test. The vehicle exhaust (VE) gas degradation capacity of sixteen PMMs was characterized under ultraviolet (UV) light and visible light conditions. The life cycle assessment (LCA) methodology was applied to evaluate the environmental impact of PMM. The results showed that the road performances of PMM were improved with the increase of the PP fibers amount. The VE gas degradation capacity was significantly enhanced with the increase of nano-TiO 2 amount. PMM with 0.2 wt% PP fibers and 60 wt% replacement of mineral filler with nano-TiO 2 was a viable alternative to improve photocatalytic degradation of VE in pavement engineering. In addition, the modified micro-surfacing mixture facilitates a significant reduction in energy consumption and greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

• The freeze-thaw cycle caused the complex modulus of asphalt binders to decrease and the phase angle to increase. • The influence of freeze-thaw cycles on SBS modified asphalt binder was more obvious than that of base asphalt binder. • The creep recovery rate of SBS modified asphalt binder was reduced, opposite to that of base asphalt binder. Perennial freeze-thaw cycles have caused frequent disasters on asphalt pavements. To investigate the effect of four types of freeze-thaw cycles on asphalt binders, the DSR and FTIR test results of #70 Jinlin base asphalt binder (J binder) and SBS modified asphalt binder (S binder) were studied. The rutting factor, creep compliance and fatigue life of binders after freeze-thaw cycles were evaluated first, and then the chemical composition was analyzed. The results show that multiple freeze-thaw cycles lead to a growth in the complex modulus of asphalt binders, but the phase angle of S binder did not decrease significantly. The attenuation of fatigue life of S binder was significantly higher than that of J binder, and there was a certain dependency on fatigue parameters and freeze-thaw damage based on the S-VECD model. Furthermore, after the freeze-thaw cycle, the creep recovery of S binder decreased, while that of J binder increased, due to the increased elasticity by the oxidation of J binder. Carbonyl index (CI) and sulfoxide index (SI) of binders gradually grew with the number of freeze-thaw cycles, and butadiene index (BI) of S binder also slightly decreased. In general, during repeated freezing and thawing, low temperature had a certain adverse influence on the binders, but it is lower than that caused by high temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel kind of microgel has been synthesized by inverse suspension polymerization. • The microgel showed a desired absorption and water retention in cement filtrate. • The drying shrinkage and compressive strength of modified mortar were improved. In this paper, three kinds of P(AM- co -MAA) microgels with different anion contents were synthesized by inverse suspension polymerization with acrylamide (AM) and methacrylic acid (MAA). The modified mortar was prepared by cement and sand as fillers and P(AM- co -MAA) as internal curing agent. The swelling behavior of P(AM- co -MAA) microgels with different anion contents in aqueous solutions was studied. The effects of P(AM- co -MAA) and commercial superabsorbent polymer (SAP) on the flowability, mechanical properties, drying shrinkage and microstructure of mortar were investigated. The results showed that the presence of multivalent cations (mainly Ca2+) weakened the absorption capacity of microgels in cement filtrate. Spherical microgels had no negative effects on the flowability and mechanical properties of cementitious materials. The compressive strength of modified mortar can be significantly improved at later curing stage due to dome structure and internal curing. Furthermore, the water content of modified mortar with 0.1% additions of microgel decreased, and the drying shrinkage rate of the modified mortar was about 36% lower than that of cement mortar without microgels. It can also be observed that a large amount of macro pores were not formed around the microgels. [ABSTRACT FROM AUTHOR]