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The V-S method was proposed to design asphalt mixtures with satisfactory high-temperature stability. However, the design procedures in the laboratory are different from the field compaction condition since the degradation rate δ c c of coarse aggregates is determined by 100 Marshall compactions (MCs). In this study, the V-S method was improved in the laboratory and was subsequently assessed in the field. In the laboratory, the MC, roller compaction by wheel tracking, and Superpave gyratory compaction (SGC) were evaluated for the degradation rate δ c c with water binder instead of asphalt binder. Results show the SGC produces less degraded coarse aggregates, so the degradation rate δ c c should be determined by 100 SGCs instead of 100 MCs. Subsequently, the improved V-S method was applied for the upper surface course of a freeway, which was surveyed and cored for rutting after approximately 3-year service. In conclusion, with the improved V-S method, asphalt mixtures possess narrower deviations between the design and actual values of volume parameters in the laboratory and satisfactory high-temperature stability in the field.

The volumetric design method based on multi-point supported skeleton for asphalt mixtures (V-S method) was proposed to design skeleton-dense asphalt mixtures. However, with this method, asphalt mixtures possess unstable performance in engineering practice. In this study, the V-S method was improved by two steps: first, the coarse aggregate condition for measuring the stacking density was improved; second, the coarse aggregate degradation was considered. The two improvements were verified through the deviations between the design and actual values of three volume parameters, including air voids in coarse aggregates, mineral aggregates, and asphalt mixtures. Results show that the stacking density measured in the dry rodded condition is effective. Moreover, the degradation rate δ of coarse aggregates is proposed, and it is determined by Marshall specimens of coarse aggregates with 100 blows on single side. By considering the degradation rate δ , the new design equations are developed and then the procedures of the second improved V-S method are determined. The volume parameter deviations of the asphalt mixtures designed by the second improved V-S method are very small. In conclusion, these asphalt mixtures possess satisfactory performance, including high-temperature stability, low-temperature performance, and moisture susceptibility.

The rheological properties of asphalt mastics and asphalt-filler interaction play key roles on the performances of asphalt mixtures. However, the rheological properties of asphalt mastics and asphalt-filler interaction are significantly influenced by aging which exists in the compaction stage of asphalt mixtures. In order to analyze the effects of aging on rheological properties of asphalt binders, asphalt mastics and asphalt-filler interaction, the Dynamic Shear Rheometer (DSR) tests and Bending Beam Rheometer (BBR) tests were conducted for unaged and aged specimens. Results indicate that the aging can enhance the cohesion properties of asphalt binders and mastics, and so the rutting resistance of asphalt binders and mastics is better with an increase in aging degree. However, the low temperature properties of asphalt binders and mastics are worse with an increase in aging degree. The two indices K-B-G∗ and K-B-δ were selected to evaluate asphalt-filler interaction ability. Results show that these two indices have the consistency to evaluate asphalt-filler interaction ability. And also the two indices can reflect the difference of interaction ability of different aged asphalt binders and fillers. The deeper aging degree of asphalt binders is, the worse asphalt-filler interaction ability is. Within the same aging degree, the interaction ability of asphalt 70# with higher asphaltene and resins contents is stronger than asphalt 90#. Therefore, the aging affects the asphalt-filler interaction ability via changes of asphalt active components.

To investigate the mechanism of aging and rejuvenation of asphalt, traditional laboratory and atomic force microscopy (AFM) tests were conducted for asphalt specimens, respectively. Experimental results indicated that the penetration and ductility of virgin asphalt significantly decreased after aging. These results could not satisfy the technical requirements of the specification. The softening point and viscosity of virgin asphalt increased due to aging process. Rejuvenator had a significant impact on the performance of aged asphalt binders. The penetration of aged asphalt binders conspicuously increased with an increase in the rejuvenator content. The softening point and viscosity of aged asphalt binders obviously decreased with the rejuvenator content increasing, and the optimum rejuvenator content was about 12% by mass in this study. Through comparing virgin and aged asphalt binders via AFM test, it confirmed that light components contents of asphalt binders greatly decreased during the aging process. The aging effect of asphalt binder was a sluggish process, and the content and microstructure of its internal components would vary with the altering of aging degree. The rejuvenator did not recompose the composition of aged asphalt binders. The results showed that the rejuvenation process of rejuvenator was a physical interaction, and the kinds and contents of rejuvenator would not alter the microstructure of recycled asphalt binders.

Loading mode plays a key role in the fatigue performance evaluation of asphalt mixtures. However, the stress-controlled mode and strain-controlled mode cannot reflect the pavement structure loading conditions. In this paper, a simplified pavement analysis model was designed to analyze the loading conditions of pavement structure, and the energy-controlled mode was put forward. The improved 4PB beam fatigue test procedures were proposed to achieve the energy-controlled mode. And the traditional 4PB beam fatigue tests were also conducted under stress-controlled mode and strain-controlled mode for comparative analysis, respectively. Results show that stress-controlled mode and strain-controlled mode can only reflect two kinds of critical loading conditions in the pavement structures, and do not have universal applicability. An intermediate loading condition that the stored energy approximately remains constant is found. The energy-controlled mode can be achieved well by improved test procedures. And the fatigue life N f of asphalt mixtures measured under energy-controlled mode falls in between fatigue life N f that is measured based on the stress-controlled mode and strain-controlled mode. The test results coincide with the theoretical analysis of simplified pavement analysis model. Therefore, the energy-controlled mode is more suitable to evaluate the fatigue performance of asphalt mixtures.

The asphalt and filler interaction plays a significant role on the performances of asphalt mixtures, and the asphalt and filler interaction ability can be evaluated by the rheological properties. In this paper, one kind of matrix asphalt binder and three kinds of fillers were selected to prepare asphalt mastics with different filler volume fractions respectively, and the dynamic shear rheological properties of asphalt mastics were measured to analyze the four evaluation indices of △G ∗ , K-B-G ∗ , L-A-δ and K-B-δ . Results indicate that △G ∗ and K-B-G ∗ cannot represent the effects of temperature on asphalt and filler interaction ability. However, the two indices can reflect the effects of loading frequency on asphalt and filler interaction ability. L-A-δ and K-B-δ not only represent the effects of temperature on asphalt and filler interaction ability but also the effects of loading frequency on asphalt and filler interaction ability. The higher temperature is, the stronger asphalt and filler interaction ability is. But the higher loading frequency is, the worse asphalt and filler interaction ability is. And then the sensitivity analysis of evaluation indices was also conducted, and finding that the sensitivity from high to low is (1) K-B-δ , (2) L-A-δ , (3) △G ∗ , and (4) K-B-G ∗ .

To evaluate the short- and long-term effectiveness of hot in-place recycling (HIR), the field measurements and laboratory tests were performed. Results indicate the HIR with favorable construction quality is positively effective in restoring high-temperature stability and is acceptable in maintaining low-temperature performance and moisture susceptibility. The findings highlight the rejuvenator application to reconstitute the rheological properties of aged asphalt and the construction control to ensure the uniformity of recycled layer and the degree of compaction. In addition, longer monitoring of pavement deteriorations is promising to determine the practically extended service life from HIR and optimize the follow-up maintenance decision-making, especially in maintenance timing.

In this paper, attempts have been made to build an equivalent-sphere mathematical model with respect to length, width, and thickness, in order to describe the coarse aggregates of asphalt mixture in the laboratory. The values of diameters calculated separately based on lengths, widths, and thicknesses have been compared to the model with actual values, which were obtained by two-dimensional digital image processing technique. Certain characteristics of movements were observed during the formation process. The results indicate that an increase of compaction time is accompanied by an increase in average diameter of 2D coarse aggregates and its standard deviation. This shows that the rotations of the coarse aggregates and their better packing effect increase with compaction time. The results also imply that there may be a considerable breaking of coarse aggregates between compaction of 40 and 60 times.

To evaluate the effectiveness of maintenance treatments for asphalt pavement, four types of treatments, including the hot in-place recycling (HIR), milling and resurfacing (M&F), thin HMA overlay (THO) and microsurfacing (MS), were analyzed. 8 highway segments, in total 491.74 km, in Jiangsu Province in China, were investigated and the data of rutting depth (RD) in their maintenance history was collected. Based on the data of RD, the effectiveness of four treatments was quantitatively compared by three indicators, namely, performance jump (PJ), deterioration rate reduction (DRR) and average deterioration reduction rate (ADRR). Moreover, the applicability of the proposed effectiveness analyses was assessed by laboratory rutting tests with field cylindrical samples. Results indicate that the HIR is the most effective treatment, followed by M&F and THO. While the MS is the least effective treatment, whose service life is only three or four years. The findings highlight the significance of the proper traffic opening time after maintenance to avoid the weakened rutting resistance caused by high-temperature mixtures, the effect of the RD before maintenance on maintenance decision-making, and the application of high-quality RAP in the timely maintenance activities. Therefore, the performance-based maintenance strategy should be establish to improve pavement performance and extend pavement service life. Further research on the pavement performance after RAP application is necessary.

Pavement deteriorations of recycled asphalt mixture (RAM) are mainly caused by the variability of reclaimed asphalt pavement (RAP). Moreover, with the increasing amount of RAP, the pavement damages tend to be more serious. Therefore, this research aims to explore an optimized gradation design method to reduce the influence of RAP gradation variability on the performance of RAM. Before that, the RAM gradation segregation with high RAP contents in transportation and construction were evaluated first. For the variability analysis, in accordance with the fractal dimension (FD) in fractal theory, a FD-based gradation segregation model was established to evaluate the variability of RAP gradation. RAP content of 20%, 35% and 50% was analyzed, respectively. It was found that the FD is applicable to evaluate the degree of RAM gradation segregation. The results reveal that the higher the amount of RAP in RAM, the more serious the degree of gradation segregation. To ensure the performance of RAM with high RAP contents, it is necessary to reduce the variability of RAP gradation. Therefore, an optimized gradation design method by increasing the 4.75 mm passing rate of RAM was proposed based on the Mohr-Coulomb theory. After the calibration and validation, the optimized gradation design method was applicable to weakening the influence of RAP variability on RAM. Through performance tests, it was confirmed that the optimized gradation design method of RAM with high RAP contents established in this paper is reasonable and effective.

This paper aims at investigating the development mechanism of early-stage strength for cold recycled asphalt mixture using emulsion asphalt. The influence parameters of early-stage strength development for cold recycled mixture by emulsion and cement (CRME) is firstly studied, and then the direct tensile test is used to determine the early-stage strength development law of emulsion asphalt–cement mortar. Lastly, the image analysis is used to identify the fracture morphology of cross-section of cold recycled mixture, and the development mechanism of cold recycled mixture is revealed. The results indicate that the cement plays the predominant role in strength of CRME in first 3 days, while emulsion asphalt plays the predominant role in both early-stage and final strength. Moreover, the adhesion between mortar and aggregate provide the strength for CRME in earth-stage, while the cohesion in emulsion–cement mortar provides the strength for CRME after curing. The findings in the paper provide new approaches to improve the early-stage strength of CRME.

This study focused on the diffusion and distribution of the rejuvenator in the aged asphalt of reclaimed asphalt pavement (RAP) materials during hot recycling. Diffusion tests were designed based on the penetration test and the dynamic shearing rheometer (DSR) test to evaluate the diffusivity of the rejuvenator in aged asphalt. The phased extraction and recovery test and the asphalt mortar transfer test were designed to determine the distribution of the rejuvenator during the recycling of asphalt and the distribution of the recycled asphalt within the asphalt mixture during recycling, respectively. Performance tests, including the wheel tracking test, low-temperature bending beam test and freeze-thaw splitting test, were conducted to evaluate the influences of the rejuvenator distribution on the performances of the asphalt mixture during recycling. The viscosity, components and rejuvenator thermal stability are found to have important influences on the diffusivity and distribution of the rejuvenator in aged asphalt. During the short blending process of recycling the asphalt mixture, it is difficult for the rejuvenator to fully diffuse into the aged asphalt. Therefore, the property and distribution of the recycled asphalt tends to be nonuniform in the asphalt mixture during recycling. This nonuniformity can lead to poor high-temperature anti-rutting performance, poor low-temperature cracking resistance and poor moisture stability of the recycled asphalt mixture.

The fatigue life obtained in the Lab is far from the service life of the field roads because of the influence of pavement maintenance. To evaluate the remaining service life of existing roads, the fracture mechanics principles were conducted to characterize the fatigue cracking of asphalt pavement in Jiangsu province of China. The statistics theory was applied to build a new model as a function of the distribution of initial cracks in order to predict the crack propagation. The annual number of cracks detected on the road and equivalent single axle loads (ESALs) per annum was seen as variables to calculate the initial cracks distribution. This aims to predict the crack growth tendency of asphalt pavement before and after maintenance. It was found that exponential function can be used to characterize the relationship between the number and the length of initial cracks. The results of the model correspond with the downward trend of pavement performance. The model is suitable for predicting the service life of pavements of different service time. Especially those were used over 10 years and data of initial pavement condition were difficult to find. After calibration and validation, a comprehensive model considering local materials, traffic information and environmental conditions were established to predict pavement performance after maintenance and propose preventative maintenance schemes for pavement.

The shape, size, angularity and surface texture properties of coarse aggregates were studied in this paper. Aggregates with different shapes were separated manually and the percentage by number of each shape was computed. The three sizes (length, width and thickness) of aggregates were extracted using an image analysis approach and their statistical distributions were studied. An indicator called angularity and surface texture (AT) index was developed to characterize the combined effect of the coarse aggregate angularity and surface texture based on two-dimensional aggregate images. The statistical distributions of the AT indices of different sized limestone and basalt aggregates and their composite AT indices were studied. The void contents of different sized limestone and basalt aggregates in loose condition were tested to validate the AT index.