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The comprehensive properties evaluation index of asphalt mixture has the characteristics of multilevel and multifactor. The weight of each road performance index is the key factor to assess the comprehensive properties of the asphalt mixture. However, how to determine the weight objectively is a very key problem in the performance evaluation model. In this study, the comparison matrix method was used to determine the performance weight objectively of rock asphalt modified bio-asphalt mixture (RABAM). First, the neat asphalt mixture (NAM), bio-asphalt mixture (BAM), rock asphalt modified asphalt mixture (RAM), and RABAM were prepared. Second, the high-temperature and low-temperature properties, water damage resistance, and fatigue characteristics of the different asphalt mixtures was analyzed. Finally, the comprehensive properties were evaluated under different climate zones in China. The results indicated that the rock asphalt improves the comprehensive performance of BAM. Applying the comparison matrix method to the field of road materials can effectively evaluate the applicability of road materials in different regions. [ABSTRACT FROM AUTHOR]

Due to viscoelastic characteristics, the strength values of the high-modulus asphalt mixtures (HMAM) obtained under different conditions (temperatures, loading rates, and stress states) are quite different, and the serving conditions of asphalt pavements are also varied. Thus, the strength under fixed conditions cannot reflect the mechanical performances of materials under real serving conditions, which leads to inaccuracies in the asphalt pavement structural design. To develop a precise strength evaluating method for high-modulus asphalt mixtures, the strength tests of high-modulus asphalt mixtures were implemented under different conditions (temperatures, loading rates, and stress states) in this study. The test results indicated that for each stress state, the variation of strength with loading rates under different temperatures can be characterized by power functions, and the variation of strength with temperatures under different loading rates can be characterized by exponential functions. The uniform characterizing model of strength under different conditions was established through the dimensionless method and the sigmoidal function. With the effects of temperature, loading rates, and stress states included, the strength obtained can better reflect the mechanical performances in actual pavement serving conditions. The research results contribute to the improvement of the structural resistance design of the asphalt pavement with high-modulus asphalt mixtures. [ABSTRACT FROM AUTHOR]

A large amount of soybean oil (20%–30% mass ratio of neat asphalt) was selected to partially replace petroleum asphalt. The high-temperature behavior of soybean oil bioasphalt was enhanced by polyphosphoric acid (PPA). Polyphosphoric acid/soybean oil composite modified asphalt (PSMA) was prepared. Temperature sweep, frequency sweep, multiple stress creep recovery, and bending beam rheometer tests were conducted to reveal the rheological behavior. Fourier infrared spectroscopy (FTIR), scanning electron microscope, and fluorescence microscope tests were carried out to reveal its microstructure characteristic. The results proved that polyphosphoric acid obviously increased the high-temperature properties of soybean oil bioasphalt. Compared with the neat asphalt at 0.1 kPa, the recovery rates of 20% bio/6% PPA, 25% bio/6% PPA, and 30% bio/6% PPA increased by 139.2%, 113.5%, and 86.4% respectively. PSMA was less sensitive to temperature and loading frequency, with remarkable elastic recovery and antirutting degeneration ability. PSMA could maintain excellent low-temperature crack resistance at −18°C. PSMA had better rheological properties when soybean oil and PPA were 20%–25% and 4%–6%, respectively. The FTIR tests verified that some new functional groups emerged in PSMA. There were evenly distributed fluorescent materials in the soybean oil bioasphalt under the fluorescence microscope. Under the modification effect of PPA, soybean oil and PPA could be evenly dispersed in PSMA. Laboratory tests verified the superior properties of bioasphalt with high content soybean oil. [ABSTRACT FROM AUTHOR]

To study the correlation between the chemical composition and rheological properties of neat asphalt after aging and rejuvenation, the neat asphalt with different aging time was prepared, and its rheological properties were tested by dynamic shear rheology (DSR) and bending beam rheology (BBR). The functional groups were tested by the Fourier transform infrared (FTIR). Based on the gray entropy correlation analysis (GECA), the correlation of test parameters was analyzed linearly. The results show that with the aging of asphalt, the complex modulus ( G * ), phase angle (δ), and creep rate (m) decrease, while the creep stiffness (S), carbonyl index (CI), and sulfoxide index (SI) increase. After the addition of regenerating agent, the rheological performance indexes and the content changes of characteristic functional groups of recycled asphalt are opposite to those of aging asphalt. The gray entropy correlation degrees among the SI/CI, δ , and G * , and among the rutting factor (G*/sinδ), creep stiffness S (−12°C , −18°C , and −24°C) and creep rate m (−12°C , −18°C , and −24°C) are more than 0.96; the rheological parameters δ , G* , G*/sinδ , and S (−18°C and −24°C) of asphalt have a unary linear relationship with the SI/CI, and its rheological parameters δ , G* , G*/sinδ , S (−18°C and −24°C), and m (−24°C) have a binary linear relationship with the composite index (AI) (SI+CI). These findings are of great significance to understanding the evolution law of rheological properties of neat asphalt after aging and rejuvenation. [ABSTRACT FROM AUTHOR]

While the monitoring of longitudinal (P) waves has been widely investigated to estimate the initial setting time of concrete mixtures based on the variation in P-wave velocities, it is difficult to accurately estimate the setting time owing to the sensitivity of P-waves to air voids and the difficulties in identifying the final setting time from smooth velocity variations. Furthermore, shear-horizontal (SH) waves are advantageous over P waves for monitoring the setting time owing to their high signal-to-noise ratio and sensitivity of the shear-wave velocity (Vs) to solid structure development. This study proposes an SH-wave-based method to identify the abrupt increase in the Vs values at the initial and final setting times. The proposed method was verified against traditional penetration resistance tests and P-wave tests with two sets of concrete specimens having different water-to-cement ratios. Although the initial setting times from the P-wave and SH-wave tests are close with the differences of 9% and 21% for the two sets of specimens, however, the smooth velocity variations from the P-wave tests cannot identify the final setting time that can be clearly captured with the abrupt increase of Vs from the SH-wave tests. Both setting times from the SH-wave tests and the penetration resistance tests have a high correlation with a coefficient of determination (R2) of 0.9875. The results demonstrated the high sensitivity of Vs to the setting time and the potential applications of SH waves for monitoring the setting time of concrete mixtures. [ABSTRACT FROM AUTHOR]

Material resistance and performance are determined by the failure criterion for an asphalt mixture, affecting the scientific design of pavement. Conventional tensile, compression, bending, and split tests for asphalt mixture cannot fully reflect the complex stress and strain state of the pavement structure. In this paper, double confining pressure triaxial tests were performed on asphalt mixtures to generate three-dimensional complex stress states. In octahedral stress space, a failure criterion was established featuring the tensile and compressive meridians as well as the failure envelope curve. According to the generalized Hooke's law (GHL), a transformed three-dimensional strain failure criterion model (FCM) was established and its accuracy was validated by the axial strain. The correlation function between stress and strain FCMs was proposed. According to the elastic layered system theory and the principle that the load response is less than the structural resistance, a three-dimensional load check was performed on a typical asphalt pavement structure. The results show that top-down cracks tend to appear in the inner edge of the load at the top of the upper surface layer. This research provides theoretical support for the study of the characteristics of asphalt mixture strength and pavement design under complex stress conditions. [ABSTRACT FROM AUTHOR]

The fatigue resistance of an asphalt mixture is crucial to the pavement's durability and serviceability of pavement. The pavement structure is in a three-dimensional (3D) stress state. However, the conventional fatigue-resistance design index mostly considers a one-dimensional stress state, which is different from the field conditions. In this paper, the unconfined compression test (UCT), direct tension test (DTT), and splitting test (SPT) were selected to conduct the strength and fatigue tests. Based on the Ayyagari Vural yield criterion, the strength damage surface under various loading rates was established. Furthermore, a normalized fatigue equation was developed in a 3D stress state by determining the fatigue-damaged path based on the yield criterion. Finally, the fatigue-resistance models for the structural design were proposed by combining the strength models (including the octahedral shear stress model and the Ayyagari Vural model) and the normalized fatigue equation. The results indicate that the strength damage surface model is in an elliptic form, and the surface is abducent as the loading rates increase, and the Ayyagari Vural yield criterion can describe the fatigue failure process. Both fatigue-resistance design methods for pavement resistance take the interaction among three principal stresses into consideration and comply with the failure characteristics of actual pavement structures; the equivalent stress as a design index is more feasible in its actual application. This study could provide a reference for the fatigue-resistance design of asphalt mixture layers in a complex stress state and improve the reliability in the pavement structure. [ABSTRACT FROM AUTHOR]

Detecting the corrosive environment of reinforced concrete (RC) bridge decks is of critical importance for evaluating the reliability and safety of bridge structures. However, accurately and automatically detecting a corrosive environment with traditional methods is challenging. This paper proposes a method for the automatic corrosive environment detection of bridge decks from ground-penetrating radar (GPR) data based on the single-shot multibox detector (SSD) model. This method can be divided into three steps: data preprocessing, automatic rebar picking, and corrosive environment mapping. First, the GPR data are preprocessed to enhance the contrast of the hyperbolic feature in GPR B-scans. Then the rebars in the B-scan images are automatically picked up by the trained SSD model. Finally, the corrosive environment contour map of the bridge deck is generated with the rebar reflection amplitudes after depth correction. The SSD model was trained with 10,316 B-scan images and tested with 2,578 images. The 300×300-pixel B-scan image typically included three to five hyperbolas. A case study with GPR data from a tested bridge was employed to validate the feasibility of the proposed method. The results show that the accuracy of the automatic corrosive environment detection method can reach 98% and is considerably higher than that of commercial software methods. [ABSTRACT FROM AUTHOR]

As an important ecofriendly material in pavement engineering, bioasphalt has received more and more attention recently. However, the negative high-temperature behavior of bioasphalt limits its extensive application. With the purpose of enhancing the bioasphalt high-temperature behavior, polyphosphoric acid (PPA) was used to modify bioasphalt. The PPA/bio-oil composite–modified asphalt's high-temperature behavior was investigated by the dynamic shear rheometer (DSR) test. The low-temperature behavior was evaluated by using the bending beam rheometer (BBR) test. Finally, the modification mechanism of modified asphalt was analyzed by carrying out a Fourier-transform infrared reflection (FTIR) test. The results indicated that compared with the neat asphalt, the rutting index of PPA/bio-oil composite–modified asphalt was significantly improved. Also, it had excellent low-temperature crack resistance. As the bio-oil and PPA contents in respect to the weight of neat asphalt were 15% and 5%, respectively, PPA/bio-oil composite–modified asphalt performance was optimal. Shear time and shear rate did not have a remarkable effect on PPA/bio-oil composite–modified asphalt performance. Moreover, bio-oil did not affect the chemical structure of the neat asphalt. But, PPA generated new chemical functional groups with neat asphalt and produced chemical modification. This research makes pavement engineering greener, more economical, and environmentally friendly. [ABSTRACT FROM AUTHOR]

An asphalt mixture is always in a complex stress state during the service life of pavement. Its resistance can be objectively characterized only by applying the strength theory to establish the failure criterion model in a three-dimensional stress state. Therefore, based on the double confining pressure triaxial test method, the failure characteristic test in complex stress state was carried out on AC-13 and AC-20 asphalt mixtures widely used in asphalt pavement in China. Meanwhile, according to the generalized octahedral theory, the experimental data of the failure characteristic point, and the strength characteristics of the asphalt mixture itself, the applicability of classical failure criteria, including Bresler-Pister, Ottosen, Willam-Warnke, Kotsovos, Podgorski, amended Zhao-Song, and twin-shear failure criteria was analyzed. In the aforementioned failure criteria models, the amended Zhao-Song failure criterion considered the difference in tension and compression of materials, the effect of hydrostatic stress, and the correlation of stress states of strength, which was consistent with the test results. Therefore, this model can be used as the resistance calculation model of asphalt mixtures in a complex stress state. [ABSTRACT FROM AUTHOR]

In this paper, styrene butadiene rubber (SBR) was utilized to improve the low-temperature performance of Buton-rock asphalt (BRA)-modified asphalt. Firstly, the optimum content of SBR modifier agent was determined by basic mechanical property tests, including penetration, ductility, and soft point tests. The comprehensive road performance, including high- and low-temperature performance, moisture resistance, and antifatigue performance at a low-temperature condition, of SBR-BRA-modified asphalt mixtures was evaluated by comparison with a base asphalt mixture, SBR-modified asphalt mixture, BRA-modified asphalt, and styrene-butadiene-styrene (SBS)-modified asphalt mixture. The fatigue test under the experimental temperature of −10°C and loading frequencies of 0.01, 0.1, 1, 5, and 10 Hz were designed to evaluate the antifatigue capacity of SBR-BRA-modified asphalt mixture under the low-temperature region. The S-N fatigue equation with the stress ratio related to loading rates was proposed to characterize the fatigue property of asphalt mixtures and reveal the different effects of loading frequency and materials on the fatigue property of asphalt mixtures. The tests results demonstrated that the SBR-BRA-modified asphalt has an equal road performance to SBS-modified asphalt. Analyzed by the S-N fatigue equation with the stress ratio related to loading rates, the fatigue test results under different loading frequencies could be fitted to a fatigue curve, and the fatigue curves of different asphalt mixtures exist at an angle and intersect at point (1,1). [ABSTRACT FROM AUTHOR]

Asphaltic material is a kind of viscoelastic material, and its performance varies with test and materials conditions, such as stress states, temperatures, aging degree, gradations, and binders. The anti fatigue design of asphalt pavement has been stifled by these interferences. The objectives of this study are to reveal and compare the effects of loading frequency and aging degree on the fatigue performance of asphalt concretes. A series of tests for tensile fatigue on aged and unaged asphalt concretes were conducted at different loading frequencies. The theory of stress ratio considering different test conditions was proposed based on the conclusion that the stress ratio varies with stress loading rates. Then, the S-N fatigue equation was modified based on the theory. The fatigue test results were analyzed with the modified S-N fatigue equation to characterize the fatigue performance of asphalt concretes aged to different degrees under different loading frequencies. The different effects of these two factors on the fatigue characteristics of asphalt concretes were analyzed and compared. It could be found from the results that the influences of loading frequencies and aging degrees on fatigue characteristics of asphalt concrete were different. The fatigue test results of asphalt concrete under different loading frequencies could be characterized by one fatigue curve fitted by the modified S-N fatigue equation. It meant that the effects of loading frequency on fatigue were equivalent to the stress level. The fatigue test results of asphalt concrete with different aging degrees were fitted into different fatigue curves, respectively. The asphalt concretes aged 1 day had better fatigue life and more stable stress sensitivity than unaged asphalt concrete. When the aging degree was over 1 day, the fatigue performance deteriorated with the increase of aging degree. Moreover, it could be observed that the strength increased with the aging degrees when it was measured by the standard test loading rates. However, when the loading rates increased to a certain range, the contrary conclusion could be obtained because the viscoelasticity of asphalt concretes changed due to aging. [ABSTRACT FROM AUTHOR]