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To study the reflection crack propagation behavior of asphalt mixture under different loading modes, composite and flexural failure load tests and fatigue tests under different stress ratios were carried out on composite trabecular specimens. The whole process of reflection crack initiation and propagation was observed based on digital image correlation technology(DIC). The crack propagation behavior was analyzed from crack width, crack propagation path, crack propagation height and fatigue reflection crack propagation rate. The results show that the reflected crack propagation behavior of asphalt mixture goes through four stages: microcrack initiation, microcrack development, microcrack transformation to macro crack, and macro crack rapid development. The reflected crack growth consists of primary crack growth and secondary crack growth, and the secondary crack growth rate is higher than that of the primary crack. It is reliable to use logistic function to fit the fatigue reflection crack propagation of the mixture. The research results are of great significance for improving asphalt pavement design and durability evaluation. [ABSTRACT FROM AUTHOR]

The discrete element method (DEM) is one of the most popular methods used to study the performance of pavement materials. However, few studies use the DEM to evaluation the damage performance of asphalt overlays on cement pavements. This paper focuses on the establishment of discrete element models to simulate the reflective crack development of asphalt overlays on cement pavement. Three contact models are selected to realise the pavement structure layer. The results show that under flexural tensile loading and shear loading, the development of reflective cracks can be inhibited with increasing asphalt overlay thickness, while the influence of the interlayer bond strength on the crack development is not obvious. In addition, the flexural tensile load can promote the development of cracks more than shear load. Under the action of thermal fatigue stress, the opening degree of crack displacement increases with the fatigue stress ratio, while the increase in interlayer bond strength can slow down the development and expansion of cracks. Moreover, thermal fatigue stress causes reflective cracks in the overlay to develop earlier and faster. [ABSTRACT FROM AUTHOR]

In order to study the repair method of reflective cracks in asphalt pavement, three kinds of structural repair materials were designed according to the width of reflective cracks. Firstly, the high-temperature stability, low-temperature crack resistance and water stability of the repair materials were evaluated by rutting test, bending trabecular test, immersion Marshall test and freeze-thaw splitting test respectively. Secondly, the optimum distribution amount of binder was determined by drawing strength test and shear strength test. Finally, the crack resistance of the repaired structure was discussed through the theory of full field strain analysis and fracture energy. The research results show that the basic properties of the three kinds of repair materials designed in the test meet the requirements of the specification. The optimal distribution amount of binder for V-shaped repair structure is 0. 6 kg/m². Through the full field strain analysis and crack resistance analysis, it is known that the flexural tensile strength of the repair material is 3. 36 times that of the traditional asphalt pouring repair, and the fracture energy of the repair material reaches 60. 1% of that of the uncracked pavement. The test verifies the feasibility of repairing road reflection crack with V-shaped, and provides a new method for repairing road reflection crack. [ABSTRACT FROM AUTHOR]

• Crack width movements in CRCT under temperature changes were measured in situ. • Contraction and reflection crack width movements were comprehensively analyzed. • Comparisons were made between contraction and reflection crack behaviors. • Relationship between crack width movements and transverse locations was evaluated. • Suggestions to improve CRCT performance concerning crack widths were proposed. This study investigated the crack width movements of a continuously reinforced concrete track (CRCT) of railways subjected to environmental loads, such as changes in temperature. To this end, in-situ experiments were carried out at two railway CRCT sections. There are two different types of cracks in CRCT namely the contraction (top-down) crack and reflection (bottom-up) crack. The behaviors of the contraction and reflection cracks were thoroughly analyzed and the differences in the crack width movements were investigated. The relationship between crack width movements and transverse locations was also evaluated. Based on the findings from this comprehensive experimental study of crack widths, we proposed multiple methods to improve the performance of CRCT. [ABSTRACT FROM AUTHOR]

The pavement in the tunnel does not expose to the sunlight and rain, thus, from the perspective of durability, it is generally considered that the pavement environment of the tunnel is more favorable than the open environment. This may not apply to the pavement of Hongkong —Zhuhai —Macao Bridge immersed tunnel. Based on the long term observation in the construction of the Hongkong—Zhuhai-Macao Bridge island and tunnel project, we found that there is continues moisture in the tunnel within 5 months each year,and there exists a reciprocating opening-closing movement in the pipe joint. By analyzing the reason, it was judged that the problem still exists in the service period. And, some recently constructed tunnels were investigated, early damages of road surface were commonly seen. The Hongkong-Zhuhai-Macao Bridge immersed tunnel is located in the middle of the 55 km cross—sea channel, there is no alternative route. In order to avoid quick damage of road surface after the tunnel is put into use, which causes repairs, and even closing of the tunnel, leading to the slow traffic or close of the entire link, we proposed improvement suggestions to the pavement. [ABSTRACT FROM AUTHOR]

Abstract: Most of overlaid asphalt pavements are facing with reflection cracking in an early age of service life. In this study, a numerical prediction model for fatigue life was developed by modifying crack growth rate, da/dN, of Paris law with horizontal deformation rate, du/dN, to compare relative performance of the material choice based on experimental test result. Experimentally, an interlayer between old concrete pavement and overlay asphalt pavement, polymer modifiers and fiber were used to retard initiation and progress of reflection crack. An expedited reflection cracking test method was developed and applied to various bitumen mixture-concrete block test bodies. The results were compared with one another in terms of resistance against reflection cracking. The coefficient of determination of predicted life and measured life was very high (r 2 =0.98). Therefore, it was shown that the fatigue life of each bitumen material and interlayer combination can be estimated using the prediction model developed in this study. [Copyright &y& Elsevier]

• Pre-overlay treatment plays and indispensable role in asphalt overlay construction. • Partial depth repair for mid-severity joints is proved to be beneficial. • Advantages and disadvantages of eight common interlayers are presented. • Overlay thickness, base condition, asphalt binder type and traffic volume are key factors. • Additional overlay thickness can retard the development of reflection cracks. Being one of the most common method to restore the structural and functional capabilities for distressed Portland cement concrete pavement, the practice of asphalt concrete overlay dates to the mid-20th century and even earlier. Workmanships and techniques adopted for the application had been widely researched. In view of the increasing demand for pavement rehabilitation, this work summarizes the following: firstly, the basic procedures for asphalt concrete overlay construction by considering about 100 papers published since 1950 to till date. Secondly, the overlay thickness design methods including the thickness deficiency-based approach and thickness analytical-based approach. Thirdly, the advantages and disadvantages of various kinds of interlayers adopted in engineering fields. Fourthly, the possible factors that would affect the propagation of reflection cracks, such as traffic volume, overlay binder type, base condition, etc. Fifthly, the possible construction alternatives in terms of construction period and traffic closure. Overall, by employing analytical-based methods, this review brings to light that additional overlay thickness can reduce the fatigue stress, thermal stress, and traffic loading stress at the bottom of the overlay, resulting in overall smaller stress level. Moreover, additional overlay thickness also contributes to the decrease in daily reflection crack length according to Paris' law. Further, this review stresses the indispensable role for pre-overlay treatment and recommends careful investigations during overlay construction. [ABSTRACT FROM AUTHOR]