INTRODUCTION
Cement stabilized macadam (CSM) serves as a critical semi-rigid base layer in Chinese highway pavement structures. Over time, environmental factors and traffic loads contribute to cracking, reducing its service life. Despite the widespread use of CSM, limited studies have examined the performance of repaired specimens. Understanding the fracture behavior and damage evolution of CSM after repair is essential for improving pavement durability. This study investigates these aspects using experimental and microscopic methods to enhance repair strategies and performance evaluation.
LITERATURE BACKGROUND
Previous research highlights the vulnerability of CSM to cracking due to cyclic loading and environmental impacts. Traditional studies focused mainly on initial damage rather than post-repair behavior. Repair methods, such as the application of polymers, have shown promise in reinforcing the semi-rigid base layer. However, systematic investigations combining mechanical tests and microstructural analysis remain scarce. This study addresses these gaps by integrating fracture mechanics, acoustic monitoring, and microstructural evaluation to assess repaired CSM under various loading conditions.
METHODOLOGY
Three-point bending tests were conducted on both original CSM and repaired CSM (RCSM) specimens to analyze fracture characteristics. Acoustic emission (AE) techniques tracked real-time damage evolution, while digital image correlation (DIC) provided strain mapping and crack development visualization. Additionally, microscopic scanning tests were performed to examine the microstructure of RCSM specimens. Permeable polymer was used in the repair process to reinforce bonding and improve mechanical performance. Loading rates were varied to assess their influence on fracture behavior.
CRACK DAMAGE EVOLUTION
RCSM specimens exhibited staged cracking, indicating gradual damage accumulation rather than sudden failure. AE monitoring revealed that higher-energy events occurred earlier as loading rates increased, reflecting accelerated crack propagation. DIC analysis confirmed that crack development differed at the repaired interface depending on the loading rate. At lower rates, interface damage was more pronounced, while at higher rates, cracks tended to propagate away from the repaired surface. These observations highlight the importance of considering loading conditions in evaluating repaired CSM performance.
FRACTURE CHARACTERISTICS
Permeable polymer improved the fracture resistance of CSM, increasing the crack initiation load, peak load, and fracture energy. Three primary failure modes were observed in RCSM specimens: hydraulic gravel failure near the repaired interface, permeable polymer failure, and polymer-aggregate interface failure. The repair material effectively reinforced aggregate bonding, demonstrating enhanced structural integrity. The fracture response depended on both the loading rate and the quality of repair, emphasizing the role of materials selection and repair techniques in extending pavement service life.
MICROSTRUCTURAL ANALYSIS
Microscopic observations revealed that the permeable polymer effectively cemented aggregates within the semi-rigid base layer, contributing to improved load transfer and resistance to crack propagation. The repaired interface exhibited varying degrees of bonding strength, influenced by both material interaction and applied loads. Cracks were often localized at weaker regions in the polymer or at the interface, consistent with observed macroscopic failure patterns. These findings provide a fundamental understanding of microstructural behavior that can guide optimized repair strategies for CSM pavements.
CONCLUSION
The study demonstrates that permeable polymer repair enhances the mechanical performance and fracture resistance of CSM pavements. RCSM specimens show staged cracking, with failure modes depending on loading rates and interface bonding. Acoustic emission and DIC techniques effectively captured crack evolution, while microstructural analysis confirmed improved aggregate bonding. The findings support the use of polymers for semi-rigid base repair and provide valuable insights for designing durable pavement maintenance strategies, ultimately extending the service life of highway infrastructure.
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