How do material properties influence the structural behavior of civil engineering systems, and how can engineers optimize these properties to enhance structural performance? Discuss the interplay between material characteristics such as elasticity, strength, ductility, and durability, and their impact on the design, construction, and maintenance of various civil engineering structures. Consider the selection of materials for specific applications, the role of material testing and analysis in ensuring structural integrity, and the challenges associated with incorporating sustainable materials into construction projects. Additionally, explore the importance of understanding material behavior under different loading conditions and environmental factors, and how this knowledge informs the design and maintenance practices in civil engineering.