Effect of Moisture on Mechanical Properties of Extruded Wood Polypropylene Composite Material

摘要

The durability of extruded wood polypropylene composite (WPC) material used in Z-section sheet piles was investigated under wet environment. An experimental technique to determine moisture content and its effect on mechanical properties was implemented. Water absorption experiments were carried out on specimens cut from flanges and webs of the Z-section by immersion in tap water at 21℃, 45℃ and 70℃. The freeze-thaw resistance of saturated specimens was studied by cycling temperatures in the range of 21℃ to -29℃. The water absorption experimental kinetics was in agreement with the Fickian diffusion process. Water absorption was modeled using an analytical solution based on Fick's second law of diffusion. Quasi-static four-point bending tests were conducted periodically on specimens immersed in water to assess changes in flexural modulus and strength. A significant decrease in mechanical properties of the water-saturated specimens compared to the dry control specimens was observed. Degradation of flexural modulus exhibited a strong correlation with moisture content. Initially, the flexural modulus decreased with increments in moisture content; the flexural modulus stabilized as the moisture content approached the saturation level. Freeze-thaw cycling did not have any significant effect on mechanical properties of saturated composite specimens.