Micromechanics-Based Durability Study of Polyvinyl Alcohol-Engineered Cementitious Composite

摘要

The durability of engineered cementitious composites (ECC) reinforced with polyvinyl alcohol (PVA) fiber is investigated in this paper. ECCs have been realized as ductile strain-hardening cementitious composites with tensile strain capacity up to 5%. This material is being applied in new construction and for the repair and retrofit of structures. A micromechanics-based approach is adopted in the present durability study. The micromechanics-based model relates the fiber, matrix, and interface parameters to composite properties through knowledge of microdeformation mechanisms beyond the elastic stage. Composite property changes resulting from environmental loading are expected to be a manifestation of changes in properties at the fiber, matrix, and/ or interface level. This concept is examined in this paper by experimentally determining the changes in the fiber and fiber-matrix interface properties with specimens exposed to accelerated testing and correlating such changes to changes in the ductility of composites exposed to the same accelerated testing conditions. The accelerated test used in this study is a hot water immersion test simulating a long-term hot and humid environment. It is found that the fiber-matrix interface chemical bond increases while the apparent fiber strength decreases when the exposure time reaches 26 weeks. Correspondingly the composite ductility also decreases. The micromechanical model provides a rational means of interpreting and correlating the data from these two levels of testing. Despite the deterioration, PVA-ECC is found to retain tensile ductility more than 200 times that of normal concrete or normal fiber-reinforced concrete after exposure to an equivalent of 70 years or more of hot and humid environmental conditions.