Failure mechanism of bonding between natural fiber and cement matrix at high temperature.

The debonding behavior of natural fibers with cement matrix at elevated temperatures has been investigated by introducing a new test method for measuring the interfacial shear strength between the fibers and the cement matrix in the field of cementitious composites research. In addition, the effects of shrinkage, surface roughness, and tensile strength changes of natural fibers on the interface at high temperatures were analyzed by characterizing the failure process of chemical bonding with the matrix due to changes in the surface functional groups of natural fibers. The results show that the bonding properties between natural fibers and the cement matrix gradually decrease with increasing temperature, which is due to the contraction of the natural fibers in the radial direction at high temperatures leading to debonding with the cement matrix on the one hand, and the degradation of chemical bonding enhancement due to the reduction of polar groups on the surface of the fibers on the other hand, which contributes to the reduction of the interfacial strength between the fibers and the matrix. In the post-high-temperature phase, the temperature dependence of the inherent material properties of the natural fibers leads to a decrease in the mechanical properties as an additional factor affecting the interfacial behavior. This work evaluates the durability of natural fibers in cement matrices under high temperature conditions from the viewpoint of their inherent physical properties and surface chemical properties, providing unique research ideas and insights for related studies. Meanwhile, a new experimental method is introduced in the field of fiber-reinforced cementitious composites interface research, which can be widely attempted to be used in the study of selective combinations of different fiber-matrix interfaces, fiber size selection, and fiber modification to optimize the overall performance of the composites, which is of great significance to the research in this field. • The bonding properties between FCNTs repair mortar and fire exposed old mortar substrate has been investigated. • The bonding strength and microscopic test were performed to determine the mechanism of FCNTs in the ITZ. • An effective prediction model is proposed to quantify the effects of porosity and different FCNTs. [ABSTRACT FROM AUTHOR]