## 1 Introduction  
The energy-efficient building and green building are conducive to solve the global energy predicament and achieve CO\({}_{2}\) emission reduction targets [1]. Currently, building energy consumption was expected to grow with the increasing of urbanization. With growing interest in energy conservation and emission reduction, interest in the use of renewable energy sources and biologically based materials in building engineering is also increasing. For example, the use of plant fibers as fiber reinforcement for conventional building materials is of interest due to their low environmental footprint, biodegradability, relatively good specific mechanical properties, and the fact that they are less harmful to people as compared to synthetic fibers. The lower density and intrinsic damping properties of plant fibers are also of interest, notably in sports equipment and building materials with a thermal or damping requirement [2]. Fax fiber is highly regarded as a construction material in China due to its high yield, environmental characteristics, and end-of-life incineration energy recovery. In flax fibers, semicrystalline cellulose microfibrils are embedded in pectin in a hemicellulose matrix [3], forming cell walls that enclose a lumen to comprise the fiber microstructure. In turn, these elementary fibers are bundled with a lignin matrix and twisted together to form the structural fiber [4]. This structure gives the flax fibers intrinsic damping performance, which is of key interest in the study of the seismic performance of cement matrix composites. Here, we build on existing research by studying the effect of flax fibers on cementitious composites. Considerable research has been conducted to develop the use of flax fibers in construction. This research has uncovered many urgent issues regarding the use of flax fibers in reinforced cement matrix composites. Firstly, the hydrophilic nature and lumen microstructure of flax fibers cause them to absorb water [5], competing with cement particles with respect to water demand. This characteristic impacts cement hydration and the bond between the fiber and the matrix [5]. Secondly, pectins from flax fibers can interact with the calcium ions of the cementitious matrix to produce a chelating effect [3], prolonging the initial setting time of the mixture [6]. Thirdly, cement hydration producing calcium hydroxide is likely to deposit on the single fiber wall of the fiber bundle or the interlayer of fiber wall, increasing the crystallinity of the plant fibers and decreasing their ductility [7]. To alleviate the impact of flax fibers on the performance of cementitious composites, studies have investigated preliminary flax fiber treatments prior to its use in the cement matrix. For example, [PERSON] [8] found that shorter flax fibers can reduce the damaging influence of the fibers on fresh concrete workability and reduce the \"wall effect\" that can form balls during mixing. Further research determined that combined use of flax fiber with other artificially synthesized fibers can ensure the benefits of flax fiber use while eliminating many of its deleterious effects [8; 9]. [PERSON] [10] found that flax fibers and continuous carbon fibers improved the damping behavior of polymers without decreasing the elastic modulus. [PERSON] [11] grafted nano-TiO\({}_{2}\) onto flax fibers to study its effects on the mechanical properties of epoxy plates and found that flax fiber significantly enhanced flexural properties in the presence of the nano-TiO\({}_{2}\). Flax fibers and carbon nanotubes were found to improve the damping properties of epoxy composites, attributed to internal sliding friction within flax fibers and the stick-slip action of the carbon nanotubes [12]. Surface modification methods have been employed to change the effect of flax fibers and alter the interface between the fiber and matrix.