# Vegetal-FRCM Failure under Partial Interaction Mechanism
## 1 Introduction  
At present, society's awareness of sustainability is rising. More and more environmentally friendly solutions are researched and demanded by all types of industries. The construction industry is not an exception. The research towards sustainability has already started, especially in the field of strengthening structures. In particular, fiber-reinforced cementitious matrix (FRCM) has been studied, replacing with vegetal fibers such as hemp, cotton or sisal [1, 2, 3] the synthetic and high-properties fibers such as glass, carbon or basalt [4], and results are meaningful. [PERSON] et al. [2] compared the mechanical properties of four different FRCMs, with fibers coated with epoxy and polyester resins, where the tensions and multi-cracking failure reached, suggesting that their properties are comparable to the synthetic-fiber FRCMs. The research on the topic of coatings is still in development. The coating of the fiber is needed to give the yarns a mesh consistency when they are extracted from the mold to protect the fibers from the alkaline environment of the freshmortar and also to improve the interphase fiber-matrix [5]. [PERSON] et al. [6] tested the difference in the interphase of a carbon yarn embedded into a mortar matrix, with and without coating. In the post-elastic phase, when the fiber is debonding from the matrix, uncoated yarns present a brittle failure, while impregnated yarns present a more ductile one. The coatings used for strengthening structures are usually synthetic ones [7]. [PERSON] et al. [8] conducted a review of vegetal fibers in polymeric composites, and the most common polymers used are epoxy, polyester (PES) and polypropylene (PP) resins. The research on more sustainable coating is limited. Mostly chemical treatments are applied to the fibers, such as silane or alkaline treatments [8; 9]. Moreover, plasma application was studied to vary the properties of the fiber [10], increasing its mechanical properties tested through a tensile test of a non-woven sample. More recently, new coatings and treatments are being developed. [PERSON] et al. [11] used beeswax emulsion to coat vegetal fibers, [PERSON] et al. [12] coated the fibers with resin and micro-silica and [PERSON] et al. [13] coated curaua fibers with polyaniline and magnetite to improve the interphase with the cement matrix. [PERSON] et al. [14] coated sisal fibers with graphene oxide to mitigate the degradation process. The interest of the field of science to increase the knowledge of coatings for structural application and the need for more sustainable materials were crucial when deciding the coatings for this research. Finally, completely natural coatings were selected to be compared with the performance of synthetic ones, specifically colophony and Arabic gum. Colophony [15] is a pine resin used in the manufacturing of adhesives, coatings or titts, and Arabic gum is a resin used in the alimentary and pharmaceutical industry to give flexibility to the products [16]. Depending on the level of flexibility required, the concentration of the Arabic gum varies between 46 and 85%. In order to test the mechanical properties of FRCM samples, the tensile test is one of the most performed. There are different gripping methods used: clamps, which apply compression to the subjected ends, anchoring it [4; 17], and the clevis grip method, which uses two metallic plates on each end to transmit the load by surface shear [17; 18]. In order to model the behavior of FRCM, common models used for tensile behavior consist of the ACK model [4; 19] or the simplified tri-linear model [4]. These models consider three stages, with the law of mixtures in the first stage until the first crack appears, constant stress until the mortar is completely cracked, and a third stage that considers that all the load is bore by the fibers. However, it has been proved that for the first and second stages, ACK can overestimate the strength of the specimens [20].