# Surface Modification of Glass Textile for the Reinforcement of a Cement-Based Composite: A Review
Both systems make use of the same kind of reinforcements, which are made up of continuous multi-filament strands, assembled in different geometry by various means such as weaving, knitting, tufting, felting, braiding, or bonding. Application can range from the production of composite for the rehabilitation and reinforcement of concrete and masonry structures [9; 10; 11; 12; 13] or the production of high performance cementitious composites with unique tensile strength and ductility [8; 14; 15]. Several studies have been conducted on the use of inorganic based composites as external reinforcement of masonry walls subjected to in-plane [16] and out-of-plane [17] loads, confining of masonry and concrete columns [18; 19], arches [20] and strengthening of concrete structures [21; 22]. Of course, the stress transfer at the fiber-matrix interface is fundamental also for this class of composites. However, along with the stress transfer between the matrix and the reinforcement, the mechanical properties of TRC and FRCM also depend on the stress transfer between the single filaments that make up the reinforcement. Indeed, tensile tests conducted on TRC and FRCM highlight that the composite strength is much lower than that of the reinforcement, because only the external filaments of the yarns are directly involved in the stress distribution. This phenomenon is due to the big dimensions of the cement grains, compared to the small size of the spaces between the filaments, that account for an incomplete embedding of the yarn in the matrix. As a consequence, only the outer filaments are directly anchored to the surrounding matrix, and since the low friction between the filaments is not sufficient to redistribute the stress between them, the composite fails when the outer filaments reach their ultimate tensile strength, while the inner filaments slip within the yarn [11; 12; 14; 23; 24]. It should be stressed out that, unlike carbon fibers, glass fibers have good adhesion to cement-based matrices [25]. Therefore, the first goal of any surface modifications introduced is not to improve the adhesion to the matrix, but rather to improve the stress transfer between the fibers. This dual necessity of improving the stress transfer between the single filaments in the yarn, while maintaining a good interfacial adhesion with the cementitious matrix, it is often a challenge in the development of TRC and FRCM composite materials. Furthermore, great care must be taken when using glass fibers in cement-based matrices due to the high alkalinity of the matrix. To address this issue, fibers produced for cement-based composites, known as alkali-resistant glass fiber (ARG), are manufactured by adding a high percentage of zirconia (typically 15-23% by weight) [1]. However, it has been proved that, although ARG fibers are less affected by alkaline attack and the loss in mechanical properties over time is reduced compared to glass-reinforced concrete (GRC) with E-glass, they are not immune to chemical corrosion in OH\({}^{-}\) rich environments [26; 27; 28]. The direct chemical attack on the fibers is not the only factor influencing the durability of GRC over time. Some of the chemical reactions responsible for the curing of the matrix are reported to modify the fiber-matrix interface, also affecting the mechanical behavior of the composite [29; 30]. Because of the peculiar chemical-physical conditions that glass fabric embedded in the cementitious matrix has to withstand, surface modifications of glass fibers for cementitious composites must fulfill specific requirements. The increase of the stress transfer between the filaments, and the improvement of the glass fibers durability are the two most important aspects that need to be addressed to improve the properties of these composite systems. However, for practical applications other requirements should also be taken into consideration. For example, fabrics employed for the reinforcement of existing structures with complex geometry have to be enough flexible to be easily adapted to the substrate.