# Surface Modification of Glass Textile for the Reinforcement of a Cement-Based Composite: A Review
## 4 Modification Techniques of Glass Fibers
### Comparison of Different Coatings
The pull-out results obtained after aging show that the best composite properties are obtained for the reinforcement coated with the epoxy resin dispersion. [PERSON] et al., investigated the effects of epoxy and styrene-butadiene impregnation among with the use of inorganic potassium silicate coating for the modification of AR-glass fabric [71]. Interestingly the authors use an automatic coating plant for the impregnation of the fabric, making some considerations on the process feasibility. All fabric samples were coated continually roll-to-roll, with the fabric being immersed in a Foulard containing the polymer and then squeezed by rollers before entering the curing oven. Since the penetration of the coating into the yarn is directly proportional to its viscosity, for aqueous potassium silicate dispersion a coating speed of 0.7 m/min was used, while for the much more viscose epoxy resin the process was slowed down to 0.2 m/min. Moreover, in order to facilitate the coating process, when the epoxy resin was applied, the Foulard and the squeezing rollers were heated to a temperature of 80 \({}^{\circ}\)C, to decrease the viscosity. The authors also report that the use of a two-component epoxy resin constrains the coating process due to the curing of the epoxy, which limited the coating usage time. Regarding the mechanical properties of the composite obtained with the coated fabrics, tensile tests showed similar results for epoxy and styrene-butadiene coatings, with the first one leading to slightly higher mechanical properties. The inorganic coating also led to an increase of the composite tensile strength but more moderate compared to the organic coatings. According to the authors, the superior load-bearing capacity of the composite observed for the polymer coated fabrics is due to the higher impregnation grade obtained. A cross-section of the coated roving reveals that for the epoxy resin the multi-filaments are completely impregnated, in the styrene-butadiene coated roving the core filaments remained uncoated and the potassium silicate coating, on and in the fabric, was randomly distributed with very little volume fractions. Different results were obtained by evaluating the effect of the coatings on the composite bending properties. First of all, the strength at the limit of proportionality (LOP), that for the dry and inorganic coated systems also corresponded to the maximum flexural strength (MFS), was much higher for the dry and potassium silicate-coated fabric than for the epoxy impregnated reinforcement. Indeed, while the inorganic coatings lead to a considerable increase of the first crack peak, for the epoxy fabric the LOP is almost the same as for the unreinforced matrix, which reflects the lower adhesion of the coated fabric with the matrix. For both styrene-butadiene and epoxy coated fabrics, after reaching the first peak, an increase in the bending strength is observed, leading to the formation of different peaks before reaching the MFS. The very high residual strength of these composites is attributed to the higher tensile strength of the polymer impregnated fabrics, although for the styrene-butadiene coating higher MFS are reached, probably due to the superior flexibility of the reinforcement. Based on the information reported on the studies reviewed, some considerations can be made on the advantages and drawbacks of different techniques. Table 1 schematizes the different techniques analyzed in this review and summarizes their effect on: the load distribution between the single filaments (stress-transfer), the interaction with the cementitious matrix and the effect on fibers durability (alkali-resistance).