# 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  
Because of the different materials, test methods and experimental protocols adopted in literature studies, the results obtained from experiments on the effects of coatings on both mechanical properties and durability of AR-glass reinforced cementitious composites are difficult to compare. In order to partially address this issue, this section tries to evaluate the advantages and drawbacks of the different techniques reported in literature studies based on the results obtained employing different coatings but maintaining unchanged the cementitious matrix and the test methods. [PERSON] et al. investigated the tensile strength of AR-glass roving impregnated with polymeric dispersions of chloroprene, polyurethane, acrylate, and an epoxy resin [54]. The epoxy impregnated yarns display the highest tensile strength and elastic modulus. For the rovings modified with the polymeric dispersion, no change in the elastic modulus was observed. The acrylic polymer leads to an increase of the tensile strength slightly lower than that obtained with the epoxy resin. Polyurethane and chloroprene polymers also lead to an increase of the tensile strength compared to the dry rovings, but the performance obtained is far lower than the epoxy and acrylic impregnated yarn. The authors attribute the superior tensile properties of the epoxy impregnated roving to the high modulus of the epoxy resin (3.3 kN/mm\({}^{2}\)), which results in two orders of magnitude higher than the one of the acrylic polymer (10 N/mm\({}^{2}\)). Unfortunately, the study provides no information about the behavior of the composites. [PERSON] et al. compared the tensile behavior of cement-based composites obtained using four commercially available AR-glass fabrics, with two geometrical configurations, provided by the producer with epoxy and styrene-butadiene coatings [81]. They report that, although the tensile strength of the fabrics was marginally influenced by the coating, the maximum tensile strength of the composite reinforced using the epoxy impregnated fabrics was 50% to 60% higher compared to the styrene-butadiene impregnated coating. The authors attribute the superior performance obtained with the epoxy impregnated reinforcement mainly to the better ability of the resins to penetrate and impregnate the glass filaments and to stiffening the nodal connections between the yarns, which enable the weft strands to provide a greater anchorage when the specimen is loaded in the warp direction. An extended study on the effect of different sizing and coatings formulation on the durability of AR-glass fibers in alkali environment was conducted by [PERSON] [28]. The author compared the alkali-resistance of AR-glass roving coated with a thermoplastic and a cross-linked styrene-butadiene polymers and an epoxy resin dispersion by immersing the roving in two alkaline solutions (5% NaOH and cement solution) and by accelerating aging of the cement-based composite obtained with the coated rovings. Rovings coated with the epoxy resin dispersion show an increase of tensile strength compared to the dry fibers, which is two times the increase obtained with styrene-butadiene coatings. After immersion in the alkali solutions for 28 days at 20 \({}^{\circ}\)C, the styrene-butadiene coatings proved to be more resistant than the epoxy coating. However, because of the better distribution of the epoxy coating on the filaments surface, it provides better protection of the glass fibers under more aggressive aging conditions. The influence of aging on the composite properties was verified by two sides pull-out test before and after exposure to different protocols. In general, if compared to styrene-butadiene, the epoxy coating leads to a higher increase of the loading force of the composite after the failure of the cementitious matrix. As a consequence, the epoxy impregnated reinforcement leads to a maximum pull-out load of the composite (about 200 N higher than that obtained for styrene-butadiene coated rovings), but smaller pull-out work.