## 3 Testing Program  
The lack of a validated and comprehensive data base for the durability of GFRP grids as related to reinforcement applications for masonry structures has been recognized as a critical barrier to the use of these composite materials. In this study environments of interest are alkalinity and fatigue effects. For many masonry structures subject to cyclic loading (for example bridge structures, smokestacks and slender towers), ageing and fatigue are an important limit state that must be considered in the design process. When embedded into a lime- or cement-based mortar, GFRP grids come in contact with alkaline media. To study the potential effects (hydrolysis, pitting, hydroxylation, etc.) of degradation due to mortar pore water solution, GFRP specimens were first aged in alkaline solution and subsequently subjected to tension-tension axial fatigue tests. In this research the fatigue protocol resulted much more severe than those situations detected in real service conditions, but this allowed to better highlight the sensitivity respect to this type of ageing. In this study the specimens that were investigated respect to long-term properties were cut from the GFRP grids along the 0\({}^{\circ}\) direction, meaning that the tensile properties were measured for the flat GFRP bars (see Figure 2a). In the following all the descriptions and results are related to the flat bars. Firstly mechanical tests were performed to measure the tensile properties of the GFRP specimens, such as tensile strength, elastic modulus and ultimate strain. Tensile tests were also performed after the ageing/fatigue protocols. Tensile tests were run firstly on twenty unconditioned specimens, which provided the characterization of the GFRP materials, without any mechanical and chemical ageing. Figure 4: GFRP grids after exposure in alkaline bath. (**a**) Comparison between aged and unaged grid; (**b**) Aged specimens. The preliminary tensile tests were run by using a [PERSON] universal testing machine, having a capacity of 100 kN. Tensile tests were run under displacement control with a controlled rate equal to 0.2 mm/min, at a room temperature of 23 \({}^{\circ}\)C and relative humidity of 50%. An electric extensometer was used to measure the strain. ASTM D3039 [34] standard was used as reference for static tests. Furthermore ten specimens were cut from the same grid, subjected only to the alkaline ageing protocol, and tested under an uniaxial monotonic tensile force as same as done for reference specimens, without any fatigue treatment. This was done in order to detect the chemical sensitivity in presence of alkaline ions, and in absence of any other agent or harsh environment. Then a set of sixteen specimens was cut from the same GFRP grid of the unconditioned specimens, to be subjected to fatigue loads with and without previous alkaline exposure. Totally eight specimens were subjected to alkaline exposure before the fatigue cycles, while the other eight were fatigued without any chemical ageing. Fatigue tests were performed on a servo-hydraulic E3000 Instron machine (Instron, Norwood, MA, USA) with a 3 kN capacity load cell. Surface temperature was monitored using a voltmeter with a sensibility of 0.15 \({}^{\circ}\)C. The load amplitude and test frequency of the fatigue treatment were constant (1.0 kN and 7.5 Hz, respectively). Tests were conducted at a room temperature of 21 \({}^{\circ}\)C in stress control using a normalized maximum tensile stress (\(\sigma_{\max}/\sigma_{\mathrm{util}}\)) of approx. 0.25, 0.35, 0.45 and 0.55 (corresponding to maximum tensile loads of 1, 1.5, 2, and 2.5 kN). Table 1 summarizes the experimental program of tensile static tests, while in Table 2 the fatigue test protocol is illustrated, including the number of specimens tested, the maximum fatigue load and number of scheduled cycles. In Figures 5 and 6 the fatigue machine and the loading histories used in this study are illustrated. For fatigue tests, GFRP specimens were dry cut from the grid with final dimensions of approx.