# Durability of Fabric-Reinforced Cementitious Matrix (FRCM) Composites: A Review
## 2 Test Methods  
Recently, US acceptance criteria AC 434 (2018) [23] and Italian Initial Type Testing procedures CSLLPP (2019) [24] proposed standard tests to evaluate the durability of FRCM composites. However, the available research does not comply with these recent procedures. In fact, different methods were adopted to investigate the FRCM long-term behavior. The changes in the mechanical properties of FRCM and TRC exposed to a control environment, approximately 23 \({}^{\circ}\)C and 60% relative humidity (RH), with respect to those of corresponding composites aged in different conditions (discussed in Section 3) were studied adopting various test procedures, such as uniaxial tensile, three-point bending, pull-out, and direct-shear tests [21; 25; 26; 27; 28]. Among them, uniaxial tensile tests were often used in the literature to evaluate the long-term behavior of the matrix, bare (non-impregnated) textile, and composite coupon. Two main tensile test set-ups, which differ for the specimen gripping method, were proposed for the mechanical characterization of FRCM coupons. (i) In the clevis-grip test [23] (Figure 1a), metal plates are bonded to the end of the specimens and then connected to the testing machine through a clevis joint. In general, FRCM coupons subjected to clevis-grip tests fail due to cracking of the matrix and subsequent debonding of the fibers at the matrix-fiber interface. The slope of the cracked phase of the axial stress-axial strain curve obtained is referred to as the tensile modulus of elasticity of the cracked composite and is employed in designing the strengthening intervention using the tested FRCM composite [23]. (ii) In the clamping-grip test [24] (Figure 1b), the ends of the FRCM coupon are clamped applying sufficient pressure to avoid slippage of the fiber within the matrix [29]. Therefore, after cracking of the matrix, the axial stress is sustained mainly by the textile and the specimen fails due to subsequent rupture of the fiber filaments [28; 29]. These two set-ups generally provide completely different results that cannot be easily compared. However, provided that the stress-transfer mechanism between matrix and fibers is properly investigated, the axial stress-axial strain curves obtained by clevis- and clamping-grip tests can be compared, deriving also information on the matrix crack spacing and opening [30].  
In addition to the uniaxial tensile test, other test methods were adopted to investigate the durability of the FRCM coupons such as three- and four-point bending tests [21; 28; 31]. However, these tests do not provide direct information about the effect of conditioning on the matrix-fiber bond behavior since several parameters, such as the matrix tensile and compressive strength, affect the specimen behavior. Therefore, they were mainly used to evaluate the durability of mortar (without textile) [32; 33; 34; 35] or they were coupled with uniaxial tensile and pull-out tests to gain further information combining the results obtained [21; 28].  
Regarding pull-out tests, different methods and procedures were proposed depending on the purpose of each study. For instance, [PERSON] et al. [27] and [PERSON] et al. [21] used two different pull-out set-ups to investigate the bond between matrix and fiber. The bond behavior of FRCM composites was also studied using single- and double-lap direct-shear tests, which allow for the study of the interaction between the composite and substrate [33; 36].