# Durability of Fabric-Reinforced Cementitious Matrix (FRCM) Composites: A Review
## 4 Durability of Composite
### Durability of Composite Matrix
% of NaCl) on the retained strength of the FRCM matrices studied. [PERSON] et al. [34] and [PERSON] et al. [33] utilized three-point bending tests of lime-based mortars specimens according to EN 1015 [32]. [PERSON] [28] studied the cracking strength of cement-based FRCM coupons using uniaxial tensile tests. The results showed that although [PERSON] et al. [34] utilized a lower ageing temperature than [PERSON] et al. [33], the degradation of the mortar was higher (up to 60%, see Figure 3). This controversial result might be attributed to the difference in the porosity and mechanical properties of the mortar investigated by the two researchers. A mortar with high porosity such as natural lime-based mortar could be more influenced by saline environments than hydraulic lime or cementitious mortars [33]. Further studies are required to relate the physical nature of the FRCM matrices with their durability in various environmental conditions. [PERSON] [28] reported a remarkable increase in the cracking strength of the cement-based matrix. This result was not significantly affected even when the exposure period was extended to 3000 h.  
Figure 3b shows the effect of wet-dry cycles in saline solutions on the retained strength of the matrices. Regarding the cementitious matrix, [PERSON] et al. [21] performed 12 h of wetting in a saline  
Figure 3: Effect of saline environments on the matrix tensile strength: (a) continuous immersion and (b) wet-dry cycles (blue bin = cement-based matrix and orange bin = lime-based matrix). Figure 2: Effect of freeze–thaw cycles on the matrix tensile strength (blue marker = cement-based matrix, orange marker = lime-based matrix). solution (5 wt. % of NaCl) followed by 12 h of drying at room temperature on TRC coupons with cement-based matrix, which were subsequently tested using a four-point bending test set-up. The results showed that the matrix flexural strength progressively decreased with increasing the number of cycles. Regarding the lime mortar, [PERSON] [33] reported similar residual flexural strengths for specimens subjected to continuous immersion and wet-dry cycles, showing a percentage reduction of approximately 10%. Alkali-aggregate chemical reaction, which is the reaction between the potassium and sodium oxide (K\({}_{2}\)O and Na\({}_{2}\)O) of the cement and the reactive silica (SiO\({}_{2}\)) present in some types of aggregate, may affect glass micro-fibers (if present) dispersed within the mortar [28]. The effect of matrix immersion in alkaline solution on the flexural [34] and uniaxial tensile strength [28] is presented in Figure 4. It can be noticed that the retained flexural strength of the lime-based mortar decreased to approximately 55%, whereas the retained tensile strength of the cement-based matrix was not significantly affected (a slight increase, lower than 10%, was observed). Finally, studies on the effect of immersion of the matrix in deionized water, which is a conditioning typically employed for GFR reinforcing bars [41], showed that this type of exposure can improve the performance of the cement-based mortar if it is followed by an appropriate drying period due to the resumption of the hydration process [33; 35]. It should be noted that the mechanical properties of the matrix affect the FRCM behavior when it is still not cracked. The results gathered show that the exposure of the FRCM to some harsh environmental conditions may lead to the formation of microcracks, which in turn affect the cracking strength and stiffness of the composite. In addition, matrix microcracks can promote the penetration of water and external agents into the composite.