# Durability of Fabric-Reinforced Cementitious Matrix (FRCM) Composites: A Review
## 4 Durability of Composite
### Durability of Composite Matrix  
The inorganic matrix employed in FRCM composites is generally cement-based or lime-based, although other types can be found in the literature (see e.g., [14; 19; 20; 21]). This section focuses on the durability of cement-based and lime-based mortars. In the figures presented in this section, the blue color indicates cement-based mortars, whereas the orange color indicates lime-based mortars. Details of the tests included in the figures below are provided in Table 1.  
Exposing FRCM matrices to freeze-thaw cycles, alkaline and sulfate attack may influence its durability. For example, the water present within the matrix voids may freeze when exposed to low temperatures, increasing its volume by 9% [22]. Consequently, it may induce damage and cracks if the internal stresses exceed the matrix tensile strength. However, researches available regarding freeze-thaw of FRCM composites did not generally report the specimen moisture content. Figure 2 presents the effect of the freeze-thaw cycles on the retained cracking (tensile) strength of different FRCM matrices, which was determined by uniaxial tensile test on FRCM [14; 28] and TRC [22; 26] coupons. The details of freeze-thaw cycles utilized in each study are indicated in the legend of Figure 2. All specimens subjected to less than 100 cycles showed an improvement of the matrix cracking strength. However, a large scatter of the results was observed [22]. Moreover, [PERSON] et al. [19] reported a continuous increase in the matrix tensile strength from 50 to 100 cycles, whereas [PERSON] et al. [26] observed a reduction for 100 cycles. The difference in the obtained results is mainly attributed to the different performance of the adopted matrices. [PERSON] et al. [22] considered a high-strength cementitious matrix (average cubic compressive strength and flexural strength equal to 97.5 MPa and 13.6 MPa, respectively [22]), whereas [PERSON] et al. [26] used a cement-based matrix with average cubic compressive strength and flexural strength of 29.6 MPa and 5.0 MPa, respectively [26]. Studies reported that concrete with a high strength is less susceptible to freeze-thaw cycles due to its low permeability [48; 49], which can explain the better performance of the matrix with the highest compressive and tensile strength. In addition, the range of temperature and the period of the freeze-thaw cycles adopted by [PERSON] et al. [22] were shorter and smaller, respectively, than those adopted by [PERSON] et al. [26]. However, after 100 cycles, Figure 2 shows that the retained matrix cracking strength decreased, which was attributed to the occurrence of microcracks [22; 26]. [PERSON] et al. [21] investigated the combined effects of freeze-thaw cycles (-18 \({}^{\circ}\)C to 5 \({}^{\circ}\)C with 3 h cycle length) and saline environment (5 wt. % NaCl) on the cracking strength of TRC composites using four-point bending test. The obtained results are not shown in Figure 2, where the effect of only freeze-thaw cycles is considered. [PERSON] et al. [21] reported a retained cracking strength after exposing to 50, 70, and 90 cycles equal to 0.98, 0.91, and 0.86, respectively. Similar to the result shown in Figure 2, freeze-thaw cycles did not have a significant effect for small number of cycles. However, the degradation gradually increased with increasing the number of cycles. The degradation developed with 90 cycles was slightly higher than the one reported by [PERSON] et al. [26] with a similar number of cycles (100 cycles). This result can be attributed to: (i) presence of the sodium chloride that may have increased the degradation process rate and (ii) test method employed (four-point bending test vs. uniaxial tensile test). Chlorides and sulfates can interact with some components of the matrix such as calcium hydroxide (Ca(OH)\({}_{2}\)) and aluminum oxide (Al\({}_{2}\)O\({}_{3}\)) leading to a reduction of the matrix durability [28]. Figure 3a presents the effect of continuous immersion in a saline solution (seawater or 3.5 wt.