# Durability of Fabric-Reinforced Cementitious Matrix (FRCM) Composites: A Review
## 3 Conditioning Environments
### Concentrated Solutions  
Sulfate and chloride attack are one of the common weathering environments that can affect the long-term behavior of inorganic materials.  
AC 434 (2018) [23] and CSLLPP (2019) [24] require uniaxial tensile tests of FRCM coupons continuously immersed in a saline solution reproducing the seawater conditions. In order to mimic the effect of marine environment (chloride attack) that generally triggers this damage, researchers immersed FRCM specimens in seawater or in aqueous solutions containing 3.5 wt. % (i.e., percentage by weight) of sodium chloride (NaCl) to reproduce a common seawater salinity [23; 28; 33; 34]. Exposure periods of 1000-3000 h were adopted in most cases. [PERSON] et al. [33] subjected FRCM-brick joints to a series of wet-dry cycles in saline solution containing 3.5 wt. % of NaCl, exposing them to 60 \({}^{\circ}\)C to accelerate the process rate. [PERSON] et al. [21] utilized saline solution with 5 wt. % of NaCl companied with a series of wet-dry or freeze-thaw cycles.  
Standards have adopted different procedures to investigate the resistance of porous materials, such as stone and bricks, to the sulfate attack. EN 12370 [45] suggests total immersion in solution containing 14 wt. % of sodium sulfate followed by oven drying at 105 \({}^{\circ}\)C. Rilem MS-A.1 [46] suggests using 10 wt. % of sodium sulfate and 10 wt. % of sodium chloride These conditions were considered too aggressive by [PERSON] et al. [43], which adopted a solution containing 2 wt. % of NaCl and 8 wt. % of sodium sulfate decahydrate (Na\({}_{2}\)SO\({}_{4}\)\(\cdot\)10H\({}_{2}\)O) to avoid FRCM failure before the end of the cycles. During the ageing procedure, FRCM-masonry joints were laid down and immersed up to 20 mm (measured from the lower face), so that the solution was not in contact with the FRCM strip. Subsequently, they were dried in a ventilated oven at 60 \({}^{\circ}\)C for 3 days. This procedure was repeated to obtain six cycles [43]. The results indicated that salt accumulation on the FRCM matrix was comparable to that found in old masonry buildings subjected to rising damp and marine aerosol spray for centuries. Indeed, in addition to the chloride and sulfate attack, durability of FRCM used to strengthen masonry structures may be also influenced by salt carried by rising damp. Salt accumulation and crystallization within the matrix-fabric and matrix-substrate interfaces can significantly affect the bond at these interfaces.  
FRCM durability can be also influenced by alkaline environments, which can have a significant effect on glass fibers embedded within the inorganic matrix [41]. The effect of exposure to alkaline environments was investigated by immersing FRCM coupons in alkaline solutions made of various components for a period ranging between 1000 and 3000 h. [PERSON] et al. [28] used a solution with pH > 12 containing calcium hydroxide (Ca(OH\({}_{2}\))), sodium hydroxide (NaOH), and potassium hydroxide (KOH). [PERSON] [34] utilized a solution with pH = 10 made with sodium bicarbonate. Instead of immersing FRCM specimens in alkaline solutions, [PERSON] et al. [47] used three types of mortars with different level of alkalinity to evaluate their influence on the embedded glass fabric textile. The studies that investigated the durability of FRCM in alkaline environments clearly showed that the results depend on the alkalinity level, exposure temperature, and exposure period. Therefore, a shared standard procedure including also wet-dry cycles is needed to allow the comparison of the results obtained.