# Durability of Fabric-Reinforced Cementitious Matrix (FRCM) Composites: A Review
## 3 Conditioning Environments
### Hygrothermal Environment  
The simplest and most utilized method to investigate the durability of FRCM composites is accelerated ageing in water, which consists in the immersion of the specimens in hot water for a certain period. However, AC 434 (2018) [23] and Italian Initial Type Testing CSLLPP (2019) [24] recommend ageing in 100% RH at approximately 38 \({}^{\circ}\)C for 1000 and 3000 h. [PERSON] et al. [33] considered the recommendations provided by ASTM D7705 [40] to evaluate the resistance of FRP bars exposed to alkaline environments and immersed the FRCM in water heated at 60 \({}^{\circ}\)C. EN 12467 [38], was also used to investigate the effect of moisture on inorganic-matrix composites. EN 12467 requires water immersion at 60 \({}^{\circ}\)C for 56 days to evaluate the durability of fiber-cement flat sheets [38]. Moreover, EN 12467 specifies heat rain (HR) tests in which the specimen is heated to 60 \({}^{\circ}\)C for 3 h using radiant heat and then cooled down to room temperature using water spray for 3 h. [PERSON] et al. [26] considered this method to study the durability of a TRC composite comprising a glass textile and a cement-based matrix. However, in order to reduce the cycle period, the heating time was reduced to 1 h and the cooling time to 30 min. In addition, the water spray was replaced by immersion in water at 15 \({}^{\circ}\)C. Finally, [PERSON] et al. [35] investigated the effects of water immersion at various temperatures (23-40 \({}^{\circ}\)C) with different exposure periods (5-74 days) on the FRCM-concrete bond behavior. Although [PERSON] et al. [35] found that increasing the ageing temperature from 23 to 30 \({}^{\circ}\)C did not significantly influence the bond behavior observed, yet this finding should not be extended to higher temperature due to the lack of studies investigating the effect of the ageing temperature on the FRCM long-term behavior. Studies on FRP composites showed that using high temperature can increase water diffusion and increase the degradation rate [41] of GFRP reinforcing bars. These observations allowed for defining accelerated testing procedures that require ageing temperature up to 60 \({}^{\circ}\)C and a conditioning period of approximately 60 days [6; 37; 42]. Since in FRCM composites the organic fraction is usually quite limited if not absent, exposure to a relatively high temperature (close to the glass transition temperature of the resin used in FRP) does not represent an issue. Therefore, an ageing temperature of 60 \({}^{\circ}\)C could be considered adequate for FRCM accelerated testing. It should be noted, however, that the maximum exposure temperature specified by AC 434 (2018) [23] and CSLLPP (2019) [24] is approximately 38 \({}^{\circ}\)C. Short-term high-temperature tests shall be carried out according to CSLLPP (2019), and the exposure temperature shall be decided by the manufacturer [24]. The limited data available in the literature did not allow to identify a clear effect of accelerating tests in water of FRCM composites. Therefore, further and detailed investigations should be performed. Another method employed to evaluate the effect of moisture on the durability of FRCM is the exposure to a series of wet-dry cycles. According to EN 12467 [38], 50 cycles of immersion in water at ambient temperature (more than 5 \({}^{\circ}\)C) for 18 h followed by drying in ventilated oven at 60 \({}^{\circ}\)C and 20% RH for 6 h are needed to investigate the behavior of fiber-cement flat sheets. [PERSON] et al. [36] found that 8 h are enough to saturate masonry specimens with externally bonded SRG strips via capillary absorption and exposure to 60 \({}^{\circ}\)C in a ventilated oven is enough to dry them. However, since the purpose of the study was investigating salt crystallization within the interfaces, two days of wetting and two days of drying at 60 \({}^{\circ}\)C were utilized to ensure adequate salt accumulation. In another study, [PERSON] et al. [43] utilized 3 days of drying. [PERSON] et al.