# Durability of Textile Reinforced Concrete: Existing Knowledge and Current Gaps
## 2 Durability
### Chemical Attack
Application of alkali-resistant coatings is often considered for enhancing the performance of these fibres to alkaline environments [14], but this leads to a significant increase in their price. It is known that coating E-glass (usually with Zirconium dioxide to produce AR-glass) helps in improving the resistance of glass fibres to alkaline environments [11, 14, 22]. However, the scientific evidence on the efficiency of the existing coatings is still limited, and few studies can also be found showing the susceptibility of proposed coating materials [23]. Additionally, different studies have used different alkaline solutions (pH levels), which makes comparison between different databases complicated. As for the matrix, most studies have focused on ordinary cement-based matrices, and fewer studies are available on blended cements, novel low-carbon cements or lime-based mortars. The experimental results are sometimes contradictory. In some cases, an improvement of the mechanical response (tensile strength) is reported after exposure to saline and alkaline conditions, which is attributed to continuous hydration of the matrix after 28 days [13], while others reported deterioration of the mechanical response of cement-based TRC [20] even when alkali-resistant glass fabrics [11] or lime-based TRCs (the results also depend on the type of lime-based mortar) [17] were used. The results are also contradictory with respect to acidic solution environments. While some studies show suitable resistance, others show a significant vulnerability under acidic environments [11]. The type of mechanical  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Ref. ** & **Fibre** & **Matrix** & **Standard** & **Methodology** & **Solution** & **Duration** & **Post-Exposed Tests** \\ \hline \multirow{4}{*}{[18]} & \multirow{4}{*}{carbon} & \multirow{4}{*}{pozzolan} & \multirow{4}{*}{-} & \multirow{4}{*}{immersion} & saline (3.5\% NaCl) & \multirow{4}{*}{1000 h} & \multirow{4}{*}{tensile} \\  & & & & & & (NaHCO\({}_{3}\) pH = 10) & & \\ \cline{5-8}  & & & & & & acidic (HCl, pH = 2.5) & \\ \hline \multirow{4}{*}{[19]} & \multirow{4}{*}{steel} & \multirow{4}{*}{ \begin{tabular}{c} lime and cement \\ \end{tabular}  } & \multirow{4}{*}{-} & \multirow{4}{*}{wet-dry} & saline (2\% NaCl+ 8\  
tests performed after ageing and the test setups used also have a significant influence on the obtained results but the available information on this is still very limited. For example, while no deterioration of the tensile strength was observed after exposure to chemical attacks in some cases, the flexural strength was observed to deteriorate. This can be attributed to the role of boundary conditions on the durability test results [14]. The vulnerability of bond strength and failure mode to alkaline and saline environments, characterised by pull-off [13; 16] or single-lap shear tests [15], also can be highly affected by the test setup used. Two critical factors that have not been discussed or investigated yet are the role of curing conditions and of post-ageing conditioning of the samples before performing mechanical tests. Additionally, most reported experimental results do not contain this information, making analysis and comparison of the data from different labs complicated.