# Experimental Study on Flexural Capacity of Corroded RC Slabs Reinforced with Basalt Fiber Textile
## 3 Experimental Results and Discussion
### Bending Deformation Analysis  
The cracking loads of the strengthened slabs were approximately between 15 and 20 kN, which was slightly enhanced when compared with the control slabs. This increase indicated some activation of the strengthening layers in tension prior to concrete cracking [14]. The bending stiffness of specimens at different stages (initial, cracking and post-yielding) is shown in Table 6 where the data were calculated from the load deflection curves as the tangent stiffness of different stages. The table also indicated the enhancement of stiffness in cracking and post-yielding stages compared to the corresponding control slabs. It was noticed that the presence of the strengthening layers also increased the cracking and post-yielding stiffness of the corroded RC slabs, especially under the severe corrosion condition. This means that the lower the initial stiffness of the un-strengthened slabs, the higher the effect of strengthening [14]. According to the criterion recorded in _Code for design of concrete structures (GB50010-2010)_[39], the mid-span deflection of slabs at the serviceability limit state is limited to within \(l_{0}/200\) mm when its span \(l_{0}\) is less than 6 m. Due to the specimen span being 2.1 m, the limited deflection (\(D_{8}\)) for 10.5 mm could be calculated, and the service loads (\(F_{8}\)) could be extracted from the corresponding load-deflection curves. Figure 14 shows that the service load of the specimens is significantly enhanced by strengthening with the BFRP/BTRM layers, and the performance of specimens was also enhanced with the increment of the strengthening layers. The promotion of load capacity was useful in cases where the serviceability limit state of deflection was the governing factor. When the slabs were strengthened by BFRP composite, the service load under the moderate corrosion condition was increased by 0.41% (3 layers) and 4.07% (five layers), respectively, and the enhancement ratio was 2.93% (three layers) and 13.66% (five layers) under the severe corrosion condition. As for the slabs strengthened with BTRM, the service load under the moderate corrosion condition was enhanced by 8.54% (three layers) and 28.05% (five layers), respectively, and enhancement under the severe corrosion condition was 1.95% (three layers) and 7.80% (five layers). It was therefore found that the strengthening effects of BTRM are better than that of BFRP, and the former actually enhanced the section height of the test slab, thereby controlling the deformation of the specimen. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Specimens**} & \multirow{2}{*}{**Initial Stiffness**} & **Cracking** & **Percentage** & **Post-Yielding** & **Percentage** \\  & & **Stiffness** & **Increase** & **Stiffness** & **Increase** \\  & & **(kN/mm)** & **(\%)** & **(kN/mm)** & **(\%)** \\ \hline M-C & 5.39 & 2.27 & - & 0.73 & - \\ M-P-3 & 7.04 & 2.40 & 5.73 & 0.86 & 17.81 \\ M-P-5 & 7.01 & 2.32 & 2.20 & 0.94 & 28.77  
The ductility performance of the specimens was evaluated by calculating their ductility index, which was the ratio of the slab deflection at the ultimate load to the deflection at the yield load [35]. The ductility index was expressed as Equation (2). \[k_{\text{d}}=\frac{D_{\text{u}}}{D_{\text{y}}} \tag{2}\]  
where \(k_{\text{d}}\) is the ductility index; \(D_{\text{u}}\) is the ultimate deflection of the slab; \(D_{\text{y}}\) is the yield deflection of the slab. The yield and ultimate deflections of all specimens were presented in Table 7. To illustrate the influence of the strengthening composites on the deformation capacity, the normalized ductility indexes of the strengthened slabs are given in Figure 15. Compared with the corresponding control slabs, the ductility indexes of M-P-3, M-P-5, S-P-3 and S-P-5 increased by 1%, 6%, 18% and 19%, respectively; in addition, these indexes of M-M-5, S-M-3 and S-M-5 increased by 3%, 35% and 33%, respectively.