# Retrofitting of Bridge Slabs for Safety Railing Refurbishment in Italy: A State-of-the-Art Review
## 4 Discussion  
The presented slab-strengthening techniques have been derived from real structural design documents and guide manuals issued by road management bodies [34]. Therefore, they are used in practical applications mainly along motorways and highways in Italy. A critical comparison can be useful to determine their applicability as well as the pros and cons, as reported in Table 2, also referring to durability requirements [37], impact on the existing structure, and costs.  
As can be seen, techniques no. 1 and no. 2 are the cheapest since they are based on consolidated techniques of RC elements' jacketing. On the other hand, they are exposed to possible corrosion (like technique no. 3), although the presence of a waterproofing layer on the slab extrados significantly reduces this risk. However, corrosion risk is absent in technique no. 4 due to the absence of metallic materials. Currently, the most used technique is no. 1 due to its versatility. In fact, as the anchors are installed after the additional rebars, small imprecisions in their positioning are admitted and do not compromise the effectiveness of interventions.  
Based on the work price lists of the major Italian road management agency (ANAS) [28], the cost of intervention no. 1 per unit bridge length has been computed as a function of the intervention width (W in Figure 6). W depends on both the slab cantilever dimension and the rebar diameter and grade, which determine the development length to be adopted beyond the external beam.  
As can be seen from Figure 10, the intervention cost is proportional to the intervention width. Based on inspected design documents of real bridges, the most frequent W value is 2 m corresponding to an intervention cost of EUR 843/m including the cost of new railings and all the works needed for the slab retrofit. These data are strongly susceptible to increase in the near future given the current inflation rates across the EU. Therefore, it should be treated as a temporary estimate.  
Figure 9: Slab strengthening through NSM composite bars.  
Looking at Figure 11, the cost of the slab retrofit varies between 50 and 60% of the total intervention cost, being in most cases higher than the new railing cost. This means that low-impact and cheap slab retrofit solutions can greatly reduce the overall cost of interventions of the wide national bridge asset.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \# & **Description** & & **Advantages** & **Limitation** & **Cost** \\ \hline \multirow{4}{*}{1} & \multirow{4}{*}{Steel rebars on posts} & \(\bullet\) & No curb demolition & \(\bullet\) & Possible corrosion effects in & \\  & & \(\bullet\) & Flexible position of & the long-term & \\  & & & anchors & \(\bullet\) & Need to fix posts’ positions & Low \\  & & & & before the intervention & \\ \cline{3-6}  & & \(\bullet\) & No curb demolition & \(\bullet\) & Possible corrosion effects in the & \\  & & \(\bullet\) & Flexible position of & long-term & \\ \cline{3-6}  & & & anchors and rebars & \(\bullet\) & Hydrodemolition impact on the & Medium-low \\  & & & anchors and rebars & & existing structure & \\ \cline{3-6}  & & \(\bullet\) & Lower impact of & \(\bullet\) & Fixed position of vertical rods & \\ \cline{3-6}  & & & hydrodemolition on the & \(\bullet\) & Using lower-yielding strength & \\ \cline{3-6}  & & & existing structure & \(\bullet\) & Curb demolition & \\ \cline{3-6}  & & & \(\bullet\) & Lowest impact of & \\ \cline{3-6}  & & & hydrodemolition on the & \(\bullet\) & Curb demolition & \\ \cline{3-6}  & & & existing structure & \(\bullet\) & Possible delamination and fragile & High \\ \cline{3-6}  & & \(\bullet\) & No corrosion & structural behavior & \\ \cline{3-6}  & & & \(\bullet\) & No anchors & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Comparison of slab-strengthening intervention techniques.  
Figure 10: Unit length cost of strengthening solution no. 1.