# Sampietrini Stone Pavements: Distress Analysis Using Pavement Condition Index Method
## 2 Methodology and Data  
### Sampietrini Pavements  
In several Italian cities, it is possible to find historical pavements such as the Sampietrini pavements, which are especially present in the center of the city of Rome. The first documented use of Sampietrini stones in Rome was during the reign of Pope [PERSON] (1566-1572). The name derives from their first use in St. Peter's Square and later, over the next centuries, the stones were used to pave all the main streets of Rome, providing a smoother and stronger surface for carriages than bricks. This kind of pavement is made of beveled stones of black basalt, also simply called Sampietrini, placed one next to the other. The shape of each block (also called sampietrino) can be approximate by a cubic or a square-based truncated pyramid solid. Sampietrini blocks of different dimensions can be used. The largest ones are characterized by a square head of 12 cm \(\times\) 12 cm and height of approximately 18 cm; however, the common height is equal to 6 cm. The smallest and rare ones, which are located in specific areas of Rome such as Navona Square, present a square head of 6 cm \(\times\) 6 cm. In Figure 1, a typical cross section of this type of pavements is represented, while Figure 2 presents the two main geometric patterns which can generally be realized using Sampietrini blocks. The mechanical properties of Sampietrini material are reported in Table 1 and, as shown by some studies performed by Penta in the 1950s, the performance of the Sampietrini pavements depends on the resistance of each block but also on the tile pattern realized, which meaningfully affects the global behavior of this kind of pavement [20]. Sampietrini pavement presents some advantages; in fact, it does not completely cover the ground, leaving small spaces for the water to pass through and can easily adapt to the irregularities of the ground. Furthermore, being of volcanic basalt, Sampietrini are very strong and resistant. The main problem associated with Sampietrini blocks concerns that they get very slippery when they are wet, being a hazard above all for two-wheeled vehicles moving in the city. In addition, due to their irregular shape, traveling on this kind of pavement is very uncomfortable and noisy; moreover, heavy vehicles passing on it may cause wide vibrations that can damage the surrounding buildings, with particular attention to historical ones. Because of their peculiarities, Sampietrini pavements are not suitable for streets where high speed is allowed, thus, nowadays, Sampietrini were replaced in many roads of Rome but they are still used in slow traffic areas (speed \(\leq\) 50 km/h), such as the center of Rome such as Trastevere (Figure 3). \begin{table}
\begin{tabular}{c c} \hline \hline
**Material Property** & **Value** \\ \hline Young’s modulus (GPa) & 37–60 \\ Poisson ratio (-) & 0.15–0.38 \\ Compressive resistance (MPa) & 241–320 \\ Flexural resistance (MPa) & 32–75 \\ Tensile resistance (MPa) & 18–20 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mechanical properties of basalt used for Sampietrini. Figure 2: Geometric patterns: (**a**) herringbone at 45\({}^{\circ}\); (**b**) arc. Although the percentage of the urban road network characterized by Sampietrini pavement is pretty low (about 2%), it presents a whole extension equal to about 100 km, which cannot be neglected in an appropriate and optimized PMS. Furthermore, the aforementioned pavements not only constitute an important historic heritage of the city of Rome, but they are also located in the most visited and prestigious areas of Rome, as can be seen in Figure 3.  
In addition to the urban road network of 100 km, several other roads in Sampietrini are located within the Lazio region and in other towns in Italy, whose extension and the accurate location is difficult to know with sufficient precision. The construction of this kind of pavement is very complex (Figure 4) and it requires very skilled and specialized workers, which are very rare nowadays.