# Sampietrini Stone Pavements: Distress Analysis Using Pavement Condition Index Method
## 1 Introduction  
In order to guarantee the proper maintenance of a road network, it is very important to monitor the conditions of road pavements along their service life. In this sense, the development of an adequate Pavement Management System (PMS) is a very useful tool for road agencies, identifying appropriate intervention thresholds and maintenance strategies for the restoration of the optimal performances, in terms of grip, bearing and roughness levels. [1; 2; 3; 4].  
Most PMSs, actually adopted, are related to major roads and airport infrastructures [5] but, nowadays, considering the lack of budget available to administrations, a general attention to the applications of PMS to urban areas is paid [5; 6; 7; 8]. Many PMSs include both visual and automatic surveys in their procedure, adopting several indices for the evaluation of road pavement performances. Among these, two of the most commonly used ones are the Pavement Condition Index (PCI) elaboratedby [PERSON] [2] and the International Roughness Index (IRI), which was elaborated from a World Bank study in the 1980s [9]. The first one provides a global assessment of pavements condition surveying several distress categories. In particular, it was designed for the assessment of distress related to rigid and flexible pavements [10], which are the most common types that can be found in a generic road network. IRI, instead, is used worldwide as road roughness evaluation criterion and its calculation requires the measurement of road profiles using specific devices, also known as profilometers [11].  
In recent studies [12; 13], the correlation between IRI and PCI was investigated, with particular attention to urban roads. In addition, based on IRI and distresses relation, some IRI threshold values to be used in urban areas are proposed in [14].  
In urban networks, however, different kinds of pavement can be found, such as block or modular pavements, which are defined as pavements composed of pre-formed modular pavers of brick and concrete, which, generally, have been successfully used worldwide for low volume roads and pedestrian areas [15; 16]. Considering the peculiar characteristics of these types of pavements, it is not possible to extend to them distresses and evenness evaluation methods designed for rigid and flexible pavements. In particular, starting from the PCI method described in [2; 10], some authors developed specific guidelines to survey and evaluate distresses affecting block pavements [17; 18; 19].  
In several Italian cities, it is possible to find historical pavements such as the Sampietrini pavements [20], which share similar features with modular block pavements. This kind of pavement is especially present in the center of Rome and, because of its peculiar characteristics, it is not possible to apply consolidated survey methods or threshold values commonly adopted for flexible and rigid pavements.  
For this reason, a specific case of study related to the Sampietrini block pavement was performed in this paper, modifying the PCI method related to block pavement in order to be suitable for this kind of pavement. Furthermore, for each section the sample surface evenness evaluation was carried out calculating the corresponding IRI value, investigating also possible correlations between the proposed PCI method and IRI. In addition, some considerations concerning users' comfort perception traveling at different speeds (<50 km/h) along this type of pavement were performed using the frequency-weighted vertical acceleration (\(a_{uzz}\)) approach described in [21; 22; 23].