# A Review and Future Directions on the Deterioration Evaluation of Concrete Utility Poles
## 1 Introduction  
Utility poles are widely utilized to support the distribution lines that deliver electricity produced at power stations to users. Wooden poles are the main material used worldwide, along with concrete and steel poles. Fiber-reinforced plastic (FRP) poles [1] have also been used in recent years. The need for utility pole maintenance has increased due to aging, and it is considered necessary to suggest standards and inspection methods for efficient maintenance.  
In Japan, prestressed concrete poles are used, as shown in Figure 1. The undergrounding rate of power lines in Japan, as shown in Table 1[2], is less than 10%, which is extremely low compared to other countries where urban undergrounding has been completed. Furthermore, as shown in Table 2[3], the total length of power lines is significantly longer than in other countries, resulting in more utility poles than in the rest of the world. Most of these utility poles were installed during the 1970s, making comprehensive repairs, replacements, and maintenance due to aging an urgent and critical issue. To define the standard service life, a visual survey of utility poles in service in Japan was conducted [4]. As a result, it was confirmed that the proportion of damaged poles exceeded 10% after 65 years of service. Based on these results, the standard service life of utility poles is set to 65 years, and a maintenance and rebuilding guideline for utility poles was organized for 2021 [5]. The poles installed in the 1970s have reached the point where they need to be repaired orreconstructed according to this standard service life. However, if rebuilding and repair plans are developed based on the standard service life, the number of poles built since the 1970s is approximately 80,000 per year, compared to a yearly replacement capacity of 30,000 poles per year, and there is concern that the annual number of poles to be rebuilt will exceed the construction capacity of local power companies. In addition, the standard service life expectancy is not optimal because the results are organized only from a visual survey of the external appearance mentioned above and have not been adequately evaluated from a structural dynamic perspective.  
To improve the efficiency of pole maintenance, it is essential to organize the deterioration process and replacement indicators based on the structural dynamic of concrete utility poles and suggest methods for evaluating deterioration using non-destructive testing.  
This paper reviews previous technical trends and challenges in the efficient maintenance of concrete utility poles by summarizing existing research on the subject.  
\begin{table}
\begin{tabular}{c c c} \hline
**City** & **Undergrounding Rate (\%)** & **Inspection Year** \\ \hline Tokyo & 7 & 2015 \\ \hline Osaka & 5 & 2015 \\ \hline London & 100 & 2015 \\ \hline Paris & 100 & 2015 \\ \hline Washington D.C. & 65 & 2012 \\ \hline New York & 85 & 2016 \\ \hline Taipei & 85 & 2015 \\ \hline \end{tabular}
\end{table}
Table 1: Undergrounding rate of utility poles [2].  
Figure 1: Japanese standard utility pole (prestressed concrete pole).