Civil Engineering

Hiroshi Yokota

Making Social Infrastructure Stronger and Longer Lasting

Hiroshi Yokota , Professor

Faculty of Engineering, Graduate School of Engineering (Civil Engineering Course, Department of Socio-Environmental Engineering, School of Engineering)

High school : Tokushima Prefectural Jonan High School

Academic background : PhD from the Tokyo Institute of Technology

Research areas
maintenance engineering
Research keywords
social infrastructure, maintenance, spatial variability

Civil engineering is the Earth’s doctor

What does the term “civil engineering” bring to mind? Is it the construction work that you regularly see? Or is it large structures or facilities such as tunnels, bridges, and airports? “Civil engineering” is a very wide-ranging discipline of science for helping people to realize healthy, comfortable lives and studying how to ensure the sustainability of human activities (civilized activities) in future generations. To this end, civil engineering plays the role of medical doctor and makes improvements to various problems on Earth to restore health, including protecting and creating a good environment, preventing and mitigating natural disasters, and planning, improving, and maintaining social infrastructure.


What is your goal?

Social infrastructure provides support to human activities, and I am studying methods to make such infrastructure healthy and as long lasting as possible. Facilities come to suffer many problems over long-term use, even those that boast exquisite beauty and splendor in their just-completed conditions. Photo 1 shows a concrete structure suffering from chloride-induced damage. Because concrete is weak against tensile force, reinforcing bars are arranged inside to make up for this weakness. The safety of this structure has been lost as the reinforcing bars were fractured due to chloride-induced corrosion. On the other hand, Photo 2 shows damage caused by the repetition of freezing and thawing. In cold, snowy regions such as Hokkaido, moisture within concrete can be repeatedly frozen and expanded to cause cracks and peeling. I have been studying how to prevent deteriorations such as these, how to forecast residual life in the event of a deterioration, and how to treat (repair) structures in the event of a deterioration, successfully developing the most effective and economical maintenance practices. These studies represent an aspect of civil engineering as being referred to – being a medical doctor of social infrastructure, as it were.

Photo 1 A concrete structure with re-bar corrosion

Photo 2 A concrete structure with freezing damage



How do you carry out your studies?

The two phenomena (degradation phenomena) introduced by the two photos above are greatly varied and present wide variability in both temporal and spatial terms. I am considering investigating the spatial variability of these degradation phenomena, substituting a mathematical model, and using it for prevention and making prediction. To this end, I have collected test samples from structures that had been in actual use for a long time (Photo 3), and carried out detailed analysis regarding the condition of the concrete and reinforcing bars embedded inside (Photo 4). Once processed, the results will be utilized to develop approaches for enhancing the accuracy of residual life analysis and forecast the residual life extension effect of repairs.

If the progress of degradation has spatial variability as shown in Fig. 1, variability in forecasting the residual life is as shown in Fig. 2 according to the extreme value statistical model. Residual life is forecast to be about 19 years at a probability of over 95%; however, with the standard deviation being ±11 years, there is still a large deviation.

In addition to surveys of these actual structures, test specimens created in the laboratory are stored under various environments to reproduce within a short period of time the progress of degradation that would take 100 years under normal conditions. The results are compared with actual phenomena and utilized as data for modeling.

Photo 3 Collection of test samples from an actual structure

Photo 4 Analysis of test samples (measurement of the dispersion coefficient and salt content)


Fig. 1 Variability in degradation phenomena

Fig. 2 Probability distribution of residual life forecast results


What is your next goal?

I will clarify and propose what kinds of surveys and tests can be used to enhance the accuracy of residual life predictions. In addition, by assessing the total cost required from the creation of a structure until its eventual disuse, the asset value of the structure, etc., I will propose an assessment method for determining what mindset is most desirable to adopt in carrying out remedial action such as repair. My aim is to bring about the use of such a mindset in the maintenance practices of actual facilities, and establish an approach that will make social infrastructure around the world stronger and longer lasting.