IAC News

Shinobu Kurokawa
(Hokkaido Regional Development Bureau, Ministry of Land, Infrastructure, Transport and Tourism)
 

1. Overview
The Port of Wakkanai’s North Breakwater Dome was built in 1936, playing an extremely important role as a facility to protect people and cargo set to travel along the Wakkanai Route, which connects Hokkaido and Sakhalin, from high waves and strong winds. Nowadays, in addition to this role, the North Breakwater Dome also undertakes a new role in showcasing history and culture as a tourist facility that holds local events and is bustling with tourists, as well as a JSCE Civil Engineering Heritage Site and a Hokkaido Heritage Site. The Hokkaido Regional Development Bureau undertook full-scale renovation work to upgrade the superstructure from the footing beams for over three years from 1978, recreating the original design as it was back in 1936. Approximately 40 years has passed since the renovation work and the North Breakwater Dome has seen the reemergence of deterioration, particularly corrosion of the rebars on the outside of the arch made of concrete slabs.

The North Breakwater Dome has a unique structure and an expansive arch made of concrete slabs. As the material performance assessment and repair scope were different to that of a general port facility, developing a repair plan that met the necessary performance standards within the confines of existing knowledge proved to be challenging.

Therefore, for this project, a unique judgment criteria to ensure preventive maintenance of the North Breakwater Dome was conceived and a maintenance approach for the outside of the arched slab area was formulated, with repairs conducted based on these.

2. Forming maintenance approach using degradation map and impact of approach
In recent years, while technical standards for maintaining the reinforced concrete structures have been established, there is limited knowledge for assessing the extent of damage based on inspection results and deriving optimal measures according to that assessment, and thus establishing precise methods for conducting specific repairs has been an issue. A new concept called the “degradation map” was conceived to tackle this issue. The degradation map is an assessment of the deformation of the inspection and diagnostic scope of each area by dividing the extensive scope into grid-like areas, categorizing the state of degradation into five levels of deterioration linked to the risk of rebar corrosion.

It was possible to optimize repair costs and make appropriate repairs by establishing repair methods on an area-by-area basis not only for the current state of the facility but also for predicting the progression of future deterioration and associated performance decline, as well as implementing appropriate preventive maintenance measures in accordance with said predictions.

The impact of the approach was as follows.

1)    Improved work efficiency
The degradation map turned the visual inspection deformation records into numerical data, and by plotting this data, we could understand deformation trends visually and simply across a broad spectrum.
The degradation map links the deformation with the risk of rebar corrosion, and therefore it is possible to ascertain the rebar corrosion state of materials.

2)    Reduced costs
For the North Breakwater Dome, it was possible to reduce the repair costs compared to conventional reactive maintenance by drawing up a preventive maintenance repair plan using the degradation map.

3)    Greater quality of maintenance
By carrying out strategic preventive maintenance with the degradation map created from the perspective of the risk of corrosion to rebars, the expenses required for inspections and repairs can be optimized, and by effectively inspecting through the simple monitoring efforts of visually inspecting the deformation, it is now possible to undertake reliable maintenance of the facility.

3. Repair approach for North Breakwater Dome
For the approach for repairing the outside of the arched slab area of the North Breakwater Dome, a construction method to remove the chloride ion and repair the rebars of the areas of degradation level three and above was selected using an area two meters by two meters as a reference in consideration of preventing cracks during making reinforcements, pour joints, and repairs, based on a preventive maintenance plan using a degradation map.

The degradation level three area was an area where the concrete was chipped away up to a depth of 5.5 cm, exceeding the chloride ion threshold concentration that initiates corrosion, and it was decided to repair the cross-section with fiber-reinforced polymer cement mortar. The degradation level four and above area was where the concrete was chipped away up to 1 cm behind the rebars (a depth of 16 cm), and it was decided to repair the cross-section with fiber-reinforced polymer cement mortar after subjecting the rebars to anti-rust treatment.

The repair work of the outside of the arched slab area was carried out from fiscal 2016 and was completed in fiscal 2022. By monitoring deformation through regular visual inspections and continuously updating the degradation map even after these repairs, appropriate maintenance is now possible and reduction in maintenance costs can be expected.

4. Infrastructure Maintenance Project Award winner
The Port of Wakkanai’s North Breakwater Dome Preventive Maintenance Project won the JSCE 2022 Infrastructure Maintenance Project Award. I would like to take this opportunity to thank all the experts who provided guidance, the consultants who conducted the surveys and design work, the construction company that undertook the construction work safely, the facility users and related parties who helped implement the project, as well as everyone connected to the project at the Ministry of Land, Infrastructure, Transport and Tourism.

 

Cross-Section of North Breakwater Dome

Table 1 Categories of Degradation in Degradation Map

Deformation Record and Degradation Map

Repairs to North Breakwater Dom

【Reported by Sinobu Kurokawa, Director of Engineering Works Division, Wakkanai Port Office, 
Wakkanai Development and Construction Department, Hokkaido Regional Development Bureau, 
Ministry of Land, Infrastructure, Transport and Tourism】

 

International students visit MLIT

【Reported by Concrete Committee, JSCE】