Associate Professor Hitoshi Hamasaki of Shibaura Institute of Technology announced the results of a research conducted by the research team of the Architectural Institute of Japan since 2011 to repair reinforced concrete (RC) buildings on Gunkanjima in Nagasaki Prefecture. On July 2015, 7, a part of Gunkanjima was registered as a UNESCO World Cultural Heritage Site as "Meiji Japan's Industrial Revolutionary Heritage".However, the RC building on Gunkanjima has been exposed to salt damage and wind and rain for many years, and is in danger of collapsing due to aging.There is an urgent need to take measures to preserve these as they are registered as World Heritage Sites.
Preservation of aging RC buildings is unprecedented in the world and is extremely difficult.The challenge is to curb aging without compromising historical value.Preservation and restoration of historic buildings is possible
(1) Use the same materials and construction methods as at that time
(2) Do not change the appearance as much as possible
(3) If the appearance changes, it can be clearly distinguished from the original and can be restored.
It is a condition that it meets.Of these, (1) is not possible, so Associate Professor Hamasaki aims to repair it by satisfying the requirements of (2) and (3).Therefore, we examined the effectiveness of a method of repairing corrosion of reinforcing bars using a substance called lithium nitrite.This is because lithium nitrite has the effect of forming a protective film to prevent further corrosion of iron.
Rust on the reinforcing bars is the main cause of concrete collapse.Since cement, which is the raw material of concrete, is alkaline, it suppresses the oxidation of iron, but as the neutralization and penetration of salt progress over the years, the reinforcing bars become rusty.Focusing on this point, it is said that the preservative lithium nitrite can stop iron rust without changing the appearance of the untouched concrete at that time.This experiment confirmed the effectiveness and required amount of lithium nitrite in the field.
If the building is successfully preserved on Gunkanjima, it is expected to be useful not only for the preservation of other historical buildings but also for stopping the expected deterioration of social infrastructure and extending the life of the building.
Source:[Shibaura Institute of Technology] Announced research on maintaining the buildings of the world heritage site "Gunkanjima"