TOKYO -- Japan's leading general contractors have developed ways to make reinforced concrete hold out for far longer than the 100 years now considered the life span limit.
Concrete is made by mixing gravel and other aggregate together with cement and water. Reinforced concrete also incorporates a latticework of steel bars, which provide the strength that makes the material useful in a broad range of applications, from tall buildings to the support structures for roadways, bridges and tunnels.
In the case where the first steel bars are 5cm below the surface, the reinforced concrete lasts around 50-100 years before the rods begin to rust. The new technologies prolong the life span of the material by making it harder in various ways for the air and water to reach the bars.
For example, Shimizu has developed a way to minimize the gaps inside the concrete. The company first solidifies the concrete using a special mixture of aggregate and water, and then wraps the hardened concrete structure in sheets of polyethylene after removing the frame. These sheets curb the evaporation of water so there is less opportunity for spaces to form inside the concrete. Keeping the concrete wrapped over the course of six months reduces the volume of gaps by 75%, and Shimizu claims that this can prolong the life of the material to around 1,000 years.
The technology adds around 10% to the initial cost of construction, but Shimizu notes that it can cut down on expenses over the long term when future repairs and updates are taken into account.
Meanwhile, Takenaka has developed a way to make concrete using half the normal amount of water. By substituting a specially developed additive in place of the water, the concrete is less likely to form cracks as it dries.
In developing these technologies, the general contractors are looking at a market bound to grow as Japan updates infrastructure at the national and municipal levels. Outlays for the upkeep and other road work for Tokyo's metropolitan highway network alone is estimated at 630 billion yen ($6.1 billion).
Japan built much of its infrastructure during the economic growth years up through the 1970s and those structures are coming due for upgrades, given the 50-100-year life span of the reinforced concrete used in their construction. Of the roughly 700,000 highway bridges managed by municipalities, around 16% passed 50 years old in 2012 and the ratio will reach 65% in 2032.