Concrete for 100 years

It is said that the saying “the soul of a child of three is the same at 100” also holds for concrete. In general, a concrete formwork is removed about one week after casting the concrete, but at the moment that the formwork is removed, water evaporates from the concrete surface. Drying in newly cast concrete is something to be prevented since it hinders a hydration reaction in the concrete, which can cause cracks to form resulting in a structure lacking long-term durability. Improving durability here requires much effort. On the other hand, if a sheet or similar is used to confine water from the moment the formwork is removed and the newly cast concrete is carefully cured, a concrete structure having a long life of more than 100 years can be obtained.

There are a variety of approaches to applying the idea behind “the soul of a child of three is the same at 100” to concrete technology, but we have focused on curing. Specifically, we have developed technology that first sticks a dedicated sheet to the inner side of the formwork that makes contact with the concrete, then casts the concrete, and finally leaves the sheet on the concrete surface after removing the formwork. For this dedicated sheet, we selected materials with high water-confining performance, superb ultraviolet light resistance, and little change in length due to temperature changes. We also discovered that increasing the water repellency of the sheet significantly decreases surface voids resulting in a beautiful finish. Additionally, we found that leaving the sheet for as long a period that construction conditions allow and performing curing to prevent evaporation of water over a long period of time results in a fine concrete surface while slowing down the ingress of degrading factors such as chloride thereby achieving a long-life structure. It took three years to achieve technology for improving this dedicated sheet and leaving the sheet after formwork removal and another three years for making further improvements.

A key feature of the developed technology is an improved appearance, and for this reason, we have named it the “Utsuku (Beautiful) Seal Curing Method.” As of 2020, we have applied it to approximately 15,000 m2 at over 20 sites with the aim of improving durability in concrete structures. From here on, we plan to expand its application to sites that need to improve productivity in addition to improving the quality of concrete structures.