ABSTRACT
Concrete structures are indispensable for disaster prevention. At the same time, its inorganic characteristics sometimes are pointed out as a symbol of environmental destruction. In Japan, concepts of ecological consideration were incorporated into River Act and Seacoast Act in the 1990s, and shapes of concrete structures have been modified. However, most of these are mitigation of environmental impacts due to development activities such as reclamation, and they were born from the conflict of “development” versus “environment”. Under these circumstances, the authors have developed SUBPLEO FRAME 1) (SPF) which can increase sliding resistance of a breakwater, and Environmentally Active Concrete 2) (EAC) using amino acids. They can achieve both “disaster prevention” and “environmental conservation”.
In this paper, examples realized improvement of the surrounding marine environment while firmly demonstrating the disaster prevention function are introduced.
Example 1
In the restoration of the north breakwater of Hachinohe port, which suffered tremendous damage due to the Great East Japan Earthquake Tsunami, SPF was adopted as a resilient structure. SPF is a structure that charges filling stones into a concrete frame block, and is installed behind a breakwater caisson. It can increase sliding resistance of the caisson embankment by interlocking of the filling stones restrained by the frame block and the rubble mound stones. The size of the inner frame is 1.8m x 1.8m (depth 1.5m), and the mass of the single filling stone is around 30kg. Since the filling stone has many voids and roughness on the surface, suspended materials such as silt settled down are hard to accumulate, and a variety of benthos habitats are created. In the breakwater at Hachinohe port, SPF and foot protection block are installed adjacently and are in the same environment. After 2 years of installation, many algae and marine organisms are inhabited in SPF. On the other hand, since the surface of the foot protection block is flat, the suspended materials are accumulated, and there are almost no algae and marine organisms. Normally, stones of about 30 kg are scattered by relatively-small overtopping waves and flows. However, because the filling stones of SPF are inside the frame block, they can stay there by shielding effect. Moreover, each height is 1.5m, and it can be piled with 2 steps, 3 steps, and used even in deep water places. Thus, SPF has a disaster prevention function (physical resiliency) and an environmental improvement function (creation of growth and habitat environment of living things).
Example 2
In the breakwater at Wajima port in Ishikawa Prefecture and the revetment of Shimonoseki coast on Yamaguchi prefecture, the EAC panels are attached to the concrete armor units which play an important role to protect main revetment body. EAC is a concrete mixed with Arginine which is one of amino acids, and it is confirmed that the growth rate of microalgae on the block surface is 5 to 10 times that of ordinary concrete. After 2 years of installation, not only are there many algae growing on the EAC panel, but the gaps created by the panels become a hiding place for shellfish. Moreover, after one year of installation in Shimonoseki port, the EAC panels have a lot of algae flourish than the ordinary concrete panel. In this way, the concrete blocks for disaster prevention, attached with the EAC panels as an environment-conscious product, can contribute environment conservation and further improvement of the fishing ground productivity.
As described above, by utilizing the stone materials and the EAC, it is possible to contribute to realization of Agenda 2030: the Sustainable Development Goals (Goal 14: Conserve and sustainably use the oceans, seas and marine resources for sustainable development). In this paper, the details of the above examples and the example of shellfish gathering effects are also introduced.
Reference
1) H. Matsushita, 2013. Breakwater Reinforcement Method against Large Tsunami, PIANC Yearbook 2013.
2) K. Sato et al., 2011. Characteristic of Periphytic Algae on Concrete Contained Amino Acid, 9th International Conference on The Environmental Management of Enclosed Coastal Seas.