Okayama: Firm Turns Oyster Shell Surplus into Sustainable Building Material

Courtesy of Daiwa Cres Co.
Concrete for gutters made with oyster shells

OKAYAMA — Efforts are underway to use oyster shells in cement at an Okayama-based concrete product manufacturer, as the shells have seen a reduced demand in chicken feed due to bird flu outbreaks in recent years.

Daiwa Cres Co. purchases oyster shells finely crushed from neighboring Hiroshima Prefecture, which is Japan’s largest oyster producer. The firm mixes the shells with cement, sand and gravel to make concrete. In Hiroshima Prefecture, about 80,000 tons of shells are estimated to be generated annually.

Oyster shells are typically pulverized for use in chicken feed and fertilizer. However, the avian influenza outbreaks between 2022 and 2023 led to the culling of many chickens, diminishing demand for feed and resulting in a surplus of shells.

Use of these shells for concrete was conceived in response to this issue and the product is already in use at the Hiroshima Prefectural Farming Fisheries Center in Takehara, Hiroshima Prefecture, for its gutters.

Daiwa Cres said that up to 12.5% of sand used for concrete can be replaced with oyster shells under its current production technology. Using a greater ratio of oyster shells, however, would fail to meet product safety standards in terms of salinity and require further pulverization. The company intends to conduct further research to increase the ratio of oyster shells in cement.