The mammoth earthquake and tsunami that resulted in the death of tens of thousands and wiped out coastal cities in northeast Japan left the region to deal with 22 million tons of rubble, perhaps the biggest recycling challenge ever. It examined a way of manufacturing the concrete block as substrata for seaweed, which used concrete rubble. The postpacked and prepacked concrete using recycled coarse aggregate, concrete rubble were experimented. As the result, the postpacked method was easy for the blocks as seaweed breeding reef to be composed. At the earthquake-stricken district, concrete blocks as seaweed breeding reef were manufactured using the concrete rubble in March, 2012. Seaweed on the block which were mounted in Otsuchi area in Iwate pref. were observed in April, 2013. Seaweed on the block was observed to 13 months after mounting. Cover of the seaweed on the block was 100 %. On the natural rock, it was 80%.
