Good-quality natural stones used as mound materials and backfill materials for offshore construction work are decreasing, and from the viewpoint of preserving the natural environment, it is becoming difficult to collect and use them. At present, this trend is limited to some regions, but it is expected to spread nationwide in the future. On the other hand, about 36.5 million tons of concrete blocks were generated as construction by-products in 1995, but only about 65% of them were effectively used, and the remainder was landfilled. In this paper, in order to investigate the applicability of concrete blocks as gravel and ground materials, the mechanical properties and the elution properties of alkaline components, etc., are investigated.
　The strength constant obtained by a large-scale triaxial test using a concrete block immediately after crushing is 30 degrees or less, assuming that the apparent adhesive force is Cd=0.2kgf/cm2. On the other hand, when the results of the medium-sized triaxial test conducted with similar grain sizes are similarly arranged, φd can be secured at 35 degrees. From the above results, it was found that it is difficult to apply the concept of similar grain size to materials such as concrete blocks where individual grains are non-uniform. According to the results of the elution test, it was confirmed that the eluted water from the concrete block satisfies the ``Ocean Disposal Regulations''.