Redefining compatibility of eco-friendly concrete: Explicit parameters and implicit prerequisites for Japanese RC design

To achieve a carbon-neutral society, a diverse array of environmentally friendly concretes , distinct from conventional concrete, has been proposed. However, the uncritical application of these new materials to existing reinforced concrete (RC) structural design frameworks harbors significant risks. This is because existing design methods are predicated on fracture behaviors and deformability that ordinary concrete possesses "implicitly." This study aims to identify the "Compatibility Range" within which new materials can align with current RC design methods, evaluating both explicit and implicit indicators. First, we defined quantitative allowable ranges for "explicit design parameters", such as the relationship between compressive strength and Young's modulus, creep, and drying shrinkage, to ensure structural safety. Furthermore, we codified "implicit performance requirements", properties traditionally taken for granted but potentially lacking in new materials, specifically: crack dispersion by aggregates, energy absorption equivalent to concrete, and the avoidance of rapid strength loss under cyclic loading, as essential conditions for structural design. The findings of this study go beyond mere comparisons of material properties; they define the boundary conditions under which new concretes can behave as "structural concrete," serving as a fundamental criterion for future standardization.