Inherent flaws within the material's protos-structure, such as molecular or atomic irregularities, can lead to weaknesses that manifest as cracks under stress or over time.
The most obvious cause. ProtaStructure calculates the required rebar for strength (ULS), but crack control often demands more rebar, especially smaller-diameter bars spaced closer together. If you use the "minimum reinforcement" option, cracks are likely. protastructure crack