Unclear on that first point. The authors claim 26 MPa for CoRncrete, which is about the same as the higher end of the range of concrete (~28 MPa) but much cheaper. On the other hand, it sounds like the paper's saying it's also much less durable.
I wouldn't count anything under 40 MPA as "high strength concrete" at all. Thats where high strength concrete starts for me. High strength concrete mixes can go up to 180-200 MPA although thats some crazy specialty stuff for very niche uses.
25 mpa concrete is "i'm doing my driveway" concrete or "I bought a bag at home depot" concrete not high strength concrete.
