"Generally, FC is designed to achieve a low compressive strength around 1–10 MPa [150 to 1,500 psi] and can be applicable in filling voids and restoring trenches but cannot be used in the construction of any structural member... To achieve the desired strength of at least 25 MPa [3,600 psi]... different innovative solutions... are economically and environmentally admissible..."
January 1, 1970
https://en.wikiquote.org/wiki/Foam_concrete