"Structural fibered foamed concrete with dissimilar densities of foamed concrete (1000, 1300, 1600, and 1900 kg/m³) [62, 81, 100, 119 lb/ft³] is essential for examining compressive, flexural and splitting tensile strengths, drying shrinkage and creep."
January 1, 1970
https://en.wikiquote.org/wiki/Foam_concrete