[55]. Johnson’s Materials of Construction, 5th Edition, 1918, p. 432.
[56]. Trans. Am. Society of Civil Engineers, Vol. 59, 1907, p. 146.
[57]. L. N. Edwards, Trans. Am. Society Testing Materials, 1918, and R. B. Young, Eng. News-Record, Vol. 82, 1919, p. 33.
[58]. Bulletin No. 1, Structural Materials Research Laboratory, Lewis Institute, Chicago, Illinois.
[59]. Proportioning Concrete by Voids in the Mortar, A. N. Talbot, read before Am. Society Testing Materials, June 22, 1921. Abstract in Eng. News-Record, Vol. 87, 1921, p. 147.
[60]. Trans. Am. Society of Civil Engineers, Vol. 81, 1917, p. 1122.
[61]. See also Tentative Specifications for Concrete and Reinforced Concrete submitted by the Joint Committee to its Constituent Organizations, June 4, 1921.
[62]. Journal Illinois Society of Engineers for 1916, p. 75.
[63]. See A. S. T. M. Standards for 1918, p. 148.
[64]. Trans. Am. Society Civil Engrs., Vol. 82, 1918, p. 459.