Low-Temperature Portland Cement.-A very good description of the low-temperature cement being used for constructing Boulder Dam is furnished by G. R. ROBERTSON in the March, 1935 Industrial and Engineering Chemistry.
It is generally known that concrete gives out heat during its setting up period. With concrete structures of ordinary size, the heat produced by hydration, escapes freely and causes no concern.
However, with so great a mass as that of Boulder, dam, which is essentially a monolith weighing about 7 million tons, normal temperature could not be attained in its depths much before the passage of 200 years. Such a condition would be intolerable, for the interior would be at a very high temperature while the exterior portions will have already radiated their heat and become fully contracted.
No concrete structure embodying such a simultaneous combination of expanded and contracted sections could endure for long. Cracks would occur throughout and the mass would never develop the maximum strength intended.
Obviously, care was necessary in order that the concrete in Boulder Dam should not become overheated and require a correspondingly longer time in which to cool.
One very good precaution was that of using a cement which would set with the development of much less heat. Fortunately this was easy to do since here was one instance where research had kept pace and even slightly surpassed the demands of the industry.
Thus, it is generally agreed today that Portland cement is composed of four major constituents: