ABSTRACT
Light microscopical studies of the products of cement hydration progressed in parallel with those on the constituents of clinker, the cement often being hydrated as thin layers on microscope slides, for example, Ambronn (1909), Stern (1909), Read (1910) and Klein and Phillips (1914). The last is particularly noteworthy: Klein and Phillips - building on the work of Shepherd et al. - prepared and hydrated synthetic compounds (CA, C5A3, C3A, CS, 7-C2S, |3-C2S and C3S) and observed the changes by petrographic methods. They described the process of hydration of Portland cement itself in some detail. A good example of their results is the conclusion that the disintegrating action attributed to the crystallization of 3CaO • A12O3 • 3CaSO4 • xH2O had been greatly exaggerated since such crystals were extremely small and began to form before the cement had set. Such studies contributed much, of course, to early theories of cement hydration: to the 'crystalloids'11 against 'colloids'12 debate. It is of relevance to the later discussion on electron microscopy studies of dispersed particles to note that in preparing their specimens many early petrographers recognized the need to exclude CO2; for example, Read (1910), and Klein and Phillips (1914).
