THE Microscopic Structure of Hydrated Portland Cement
L. T. Brownmiller
Appears on pages(s):
Microphotographs illustrate the structure of neat hydrated portland cements as seen in reflected light. They show that a considerable amount of unhydrated cement remains in Type I and Type II cements after hydration for 28 days. Type I II cements show much smaller percentages of unhydrated material even at earlier ages. Most of the principal constituents of the original clinker can be recognized in the unhydrated fractions. The photographs give no evidence that any major constituent of the cement is selectively or completely hydrated at any age. The rate of hydration depends more specifically on the surface exposed to the action of the water than on the chemical constitution. The effects of laitance formation are shown by illus-trations of the difference in particle size distribution in the laitance as compared to that within the main body of the cement. Other photoaraphs show the size, amount, and dis- tribution ’ of the Ca(OH) z which i’s liberated during the hvdration processes. It is estimated that about 15 oercent of Ca(OH)? has formed at 28 days in the cements examined. ’ the polishing and etchfng tech- niaue described could be applied readily for the preparation of specimens for’ accurate measurement o f t h e Ca(OH) 2 by mechanical devices such as a Wentworth micrometer. The final photographs show some detail of the structure of the hydrates other than the Ca(OH)z. That structure is extremely complicated, but a further development of microscopic technique should be useful in solving some of the riddles which confront cement technicians in attempting to evaluate cements on the basis of performance in concrete.