336 ANNUAL REPORT 
CHAPTER IX. 
THE PROPERTIES OF PORTLAND CEMENT AND THE 
TESTING OF CEMENT. 
The subject will be considered under the following headings: 
1. Hydration and heat of hydration. 
2. Setting and hardening. 
3. Tensile and crushing strengths. 
4. Constancy in volume. 
5. . Specific. Sravity. 
6. Fineness of grain. 
7. Some physical and chemical constants. 
8. The effect of various reagents on the properties of Portland 
cement. 
g. The enduring qualities of Portland cement with special ref- 
erence to the action of sea water. 
to. American standard specifications. 
HYDRATION. 
rt. On adding water in proper quantity to Portland cement it is found 
to stiffen gradually until it becomes so hard that the mass cannot be pene- 
trated by a rod. Under the microscope white, needle-like crystals of cal- 
cium hydrate are seen to grow rapidly, and the grains of cement appear 
to swell, forming a mass of colloid particles. The phenomenon of hard- 
ening must, in the nature of the case, be strongly analogous to the 
crystallization of supersaturated solutions.* The more the crystal sur- 
faces in contact are developed, the greater the total adherence and the 
strength of the mass. Crystals in long plates or in interlocked fibers should 
give greater strength than blunt and heavy crystals. But the result of 
this crystallization depends on many factors, the degree of supersatura- 
tion, 1. e., the amount of water present, the fineness of the salt and many 
other conditions. At the same time the production of the colloid par- 
ticles, distinct from the crystals of lime hydrate, raises the question 
whether the hardening due to hydration might not be due to the drying 
of the greater mass of colloid material. This question has not as yet 
*Chatelier, Engineering Congress, Chicago, 1893, 
Trans. Am. Inst. Min. Eng., 1893. 
