STATE GEOLOGIST. 4] 
CHAPTER II. 
RAW MATERIALS OF THE CEMENT INDUSTRY. 
In this chapter will be taken up the various raw materials of the 
four kinds of hydraulic cements, taken in the order of the classification 
adopted, which brings the highest class of cements as the last and most 
complex of the series. ‘ 
RAW MATERIALS FOR POZZUOLANE CEMENT. 
In the oldest type of hydraulic pozzuolane materials we have as the 
main constituent a substance containing hydrous silicic acid which on 
the simple addition of slaked lime becomes a hydraulic cement. These 
materials show extreme variety in composition and physical behavior. 
Modern metallurgical processes furnish us in addition artificial pozzuo- 
lanes which are finding application as valuable cement materials. We can 
thus distinguish natural and artificial pozzuolanes. 
We have no natural pozzuolanes in Ohio, and yet they deserve some 
discussion due to the fact that as an addition to Portland cement for work 
in sea water they have shown valuable properties. Owing to the great 
solvent action of sea water on concrete, the question of the life of 
cement work has become an extremely important one. ‘There is no doubt 
but that some concrete work exposed to sea water has suffered consider- 
ably, and the knowledge of the fact has caused apprehension on the part 
of engineers, many of whom still look with suspicion upon cement as a 
proper material to be subjected to the action of sea water. Since the 
capital involved in concrete construction of this kind is enormous, it has 
become a vital task to users as well as sellers of cement to study the 
behavior of this material under various conditions and to devise means 
of improving it when necessary. 
The principal natural pozzuolanes are pozzuolane proper, trass and 
santorin-earth. All of these when mixed with slaked lime harden and 
form a hydraulic mortar. 5 
The pozzuolane proper is a hydrous, volcanic, porous rock whose 
specific gravity is from 2.3 to 2.55, found in Italy, especially near the 
