21,4 Witt: Cement and Concrete 371 
to the calicium oxide is unlimited. A number of disintegrated 
concrete tiles recently examined contained sulphuric anhydride as 
high as 50 per cent of the calcium oxide present. 
In the first paper it was stated that— 
The great variety of uses which modern industry is finding for concrete 
is continually presenting new problems for research and likewise increasing 
the importance of work that was completed at a time when the theoretical 
side was perhaps the only one under consideration. * * * This field 
of research is becoming more important year by year, because of the many 
new demands being made on the material. Sewer and drain pipe, storage 
tanks for various liquids, and even boats are now made of concrete. There- 
fore it is not suprising that the material should be called upon to resist 
conditions which were not known a few years ago. 
These statements are even more applicable to-day than they 
were five years ago. Notwithstanding the retarding influence 
of the World War, when labor, fuel, equipment, and transporta- 
tion were all difficult to obtain, more cement has been produced 
in the United States during the last two years than during 
any other two years in the history of the industry. Develop- 
ment of new uses for cement has kept pace with the increase 
in production of the material and we are approaching that time 
when, according to Sunderland,* everyone will have the privilege 
of studying in a fireproof concrete schoolhouse, living in a city 
paved and drained with concrete, traveling all over America 
on concrete roads, and finally being buried in a concrete coffin. 
During the last few years there has been great activity in 
the manufacture of various substances to modify the properties 
and behavior of cement. There are hardeners, set accelerators, 
antifreeze mixtures, waterproofing compounds, and paints and 
coatings for decoration and protection against various sub- 
stances. There are compounds for making cement more econom- 
ical, for increasing the early strength, for increasing the ultimate 
strength, for increasing density, and for decreasing density. 
Without discussing the merits of these compounds, it may be 
readily seen that they introduce many new problems. 
* Address by L. T. Sunderland, president of the Portland Cement Asso- 
ciation, May 16, 1921. tes 
