STATE GEOLOGIST. 129 
of the number stood in the air of the room. At the end of twenty-one 
days all were cut open. Unprotected steel subjected to similar tests was 
badly corroded. In the concretes wherever a crack or a void occurred 
the steel was more or less corroded. In neat cement no corrosion showed. 
Prof. Norton’s conclusions are: 
Ist. Neat cement thoroughly prevents rust. 
2nd. Concretes should be dense and without voids and mixed quite 
wet to prevent rusting the metal. 
3rd. Corrosion found in cinder concrete is mainly due to iron rust 
in the cinders and not to the sulphur. 
4th. Cinder concrete free from voids and well rammed wet is nearly 
as effective as stone concrete. 
5th. It is of the utmost importance that the steel should be clean 
when it is imbedded. 
THE ADHESION OF CONCRETE TO METAL. 
The necessity of taking additional precaution for preventing the 
separation of the metal and the concrete when placed under great strain. 
is viewed quite differently by the various experts in reinforced concrete 
construction. Prof. Bauschinger of Germany determined by a series of 
tests that steel or iron and cement adhere to the extent of 625 pounds per 
square inch of surface. Messrs. Krumm and Senter, civil engineering 
eraduates of the Ohio State University, found by a series of tests that one 
inch iron rods set 12 inches into neat cement mortar after 22 weeks, re 
_ quired a pull of 530 pounds per square inch of imbedded surface to draw 
them out. In a mortar of 1 cement to I sand, 12 to 16 weeks of age, it 
required from 723 to 772 pounds per square inch of adhering surface to 
extract the rods. Assuming the tensile strength of iron or steel at 60,000 
pounds per square inch and the adhesion of cement mortar to steel at 
625 pounds per square inch, round steel bars would need to be set 
but 24 diameters depth in the mortar to require the breaking limit of the 
bar in order to pull them from the cement. 
On the other hand, experts say that as soon as sufficient force has 
been applied to elongate the metal rod appreciably, the rod has then become 
lessened in cross sectional area, and as concrete is not elastic to any 
measurable extent such decreased rod area means a breaking away from 
the adhesion and consequently a decreasing reinforcement to the concrete. 
If, however, the bar is completely imbedded in the concrete and is 
gripped over each particle of its superficial area by a grasp equal to 625 
pounds per square inch, it must take a very much greater stress to begin 
the process of elongation. Some of the most successful armored concrete 
builders ignore any additional mechanical means of uniting metal and 
concrete. Among the number may be named Monier, Hennebique, 
Weber and others. On the other hand, Ransome, Thacher, Roebling and 
others provide special means to cause a more perfect union between the 
two materials. | 
9—S. G. 
