A compact cinder concrete has proven about as effective a protection for steel as stone concrete. The corrosion found in cinder concrete is mainly due to iron oxide or rust in the cinders, and not to the sulphur. The amount of sulphur in cinders is extremely small, and there seems to be little danger from that source. A steel-frame building erected in New York in 1898-had all its framework, except the columns, imbedded in cinder concrete; when the building was demolished in 1903, the frame showed practically no rust which could be considered as having developed after the material was imbedded.

125. Practical Illustrations

Cement washes, paints, and plasters have been used for a long time, in both the United States and Europe, for the purpose of protecting iron and steel from rust. The engineers of the Boston Subway, after making careful tests and investigations, adopted Portland cement paint for the protection of the steel work in that structure. The railroad companies of France use cement paint extensively to protect their metal bridges from corrosion. Two coats of the cement paint and sand are applied with leather brushes.

A concrete-steel water main on the Monier system, 12 inches in diameter, l 6/10 inches thick, containing a steel framework of 1/4-inch and 1/16-inch steel rods, was taken up after 15 years' use in wet ground, at Grenoble, France. The adhesion was found perfect, and the metal absolutely free from rust.

William Sooy Smith, M. Am. Soc. C. E., states that in removing a bed of concrete at a lighthouse in the Straits of Mackinac, twenty years after it was laid, and ten feet below water surface, imbedded iron drift-bolts were found free from rust.

A very good example of the preservation of steel imbedded in concrete is given by Mr. H. C. Turner (Engineering News, Jan. 16,

1908). Mr. Turner's company has recently torn down a one-story reinforced-concrete building erected by his company in 1902, at New

Brighton, Staten Island. The building had a pile foundation, the piles being cut off at mean tide level. The footings, side walls, columns, and roof were all constructed of reinforced concrete. The portion removed was 30 by GO feet, and was razed to make room for a five-story building. In concluding his account, Mr. Turner says:

"All steel reinforcement was found in perfect preservation, excepting in a few cases where the hoops were allowed to come closer than 3/4 inch to the surface. Some evidence of corrosion was found in such cases, thus demonstrating the necessity of keeping the steel reinforcement at least 3/4 inch from the surface. The footings were covered by the tide twice daily. The concrete was extremely hard, and showed no weakness whatever from the action of the salt water. The steel bars in the footings were perfectly preserved, even in cases where the concrete protection was only 3/4 inch thick."