Experiments on Concrete and Iron.

Progress, Volume II, Issue 2, 1 December 1906, Page 46

Experiments on Concrete and Iron.

lii the course of the construction of the East Boston tunnel the engineers of the Boston Transit Commission made some interesting experiments to determine how rusting of iron was affected byconcrete. The results are reported m the Commission's Tenth Annual Report, as follows — To Indicate Whether Iron Rusts When Embedded in Concrete. Nine strips of sheet iron (2 in. x 6 in.) were cleaned till their surfaces were bright and free from rust. Then they were embedded in concrete, moulded into the form of a hollow cylinder, the outside dimensions of which were 14 in. x 20 in., the walls being 3 in. thick. This cylinder, when hardened, was kept filled with water, and was placed in the tunnel. At first the water percolated through the concrete very readily, but the amount of percolation gradually diminished so that at the end of about two months the cylinder became practically watertight. At the end of two years the sheet-iron strips were removed from the concrete and examined. They

were found to be free from any rust, and in as bright condition as when placed in the concrete. The concrete was made in the proportions of i barrel of Portland cement, 9 cv. ft. of stone dust, and 1 1 cv. ft. of broken stone. To Indicate Whether Steel Imperfectly Cleaned is Preserved from Further Rusting by Embedding the Same m Concrete. A square plate (4 x 4 x \ 111 ), which had become badly rusted, was cleaned by filing till its general surface was bright, but the rust still remained m the numerous small pits. This plate was then surrounded by about i\ in. of concrete, moulded in the shape of a square block. The concrete was proportioned as follows 1 barrel of Portland cement, 9 cv. ft. of stone dust, 1 1 cv. ft of broken stone. The concrete block, when hardened, was placed in water for three or four days, then taken out and dried in air for three or four days. This process of first wetting and then drying was continued for two years, and then the plate was removed from the concrete and examined. The portion of the plate that was bright had remained unchanged. There was apparently no increase of rust m the small pits, but in some of them the colour had changed from the originally reddish brown to a yellow. Professor Norton, of the Massachusetts Institute of Technology, judges this to be merely a change m the composition of the old rust and not a formation of the new rust Two other pieces of steel treated in the same way gave the same results.