to 15s. per cubic yard, according to the quality and proportion
of the cement, and the facility with which the other materials
can be obtained. Lime concrete costs from 6s. to los. per cubic
yard. Portland cement costs from is. 8d. to 2s. per bushel.
In some iron bridges constructed by A. Handyside & Co.,
as part of the new Holborn Viaduct, London, where very heavy
traffic has to be sustained, the roadway was formed of granite
"setts" laid upon concrete specified by Mr. Haywood, the
Engineer of the Corporation, as follows : — •

" The foundation for the granite pavement is to be formed in
the following manner : — A layer of concrete 9 in. thick, com-
posed of six parts ballast to one of Portland cement of the best
quality, ground extremely fine, and weighing not less than no
lbs. to the imperial striked bushel, is to be first spread over
the iron covering plates. The surface of this layer of concrete
is to be carefully levelled and well grouted with liquid cement,
so as to form a perfectly smooth surface. When it is com-
pletely dry and set, a composition of tar, asphalte, and tallow,
mixed in such proportions that it shall not be brittle, but always
be slightly soft and elastic under all conditions of temperature,
shall be spread over the concrete in two thicknesses, amounting
altogether to | in. This asphalte is to be turned up or flashed



94 Works in Iron.
