Engineering Wonders of the World
Volume I

REINFORCED CONCRETE CONSTRUCTION. 419 brick construction, engineers began long ago to introduce cast-iron columns into structures of various kinds, the object being to obtain strength and stiffness with a minimum ex- penditure of material. Cast-iron beams were also applied instead of stone or brick arches combination embodying concrete and steel, so applied that the distinctive properties of each are utilized to the fullest extent. Concrete is by no means new as a structural material. Briefly defined, it is a variety of artificial stone formed of pebbles or stone Fig. 1.—CONGLOMERATE, OR PUDDINGSTONE, A NATURAL FORM OF CONCRETE. Fig. 2.—CONCRETE MADE WITH PEBBLES, SAND, AND PORTLAND CEMENT. I to carry walls and floors in buildings, and to support road platforms in bridges. Cast iron, however, was not altogether satis- factory because of its brittle nature, and of the fact that its resistance to tension is little more than one-sixth of its re- Cast-Iron and • , , . . _. , r> sistance to compression. After Steel Beams. r a time wrought iron was pro- duced in the form of rolled beams and other convenient sections, which enabled engineers and architects to make further advances in scientific construction ; and finally came mild steel—a still more useful variety of iron, costing no more than ordinary wrought iron, though possessing one and a half times the strength of that material. Nevertheless, we are to-day in the early stages of yet another revolution, due to a chips cemented together by hydraulic or other mortar. Therefore it resembles very closely those types of natural rock described by geologists as What C°n- “ conglomerate.” (Compare e e 1S* Figs. 1 and 2.) But as’produced in the present day, with Portland cement mortar as the cementitious substance, and small, carefully- graded pebbles or fragments of hard rock, high-class concrete is stronger and more dur- able than similar conglomerates turned out from the laboratory of Nature. The skilled maker of concrete for combina- tion with steel employs pebbles or stone chips in assorted sizes from j-inch to |-inch across (see Fig. 3). He gauges the volume of voids or air spaces between the particles of stone, and adds sufficient mortar to fill up all such