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Concrete is a mixture of sand, stone and cement that hardens into a rock-like mass when mixed with
water. Although known to the ancient Romans, concrete was not widely used for bridges until methods
of reinforcing it with steel were developed. Like stone, concrete has tremendous resistance to
compressive forces but relatively little tensile (bending) strength. Imbedding steel in the
concrete, however, gives it tensile strength as well.
The first reinforced-concrete bridge in America was built in 1889, but the material remained in an
experimental phase until the early 1900s. Bridge engineers found that varying the proportions of
the ingredients affected the strength of the concrete, and they tried several methods of
reinforcement, including steel beams, twisted bar, and cable, before settling on the ridged rod
still in use today.
Reinforced concrete had many advantages. The material itself was inexpensive, consisting mostly of
locally available sand and stone. Since concrete was also being introduced for dams, roads, and
buildings in the early 1900s, many Connecticut contractors quickly gained experience working with
the new material. Concrete also promised lower maintenance costs compared with metal trusses, which
required frequent painting and replacement of rusted components. The State Highway Department
recommended concrete for town bridge construction and built most of its own early bridges using
concrete.
Not all reinforced-concrete bridges were arches. Most of Connecticut's bridges from the 1920s and
1930s consisted of a single thick slab or a series of concrete beams. Arches, however, were used for
the State's larger bridge projects and for the many "City Beautiful" bridges erected in urban areas
in the early 20th century.
Take a virtual tour of Connecticut's historic concrete bridges via the links in the sidebar to the left.
