As with steel, whole careers are dedicated to the development of new and improved concrete mixes, utilizing new polymer and fibrous additives, plasticizers, lightweight aggregates, and even recycled materials. An excellent example of the use of concrete to revolutionize construction is the move towards using more and more reinforced concrete in the construction of long-span bridges. Concrete is so useful, lending itself and its strength to be formed in any shape a mold can be created in, and this ease of construction leads to some extremely attractive, strong, and useful structures. Bridges are now spanning record distances with higher safety factors than ever before, thanks in large part to the use of concrete. Cable Bridges Cable structures are some of the most beautiful and recognized structures in engineering.
Cables make use of the tensile strength of steel, and can support incredible forces for their size.
Arch Bridges Arches have been, historically and in modern times, an industry standard for stable construction, though they are used as the main support structure most often in bridge spans. The aqueduct is still in use in some areas of Europe. Arches can be constructed of many materials - stone, wood, concrete, or steel. Today's beam structures are somewhat more sophisticated than the traditional 'log across the creek' approach, however. Utilizing pre-stressed members, new materials, and innovative reinforced concrete mixes, spans are becoming steadily longer and at the same time more safe and usable for the public.