An experienced civil contractor with a nearly 150-year history, the Mercer Fraser Co. manages complex public works projects through its headquarters in Humboldt County, California. The Mercer Fraser Co. works on such heavy civil construction transport initiatives as highways and bridges.
On American highways, large concrete bridges are commonplace. Pure concrete is at its best when serving as a support, as with a post supporting a bridge. However, when made into a horizontal slab, it’s liable to crack unless laid very thickly.
Concrete’s properties at first glance seem to disqualify it as a bridge construction material, since bridges have significant horizontal components, which would require concrete too thick to be practical. However, around the turn of the 20th century, engineers figured out that concrete reinforced by metal bars can be poured out into slabs of a practical thickness without cracking. Reinforced concrete is therefore now a common material on American highways, making up both road surfaces and bridges.
Further advances made just before the onset of WWII made concrete stronger and lighter. European engineers innovated a process by which concrete beams are compressed by pressure applied at both ends. Called “pre-stressing,” the process produces thinner and lighter concrete beams without the risk of cracking.