Quick fix: Researchers at the University of California recently discovered that hybrid fiber-reinforced concrete (HyFRC) tubes performed better than HyFRC cast-in-place columns during bridge seismic-testing scenarios. In the future, these HyFRC tubes could replace current precast column techniques for bridges.
Making concrete bridges stronger
During America’s amazing growth from 1945 through 1970, many reinforced concrete bridges were installed. Impressively, several of those bridges remain operational today. But there are growing safety concerns as concrete cracks expose reinforcement bars to the elements.
The Associated Press performed an analysis of 607,380 bridges back in 2013 and found the National Bridge Inventory classified more than 65,000 as structurally deficient and more than 20,000 as “fracture critical.”
Now, most engineers know that despite the menacing-sounding classifications, these bridges are not on the brink of collapse.
Still, that doesn’t mean we shouldn’t be researching ways to make concrete bridges stronger and last even longer.
In a recent study, researchers measured the seismic response of bridge columns using precast concrete with HyFRC tubes compared to a column made completely of HyFRC.
Their main concerns were areas with high-intensity seismic events or earthquakes – like bridges located at the New Madrid fault line, right where we happen to operate.
The researchers constructed the test column tube in the engineering laboratory at Berkeley, using the lab’s mixer. The batch contained HyFRC and was poured in at the top of a mold to form a precast tube. Vibration equipment helped the batch flow to the bottom of the mold. After curing for 14 days, the mold was removed. Researchers verified the precast concrete tube had no defects before moving on to the next step. They used a crane to lift and place the tube onto a concrete foundation. The hollow precast tube was then filled with plain concrete.
The tests took place with static, unidirectional and cyclic loading. The HyFRC tube improved the sturdiness of the column and reduced rebar buckling.
Strain tests were promising. If this process is further pursued, the researchers believe bridge construction speed will improve, in addition to bridge strength and life expectancy in seismic zones.