Salvaged utility poles recycled into bridge systems

Colorado State engineers are turning the discards of yesterday into the bridges of tomorrow. Using salvaged utility poles from road expansion projects, civil engineering Professor Richard Gutkowski and graduate student Matthew LeBorgne are recycling the reusable wood to create short- and medium-span bridges.

"The idea came to me when I saw them removing the poles as I passed by each day on the way to the Engineering Research Center," Gutkowski said, referring to utility poles displaced from a road widening project in Fort Collins. "It was like a light bulb coming on."

New composite less costly

Gutkowski is replacing the conventional and costly reinforced concrete-slab bridges with a composite design. Integrating an innovative cambering, or arching, technique, the researchers are setting the tapered utility poles in alternating directions beneath a thin concrete slab.

The concrete layer provides the compression strength and durable surface necessary for vehicle wheels, while keeping snow and rain off the wood. The wood layer provides tensile strength that self-shores the concrete during the curing process.

Worldwide cooperation

Although the idea was the result of local road work, the project has generated worldwide interest. Researchers in New Zealand, Germany, Italy, and Sweden have joined forces to study long-term creep (fatigue tests), hygrothermal effects (change in properties due to moisture absorption and temperature change), and the humidity-change effects on deflection over time in composite bridge designs.

Gutkowski and his team are studying the effects of Colorado’s arid climate and the special properties of dry wood – which draws water from adjacent concrete and shrinks it, delaying the curing process – on the design.

A notched system of grooves cut in the wood filled with concrete when it is cast interconnects the two layers, but it has provided a challenge. The mechanics of shrinking concrete have not been studied at relative humidity of less than 40 percent, and Gutkowski plans to examine this issue using environmental test chamber equipment at the CSU Engineering Research Center in a later phase of the project.

"Our challenge has been the need to prevent very dry wood from extracting water from the concrete in our notch connection," said Gutkowski. "We appear to have overcome that important piece of the mechanics puzzle."