Implementing the test
Application of UHPC in bridge deck repair is a straightforward process. The contractor uses water jets to remove the chloride-laden concrete and expose the existing reinforcement steel without damaging it. Crews use hammers to gain clearances around the rebar, and vacuum trucks perform the final deck preparation and cleanup.
Meanwhile, the contractor batches and mixes the UHPC directly on-site. Large sacks containing premeasured UHPC dry materials are dumped into the mixer with the appropriate amount of water. Once the dry materials and water reach the right consistency, the contractor adds a large sack of steel fibers.
“UHPC is made of portland cement, fine aggregates of quartz and sand and hair-like metallic reinforcing fibers,” Bistline said. “It resembles a Brillo pad dipped in pancake batter.”
For a deck repair, the UHPC mix must be stiff enough to stand up to the grade and cross slopes, but fluid enough to flow into all the nooks and crannies when vibration is applied.
Because achieving the right consistency is a skill and essential to the project’s success, the contractor was required to demonstrate his ability to mix and place the UHPC material before the project began.
“If you put the material down incorrectly, it could be a real challenge to get it back up,” Bistline said. “That’s why we do the mock tests, and why we have a UHPC manufacturer representative on-site overseeing the mixing operation.”
Each batch is tested for quality and consistency before it is transferred by backhoe and self-propelled buggies to the bridge deck. As the paste-like mixture is poured onto the exposed rebar, concrete workers vigorously spread it out ahead of a vibratory screed. After the screed passes, they visually inspect the fresh layer of UHPC and add finishing touches. Similar to the curing process of traditional concrete, workers apply a curing compound and vapor barrier and finish it with a diamond grind for a smooth, safe surface.
“Within 24 hours, the material reaches a strength equal to a carbon steel plate,” Bistline said.
Venuto said the project should be completed by the end of this year.
Evaluation and next steps
At the end of the one-year test, the Authority will drill core samples into the bridge deck and pull on the cores to see where they break.
“The goal is for the core sample to break somewhere within the original concrete deck. That will show the bond between the UHPC and the original concrete is stronger than the bond of the original concrete deck itself,” Bistline said.
The DRPA will consider results of its test along with other industry experiences before making a final decision about a full-scale deck application.
About The Author: Summers has been writing for the transportation industry for 15 years. She owns Cowbell Creative LLC in North Kansas City, Missouri.
