A team of researchers from University of Houston Cullen College of Engineering and Qatar University has won a $779,000 grant to develop a new way to rehabilitate deteriorating reinforced concrete structures.
The three-year grant, from the Qatar National Research Fund, goes to a team led on the UH end by civil and environmental engineering assistant professor Mina Dawood. His UH collaborators are professor Abdeldjelil Belarbi and assistant professor Bora Gencturk, also from civil and environmental engineering. They are teaming up with Mohammed Al-Ansari, a civil engineering professor at Qatar University in Doha, Qatar.
There's nothing new about attempts to extend the life of old concrete structures. It's often far cheaper to extend the life of an existing bridge or building by several years (or decades) through rehabilitation than to replace it completely.
One well established technique in this field is the use of fiber-reinforced polymers (FRPs), which are essentially super-strong fabrics that can be wrapped around a column. This, said Dawood, is an example of passive confinement. When a truck travels over a bridge, for example, the columns supporting that bridge shorten axially and expand radially outward. FRPs wrapped around a column confine the structure and limit that outward expansion. The repair materials are engaged when, and only when, the column deforms or experiences damage.
Dawood and his colleagues are proposing an active confinement system that confines the column at all times.
"With passive confinement, the material has to deform, expand and experience some amount of damage before the reinforcement kicks in. Active confinement squeezes the structure all the time, preventing that damage from occurring. This should lead to enhanced performance for these structures," said Dawood.
At the heart of this research are shape memory alloys (SMAs), materials that can take on a specific shape when exposed to specific conditions. This research uses commercially available SMAs that are long pre-stretched wires or rods that will contract back to their original length when heated.
The research team will wrap these SMA rods around concrete beams and columns and then heat the rods, causing them to contract. This contraction will confine the deteriorated concrete members, improving their strength and limiting future damage.
The investigators will study many variations of this approach, including using different amounts of SMAs and different ways to wrap the SMAs around the structural members. The team will also consider the different types of loading configurations that typically effect reinforced concrete beams and columns. They will also conduct a thorough life cycle cost analysis of this approach to quantify the savings that can be achieved with this new repair technique.
While these initial efforts will focus on the type of deterioration caused by Qatar's harsh environment, the research team plans to develop a fundamental model of the behavior of SMA-reinforced concrete. Such a model would allow this reinforcement technique to be translated to different structural members with varying degrees of deterioration.
"To our knowledge, nobody has used this approach with these materials to extend the service life of corrosion-damaged concrete structures. We'll see what kind of enhancement we get in performance and how that translates to lifecycle," Dawood said.