Florida International University (FIU) researchers in Miami advance a new high-performance high-performance concrete approach (UHPC), based on a successful field test to illustrate how high endurance material could offer a more practical and profitable alternative for structural repairs. Next year, the FIU team plans to build a mobile unit that houses all the necessary equipment to make concrete repairs, from preparation to cleaning.
Already used in Europe, the UHPC spray has long been a faster and more effective means of repairing corroid bridge walls, columns and ends of beam without the need for formulas or other distribution application elements. Although the concept is similar to the application of Shotcrete, a key obstacle to wider use has been the high cost of the commercial UHPC and owner, up to 20 times more expensive than conventional concrete mixtures, according to recent studies.
Fiu, the uNiversity by Michigan, the University of Minnesota and the Iowa State University have all programs which have focused on the development of open source and non -owners’ mixture that provides the same performance at less cost than their commercial counterparts. The professor gives Azizinamini, director of the FIU Infrastructure Innovation and Innovation, explains that, while the modified combination for spray applications costs about $ 700-800 per cubic courtyard, “ it is still profitable because the amount you use is very small. However, it provides the same performance with respect to mechanical properties and durability. ”
Azizinamini estimates that a UHPC sprayed coaching of an inch or less may be enough for many routine and corrosion repairs, while the most damaged elements would require thicker coatings along with additional reinforcement.
Transforming laboratory performance into a viable spray application system for field applications has been shown as difficult as adjusting the combination itself.
“It seems easy to the surface,” says Azizinamini. “But when you reach the field, make large lots with different considerations of specific materials for the location, as well as different teams involved in all stages of the process.”
Time is also a factor. As the mixture begins to establish -after 30 to 40 minutes, users must balance the size and composition of the lot with the time available to spray.
“If you don’t take care, risk -you ruin all teams,” says Azizinamini.
A milestone in the effort of the FIU to perfect its system for the UPHC sprayed last year through a collaboration with the Virgina Department of Transport, marking the first time that the process has been used for a concrete repair project.
The vdot district bridge engineer Sam Fallah explains that, as with other agencies, the deterioration of structural concrete resulting from the use of salts of the road misery is a long -term maintenance problem.
“Repairing vertical surfaces with conventional concrete in the site requires no less than 4 to 6 inches, which brings weight to the foundation,” says Fallah. In addition to being a more efficient application process, it adds, the UHPC spray can armor structure to protect more intrusions.
Vdot chose to test the FIU sprayed UHPC system on a bridge on the starting ramp within the Beltway Capital Exchange/Us Route 50 in Fairfax. Built in 1985, the buttresses of the structure showed the concrete and exposed, the receipt of corroïda derived from the joint leaks.
Photo courtesy of fiu
Directed last August, the test team prepared an area of approximately 20×8 feet eliminating the delamininat and not lonely concrete through the sand and water. The FIU team sprayed four layers of UHPC to build an average thickness of an inch. Each layer required about three minutes to apply.
Although the plans to repeat the test on the opposite buttress were reduced due to the mixer size limitations, Azizinamini was satisfied with the results, emphasizing that a monitoring visit to the site earlier this year did not reveal any additional deterioration, although Vdot had later applied a coating in the area for aesthetic purposes.
“When aesthetics is not a problem, the resulting rough surface is fine as it is,” says Fallah. “Any coating or softening can be done at the same time as the app.”
Although impressed with the general system, Fallah says that the process must be standardized. “The typical road worker must be able to win the ability to apply it correctly,” he says.
Azizinamini agrees, noting that, while the UHPC is a cement material, the spraying process must be addressed as a system that requires a well-formed team to execute it correctly.
“Even a small deviation from the required steps will cause the whole process to collapse,” he says. “It’s not something you can learn by reading a manual or seeing a presentation; it requires practical experience.”
The development of this experience with the planned mobile unit will be the next step of the FIU’s search effort, thanks to a federal subsidy granted through the South Florida Risk + Resilience Tech Hub to market the UHPC Ruixable system.
“We will use the mobile unit to carry out workshops across the country for the formation of the contractor,” says Azizinamini, who adds that the UHPC Ruzable system should be feasible for any type of built installation, as well as buildings.
“In all our experiments, we have still seen a failure in the bond,” says Azizinamini. “It allows us to do things that in the past we could not do.”
