Researchers at Florida International University (FIU) in Miami set a new approach to sprayable ultra-high performance concrete (UHPC) and build on a successful field test to illustrate how the long-lasting, high-strength material could offer a more practical and cheaper alternative for structural repairs. Next year, the FIU team is planning to build a mobile unit in which all devices are required for the implementation of concrete repairs from preparation to cleanup.
Sprayable UHPC, which has already been used in Europe, has long been cast as a faster and efficient means for repairing corroded bridge walls, columns and wearers without formwork or other elements of the application. Although the concept of using spray concrete resembles, the high costs for commercial UHPC were an essential obstacle for broader use – as well as 20 – more expensive than conventional concrete mixtures according to recent studies.
Fiu, the uNoversities from Michigan and Minnesota and Iowa State University have all programs This focused on the development of open source blends without proprietary, which deliver the same performance at fewer costs than their commercial colleagues. Professor ATOROD Azizizinamini, director of infrastructure research and innovation of FIU, explains that the mix of spray applications costs around $ 700 to $ 800 per cubic meter.
Azizizinamini estimates a sprayed UHPC coating of one inch or less for many routine processes and corrosion repairs, while more deteriorated elements together with additional reinforcement would require thicker coatings.
The conversion of the laboratory performance into a sustainable spray application system for field applications has proven to be challenging, such as the fine -tuning of the mix itself.
“It seems easy on the surface,” says Azizizi team. “But when you come in the field, you carry out large batches with different local material considerations and different devices that are involved in all phases of the process.”
Time is also a factor. If the mixture is set after 30 to 40 minutes, users have to balance the size and composition of the stack size and composition, whereby the time available for sprays is available.
“If you don't be careful, you risk ruining all devices,” says Azizizi marine margin.
A milestone in the FIU's efforts to refine its system for sprayable UPHC took place last year through a collaboration with the Ministry of Transport by Virgina and marks the first time that the process for a concrete repair project was used.
Sam Fallah, Bridge engineer of the VDOT District Bridge, explains that, as with other agencies, the deterioration of the structural concrete is a long-term problem due to the use of salts with motorway cuts.
“The repair of vertical surfaces with conventional concrete is no less than 4 to 6 inches, which gives the foundation weight,” says Fallah. In addition to the more efficient application process, he adds that the sprayable UHPC armored structure protects another penetration.
VDOT decided to test the sprayable UHPC system from FIU on a starting ramp bridge in the Capital Beltway/US route 50 in Fairfax. The abutments of the structure built in 1985 showed tense concrete and exposed, corroded reinforcement rod, which resulted from joint leakage.
Photo with the kind permission of fiu
The test team was carried out last August and created an area of ​​approximately 20×8 feet by removing a delaminated and unclear concrete by sand and water flavors. The FIU team then sprayed four layers of UHPC to build an average thickness of one inch. Each layer required about three minutes to apply.
Although the plans to repeat the test to the opposite abutment were restricted by restrictions on the mixer sizes, Azizizi marine team was satisfied with the results and found that a follow -up examination of the location at the beginning of this year did not result in any further deterioration, although VDot then applied a coating for aesthetic purposes for aesthetic purposes.
“Where aesthetics are not a problem, the resulting rough surface is as good as follows,” says Fallah. “Every coating or smoothing can be carried out at the same time as the application.”
Although the overall system is impressed, the process must be standardized. “The typical motorway worker must be able to achieve the ability to correct it,” he says.
Aziziziamini agrees and finds that UHPC is a cement -like material, but the spray process must be tackled as a system that a well -trained team must carry out properly.
“Even a small deviation from the necessary steps means that the entire process collapses,” he says. “It is not something you can learn by reading a manual or looking at a presentation. It requires practical experience.”
The development of this specialist knowledge with the help of the planned mobile unit will be the next step of the FIU research efforts thanks to a federal scholarship of the South Florida Risk + Resilience Tech Hub in order to commercialize the sprayable UHPC system.
“We will use the mobile unit to carry out workshops throughout the country for the training of contractors,” says Azizizi marine team and adds that the sprayable UHPC system should be possible for any kind of constructed facilities – bridges and buildings.
“In all of our experiments, we have to see a failure of the bond,” says Azizizi marine margin. “It enables us to do things that we have not been able to do in the past.”