Emergency Repairing with UHPC

December 14, 2022 | Emergency Repairing with UHPC

As construction workers, we are often pushed up against deadlines. No matter how many workers we have on the site, no matter how detailed the schedule is, we always catch a snag somewhere. Mistakes are inevitable, and even the small ones can put us weeks behind if they are on the critical path.

There needs to be an easy way to fix minor structural damage on projects without having to bring in new subcontractors or new equipment. There needs to be a material versatile enough to be used in many different situations. It has to be strong enough and durable enough to fill in where other materials fall short.

Ultra High Performance Concrete might just be the material we are looking for in these situations. It can be a modern and versatile solution to numerous distinct construction problems. You may have already heard of UHPC’s role in the repairing of bridge superstructures. It can be used to repair rusted and eroding beams and girders, overlays, abutments, and more. What you may not know is that UHPC is also able to fill in minor repairs in almost any part of the bridge. Ultra High Performance Concrete along with a well trained crew of UHPC technical representatives can neutralize the delays and expenses that come with fixing repairs.

ceEntek’s team has completed several on site emergency repair jobs. One that stands out is a project done in Spring of 2021, in Miami, Florida.

This bridge is a classical example of a side by side box girder bridge that was built in 1966. Over time the grout that acted as a lateral load transfer mechanism between these precast box girders wore away. Reflective cracking could be seen in the asphalt overlay, this indicated that there was movement between the box girders. It was deemed necessary to remove the old grout and replace it with a material that would be durable and long lasting, to prevent future repairs. The engineers decided that UHPC would be ideal for filling in the longitudinal connections.

As construction began on the project, old material had to first be removed from the deck and connections. This was done by using both a milling machine and hydrodemolition. The Florida Department of Transportation decided to use this method to remove old grout between box girders and the existing asphalt bridge deck surface. Both milling and hydrodemo are very effective when preparing a bridge for UHPC casting. They remove the old weak material and leave the surface rough and scoured. The rough surface allows the UHPC to create a stronger bond to the substrate. When doing any type of demo it is important to take into account the strength of the concrete you are demolishing, as well as the depth of rebar and other structural elements. During this specific hydro demolition, there was accidental damage done to one of the box girders. This damage required an emergency repair before the contractor could move forward with much of the project.

The damaged portion of the bridge was the top portion of a box girder. This occurred because during the demolition of the asphalt roadway, the milling machine removed too much material off of the surface. The steel rebar stirrups that lined the box girder were now exposed. This damage, if left unresolved, would lead to low spots in the final overlay, and accelerated deterioration of the area around the exposed rebar. Repairing a damaged box girder and overlay could be an expensive repair. In most cases, this would require a few extra days of work, and extra man power. This would set the contractor back and delay the project as a whole. Major problems could occur if the project has a tight schedule, especially if penalties are incurred due to delays.

Luckily, this project required UHPC for the longitudinal connections between the box girders. This meant that a trained team of UHPC engineers and technicians would be able to assist in the repair process. That, along with the versatility of ceEntek’s Next Generation UHPC 2.0™ would allow the repair and construction of this bridge to be completed on time. The emergency repair was able to be done concurrently during the casting of the longitudinal connections.

The ceEntek team has an emergency repair procedure in place to address and solve problems just like this. The process started by assessing the damage done to the bridge overlay. The team and contractor found the volume of the box girder that was removed in the damage. This allowed them to determine the amount of UHPC needed to be batched to complete the project as a whole. This emergency repair was small enough that it wasn’t necessary to ship extra material, and could be done on the same day as the casting of the UHPC closure pours.

The versatility of ceEntek’s UHPC allowed the technicians to batch two separate products in the same mixer one after the other. The planned procedure was to use ceEntek’s variable speed IMER750 Mixers, which have a 0.182 cubic yard (0.14 cubic meters) batch size. The team first batched ce200SF-G which was used to fill the connections. ceEntek shipped 2.5 cubic meters (3.0 cubic yards) of material, enough for the six longitudinal connections and the repair.

Once the planned procedure was completed, the construction team began the emergency repair procedure. This required the team to batch some ce200SF-t. This product is a thixotropic mix, made specifically for overlays. The major difference is that the thixotropic mix requires more steel fibers, creating a higher tensile strength. The ce200SF-t was ideal for this repair, as what was needed was a flowable material that could fill the amorphous shape of the damages. The material had to also have a strong bond to the existing concrete to avoid chipping off and causing problems in the future. The plans for this bridge stated it was going to have an asphalt overlay. Any low or uneven spots would have led to the asphalt surface having cracks and/or blemishes over time.

This emergency repair was easily handled with the same crew, same materials, and done the same day as the casting of the UHPC connections. The UHPC was able to create a tight bond to the exposed steel rebar and roughed up concrete surface. The emergency repair proved to be not a large problem thanks to the help of ceEntek’s Next Generation UHPC 2.0™. This saved the contractor time and money on the project despite the mistake during the demolition. There are many benefits to using UHPC on your bridge projects, and they should be considered when deciding what materials to use. Not only will UHPC make your bridge stronger and last longer, but it can also be used to get you out of tough situations.