Cutting 3/4" Slots

Graphic of NSM rod placed in slot

Graphic of NSM rod after installation and sealing

Placing NSM Rod

Finishing after NSM rods are installed

Project complete after NSM rods are installed

A new large water tank was undergoing construction when cracking on the top side of the concrete slab occurred. Structural Preservation Systems (SPS) was contacted to develop a comprehensive repair strategy.

The steel reinforcing bars were installed in a way that resulted in insufficient development length. Because the tank was divided into four partitions and the steel did not extend 10 feet into the slab at the inner partition, the slab did not have the strength that it needed to withstand the load. After a review of the structure, SPS determined that this could be overcome by installing near surface mounted (NSM) rods in the concrete slab.

A Design-Build project, SPS began the repair by cutting 5,000 linear feet of grooves that were ¾-inch wide and ¾-inch deep on the top side of the slab. Crews used a gas-powered floor saw to make the grooves, which required special safety precautions. The tank was a modified confined area, so carbon monoxide levels had to be constantly monitored to ensure the safety of the workers using the gas-powered machine. Installation of NSM carbon fiber reinforced polymer (CFRP) rods is a precise art, and it was critical to ensure that the resins were bonding with the concrete on all three sides.

In addition to the installation of CFRP in the slab, the outside wall of the tank was also in need of strengthening due to a reinforcement detailing challenge at the construction joint. Crews installed the VSL product, V-Wrap C200, on the outside wall because of its convenient and speedy application.

This project had an extremely tight schedule, and the weather presented a challenge. It was critically important to the owner that the project was completed on time, so a detailed plan was developed. However, rainy weather halted the project for one week, which caused the crew to lose valuable time. In addition, the temperature dropped, so an alternate FRP material had to be used.

Despite these challenges, the project was completed in two-and-a-half weeks, and the owner was extremely pleased with the outcome of the project.