Coordinated Systems Consulting was approached by One70 Group with a full rehabilitation project consisting of a multi level concrete slab structure being renovated for a client located in Woodmere NY. A survey of the slab was conducted and it was determined to be a post tensioned slab. The current reinforcement in some locations was deficient which led to the use of composite reinforcement to provide additional capacity to the structure. One70 Group, CSC and Pennoni (the engineer of record) collaborated and partnering with our composite manufacturer developed a system using Tyfo uni-directional carbon fiber in specific locations throughout the structure in order to develop the capacity required.

PICTURED: Preparing the surfaces using hand grinders and other tools. Preparing the surface for FRP installation.

Pennoni was able to develop supplemental capacities for the slab areas. A small section of the slab is detailed here in figure 1 showing the strips and orientation of the carbon fiber within the slab. Most of the carbon composite was concentrated within the hallways since new structural metal stud partitions were installed to carry some of the additional loading. The carbon fiber used was Tyfo SCH-41-2X uni-directional carbon fiber. This system was paired with Albi Cote FRL X, a roll on intumescent paint to provide the flame and smoke spread required by the engineer of record. Shop drawings were developed and provided to One70Group in order to assist in coordination with moving materials and other trades on site. Due to the original delay on site CSC was provided (5) five weeks to complete the strengthening on all slabs within the project.

FIGURE ONE: A small section of the slab is detailed here showing the strips and orientation of the carbon fiber within the slab.

Surfaces were laid out to ensure all obstructions were removed that could be removed. The prep of both the top of the slab and underside of slab was conducted using hand grinders to achieve a CSP-2 Surface Profile as required per Fyfe Co Standard Installation procedure. Underside of ceiling was painted, all paint within the FRP area needed to be removed to provide a substrate with laitance removed appropriate for the adhesion of the composite.

Installation of the composite was performed per the wet layup method. Dry fiber was rolled out to the appropriate length and width as needed. Tyfo S two part epoxy was blended together and used to saturate the dry fiber completely prior to installing onto the concrete surface. Cabosil fumed silica was added to a partial batch of blended epoxy to thicken and used as a primer. The thickened epoxy was troweled onto the concrete surface prior the saturated composite was installed. After the composite is laid onto the surface additional thickened epoxy is used to feather the edges and ensure not tripping issues. This process is repeated for all locations within the structure. Two part epoxy has a working time of roughly 2-3 hours depending on temperature. Any partial rolls are used with an overlap splice as required within the approved shop drawing. ASTM 4541 pull tests are conducted randomly throughout the project to ensure appropriate adhesion of the composite to the existing concrete substrate. A positive break per AC 178 guidelines is over 200 psi within the concrete. Results higher than that are also passing but might break within the composite itself.

The FRP requires roughly 12-48 hours to tack up and cure, at which time the intumescent paint is applied to the surfaces of the cured composite.