PVA Fiber Reinforced Shotcrete for Rehabilitation and Preventative Maintenance of Aging Culverts

The goal of this project was to investigate the potential for using PVA (polyvinyl alcohol) fiber reinforced mortar for the rehabilitation and preventative maintenance of aging metal highway drainage culverts using a spray-on liner application approach. The interest and impetus for the investigation resulted from prior work of the investigators with county engineers that pointed towards the need for new cost-saving technologies for rehabilitating deteriorated metal highway drainage culverts that preclude the need to close the roadway and excavate the existing structure. The investigation was conducted by a team comprised of the polymer materials expertise of the UAB Department of Materials Sciences and Engineering, the civil/structural engineering expertise of the Auburn University Department of Civil Engineering, and the concrete application solutions expertise of Blastcrete Equipment Company, Inc. The investigation focused on the strength and toughness advantages provided by reinforcing spray-on concrete (shotcrete) with high performance PVA fibers. Tasks included developing and optimizing the material concept, laboratory strength testing, and developing engineering design methodology. Full scale demonstrations of the concept were accomplished by Blastcrete Equipment Company, Inc., at their facility in Anniston Alabama. The laboratory-scale component of the investigation verified the significant tensile strength, ductility, and strain-hardening characteristics that have been presented by others for PVA-ECC (engineered cementitous composite). However, achieving the performance demonstrated by others proved to be challenging, even in a controlled laboratory environment. Ductility and strength performance depends upon using very precise and specific constituents, including fine silica sand with average particle diameter of 110 µm or less, and proprietary admixtures required to prevent clumping of the fibers. Also, since PVA fibers are hydrophilic, achieving proper water content proved challenging. These challenges were amplified when developing a methodology for pumping and spraying the PVA reinforced mortar on the inside of a corrugated steel pipe. Many iterations were required to balance the challenges of pumpability and sprayability with the requirement that the liner material must readily adhere to the obvert of the metal pipe. After successfully lining a 48 inch pipe, a three-point bending test was conducted to illustrate the strength and stiffness enhancement provided by the liner. Finally, an analytical approach was derived for designing the required liner thickness, and practical field implementation challenges were outlined. Overall, it was concluded that the approach offers great potential as a solution to the metal culvert deterioration problem. PVA-ECC offers intriguing and unique characteristics that would minimize the required liner thickness …