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 while providing the tension strength, rigidity and ductility

required. It was recommended that the next step be to demonstrate that that a uniform

structurally sound liner can be applied under field conditions. Additional recommendations

included to (1) develop field construction guidelines, (2) investigate long-term stability issues to

ensure stable strength over the service life of the culvert, and (3) refine and validate engineering

and design methodology through controlled laboratory testing.