The Best Engineered Long-Term Structural Solution
Pile jackets available in North America have tensile strengths between 15 - 20 ksi which is significantly lower than the 60 - 155 ksi strength offered by PileMedic®. All other pile jackets have either one or two weak seams along the height of the jacket that must be bolted or epoxied in the field. These seams introduce planes of weakness in the jacket. The strength of the fibers in a jacket cannot be developed to provide structural confinement when they terminate at a seam. Weak seams are also an entry point for water and oxygen to weaken the system overtime. PileMedic® is a structural strengthening system for piles. The laminates contain fibers in two directions (longitudinal and transverse). When wrapped around a pile or column, the jacket creates a seamless shell around the column with tremendous confining pressure on the column. It is well known that the axial capacity of a column is proportional to the degree of confinement. As an example, a 4000 psi concrete pile may resist axial loads like a 5000 or 6000 psi concrete pile depending on the number of wraps and the confining pressure the jacket places on the pile. Small Annular Spaces
In repair of deeper piles such as those encountered in ports, larger bridges and off-shore structures, a significant cost of the repair has been the divers. PileMedic® installation is not a dive intensive process. PileMedic® laminates are wrapped around the pile at the waterline and slid down the pile while another laminate is wrapped around the pile with a small overlap on the previous jacket. This process eliminates the need for divers to assemble jacket shells underwater. This is the quickest and most economical method to wrapping piles.
One type of filler material is cementitious or underwater grout. These are the least expensive fillers and are ideal when a large annulus (greater than 1 inch) is to be filled. Grouts can be either pumped through ports installed on the jacket or placed using the tremmie technique. The drawback of cementitious grouts is that the large particle size prevents the grout from penetrating into narrow cracks in concrete piles or filling the voids inside a deteriorated timber pile. Cementitious grouts also have poor bonding capacity to the smooth surface of PileMedic® jackets. Thus, when using a cementitious grout, only the confining benefits of the jacket can be realized; contribution of the jacket to the flexural capacity of the retrofitted pile is conservatively ignored. If necessary, longitudinal reinforcing elements such as steel or GFRP rebars can also be placed in the annular space; these increase both flexural and axial capacity of the retrofitted pile.
A second type of filler material is epoxy grout; these are essentially epoxy resins that are extended with sand and small gravel to make a product with a unit cost between plain resin and cementitious grout. Depending on the particle sizes in epoxy grouts, they usually require an annular space of 1 inch or wider to ensure the grout flows freely and does not leave any air pockets in the annular space. Epoxy grouts also bond the PileMedic® laminate to the host pile and engage the jacket in resisting axial, shear and flexural loads. Additional longitudinal reinforcing elements such as carbon strips, GFRP or steel rebars can also be placed in the annular space when epoxy grouts are used.
A third type of filler material is a low viscosity epoxy resin. These cost more than cementitious grouts and are best used when a small annular space (less than approx. 1/8 inch) is to be filled. Small diameter injection tubes can be positioned at 90 or 120 degrees apart along the height of the pile, or can be embedded in grooves cut along the pile; the PileMedic® jacket is tightly wrapped around the pile and the injection tubes and low viscosity resin is pumped into the annular space through the injection tubes. QuakeBond™ 320LV, for example, is one such resin that cures under water, eliminating the need for costly coffer dams in such repairs. The resin is also 2-3 times stronger than concrete or wood in compression. As shown in Figure 2, even under a gravity flow condition, the resin fills all internal cracks and voids in a deteriorated timber (or concrete) pile. The thin film of resin that is formed in the annular space around the pile, serves as an impervious layer that encapsulates the pile and further prevents moisture and oxygen ingress (in addition to the same behavior provided by the PileMedic® jacket itself); this will significantly reduce corrosion and deterioration rate.
Moreover, the use of epoxy as a filler material will bond the PileMedic® jacket to the host pile. In this case, the jacket will significantly increase the axial, shear and flexural strength of the pile, with minimal increase in pile diameter! These contributions can be calculated using established procedures such as those recommended by ACI Committee 440. The narrow width of the annular space makes it impractical to add any reinforcing bars. However, if necessary, unidirectional carbon strips that are 0.05 inch thick can be positioned in the annular
Tests by Nebraska Department of Roads on Timber Piles
In a research project sponsored by Nebraska Department of Roads, five timber bridge piles were repaired with PileMedic® jackets and tested. The results of this study entitled "Assessment and Evaluation of Timber Piles Used in Nebraska for Retrofit and Rating" were published in this interim report in 2014 and are available in pdf format here. A paper entitled Experimental-Evaluation-of-Repair-Options-for-Timber-Piles-TRB-Paper-2481-16.pdf was presented at a Transportation Research Board (TRB) Conference and is available here.