Planning and Estimating Data for Concrete Pile Repair Using Concrete Encasement
Description of Task: Repair a deteriorated concrete pile by installing a concrete encasement from 1 foot above the high waterline to 1 foot below the mudline. The total length of encasement is 20 to 30 feet. Reinforcement of the pile is not required.
Size of Crew: Dive station, two laborers.
Training Requirements: Familiarity with the jacket to be used, concrete pump operation, jetting or air lifting procedures, and removal of marine growth.
Equipment Requirements: High-pressure waterblaster, hydraulic grinder with Barnacle Buster attachment, hydraulic power unit, concrete pump with adequate hose, concrete mixer (if ready-mix concrete is not available), jetting pump and hose, rigging equipment, float stage, scaffolding.
Productivity of Crew: 8 hours per pile repair.
Form Material - When using proprietary forms, follow manufacturers' recommendations regarding lengths and diameter of forms, top and bottom closures, spacers, bands, straps, and special fittings. Provide 20 percent extra fittings for breakage if the forms are to be reused. Forms are ordered prefabricated in the required length and diameter. For flexible forms, allowance on the length must be made for extra fabric that may be required around blocking at the top and bottom of the jacket. Some proprietary systems require that different types of forms be used in the tidal and submerged zones.
Spacers - A conservative estimate of the number of spacers must be made. In calm water and with vertical piles, relatively few spacers will be required. Rough water and batter piles will require more spacers.
Wire Mesh Reinforcing - Usually 6x6-10/10 welded wire fabric is adequate. Calculate the width of wire fabric required based on its circumference, taking into consideration the thickness of the spacers between the pile and reinforcing and allowing a 9-inch overlap of the ends.
Concrete - To determine the amount of concrete required to fill die form, be conservative. When using flexible jackets allow for reduction of concrete volume due to loss of water through the permeable fabric, enlargement of the jacket caused by stretching, and waste. Usually an allowance of 10 percent extra concrete over the theoretically calculated quantity is sufficient.
Concrete should be pumped using 15-psi minimum pressure through a suitable pipe or hose which extends down to the lowest point in the form. It is important to start filling with the hose at the bottom and to keep the discharge submerged in concrete during the pouring operation. This procedure will prevent voids fonning. Care must be taken when using the hose-tremie method as there is a tendency for the hose to become snagged on the wire mesh reinforcing. Some forms have built-in filling and overflow ports where the lower port is used for filling. Filling from a bottom port is preferred over extending the hose to the bottom of the form.
5.7.2 Epoxy Patching/Injection
Epoxy patching is used where localized spalling or cracking occurs. The deteriorated area must be thoroughly cleaned to allow the patch to adhere to the concrete. Once cleaned, the epoxy compound is mixed in accordance with the manufacturer's instructions, forced into the spalled area, and worked smooth by hand. Epoxy will not stick to a wet surface so it must be kneaded to the surface to displace water. The patching epoxy used is described in Section 2.11.1. TTiese epoxy patching compounds should be limited to thicknesses of less than 3/4 inch because of the difference in temperature-related expansion between the epoxy and underlying concrete. Thicker patches will deteriorate when subjected to temperature variations. Poitland cement may be substituted for the epoxy grout, but it is more difficult to work with.
Cracks can be repaired by injecting low-viscosity epoxy mortar under pressure into the crack (Figure 5-21) as described in Section 2.11.3. This procedure is summarized in Table 5-23. The first step is to clean the area to be repaired. Plastic fill ports are available from manufacturers of epoxy injection systems. The plastic ports are attached to the crack entrance with an epoxy sealer. The crack surface is also sealed. The epoxy seal is allowed to cure overnight. The next day a low viscosity epoxy resin is injected through the ports to overflowing. After cure, the ports and excess surface materials are removed by grinding.
For deep cracks with wide entrances, fiberglass cloth in conjunction with an epoxy sealer are used to dam the surface. After the dam has cured, holes should be drilled into the crack every 6 inches along its length and used as injection ports so that the epoxy grout extends to the base of the crack. The epoxy grout is injected into the ports, starting at the bottom. After injection is complete, the port holes should be plugged to prevent the epoxy weeping out before setting.
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