Grouts for underwater use can be generally classified as either a hydraulic cement or anepoxy. Several variations of both the hydraulic cement and the epoxy are commercially available for use in different applications.
A hydraulic cement is a single-component cement that is capable of setting and hardening underwater because of the interaction of water and the constituents of the cement. Admixtures are available from hydraulic cement manufacturers for obtaining specific performance goals (i.e., accelerate or slow down the reaction rate).
Epoxy grouts are used for bonding different surfaces or for filling thin voids. All epoxy grouts have at least two components: a resin component and a hardener component. Some epoxy grouts also have additions of fillers or aggregates to "extend" or increase the usable volume of the grout or to modify the characteristics of the grout. Epoxy grouts without additions or fillers are called "neat" grouts. Epoxy grouts are commercially available in different formulations, each having a specific performance or physical characteristic (i.e., strength, mixing ration, pot life, moisture sensitivity, etc.).
Table 2-29 lists the materials for the grouting applications described in Sections 2.11.2 through 2.11.5.
Securing U-bolts or rock anchors to seabed
Repairing deteriorated concrete surfaces
Repairing cracks in concrete
Installing anchor bolts in concrete
• Hydraulic cement grout
• Neat epoxy resin grout
• Epoxy resin/oven-dried aggregate grout
• Hydraulic cement grout
• Neat epoxy resin grout
• Prepackaged epoxy grout
• Hydraulic cement grout
• Neat epoxy resin grout
2.11.2 Securing U-Bolts or Rock Anchors to Seabed
Grouted-in-place U-bolts or other types of anchor bolts provide an excellent anchoring technique for pipelines or for split-pipe cable protection systems in soft rock or coral seabeds. Either hydraulic cements or neat epoxies are used for grouting these anchor bolts.
The first step in securing the U-bolt or rock anchor is to drill a hole of the required dimensions (usually 1 to 1-1/2 inches in diameter, 12 to 16 inches deep) at the desired anchoring location. See to Section 2.2.3 for a discussion of drilling equipment and techniques. In some locations, drifting sand can be expected to fill the drilled hole before the grout can be inserted. In this case, compressed air should be used to blow the hole free of sand just prior to inserting the grout. If compressed air is not available, the hole can be temporarily plugged by placing a pipe into the hole immediately after drilling. The diameter of the pipe should be slightly smaller than the diameter of the hole and the upper end of the pipe should extend 6 inches to 1 foot above the seabed to keep the sand out.
18.104.22.168 Hydraulic Cement. Hydraulic cement is placed by either of two methods. In the surface mix method, the cement-sand mixture and water are poured into a 4- to 5-foot length of flexible plastic tube, about 5 inches in diameter and 6 mils thick, with a knot in the lower end. The mixture is shaken and kneaded on the surface, the tube is carried to the bottom by a diver, and the contents are squeezed into the drilled hole. This procedure has often proved to be unsatisfactory because the mixture tends to harden too rapidly. A better solution, referred to as the toothpaste-tube method, is to pour the cement-sand mixture into a tied-off tube, twist and hold the tube at the center, pour in the freshwater, and then tie off the top of the tube. The tube is then lowered to the diver in a tool bag, who releases the twist in the tube and mixes the grout on the bottom. This will allow sufficient time to squeeze the grout into the hole before the mixture hardens.
When working with hydraulic cement it is prudent for the diver to have voice communications (COMS) with the surface. Using COMS, the diver can inform the tenders when to lower tubes of cement to the worksite.
22.214.171.124 Epoxy Resin. When selecting an epoxy resin material, the water temperature at the worksite as well as the manufacturer's packaging and application technique should be considered. Generally, for applications where the water temperature is greater than 60 degrees, a polyester resin approved for marine use may be used. However, for temperatures between 23 and 60 °F, a vinylester resin (or other specially formulated resin) should be used. The vinylester resin can also be used for warmer areas.
Generally, epoxies consist of two components (resin and catalyst) that may come in a variety of different mixing ratios. One manufacturer's product (HILTI) comes packaged in a self-contained glass vial that is inserted into a hole (made by a rock drill) and then mixed by rotating a threaded fastener down into the glass vial. The hammering/rotary action applied by the drill breaks the glass vial and mixes the components of the capsule together. The advantage of this particular system is that the mixing technique minimizes the amount of handling. However, because the mixing takes place in the fastener hole, it is important that the hole fully contain the epoxy during the mixing process. For this reason, the use of glass vial products is not recommended in coral seafloors (where the epoxy may not be well contained during the mixing process).
For applications requiring flexibility in the amount of grout dispensed, the epoxy is placed by using either a caulking gun or the NFESC grout dispenser. Both of these techniques have been used in coral seafloors, where it has been shown that increased fastener holding strength can be achieved by completely filling all of the void spaces in a fastener hole with epoxy (ef fectively strengthening the foundation material).
Pneumatically-operated caulking guns (60 to 100 psi) that dispense epoxy grouts from disposable plastic cartridges are commercially available.
The grout is usually premixed in buckets on the surface, poured into the cartridges, and then relayed to the divers at the work site. The divers then systematically load and dispense the contents of each cartridge. Since most epoxy grouts have a relatively short pot life (30 minutes or less), successful application using this technique requires quick execution and teamwork.
The NFESC grout dispenser, shown in Figure 2-56, is a pneumatically-powered diver tool. The grout dispenser simultaneously mixes and dispenses neat epoxy (1:1 mixing ratio) from two 20-fluid ounce disposable plastic car r Figure 2-56 Diver-operated epoxy grout dispenser.
tridges. The tool can be reloaded underwater with full cartridges of epoxy and can dispense epoxies at a repetitive rate of 1,000 fl oz/min. In addition, the tool incorporates a "blow-out" system for cleaning residual epoxy from the mixing mechanism. This helps prevent epoxy from hardening inside the tool. The tool weighs approximately 35 pounds dry and 8 pounds submerged. In comparison with other underwater grouting techniques, this method delivers larger quantities of grout in shorter periods of time, employs air pressure rather than muscle to mix and dispense epoxy, and eliminates errors in mixing.
Also, if desired, the epoxy components can be preassembled (by the epoxy manufacturer, cartridge manufacturer, or a contractor), thereby minimizing exposure or contact with dive personnel and equipment.
For repairing deteriorated underwater concrete surfaces, either epoxy resin/oven-dried aggregate mortar, portland cement mortar, or specially formulated prepackaged concrete mixes are used. If epoxy mortar is used, the epoxy resin must be formulated for beading to wet surfaces and underwater application. The concrete surfaces to which the mortar is to be applied must be cleaned by sandblasting or waterblasting to allow for good bonding action. Loose concrete must be chipped out and corroded reinforcing bars cleaned and supplemented by new bars if necessary. The mortar should be mixed and applied in accordance with the manufacturer's directions. The mortar can be applied either by hand or tool smearing.
The prepackaged concrete mixes can be either hand applied or pumped. Surface preparation is as described above for the mortar. The special formulation provides dimensional stability underwater with minimal washout.
The best method for repairing small to medium cracks in concrete piles or structures is pressure injection of neat epoxy resin. This method can generally be used for cracks up to 1/4-inch wide. The epoxy selected should be a low-viscosity formulation suitable for wet surfaces and underwater application. In choosing the appropriate resin, it is important to confer with the manufacturer to ensure that the resin is compatible with the crack size and depth, temperature variations, characteristics of the concrete, and the equipment to be used to apply the resin. Holes should be drilled into the bottom of the crack every 6 inches to 3 feet along its length, and small tubes, or one-way polyethylene valves, should be installed. The area around the tube or valve and the entire surface of the crack should be sealed with a quick-setting epoxy paste adhesive. Fiberglass tape can be used in conjunction with the paste as described later in Section 5.7.2. The low-viscosity epoxy resin is then injected into the lowest valve until it reaches the level of the next valve. The lower valve is closed. The epoxy is then injected in the upper valve and the procedure repeated until the crack is filled. In the event of unanticipated leakage from previously undetected cracks, hydraulic cement is used as a sealer.
2.11.5 Installing Anchor Bolts in Concrete Structures
Using prepackaged epoxy grout in glass tubes is an extremely efficient method of installing anchor bolts in existing concrete structures. The action of screwing the an chor into the tube breaks the glass, which then acts as a coarse aggregate, and mixes the resin to start the setting action. This type of grouting system is very cost effective for small projects.
Alternatively, portland cement mortar or epoxy resin can be used. With these materials the grout is squeezed or injected into the drilled and cleaned hole so that the hole is almost full. The anchor bolt is then inserted into the hole, forcing some of the grout out and ensuring that the hole is completely filled.
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