 Over the years it seems we've tried just about every option for making full depth repairs in jointed concrete pavement. Some of the options have worked great. Others, not so great. The purpose of this program is to pass along sharps findings under the C206 project. The user's guide for this topic contains all the information in this videotape as well as specification guidelines. The findings can be explained best by covering five major topics. Distresses requiring full depth repair, field survey, transverse joint design, materials, and repair procedure. We'll start with distresses. As a rule, any damage that extends the full depth of the slab will require full depth repair. This applies to blow ups, corner breaks, and deteriorated joints and cracks. In addition, full depth repairs are frequently required where deteriorated cracks have developed in an asphalt concrete overlay or in an existing concrete repair. Spalls, however, should be examined closely. If the deterioration doesn't extend deeper than one-third of the slab depth, a partial depth repair is usually adequate. But if the spall is a result of material problems, such as de-cracking from non-durable aggregates, a full depth repair is normally the only effective solution. In areas where the pavement is severely deteriorated, it's usually more economical to completely remove and replace large areas rather than make numerous separate patches. The same holds true for jointed plain concrete pavement with joint spacing between 12 and 20 feet. Often, it's better to replace an entire slab rather than make full depth repairs for economic and performance reasons. With that in mind, let's look at the field survey. A field survey should be made during planning to identify the repair locations and the extent of rehabilitation necessary. This can be accomplished by a trained crew performing a condition survey for the entire project. The survey should be conducted as close to project bidding as possible to accurately determine areas needing repair. Later, but before any work begins, the boundaries of each repair must be defined and clearly marked on the slab surface. It's important to include all significant underlying deterioration in the repair. The deterioration near joints and cracks may be greater at the bottom of the slab than at the top, particularly in freeze-thaw climates. Repair dimensions play a major role in repair performance. The width of the repair should not be less than a full length, and the length should be at least six feet. Smaller repairs tend to rock and pump under heavy traffic loads. Again, refer to Sharp's full depth repair user's guide for important details about selecting repair boundaries. Now let's look at transverse joint design, perhaps the most critical factor influencing the performance of full depth repairs. Poor load transfer at transverse joints allows differential movement of the slabs under load. This, in turn, can cause serious spalling, rocking, pumping, faulting, even break up of the adjacent slab or the repair itself. The most reliable method of providing load transfer is to anchor smooth dowel bars or deform tie bars in holes drilled into the face of the existing slab. The smooth dowel should be used in at least one of the repair joints because they provide a working joint, one that allows horizontal movement of the slab. Without the horizontal movement, damage could result because of restraint at the joint. Tie bars do not allow this movement, so they're not recommended for use on long repairs. However, on short repairs, one end of the repair may be tied to the adjacent slab. A tied joint provides better load transfer and reduces the chance that the repair will rock under traffic. On high volume roads, at least four or five dowels should be provided in each wheel path. For most highway applications, the minimum dowel diameter recommended is one and one quarter inches. But one and a half inch diameter dowels have performed very well on roads with heavy traffic. The size and number of dowel bars should be determined based on the slab thickness, type of base, expected traffic, and drainage. The user's guide contains more information on load transfer design. OK, let's move on to materials. Recent developments in concrete make it possible to complete full depth repairs in a matter of hours. Now repairs can be made during off-peak hours, so that all traffic lanes can remain open during rush hours. The high early strength required for early opening is obtained by increasing the cement content of the mix, adding an accelerator, and minimizing the water-to-cement ratio. Special cements can also be used to obtain high, very early strength. Typical fast-track mixes contain seven to nine bags of type one or type three cement per cubic yard of mix. Depending on cement type, cement content, the use of an accelerator, and curing conditions, these mixes allow opening of the repair in four to twenty-four hours. The selection of the concrete mixture should be based on available lane closure time. Sometimes it may be acceptable to let the concrete cure for several days, which allows a regular concrete mixture to be used. Now we're ready to examine the repair procedure in detail. There are several alternatives, but you'll be shown a generally accepted procedure that has given successful results. The first step is to saw the repair boundaries full depth with diamond saw blades. On hot days it may not be possible to make this cut without first making a wide pressure relief cut within the boundaries. A carbide-tipped wheel saw may be used for this purpose, but care must be taken not to damage the adjacent slabs or the base. This saw produces cuts with ragged edges that promote excessive spalling. Therefore, the saw cuts must be made at least eighteen inches away from the repair boundaries. And they must not be allowed to penetrate more than a half inch into the base. Frequently the repair boundaries are cut at night after the pavement is cooled. This helps keep the saw from binding. The longitudinal joint between lanes and at the concrete shoulder should also be cut full depth. This cut must completely sever all existing tie bars. If there's an asphalt shoulder, about six inches of it along the repair boundary must be removed. This helps prevent damage to the shoulder during concrete removal and provides space for the outside edge form. A wheel saw may be used to make this cut. The concrete within the boundary cuts is now ready for removal. It's very important that this be done without damaging the adjacent slab or the base. The preferred way of removing concrete is the lift-out method because it's fast and causes the least amount of disturbance to the base. The concrete is lifted out in one or more pieces using chains and lift pins or other devices. After the concrete is removed, all loose or disturbed base material must be removed and replaced. For small repairs, replacing all or part of a deteriorated base with concrete gives the best result. That's because it's very difficult to adequately compact granular material in a confined repair area. Hand vibrators normally don't produce sufficient compaction to prevent settlement of the repair. During both concrete removal and base preparation, it's very important not to disturb the base any more than is absolutely necessary. The next step is to install dowels and or tie bars along the exposed faces of the slabs. The dowels on transverse faces are installed by drilling holes on 12-inch centers at mid-slab depth. The holes can be drilled rapidly by tractor-mounted gang drills that drill several holes simultaneously while maintaining proper horizontal and vertical alignment. Use of a single handheld drill is not recommended because of the likelihood of misalignment. Proper hole alignment is crucial to proper functioning of the joint. Following the proper dowel embedment procedure is also critical to good repair performance. First, the debris and dust in the drilled holes must be blown out with compressed air. If the holes are wet, they should be allowed to dry before dowels are installed. A quick-setting, non-shrinking cement grout or epoxy resin is then placed in the back of each dowel hole. It's important to place this material all the way into the holes so that it will be forced out when the dowels are inserted. This will ensure that it completely surrounds each dowel for its entire embedment length. Next, thin, tight-fitting plastic discs called grout retention discs are fitted over the dowels. The dowels are then inserted into the holes with a twisting motion. At least one-and-a-half turns should be made during insertion to ensure a uniform coating of the anchoring material around each dowel bar. The grout retention discs are pushed against the slab face to prevent the anchoring material from flowing out of the holes. They also help create an effective face at the entrance of the dowel holes where the bearing stress is most critical. After dowel placement, the protruding ends of the bars are lightly greased to facilitate movement in the new concrete. The final step of preparation is the isolation of the longitudinal joints, required when the repair spans a transverse joint or crack in the adjacent lane. Longitudinal joints are usually not tied on full-depth repairs to allow free movement of the repair at these joints. This is accomplished by placing fiberboard along the existing longitudinal joint. If there's an asphalt shoulder, an edge form must be placed along the shoulder joint. Now, we're ready to place the concrete. The critical aspects are consolidating the concrete adequately and finishing at level with the surrounding pavement. As for consolidation, all the concrete has to be properly vibrated. This is especially important along the edges and in the corners of the repair. The repair must then be finished level with the surrounding surface. It's best to operate the screed parallel to the pavement center line, conforming the repair surface to any ruts in the existing surface. The repair surface should be struck off two or three times to ensure that it's flush with the adjacent concrete. As soon as the bleed water has evaporated, the repair surface should be textured to match the texture of the surrounding pavement as closely as possible. Then, immediately after texturing, the repair area should be covered completely and uniformly with a pigmented curing compound. The curing compound seals the surface to reduce moisture loss. If conditions are hot and dry at the time of placement, additional curing measures may be needed, such as covering the repair area with wet burlap. Both transverse and longitudinal repair joints should be sawed and sealed as soon as possible to reduce spalling and minimize the infiltration of water. The sealant reservoir should be made at least two inches deep to avoid point-to-point contact at the top of the slab, which can cause spalling. It's important that the reservoir shape factor, or the depth-to-width ratio, be consistent with the joint spacing and sealant type. The sealant manufacturer's recommendation should be followed. And that completes the repair procedure. All that remains is to wait until the concrete has reached adequate strength for opening to traffic. Adequate strength is based on either the compressive strength or the flexural strength at the time of opening. Either a compressive strength of 2,000 psi or a center-point flexural strength of 300 psi is frequently used as the criterion for opening to traffic. The concrete strength can be determined either by direct strength testing or non-destructive testing procedures, such as maturity or pulse velocity. And that brings us to the end of the program. As you've seen, there are many important aspects of performing full-depth repairs on jointed concrete pavements. If you're planning full-depth repairs, consult the user's guide. It provides complete guidelines and guide specifications.