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The repair process begins after the final cleaning of the area. The area must be dry and free of dust, oil, dirt, etc. A good repair begins with a clean surface. Since the volume of most spall repairs is usually small, most mixing must be done in a small drum or mortar mixer. Some repair materials come premixed and others allow the mix to be extended by adding aggregate (maximum recommended size is 3/8 inch or 10 millimetres). The material must be consolidated through tamping, supplemented, when possible, by vibration, and the surface worked to match the surrounding finish as closely as possible.
Joint Filler
If the spalled area is adjacent to an expansion joint or a crack, a joint filler must be employed to prevent the repair material from fouling the joint and to retain the joint shape. If the spall is next to a crack, the crack must be treated as an expansion joint. Spall repairs must not bridge cracks or expansion joints. The crack must be formed up just as an expansion joint. The joint filler should be the same width as the existing joint or crack, long enough to cover the spall area, and deep enough to cover the full depth of the spall.
NOTE: Application of bonding agent to the concrete surface. Note the joint filler bordering the repair area
Bonding Agents
Bonding agents are utilized to improve the bond between the patch and the patch repair materials. A light coating of bonding agent must be used when using PCC as the repair material. If using a rapid setting or polymer concrete, consult the manufacturer’s recommendations on the use of bonding agents. For PCC repairs, the bonding grout used is a mixture of one part Portland cement to one part sand with a water-to-cement ratio less than 0.45. The bonding agent must be brushed into cracks and crevices to ensure good contact with the repair surface (See Figure above). Many repair materials are proprietary and may also require a proprietary bonding agent. When employing these types of material in the repair, the manufacturer’s recommendations must be followed closely. The entire surface of the repair area must be lightly coated or sprayed with the bonding agent, and the repair material must be placed when the bonding agent has reached a tacky consistency. If the bonding agent is dripping through small openings where the joint filler meets the bottom of the spall recess, a small bead of caulk may be placed to prevent the dripping.
Mixing and Placing
The mixing and placing of spall repair materials often varies considerably due to the widely different materials that can be used. It is good practice to place the repair material at pavement temperatures above 55 degrees Fahrenheit (13 degrees Celsius) and below 90 degrees Fahrenheit (32 degrees Celsius). If water is required, the correct amount of clean, fresh water must be added and thoroughly mixed. Hand mixing almost always requires more time than drum or mortar mixers. When hand mixing, there is also a tendency to add more water than required to ease the mixing effort. Manufacturer’s recommendations for mixing and curing of materials must always be strictly followed to ensure a quality patching job. Repair materials must not be placed at temperatures less than 40 degrees Fahrenheit (4 degrees Celsius) and only with special insulation and longer cure times for temperatures less than 55 degrees Fahrenheit (13 degrees Celsius). In summer, it is best to place repair materials in the morning when pavement temperatures are lower. In winter, afternoons are best.
Consolidation
After placement, the repair material must be thoroughly consolidated to remove trapped air. Cementations and polymer concrete materials require some type of consolidation, by tamping or, if suitable, supplemented by vibration . Vibrators with a small (less than 1 inch or 25 millimetres) head or vibratory screeds are recommended for small repairs. Grate tampers must not be used. After consolidation, the repair material must be finished to match that of the surrounding pavement. A completed patch is shown in figure below. Where the spall repair was conducted on both sides of the expansion joint. Note the joint filler separating the spall repair.
1.Consolidation of the repair material by vibration(above)
2.Finishing the patch surface(above)
3. A completed spall repair that bridges an expansion joint(above)
Curing
Curing of the material is very important, especially for partial-depth repairs where the surface-area-to-volume ratio of the repair area is larger than a full-depth repair, and bond strength develops much slower than compressive strength. Rapid water loss from the surface due to high temperature, low humidity, and/or windy conditions can result in severe shrinkage cracking on the surface. Curing should consist of covering the patched area with two layers of presaturated burlap which is then covered with clean polyethylene sheeting. The burlap and sheeting is then covered with weighted plywood or form board. All cover layers should extend 12 inches (300 millimetres) beyond the outline of the patch. Covers should be removed, the burlap resaturated, and the covers replaced daily for at least 7 days. The fresh PCC should be covered as soon as possible after finishing the surface. Special curing procedures for rapid-setting concretes must be followed to prevent excessive shrinkage cracking. These materials harden rapidly and severe plastic shrinkage cracking may develop on the surface if the materials dry too fast. Manufacturer’s recommendations for curing of proprietary concretes must be followed.
Resealing
After the patch has cured, the final repair step is to replace the sealant to maintain the existing joint or crack. Joint or crack resealing should not begin until the concrete curing process is complete. The joint sealing operation is analogous to crack sealing. The joint or crack adjacent to the spall is sawed out to the same width as the existing joint or crack using a concrete saw, router, or hand saw. The joint filler must be removed by hand or by sawing.. The sides of the saw cuts are then sandblasted, air blasted with compressed air, and washed with high-pressure water to prepare a good surface for sealant adhesion. The area surrounding the repair should be swept with a vacuum broom to remove debris, etc. After cleaning the area, backer rod is installed in the joint or crack recess.
Placing Sealant
Placement of the sealant is similar to that of crack sealants in that the sealant should be placed from the bottom up and in a smooth stroke from the beginning to the end of the joint or crack, if practical
Cleanup
After the repair is complete, all equipment should be cleaned, lubricated if necessary, and properly stored until needed for the next repair operation.
