277 SECTION 511 DOWEL BAR RETROFIT
511.1 -DESCRIPTION : Dowel bar retrofit consists of installing epoxy -coated, round steel dowels into existing concrete pavement across transverse joints and/or cracks. Slots are cut using diamond -tipped saw blades, the existing concrete is removed, the dowels are placed in the slots across the joints or cracks, and the slots are backfilled.
511.2 -MATERIALS : Materials shall meet the requirements of the following Sections:
MATERIAL SECTION OR SUBSECTION Bond Breaker 511.2.1 or 707.9 Caulking Filler 511.2.1 Dowel Bar Support Chairs 511.2.1 Epoxy -Coated Dowel Bars 709.15 Expansion Caps 511.2.1 Foam Core Insert 511.2.1 Non-Shrink Concrete Backfill Material ASTM C928 and 511.2.1
511.2.1 -Material Requirements:
Bond Breaker: Acceptable bond -breaking compounds include white pigmented curing compound or other approved bond breaker materials. Apply bond breaker coating on all surfaces of the dowel bar, either at the manufacturing facility before shipment, or on -site. Do not apply bond breaker while the dowel bars are in place within the pavemen t section.
Dowel Bar End Caps (Expansion Caps): Use tight -fitting, commercial quality end caps made of a non -metallic, non -organic material that allow for ¼ inch of movement at each end of the dowel bar.
Dowel Bar Support Chairs: Use chair devices for supporting the dowel bars that conform to the epoxy -coated steel requirements of ASTM A884, or are fabricated from commercial quality, nonmetallic, non -organic material. Dowel bar chairs are used to firmly hold the dowels centered in the slots during b ackfill operations. Design the dowel bar chairs to hold the bar a minimum of ½ inch above the bottom of the slot while the backfill material is placed and consolidated.
Foam Core Insert: Use a foam core insert to re -establish the joint or crack. The insert shall consist of rigid styrofoam material or closed cell foam, faced with poster board or plastic material. The foam core insert (joint/crack re -former) allows each side of the slot to expand and contract. Ensure that the insert extends up to the bottom of the existing joint sealant reservoir.
278 Caulking Filler: Acceptable silicone caulking filler used for sealing the existing transverse joint or crack at the bottom and sides of the slot includes any commercial silicone caulk designed as a concrete sealant that is compatible with the patch material being used. Caulking filler is used to prevent backfill material from flowing into the joint or crack.
Non-Shrink Concrete Backfill Material – Use concrete backfill material tested as Dry, Rapid -Hardening Cementitious Materials for Concrete Repairs in accordance with ASTM C928. Only use material that: (1) provides a compressive strength of 3000 psi prior to the time anticipated for op ening to traffic; (2) has a calculated minimum durability factor of 90 percent (90%) at the end of 300 freeze -thaw cycles per ASTM C666; and (3) has a total chlorideion content less than 0.75 lb/yd3. Provide certified material test results, for this mate rial, from an approved independent testing laboratory to the Engineer at least thirty ( 30) calendar days prior to any placement operations. A manufacturer’s representative shall be on - site at the beginning of the backfill operation.
511.22-Material Su bmittal Requirements: Submit samples of the following materials
to the Engineer for approval prior to the installation of the following items: Dowel Bar End Caps Dowel Bar Support Chairs Foam Core Insert Caulking Filler
Submit the material samp les at least 30 calendar days prior to use or at the pre -construction conference, whichever occurs first.
511.3 -CONSTRUCTION METHODS : Install dowel bars in the existing portland cement concrete paveme nt at locations as shown in the plans. When retrofitting existing doweled joints, the Contractor shall be responsible for locating any existing dowel bars. The location of the retrofit dowel slots shall be adjusted so that the retrofit slots are mid -way between pairs of existing dowels. The Contractor shall use non - destructive testing methods, such as the MIT Scan -2 technique, as approved by the Engineer, to confirm the locations of any existing dowels.
511.3.1 -Saw Cutting: Make two saw cuts in the pavement to outline the longitudinal sides of each dowel bar slot. These saw cuts shall be parallel to each other and shall create a slot which is 2 ½ ± 1/8 inches wide. Saw to a depth and length that allows the center of the dowel to be placed at mid -depth in the pavement slab. The slots shall be sawed so that half the length of each dowel bar is located on either side of the transverse joint and/or crack. Saw slots parallel to each other and to the centerline of the roadway with a maximum tolerance o f ¼ inch per twelve ( 12) inches of dowel bar length. Use saws equipped with gang mounted diamond blades capable of cutting a minimum of three or four slots simultaneously in each wheel path. Skewed joints or cracks may require slots longer than the length specified in the plans. Pick up and remove water and residue from the pavement surface immediately by means of a vacuum attachment on the sawing machine. This material shall become property of the Contractor and shall be disposed of in accordance with all applicable local, state, and federal regulations. For smaller projects, a slot sawing machine might not be feasible. The Engineer may approve the use of walk -behind saws for slot cutting when the project contains less than 100
279 retrofit bars. The Contra ctor shall take additional steps to ensure proper slot alignment and spacing when using walk -behind saws for creating the slots.
511.3.2 -Concrete Removal: Use maximum weight 30 lb . jackhammers to remove the concrete remaining between the saw cuts. If t he concrete removal operations cause damage to the pavement that is to remain, discontinue concrete removal operations and only resume after taking corrective measures. Repair or replace pavement damaged during concrete removal operations at no additional expense to the owner and to the satisfaction of the Engineer. During concrete removal operations, use appropriate equipment as necessary to produce a flat, level surface within the slot, so the backfill flows and consolidates under the dowel bars. Dispose of any debris generated during concrete removal operations outside the right -of-way in accordance with Section 207. Installation of retrofit dowels, with dowel bars and placement of backfill must be completed prior to reopening the lane to public tr affic.
511.3.3 -Slot Cleaning and Preparation: Sandblast all exposed surfaces in the dowel bar slot to remove saw slurry and debris such that clean aggregate is exposed. After sandblasting, clean the slot by blowing with moisture -free, oil -free compressed air having a minimum pressure of 150 psi to remove any dust, residue, or debris left in the slot.
511.3.4 -Sealing Joints and Cracks in Slot: Seal the existing transverse contraction joint and/or all cracks at the bottom and the sides of the dowel ba r slot with an approved caulking filler to prevent any of the backfill material from entering these areas. Prior to sealing, ensure that surfaces receiving the caulking filler are clean and free of moisture. Do not extend the caulking filler beyond 3/8 inc h of each side of the existing joint or crack.
511.3.5 -Placing Dowel assembly in slot: Use good construction practices to prevent contamination of the cleaned slot before or while placing dowel assemblies to limit the potential of bonding loss with the backfill material. Refer to Figure 511.3.5 as a guide for dowel bar placement in the slot. Dowel bar end caps shall be installed on the end of each dowel bar, and an approved bond breaker material shall be applied to each dowel bar prior to placeme nt of the bar in the slot. Place the dowel bars in the slots to within 5% tolerance of the depth shown on the plans, and parallel to the traffic lane centerline and top of roadway surface within a tolerance of ¼ inch per twelve ( 12) inches of dowel bar l ength. Center dowels at the transverse joint or crack, such that approximately one -half of the dowel extends into each adjacent panel. Cease and adjust operations if the chairs do not hold dowel bars securely in place during placement of the backfill mate rial. Place a foam core insert at the middle of the dowel bar and two ( 2) inches below the surface of pavement. Place the insert so it covers the existing transverse joint or crack and is capable of remaining in a vertical position, tight to all edges d uring backfill placement operations. Re - establish the joint or crack above the foam core insert within four ( 4) hours of backfill placement by means of sawing when the backfill material has hardened sufficiently.
280 FIGURE 511.3.5
511.3.6 -Mixing and Placing Backfill Material: Mix backfill material in accordance with the manufacturer’s instructions and the specifications. Refer to manufacturer’s information on handling, mixing, and placing backfill material. Take extreme care rega rding backfill material mix proportions, water cement ratio, and the condition of the mixing equipment. Improper mix proportioning and/or inefficient mixing apparatus can result in premature deterioration of the backfill material. When using auger type mixing equipment, take steps to keep the auger flights free from material buildup, causing inefficient mixing operations. Fill each dowel bar slot with backfill material after placement of the caulking filler, the dowel bar, expansion caps, support chairs, and the foam core insert. Ensure that the foam core inserts remain upright and over the existing joint or crack during the backfill process. Vibrate the backfill material with a small hand held vibrator capable of thoroughly consolidating the backfill mat erial into the slot around the dowel bars and support chairs. Place backfill while fresh, and before the backfill has taken an initial set. Do not re -temper the backfill with water. Discard unacceptable backfill material outside the right -of-way in accordance with Section 207 . Overfill, by approximately 1/8 inch, the slot and finish the surface of the filled slot level with the existing concrete. It is acceptable to leave the slot slightly overfilled if diamond grinding is to be employed. Cure backfill material in accordance with the backfill manufacturer’s recommendations. Apply curing compound within 60 seconds after placing the backfill material.
511.3.6.1 -Testing: Fabricate a minimum of six compressive strength specimens in accordance with AASHT O R 100 for each day of backfill placement. The compressive strength of an average of three of these specimens shall represent the compressive strength of all backfill material placed after the batch from which the previous compressive strength specimens were fab ricated through the batch from which these specimens were fabricated.
511.3.7 -Diamond Grinding: Diamond grinding shall c onform to the requirements of operations. Diamond grind dowel bar retrofitted joints after the backfill material has cured properly in the dowel bar slots and has achieved a compressive strength of at least 3000 psi. Diamond grinding must be completed within 14 calendar days of the instal lation of the project’s final dowel bar. Diamond grind the entire width of the pavement lane, from longitudinal joint to longitudinal joint.