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.
281 511.3.8 -Sealing Joints and Cracks: If specified, widen the transverse joints or cracks by diamond saw cutting after completion of the retrofit dowel installation if diamond grinding is not employed, or after the grinding has been completed. This work shall be done and paid for in accordance with Section 510 of the Specifications.
511.4 -OPENING TO TRAFFIC : Unless otherwise permitted in writing by the Engineer, do not permit traffic on dowel retrofitted pavement until the backfill attains a compressive strength of 3000 psi or greater as verified by specimens fabricated and tested in accordance with Section 511.3.6.1.
511.5 -DOWEL BAR ALIGNMENT ASSURANCE : The Contractor shall use one of the two methods below to assure dowel bar alignment.
511.5.1 -Coring: The Contractor may use diamond coring to confirm dowel placement and to randomly check dowel positioning. Check each day’s retrofitting within two calendar days by performing one test for every 600 dowels placed. One test co nsists of drilling two cores, one on each end of a dowel bar to expose both ends and allow measurement for proper alignment. Identify the concrete cores with a location description immediately after coring and submit to the Engineer for inspection. Core t he holes by a method that will not shatter or damage the concrete adjacent to the holes. Use a minimum diameter of four ( 4) inch cores. Clean and fill the core holes in the concrete pavement using the same requirements for the backfill materials as spec ified earlier in this document. Finish the core hole backfill material after placement to match the adjacent pavement surface. The backfill shall not evidence any depressions or surplus material above the level surface of the existing pavement. If tests indicate dowel bars are aligned incorrectly or backfill material is improperly placed, the Engineer shall select the number and location of any additional coring tests to determine the severity. Suspend dowel retrofitting operations if: (1) dowels are i nstalled improperly and (2) dowel alignment does not meet the specified tolerances. Do not allow dowel retrofitting operations to resume until the Contractor demonstrates to the Engineer that the problem has been corrected. Replace any individual dowel bar retrofit not functioning or damaged.
511.5.2 -Non-Destructive Testing: The Contractor may use non -destructive testing methods, such as the MIT Scan -2 technique, approved by the Engineer, to confirm dowel placement and alignment. Check each day’s re trofitting operation the next calendar day by testing 10% of the joints completed on the first day of operation and 5% of the joints completed each day thereafter. Suspend dowel bar retrofitting operations if dowels are installed improperly and/or dowel alignment does not meet the specified tolerances. Do not allow dowel retrofitting operations to resume until the Contractor demonstrates to the Engineer that the problem has been corrected. Replace any individual dowel bar retrofit not functioning or dam aged.
511.6 -TEST SECTION : In the presence of the Engineer, construct a test section that consists of slot sawing, concrete removal, and placement of dowel bars and backfill material at a location directed by the Engineer prior to the start of major operations. A test section shall be one lane wide and of a length which contains three joints and/or cracks to be retrofitted. This test section may consist of a section of existing concrete which is not within the limits of the project.
282 Take six full depth cores (one at each end of t wo dowel bars and one at the midpoint of two additional dowels), at least four ( 4) inches in diameter as directed by the Engineer at least twenty -four hours after the completion of the retrofit test section. These cores shall be used to determine the comp leteness of the slot removal, dowel bar installation, and backfill placement operations. Begin production operations upon approval from the Engineer. If the test section does not conform to the plans and specifications, construct additional test sections at the direction of the Engineer to demonstrate ability to install the retrofit dowels in a fashion that meets the requirements of the plans and specifications. If a Contractor can provide evidence that they have sufficient experience with this type o f work, based on experience with previous projects, then this test section requirement may be waived by the Engineer.
511.7 -METHOD OF MEASUREMENT : Dowel bar retrofit is measured by each dowel bar installed and accepted.
511.8 -BASIS OF PAYMENT : The contract unit price paid for each dowel bar includes full compensation for all material removal and fo r furnishing and placing all the materials and doing the work herein prescribed in an acceptable manner including all labor, tools, equipment, supplies, and incidentals necessary to complete the dowel bar retrofit. This also includes the cost of each dowe l bar assembly installed in the construction of the dowel retrofit test section and the cost of dowel bar placement alignment assurance.
511.9 -PAY ITEMS: ITEM DESCRIPTION UNIT 511001 -* Installation Of Dowel Bar Each 511002 -* Installation Of Dowel Bar at Existing Doweled Joint Each
* Sequence number
283 SECTION 512 CONCRETE SLAB STABILIZATION
512.1 -DESCRIPTION : This item of work shall consist of drilling holes in Portland cement concrete pavement as directed, pumping a portland cement/fly ash grout through the holes to fill voids under the pavement, and filling the drilled holes with mortar.
512.2 -MATERIALS : Materials shall meet the requirements of the following Sections:
MATERIAL SECTION OR SUBSECTION Accelerating Admixtures 707.13, 707.14 Curing Compound 707.9 Fine Aggregate 702.1 Fly Ash 707.4.1 Portland Cement 701.1, 701.3 Water -Reducing Admixtures 707.3
512.3 -PROPORTIONING : 512.3.1 -Mix Design Requirements: The subsealing grout mix shall be as follows: 94 pounds of portland cement (minimum) 210 pounds of fly ash Water -reducing admixture dosed at the Manufacturer’s recommended dosage rate for the cementitious material content listed above Water to achieve required fluidity
If ambient temperatures are below 55°F, an accelerating admixture shall be used. Prior to the start of construction, the Contractor shall design and submit to the Engineer for approval the prop ortions of materials, including admixtures, to be used which will result in a workable subsealing grout mixture having the desired properties. Submittals shall include tests of the grout by an approved laboratory showing 1 -day, 3 -day, and 7 -day compressiv e strengths and flow cone efflux time. An approved laboratory is defined as a laboratory which is regularly inspected by the Cement and Concrete Reference Laboratory. The 7 -day strength shall not be less than 400 psi as measured by ASTM C109. The subsealing grout efflux time shall be measured by ASTM C939 (Flow Cone Method) and shall be between 16 and 25 seconds.
512.4 -EQUIPMENT : The grout plant shall consist of a positive displacement cement injection pump and mixing equipment that is capable of providing a thoroughly mixed and homogenous mixture. Rock drills or other devices capable of drilling the grout injection holes throug h the pavement and base material will be permitted. The rock drill shall not be heavier than 60 pounds, and the downfeed pressure whether by hand or mechanical means shall not damage the bottom portion of the slab. The Contractor shall supply equipment c apable of detecting the lift of the pavement near the hole being grouted. These devices shall make lift measurements from a stable reference point and shall be of a design satisfactory to the Engineer.