SPECIAL SPECIFICATION 4899 Aluminum-Zinc-Indium Cathodic Protection System

Transcription

1 1993 Specifications CSJ SPECIAL SPECIFICATION 4899 Aluminum-Zinc-Indium Cathodic Protection System 1. Description. This Item shall govern for the furnishing, installing and energizing a sacrificial aluminum-zinc-indium anode cathodic protection system. This work include connection to the embedded reinforcing steel, materials, testing and ensuring electrical continuity between embedded reinforcing steel components on designated footings, tie beams, concrete walls and columns of the Queen Isabella Causeway in accordance with the plans and the requirements of this item. The cathodic protection system consists of a thermal sprayed Aluminum-Zinc-Indium anode coating and connector plates. The Cathodic Protection system furnished by the Contractor shall include all materials identified in these specifications and shown in the plans. The following guidelines shall be followed: a. Each bent shall have a minimum of two anode connector plates. b. Four bents shall be "instrumented" test structures in accordance with Item 4901 Aluminum-Zinc-Indium Instrumented Bents and with the schedule shown in the plans. To facilitate testing of anode current and depolarization, the anode system for the instrumented bents shall be electrically isolated from the reinforcing steel except through a cable at the isolated anode connector plate. The instrumented bents shall include permanently embedded reference electrodes, isolated anode connector plates, junction boxes, wiring and conduit. c. The anode system for the remaining bents shall be connected directly to the reinforcing steel and no provision for electrical isolation shall be made. 2. Referenced Specifications. The following standards shall be observed: ASTM D1002 ASTM D4285 ASTM D4541 ASTM D4263 Strength Properties of Adhesives in Shear by Tension Loading Standard Test Method for Indicating Oil or Water in Compressed Air Standard Test Method for Pull-off Strength of Coatings Using Portable Adhesion Testing Standard Test Method for Indicating Moisture in Concrete by the Plastic Sheet Method ICRI No Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings and Polymer Overlays SSPC CS Guide for Thermal Spray Metallic Coating Systems SSPC Guide 6 Item 4901, Guide for Containing Debris Generated During Paint Removal Process Aluminum-Zinc-Indium Instrumented Bents

2 3. Materials and Equipment. All materials, fabrication and installations are subject to inspection and testing by TXDOT or it s designated representative. Use only specified materials. (1) Anode System. The galvanic aluminum-zinc-indium anode wire shall be the CORRSPRAY TM system, as supplied by Corrpro Companies, Inc West Smith Road, Medina, Ohio 44256, or approved equal. The material shall meet the following specifications: Nominal Chemical Composition: Max. Cu Content: Wire Diameter: Type: Density: Open Circuit Potential in Simulated Concrete Pore Solution w/ph = 12-13: Al-20Zn-0.2In 100 PPM mm (1/8 in.) Cored Wire 3.24-g/cubic cm > -1.6 V (CSE) The anode connector plate shall consist of a perforated 16-gage aluminum alloy sheet, galvanized steel stud, nut and washers. The anode connector plates shall be 4.0 inches by 4.0 inches and 1/16 inches thick. The perforated hole size in the plate shall be in. diameter. Center to center spacing of the perforated holes shall be 1/4 inches and the open area shall be 51%. The connector plate shall have 4 holes for attachment to the concrete surface and one hole in the center of the plate for attachment of the steel stud or screw. The size of these holes shall be 1/4 inches in diameter. Attaching the connector plate to the concrete surface shall be self locking fasteners. The anode connector plate shall be sand blasted on both sides to remove any surface film and to provide a profile for bonding. The anode and anode connector plates shall be kept clean, dry and free from oxides at all times. (2) Application Equipment. The coating shall be applied using electric-arc spray equipment. The arc spray equipment shall consist of a spray gun, wire feed unit, power supply, and air compressor. A straightening device may be necessary to readily spray the coiled anode wire, The Contractor shall be responsible for making any necessary modifications and adjustments to the thermal spray equipment, so that the alloy wire can be sprayed properly. 4. Construction Methods. The Contractor shall demonstrate that they are capable of spraying the sacrificial alloy prior to installation at the job site. The Thermal Spray Contractor shall have adequate technical training and field experience, to safely and proficiently apply the anode coating on concrete structures. The Thermal Spray Technician must have a minimum of two years experience with the operation of Thermal Spray Equipment. The metalizing Contractor conducting the installation of the metalized coating shall have a minimum of three years of previous experience in metalizing operations in the field. The metalizing Contractor must have performed at least one similar project within the last two years The Contractor shall submit qualifications of the Thermal Spray Sub-Contractor, and the Thermal Spray Technicians for approval prior to performing any metalizing work

3 The Contractor shall submit a detailed Work Plan for all phases of work and a description of proposed materials to be used in this project. The Work Plan shall be submitted to the Engineer for approval prior to any repair or metalizing work taking place. Independent validation tests may be conducted by the Engineer. The Contractor shall coordinate installation of the system components with all other construction operations. The Contractor shall provide a platform that provides safe access for workers, supervisors and inspectors to all areas where work is being performed. The Contractor shall collect and safely dispose of all project wastes in accordance with Local, State and Federal Regulations. The facilities for confining and safely disposing of these wastes shall be provided and operated by the Contractor and shall be approved by the Engineer. Wastes include scrap metal, demolition debris, concrete and concrete dust, blasting materials and aluminum-zinc-indium dust. Any damage to property due to the Contractor s operations shall be the responsibility of the Contractor. The plans for the cathodic protection system are diagrammatic and shall not be scaled for exact locations unless scales are explicitly stated on the drawing. Field conditions and noninterference with structural features shall determine exact locations. (1) Steel Continuity Testing. The reinforcing steel shall be checked for electrical continuity at a minimum of 5 locations per 1,000-sq. ft. between all exposed rebars or other metallic members by using the DC millivolt technique. This testing shall be conducted during the delamination repair stage, so as to alleviate unwanted excavation of sound concrete. Test equipment for this procedure shall consist of a standard digital DC voltmeter, test leads and wire reel. The millivolt drop between the steel is measured. Readings greater than 1.0 mv indicate electrical discontinuity and the discontinuous steel must be bonded back into the steel network. All reinforcing steel, which is found to be electrically discontinuous, must be bonded back into the steel network by welding or by using uncoated steel wire ties. (2) Installation of Anode Connector Plates. The anode connector plates provide a direct electrical connection between the sacrificial anode and the reinforcing steel (except for the instrumented bents. See Item 4901, Aluminum-Zinc-Indium Instrumented Bents for details for insulating the anode surface from the galvanized steel rod). For each anode connector plate, a ¼-20 threaded galvanized steel rod (stud) shall be attached to the reinforcing steel to facilitate attachment of the anode connector plate, as shown in the plans. The following procedure shall be followed: l. Using a concrete cover meter or pachometer, locate the reinforcing steel at the location where the shorted-system anode connector plated is to be installed. 2. Drill a 1 inch diameter hole into the concrete to expose the reinforcing steel. 3. Attach a 1/4 inch diameter galvanized steel threaded rod (stud) to the exposed steel, using the tapping method. The threaded rod must extend to the outer concrete surface to facilitate attachment of the anode connector plate. Secure the rod in the hole by backfilling with an epoxy adhesive. Take care not to drip epoxy on the

4 surrounding concrete surface. Make sure that the epoxy is flush with the surface, but does not overlap onto the concrete. The threaded rod must extend a minimum of 1 inch beyond the outer concrete surface to facilitate attachment of the anode connector plate. 4. Place duct tape over the exposed rod and proceed with the abrasive blasting and metallizing process. Do not over apply the aluminum-zinc-indium in the anode connection plate area. 5. After the metallizing process is complete, remove the duct tape and install the anode connector plate over the stud. Secure with a galvanized steel washer and nut. After the anode plates are installed and tightened any excess length of the threaded rod shall be sheared off to prevent damage caused by fishing lines or vessels tying off to the rod. 6. Clean surface and proceed with a final coat of aluminum-zinc-indium over the connector plate and surrounding concrete. Ensure good contact between the coating and connector plate by measuring the resistance and voltage drop between surrounding coating and steel stud. (3) Preparation of the Concrete Surface. Work performed under this section consists of cleaning the concrete surface and providing an anchor profile by abrasive blasting, so that an adequate bond between the concrete and thermally sprayed anode can be obtained. As a minimum Class 4A containment as described in SSPC Guide 6 is required. The main purpose of the concrete surface preparation is to remove dust, grit, chalk marks, paints, curing compounds, and other substances, which might inhibit bonding of the anode to the concrete. Abrasive blasting shall not commence before concrete repairs are completed and patch materials are allowed to cure properly. Abrasive blasting shall not take place on surfaces that will be wet or damp following blasting. The following are equipment and material requirements for this item of work: (a) Abrasive Blasting Equipment Abrasive blasting equipment shall be conventional, air pressure-type blasters. A minimum pressure of 80 PSI shall be maintained at the blast nozzle. (b) Abrasives The abrasive material shall be clean and dry silica sand or other suitable material. The blast material must be plant packaged and maintained in a clean and dry condition at all times. Material stored in the sand blaster pot overnight shall not be used. A copy of the material safety data (MSD) sheet shall be provided to the Engineer prior to performing any sandblasting. Spent abrasives shall not be reused. (c) Compressed Air Compressed air used for abrasive blasting shall be clean, oil free, and dry, per ASTM D Air line filters and moisture separators shall be installed upstream from the blasting equipment. These shall be inspected daily for cleanliness and correct operation. Any indication of malfunctioning equipment shall be corrected immediately

5 The Contractor shall submit detailed descriptions of all equipment and materials to be used to the Engineer for approval. This information must provide all relevant constituents and properties of each material and the specifications to which each complies. Data published by the manufacturers will be acceptable except where certifications of materials characteristics are required. (4) Application of Aluminum-Zinc-Indium Anode Coating. Anode connector plates shall be installed before application of the anode coating. The Contractor shall furnish all necessary labor, materials and equipment for installation of the anode system, in accordance with the following procedure. 1. Concrete repair material shall cure for a minimum 14 day period or until full strength is achieved before abrasive blasting and metallizing. The enclosure temperature and surfaces to be sprayed shall be at a minimum of 5 C above the dew point. 2. Surfaces shall be thoroughly vacuumed or blown clean within 15 minutes before thermal spray application is started. Any oil, grease, soil, water, or other foreign matter that may have deposited on the surface after the surface preparation has been completed shall be removed before spray application. Coating application shall only be performed when the concrete surface is clean and dry. Tests shall be performed prior to metallizing to determine the presence of moisture in the concrete. The test methods shall use ASTM D or a surface moisture meter for concrete, such as the Tramax Concrete Encounter Meter. If significant moisture is present, which adversely affects bonding of aluminum-zinc-indium alloy coating, a portable propane powered weed burner may be used to achieve adequate low concrete moisture levels. When using the weed burner, keep the burner moving slowly at an even pace, heating the concrete surface to a maximum temperature of 150 C. 3. All metallic components or appurtenances such as drainpipes, conduit, or bearing steel plates shall be isolated from the anode and temporarily covered with suitable masking materials, which shall extend, from the objects, by at least one inch on the concrete surfaces. 4. The installation areas shall be enclosed during spraying for dust containment. The enclosure shall consist of tarps, panels, or other methods to prevent dust from escaping the immediate area such that it would constitute a health hazard. Personnel conducting spraying operations within the enclosure shall be provided with a hood with external air supply for respiration in accordance with OSHA Concrete surfaces shall not be sprayed when the surface temperature is less than 5 C (41 F), unless the concrete surface is preheated with a torch prior to the thermal spray application. 6. During application, the thermal spray nozzle shall be maintained at a travel speed and a distance from the work surface such that the anode deposit efficiency and bond strength are maximized. Travel speed shall be approximately 16 inches per second. The distance from the nozzle to the surface should be approximately 6 inches

6 7. The spray application of the sacrificial anode shall begin by metallizing the concrete area where the anode connector plates are to be installed. Install the connector plate and then continue spraying the anode coating over the connector plate and then proceed toward the surrounding concrete. 8. The coating should be applied in multiple passes and should overlap on each pass in a crosshatch pattern, before the first layer of material has cooled down. Uniform gun movement should be used to ensure a consistent thickness. Sufficient anode material shall be sprayed to achieve uniform deposition of material to an average thickness of 300 microns (12 mils). This should correspond to a deposition rate of approximately 0.2 pounds of anode material per square foot of treated surface. Material usage logs shall be used to document installation of the proper anode quantity. For confirmation of the material usage, the thickness of the coating shall be measured at a minimum of 5 locations per 100 ft 2 using a reverse eddy current thickness gage, such as the DeFelsko PosiTector The test instrument shall calibrated for the aluminum-zinc-indium alloy being tested. The average of the 5 readings shall be a minimum of 300 microns (12-mils). If the average is less than 300 microns (12-mils), the areas of low thickness shall be identified and repaired as follows: a. Clean existing anode by lightly blasting the areas without exposing large aggregates. b. Re-apply sacrificial anode coating using the procedures outlined in this specification. c. Inspect the sprayed anode for proper thickness and adhesion to the existing coating. 9. Compressed air used for spraying shall be clean, oil-free and dry, per ASTM D Airline filters and moisture separators shall be installed upstream from the spraying equipment. These shall be inspected daily for cleanliness and correct operation. Any indication of malfunction in the equipment, indicated by oil or water in the filter or traps, shall be corrected immediately. 10. The anode coating shall be continuous without lumps or blisters and be of a smooth texture. The coating shall not contain any loosely adhering particles, nor shall it contain any cracks, pinholes, or chips, which expose the concrete substrate. It shall have a uniform homogeneous appearance. Unacceptable areas shall be repaired. Repair work shall be conducted as follows: a. Remove all degraded anode coating by scraping, strip blasting or both. During this process, light blasting shall be applied to the areas without exposing large aggregates. b. Re-apply sacrificial anode coating. c. Inspect the sprayed anode for proper thickness, as described above. (5) Testing Adhesion Strength. Adhesion strength between the anode coating and concrete substrate shall be measured with a calibrated Proceq, Model DYNA Z5, or

7 approved equal. The Contractor shall use the procedure and test equipment provided by the manufacturer for calibration. Dolly size shall be 2-in. diameter. Dollies may be left in place. If they are removed, the area shall be cleaned of epoxy and the sacrificial coating reapplied. A minimum of one adhesion test shall be performed per 540-ft 2 of concrete surface. The target adhesion strength of the sacrificial anode coating shall be greater than 60-psi. (This target value shall be verified at the beginning of the thermal spraying process by preparing and spraying two horizontal and two vertical 2 x 2 test patches with the aluminum-zinc-indium coating in accordance with these specifications on a typical bent structure that is to receive cathodic protection. Two adhesion strength measurements shall be made on each patch and the target value adjusted if necessary based on the results of the test patches. The test verification shall be performed in the presence of the TXDOT representative. The Contractor shall remove the anode coating from areas where the adhesion strength is less than the established target value and re-apply the anode coating in accordance with these specifications. 5. Method of Measurement. This Item will be measured by the square foot basis of Aluminum-Zinc-Indium applied to the concrete surface. 6. Payment. The work performed and the materials furnished in accordance with this item and provided under Measurement will be paid for at the unit price bid " Aluminum-Zinc- Indium Cathodic Protection System and shall include all materials, continuity bonding of discontinuous steel, scaffolding, anode connector plates, surface preparation, enclosures, equipment, tools, testing, repair of defective area, labor, transportation and all other incidentals necessary to make the cathodic protection system operate as designed