Division 3 — Concrete

Concrete Removal Using Hydrodemolition

1.1 Description. This section addresses the concrete removal work to be performed using hydrodemolition. The depth of concrete removal required will be shown on the drawings and/or specifications. This section includes all labor, materials, equipment and supervision necessary to remove existing concrete using hydrodemolition as indicated on the drawings and in the specifications, including, but not limited to:

  1. Removal of concrete by means of hydrodemolition.
  2. Removal of concrete inaccessible to the hydrodemolition machine with hand-held water blasting equipment or conventional chipping hammers, including shadows under the reinforcing steel.
  3. Containment, collection, treatment, and disposal of hydrodemolition wastewater and water used for cleanup.
  4. Collection of debris from the demolition operation using a vacuum system and disposal of all debris.
  5. Final preparation of surface prior to placement of concrete.

1.2 References.

  1. International Concrete Repair Institute (ICRI) Technical Guideline 310.3R-2014 Guide for the Preparation of Concrete Surfaces for Repair Using Hydrodemolition Methods.
  2. ACI RAP-14: Field Guide to Concrete Repair Application Procedures – Concrete Removal Using Hydrodemolition.

1.3 Submittals. Submit the following items prior to beginning hydrodemolition operations:

  1. Hydrodemolition equipment specifications, including robot size and weight, supply water requirements, water consumption, and ultra-high-pressure hose specifications.
  2. Location and layout of the hydrodemolition equipment.
  3. Location and layout of the temporary water supply, including materials to be used and any permits required to secure the use of the water.
  4. Vacuum equipment specifications, including type, manufacturer, capacities, and filtration systems.
  5. Location and layout of any fuel system required for the equipment.
  6. Debris removal equipment specifications and method for concrete debris removal.       The debris removal process must not impact the ongoing hydrodemolition operations.
  7. Location and layout of the wastewater containment, treatment and disposal system(s), including any permits required to properly discharge the water.
  8. Copies of hydrodemolition water quality tests performed.
  9. Qualification certification(s) of the hydrodemolition operator.
  10. Hand-held water blasting equipment and/or chipping hammer specifications to be used for detail chipping, if necessary.
  11. Equipment to be used for final wash down of the hydrodemolished surface to create a pour-ready surface.

1.4 Quality Control. Hydrodemolition companies, as well as individual employees performing and supervising hydrodemolition concrete removal, must meet the following requirements:

  1. Work shall be performed by organizations that have successfully performed at least ten verifiable projects similar in scope to this project within the last three years.
  2. Work shall be under the immediate control of a person experienced in hydrodemolition who has supervised five verifiable projects of similar type and size within the last three years. Supervising personnel shall be present during all operations.
  3. The hydrodemolition equipment operator must be trained and certified by the equipment manufacturer in the proper use and safe operation of the equipment and have a minimum of two years’ experience with the equipment on jobs of similar type and size.

2.1 Hydrodemolition Equipment. Concrete removals shall be performed with a computerized, self-propelled hydrodemolition machine that utilizes a 36,000 psi ultra-high-pressure water jet stream and required water consumption of 16 gallons per minute (or less) per pump. Equipment shall be capable of removing concrete to the depth specified herein and/or as shown on the drawings and shall be capable of removing rust and laitance from exposed reinforcement designated to remain in place. The equipment shall be capable of removing concrete to within one inch of vertical surfaces.   Independent of the number of passes required to achieve the specified depth of removal, rotary heads only shall be used for the final pass of the hydrodemolition machine.

Hand-held high-pressure [10,000 psi (690 bar) minimum] wands or 35 lb. (16 kg) maximum jackhammers shall be used in areas that are inaccessible to the self-propelled machine or in patching areas that require work to remove the remaining unsound concrete.

2.2 Vacuum Equipment. Vacuum equipment shall be of sufficient capacity to collect all debris from the hydrodemolition operation. The vacuum equipment shall be capable of removing wet debris and water in the same pass.

2.3 Wastewater Treatment Equipment. All wastewater collected must be treated in accordance with Federal, State and Local requirements for water quality and discharge capability. The wastewater treatment equipment utilized must be capable of adjusting the pH, lowering the Total Suspended Solids (TSS), and lowering the turbidity of the wastewater. At a minimum, wastewater shall be treated to reduce Total Suspended Solids (TSS) to < 20 mg/L, Nephelometric Turbidity Units (NTUs) to < 50, and pH to between 6.0 and 9.0. Some jurisdictions may have more stringent treatment requirements.

3.1 Testing and Acceptance of the Hydrodemolition Equipment. Prior to the commencement of the hydrodemolition concrete removal operation, the equipment shall be calibrated on an area of sound concrete as designated by the Engineer. In case of an existing overlay, calibration shall be performed on original deck concrete that is sound and not on any concrete overlay material. After calibration, the equipment shall be moved to a known unsound area to verify that all unsound concrete is removed by the established recorded settings. Each test area (sound and unsound) shall be approximately 50 square feet. If a satisfactory result is obtained, the minimum depth and quality of removal demonstrated in the test areas shall be used for the hydrodemolition production.

The Engineer shall verify the following settings:

  1. Water pressure gauge (36,000 psi minimum)
  2. Water usage/flow rate (16 gallons per minute per pump minimum)
  3. Machine staging control (step)
  4. Nozzle size
  5. Nozzle speed (travel)

During the calibration, any or all of the above settings may be modified in order to achieve removal of all unsound concrete. The settings may be changed by the Hydrodemolition Contractor to achieve total removal of unsound concrete, but the Engineer must be notified of all changes. The Engineer may with input of the Hydrodemolition Contractor change any or all of the settings in order to achieve the goal of removing unsound concrete with hydrodemolition. Calibration shall be required on each structure, each time hydrodemolition is performed, and as required to achieve the results specified by the plan.

4.1 Execution. Execution of the hydrodemolition concrete removal shall include the following:

  1. Protect and/or relocate existing utilities within the work area that may be damaged during the hydrodemolition work. Provide temporary service until affected utilities are restored.
  2. Install temporary protection and other safety requirements prior to starting hydrodemolition. The General Contractor shall adequately shield the work area to prevent debris resulting from the hydrodemolition operation from traveling beyond the boundaries of the work area in order to protect the public from flying debris both around and/or under the work area.
  3. Provide adequate lighting as required to perform the work of this section.
  4. Remove the concrete in the areas designated on the drawings using hydrodemolition to the depth specified in the drawings, in these specifications, and as demonstrated and approved by the Engineer in the hydrodemolition test cut area. Maintain the quality and depth of cut demonstrated in the test area throughout the project. If delaminations exist beyond the minimum removal depth, removals shall continue until all unsound and delaminated concrete has been removed.
  5. Areas inaccessible to the hydrodemolition equipment shall be removed using hand-held high-pressure water blasting or pneumatic tools. If the hydrodemolition removal exposes reinforcing steel, then shadows under reinforcing steel scheduled to remain in place shall be removed to ¾ inches below the steel using hand-held high-pressure water blasting or pneumatic tools.
  6. Clean the area to remove all loose debris and other materials scheduled to be removed during the hydrodemolition. Thoroughly clean the demolished area using a water blaster held at a maximum of 12″ from the deck surface. The surface shall be vacuumed immediately following the high-pressure water cleaning to remove any debris or wastewater. Following the cleaning, the surface shall be free of all debris, loose material, slurry, cement paste and any other material that might interfere with the bond of the new concrete overlay leaving a pour-ready surface.
  7. Areas where pneumatic tools were used must be thoroughly cleaned to remove rust and laitance from existing reinforcing.
  8. Any areas contaminated by materials detrimental to a good bond as a result of the General Contractor’s operations shall require additional removals and/or cleaning until a clean surface is obtained, at no additional cost to the owner.
  9. At all locations where exposed reinforcement is designated to remain in place, exercise caution to avoid damaging the reinforcement during removal of concrete. Any reinforcement damaged by these operations shall be repaired or replaced at no cost to the owner.
  10. For projects that contain a concrete overlay, rotomilling may be allowed to within 0.5 inch of the top mat of reinforcing bar, prior to hydrodemolition. Verify capacity of structure to support rotomilling equipment.

4.2 Supply Water. All water used for hydrodemolition operations must be potable water. The owner shall designate the location from which the General Contractor shall obtain potable water. The General Contractor is responsible for supplying all material, equipment and tools necessary to tap into the water source. The General Contractor shall install a meter to measure the water consumption.

4.3 Cleanup of Solid Debris and Water. All debris shall be removed quickly enough to prevent rebonding of the concrete debris to the hydrodemolished surface. Solid debris shall be collected using vacuum equipment. Water collected during the hydrodemolition operation shall be directed to a wastewater collection system. Solid debris shall be properly disposed of with other concrete debris.

4.4 Wastewater Containment, Treatment, and Disposal. Wastewater containment shall be the sole responsibility of the General Contractor. The General Contractor shall provide a comprehensive plan for hydrodemolition wastewater containment, treatment, and disposal. At no time, shall water be allowed to run freely into live traffic areas, into other areas of the structure, or into areas accessible to the public.

All equipment needed, including piping, pumps, hoses, settling areas and pH adjustment equipment (if needed) required for the proper collection, clean up and disposal of wastewater from the work area shall be provided and maintained by the General Contractor. The system shall be designed by the General Contractor and approved by the engineer to meet the discharge requirements of the local governing authority.

The General Contractor shall obtain any permits required for the discharge of the wastewater. The General Contractor shall establish and maintain any testing program required by the local governing authority for the wastewater discharge.

All wastewater generated by the General Contractor’s operations including hydrodemolition and clean up water must be contained by the General Contractor and must pass through the General Contractor’s approved collection system. No water will be allowed to flow directly into any drainage system without pre-treatment. At no time will wastewater be allowed to enter any body of water (river, lakes, ponds, etc.)

At a minimum, wastewater shall be treated to reduce Total Suspended Solids (TSS) to < 20 mg/L, Nephelometric Turbidity Units (NTUs) to < 50, and pH to between 6.0 and 9.0. Some jurisdictions may have more stringent treatment requirements. All wastewater treatment must meet the discharge requirements of Federal, State or Local entities. With a valid permit, treated wastewater can be discharged into sanitary sewer systems, land discharged in areas where this is permitted, or hauled via tanker truck to a local wastewater treatment plant.

The General Contractor shall remove daily from the site all concrete debris, sludge and other materials generated by his work and legally dispose of all such materials.

4.5 Inspection of Exposed Surfaces and Reinforcement. After the hydrodemolition, when surface preparation operation has completed the initial pass and the deck is dry and frost free, resound the deck to ensure that all unsound material has been removed. Remove unsound materials detected by the Engineer by pneumatic hammers (not heavier than 30-pound class) or by hydrodemolition.

After removals are complete, but prior to final cleaning, all exposed concrete surfaces and all reinforcement designated to remain in place will be inspected by the engineer for compliance with the plans and specifications. Where the engineer finds unsatisfactory surface preparation, the engineer will direct the General Contractor to perform additional removals. The Engineer will re-inspect after additional removals. If reinforcing steel is exposed during the hydrodemolition operation, the engineer will inspect all reinforcement designated to remain in place for defects due to corrosion or damage caused from General Contractor’s removal operations.

4.6 General Requirements.

  1. During concrete removal do not damage existing reinforcement steel intended to remain in place.
  2. Do not drive or place equipment in the work area that may damage the reinforcing steel to remain in place. Bars that are bent or damaged shall be replaced by the General Contractor at no charge to the Owner.
  3. Following removal of debris, and prior to placement of new reinforcement steel, the entire surface shall be cleaned to remove any contamination or loose material remaining in the area.
  4. All water from the hydrodemolition and cleaning process must be contained within the construction barrier limits of the work area.
  5. Following final preparation of the area, including all other work items that must be completed prior to placement of concrete, but before final inspection and placement of concrete, the area shall be thoroughly cleaned using a water blaster with a rotating, multi-jet nozzle held at not more than 12 inches from the surface. Following the final cleaning, the surface shall be clean and free from all dirt, debris, slurry or any other material that might interfere with the bond of the new overlay.

5.1 Method of Payment. Hydrodemolition shall be measured and paid for by the square yard.