Concrete Removal Using Hydrodemolition
This section includes all labor, materials, equipment and supervision necessary to remove existing concrete as indicated on the drawings and in the specifications, including, but not limited to:
- Removal of concrete by means of hydrodemolition.
- Removal of concrete inaccessible to the hydrodemolition machine with conventional chipping hammers including shadows under the reinforcing steel.
- Containment, collection, treatment and disposal of hydrodemolition wastewater and water used for clean up.
- Collection of debris from the demolition operation using a vacuum system and disposal of all debris.
- Final preparation of surface prior to placement of concrete.
Submit the following items:
- Hydrodemolition equipment specifications. Include robot size and weight, supply water requirements, water consumption, and high-pressure hose specifications.
- Location and layout of the hydrodemolition equipment.
- Location and layout of the temporary water supply including materials to be used and any permits required to secure the use of the water.
- Vacuum system including type, manufacture, capacities, filtration systems.
- Location and layout of any fuel system required for the equipment.
- Location and layout of the system to be used to contain the wastewater including methods of reducing the suspended particles to acceptable levels, adjusting the pH, if required, and discharging the wastewater. Include any permits required to properly discharge the water.
- Copies of all water quality tests performed.
- Certification of the hydrodemolition operator’s qualifications.
- Chipping hammer and air compressor specifications to be used for detail chipping.
- Equipment and method of removal for the debris from the concrete demolition. Include proposed drive lanes to move debris outside the structure such that the removal does not impact the ongoing operations.
- Equipment to be used for final wash down of the hydrodemolished surface.
- Methods to insure the safety of all personnel.
- Work shall be performed by organizations that have successfully performed at least five verifiable projects similar to this project within the last five years.
- Work shall be under the immediate control of a person experienced in hydrodemolition who has supervised three verifiable projects of similar type and size. Supervising person shall be present during all operations.
- An individual trained and certified in the proper use and safety of the equipment and having a minimum of two years experience with the equipment on jobs of similar type and size shall operate the hydrodemolition system.
- Chipping hammers used for detail chipping shall not exceed 15 lbs.
- Final wash-down shall be done using a minimum of 8,000 psi and 8-gpm water blaster.
- Wastewater shall be tested, as required, to insure compliance with the wastewater discharge requirements established by the governing authority.
- All water used for hydrodemolition and final clean up shall be potable.
Concrete removals shall be performed with engineer approved high-pressure hydrodemolition equipment. Equipment shall be capable of removing concrete to the depth specified 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 operating at a minimum of 35,000-psi water pressure with flow rates not exceeding 32 gallons per minute. The equipment shall be capable of removing concrete to within one inch of vertical surfaces.
Hydrodemolition contractor shall supply all necessary equipment, parts and manpower to maintain pre-established production rates and assure adherence to construction schedule. Contractor shall maintain, on the job site, an inventory of common wear parts and replacement accessories for equipment adequate to ensure that routine maintenance tasks can be performed without delay to the hydrodemolition schedule.
Equipment shall be capable of performing concrete removals as shown on the drawings at a minimum production rate of square feet per eight-hour shift.
Vacuum equipment shall be of sufficient capacity to collect all debris from the hydrodemolition operation no latter then two hours following the hydrodemolition operation. The vacuum equipment shall be capable of removing wet debris and water. Water collected during the vacuuming operation shall be discharged to the contractor’s wastewater collection system.
Testing and Acceptance of the Hydrodemolition Equipment
A trial area will be designated by the engineer to demonstrate that equipment, personnel and methods of operation are capable of producing results satisfactory to the engineer. The trial area shall consist of two sections of approximately 50 square feet each. One section shall contain deteriorated concrete and the other shall contain sound concrete.
In the area of sound concrete, the equipment shall be adjusted to remove:
A minimum of _____ inches of concrete.
An average of _____ inches of concrete.
A minimum of ¾” inches below the bottom bar of the top mat of reinforcing steel (excluding any carrier bar). It is anticipated that the minimum removal of ____(same as 1. above)__ inches will meet this requirement.
After completion, the equipment shall be moved to the area of deteriorated concrete and using the same parameters for sound concrete removal, a test cut shall be performed to ensure that all deteriorated concrete is removed. 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.
If in the sole opinion of the engineer the hydrodemolition equipment does not produce satisfactory removal of the concrete or the unit does not meet the minimum production requirements of the project, then the engineer may require that the equipment be removed from the project and replaced with equipment that will meet the requirements of the specifications.
The hydrodemolition equipment shall be adjusted, as required, to maintain the quality and depth of cut demonstrated in the test area and to compensate for variations in the compressive strength of the concrete and other factors that may effect the actual depth of removal during the hydrodemolition operation.
Protect and/or relocate existing utilities within the work area that may be damaged during the demolition work. Provide temporary service until affected utilities are restored. Take adequate measures to protect existing sprinkler system.
Install temporary protection and other safety requirements prior to starting demolition. Contractor shall adequately shield the work area to prevent debris resulting from hydrodemolition operation from traveling beyond the boundaries of the work area.
Provide adequate lighting as required to perform the work of this section.
Remove the concrete in the areas designated on the drawings using hydrodemolition to the minimum depth specified in the drawings and 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.
Following hydrodemolition, the bulk debris shall be removed from the area using the vacuum system. Areas inaccessible to the hydrodemolition equipment shall be removed using hand-held pneumatic tools. Shadows under reinforcing steel scheduled to remain in place shall be removed to ¾ inches below the steel using hand-held pneumatic tools.
Clean the area to remove all loose debris and other materials scheduled to be removed during the demolition. Thoroughly clean the demolished area using an 8,000-psi water blaster using a minimum of 8 gpm 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.
Areas where pneumatic tools were used must be thoroughly cleaned to remove rust and laitance from existing reinforcing.
Any areas contaminated by materials detrimental to a good bond as a result of the contractors operations shall require additional removals and/or cleaning until a clean surface is obtained, at no additional cost to the owner.
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 contractors operations shall be repaired or replaced at no cost to the owner.
Additional Removals – Option 1 – Measure actual depth.
(Note: The “Additional Removal” language is optional but is given to provide protection to the owner and engineer from a contractor who may remove concrete beyond the specified depth and claim added cost resulting in a cost over run for the project. The additional removal language also protects the contractor in the event the steel is low. Rampart prefers Option 2 – “Variable Depth” as it requires less inspection by both parties and when part of the original bid usually results in a unit price cost that reflects the incremental cost to perform the work.)
It is anticipated that the minimum removal of ______ inches and average removal of _____ inches will provide a minimum of ¾” clearance under the bottom bar of the top mat of reinforcing steel excluding any carrier bars. In the event the specified removal does not provide the minimum clearance below the reinforcing the contractor shall immediately notify the engineer. The contractor and the engineer shall jointly measure the depth of the reinforcing steel within the existing concrete by measuring along the edge of the hydrodemolition removal from the surface to the top of the top bar of the reinforcing mat. If this distance, when added to the diameters of the existing reinforcing, plus ¾ inch, exceed the minimum specified depth of removal for the project, then the engineer will either authorize the contractor to continue cutting at the specified depth or authorize the contractor to increase the depth of cut to a new minimum and average sufficient to meet the specification requirements.
The contractor will be entitled to additional compensation for the increased depth of removal if, and only if, all of the following criteria are meet.
The contractor has immediately notified the engineer of the need to cut deeper to provide the minimum of ¾” below the reinforcing.
The engineer has verified the need to cut deeper and has authorized the contractor, in writing, to cut to a new specified depth.
During the period the contractor is cutting deeper he shall measure, after each four hours of work, the actual depth required to provide the ¾” clearance below the reinforcing steel and the square footage of area that was hydrodemolished during the four hour period. The actual depth required shall be determined along the edge of the hydrodemolished area by measuring from the surface to the top of the top reinforcing bar, adding the diameter of the reinforcing steel (excluding carrier bars, chairs, etc.) and adding ¾ inches. Multiple measurements are to be made to insure that a true average is obtained.
At the end of each shift the contractor shall submit to the engineer a daily report including the measurement for the depth of cut required; the area hydrodemolished; and the location of the areas requiring the additional removals either on a drawing or by column line. The engineer shall immediately verify the increased removals and upon verification return a signed copy of the daily report to the contractor. The engineer may require that they be present when the measurement is made. The contractor shall give the engineer at least one-hour notice of the time at which the measurements will be made.
Provided that all of the above criteria are met, the contractor shall be entitled to a linear increase in the unit price for hydrodemolition as full compensation for the additional removal and replacement of concrete only at the locations where the engineer approved additional removal in writing.
No claim for additional compensation due to increase removal will be allowed under the unit price for Removal and Replacement of Concrete unless the above criteria are meet. These criteria are mandatory due to the fact that it is very difficult, if not impossible, to accurately determine the depth of removal once a large area has been hydrodemolished. Measurements must be made as the demolition proceeds and must be done along the edge of the hydrodemolition cut where the location of the rebar within the concrete can be accurately measured. No other method of determining the actual depth of cut, including before and after surveys, will be allowed.
Additional Removals –Option 2 – Variable Depth Method
Note: You can also specify an average depth of removal, for example 50,000 square feet at 4.0 inches deep (617 cy plus 2% waste = 630 cy). If the concrete is to be placed at the original elevations then you can add a variable depth pay item for all concrete placed in addition to the 630 CY. This pay item would include any additional hydrodemolition, cleanup, water control, disposal, new concrete and placement. The line item would be “Variable Depth Concrete – Additional cost to replace areas of deep removal resulting from deteriorated or unsound concrete or where the reinforcing is deeper then anticipated. This unit price includes all cost resulting from the deeper removal including, but not limited to, the cost of hydrodemolition, water control, cleanup, disposal, concrete, and placement”. The unit price is Cubic Yards. Recommend using an additional ½” of concrete or 77 CY in the example above.
Wastewater Containment and Disposal
Wastewater containment shall be the sole responsibility of the contractor. 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 contractor. The system shall be designed by the contractor and approved by the engineer to meet the discharge requirements of the local governing authority.
The contractor shall obtain any permits required for the discharge of the wastewater.
All wastewater generated by the contractor’s operations including hydrodemolition and clean up water must be contained by the contractor and must pass through the contractor’s approved collection system. No water will be allowed to flow directly into the drainage system of the facility.
The contractor shall establish and maintain any testing program required by the local governing authority for the wastewater discharge.
The 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.
The owner shall designate the location from which the contractor shall obtain potable water. The contractor is responsible for supplying all material, equipment and tools necessary to tap into the water source. The contractor shall install a meter to measure the water consumption. The owner will provide, at no charge to the contractor, 75 gallons of potable water per cubic foot of concrete demolition for the contractor’s operation. Additional water may be consumed by the contractor at a cost of $10 per 1,000 gallons.
During concrete removal do not damage existing reinforcement steel intended to remain in place.
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 by the contractor shall be replaced by the contractor at no charge to the Owner.
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.
All water from the hydrodemolition and cleaning process must be contained within the construction barrier limits of the work area. The remaining facility will be operating under normal conditions. Any water that escapes the work area will immediately and without any delay, be removed from occupied areas. The construction barriers shall then be resealed to eliminate the leak.
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 an 8,000 psi minimum water blaster at 8 gpm using a rotating, multi-jet nozzle held at not more then 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.
Inspection of Exposed Surfaces and Reinforcement
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 contractor to perform additional removals. Engineer will re-inspect after additional removals.
Engineer will inspect all reinforcement designated to remain in place for defects due to corrosion or damage caused from contractors removal operations.
After inspections are complete and all preparation accepted, the engineer and contractor shall measure and document removal and replacement quantities for payment. Payment will be made at the unit price for Concrete Removal.