Hydrodemolition - Unit Price Approach

Controlling Cost and Claims for Excessive Removals

Over the years arguments, and thus claims, have arisen over the depth of concrete removal performed by hydrodemolition equipment. Typically the contractor argues that the concrete was "bad" and thus should have been removed while the Owner believes that the contractor has failed to adequately control his operation and thus has removed good concrete. In fact, it is likely that both positions will have merit. Clearly, if the concrete was bad, it should be removed to insure a quality restoration. Equally true, the contractor should not be rewarded with additional compensation for either failing to adequately control his operation or intentionally removing good concrete.

Hydrodemolition may not remove concrete to a uniform depth. The hydrodemolition equipment is designed to run at a constant pressure and volume. The speed at which the nozzle moves over the surface controls the depth of cut. If the concrete were uniform, and the nozzle speed constant, the removal would be to a uniform depth. However, factors such as the level of deterioration, compressive strength and overall quality and condition of the concrete will impact the depth of removal. If, for example, during removal of an average of 4" of concrete, a 3" delamination is encountered, the actual removal at that location may increase to 5". Or, if there is an area of low compressive strength or poorly consolidated concrete, the hydrodemolition unit will also cut deeper. Conversely, if an area of hard concrete is encountered such as a previous repair, the depth of removal will be reduced. Only by increasing or decreasing the speed of the hydrodemolition nozzle over the surface of the concrete can the depth of cut be controlled. It is critical that the hydrodemolition operator carefully monitor his equipment to maintain a uniform quality and depth of cut. With these inherit conditions impacting the depth of the removal, it is not unusual to see variations in the overall removal regardless of how diligent the hydrodemolition operator is in performing the work.

Herein lies the potential controversy over the depth of cut and the potential for a claim. Since the depth of removal will most likely not be uniform, two pay items should be incorporated in the specifications to account for this variation. They will allow the contractor to be fairly compensated for the additional removal resulting from unforeseen conditions while protecting the owner from claims of excessive removals and added cost and time.

The use of hydrodemolition provides a high level of assurance that all of the deteriorated concrete will be removed and, further, that the removal process will not result in any additional damage to the substrate. If properly specified, the cost of hydrodemolition can be controlled and claims of excessive removal and added costs can be eliminated. A well-defined unit price approach will achieve these results.

Unit Prices

The specifications should contain two unit prices for this work. The first covers the typical removal and replacement of the concrete to the specified average depth (Remove and Replace Unit Price - RR). The second covers additional concrete that may be required for drainage improvements as well as additional removal below the averaged specified depth due to deteriorated or "bad" concrete (Variable Depth Unit Price - VD).

The RR would include all of the contractor’s cost for hydrodemolition; clean-up; water control; disposal; final clean-up; and place, finish and cure of the new concrete overlay to a specified depth of, for example, of 4 inch average and 3.5" minimum. It also includes overhead and profit and, depending on the bid items, may also include general conditions, shoring, protection, etc. It also includes the concrete required to replace the concrete removed to the average depth, in this case, 4" (defined as the average depth of removal multiplied by the area and measured in cubic yards).

The VD is for all additional concrete placed over and above the amount specified in the RR. This would cover additional concrete required to fill deep removals caused by "bad" concrete as well as concrete required to improve drainage. This unit price would include all of the contractor’s incremental cost for hydrodemolition, water control, clean-up, debris removal, placing the additional concrete and the actual additional concrete used in addition to that required as part of the project under the RR.

Added Cost and Delay Scenario

Often, after the job has been bid and the work started, the contractor determines that additional concrete, beyond the 4" specified, has been removed. If, for example the contractor determines that an average of 5 inches was removed (normally calculated from the concrete placement tickets), the contractor typically wants to extend the unit price to cover the additional cost of removal and replacement. The increase from 4" to 5" represents a 25% increase in the specified depth. As a result, the contractor will want to increase his unit price by 25%.

Normally, the additional removal (if it was caused because the concrete was deteriorated) is incidental to the project because the hydrodemolition equipment is simply removing bad concrete as it is encountered during the hydrodemolition process. The equipment was set at a predetermined cut rate in sound concrete to achieve the minimum specified depth (4"). The machine continues at the same speed but is simply removing more concrete due to the deterioration. Unless the problem is severe, this additional removal in local areas does not typically extend the length of the project or increase the hydrodemolition cost.

However, there are incremental costs incurred by the contractor including the removal of the additional debris from the work area; disposal; and additional concrete that must be placed to fill the deeper areas. Keep in mind that the equipment and manpower are on the job and already working. The additional removal should not impact detail chipping, final clean up, or the cost of finishing and curing the new concrete. Nor does it impact general conditions or items such as shoring and protection. As a result, the contractor only needs to be compensated for the incremental cost. As can be seen, this incremental cost does not have a linear relationship with the base bid price for removal and replacement and therefore needs to be priced under a separate unit price. The second unit price, VD, is provided to allow the contractor to cover these incremental costs.

Exception to the Rule

The exception to this would be if the steel was uniformly deeper in the concrete than was specified, thus causing the contractor to readjust the entire removal and replacement procedure to increase the minimum and average depths of removal. If this should occur, it could result in a significant increase in the contractor’s cost as well as requiring additional time to complete the work. Generally, this increased cost should be compensated with a linear increase in the RR. For example, if the RRUP is $20.00 for 4" average removal, and the contractor has documented and obtained approval to remove an average of 4.5" then the unit price for the area requiring the additional removal should be increased to $22.50 per sf ($20.00/4" * 4.5"). Once the time required to complete the work has increased, the contractor’s general conditions, overhead and profit will be impacted. A linear increase in the unit price should adequately compensate the contractor for all of the added cost including the incremental cost for the added concrete. The quantity of concrete, specified to be used under this unit price, would also be increased to avoid paying for the additional concrete under the VD. Documentation and approval of increased removals under this exception must be strictly enforced. The Guide Specifications describe a method to carefully monitor increased removals when the steel is not at the specified depth within the concrete. However, if the minimum and average depth of cut is set sufficiently deep in the original bid documents, most variations in the depth of the reinforcing steel will be covered within the unit price for removal and replacement and this situation will not arise. Furthermore, the documentation and approval procedure outlined in the Guide Specifications, are sufficiently stringent to discourage the contractor from making minor claims.

By incorporating both the Removal and Replacement Unit Price and the Variable Depth Unit Price into the contract, the owner can be assured that he gets the best price for all the work at the time of the bid. The contractor knows that he will be fairly compensated for the incremental cost of additional removals.

 

Pay Items for Concrete Overlays Following Hydrodemolition

 

1. Remove and replace a minimum of ______ inches and an average of _____ inches from the existing concrete decks according to the specifications including all incidental items. Included in this unit price is _____ CY of new concrete.

 

______ Square Feet $ _______ per Square Foot $____________

2. Additional concrete required above the quantity in item #1 for areas where removal exceeded the average depth or where additional concrete is required to provide new drainage. This unit price covers all costs associated with the additional removal beyond the average depth of _____ inches, including hydrodemolition; clean up; disposal; water control; placement, finishing and curing of the concrete; general conditions; overhead and profit and any other related cost. No extension of time will be allowed for additional concrete placed under this item. (Note: The quantity of concrete should be sufficiently large to insure competitive pricing for this unit price).

______ CY Concrete $ ________ per CY $ ____________

 

Discussion: (See Figure 1.)

There are several items that must be given careful consideration. In bid item #1 the minimum depth of removal to achieve the project requirements must be reasonably determined. If the objective is to remove all the concrete from around the rebar and provide a minimum of ¾" clearance under the bottom bar (excluding the carrier bar) then the following calculation needs to be made.

Average Cover 1.25"

2-#5 bars 1.25"

¾" clearance under the bottom bar .75"

Total Minimum Removal 3.25"

 

This minimum removal will leave any carrier bars laying on the surface. Furthermore, it presupposes that the rebar was laid perfect and the 1.25" cover is uniform through out the project, which is unlikely. To account for this potential variation in the depth of the steel, it would be better to require a minimum depth of 3.50".

A second consideration is that the surface left by the hydrodemolition is very rough (great for bonding but difficult to measure). In sound concrete the variation in the average depth of removal is typically equal to ± one-half the diameter of the large aggregate. Thus, if the existing concrete contains 1.0" aggregate the range in the profile of the hydrodemolished surface would be ±0.5". If the specification requires a minimum of 3.5" removal, the average removal will be 4.00" and the maximum will be 4.5". In the above example, requiring a minimum removal of 3.5" will better insure proper clearance under the rebar, while stating that the average removal is 4" will allow the contractor to calculate his hydrodemolition, clean-up and disposal, and new concrete cost. The average removal also becomes the quantity of concrete that the contractor expects to place under the unit price for Removal and Replacement. Additional concrete required above this amount would be paid under the Variable Depth Unit Price.

If the project contained 100,000 sf with an average specified depth of removal of 4", the bid items would be as follows:

1. Remove and Replace a minimum of 3.5 inches and an average of 4.0 inches from the existing concrete surface according to the specifications including all incidental items. Included in this unit price is 1,260 CY of new concrete.

100,000 Square Feet Note: 100,000 SF*4 /12/27*1.02 = 1,260 CY The factor of 1.02 is for waste.

2. Additional Concrete required above 1,260 CY for areas where removal exceeded the average depth or where additional concrete is required to provide new drainage. This unit price covers all costs associated with the additional removal beyond the average depth of 4 inches, including hydrodemolition; clean up; disposal; water control; placement, finishing and curing of the concrete; general conditions; overhead and profit and any other related cost. No extension of time will be allowed for additional concrete placed under this item.

154 Cubic Yards Note: in this example, 0.5" for additional removal was used.

It is important to provide a quantity large enough to insure a competitive price for the work. One-half inch should be used as the minimum for additional removals.

In larger and more extensive restorations the entire floor may be hydrodemolished and overlaid. In so doing the engineer will often take the opportunity to improve the drainage by introducing a new drainage profile. This typically requires placing additional concrete at the high points to provide adequate slope to new drains. If this is done a calculation should be made to approximate the additional concrete that will be required and to include this as part of this line item.

The two unit prices given above are easily monitored. The actual area removed and replaced area can be easily measured at any time. The total amount of concrete used can be verified during each pour and by requiring submission of all concrete delivery tickets.

The advantage to the owner is that in preparing the bid, the contractor knows that the removal and replacement work will be done; however the additional concrete is speculative. Therefore, his entire general conditions, overhead and profit will be placed in the removal and replacement line item. Additional concrete may or may not be used, or the quantity may be significantly less than specified; therefore the contractor will normally bid this item at essentially cost to be competitive and to avoid placing his general conditions, overhead and profit at risk in a line item that may not be done. Thus, if added concrete must be placed, the owner will receive a favorable price obtained through the bidding process and the contractor will be fairly compensated for any additional concrete that has been removed and must be replaced. Because the contractor has bid the item with little or no mark up he has no incentive to over excavate the deck.

By specifying the two unit prices, the owner can have all the advantages provided by the use of hydrodemolition, without the fear of increased cost resulting from excess removals.