Bridge Office 301 St. Paul Street, 2nd Floor St. Catharines, ON L2R 7R4 (905) 704-2406

Memorandum Date: May 12, 2004 From: Bala Tharmabala Manager, Bridge Office To: Distribution List (Attached) Re: Bridge Office Design Bulletin Concrete Removal Criteria for Bridge Deck Rehabilitation Background Prior to 1989, rehabilitation of bridge decks involved removal and replacement of delaminated concrete only. Since 1989, the Ministry adopted the policy of removing and replacing delaminated concrete and concrete in areas where the corrosion potential is more negative than -0.35V. It was believed that removing all concrete with high corrosion potentials, generally corresponding to areas of high chloride contamination, provided an effective means of reducing the likelihood of continued corrosion and maximizing the life expectancy of the rehabilitation treatment. The Ministry’s recent field experience has demonstrated that this approach is costly because the cost of removing chloride contaminated in otherwise sound concrete is high, and there are difficulties in accurately predicting removal quantities based on half cell potentials and controlling its removal in the field. Limited in-house research investigations have also shown that while removal by delamination alone does reduce the service life of a rehabilitation treatment, this reduction may not be as significant as expected. This new concrete removal policy will confine removal to delaminated concrete and sound concrete in high potential areas that are heavily chloride contaminated and at greatest risk for continued corrosion activity. Where the chloride content exceeds 0.05 % by mass of concrete (twice the previously accepted threshold for corrosion to occur), it is recognized that there is a need to remove this concrete to reduce the possibility of future corrosion activity. The proposed protocol is expected to result in removal of less concrete and reduce the occurrence of costly overruns, while still achieving a reasonably long service life for the rehabilitation.

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New Concrete Removal Policy Concrete removal for decks with average chloride content at the top reinforcement level less than 0.05% by mass of concrete shall include delaminated concrete only. Concrete removal for decks with average chloride content at the top reinforcement level greater than 0.05% by mass of concrete shall include delaminated concrete and concrete in areas where half-cell potentials are more negative than –0.35 volts. The chloride limit of 0.05% by mass of concrete after adjustment for background chloride is equal to twice the chloride threshold used in the past and is considered to be a safe and practical upper limit to exclude deleterious chloride contaminated concrete. Condition Survey The number of cores to be tested for chloride profile shall be as follows: Locations No. of Cores Min. Max. Corrosion Potential < -0.35 V 1 per 30 sq. m 8 (Min. 2) Corrosion Potential 0 to -0.35 V 1 per 250 sq. m 8 (Min. 2) For decks with less than 10% of the total deck area more negative than –0.35 V, the average chloride content shall be calculated using all the cores tested. For decks with more than 10% of the total deck area more negative than –0.35 V, the average chloride content shall be calculated using only the cores taken in the high corrosion potential areas. This policy does not apply to post-tensioned decks and decks that are to be cathodically protected. Tender Quantity Estimates If concrete removal is by delamination only, the tender quantity for partial depth Type A removal shall include the area with corrosion potential < -0.45 V, and an allowance for annual growth of the removal quantities as is currently required in the Structure Rehabilitation Manual. This is to minimise the risk of overrun of the removal item due to growth of delamination in the high corrosion potential areas. In such cases, half-cell survey during construction would not be required. The rehabilitation treatment selection shall be based on the tender removal quantity accordingly.

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Implementation 1) This criteria shall be effective immediately for all new condition survey assignments and

rehabilitation contracts. 2) For stockpiled designs and designs currently underway, the regional structural sections

should assess whether the existing condition surveys provide sufficient information on the chloride content and decide accordingly.

2) Consultants working on ministry projects should be notified of these requirements by the

office responsible for the contract assignment. 3) These requirements will be included in the next revision to the Structural Rehabilitation

Manual. Original signed by: Bala Tharmabala, Manager, Bridge Office cc: R. Mantha, Chief Engineer Distribution List: Managers of Engineering Heads, Regional Structural Sections K. Bentley, Southwestern Region P. Furst, Northeastern Region P. Makula, Northwestern Region A. Ho, Central Region Mgr of Engineering, Northeastern Region Q. Islam, Eastern Region L. Politano, Central Region R. Krisciunas, Northwestern Region K. Williams, Eastern Region W. Young, Southwestern Region Heads, Bridge Office D. Bagnariol, Evaluation R. Haynes, Standards I. Husain, Design D. Lai, Rehabilitation C. Lam, Bridge Research T. Merlo, Design Systems R. Mihaljevic, Quality Assurance

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