evaluation - 2012-256 - responsive - 4

7/30/2019 Evaluation - 2012-256 - Responsive - 4

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Obtained by Bob Mackin via Freedom of Information

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Bridge Evaluation ReportBurrard Street Bridge

Prepared for:

Associated Engineering (BC) Ltd.300-4940 Canada WayBurnaby, BC V5G 4M5

Attention: Mr. Shane Cook, P.Eng.


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Bridge Evaluation Report

Burrard Street Bridge


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TABLE OF CONTENTS

1 INTRODUCTION ....................................................................................................................... 12 DECK SOFFIT AND SUBSTRUCTURE ................................................................................... 1

2.1 VISUAL REVIEW............................................................................................................... 12.2 LABORATORY TESTING .................................................................................................... 2

2.2.1 Water-Soluble Chloride Ion Content ......................................................................... 22.2.2 Extracted Cores ......................................................................................................... 2

3 DECK SURFACE ...................................................................................................................... 23.1 VISUAL REVIEW............................................................................................................... 33.2 CORROSION POTENTIAL MEASURMENTS.......................................................................... 43.3 LABORATORY TESTING .................................................................................................... 5

3.3.1 Water-Soluble Chloride Ion Content ......................................................................... 54 CONCRETE PARAPETS .......................................................................................................... 5

4.1 VISUAL REVIEW............................................................................................................... 54.2 LABORATORY TESTING .................................................................................................... 5

4.2.1 Extracted Cores ......................................................................................................... 54.2.2 Water-Soluble Chloride Ion Content ......................................................................... 6

5 INTERPRETATION OF FINDINGS ........................................................................................... 65 1 D C SO S S C 6


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1 INTRODUCTION

As part of their contract with the City of Vancouver for the condition assessment anddevelopment of rehabilitation strategies for the Burrard Street Bridge, Associated EngineeringLtd. has engaged Levelton Consultants Ltd. to conduct the following:

A brief visual review of the visible concrete portions of the substructure and samplingfrom select areas of the substructure to assess water-soluble chloride ion content, pH,and the presence of alkali-silica reactivity (ASR). It is understand that Associated hasconducted a visual detailed survey of the structure, complete with recording size andlocation of observed deterioration.

Visual review of the concrete parapet along the west side of the bridge and sampling atselect locations to determine water-soluble chloride ion content, pH, and the presence ofalkali-silica reactivity (ASR).

Sampling from the top side of the concrete deck in the north and southbound curb lanes,and the southbound bike lane to assess the condition of the deck and to determine thewater-soluble chloride ion profile.

the City requested that the survey beconducted by extraction of a number of cores.

The following presents the findings of the investigation and recommendations for repairs andrehabilitation with respect to the concrete portions of the structure.

s.15(1)(l); s.18(a); and s.19(1)(b)


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There is evidence that many of the expansion joints are leaking, which has resulted in corrosion-related deterioration on several of the concrete members adjacent to the joints and on the piersbelow the joints. The extent of the deterioration indicates that there has been active corrosionwithin the structure for several years.

Most of the onshore piers are in good condition with minor corrosion-related deterioration orminor cracking which is most likely a result of expansion due to ASR.

2.2 LABORATORY TESTING

2.2.1 Water-Soluble Chloride Ion Content

Concrete powder samples were collected from various locations throughout the deck soffit andsubstructure. Samples were collected by drilling into the concrete with a 25 mm diameter drill bit.

At all locations, except Location 1, the water-soluble chloride ion content is below the corrosioninitiation threshold of 0.03 0.05% by mass of concrete.

New concrete generally has a pH greater than 12.0. When steel is in a highly alkalineenvironment (pH >10.0) a passive layer forms on the steel surface which protects the steel fromaggressive corrosion (in the absence of chlorides). When atmospheric carbon dioxide diffusesinto the concrete a chemical reaction occurs which lowers the pH; when the pH drops below

about 10 the passive layer is no longer stable and the steel is no longer protected fromcorrosion. The pH of the concrete powder samples at several of the locations is slightly lowerthan that typically observed in new concrete, however, at all locations the pH is above thegenerally accepted threshold for carbonation-induced corrosion. These results indicate that thedepth of carbonation is minimal.

s.15(1)(l); s.18(a); and s.19(1)(b)


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3.1 VISUAL REVIEW

The concrete deck is reinforced with undeformed round bars varying from 10 to 15 mm indiameter, and square bars that are approximately 10 mm in section. Due to the layer of asphalton top of the concrete deck it was not always possible locate reinforcing steel and collect asample by coring.

Table 1 presents a summary of the condition of the extracted cores; the FDWHJRU\ %URNHQ applies to cores that Levelton had to break into several pieces to extract; these cores generallycorrespond to the location where the half-cell equipment was grounded, so no reading could betaken at this location. Table 2 presents a summary of the condition of the rebar sampled from thedeck.

As can be seen from Tables 1 and 2 the majority of the deterioration observed is in the two

under-deck truss spans and the north approach. It should be noted that the review of the deckcarried out under this program is quite limited given the size of the structure, however, it doesindicate that there has been some corrosion-related deterioration within the concrete deck and isuseful in targeting future surveys and repairs.

Table 1: Summary of Core Condition

Number of Cores

Span Lane Good

Vertical

Crack Broken Delamination

South ApproachNorthbound 8 2 1 0

Southbound 8 0 1 1

South UnderdeckTruss Span

Northbound 2 0 1 0

Southbound 1 0 1 3


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Table 2: Summary of Rebar Condition

Number of Cores

Span Lane Good Fair PoorNone

Visible

South ApproachNorthbound 4 2 1 4

Southbound 2 4 0 4

South UnderdeckTruss Span

Northbound 0 1 1 1

Southbound 2 1 2 0

Main SpanNorthbound 0 1 0 5

Southbound 1 1 0 3

North UnderdeckTruss

Northbound 0 2 2 2

Southbound 1 2 1 1

North ApproachNorthbound 1 3 0 1

Southbound 1 2 1 0

Total 12 19 8 21

3.2 CORROSION POTENTIAL MEASURMENTS

Corrosion potential values provide information about the probability of active corrosion of therebar embedded in concrete. %DVHGRQ/HYHOWRQVH[SHULHQFHDFWLYHFRUURVLRQRIVWHHOLQEULGJHdecks is often observed when potential values are more negative than about -200 mVCSE and thechloride levels at the rebar are elevated.

At most core locations corrosion potential measurements were taken on the exposed concrete


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Table 4: Summary of Corrosion Potential Measurements

Number of Readings

Corrosion Potential

(ASTM C876)

South

Approach

South

Under-deckTruss

Main

Span

North

Under-deck

North

Approach

>10%(>-200 mVCSE)

6 0 4 2 3

Uncertain(-200 to -350 mVCSE)

10 3 1 6 6


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4.2.2 Water-Soluble Chloride Ion Content

Levelton extracted concrete powder samples from five locations in the west parapet and testedthe samples for water-soluble chloride ion content and pH. At all locations the water-solublechloride ion content is below the generally accepted corrosion initiation threshold limit of 0.03-0.05% by mass of concrete and the pH of at all sample locations is greater than 10.0.

5 INTERPRETATION OF FINDINGS

In general, the concrete elements of the Burrard Bridge are in relatively good condition for their

age. The notable exception is the parapets, which are showing advanced deterioration in theform of spalling. It is noted that the bridge was constructed prior to the use of air entrainment forfreeze-thaw protection, using what is likely to be relatively high-permeability concrete. Hence, theobserved deterioration is likely the result of freeze-thaw attack, ASR, and rebar corrosion actingtogether.

Elsewhere, localized spalling and deterioration is observed, but generally the concrete is soundand in good condition.

Some evidence of early-stage ASR is present. More extensive laboratory analysis, together within-situ monitoring is required to assess the future progression of this form of deterioration.

5.1 DECK SOFFIT AND SUBSTRUCTURE

Throughout the deck soffit there are numerous spalled areas which have exposed the reinforcing

s.15(1)(l); s.18(a);

and s.19(1)(b)


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The corrosion potential measurements at many of the sample sites indicate an uncertainprobability of corrosion, and review of the condition of rebar exposed during sampling indicatesthat the steel is generally in good condition at most locations. Chloride ion concentrations atmost locations are quite low, which indicates that the waterproofing membrane and theasbestos-modified asphalt have done a reasonably good job of protecting the concrete deck.

The samples were taken from the northbound curb lane, and the current southbound curb andbike lanes; until recently the current southbound bike lane was the curb lane for vehicular traffic.These lanes were chosen as they are where the most advanced deterioration would be expectedto occur. However, it should be noted that this is a very small sample size, particularly given thesize of the structure and it is difficult develop a complete assessment of the condition of thedeck.

In general, the deck was found to be in sound condition with localized deterioration. If left in its

current state, the corrosion-related deterioration will continue to accumulate, eventuallynecessitating extensive repairs.

5.3 PARAPETS

The parapets are generally in poor condition with extensive spalling throughout, which hasexposed the reinforcing steel extensively. At several locations these spalls have been coatedwith paint, however, as with the deck soffit, this method provides only minimal protection to steel,

and it is likely that the spalls will continue to expand.

Laboratory testing indicated that the chloride concentrations and pH levels have not reached thegenerally accepted corrosion initiation thresholds; however, it is obvious that there are activedeterioration mechanisms within the parapets. The deterioration is likely the result ofsimultaneous freeze-thaw attack, ASR, and corrosion.

Th t f l t d d i i ifi t d it i t t d th t d bl i


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s.13(1); s. 15(1)(l) and s.17(1)(c), (d), & (f)

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s.15(1)(l); s.18(a); and s.19(1)(b)


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s.15(1)(l); s.18(a); and s.19(1)(b)


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evaluation - 2012-256 - responsive - 4

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