Durability of parking structures: analysis of field survey

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Durability of parking structures: analysis of field survey

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N21d

no.

1479

c .

₂

BLDG

Council Canada

de recherches Canada

Institute for

lnstitut de

Research in

recherche en

Construction

construction

Durability of Parking Structures:

Analysis

of

Field Survey

by G. Litvan and J. Bickley

ANALYZED

Reprinted from

Proceedings

Katharine and Bryant Mather International Conference

on Concrete Durability

American Concrete Institute

Special Publication 100, SP 100-76, Vol. 2

p. 1 503

-

1525

(IRC Paper No. 1479)

Price $4.00

NRCC 28325

NRC

-

CISTI

I R C

L I B R A R Y

JAN

11 B I B L I O T M ~ Q U E

I R C

C N r l C

-

1CIS-r 1 rmu

4

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criteres suivants : desagr6gation superficielle, difference de potentiel mesurge B la demi-cellule, epaisseur de recouvrement

et Stat des 6lhents. De plus, des essais de mesure de la

teneur en chlorures, de la resistance 2 la compression et de la

permeabilite aux chlorures ont 6te effectu6s sur des carottes, et la teneur en vides a 6te analys6e. Les resultats demontrent que des garages durables peuvent Stre construits et que les

dSfectuositSs peuvent &re attribuees B une conception ou 2 des

pratiques de conception ma1 adaptees aux conditions

environnementales. ~~ - - ~ I1 s'ensu Cventuellr avant quc seuil c.ri de "rapil 70 pour Aucune dl menbran<- en chlo de la f issurer dif Cerer que l'e d6sagrQ

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Analysis

of

Field Survey

by

G. Litvan and

J. Bickley

Synopsis:

A total of 215 garages in Toronto, Ottawa and

Montreal, Canada, have been surveyed to various extents by

assessing delamination, half-cell potential, depth of cover, and

component condition. In addition, tests were carried out on

cores, in which chloride content, compressive strength, and

chloride permeability were determined and the air void system was

analysed. The evidence indicates that durable garages can be

built, and that poor performance must be attributed to design and

construction practices whose effectiveness falls short of that

required by the environment.

It follows that almost all previously built garages will

eventually require repair unless upgraded before the chloride

concentration of the concrete reaches a critical level. Repair

by the "patch and waterproof" method was found to decrease the

rate of corrosion of deteriorated garages by approximately 70

percent. Detrimental effects following installation of a

waterproofing membrane over concrete with elevated chloride

concentration were not observed. No relation was detected

between extent of delamination and crack density or compressive

strength. Half-cell potential did not prove more sensitive than

the chain-drag test in detecting delamination.

corrosion; parking facilitii

waterproofing

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G.G. L i t v a n i s a S e n i o r Research O f f i c e r , I n s t i t u t e f o r Research i n C o n s t r u c t i o n , N a t i o n a l Research Council of Canada, a member of ACI and CSA Committees on P a r k i n g S t r u c t u r e s , and of v a r i o u s committees of CSA and RILEM, P a s t P r e s i d e n t , E a s t e r n O n t a r i o and Quebec A C I C h a p t e r , and V i c e - P r e s i d e n t , American Ceramic S o c i e t y . John A. B i c k l e y , P.Eng., Trow Ltd. C o n s u l t i n g E n g i n e e r s , i s chairman of a CSA Committee p r e p a r i n g a Canadian s t a n d a r d on de- s i g n , c o n s t r u c t i o n and maintenance of d u r a b l e p a r k i n g s t r u c t u r e s , a member of A C I Committee 362, p a r k i n g s t r u c t u r e s , a f e l l o w of ACI and 1981 r e c i p i e n t of t h e i r c o n s t r u c t i o n p r a c t i c e award.

INTRODUCTION

D e t e r i o r a t i o n of p a r k i n g g a r a g e s i s a major concern i n Canada. The f u l l e x t e n t of t h e problem and t h e c o s t of r e p a i r s i s d i f f i c u l t t o d e t e r m i n e a c c u r a t e l y , b u t i t is f a i r l y c e r t a i n t h a t i t exceeds $3 b i l l i o n s . .Uthough t h e r e i s l i t t l e doubt t h a t t h e t e c h n i c a l a s p e c t s of s u c h d e t e r t o r a t i o n could be s o l v e d by a d o p t i n g the technology developed f o r c o n s t r u c t i o n and r e p a i r of

hilghway b r i d g e decks, t h i s approach i s p r o b a b l y u n n e c e s s a r i l y expensive.

The

performance r e q u i r e m e n t s f o r g a r a g e s , though d i f f e r e n t , a r e less demanding. The a p p r o p r i a t e l e v e l of b r i d g e deck technology t o p r o v i d e a d e q u a t e p r o t e c t i o n of g a r a g e s h a s t h u s t o be determined.

The two most i m p o r t a n t q u e s t i o n s a r e , how t o r e p a i r d e t e r i o r a t e d and how t o b u i l d d u r a b l e g a r a g e s i n a t e c h n i c a l l y s a t i s f a c t o r y , c o s t - e f f e c t i v e manner. U n f o r t u n a t e l y , l i t t l e guidance based on e x p e r i m e n t a l e v i d e n c e c a n be found i n t h e l i t e r a t u r e . The r e s u l t s of l a b o r a t o r y e x p e r i m e n t s , i f u n d e r t a k e n , would have t o be t e s t e d i n f i e l d t r i a l s and t h e e v i d e n c e e x t r a p o l a t e d t o t h e p r o j e c t e d 50-year l i f e s p a n of g a r a g e s . The u n c e r t a i n t i e s i n t r o d u c e d i n t h i s p r o c e s s , however, c a s t s e r i o u s d o u b t s on t h e v a l u e of any c o n c l u s i o n s s o o b t a i n e d . A t t h e same t i m e , t h e r e i s r e a l urgency t o d e v e l o p s u i t a b l e r e p a i r and c o n s t r u c t i o n methods t h a t a v o i d p o t e n t i a l l y c o s t l y m i s t a k e s i n r e p a i r and c o n s t r u c t i o n . Under t h e s e c i r c u m s t a n c e s a s u r v e y of e x i s t i n g g a r a g e s appeared t o b e t h e most u s e f u l approach. By i d e n t i f y i n g t h e d e s i g n c h a r a c t e r i s t i c s of d u r a b l e g a r a g e s and e v a l u a t i n g t h e performance of t h o s e t h a t have been r e p a i r e d , i t was hoped r e a l p r o g r e s s c o u l d b e made towards f o r m u l a t i n g e f f e c t i v e c o n s t r u c t i o n and r e p a i r methods i n a r e a s o n a b l y s h o r t t i m e . Accordingly, Canada Mortgage and Housing C o r p o r a t i o n , P u b l i c

Works

Canada, and

t h e I n s t i t u t e f o r Research in C o n s t r u c t i o n , N a t i o n a l Research

Council

of Canada, t h e o r g a n i z a t i o n s r e s p o n s i b l e f o r various a s p e c t s of c o n e t r u c t i o n and maintenance of p a r k i n g g a r a g e s ,

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commissioned a survey in Toronto, Montreal and Ottawa. The

present communication is an analysis of the survey report.

EXPERIMENTAL

Sample

In selecting parking structures for study, two types were

sought: well-performing garages that have not required repairs,

Series b, and rehabilitated garages with known case histories,

Series c. In addition, visual survey and detailed investigation

reports were obtained from various sources: 22 of a group of 159

garages owned by a public housing authority, Series e, and three

of approximately 100 garages designated by a municipal building

department as well-performing garages, Series f. Surveys of over

175 structures carried out for clients were also made available

by a consulting firm. Thus, a total of 215 structures formed the

sample of the study. Characteristic features of the garages are

summarized in Tables 1 through 4.

On-site Investigation

Grid layout--Site plans (scale 1:96) of the garages were

prepared and the areas divided into a 2- by 2 3

grid system,

using columns and perimeter walls as reference points.

Visual survey--Qualified, experienced personnel surveyed

each garage, noted the location and nature of any defects

(cracks, spalls, rust stains, patches, wet spots, exposed

reinforcing bars, etc.) on the drawings, and recorded their

,

observations on the condition of expansion joints, drainage

system, and other components. Representative areas,

approximately 10 percent of the total, were subjected to detailed

investigation that included delamination, half-cell potential,

\

depth of cover, and component condition surveys plus laboratory

I

tests on sample cores.

I

Delamination survey--Potentially delaminated or debonded

areas, as indicated by the chain-drag test, were recorded on the

drawings.

Half-cell potential survey--The electro-chemical potential

of the reinforcing steel was measured against a

copper/copper-sulfate electrode according to ASTM C 876-80

Standard Test

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at the intersection of the grid lines of the

..

1 2-

x

2-m network.

I

_{Depth of cover--A pachometer (James Electric Co.) was used}

I

to determine the thickness of the cover at the intersection of

the 2-

x

2% grid lines, conforming to the requirements of the

British Standards Institution, Standard BS 4408 (2).

The

reinforcing bar size was determined by measuring the steel

exposed by coring.

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Components c o n d i t i o n survey--Inspection of components o t h e r t h a n t h e c o n c r e t e s l a b s of t h e p a r k i n g s t r u c t u r e was c a r r i e d o u t i n d e t a i l .

L a b o r a t o r y T e s t i n g

Cores ( o b t a i n e d u s i n g a lOO-mm diam diamond d r i l l ) were t e s t e d t o d e t e r m i n e t h e c h l o r i d e c o n t e n t and compressive s t r e n g t h of t h e c o n c r e t e f o r v e r i f i c a t i o n of t h e r e s u l t s of d e l a m i n a t i o n and depth-of-cover s u r v e y s , and f o r a s s e s s i n g t h e c o n d i t i o n of t h e r e i n f o r c i n g s t e e l and t h e q u a l i t y of t h e a i r v o i d s y s t e m of t h e c o n c r e t e . D e t e r m i n a t i o n of C h l o r i d e C o n t e n t The c o r e s were c u t p a r a l l e l t o t h e w e a r i n g s u r f a c e a t t h e l e v e l of t h e t o p s t e e l t o p r o v i d e a s l i c e o f c o n c r e t e whose c h l o r i d e c o n t e n t was d e t e r m i n e d a c c o r d i n g t o a p r o c e d u r e developed by t h e F e d e r a l Highway A d m i n i s t r a t i o n ( 3 ) . Compressive S t r e n g t h

These t e s t s were c a r r i e d o u t i n c o n f o r m i t y w i t h Canadian

S t a n d a r d s A s s o c i a t i o n S t a n d a r d 423.2-14C, 1977 ( 4 ) on c o r e s

I

judged t o be s u i t a b l e .

I

C h l o r i d e P e r m e a b i l i t y

The a p p a r a t u s developed by Whiting ( 5 ) was used t o d e t e r m i n e t h e p e r m e a b i l i t y o f c o n c r e t e c o r e s t o c h l o r i d e i o n s . An 80-V d-c p o t e n t i a l d i f f e r e n c e i s m a i n t a i n e d a c r o s s a 50-mm l o n g c o r e s e c t i o n s u r r o u n d e d by a 3 p e r c e n t sodium c h l o r i d e s o l u t i o n f o r a p e r i o d of 6 h and t h e e l e c t r i c a l c u r r e n t p a s s i n g t h r o u g h t h e specimen i s determined. The t o t a l e l e c t r i c c h a r g e p a s s e d i s a measure of t h e c h l o r i d e i o n s m i g r a t i n g t h r o u g h t h e c o n c r e t e under t h e d e s c r i b e d c o n d i t i o n s . A i r Void System P o l i s h e d s e c t i o n s of c o n c r e t e were t e s t e d i n a c c o r d a n c e w i t h ASTM C 457-82 ( 6 ) f o r t o t a l a i r c o n t e n t , s p a c i n g f a c t o r , and o t h e r a i r v o i d c h a r a c t e r i s t i c s . RESULTS The r e s u l t s of t h e s u r v e y s of S e r i e s b and c s t r u c t u r e s a r e summarized i n T a b l e s 5 and 6. Garages i n S e r i e s f were a s s e s s e d o n l y by a v i s u a l survey. The suspended s l a b s i n f l were found t o c o n t a i n numerous d e l a m i n a t e d a r e a s and v i s i b l e s p a l l s and t h i s g a r a g e was t h e r e f o r e r a t e d t o be i n poor c o n d i t i o n . Garage f 2 had undergone a n n u a l in-house r e p a i r s c o n s i s t i n g o f removal of c o n c r e t e i n d e l a m i n a t e d a r e a s t h a t were t h e n r e p l a c e d by l a t e x - m o d i f i e d c o n c r e t e . The embedded e l e c t r i c a l c o n d u i t s had been abandoned and a new e l e c t r i c a l s y s t e m i n s t a l l e d . Some

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leakage was n o t e d a t t h e expansion j o i n t s , b u t t h e roof s l a b ( p a r t l y l a n d s c a p e d , p a r t l y a s p h a l t - c o v e r e d ) was i n good

c o n d i t i o n . O v e r a l l , t h i s g a r a g e was r a t e d f a i r . The under s i d e of t h e roof and t h e i n t e r i o r suspended s l a b s i n g a r a g e f 3 showed numerous c r a c k s and d e p o s i t s of l e a c h e d s a l t s . Rate of Delamination I n f o r m u l a t i n g r e p a i r s t r a t e g i e s , one of t h e most i m p o r t a n t f a c t o r s i s t h e e x p e c t e d r a t e of d e t e r i o r a t i o n . E f f o r t s were made t o o b t a i n i n f o r m a t i o n on t h i s a s p e c t s i n c e few d a t a a r e a v a i l a b l e i n t h e p u b l i s h e d l i t e r a t u r e . I n one p r o j e c t o f , a c o n s u l t i n g f i r m , a g a r a g e comprising s i x decks of over 10 000 m2 e a c h was surveyed o v e r a f o u r y e a r i n t e r v a l ( T a b l e 7 ) . R a t h e r wide v a r i a t i o n i s shown by t h e r e s u l t s because t h e r a t e of

d e t e r i o r a t i o n i s probably non-linear and t h u s t h e increment p e r y e a r depends on t h e d e g r e e of d e t e r i o r a t i o n a t t h e t i m e of t e s t i n g . The p l o t of t h e p e r c e n t a g e of t h e d e l a m i n a t e d a r e a a g a i n s t t h e a g e of t h e s t r u c t u r e a p p e a r s t o s u p p o r t t h i s assumption. A v a i l a b l e d a t a f o r f o u r s t r u c t u r e s a r e shown i n F i g u r e 1.

The a v e r a g e a n n u a l r a t e between s i x and n i n e y e a r s of a g e i s 2.3 p e r c e n t . I n t e r e s t i n g l y , i n a b r i d g e deck s t u d y t h e a n n u a l r a t e of d e t e r i o r a t i o n was 2.1 p e r c e n t (7). The s h a p e of t h e

I d e t e r i o r a t i o n v e r s u s time c u r v e and t h a t of t h e c h l o r i d e

p e n e t r a t i o n v e r s u s time c u r v e were found t o be s i m i l a r s ( 7 ) . It may be s i g n i f i c a n t t h a t s i m i l a r i t i e s between b r i d g e and p a r k i n g g a r a g e decks e x i s t .

Delamination a t Commencement of Survey

According t o 69 c a s e h i s t o r i e s r e p o r t e d by a c o n s u l t i n g f i r m t h e g a r a g e s showed, on a v e r a g e , 13.1 p e r c e n t d e l a m i n a t i o n a t t h e time t h e owners commissioned t h e i r survey. F i g u r e 2 i s a h i s t o g r a m showing t h e p e r c e n t a g e of d e l a m i n a t i o n of i n d i v i d u a l s t r u c t u r e s . C l e a r l y , owners a r e prompted t o s e e k t h e a d v i c e of a c o n s u l t a n t when g a r a g e s show v e r y d i f f e r e n t l e v e l s of

d e t e r i o r a t i o n . I n 46 c a s e s t h e a g e of t h e s t r u c t u r e s a t t h e t i m e of t h e s u r v e y was known and t h i s i n f o r m a t i o n i s shown i n

F i g u r e 3.

I

Concrete Cover The a v e r a g e s f o r t h e c o n c r e t e c o v e r s determined i n c o r e s a r e shown i n F i g u r e 4. That f o r a l l t h e c o r e s i s 50 mm o v e r t h e s t e e l . The a v e r a g e of 36 s u r v e y s c a r r i e d o u t by a c o n s u l t i n g f i r m i s 42.4 mm ( F i g u r e 5). The mean s t a n d a r d d e v i a t i o n of t h e 8000 cover t h i c k n e s s d e t e r m i n a t i o n s i s 14.3 mm, a v a l u e t h a t compares w e l l w i t h t h e 13-mm a v e r a g e s t a n d a r d d e v i a t i o n of r e i n f o r c i n g s t e e l cover i n b r i d g e decks t h a t h a s been

r e p o r t e d ( 8 ) . The d i s t r i b u t i o n i s shown i n F i g u r e 6. I n t h e most extreme c a s e t h e mean cover was 64 mm, w i t h a s t a n d a r d

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d e v i a t i o n of 1 3 mm. The o t h e r extreme was 30 a m , w i t h 13-mm s t a n d a r d d e v i a t i o n .

I n t h e sample 36 g a r a g e s , h a l f had over 13.8 mm minimum cover and were i n d i s t r e s s , a s e v i d e n c e d by t h e need f o r a survey. I n c o n t r a s t , g a r a g e s i n S e r i e s b had 3, 25, and 17 mm minimum c o v e r , r e s p e c t i v e l y , and were i n c l u d e d i n t h e p r e s e n t s t u d y because of t h e i r e x c e l l e n t performance. While b l h a s a d e n s e c o n c r e t e o v e r l a y t o p p i n g and b2 i s p o s t - t e n s i o n e d , b3 h a s no w a t e r p r o o f i n g membrane and f o r t h e t i m e b e i n g a p p e a r s t o b e i n good c o n d i t i o n . T h i s seems t o imply t h a t c o v e r i s n o t of

o v e r - r i d i n g importance, and t h a t i t i s p o s s i b l e t o have a d u r a b l e g a r a g e w i t h o u t a v e r y t h i c k cover.

C h l o r i d e Content

The c h l o r i d e c o n t e n t of t h e c o r e s o b t a i n e d from g a r a g e s

i n

S e r i e s b i s g i v e n i n T a b l e 8. The t h r e s h o l d v a l u e of s o l u b l e c h l o r i d e i o n c o n c e n t r a t i o n by weight of c o n c r e t e , a c c o r d i n g t o t h e N a t i o n a l C o o p e r a t i v e Highway Research Program, S y n t h e s i s of Xighway P r a c t i c e 57, i s a p p r o x i m a t e l y 0.026 p e r c e n t , assuming

400 kg/m3 cement c o n t e n t (9). The l i m i t s e t by ACI Committee 201

f o r c o n c r e t e i n c o n v e n t i o n a l l y r e i n f o r c e d c o n c r e t e i n a m o i s t environment exposed t o c h l o r i d e

i s

l e s s 0.015 p e r c e n t w a t e r s o l u b l e c h l o r i d e by weight of c o n c r e t e (10). The well-performing g a r a g e s of S e r i e s b a l l have c h l o r i d e c o n t e n t h i g h e r t h a n t h a t r e q u i r e d by ACI, and o n l y one s t r u c t u r e , b2, h a s c h l o r i d e c o n c e n t r a t i o n below t h e t h r e s h o l d v a l u e r e p o r t e d i n S y n t h e s i s 57. C o r r o s i o n A c t i v i t y

I

The g e n e r a l l y a c c e p t e d c r i t e r i a of c o r r o s i o n a c t i v i t y of s t e e l r e i n f o r c e m e n t i n terms of e l e c t r o d e p o t e n t i a l i s -0.35 V measured a g a i n s t a copper/copper s u l f a t e e l e c t r o d e ( 9 ) . I n t h e well-performing b l s t r u c t u r e , 14 p e r c e n t of t h e t e s t r e s u l t s exceeded t h e t h r e s h o l d v a l u e , i n d i c a t i n g t h a t 14 p e r c e n t of t h e a r e a i s a c t i v e l y corroding. Three g a r a g e s i n S e r i e s c ( c 5 , c6, c7) showed q u i t e a h i g h p e r c e n t a g e of r e a d i n g s above t h e t h r e s h o l d value. Sixty-one s t r u c t u r e s surveyed by a c o n s u l t i n g f i r m showed t h e d i s t r i b u t i o n p r e s e n t e d i n Fig. 7.

Compressive S t r e n g t h

The compressive s t r e n g t h of c o n c r e t e c o r e s o b t a i n e d from t h e S e r i e s b s t r u c t u r e s i s q u i t e h i g h ( T a b l e 5). T h i s might l e a d t o t h e assumption t h a t t h e good performance of t h e g a r a g e s

is

due, a t l e a s t i n p a r t , t o h i g h s t r e n g t h of t h e c o n c r e t e . A summary of compressive s t r e n g t h d a t a o b t a i n e d by a n independent s u r v e y of 60 d e t e r i o r a t e d g a r a g e s , however, shows h i g h compressive s t r e n g t h v a l u e s r a n g i n g between 32.1 and 67.4 MPa, t h e mean b e i n g 47.4 W a . It h a s t o b e concluded t h a t compressive s t r e n g t h i s n o t r e l a t e d t o d u r a b i l i t y .

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C h l o r i d e P e r m e a b i l i t y Under t h e c o n d i t i o n s a d o p t e d as s t a n d a r d i n t h e FHWA t e s t , t h e p a s s a g e of more t h a n 4000 C i s c o n s i d e r e d t o be h i g h and 2000-1000 C t o be low c h l o r i d e p e r m e a b i l i t y (5). I n c o r e s o b t a i n e d from S e r i e s b g a r a g e s , t h e a v e r a g e p e r m e a b i l i t y v a l u e ranged from 2675 ( b 2 ) t o 6203 C (b3). I n b l , t h e p e r m e a b i l i t y was s o h i g h t h a t i t was beyond t h e r a n g e of t h e measuring i n s t r u m e n t . The v a l u e s f o r S e r i e s c g a r a g e s i n d i c a t e d n o p e r m e a b i l i t y where a w a t e r p r o o f i n g membrane w a s p r e s e n t , e x c e p t f o r W-3 which (owing t o i t s i o n i c c o n s t i t u e n t s ) showed h i g h c h a r g e t r a n s f e r a l t h o u g h i t may, i n f a c t , b e q u i t e impermeable. I n a d d i t i o n , most l a t t i c e s c o n t a i n v i n y l i d e n e c h l o r i d e , s o t h a t h i g h e r c h l o r i d e c o n c e n t r a t i o n u n r e l a t e d t o p e r m e a b i l i t y may a l s o e x i s t . The s i g n i f i c a n c e of t h e r a p i d p e r m e a b i l i t y measurement h a s n o t been e s t a b l i s h e d u n d e r t h e v a r i o u s f i e l d c o n d i t i o n s . A i r E n t r a i n m e n t The c o n c r e t e i n i n d o o r g a r a g e s i s n o r m a l l y n o t air- e n t r a i n e d . I n t h e c o u r s e o f 129 s u r v e y s performed by a c o n s u l t i n g f i r m , none was found t o c o n t a i n a i r - e n t r a i n e d c o n c r e t e . The c o n c r e t e i n g a r a g e b l d i d c o n t a i n a i r - e n t r a i n e d c o n c r e t e , b u t t o a l e s s e r d e g r e e t h a n i s n o r m a l l y r e q u i r e d : 3.1 p e r c e n t a i r i n t h e s t r u c t u r a l c o n c r e t e and 2.6 p e r c e n t i n t h e c o n c r e t e o v e r l a y . The s p a c i n g f a c t o r i s , of c o u r s e , much g r e a t e r t h a n t h e r e q u i r e d 0.2 mm (1.19 mm and 0.85 mm, r e s p e c t i v e l y ) . T h i s c o n c r e t e , t h e r e f o r e , cannot be c o n s i d e r e d p r o p e r l y a i r - e n t r a i n e d . S t r u c t u r e s b2 and b3 a r e exposed t o f r e e z i n g t e m p e r a t u r e s and a r e p r o p e r l y a i r - e n t r a i n e d , w i t h a p p r o x i m a t e l y 8.0 p e r c e n t a i r c o n t e n t and 0.16 mm s p a c i n g f a c t o r . DISCUSSION S e r i e s b S t r u c t u r e s S t r u c t u r e b l h a s a c o n c r e t e t o p p i n g o v e r t h e s t r u c t u r a l s l a b , w i t h saw c u t s on g r i d l i n e s f o r c r a c k c o n t r o l . The o v e r l a y i s , however, h i g h l y permeable t o c h l o r i d e i o n s and h a s debonded e x t e n s i v e l y from t h e s t r u c t u r a l s l a b . It h a s f a i l e d . It seems p r o b a b l e t h a t , i n t i m e , t h e s t r u c t u r a l s l a b w i l l d e t e r i o r a t e u n l e s s r e m e d i a l measures a r e t a k e n . C o r r o s i o n a c t i v i t y i s a l r e a d y s i g n i f i c a n t , a s i n d i c a t e d by t h e h a l f - c e l l p o t e n t i a l measurements. It s h o u l d be n o t e d t h a t t h i s g a r a g e h a s performed v e r y s a t i s f a c t o r i l y f o r e i g h t y e a r s , o b v i o u s l y because o f ' t h e c o n c r e t e topping. While d e t e r i o r a t i o n can u s u a l l y be d e t e c t e d a f t e r f o u r t o f i v e y e a r s of s e r v i c e , t h e owner c o n s i d e r e d t h a t t h e s t r u c t u r e was performing e x t r e m e l y w e l l a f t e r e i g h t y e a r s . T h i s s u g g e s t s

t h a t e v e n a poor p r o t e c t i v e s y s t e m c a n p r o v i d e s i g n i f i c a n t p r o t e c t i o n . Had t h e t o p p i n g been r e p l a c e d a few y e a r s ago, t h e p r o s p e c t s f o r c o n t i n u e d e x c e l l e n t performance would b e v e r y good.

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The c a s t - i n - p l a c e p o s t - t e n s i o n e d s t r u c t u r e , b2, was i n e x c e l l e n t c o n d i t i o n e l e v e n y e a r s a f t e r c o n s t r u c t i o n . T h i s and s i m i l a r s t r u c t u r e s s u g g e s t t h a t p o s t - t e n s i o n e d d e s i g n p r o v i d e s a d u r a b l e g a r a g e i f t h e cover i s good and i s uniform, t h e expansion j o i n t s a r e i n good c o n d i t i o n , t h e c o n c r e t e i s of h i g h q u a l i t y , and moderate c h l o r i d e p e r m e a b i l i t y and good d r a i n a g e a r e a s s u r e d . The t e n d o n s themselves have t o b e , of c o u r s e , w e l l p r o t e c t e d from c o r r o s i o n .

S t r u c t u r e b3 a p p e a r s t o be i n a v e r y good c o n d i t i o n a f t e r f i v e y e a r s of s e r v i c e . Uniform c o v e r of t h e r e i n f o r c i n g s t e e l w i t h p r o p e r l y a i r - e n t r a i n e d c o n c r e t e and good d r a i n a g e seem t o have been s u f f i c i e n t t o p r e v e n t d e t e r i o r a t i o n .

The c o n c r e t e

i s more permeable t o c h l o r i d e t h a n i s c o m p a t i b l e w i t h good

performance, however, and may n o t be d u r a b l e i n h i g h t r a f f i c a r e a s , which a l r e a d y show h i g h c h l o r i d e c o n c e n t r a t i o n . T h i s s t r u c t u r e d o e s n o t have a w a t e r p r o o f i n g membrane, b u t one would c l e a r l y be of b e n e f i t .

The u n u s u a l l y t h i c k c o n c r e t e t o p p i n g i n s t r u c t u r e b4 and a membrane of m u l t i - l a y e r p a p e r and m a s t i c have provided a l m o s t p e r f e c t p r o t e c t i o n f o r t h e s t r u c t u r a l s l a b f o r 20 y e a r s . T h i s i s proof t h a t d u r a b l e g a r a g e s c a n be b u i l t , and f u r t h e r , t h a t even i n e x p e n s i v e w a t e r p r o o f i n g systems can g i v e s a t i s f a c t o r y

p r o t e c t i o n .

S e r i e s c S t r u c t u r e s

The g a r a g e s i n t h i s group had d e t e r i o r a t e d t o s u c h a n e x t e n t t h a t r e s t o r a t i o n was n e c e s s a r y . Although no r e c o r d s of s u r v e y s made a t t h e t i m e of r e p a i r s and i n t h e s u b s e q u e n t p e r i o d a r e a v a i l a b l e , t h e s e g a r a g e s c a n y i e l d i n f o r m a t i o n on some a s p e c t s of t h e performance of r e p a i r e d s t r u c t u r e s . The most i m p o r t a n t i s t h a t d e t e r i o r a t e d g a r a g e s c a n b e r e p a i r e d t o p r o v i d e r e a s o n a b l e s e r v i c e . True, n o t e v e r y r e p a i r e d g a r a g e i s i n good c o n d i t i o n , b u t t h i s may b e due t o v a r i o u s f a c t o r s s u c h a s t h e thoroughness w i t h which a l l d e t e r i o r a t e d a r e a s were d e t e c t e d and r e p a i r e d , t h e adequacy and a p p r o p r i a t e n e s s of t h e r e p a i r p r o c e d u r e , t h e e f f e c t i v e n e s s of t h e i n s t a l l e d w a t e r p r o o f i n g system, and t h e q u a l i t y of c o n s t r u c t i o n , a g e of s t r u c t u r e , t y p e of usage and maintenance. S t r u c t u r e s c2, c8 and c 9 a r e d e f i n i t e l y i n a n a c c e p t a b l e c o n d i t i o n f i v e y e a r s a f t e r r e h a b i l i t a t i o n . It h a s been s u g g e s t e d t h a t u n l e s s a l l s a l t - c o n t a m i n a t e d c o n c r e t e i s removed m o i s t u r e w i l l be t r a p p e d u n d e r n e a t h t h e i n s t a l l e d w a t e r p r o o f i n g system and promote c o r r o s i o n . No e v i d e n c e of t h e d e t r i m e n t a l e f f e c t of w a t e r p r o o f i n g systems was

found i n t h e t h r e e s t r u c t u r e s mentioned above. Furthermore, i t

may be s i g n i f i c a n t t h a t t h e g a r a g e i n t h e w o r s t c o n d i t i o n , c6, h a s a s e a l e r r a t h e r t h a n a w a t e r p r o o f i n g membrane; i t s poor c o n d i t i o n may b e r e l a t e d t o t h e l e s s p o s i t i v e w a t e r p r o o f i n g a c t i o n of s e a l e r s compared t o membranes. It i s r e a s o n a b l e t o assume t h a t t h e m o i s t u r e c o n t e n t i n t h e deck of c6 was q u i t e h i g h and t h e c o r r o s i o n a c t i v i t y probably due t o t h i s f a c t o r . T h i s

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i n d i c a t e s t h a t membranes a r e b e n e f i c i a l , i n p a r t a t l e a s t ,

because t h e y c r e a t e a b a r r i e r a g a i n s t t h e d i f f u s i o n of oxygen, a n e s s e n t i a l c o n s t i t u e n t of t h e c o r r o s i o n r e a c t i o n .

The r a t e of d e t e r i o r a t i o n can be e s t i m a t e d by assuming t h a t a t t h e t i m e of c o m p l e t i o n o f r e p a i r t h e i n d u c t i o n p e r i o d i s o v e r and t h e a c t u a l d e l a m i n a t i o n 0 p e r c e n t . I n Fig. 1 t h i s s t a t e c o r r e s p o n d s t o t h e b r e a k p o i n t of t h e curve. The p e r c e n t a g e d e t e r i o r a t i o n of t h e S e r i e s c s t r u c t u r e s i s p l o t t e d i n Fig. 1 u s i n g normalized a g e v a l u e s (5 y e a r s

+

number of y e a r s s i n c e r e p a i r s ) and assuming t h a t r e p a i r s r e s t o r e d t h e s t r u c t u r e t o i t s c o n d i t i o n a t 5 y e a r s : c10 and c 3 f a l l on t h e e s t a b l i s h e d l i n e ; t h a t t h r o u g h c5 and c l h a s t h e same s l o p e s h i f t e d by two y e a r s ; and c2, c8, c9 and c l l show minimal d e t e r i o r a t i o n . Although t h e number of samples is e x t r e m e l y l i m i t e d , t h e f i g u r e shows t h a t a f t e r r e p a i r s t h e r a t e of d e t e r i o r a t i o n i n t e r m s of d e l a m i n a t i o n was a p p a r e n t l y u n a l t e r e d i n two c a s e s , p r o v i d i n g a d v a n t a g e t o t h e e x t e n t t h a t d e t e r i o r a t i o n remained on t h e l i n e a r s e c t i o n of t h e e x p o n e n t i a l o r o g i v e r a t e curve.

The r e p a i r of g a r a g e s c5 and c l a p p e a r s t o have r e s u l t e d i n a n a d d i t i o n t o t h e two-year a d v a n t a g e ; f o r c2, c9 and c 8 , s u c c e s s seems t o have been e s s e n t i a l l y complete. On t h e o t h e r hand, g a r a g e c7 d e t e r i o r a t e d r a p i d l y and must b e c o n s i d e r e d t o be u n a f f e c t e d by r e p a i r . T h i s is t o be e x p e c t e d , s i n c e p l a i n a s p h a l t d o e s n o t p r e v e n t i n g r e s s of water. The poor performance of c7 d e m o n s t r a t e s , t o o , t h e need f o r a w a t e r p r o o f i n g system. c6 a p p e a r s t o h a v e d e t e r i o r a t e d a t a r a t e g r e a t e r t h a n normal.

I f t h e p e r c e n t a g e of d e l a m i n a t i o n i s p l o t t e d a g a i n s t t h e a g e of t h e s t r u c t u r e , i r r e s p e c t i v e of t y p e of r e p a i r (Fig. 8), a d i f f e r e n t p i c t u r e emerges. c6 a p p e a r s t o have d e t e r i o r a t e d a t t h e u s u a l r a t e and r e p a i r n o t t o h a v e improved i t s performance. c7, on t h e o t h e r hand, though s e v e r e l y d e t e r i o r a t e d , shows some b e n e f i t from r e p a i r and t h e added a s p h a l t cover. It a p p e a r s t h a t a f t e r r e p a i r g a r a g e s normally d e t e r i o r a t e a t a s i g n i f i c a n t l y lower r a t e t h a n d o u n p r o t e c t e d o n e s (0.64 p e r c e n t v e r s u s 1.67 p e r c e n t p e r y e a r ) , t h e r a t e of d e l a m i n a t i o n b e i n g a l i t t l e o v e r one t h i r d . Garage c10 performed b e t t e r and c2 b e s t , w i t h o n l y 0.2 p e r c e n t d e l a m i n a t i o n 16 and 5 y e a r s a f t e r r e p a i r . These o b s e r v a t i o n s a r e t e n t a t i v e , of c o u r s e , s i n c e f a c t o r s s u c h a s q u a l i t y of c o n s t r u c t i o n , d e s i g n , and e x t e n t of r e p a i r , a l l of which h a v e g r e a t i n f l u e n c e on performance, a r e unknown.

An e v a l u a t i o n of p r o t e c t i v e systems i s n o t p o s s i b l e because t h e number of samples i s s m a l l and t h e impact o f t h e i n f l u e n c i n g f a c t o r s unknown and non-uniform t h r o u g h o u t t h e groups. The e s s e n t i a l l y u n p r o t e c t e d c7 s t r u c t u r e and t h e s e a l e r - p r o t e c t e d c6 a p p e a r t o perform l e a s t s u c c e s s f u l l y . Debonding of t h e r e i n f o r c e m e n t from t h e c o n c r e t e m a t r i x i s t h e most i m p o r t a n t consequence of g a r a g e d e t e r i o r a t i o n . S u c c e s s f u l r e h a b i l i t a t i o n r e q u i r e s t h a t i t be c o r r e c t e d . The merit of any t e s t , s u c h a s h a l f - c e l l p o t e n t i a l , C1-

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.

1512

Litvan and

Bickley

c o n c e n t r a t i o n , c r a c k i n g o f t h e c o n c r e t e c o v e r , a l l c a r r i e d o u t f r e q u e n t l y i n s u r v e y s , must be judged by i t s a b i l i t y t o d e t e c t debonding r e l i a b l y , a c c u r a t e l y , and a t a s e a r l y a s t a g e a s p o s s i b l e . The p e r c e n t a g e of debonded a r e a s i n t h e e l e v e n t e s t s i t e s of s t r u c t u r e b l i s p l o t t e d a g a i n s t t h e p e r c e n t a g e of measurements of h a l f - c e l l p o t e n t i a l e x c e e d i n g -0.35 V a g a i n s t Cu/Cu SO,, e l e c t r o d e i n Fig. 9. It may be s e e n t h a t t h e h a l f - c e l l p o t e n t i a l t e s t i s markedly l e s s s e n s i t i v e t o debonding t h a n t h e chain-drag t e s t . P l o t t i n g t h e p e r c e n t a g e of debonded a r e a s a g a i n s t t h e p e r c e n t a g e of r e a d i n g s e x c e e d i n g -0.20 V y i e l d s a n a l m o s t l i n e a r r e l a t i o n ( F i g . 10). T h i s , o f c o u r s e , i s o n l y a s i n g l e s e t of measure~nents and f u r t h e r s t u d i e s w i l l have t o be conducted t o d e t e r m i n e

whether t h e t h r e s h o l d v a l u e f o r c o r r o s i o n a c t i v i t y s h o u l d ,

i n d e e d , be c o n s i d e r e d a t -0.20 V Cu/Cu SO, i n s t e a d of t h e p r e s e n t -0.35 V , and f u r t h e r m o r e whether h a l f - c e l l p o t e n t i a l measurements s h o u l d r o u t i n e l y be c a r r i e d o u t i n c o n d i t i o n surveys.

There a p p e a r s t o be no r e l a t i o n between t h e e x t e n t of c r a c k i n g and debonding, a c c o r d i n g t o t h e r e s u l t s shown i n Fig. 11. It i s c o n c e i v a b l e t h a t c r a c k i n g a c c e l e r a t e s c o r r o s i o n by p r o v i d i n g a pathway f o r t h e b r i n e t o t h e s t e e l , a s w e l l a s by r e d u c i n g t h e e x t e n t of debonding by s t r e s s r e l i e f . I f s u c h e f f e c t s a r e p r e s e n t , t h e d a t a d o n o t i n d i c a t e it. It i s concluded t h a t c r a c k w i d t h h a s l i t t l e i n f l u e n c e on

I

c o r r o s i o n , i n agreement w i t h r e s u l t s p u b l i s h e d i n t h e l i t e r a t u r e c i t e d by Beeby ( 9 ) . It h a s t o be remembered t h a t c h l o r i d e c o n t a i n i n g w a t e r c a n r e a c h t h e r e i n f o r c i n g s t e e l by d i f f u s i o n t h r o u g h t h e c o n c r e t e as w e l l a s t h r o u g h c r a c k s . While c r a c k s change t h e p a t h l e n g t h d r a m a t i c a l l y , t h e a f f e c t e d a r e a i s r e l a t i v e l y s m a l l . A l t e r n a t i v e l y , i f c o n c r e t e i s h i g h l y permeable, o v e r a l l c o r r o s i o n w i l l b e s u b s t a n t i a l and a n a d d i t i o n a l c r a c k w i l l n o t make t o o g r e a t a d i f f e r e n c e . Again, i f c o n c r e t e i s of good q u a l i t y , i . e . , low p e r m e a b i l i t y , a l i m i t e d number of c r a c k s w i l l a f f e c t a c o r r o s i o n - f r e e s y s t e m v e r y l i t t l e .

The C1- c o n t e n t and, i n p a r t i c u l a r , any e x c e s s o v e r t h e t h r e s h o l d l i m i t ( t h e u n d e r l y i n g c a u s e of d e t e r i o r a t i o n ) must b e e v a l u a t e d i n t h e p r o p e r c o n t e x t when p l a n n i n g a r e p a i r s t r a t e g y . T h e r e a p p e a r s t o b e l i t t l e v a l u e i n making numerous C1- c o n c e n t r a t i o n d e t e r m i n a t i o n s i n t h e c o u r s e of r o u t i n e s u r v e y s ; h i g h c o n c e n t r a t i o n s w i l l c e r t a i n l y be found i f c o r r o s i o n h a s o c c u r r e d , and t o remove a l l c o n c r e t e w i t h c h l o r i d e c o n t e n t h i g h e r t h a n t h e t h r e s h o l d v a l u e i s a l m o s t always i m p r a c t i c a l . I n any c a s e , c o n s i d e r a b l e doubt e x i s t s a b o u t t h e c o r r e c t v a l u e f o r t h e t h r e s h o l d c o n c e n t r a t i o n ( 1 2 ) .

It i s u s e f u l t o examine t h e age d i s t r i b u t i o n of a sample 46 g a r a g e s i n d i s t r e s s a t t h e t i m e t h e y were s u r v e y e d (Fig. 3). Understandably, few i n t h e 0 t o 4-year age group a r e i n c l u d e d because t h e r e i s a n i n c u b a t i o n p e r i o d b e f o r e damage m a n i f e s t s

(14)

i t s e l f . It i s expected t h a t t h e number of d e t e r i o r a t e d g a r a g e s

i n t h e group w i l l i n c r e a s e with age. Even a l l o w i n g f o r fewer

garages a decade ago, t h e e x i s t e n c e of a r e l a t i v e l y s m a l l number

oE o l d garages i n t h e group i s s u r p r i s i n g . It i s p o s s i b l e t h a t

some change i n d e s i g n o r c o n s t r u c t i o n p r a c t i c e s i s r e s p o n s i b l e , a t l e a s t i n p a r t , f o r t h e poorer performance of g a r a g e s of more r e c e n t vintage. T h i s a s p e c t should be i n v e s t i g a t e d f u r t h e r .

To meet one of t h e o b j e c t i v e s of t h e p r o j e c t , examples of

d u r a b l e g a r a g e s were sought. Of s e v e r a l hundred s t r u c t u r e s , only

f o u r , S e r i e s b s t r u c t u r e s , were i d e n t i f i e d a s such. This i s a c l e a r i n d i c a t i o n of t h e g r o s s inadequacy of t h e accepted s t a n d a r d

by which garages have been b u i l t u n t i l very r e c e n t l y . It

f o l l o w s , t h e r e f o r e , t h a t almost a l l c o n v e n t i o n a l l y - b u i l t garages w i l l , i n due c o u r s e , d e t e r i o r a t e and r e q u i r e r e h a b i l i t a t i o n . R e p a i r s a r e b e n e f i c i a l b u t n o t completely s u c c e s s f u l because once t h e c h l o r i d e c o n t e n t of t h e c o n c r e t e h a s become high i t i s

d i f f i c u l t , probably impossible, t o s t o p c o r r o s i o n completely. A t

p r e s e n t , garages a r e r e p a i r e d only when t h e c o n d i t i o n s become i n t o l e r a b l e . It seems a d v i s a b l e t o upgrade c o n v e n t i o n a l l y - b u i l t garages a s e a r l y a s p o s s i b l e b e f o r e t h e c h l o r i d e c o n c e n t r a t i o n i n t h e c o n c r e t e h a s i n c r e a s e d f u r t h e r , even i f no s i g n s of

d e t e r i o r a t i o n can be d e t e c t e d . To upgrade c o r r o s i o n p r o t e c t i o n a t an e a r l y s t a g e p r o v i d e s n o t only g r e a t b e n e f i t i n t e c h n i c a l

terms but i s a l s o t h e most c o s t - e f f e c t i v e approach t o t h e

problem.

CONCLUSIONS Durable garages can be b u i l t .

The poor performance of e x i s t i n g g a r a g e s i s a r e s u l t of

d e s i g n and c o n s t r u c t i o n p r a c t i c e s t h a t f a l l s h o r t of t h o s e r e q u i r e d by t h e environment.

Almost a l l g a r a g e s b u i l t u n t i l very r e c e n t l y by c o n v e n t i o n a l methods w i l l r e q u i r e r e h a b i l i t a t i o n .

It i s a t e c h n i c a l and economic advantage t o upgrade e x i s t i n g garages a s e a r l y a s p o s s i b l e , b e f o r e c h l o r i d e c o n c e n t r a t i o n

becomes higher. To w a i t u n t i l c o n d i t i o n s become i n t o l e r a b l e

l e a d s t o more e x t e n s i v e r e p a i r work and l e s s s a t i s f a c t o r y r e s u l t s .

Repair by t h e " p a t c h and waterproof" method lowers t h e r a t e

of d e t e r i o r a t i o n s i g n i f i c a n t l y , i.e., t o approximately 30

p e r c e n t of t h a t p r i o r t o r e h a b i l i t a t i o n . Such r e p a i r s do n o t , however, completely s t o p f u r t h e r c o r r o s i o n .

There a r e no d e t r i m e n t a l e f f e c t s from i n s t a l l i n g a

waterproofing membrane over c o n c r e t e w i t h e l e v a t e d c h l o r i d e c o n c e n t r a t i o n .

Durable g a r a g e s c a n be b u i l t without u s i n g e x o t i c methods. High-quality dense c o n c r e t e , adequate cover, e f f e c t i v e waterproofing, and good d r a i n a g e seem t o be e s s e n t i a l . No r e l a t i o n e x i s t s between e x t e n t of delamination and t h a t of cracking.

No r e l a t i o n h a s been f o u n i between e x t e n t of delamination and compressive s t r e n g t h .

(15)

10. H a l f - c e l l p o t e n t i a l , u s i n g t h e -0.35 V Cu/Cu SO4 l e v e l c r i t e r i a , i s n o t more s e n s i t i v e i n d e t e c t i n g debonding t h a n i s t h e chain-drag t e s t . 11. C o n d i t i o n s u r v e y s s h o u l d r o u t i n e l y i n c l u d e v i s u a l i n s p e c t i o n and t h e chain-drag t e s t . A d d i t i o n a l t e s t s a r e u s e f u l i f s p e c i f i c q u e s t i o n s a r i s e . REFERENCES 1 I. ASTM C876-80 Standard T e s t , "Half-Cell P o t e n t i a l s of

R e i n f o r c i n g S t e e l i n Concrete," Annual Book of ASTM Standards. ASTM, P h i l a d e l p h i a , PA, Vol. 04.02, 1984,

pp. 557-563. !

2. B r i t i s h S t a n d a r d s I n s t i t u t i o n , Standard BS 4408,

"Recommendations f o r Non-Destructive Methods of T e s t f o r Concrete, P a r t I: Electro-Magnetic Cover Measuring Devices," 1969.

3. C l e a r , K.C. and H a r r i g a n , E.T., "Sampling and T e s t i n g f o r C h l o r i d e I o n i n Concrete," Report No. FHWA-RD-77-85, F e d e r a l Highway A d m i n i s t r a t i o n , Washington, DC, 1977, 21 pp.

4. Canadian S t a n d a r d s A s s o c i a t i o n T e s t Method A23.2-14C, " O b t a i n i n g and T e s t i n g D r i l l e d Cores f o r Compressive S t r e n g t h T e s t i n g , " CAN3-A23.2-M77, "Methods of T e s t f o r Concrete," Canadian S t a n d a r d s A s s o c i a t i o n , Rexdale, O n t a r i o , 1977.

5. Whiting, D., " I n S i t u Measurement of t h e P e r m e a b i l i t y of C o n c r e t e t o C h l o r i d e I o n s , " I n Situ/Non D e s t r u c t i v e T e s t i n g of Concrete, V.M. Malhotra, Ed., American Concrete I n s t i t u t e , SP-82, D e t r o i t , 1984, pp. 501-524.

6. ASTM, Standard P r a c t i c e C457-82a, "Microscopical - D e t e r m i n a t i o n of Air-Void Content and P a r a m e t e r s o f ' t h e Air-Void System i n Hardened Concrete," Annual Book of ASTM S t a n d a r d s , ASTM, P h i l a d e l p h i a , PA, V. 04.02, 1985,

pp. 287-302.

7. Cady,

P.D.

and Weyers, R.E., " D e t e r i o r a t i o n Rates of C o n c r e t e Bridge Decks," J. T r a n s p o r t a t i o n E n g i n e e r i n g , Am. Soc. C i v i l Eng., Vol. 110, No. 1, 1984, pp. 34-44.

8. Weed, R.M., "Recommended Depth of Cover of Bridge Deck S t e e l , " Transp. R e s . Record, No. 500, 1974, pp. 32-35. 9. " D u r a b i l i t y of Concrete Bridge Decks," N a t i o n a l Cooperative

Highway Research Program, S y n t h e s i s of Highway P r a c t i c e 57, T r a n s p o r t a t i o n Research Board, N a t i o n a l Research Council, Washington, DC, 1979.

10. ACI Committee 201, "Guide t o Durable Concrete," American C o n c r e t e I n s t i t u t e , D e t r o i t , 1977, pp. 22.

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11. Beeby, A.W., "Cracking, Cover and Corrosion of

Reinforcement," Concrete International,

V.

5, No. 2, 1983,

pp. 35-40.

12. Anderson, A.R. and Black, R.W., "Questioning the Limit,"

Concrete International,

V. 7,

No.

9,

1985, pp. 28-34.

This paper is a contribution from the Institute for Research in Construction, National Research Council of Canada.

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Area of Length of Age a t Main No. of suspended Area of expansion t i m of s t r u c t u r a l suspended s l a b s ramps P r o t e c t i v e j o i n t s survey, Code Description l o c a t i o n Type* system l e v e l s m2 m2 system m y e a r s

b l O f f i c e and Ottawa BI Reinforced 2 8 423 Concrete 113 8

shopping mall overlay

b2 Hotel Toronto AE Two-way 6 9 590 786 156 11

post- tensioned

b3 Apartm~nt Toronto A Twonay LO 11 055 566 None No 5

r e i n f o r c e d j o i n t s

b4 Office complex Montreal 0 Reinforced 2 11 LBO 300 Tar paper 145 20

s p l i t s l a b mastic

(18)

Area of Length of Age at Age at Main No. of suspended Area of Protective expansion time of time of structural suspended slabs ramps system joints repair, survey. Code Description Location Type* system levels m2 m2 type** m years years

cl Gov't office Ottawa BI 1 11 148 7 0 W- 3 263 10 13

c2 Office and Hull n l One-way 7 14 865 'a-4 Ni 1 11 16

shopping mall slab on

beams

c3 Cov't office Toronto A1 On steel 6 2 360 410 Various f rame

c4 Condominium Toronto 01 Nil 7 962 + 275 11 13

c5 Shopping mall Kitchener AE O n e r a y 7 20 786 850 W-1 222 7 9

slab on beams

e6 H o a ~ i t a l Toronto A!3 6 6 317 Sealer 98 12-13 15

c7 Shopping mall Hamilton AE b 15 868 1069 Asphalt 198 21 26

c8 Apt. complex Toronto B I 1 21 218 485 U-? 7 20 a 9

-. . -

c9 Apt. complex Montreal Ilf

c10 Bank and Montreal 61 Some on 3 3 590 811 W-3 on 19 21

shopping mall steel, asphalt

Some on R.C. beams

cll Apartment fandon BT I 4 048 269 Sealer 36 7-8 10

(S-1) *A Above grade B Belov grade I Interior E Exposed '**For description of waterproofing systems see Table 3

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TABLE 3--Description of Waterproofing Systems

Code Generic description

1 Formed-in-place, celoentitious topping reinforced vith short alkali-resistant glass fibre

U-2 Formed-in-place, rubberized-asphalt vaterproofing membrane with e divorcing sheet and s mastic asphalt wearing couraa

W-3 Formed-in-place, latex-neoprene waterproofing membrane with a coal tar epoxy wearing course

U-h Formed-in-place, two-component polyurethane waterproofing membrane with a polyurethane and sand mix wearing course U-5 Formed-in-place, coal-tar-epoxy waterproofing system

reinforced with a glass fibre mat and surfaced with silica sand

'd-6 Formed-in-place, rubberized-asphalt-polyoer waterproofing membrane with a laterrubberized-asphalt vearing course

1-1 Forred-in-place, cementitious waterproofing system. containing catalytic chemicals and treated quartz

S-1 Formed-in-place, two-component, solvent-based solution o f flexible epoxy resin

TABLE 4--Characteristics

of

Garages, Series

f

Area of Age at Years Main No. of suspended time of since structural suspended slabs Protective survey. repair Code Description Location Type* system levels m2 system years

fl Apt. complex North York A1 T v o r a y 3 650 None 22 Nona flat slab

f2 Apt. complex North York BI T v w a y 2 6 000 Wms 20 7 flat slab

f3 Apt. complex North York %I Tvo-way 2 4 500 Hone 19 h o e

flat slab

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W e Concrete cover Average Corrosion activity Delaminated Scaled chloride V (C.S.E.) area area Water Compressive Chloride Standard concen- Area, Z of Total X of total X of total

Density absorption strength Air void permeability Average deviation tration

kg/m3 % MPa svstem (6) C mm mm X k n n D-0.35

bl 2 385 6.4 6g p w r too high to 23 13 0.247 0.24 I 4 42 (1) 84 (2) record (3)

b2 2 349 4.9 50 good 2 675 (4) 43 9 0.019 0.18 Nil Nil Neglible

b3 32 good 6 203 37 10 0.042

-

Nil Slight

br ( 5 ) (5)

-

~ i l slight (7)

NOTES: (1) Uainly debonding of concrete topping (5) Slabs protected by 98-ram thick concrete topping and 9- (2) Scaling of concrete topping thick waterproofing. No delamination evident (3) Chloride permeability of concrete topping (6) Based on criteria of CSA A23.1-M77

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Old6 Chloride Cover ( 2) Corrosion % of s l a b Cracks permeability (I) mm a c t i v i t y , delaminated i n cm/m2

C V (C.S.E.) t e s t a r e a s Range Man Range Mean Standard Range Mean >-0.35 Range Average

d e v i a t i o n Z C l 0-120 51 20-90 46 13 0.08-0.32 0.16 N i l 1.7-11.1 4.6 6.41 CZ N i 1 N i l 25-90 50 1 A 0.01-0.28 0.12 N i l 0-0.5 0.2 10.64 c3 N i 1 N i 1

-

(3)

-

0.10-0.38 0.20 2.8 0-29.2 17.4 6.71 c l

-

4195 (4)

-

+

-

1.0 2.30 c5 641-2329 1316

-

0.10-0.47 0.27 28.0 0.8-1.2 1.0 0.20 c6 2085-2890 2517 (5)

-

0.13-0.61 0.35 48.7 5.1-59.5 26.6 2.50 297-1741 923 (6) 950-1096 1020 (7)

c7 Too high t o record

-

0.12-0.61 0.31 35.2 27.2-47.9 39.4 7.41 cB N i l N i 1

-

0.09-0.43 0.17 1.7 1.2-2.3 1.8 9.90 c9 N i l N i l 70-105 94 5 0.03-0.32 0.11 N i l 0-3.6 0.8 7.00 ,210

-

0.08-0.28 0.16 N i l

-

6.6 5.99 C l l 2042-4327 2899 (8) 20-65 39 12

-

0-1.2 7 23.26 60-617 404 ( 8 ) 1676-2063 1881 (9)

NOTE: A l l s t r u c t u r e s were cast-in-place, r e i n f o r c e d c o n c r e t e , f l a t s l a b c o n s t r u c t i o n . Cover d a t a from c o r e s not included i n t a b l e s i n c e i t was n o t always c l e a r which b a r s were from top and which from bottom mats

c4 s t r u c t u r e e v a l u a t i o n l i m i t e d t o crack r e p a i r system

(1) R e s u l t s a r e f o r t h r e e t e s t s (5) O r i g i n a l concrete

(2) Data from coverneter survey (6) O r i g i n a l epoxy overlay

(3) Mostly debonding of concrete overlay (7) Repair concrete

(4) One t e s t only (8) Unsealed concrete

(9) Sealed concrete

(22)

TABLE 7--Rate of Delamination of Concrete in a Garage

Percentage of area delaminated

&ma 6 years 9 years

1 7.3 1 0 . 0

TABLE &-Chloride Content of Concrete Cores, Series b

Chloride ion content expressed i n percent of concrete Code Average 3 0 3 , , , , 1 , 1 1 1 1 2 8

-

26 - 0 6 - 2 4

-

RATE OF DELAMINATION - OF A RAMP 2 2

-

.

GARAGE ITABLE 71 2 0

-

0 APARTMENT UNDERGROUND

g

1 8

-

c 1 6 - Q 5 1 4

-

12

-

5 u

,

1 0 - 8 - 6

-

4

-

2

-

0 ' I

'

I " ' 0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 TIME, y e a r s

Fig. 1--Rate of deterioration of four structures after repairs,

expressed as percentage of delaminated area, as a function of

normalized age (years since repair ? 5 ) , Series c

-

Point

7,

39.4% delamination and 23 years of age, has been omitted

(23)

% OF S L A B A R E A D E L A M I N A T E D

Fig. 2--Percentage of slab delamination at time of

survey,

69 structures

y 0 9 0 "

- " , . A 4

;

A G E , y e a r s

Fig. 3--Age of structure at time of survey, 46 structures

Fig. 4--Average

A V E R A G E C O V E R , rnrn

(24)

23 28 33 38 43 48 5 3 A V E R A G E C O V E R .

Fig. 5--Average thickness of concrete cover over

reinforcement,

36 structures

Fig. 6--Variabi

reinforcement,

5

k

o _ y o m o

, , N N C

.lity of thickness of concrete over

expressed as standard deviation

9C OF TEST GREATER

RESULTS NUMERICALLY THAN -0.35 V C.S.E.

Fig. 7--Corrosion activity as indicated by electrode potential

exceeding

-0.35 V (Cu/Cu

SO4

reference electrode),

61 structures

(25)

UNDERGROUND APARTMENT 0 OUTSIDE MULTI-STOREY GARAGE 32 - RAMP I N UNDERGROUND

*

26 - 24 Z 0- 22

:

16 14 12 10 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 AGE. y e a r s

Fig. 8--Extent of delamination as a function of age

of

garage

1 2 0 r I I I I ~ 110

-

IW-

-

e P O -

-

>- 80

-

- 011 rn 70 -

-

" d LO

-

- A 50

-

a - 40

-

3 0 -

-

20

-

0 7 D l ;I6 - 0 10 lo

_-

₃₉ _{5 0 2}_{0 8} - a o E n i o 4onsb Qo

Ib

so so loo D E L A M I N A T I O N . I

Fig. +-Extent of delamination in test areas versus percentage

of half-cell potential exceeding -0.35

V

(Cu/Cu

SO4

(26)

Fig. 10--Extent of delamination

in test areas versus percentage

of half-cell potential exceeding -0.20

V

(Cu/Cu SO4 reference

electrode), garage bl

110 100 9 0 -

*

8 0 - > 7 0 - 0 60 D

;

50 2 _{4 0 -}

2

3 0 - 20 10 D E L A M I N A T I O N . %

-

0 11

-

O 7 0 1 0 A 0 8

-

- - 0 1

-

- O6 0 5 0 2

-

0 9 - 0 3

-

O t l l l l l l l l l

Fig. 11--Extent of cracking versus percentage of debonded

area, Series b and c

0 10 20 30 40 50 60 70 80 90 100 D E L A M I N A T I O N , %

(27)