University of TorontoFaculty of Applied Science & Engineering

Department of Civil Engineering

Project II: Deterioration Assessment of Parking Structures

CIV 1201H – Concrete Technology and Non-Destructive Testing

Prepared for: Dr. D. K. Panesar

By: Arman Khabbazian

Ali Elmizadeh

March 24th, 2015.

Table of Contents

Table of Contents........................................................................................................................................2

Background..................................................................................................................................................3

Procedure....................................................................................................................................................6

Visual Inspection......................................................................................................................................6

Non-destructive Testing..........................................................................................................................6

Condition Assessment...............................................................................................................................10

Discussion and Conclusions.......................................................................................................................15

References:...............................................................................................................................................17

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Background Parking structures are considered a critical component of the infrastructure in highly populated

urban areas. They provide efficiency in storing a large number of vehicles, as well as protection against

harsh weather conditions, such as heavy rainfall, snow, hail, and high or low temperatures. The rapid

growth of the population around the GTA emphasizes even further the importance of parking structures

in high traffic areas. More funding is being poured into the construction of these beneficial structures, as

the price of land rises continually. On the other hand, aside from construction costs, parking structures

induce repair and maintenance costs much higher than on-grade parking spaces. But in the end, as this

metropolitan area grows rapidly, the benefits override the cost. Nevertheless, with the aging

infrastructure around the GTA, the repair and maintenance of parking structures has gained more

importance. As such, the proper assessment of the condition of these structures has become critical, so

that adequate remediation measures can be undertaken for a safe utilization.

In order to appropriately asses the condition of a parking structure and come up with a

restoration program, the type of parking structure must be identified. In terms of exposure, parking

garages can be underground or above ground. Whether the structure is above or below the ground

dictates the degree of exposure to harmful chemicals, freeze-thaw cycles and groundwater seepage. The

criticality of deterioration processes caused by such agents/factors ultimately depends on the

implication to the structural integrity of each of the structural components of the garage. Parking

garages structural systems are mainly classified into five types:

Reinforced Concrete Flat Slab, which consists of flat slabs that rest on reinforced concrete

columns by means of a drop panel.

Reinforced concrete beam and slab- this system is used to attain longer clear spans and is

commonly utilized in the design of underground parking levels of buildings and independent

structures.

Post- tensioned structures- post tensioning can be used in certain or all elements of structures

in order to reduce construction depth and cracking of the members

Precast Concrete Structures- Standard T-beams or slabs are used to form the floors of the

parking structure and maybe supported by a variety of systems such as precast columns & walls,

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reinforced concrete columns and walls, or structural steel frames. These design are used where

long spans are required to minimize the number of columns

Steel structures- structural steel frames are used to support one or more types of floor systems,

and include reinforced concrete, precast concrete slabs or T-Beams or metal deck with

composite concrete floor.

The damage resulting from sulphate attack, alkali aggregate reaction, and freeze-thaw action are usually

considered structurally insignificant, as the deterioration could take a long time and the extent of it

could not pose a considerable problem to the integrity of the structure. Rapid and progressive structural

deterioration of parking garages is mainly caused by corrosion of the reinforcing steel in the concrete, as

already mentioned, or of the steel tendons in post-tensioned or pre-tensioned concrete (Toronto

Ministry of Housing, 1988).

As shown in Figure 1, the corrosion rate of steel is a function of the alkalinity of its environment.

Concrete contains large amounts of lime which makes the environment of concrete strongly alkaline,

having a pH of between 12 and 13. Thus, steel embedded in concrete normally does not rust. If,

however, the lime in the concrete is leached out or neutralized by carbonation (the transformation of

the lime into calcium carbonate through a reaction with carbon dioxide), the passive state of the steel is

terminated and corrosion will occur. Even if the environment is highly alkaline there is still a risk of

corrosion if chloride ions are present. They act as catalysts for corrosion and once the process has begun

it does not diminish with time ( G.G. Litvan, 1982).

Harsh winters and low temperatures in

Ontario, require the continuous use of deicing

salts on the roads in order to facilitate traffic

and keep the roads operational. These salts are

chlorine based and when mixed with snow and

ice, they are transported into parking garages

by moving vehicles. Chlorides infiltrate the

concrete and reach the embedded steel in a relatively short time (depending on how porous the

concrete is and how close to the surface the rebar is). Because of steel corrosion, the volume of the

corrosion products increases and it causes cracking of concrete. This will break the bond between

concrete and steel and the load carrying capacity of the structure starts diminishing quickly. Eventually

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Figure 1 - Corrosion rate in steel ( G.G. Litvan, 1982)

concrete cracks become bigger and wider as corrosion continues and spalling starts to occur which

exposes reinforcing steel to the environment of salt and moisture (G.G. Litvan, 1982).

Figure 2 - Effect of corrosion in reinforced concrete (G.G. Litvan , 1982)

During the first years of a parking structure, no delaminations will occur even though moisture and salts

are accumulating on the top steel in the concrete slab. During this time the passivity of the steel has

been maintained. When corrosion occurs, it is an indicator that passivity of steel is lost. Delamination

will take time to occur and it happens when the corrosion products exert tensile forces bigger than

concrete’s tensile strength. Usually the top surface delamination of the slab happens much earlier than

the underside delamination. The reasons for periodic inspection of parking garages are to detect

deficiencies and deteriorations range from the need for safety (related to the load bearing capacity of

the parking floor), to the need for timely information on the condition of the structures to ensure

prompt and cost-effective maintenance and repair. Evaluation procedures usually involve a visual

inspection to identify the problems, and detailed methods which include an experienced engineer and

NDT methods to help in making a diagnosis of the structure condition (Toronto Ministry of Housing,

1988).

Assessment and testing to determine the integrity of parking garages are done by an experienced

engineer after a visual inspection. The following pages present a possible approach and detailed steps

including photographs of selected structures to the monitoring and NDT proposal of parking garages.

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Procedure

Visual InspectionThe visual inspection of parking structures provides an external view of the condition of

concrete members. A thorough inspection must always be the starting point for any condition

assessment of concrete structures. Based on the type and degree of deterioration of concrete noticed, it

can be decided whether the condition assessment should be taken further to testing methods, in order

to get a more in depth view of the condition of the structure at hand, and also which types of testing are

adequate for use. If certain parts of the garage have limiting access, certain tests cannot be performed.

This serves as one of the challenges with visual inspection. Another challenge would be that it requires a

well experienced eye to spot the types of deterioration, the severity, its implication to the overall

structural integrity of the garage, coupled with a sound engineering judgement to make the appropriate

calls for action.

For the purpose of this report, seven parking structures around the GTA were visited. These

garages were different in terms of exposure and also structural type. The visual inspection yielded a

variety of deterioration modes in concrete members with different extents of damage. The pictures of

the deteriorations taken during the site visits can be found in the Appendix section of the report. They

were further analyzed to identify the type of deterioration, the possible cause and remediation

measures.

Non-destructive TestingBased on the visual inspection results, it can be decided whether non-destructive testing is

required for a better understanding of the condition of each parking structure. If visual inspection yields

good results with minor deteriorations in concrete which have no structural integrity implications, then

testing on the concrete becomes unnecessary. Also, based on the type of deterioration noticed and the

type of structure along with its geometry limitations, the types of non-destructive testing methods can

be suggested. The following are the tests that are applicable to parking structures. The limitations

mentioned for each one of them are those that arise from their application to parking structures, and

not their general limitations.

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Covermeter Survey

A covermeter can be used to survey the structure in order to accurately determine the location, size and

depth to the steel reinforcement. This apparatus is able to estimate sizes of reinforcing bars between

3/8 and 2 inches, a range which includes the bar sizes used in parking garages. (Lauer, 2004) Based on

the location and size of bars detected, the structural engineer can judge whether the current

reinforcement in the deteriorated area is enough to provide adequate structural support. Also, based on

the amount of concrete cover over the reinforcing bars, the appropriate repair measures can

undertaken to increase the concrete cover where it is below requirement for durability. Lastly,

covermeters are adequate for use in parking structures because they require only single-side access to

the concrete member of the structure, as underground parking garages generally do not provide

exterior access.

Pull-Out Test

Pull-out test can be performed to estimate the in-situ compressive strength of concrete in

parking structures. As this test is usually used to determine the in-place strength of concrete during the

construction phase, for existing structures, the pullout mechanism must be post-installed by drilling into

the concrete surface. (Carino, 2004) Based on the results of the test, it can be judged whether a certain

concrete member requires structural restoration. The pull-out test can be utilized in parking structures,

since it requires one sided access to the member to be tested.

Pull-Off Test

Just like the pull-out test, pull-off test can be used to estimate the compressive strength of the

concrete in parking garages. It is based on the concept that the tensile force required to pull a metal

disk, together with a layer of concrete surface, is related to its compressive strength. (Henderson et al,

2004) This method is adequate for parking structures since it used for existing structures, and not during

the construction phase. Just like the previous tests, pull-off test requires one sided access to the

concrete to be evaluated.

Resistivity Test

Since reinforcing bar corrosion is the most problematic deterioration mode in parking

structures, testing for corrosion becomes a priority. To test for the likelihood of corrosion in

reinforcement, the Half-cell Potential Test could be used. However, this method does not provide direct

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information on the actual rate of corrosion in rebars. Therefore, Concrete Resistivity Test can be used in

conjunction with Half-cell Test. This test relies on the fact that the rate of corrosion depends on the

electrical resistance of the concrete, which reflects how easily the harmful ions travel through the

concrete towards the reinforcement. As the presence of reinforcement in the concrete affect the results

of the resistivity test, the test should be performed midway between two bars. In parking structures, the

depth of cover is generally between 35-45mm and the rebars are closely spaced. Hence, the results

must be adjusted accordingly, provided that the layout of the reinforcement is known. (Carino, 2004) In

the aspect of access and orientation, both of these tests have no limitations.

Ultrasonic Pulse Velocity Test

This test would be very useful for parking structures condition assessments since it can provide

information about various properties of concrete members. First, it can estimate compressive strength

of the concrete for situations where structural restoration of garage is contemplated upon. Second, it

provides information about the extent of deterioration in concrete as it can estimate crack depths.

Third, it can serve as an indicator for durability properties of the concrete for regions that have no

visible cracks. (Malhotra et al, 2004) Since in parking structures, especially those underground, there is

not always double sided access, the transmitter and receiver can be placed on the same side. However,

appropriate adjustments must be made to the results to account for the effect of reinforcing bars in the

concrete member.

Infrared Thermography

This test can be used in parking garages in order to detect subsurface anomalies such as voids,

cracks and delaminations. Since it uses the emission of thermal radiation in concrete, it requires a

thermal gradient between the two opposite surfaces of the concrete member (Weil, 2004). Therefore,

for parking structure components which are not exposed to the sun’s radiation, uniform heating of the

concrete can be achieved using a set of heaters. In terms of access and orientation, this test has no

limitations.

Permeation Tests

Whether underground or above ground (covered or uncovered), parking garages are exposed to

several deterioration hazards. The durability of the concrete against these agents is related to its

transport properties. Several permeation tests learned in CIV 1201 are available to investigate these

properties of the concrete. Based on the results from these tests, it can be judged whether the concrete

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member requires remediation measures to improve its durability such as patching, installing waterproof

membranes, or applying sealant to the concrete surface. The most adequate for the investigation of

parking structures would be:

Initial Surface Absorption Test (ISAT). This test would be useful in measuring the amount of

water that the concrete absorbs by capillary action to fill its pores. (Henderson et al, 2004) It should be

mentioned that ISAT has limitations when it comes to its application to parking structures. First, it

requires access to both sides of the concrete member as the apparatus needs to be clamped. Second, it

requires a horizontal surface to test its absorption, as water is not pressured and vertical or inverted

orientations would affect the results of the test. Lastly, ISAT results are affected by the surface coating of

the concrete. Usually, underground parking garages in residential units have painted walls and columns.

Hence, ISAT would be useful for investigating the transport properties of only intermediate slabs and

other horizontal surfaces, provided that they are not coated.

Autoclam Sorptivity Test. This test also measures the water absorption of the concrete, but

would be even more adequate for parking structures due to its reduced limitations of application. First,

it does not require access to both sides of the member as the apparatus is glue to its surface. Second,

the water to be absorbed by the concrete surface is kept under pressure. As such, the results of the test

are not affected by the orientation of the concrete surface (i.e. vertical or inverted). Therefore, this test

is applicable to all concrete members of parking structures, once again provided they are not coated.

Figg Water Absorption Test (FWAT). This test is based on the same principle as the previous two,

but it is an intrusive test since it requires drilling into the concrete member, which could serve as a

limitation in situations where the structural integrity of the concrete member to be tested could be

compromised. Besides having no limitations in terms of access and orientation of the member, FWAT is

not affected by the coatings and surface layer of the concrete in parking structures.

Autoclam Water and Air Permeability Tests. These tests measure the amount of water or air that

enters the concrete due to a pressure gradient. (Henderson et al, 2004) Hence, their results are not

affected by the orientation of concrete surface. Also, since it is the same autoclam apparatus, it has no

limitation in terms of access to the sides of the concrete member. But just like the other non-intrusive

tests, it requires an exposed concrete surface and also its results are affected by the concrete surface

layer condition.

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Figg Air Permeability Test. Since it uses the same apparatus as the figg water absorption test,

this test has no limitations in terms of access, orientation and coatings. But again, it is an intrusive test

which can serve as a limitation to certain situations in parking structures.

Schonlin Test and Surface Airflow Test. The air permeability of the concrete is measured using

apparatuses that are attached to the concrete surface by means of vacuum. As such, they require no

permanent attachment or clamping, and also have no limitations in the aspect of orientation and access

sides to the concrete member of the garage. However, since they are not intrusive tests, they require an

exposed concrete surface.

Condition Assessment The following were the results of the visual inspection performed in each of the sites. Based on

these results, the appropriate non-destructive testing methods were suggested for each of the parking

structures. However, in some cases, the condition assessment arising from the use this procedure might

not be enough to decide whether rehabilitation or demolition action must be taken. As such, destructive

testing methods can be utilized to provide definite results for adequate decision making.

The following were the results of the visual inspection performed in each of the sites. Based on

these results, the appropriate non-destructive testing methods were suggested for each of the parking

structures.

Parking Structure #1:

This structure was located at 210 Markland Drive,

Etobicoke. The site was visited on March 10, 2012 at 2:04 pm. The

weather was humid and cloudy and the temperature was 20°C. In

terms of exposure, this structure was an underground garage. As

for its structural type, this garage was composed of concrete

reinforced slabs resting on concrete columns with drop panels.

Once the structure was examined, a few areas of deterioration

were observed, with mechanisms such as efflorescence, cracking, seepage and leakage, rusting of rebar,

and pitting. Figure 3 shows the deterioration of the wall in the bottom of the stairwell, just before

entering the parking garage. The whole area was moist, especially the bottom meter of the wall. This is

due to seepage of the groundwater coming from the soil behind the wall. The picture shows a location

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Figure 3 - Popout

where pitting has taken place in the form of small pop outs. Peeling of

paint was observed in all the wall area before entering the garage.

Some delamination in the wall next to the stairwell was also observed,

but this was localized (Figure 4). The overall structural integrity of the

parking garage was found to be adequate. The concrete damages

observed mostly affected aesthetic appearance of the structure.

Remediation measures can be undertaken to restore it, such as

repainting, grouting and sealing.

Parking Structure #2:

The structure was located below Bahen

Centre, 224 Huron Street, Toronto. The site was

visited on March 16, 2012 at 1:40pm, and the weather

was sunny and dry and the temperature was 18 °C.

This 4 level underground garage was constructed

using cast-in-place concrete slabs resting on

reinforced concrete columns with drop panels. During

the visual inspection, the most prevalent forms of

deterioration were diagonal cracking, seepage,

stalactites, pop-out, corrosion and peeling. Figure 5

shows a diagonal crack of the retaining wall in the entrance ramp of the garage. This crack was observed

approximately mid-way into the entrance of the garage so this mode

of failure could be explained by the fact that the pressure of the soil

behind the wall which is exerted at the lower 1/3 of the wall’s height

exceeds the concrete load bearing capacity. A poor concrete mix or

batch could be the reason for the deterioration observed.

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Figure 4 - Delamination

Figure 5 - Diagonal cracking

In the corner of the first level (Figure 6) there is an

evident sign of leakage of water from the above grade.

The formation of black mould on the wall suggests that

this is an ongoing problem and faulty drainage is the

cause of the deterioration. The icicle look-alike picture

observed in Figure 7 is called Stalactite.

It was seen on the ceiling of the first level of the parking

garage. The stalactites followed a long crack on the

ceiling slab which suggests that water permeated

through the top floor and as it evaporated, the mineral formation was left behind. A possible

explanation for the crack would be a thermal gradient which is the difference in temperature between

the core and the surface of the slab when concrete was poured.

Also on the lower levels (P3-P4) minor corrosion stains were observed on the walls from all 4 sides.

Deicing salts have increased the chloride ion concentration and the steel has been depassivated.

Although the structural integrity of the members seemed intact, we know from experience that

corrosion progresses rapidly and it will be matter of time before we observe delamination and spalling.

Despite the visual minor deteriorations that were mentioned above, the only immediate

recommendation is to repair the leakage problem on the first floor and provide a thorough cleaning of

the mold. Also a thorough repair of the crack where the stalactites are formed is necessary.

Parking Structure #3&4

These structures are located in Mississauga

( Bloor st and Rathburn rd) in the Square One

shopping centre. We mainly looked at Bay

and Wal-Mart parking garages. They are 2

and 3 stories high respectively. They were

visited on March 16th at 1 PM and the

weather was sunny and dry with a

temperature of 20 °C. These garages were

constructed with precast concrete structures

where standard T-beams and slabs are used

to form the floors. The first level parking

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Figure 6 - Black mold

Figure 7 - Stalactite

Figure 8 - View of P2 Level

walls were found to be in an almost excellent condition in both parking garages. There were visible

hairline cracks on close inspection on all walls at first floors.

The main problem with some of the external columns and

stairwells connecting The Bay store with the parking garage

was segregation and honeycombing. Drying shrinkage

cracks were observed on precast slabs and they did not

seem to follow a particular pattern. It was observed that

the structural integrity of the parking facilities were sound

since there were no obvious signs of performance

deficiencies. On the above grade exposed parking space,

there were visible signs of efflorescence and chalking on the

parapet walls. Pitting was a common characteristic of all the

walls especially the ones above grade on both parking lots.

Corrosion was observed on the top part of the parapet walls very close to the surface and some of the

stirrups were exposed. This is due to the lack of adequate cover that needed to be provided during

construction. The chloride ions brought in by the moving

vehicles have started to corrode the stirrups and it is a

matter of time before visible rust stains appear on the

sides of the walls. Major cracking was observed in one

staircase and slab connection in Wal-Mart. The slab near

the edge was cracked (>5mm) and delamination was

observed. This was a localized event and a poor

construction method is to be blamed since there was no

water or de-icing salts signs. On the entrance ramp of

the P2 level of Bay garage there was corrosion at

column to beam interface and also signs of efflorescence and spalling. The main reason for this seemed

to be the extensive leakage of water with chloride ions from the top exposed level. There is poor

drainage provided and the joint is not sealed properly. Although the structural integrity of the beam

seems to be adequate, further structural analysis is recommended to properly assess the load carrying

capacity of the member is recommended.

Similar deterioration modes were observed in the other two parking structures. Leakage due to poor

drainage, seepage of groundwater from the soil behind the wall and de-icing salts, were the main

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Figure 9 - Honeycombing

Figure 10 - Rusting of stirrups

reasons for the deterioration mechanisms. On all the structures visited there is need for repair for both

aesthetical reasons and preservation of structural integrity. The only structure that virtually showed no

signs of damage was the Lester Pearson Airport terminal 1.There were some signs of minor repair and

patches in the 8 story parking structure which suggests that it is being periodically and properly

inspected and also better construction methods were used. The table below summarizes the modes of

deterioration observed on all the parking structures.

DeteriorationMode

Markland Airport Ikea Wal-Mart Bay Guelph Bahen

Diagonalcracking

X X X X X

Corrosion X X X X X X

Efflorescence X X X X X X

Spalling X

Delamination X X

Pitting X X X X X

Leakage X X X X

Seepage X X X

Segregation X X

Stalactites X X

Peeling X X

Shrinkagecracking

X X

Blistering X

Map cracking X

Scaling X

Based on the deterioration modes detected during the visual inspection, the following non-destructive tests were suggested for each site:

NDT Markland Airport Ikea Wal-Mart Bay Guelph BahenCovermeter X X X X X X

Pull-outPull-off X X

Half-Cell X X X X XResistivity X X X X X X

UPV X X X X XInfrared X X

Autoclam SorptivityFigg Water Absorption

X

Autoclam X X

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Water/Air Permeability

Figg Air Permeability

Discussion and ConclusionsDuring the literature review, no national or international codes or formal guidelines for normal

practices in assessing, managing and testing parking structures were found. Each paper author had their

own criteria for assessing concrete condition. In relevance to Southern Ontario, there was found a short

report compiling important information about parking structure investigation put forth by a committee

of Ontario Ministry of Housing in 1988. It provided concise information about modes of deterioration in

parking garages in Ontario, focusing more on corrosion of reinforcing bars as the main concern for this

type of structure.

Severity of exposure conditions to environmental factors of parking garages is higher than in

most other buildings. In winter, road salt penetrates the concrete causing corrosion of reinforcing steel

and extremes of temperature and humidity within parking garages tends to promote further

deterioration. In industry, several restoration companies have their own set of guidelines for standard

practices in concrete condition assessment and classification. According to the classification, the

engineer can make an informed decision as to whether to test the structure and even what types of

testing might be necessary for an in depth view of the condition of the parking structure. Therefore, it

remains up to engineer to decide what class does a certain situation belongs to and what testing

methods should follow.

Some recommendations in terms of prolonging the life of parking structures put forth from our team

are :

Provide cathodic protection of reinforcing steel in parking garages

Install water proof membranes on top surface of slabs to prevent salt and water penetration

More rigorous inspection during construction

Increasing concrete cover would slow down the penetration of chloride ions and other

deleterious materials

Maintenance and inspections of the parking garages should be done yearly

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Excellent drainage should be maintained at all times and monthly inspections and cleaning of

drains is recommended to prevent water ponding, etc.

As for the challenges in context with the non-destructive testing of concrete in parking

structures, accessibility to both sides of the structure remains a major one. This is typical for

underground parking garages. As such, the tests are to be selected to account for this limitation.

Another challenge would be performing the NDT methods with minimal operational disruptions to the

parking structure. The testing technician must coordinate with the management personnel of the

structure for a safe and time efficient evaluation of the parking garage. Lastly, deciding whether to use

non-intrusive or intrusive NDT would serve as a challenge. There’s a trade-off between getting better in

depth results using intrusive NDT methods and keeping the structure intact with no incurred damage as

the management would usually prefer. Therefore, it requires a well experienced engineer to properly

assess the situation and make the necessary decisions while keeping the management informed of the

proceedings.

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References:

Litvan, G.G.(1982). Evaluation and repair of deteriorated garage floors. CBD 225, Division of Building Research, National Research Council Canada, Ottawa.

Advisory Committee,(1988). Deterioration, Repair and Maintenance of parking Garages. Minisitry of Housing, Ontario Buildings Branch.

Lauer,K.R.(2004).Magnetic/Electrical Methods. Handbook on nondestructive testing of concrete, (2nd ed)., V. M. Malhotra and N. J. Carino, eds., CRC, Boca Raton, Fla.

Carino, N.J.(2004). Pullout Test. Handbook on nondestructive testing of concrete, 2nd Ed., V. M. Malhotra and N. J. Carino, eds., CRC, Boca Raton, Fla.

Weil,G.J.(2004). Infrared Thermographic Techniques. Handbook on nondestructive testing of concrete, 2nd Ed., V. M. Malhotra and N. J. Carino, eds., CRC, Boca Raton, Fla..

Henderson,G.D.(2004).Pull-Off Test and Permeation Tests. Handbook on nondestructive testing of concrete, 2nd Ed., V. M. Malhotra and N. J. Carino, eds., CRC, Boca Raton, Fla.

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APPENDIX : ASSESSED STRUCTURES

Square One Walmart Parking Garage

-Location: Mississauga City Centre

-Built: 1995

-Height: 3 stories

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Square One Bay Parking Garage

-Location: Mississauga City Centre

-Built: 1994

-Height: 2 stories

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Pearson Airport Terminal 1 Parking Garage

-Location: Malton, Mississauga

-Built: 1960

-Height: 8 stories

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364 Waterloo Avenue

-Location: Guelph, Ontario

-Height: 1 story

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Bahen Centre

40 St.George Street, Toronto

-Fully operational in 2005( built in 2002)

-4 levels underground

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Ikea Store

1475 The Queensway , Etobicoke

-Built in 1999

-1 levels underground and one above grade

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