jestec- ukmitc_6_2015_001_012.pdf

Journal of Engineering Science and Technology Special Issue on 4th International Technical Conference 2014, June (2015) 1 - 12 © School of Engineering, Taylor’s University

1

CONCRETE DELAMINATIONS LOCATION AND ITS SEVERITY DETECTION BY VISUAL INSPECTION AND

GROUND PENETRATING RADAR

A. M. SHAMSUDIN, S. F. SENIN, R. HAMID*, K. YUSUF

Department of Civil and Structural Engineering, Faculty of Engineering and Built

Environment, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor DE, Malaysia

*Corresponding Author: [email protected]

Abstract

Concrete delamination is a problem commonly found in reinforced concrete

bridge deck and may cause severe damage to the structural component. The need to access the severity of this defect is pertinent as the detachment of

the concrete cover from the rebar is invisible and only showing when

cracks and spalling had reached the top of asphalt layer. Most of the bridge

inspections on concrete delamination rely on human interpretation based on

visual inspection (VI). VI is a very subjective assessment and should be conducted by highly trained bridge inspectors. It is also a time consuming

method. Alternatively, Ground Penetrating Radar (GPR) is a rapid and non-

destructive method to detect rebar delaminations within the bridge deck and

quantify this defect based on the reflection of electromagnetic waves by the

air void within the delamination. Therefore, VI and GPR method were

employed at a case study site to detect the location of the delamination and to estimate the extent of its severity. Based on the VI result, the

delamination was detected in almost of deck area where 8.7 m and 9.5 m

length was observed at area A1 and A8, respectively. Meanwhile, through

GPR, delaminations were measured at 4 different areas (A1, A4, A7 and

A8) with coverage of 8.5 m, 5.2 m, 4.1 m and 6.4 m respectively. GPR had

confirmed the existence of delamination at A1 and A8 and further had detected size of delaminated area at A4 and A7. The differences of

delamination extent detected by both methods are 2.3% at A1 and 32.6% at

A8. GPR has shown better capability in detecting size and location of

hidden delaminated area under asphalt layer of a bridge deck which is very

useful in maintenance decision.

Keywords: GPR, Visual inspection, Bridge inspection, Delamination, Location

and severity.

Concrete Delaminations Location and Its Severity Detection by Visual . . . . 2

Journal of Engineering Science and Technology Special Issue 6/2015

Nomenclatures

A1 Area 1 on bridge deck




c

w

Speed of light in vacuum media, = 0.3 m/ns

Moisture content of concrete (kg/kg)

Greek Symbols

ε Dielectric value of media

Abbreviations

ABIM Annual Bridge Inspection Manual

GPR Ground Penetrating Radar

PWD Public Works Department

VI Visual inspection

1. Introduction

Delamination of concrete structures is a type of defect manifested by the

discontinuity of concrete surface as the result of widening fracture that extends

partly or completely through the member [1]. The growth of such defects on

high-performance structural component such as bridge deck structure is

inevitable as heavy traffic loads and harsh environment, i.e., climate changes

will accelerate the delamination growth [2]. Usually the defects were hidden in

the deck and not manifested on the surface until the significant deck cover

separate from substrate concrete, which impair the appearance and

serviceability problems [3]. Therefore, a precise routine assessment of the

delamination bridge’s condition is very important in order to maintain and

preserve the bridge appearance and structural serviceability.

As mentioned previously, concrete bridge is a high performance structure that

is frequently exposed to moist environment and repeated traffic loading of

vehicles. According to Shah and Chandra [4], the repeated traffic loading will

result in progressive microcracks on concrete surface. With the penetration of

rainwater inside the microcracks, steel bar will start to corrode as the steel surface

is attacked by moisture and oxygen. As rebar corrosion continues, the corrosion

products or rust can occupy several times than the original steel, resulting tensile

forces to develop in the concrete deck. Since concrete is relatively weak in

tension, internal cracks will develop and expose the steel surface to even more

moisture and oxygen. This situation will promote more accelerated corrosion

process surround the steel bar and causing the bond between steel bar and the

surround concrete breaks. Eventually, at the late stage, pieces of concrete break

away, forming large scale spalls in the concrete and huge potholes are easily

visualized and located by the bridge inspector. Therefore, a need on accessing the

delamination problem at an early stage is required before huge potholes started to

formed on the bridge deck surface.

3 A.M. Shamsudin et al.


Ground Penetrating Radar (GPR) is one example of a method that has

potential to detect delamination in bridge deck structure. Wielen et al. [5], and

Wang et al. [6] have shown the capability of GPR on detecting the location of

embedded cracks inside a bridge deck and its length estimation. On the other

hand, visual inspection method is limited only on concrete surface observation

that is rated based on subjective scale provided by bridge authorities.

In this paper, a comparison study by both method was conducted at an aging

bridge located in Kuala Lipis, Pahang, Malaysia. Inspection works were done in

order to determine the location and the length of delaminations by both methods.

2. Methodology

2.1. Visual inspection (VI)

This study focused on the bridge deck component evaluation that was carried out

by inspecting bridge deck based on the Annually Bridge Inspection manual. The

bridge has been closed for replacement works due to its critical conditions. The

visual inspection method was done according to the Annual Bridge Inspection

Manual (ABIM) [7] by Public Works Department (PWD) Malaysia. The bridge

deck was evaluated by visually inspecting the bridge deck component

delamination defect. The characterisation of severity is given in Table 1 to

categories the delamination severity in this study.

Table 1. Severity of delamination on concrete bridge deck structure [7].

Severity Description

No defect No visible delaminated area

Light Delaminated area measuring < 150mm in any direction

Medium Delaminated area measuring 150mm - 300 mm in any direction

Severe Delaminated area measuring 300mm - 600 mm in any direction

Very severe Delaminated area measuring > 600mm in any direction

2.2. Ground penetrating radar (GPR)

The plan view of the surveyed bridge deck slab in this study is shown in Fig. 1.

Before the GPR data collection is performed on the deck by scanning the antenna,

the deck width is divided into eight equal areas as depicted in Fig. 1. The width of

each slab areas is marked on the deck surface and recorded for the purpose of

GPR analysis. The surface condition of the deck should be free from any water to

ensure no influence of water on the GPR signals.

The GPR system consist of 1.6 GHz antenna, mounted on a lightweight and

highly manoeuvrable wheel cart and a controller unit to record the scanned data.

The data collection is performed for each of the slab areas by pushing the GPR

system in the direction shown in Fig. 1. As the GPR system is pushed along the

bridge deck, electromagnetic wave will be transmitted by the antenna and

propagates inside the bride deck and reflected to the receiver antenna once

encountered layer of different electrical impedance.



Fig. 1. Eight equal areas division bridge deck slabs (Plan view).

After the GPR scan performed for each of the slab areas, the scanned data is

analysed to determine the defect area. The location of the delamination on the

bridge deck is identified by analysing the hyperbolic feature on the radargram

produced by scanning GPR on the bridge deck surface for initial fracture position

as shown in Fig. 2. The initial fracture position is identified by identifying the

presence of a horizontal band layer; which is characterised by three colours in the

following sequence; dark-white-dark layer as shown in Fig. 2. The migration

algorithm will be applied on the selected initial fracture position using Radan 7

software to obtain the dielectric value of the selected point, ε.

Using Eq. (1), the electromagnetic wave velocity, v, of the medium, is

computed and conclusion can be made on the defect condition, whether the defect

is filled up with air or water. The defect with wave velocity value closer to 0.3

m/ns, then it is assumed to have filled with air, whereas for defect which is filled

with water will have the value of almost close to 0.03 m/ns. Table 2 shows the

typical medium that will be encountered in concrete scanning by GPR and its

dielectric constant, ε, or the wave velocity, v. The procedure is then repeated and

stopped until the computed wave velocity of the potential delamination area is not

either closer to 0.3 m/ns nor 0.03 m/ns. The estimated length of the delamination

can be computed by subtracting the final fracture position with the initial fracture

position analysed by the procedure.



� =�

�� (1)

where ε is the computed dielectric value of the medium, v is the electromagnetic

wave velocity from radiogram analyzed by Radan 7 (m/ns) and c is the speed of

light in vacuum medium (0.3 m/ns).

Fig. 2. A hyperbolic feature is selected at a fracture point on GPR radargram.

Table 2. Dielectric constant or wave velocity for typical medium.

Dielectric constant, εεεε Wave velocity, v (m/ns) Medium

1 0.3 Air

81 0.03 Water

In this study, the bridge deck is divided into eight equal areas and the above

procedure is applied on each of the areas in order to detect the delaminations

position and its severity.

3. Results and Discussion

3.1. Description of the case study bridge

This case study applied on a deteriorated bridge having length 12.45 m and width

5.5 m consisted of single deck slab and 17 beams. The deteriorated bridge deck

was inspected using VI and GPR methods. The GPR methods of the badly

deteriorated bridge deck allowed the validation of the VI method. The inspected

bridge deck area were divided into eigth areas which named A1 to A8 as shown in

Fig. 1. The bridge deck condition were evaluated based on surface defect, crack

of concrete, delamination, spalling, corrosion of reinforcement and water leakage.

3.2. Visual inspection

Based on the visual inspection observation, two obvious delaminations with finite

length were detected on area 1 and area 8 of the bridge grid. The length of

delaminations on area 1 and 8 are estimated at 8.7 m and 9.5 m respectively and

Horizontal band layer (black-white-black layer)



the condition rating of the delaminated area was very severe. Furthermore, at area

4 and 7 (A4 and A7), there were repetitive potholes formation on the asphalt

surface which was an indication of the presence of delamination on the deck

where have given a medium rating. The condition rating of the detected

delamination area is shown in Fig. 3.

Fig. 3. Two obvious delaminations and its element rating.

Based on Fig. 4, severe cover spalling on deck soffit and accompanied by the

exposed rebar with reduced cross sections may reduce the flexural capacity of the

bridge deck. This existence of moisture can be observed as the "damp spot"

located at the deck and a corrosion agent that induced rebar corrosion inside the

bridge deck.

Fig. 4. The possible cause of the delamination on the bridge deck.

3.3. Bridge deck defects rating

The inspected surface and bridge deck condition using visual inspection are

evaluated based on the ABIM condition system rating [7] and the results shown in

Table 3. The condition rating system are a numerical system where a number

from 1 to 5 is assigned to each component of the structure based on the observed

Rating :

very severe

Rating :

very severe

Exposed rebar

Rating :

Medium



material defects and the resulting effect on the ability of the component to

perform its function in the structural system.

Table 3. Defects condition rating on the bridge deck.

Type of defect Condition of defect Defect's

rating

Surface cracks • Obvious longitudinal cracks on the bridge surface and underneath deck

5

Delamination • Suspected delamination defect in the

bridge deck as indicated by cracks on

the bridge surface and exposed of

rebar

4

Steel corrosion • Obvious rust stains formed on

underneath the bridge deck

4

Water leakage • Damp spots observed underneath the

bridge deck and beam

2

Concrete spalling • Mild severe concrete spalling

observed

1

From the rating shown in Table 3, it is found that the cracks formed on the

bridge surface is heavy and critically damaged, that need immediate repair or

rehabilitation work. The suspected cause of the surface crack, the steel corrosion

and concrete delamination, were given the rating of 4. According to ABIM [7],

this rating is correspond to critical damage that require a detailed inspection to

determine whether any rehabilitation works are required. The water leakages and

concrete spalling observation were found not to be so critical.

3.4. GPR scanning results

Several hyperbolic features on selected locations on bridge deck areas at area 1, 4,

7 and 8 (A, A4, A7, A8) was analysed by Radan 7 software after GPR scanning

was conducted to obtain its dielectric constant and wave velocity. Figures 5 to 7

show the example of GPR scanning on three selected locations for area A4 on the

bridge deck. The delamination locations in Figs. 5 to 7 was selected based on the

horizontal band feature which is characterised by black-white-black layer as

shown in red oval shape. Table 4 lists the dielectric constants and its corresponding

wave velocity on area 1,4,7 and 8 (A1,A4,A7,A8) of the bridge deck.

Table 4. Properties of delamination defects by GPR.

Area Dielectric

Constant

(location

1,2,3)

Wave velocity

(location

1,2,3)

(m/ns)

Delamination

depth

(m)

Conclusion on

defect

A1 1.8,1.69,1 0.2,0.2,0.3 0.18 AD

A4 11.6,11.6,11.6 0.09,0.09,0.09 0.18 WD

A7 1.11, 1.63 0.28,0.24 0.025 AD

A8 11.6,11.6,11.6 0.09,0.09,0.09 0.14-0.18 WD

AD = air-delamination type , WD =water-filled delamination type



GPR had detected 4 delaminations in 4 different areas of the bridge which is

on area A1, A4, A7 and A8 with the length of delaminations are 8.5 m, 5.2 m, 4.1

m and 6.4 m respectively. Based on Table 2, the type of delamination detected by

GPR can be concluded based on the dielectric constant values. Air-filled

delaminations can be possibly concluded at area A1 and A7 as the dielectric

constant on those part are almost close to 1.

Fig. 5. Hyperbolic curve at location 1 on area 4 of the bridge deck.






In order to conclude whether the water is a medium inside the detected

delaminations in area A4 and A8, the dielectric constants in a deteriorated

concrete has to be estimated based on moisture content. According to Senin

and Hamid [8], the maximum of water content in high water-to-cement-ratio

concrete is within the range 10.2% to 12% of the dry weight of the sample. An

estimate of dielectric constant of concrete due to moisture content, w, is given by

Han et al. [9] and shown in Eq. (2);

� = �� (2)


Adopting the moisture content of the bridge deck concrete as 12% of

moisture content, the estimated dielectric constant is equal to 12.24, which is

closed to the provided dielectric constant shown in Table 4 for area A4 and

A8. It was concluded that the delaminations at area A4 and A8 were filled

with water.

The severity of the detected delaminations were evaluated based on the

severity scales given by Table 1. Table 5 shows that all of the delaminations

were evaluated as "very severe" as the all delamination lengths were

exceeding 0.6 meter.

Table 5. Delamination severity of the GPR results.

Area Delamination length (m) Severity

A1 8.5 Very severe

A4 5.2 Very severe

A7 4.1 Very severe

A8 6.4 Very severe




3.5. Comparison between the visual inspection and ground

penetrating radar

A comparison was made between both methods of accessing the detection

capabilities on each area of the bridge. Based on Table 6 and Fig. 8, it

is suggested that GPR has the ability to detect the location and size of

the delaminated area more accurate, located at area A1, A4, A7 and A8

having length 8.5 m, 5.2 m, 4.1 m and 6.4 m, respectively. Meanwhile, VI

method was only able to detect size of the delaminated area at A1 (8.7 m) and

A8 (9.5 m). The percentage of difference on delaminations extend by both

methods was 2.3 % at location A1 and 32.6 % at location A8. This

observation suggests that GPR showed its superior detection capability over

VI method as its ability to detect another two hidden delamination features on

the bridge deck.

GPR was able to detect more hidden delaminations features than visual

inspection as the method characterising the delamination based on the

electromagnetic wave reflection on air or water that trapped within the

delamination gap.

Fig. 8. Result of the delaminations detected using both methods.



Table 6. Size and rating of the detected delamination area.

Area

of the

bridge

Presence of

visible

delamination

indicator

Visual inspection GPR method

Length

(m) Rating

Length

(m) Rating

A1 Yes 8.7 Very

Severe 8.5

Very

Severe

A4 Yes ND Medium 5.2 Very

Severe

A7 Yes ND Medium 4.1 Very

Severe

A8 Yes 9.5 Very

Severe 6.4

Very

Severe

ND – Not Detected

4. Conclusions

GPR and VI methods have been used to detect the location and length of

delaminations on the bridge deck. Both methods showed good agreement on

locating the delamination on the bridge, however, the visual inspection method

was not able to detect the size of delaminations on area area A4 and A7. GPR is

able to detect the size of hidden and early delamination location that cannot be

observe by visual inspection possibly created by the corrosion of rebar. The

difference on the delamination length detected by both method are 2.3% at area

A1 and 32.6% at area A8. GPR method is recommended to supplement theVI

method in detection of delamination occurred in bridge deck as sometimes the

delamination is not visible by the VI method.

Acknowledgement

The authors acknowledge Universiti Kebangsaan Malaysia for providing

the financial support through projects GUP-2013-017 and DLP-2013-033.

References

1. REAM (2003). A Guide to bridge inspection. Road Engineering Association

of Malaysia, Kuala Lumpur.

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condition assessment with automated multisensor techniques, Structure and

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3. Xing, S.; Halling, M.W.; and Barr, P.J. (2012). Delamination detection of

reinforced concrete decks using modal identification. Journal of Sensors,

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4. Shah, S.P.; and Chandra, S. (1970). Fracture of concrete subjected to cylic

and sustained loading. ACI Journal, 67(10), 816-827.



5. Wielen, A.V.D.; Nguyen, F.; and Courard, L. (2010). Nondestructive

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6. Wang, Z.W.; Zhou, M.; Slabaugh, G.G.; Zhai, J.; and Fang, T. (2011).

Automatic detection of bridge deck condition from ground penetrating radar

images. IEEE Transactions on Automation Science and Engineering, 8(3),

633- 640.

7. PWD. (2003). Annual bridge inspection manual. Bridge Unit, Roads Branch,

Public Work Departement Malaysia.

8. Senin, S.F.; and Hamid, R. (2014). Effect of moisture and chloride content on

Ground Penetrating Radar normalized amplitude ratio of concrete slab.

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water content testing. Advanced Materials Research, 250-253, 3103-3106.

jestec- ukmitc_6_2015_001_012.pdf

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