GPR application on construction foundation study

IOP Conference Series: Materials Science and Engineering

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GPR application on construction foundation study To cite this article: T S T Amran et al 2017 IOP Conf. Ser.: Mater. Sci. Eng. 271 012089

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GCoMSE2017 IOP Publishing IOP Conf. Series: Materials Science and Engineering 271 (2017) 012089 doi:10.1088/1757-899X/271/1/012089 1234567890

GPR application on construction foundation study T S T Amran 1, M P Ismail1, M A Ismail1, M S M Amin1, M R Ahmad1 and N S M Basri2 1

Non Destructive Testing-Material Structure Integrity Group (NDT-MSI), Industrial Technology Division, Malaysian Nuclear Agency, 43000 Kajang, Selangor, Malaysia 2 The Faculty of Science, Technology and Human Development, Universiti Tun Hussein Onn Malaysia (UTHM), 86400 Parit Raja, BatuPahat, Johor, Malaysia Corresponding author: [email protected]

Abstract. Extensive researches and studies have been carried on radar system for commercialisation of ground penetrating radar (GPR) technology pioneered in construction, and thus claimed its rightful place in the vision of future. The application of ground penetrating radar in construction study is briefly reviewed. Based on previous experimentation and studies, this paper is focus on reinforcement bar (rebar) investigation on construction. The various data through previous references used to discuss and analyse the capability of ground penetrating radar for further improvement in construction projects especially in rebar placement in works.

1.Introduction In year 1904, Huelsmeyer, a German inventor, introduced radar to detect metallic objects [1]. Radar is a detection system that uses radio waves to detect things.Ground Penetrating Radar (GPR) is one of the radar devices that use electromagnetic reflection method. GPR is one of the non-destructive testing (NDT) technique that can imaging at subsurface depthin high resolution.GPR has already established itself in various field such as archaeology, military and construction. GPR is applied in construction to evaluate the concrete depth, detect and locate of the reinforcing bars and metallic ducts andalso calculate the localization of crack and dimension of voids.Construction foundation study using GPR mostly emphasis on reinforcement bar (rebar). Rebar refers as a tensioning devise to reinforce concrete to help hold the concrete in a compressed state as depicted in figure 1. GPR is a very effective device to locate and map steel rebar in concrete structures and has been utilize to investigate rebar-related issues such as rebar location and rebar spacing. The evaluation of rebar using GPR has been a choice as non-destructive assessment of condition for engineering structures.

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Figure 1. The location of rebar in concrete. GPR used electromagnetic reflection strength approaches as the reflection strength of electromagnetic waves is examined in between two different dielectric components. It was proven that the reflection strength of a rebar decreasing with size of rebar, but increasing with depth of rebar through previous experiments using GPR. The reflection strength also refer to amplitude, where the amplitude decreasing with the presence of rebar corrosion. Rebar diameter cannot be measured directly through GPR scanning, and antenna polarization is used for determination of rebar diameter. The dipole and co-pole antenna are the types of antenna polarization. This paper is briefly reviewed on various radar equipment for locating rebar as well asrebar detection, estimation of rebar diameter and rebar spacing using GPR technique was discussed in this paper. 2.Radar Equipment Various radar devices are applicable and can be used for the detection of reinforcement bar, rebar. By using these radar equipment that utilize non-destructive testing, the evaluation of rebar does not require any grinding or drilling that causes any damages to the surface and the building during the inspection. Cost effective is also one of the advantages on using radar for rebar detection. Other than GPR, radar devices such as cover meter and rebar locator can be employed on construction study to detect rebar. 2.1. Cover Meter One of the radar equipment that useful for rebar locating is cover meter. Cover meter refers to magnetic device, where delivers information on cover of concrete to reinforcement steel bar by utilizing magnetic field. The cover meter is operated on electromagnetic pulse induction, where the eddy current reside two sections. The two sections are locating probe and meter. For that matter, the locating probe is a cover unit that have a search coil, while the meter is conveying the dimension of the cover over a strength of signal. And so, the meter displays a stronger magnetic field as the larger rebar size detected by the cover meter. To getan adequate result, a very detailed calibration of cover meter is necessary. Following the detailed information on cover meter, an experimental investigation under laboratory condition was performed by Sivasubramanian[2]. Experiments were ran to observe the capability of cover meter in verifying cover depth. Two different cover thickness probes were used, small and large thickness probe, where the small probe used for smaller cover depths and the large probe employed for larger cover depths. For detecting clear covers depth larger than 70 mm, larger probe is more effective compared to smaller probe. Figure 2 shows, asthe cover depth increase, the error of detection the diameter of rebar also increasing. The results then prove that cover meter is not very accurate in detecting rebar based on error percentage that had been observed throughout the study.

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The difference between cover meter and GPR is cover meter has a very limited detection range compared to GPR, because cover meter can onlydetermine the cover depth of the rebar while GPR is implemented to determine the cover depth, rebar spacing and rebar size.

Figure 2. A graph of error in detection for rebar diameter vs cover depth [2]. 2.2. Rebar Locator Rebar locator is a device that specifically made on detecting rebar. The rebar locator can give an accurate location of rebar in building, where it massively can be mark the exact areas without causing any damages to the building. Other than that, rebar locator can efficiently scan concrete and discover any internal rebar, thus allows the interpreter to find the rebar position and its size precisely. Rebar locator can be greatly differentiate from GPR, where rebar locator can only locate rebar at shallow depth such as in beam, rather than GPR, which the GPR can locate rebar at deeper depth such as in concrete slab of floor area. 3.Rebar Detection This section reviews the literatures that revised from previous experiment on rebar using GPR. Laboratory experiment was conducted by Einsenmann[3], where the group of researchers are doing experiment on the effect of position and orientation of GPR from structural rebar of highway bridge.The hypothesis that proposes on thin rebar would produce significant difference in signal amplitudes as between a flush-with-road-deck measurement and an elevated measurement is proven on the study [3]. Several attempts to locate rebar by recreating laboratory experiment was ran by Lakshmi [4].2.6 GHz antenna was used to collect data on locating rebar, where the scanning depth was 0.40 m. Figure 3 depicts the raw radar collected for the study conducted. The hyperbola peak as marked in figure 3 indicates the position of rebar in concrete slab.

Figure 3. Radar profile of concrete slab, represents rebar position [4].

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GPR scanning was also run by Einsenman [5] to detect rebar. Radar wave can detect rebar through different antenna positions. The line scan along X-axis as depicted in figure 4 (a) below resulting on one-dimensional scan of antenna. Figure 4 (b) shows vertical axis that represent arrival time, while the horizontal axis illustrates scan distance or the position of antenna. A-scan was presented in figure 4 (c), where the signal response of rebar is depicted in the same figure. It was concluded that the distance between the rebar and the antenna plays crucial part on determining the arrival time of the rebar echo.

(a)

(b)

(c)

Figure 4. One-dimensional scan of GPR on concrete slab above an embedded rebar [5]. Hugenschmidt performed an inspection of retaining wallsusing different frequency antenna [7]. Figure 5 illustrates the radargram data obtained, where in figure 5(a) three rebar are obviously detected by 1.5 GHz antenna, while figure 5 (b) presents the corresponding three rebar using 900 MHz, and figure 5 (c) depicts another corresponding three rebar using 400 MHz antenna. It showed that radargram with lower frequency exhibit clear images of rebar compared to others two frequency antenna. Low resolution images wasproduced due to low frequency antenna but can penetrate more in term of depth of penetration.

Figure 5. Radargram of three rebar located in retaining walls using different frequency antenna (a) 1.5 GHz (b) 900 MHz (c) 400 MHz [7]. We also carry out an inspection of concrete floor using different MALA GPR antenna equipment as shown in figure 6. The inspection was done using 800 MHz and 500 MHz frequency antenna. It is interesting to note that the 800 MHz frequency antenna (figure 7) demonstrate an obvious rebar images compare to 500 MHz frequency antenna (figure 8). It concluded that, high frequency antenna produce high resolution data of rebar through GPR scanning.

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Figure 6. MALA ground penetrating radarequipment set

Figure 7. Radargram of rebar located at concrete floor using 800 MHz frequency antenna

Figure 8. Radargram of rebar located at concrete floor using 500 MHz frequency antenna

4.Rebar Diameter A study had been carried out, the research suggest to use different antenna polarization in order to measure the diameter of rebar. Special and specific conditions are required to estimate diameter of rebar, due to GPR do not measure the diameter of rebar directly from the signal [6]. The GPR is capable to measure the rebar diameter by the strength of reflection signal that come from small, medium or large of target (rebar) sizes. Measuring rebar diameter of reinforced concrete is quite demanding task and its plays vital role to appraise the load bearing capacity of structures for construction. Following the successful studies from previous researches by Utsi [12], it was deduced that the method using different antenna polarization reach up to 20% of accuracy for rebar diameter evaluation [8]. Typical GPR antenna during scanning is the co-pole configuration as shown in figure 9. The co-pole arrangement is the alignment of transmitting and receiving antennas are aligned as parallel to each other. Thetransmitter and receiver antenna represent electric and magnetic field respectively [9]. The co-polarized and cross polarized antenna configurations as illustrated in figure 9 (a) and (b) respectively, are important for measurement of rebar diameter since difference method of antenna polarization are required.

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(a)

(b)

Figure 9. Co-pole arrangement of GPR (a) co-polarized (b) cross polarized [9]. However, the method approach is easy to be distorted. Analysing data taken with transducer and signal axis parallel and then orthogonal to the bar using Multilayer Perceptron (MLP) neutral network has been established by Shaw as to get the automatic estimation of rebar diameter [10].A cylinder shape target can be contemplated as rebar for GPR detector. The typical reflection signal presented in radar profile for rebar is hyperbola fitting as depicted in figure 10 [9].

Figure 10. Hyperbola produced from cylinder object [9]. The connection between the rebar radius and the geometry of the hyperbola is verified as the presence of the reflection signal as mentioned. In year 2005, Al-Nuaimy has created an equation that illustrates cylinders can be detected and remarked from a single radar profile. He also demonstrated a model, that describes two-way travel time, t to the horizontal position, x, and the propagation velocity, v [11]. The model presented to characterize the signatures of rebar, and the model depends on hyperbolic signatures, which resulted in point reflectors. A series of tests and experiments were performed and inspired by Utsi’s previous research and findings to estimate the diameter of rebar. It was revealed from the study, the rebar yielded weak reflections when oriented orthogonal to the transmit antenna and produced strong reflections when oriented parallel to the long axis of a dipole transmit antenna [12]. Figure 11 illustrates the difference on radar wave for signal along EM field and signal across EM field [9].

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(a)

(b)

Figure 11. Radar profile on rebar signal (a) along electromagnetic field (b) across electromagnetic field [9].

5. Rebar Spacing Rebar spacing also can be determined using ground penetrating radar (GPR). The integrity of structure for every reinforced concrete is also depends on size and spacing of reinforcement steel bar. A bridge girder was scanned using GPR by Ekes as shown in figure 12[13]. The inspection was operated by using a 1GHz antenna, where high metallic object such as rebar was detected as rebar has a huge conductivity contrast. Rebar spacing was detected through the GPR scanning as presented in figure 13 [13].

Figure 12. Inspection of bridge girder using GPR [13].

Figure 13. Radar profile of rebar spacing as detection of bridge girder through GPR scanning [13].

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6.Conclusion Ground penetrating radar (GPR) can be applied on construction foundation study where GPR can be used to identifying and detecting the location of rebar. Rebar diameter can be estimated by using different antenna polarization and configuration of GPR however further researches are needed to measure the diameter of rebar precisely. 7. References [1] Ulricksen C P F 1982 Application of Impulse Radar to Civil Engineering Doctoral Thesis (Department Of Engineering Geology, Lund University of Technology, Sweden) [2] Sivasubramanian K, Jaya K P and Neelemegam M 2013Covermeter for Identifying Cover Depth and Rebar Diameter in High Strength Concrete Int J. Civil and Struct. Engr. 3(3) 557563 [3] Eisenmann D, Margetan J F, Chiou P, Ellis S, Huang T and Tan Y J 2017 Effects of Position, Orientation, and Metal Loss on GPR Signals from Structural Rebar AIP Conference Proceeding vol 1806 (United States: AIP Publishing) 080005 [4] Lakshmi A K, Sangoju B, Vasanthakumar, and Rahamath A 2016 Estimation of Rebar Radius Using Ground Penetrating Radar. Int J. of Emerging in CS & Electronics (IJETCSE) 22 2. [5] Einsenmann D, Margetan J F, Koester L and Clayton D 2016 Inspection of a Large Concrete Block Containing Embedded Defects using Ground Penetrating Radar AIP Conference Proceeding vol 1706 (United States: AIP Publishing) 020014 [6] Geophysical Survey Systems, Inc. 2006 GSSI Handbook for RADAR Inspection of Concrete (New Hampshire USA: Geophysical Survey Systems Inc. Salem) [7] Hugenschmidt J and Kalogeropoulos A 2009 The Inspection of Retaining Walls using GPR. J. of ApplGeophy. 67 335-344. [8] Hugenschmidt J and Wenk F 2016 Rebar Diameter and Rebar Orientation Using Different Polarizations. 16thIntConf of Ground Penetrating Radar (GPR) (Hong Kong:IEEE Explore) [9] Leucci G 2012 Ground Penetrating Radar: An Application to Estimate Volumetric Water Content and Reinforced Bar Diameter in Concrete Structures. J of Adv. Concr Tech 10(12) 411-422 [10] Shaw M R, Molyneaux T K, Millard S G, Taylor M J and Bungey J H 2003 Assessing Bar Size of Steel Reinforcement in Concrete using Ground Penetrating Radar and Neural Networks Insight: Non-Destructive Testing and Cond MNT 45(12) 813-816 [11] Nuaimy A, Huang Y, Nakhkash M, Fang M., Nguyen V and Eriksen A 2000 Automatic Detection of Buried Utilities and Solid Objects using Neural Networks and Pattern Recognition. J. Appl.Geophys. 43(2-4) 157-165 [12] Utsi V and Utsi E 2004 Measurements of Reinforcement Bar Depths and Diameters in Concrete. Tenth IntConf on GPR. (Delft: IEEE Xplore) [13] Ekes C 2011 GPR: A New Tool for Structural Health Monitoring of Infrastructure Proc. of 3rd International Conference on Structural Health Monitoring of Intelligent Infrastructure (SHMII-3) (Vancouver, BC Canada) Acknowledgments Authors wishing to acknowledge assistance and encouragement from colleagues, technical staff as wellas the Non Destructive Testing - Material and Structure Integrity Group (NDT-MSI) for the support. Lastly, authors would like to acknowledge the financial support from MOSTI and AgensiNuklear Malaysia.

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