Delamination Assessment of an Ultra-High Performance Concrete Deck Overlay Using Infrared Imaging

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1 Delamination Assessment of an Ultra-High Performance Concrete Deck Overlay Using Infrared Imaging Authors & Affiliation: Hartanto Wibowo, Post-Doctoral Research Associate, Department of Civil, Construction, and Environmental Engineering, Iowa State University, Ames, IA , Richard L. Wood, Assistant Professor, Department of Civil Engineering, University of Nebraska- Lincoln, Lincoln, NE , Sri Sritharan, Wilson Engineering Professor, Department of Civil, Construction, and Environmental Engineering, Iowa State University, Ames, IA , Abstract: Deterioration of bridges is a common issue in the nation s aging infrastructure system. One of the most common problem is concrete deck degradation, which when left untreated can lead to spalling, exposure and corrosion of the reinforcement, and eventually reduced capacity of the bridge. Use of ultra-high performance concrete (UHPC) as a bridge deck overlay has the potential to reduce the deck degradation in these situations and extend the service life of the deck. However, reliable bond between the UHPC overlay and the normal concrete (NC) deck interface must be ensured, which may be affected by time depended behavior of UHPC, temperature variations, and seasonal freeze-thaw cycles. This paper presents a method to assess condition of the interface between the UHPC overlay and NC deck. The potential delamination between UHPC and NC is evaluated using infrared imaging, which is a non-destructive technique. A delaminated deck interface area may consist of a complex region comprising of cementitious material, steel fibers, moisture, and air voids. A thermal radiation gradient is expected due to the different thermal conductivities of each material. It is shown that this concept can be used to evaluate delamination of the UHPC layer placed on top of NC deck. Keywords: UHPC, delamination, deck overlay, concrete bridge deck, infrared imaging 1. Introduction and Motivation The most common bridge deterioration initiates with cracking on the deck surface followed by water and chloride infiltration into the core concrete and corrosion damage to steel reinforcement. Progressive damage to bridge deck occurs due to the impact of freeze-thaw cycles. One potential retrofit or preventive solution is to place a thin overlay layer of highly durable, self-consolidating, ultra-high performance concrete (UHPC) integrally on top of the normal concrete (NC) deck. Hartanto Wibowo, Richard L. Wood, and Sri Sritharan 1

2 UHPC is less susceptible to cracking and subsequent damage due to its compressive strength (approximately 26 ksi), tensile strength (approximately 1.3 ksi), and highly desirable durability properties (Sritharan, 2015). An experimental study has been previously carried out at Iowa State University to determine a suitable interface roughness so that adequate bond between UPHC and NC can be ensured (Aaleti et al., 2013). Recommendations from this study indicate that an acceptable composite performance can be achieved when a minimum interface roughness of 0.08 in (2 mm) is provided. This roughness can be accomplished in several different ways. Depending on if the NC is wet or cured, chemical retarder may be to expose the aggregate on the surface, use a broom to finish the surface, or sand-blasting. However, once the UHPC overlay is placed, it is difficult to monitor any potential delamination at the interface. The interface monitoring of deck overlays is a challenging problem in bridge maintenance and monitoring and several different techniques have been used. To assess the delamination potential at the UHPC-NC interface, infrared or thermal imaging was selected for study report in this paper. This technique was preferred over others because it can provide time-efficient, detailed, and repeatable results. The time efficient evaluation would limit the road and lane closures, which in turn would reduce traffic disruptions. The main objective of this study is to evaluate the UHPC- NC interface after it is subjected to several freeze-thaw cycles. 2. Literature Review The applications of infrared imaging for damage detection of concrete structures have become popular in recent years (Popovics, 2003; Clark et al., 2003; Yehia et al., 2007; Bhalla et al., 2011; Scott and Kruger, 2014; Matsumoto et al., 2014; Bauer et al., 2015). For concrete bridge decks, this method is most appropriate to provide rapid defect (especially delamination) detection. A comparison of different non-destructive evaluation techniques by Popovics (2003) placed infrared imaging and impact-echo methods as the most suitable techniques to evaluate delamination. However, infrared imaging has the advantage of being fast so the results can be evaluated rapidly in real time (Yehia et al., 2007), while the results are established objectively (Scott et al., 2003). In comparison, subjective data interpretation associated with estimating wave velocities and the threshold value of attenuation can influence the outcomes when using the impact-echo and ground penetrating radar techniques, respectively. As with any non-destructive technique, infrared imaging has its own limitations. This technique is less sensitive with increasing depth where more defects may be present. While a defect or delamination can be located near the surface, the actual depth of the defect remains unknown. Studies have shown that this technique cannot capture smaller defects that are located at larger depths (Cheng et al., 2008; Kee et al., 2012; Oh et al., 2013; Gucunski et al., 2013). This is because of the lateral diffusion of heat and the low temperature gradients that exists when the defects are located deeper than the lateral dimension (Bhalla et al., 2011). However, the continuous advancements of the technologies have produced more thermally sensitive cameras that can identify temperature changes below 0.1 F. However, due to the shallower depth of the UHPC-NC interface (overlay thickness of 1.5 in), this is not a significant concern in the current project. The infrared imaging detection is dependent on the camera and its associated field of view of the camera used (Vaghefi et al., 2015), which can be tackled by using a more sensitive camera. The biggest challenge in conducting infrared imaging is mostly due to environmental effects such as moisture, surface debris, and shadows that can affect the quality of data. One example is to capture the image when the structure is not directly exposed to solar radiant heating, which aids in the Hartanto Wibowo, Richard L. Wood, and Sri Sritharan 2

3 development of the thermal gradients in concrete. However, a recent study by Washer et al. (2013) showed that good results can be still obtained if there is a change in ambient temperature of at least 8 C (approximately 15 F) during the time required for data collection. Hiasa et al. (2014) proposed that the imaging be conducted during the night since the temperature differences are often more consistent. Moreover, Washer et al. (2009) also found that optimum conditions for imaging are sustained solar heat and low wind speeds. 3. Methodology Infrared imaging relies on the difference between thermal conductivities of the materials. A delaminated bridge deck may consist of a complex system of concrete, reinforcement steel, water, and air voids. As a result, a thermal radiation gradient is present due to the unique thermal conductivities of each material, and, therefore, areas of potential delamination can be determined by way of the observed thermal gradient emitted from the deck. Specifically, concrete and air are characterized by thermal conductivities on the order of and W/m/K, respectively. Due to this order of magnitude difference, the infrared imaging can detect voids within a concrete deck. For the current research, the thermal infrared image scanning will be done in two stages. The first stage was completed in November 2015, approximately four months after the UHPC overlay was placed, and the second stage will be done after the winter months in June This is to assess the potential delamination after the test specimens experienced freeze-thaw cycles in winter, under local environmental conditions in Ames, IA. 4. Validation Test Infrared imaging of a bridge deck mock-up with known delamination locations was conducted to validate the non-destructive evaluation technique. The slab had dimensions of 8 ft (Length) by 6 ft (Width) by 8 in (Depth). Within this slab seven localized delaminated zones of various dimensions and depths were placed at known locations, as shown in Figure 1. Area number 9 in Figure 1 is a solid reference zone. For this proof-of-concept test, a FLIR b50 series thermal camera was utilized. This is an infrared camera that is specifically designed for building inspections (i.e., insulation quality control, presence of moisture, etc.). However, its wide temperature range of -4 to 248 F (-20 to 120 C) was sufficient for field evaluation of concrete slabs. Detailed specifications of this camera include a field of view of 25º x 25º, spectral range of 7.5 to 13 nm, thermal sensitivity of less than 90 mk, and an image resolution of 140 x 140 pixels. While this camera is particularly limited in regard to its image resolution compared to stateof-the-art models, it was still adequate to identify six (out of the seven) areas of potential deck delamination. These locations are detailed in Figure 2a and Table 1. An example of a representative infrared image of the deck is presented in Figure 2b. It is shown that this technique can provide reliable estimations of the delamination area for the most cases, particularly when the area is large and the defect is near the surface. Note that in this thermal infrared technique, only the shallow to moderate depth delamination zones were clearly identified, which is the most common case for bridge deck delamination. Two smaller delamination areas (numbers 5 and 7 in Figure 1) were not detected due to the low thermal sensitivity of the employed equipment. However, this issue may be minimized with the use of a more sensitive device. As a comparison, the results from an impactecho test on the same slab can be found in Lu (2015). From this validation test, the infrared imaging technique is deemed sufficient to detect moderately sized areas of potential deck delamination. Hartanto Wibowo, Richard L. Wood, and Sri Sritharan 3

Summary of Detected Delaminated Zones Dimensions Thermal Gradient* Approximate Depth (From Lu, 2015) 1 12.3 in dia. Strong 3.27 in 2 9.6 in x 8.9 in Moderate 5.

4 Figure 1. Plan and Section Views of the Validation Concrete Slab (After Lu, 2015) (a) (b) Figure 2. (a) Plan View of Infrared Detected Delamination areas and (b) Example Infrared Image of Delaminated Zone 1 Delaminated Zone (Refer to Figure 2) Table 1. Summary of Detected Delaminated Zones Dimensions Thermal Gradient* Approximate Depth (From Lu, 2015) in dia. Strong 3.27 in in x 8.9 in Moderate 5.94 in in x 12.8 in Slight 5.91 in in x 12.5 in Moderate 5.35 in in x 12.5 in Strong 3.29 in in x 12.0 in Slight 3.28 in *Based on the contrast of the thermal images Hartanto Wibowo, Richard L. Wood, and Sri Sritharan 4

5 5. UHPC Overlay Test Specimens For this research, two 8 ft (L) by 8 ft (W) by 7.75 in (D) concrete slabs were designed and constructed; one with an exposed aggregate surface (Slab A) and the other with a broom finish surface (Slab B) with surface roughness xx in. or greater. The deck reinforcement design followed the AASHTO LRFD Specifications considering the dead and live loads. When the slabs were 43 days old, a 1.5 in thick UHPC overlay was placed the top of the slab on July 22, The drawings of the slabs showing the reinforcement details are presented in Figure 3. Concrete curing of the slab specimens was performed within a climate controlled structures laboratory. Afterwards, the slab specimens were moved outdoor for environmental exposure, as depicted in Figure 4. Figure 3. Plan and Section Views of the Concrete Slabs with UHPC Overlay (a) (b) Figure 4. Test Specimens Placed Outside of the Laboratory: (a) Slab A and (b) Slab B 6. Results and Discussion The infrared imaging scans on the test specimen was carried out using a FLIR T650sc camera. Detailed specifications of this camera include a field of view of 25º x 19º, spectral range of 7.5 to Hartanto Wibowo, Richard L. Wood, and Sri Sritharan 5

13 μm, thermal sensitivity of less than 20 mk, and an image resolution of 640 x 480 pixels.

The infrared imaging results of the stage one scanning are shown in Figure 5.

inspected, which is believed to be due to the free edges.

This may be a result of a high moisture content resulting from rain and a slightly concave surface defect is present in this region, which

Nonetheless, reduced thermal gradients indicate potential delamination areas in the middle zone as shown in Figure 5a.

in Figure 5b. Slab B is found to have more scattered locations of potential delamination compared to Slab A.

With the available data, some potential delamination areas on the UHPC-NC interface may have been indicated by the infrared imaging

The data from the first imaging sequence will be compared to future data from the upcoming second sequence of scanning to assess and

6 13 μm, thermal sensitivity of less than 20 mk, and an image resolution of 640 x 480 pixels. The temperature range for this camera is -40 to 3632 F (-40 to 2000 C) with an accuracy of ±1%. The infrared imaging results of the stage one scanning are shown in Figure 5. In general, some possible delamination areas, shown as darker spots, were identified at the edges of the specimens that can also be visually inspected, which is believed to be due to the free edges. For Slab A, a relatively strong thermal gradient or cold region was identified in the middle of the specimen. This may be a result of a high moisture content resulting from rain and a slightly concave surface defect is present in this region, which permits the deposit of water puddle. This phenomenon may alter the scanning results. Nonetheless, reduced thermal gradients indicate potential delamination areas in the middle zone as shown in Figure 5a. For Slab B, some smaller potential delamination areas were observed at more scattered locations on the specimen as indicated by darker spots in Figure 5b. Slab B is found to have more scattered locations of potential delamination compared to Slab A. However, no large potential delamination area was observed on these two slabs. With the available data, some potential delamination areas on the UHPC-NC interface may have been indicated by the infrared imaging technique. To date, no significant areas of delamination have been identified to question the integrity of the UHPC-NC interface. The data from the first imaging sequence will be compared to future data from the upcoming second sequence of scanning to assess and potentially quantify the delamination as a result of the freezethaw cycles. (a) (b) Figure 5. Stage One Infrared imaging Results for (a) Slab A and (b) Slab B 7. Concluding Remarks The validation study on an NC slab with known delamination areas shows that thermal infrared imaging technique can detect most delamination and defect areas in the mock specimen. Preliminary findings on a non-destructive evaluation of deck delamination on two concrete slabs overlaid by UHPC using infrared imaging have been presented in this paper and are summarized as follows: Hartanto Wibowo, Richard L. Wood, and Sri Sritharan 6

7 - Rapid assessment using infrared imaging technique can locate and quantify delamination and other defects in concrete, especially delamination located at shallow depths. - Delamination potential locations at the UHPC and NC interface were rapidly detected. Currently, the slab with broom finish surface (Slab B) has more scattered locations of potential delamination compared to the exposed aggregate surface (Slab A). However, no large potential delamination area was found. The results from the first imaging sequence will be compared to the results from upcoming sequence conducted at the conclusion of one winter season consisting of numerous freeze-thaw cycles in Ames, IA. 8. References Aaleti, S. Sritharan, S., and Abu-Hawash, A., Innovative UHPC-Normal Concrete Composite Bridge Deck, RILEM-fib-AFGC International Symposium on Ultra-High Performance Fibre- Reinforced Concrete, Marseille, France, October 1-3, 2015, 9 pp. Bauer, E., de Freitas, V. P., Mustelier, N., Barreira, E., and de Freitas, S. S., Infrared Thermography Evaluation of the Results Reproducibility," Structural Survey, 33 (1), 2015, pp Bhalla, S., Tuli, S., and Arora, R., "Defect Detection in Concrete Structures Using Thermal Imaging Techniques, Experimental Techniques, 34 (4), 2011, pp Cheng, C. C., Cheng, T. M., and Chiang, C. H., Defect Detection of Concrete Structures Using Both Infrared Thermography and Elastic Waves, Automation in Construction, 18 (1), 2008, pp Clark, M. R., McCann, D. M., and Forde, M. C., Application of Infrared Thermography to the Non-destructive Testing of Concrete and Masonry Bridges, NDT&E International, 36 (4), 2003, pp Hiasa, S., Birgul, R., Watase, A., Matsumoto, M., Mitani, K., and Catbas, F. N., A Review of Field Implementation of Infrared Thermography as a Non-destructive Evaluation Technology, Proceedings of 2014 International Conference on Computing in Civil and Building Engineering, Orlando, FL, June 23-25, 2014, pp Gucunski, N., Imani, A., Romero, F., Nazarian, S., Yuan, D., Wiggenhauser, H., Shokouhi, P., Taffe, A., and Kutrubes, D., Nondestructive Testing to Identify Concrete Bridge Deck Deterioration, SHRP 2 Report S2-R06A-RR-1, Washington, DC: TRB, Lu, J., Advancements in Evaluation of Air-coupled Impact-echo Test Method, MS Thesis, Department of Civil, Construction, and Environmental Engineering, Iowa State University, Matsumoto, M., Mitani, K., and Catbas, F. N., Non-destructive Bridge Deck Assessment Using Image Processing and Infrared Thermography, Proceedings of TRB 93 rd Annual Meeting, Washington, DC, January 12-16, 2014, 10 pp. Hartanto Wibowo, Richard L. Wood, and Sri Sritharan 7

8 Oh, T., Kee, S. H., Arndt, R. W., Popovics, J. S., and Zhu, J., Comparison of NDT Methods for Assessment of a Concrete Bridge Deck, Journal of Engineering Mechanics, 139 (3), 2013, pp Popovics, J. S., NDE Techniques for Concrete and Masonry Structures, Progress in Structural Engineering and Materials, 5 (2), 2003, pp Scott, M. and Kruger, D., Infrared Thermography as a Diagnostic Tool for Subsurface Assessments of Concrete Structures, Proceedings of the First International Construction Materials and Structures, Johannesburg, South Africa, November 24-26, 2014, pp Scott, M., Rezaizadeh, A., Delahaza, A., Santos, C. G., Moore, M., Graybeal, B., and Washer, G., A Comparison of Nondestructive Evaluation Methods for Bridge Deck Assessment, NDT&E International, 36 (4), 2003, pp Sritharan, S., Design of UHPC Structural Members: Lessons Learned and ASTM Test Requirements, Advances in Civil Engineering Materials, 4 (2), 2015, pp Vaghefi, K., Ahlborn, T. M., Harris, D. K., and Brooks, C. N., Combined Imaging Technologies for Concrete Bridge Deck Condition Assessment, Journal of Performance of Constructed Facilities, 29 (4), 2015, 8 pp. Washer, G., Fenwick, R., Bolleni, N., and Harper, J., Effects of Environmental Variables on Infrared Imaging of Subsurface Features of Concrete Bridges, Transportation Research Record, 2108, 2009, pp Washer, G., Fenwick, R., Nelson, S., and Rumbayan, R., Guidelines for Thermographic Inspection of Concrete Bridge Components in Shaded Conditions, Transportation Research Record, 2360, 2013, pp Yehia, S., Abudayyeh, O., Nabulsi, S., and Abdelqader, I., Detection of Common Defects in Concrete Bridge Decks Using Nondestructive Evaluation Techniques, Journal of Bridge Engineering, 12 (2), 2007, pp Acknowledgements This study is a part of a project funded by Iowa Department of Transportation, Iowa Highway Research Board, and Federal Highway Administration (FHWA) under contract number RB30-015/Add 574. The authors would like to acknowledge the support of FHWA and Turner-Fairbank Highway Research Center for the equipment loan, through David Mraz of FHWA Nebraska Division along with Dr. Hoda Azari and Blake Cox of the FHWA NDE Center. Equipment loan from Dr. Terri Norton of the University of Nebraska-Lincoln at Omaha for the verification study on the NC slab specimen is also greatly appreciated. The authors also express gratitude to Doug Wood and Owens Steffens of the Iowa State University Structural Engineering Laboratory for specimen construction, Gaston Doiron of Lafarge North America as well as Laurent Ferreira and Julien Verne of Holcim in France for their technical support on the UHPC overlay, and Dr. Jeramy Ashlock of Iowa State University for the use of the NC deck specimen for the validation study. Hartanto Wibowo, Richard L. Wood, and Sri Sritharan 8

Application of Passive Infrared Thermography for the Detection of Defects in Concrete Bridge Elements

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