ANOTHER LOOKS: APPLICATION OF STICK SCANNER IN RC STRUCTURES ASSESSMENT (BM-003)

Transcription

1 ANOTHER LOOKS: APPLICATION OF STICK SCANNER IN RC STRUCTURES ASSESSMENT (BM-003) Achfas Zacoeb 1*, Yukihiro Ito 2, and Koji Ishibashi 3 1 Lecturer, Department of Civil Engineering, Brawijaya University, Malang, INDONESIA 2 Assoc. Prof., Department of Civil Engineering, Saga University, Saga, JAPAN 3 Prof., Department of Civil Engineering, Saga University, Saga, JAPAN * of corresponding author: zacoeb@ub.ac.id ABSTRACT One of the remedial measures to a technical judgment of the symptoms and modes of deterioration is visual inspection that assessing the structures by visual observation. Visual examination is the most effective qualitative method of evaluation of structure soundness and identifying the typical distress symptoms together with the associated problems. The needs for a reliable partial and small-scale destruction test method to obtain a plural information about the inside deterioration in concrete structures from small inspection borehole. The application of scanning image principles in non destructive test has grown in recent years, one of them is stick scanner that developed by authors. In this paper, the utilization of stick scanner to assess existing RC structures is presented. From the capturing image, the internal deterioration in RC structures can be evaluated such as carbonation, crack, void, ASR, and bonding behavior from one inspection mark of borehole. Keywords: Borehole, capturing image, plural information, small-scale destruction, stick scanner. 1. INTRODUCTION Presently, bridges are evaluated through either a visual inspection or structural analysis to estimate their strength and condition. In case that bridge evaluation is conducted by using visual inspection method, a subjective grading will be assigned to the bridge components by the responsible inspector. Visual inspection provides no useful information until visible defects starts to appear in the structural members [1]. For example, the presence of crack can offer valuable information, but they will not appear until late into the fatigue life of the structure. It is difficult to identify of inside defect or subsurface deterioration, because it is not visible [2]. One of the remedial measures to a technical judgment of the symptoms and modes of deterioration is visual inspection that assessing the structures by visual observation, sometimes with another method assists, and conducted in once a month, once a year, or once in several years, according to the need of inspection after the construction finished. The periodic inspection covered the visual information data such as cracking, scaling, color change or stain, spalling, exposure, corrosion and rupture of steel reinforcement inside concrete [3]. Imaging of concrete structures for non destructive testing purposes can be defined in a broad sense as obtaining a representation of certain physical properties of the concrete material and characteristics of the physical system by indirect or remote sensing methods which will not damage the structure, or permanently impair its serviceability. Imaging concrete is a challenging task, since concrete is a highly non-homogeneous material. It is generally produced in the field with limited quality control. Grain size distribution is highly variable and the properties of the constituent materials are greatly varied making it difficult to obtain accurate images. Other sources of difficulties in imaging concrete structures include the generally complex physical geometry, existence of inclusions, restricted accessibility of the object, and the problems related to the sensitivity of the method used to the in-homogeneities of concrete [4]. Visual examination is the most effective qualitative method of evaluation of structure soundness and identifying the typical distress symptoms together with the associated problems. This provides valuable information to an experienced engineer in regard to its workmanship, structural serviceability and material deterioration mechanism. It is meant to give a quick scan of the structure to assess its state of general health. This paper deals with another features and the improvements of special device, namely as stick scanner (SS) to assess the inside deterioration in concrete structure by capturing an inside surface image. Small diameter of borehole core is preferred to minimize the damage for giving a concrete segment restoration from inspection activities with partial and small-scale destruction. The capability and performance from the 1 st generation of SS in field application has shown in 2007 [5]. The 3 rd International Conference of EACEF (European Asian Civil Engineering Forum) B - 21

2 Building materials Engineering 2. METHODOLOGY Generally, RC structures inspection consists of two steps: a preliminary inspection and a detailed inspection. The preliminary inspection is mainly performed by people, and the results are used for a preliminary evaluation of the bridge s safety. Inspection for cracks is an important part of the preliminary inspection. More detailed inspection, such as, for non-fracture or fracture inspections, loading tests and earthquake resistance evaluations, means of further inspections with different kinds of instruments [6]. For assisting the inspection method like core drilled will gather an existing concrete condition, and investigate the inside defects, such as carbonation depth, chloride ion diffusion, cracking, void, and corrosion. By this method, relatively big device is required and became difficult to determine the number of inspection mark related with cost and work problems. In addition, there is a partial damage or danger to cut off a steel reinforcing bar in core drilling process. To solve the problems, an alternative method such as narrow path drilled hole will be applied with small breaking test to inspect carbonation depth or chloride ion diffusion of inside structure members after several years, but it is not effective to conduct only one inspection item in one mark of measurement. This inspection method is developed by using a stick scanner technology to capture inside concrete surface image from small diameter borehole, whereas the measurement and analysis is confirmed by image processing in photograph stage. Investigation of inside concrete surface defect such as cracking or void is possible to capture an image by inserting the sensor part of SS into inspection borehole after having sprayed with phenolphthalein solution for carbonation depth measurement in dry or wet core drilling process. While for chloride ion diffusion, it must be performed in dry process and sprayed with nitrate silver solution (AgNO 3 ). The image capturing process must be conducted on dry condition of inside inspection borehole to prevent the sensor part damage from liquid material. The measurement is possible by calculating a number of pixels in the capturing image with color changes part. Inspection procedure with this device for various investigations is shown in Figure 1. Figure 1. Flow chart of various investigations B - 22 The 3 rd International Conference of EACEF (European Asian Civil Engineering Forum)

3 Building Materials Engineering 3. OUTLINE AND SPECIFICATIONS The SS for capturing inside concrete image from drilled hole is shown in Figure 2 and the specification of device is shown in Table 1. The image is captured by inserting the stick scanner aperture mouth inside borehole. It is easy to make the stick scanner a manual rotation movement inside drilled hole with one hand to capture all inside surface of borehole. The SS is enabled for capturing image of inside borehole in depth up to 250mm (for the 1 st SS) and 350mm (for the 2 nd SS and the 3 rd SS). From this image, it can be useful for various analyze such as mortar thickness, rebar position, propagation of crack and segregation degree of concrete by counting a pixel number of captured image for each measurement position. For the resolution of 300dpi, the actual measurement as per mm as 1 pixel is 0.084mm, while for resolution of 600dpi as 1 pixel is 0.042mm. a. The 1 st Generation of SS b. The 2 nd Generation of SS c. The 3 rd Generation of SS Figure 2. The appearance of SS model The principle of image reading is similar with general handy scanner that measured movement distance of image sensor by encoder, and then read line data of image by image sensor as two dimensions image. The SS has a sensor of a CIS type with focus depth of 1mm. The resolutions of capturing images in dpi (dot per inch) are 300dpi (for the 1 st SS) and 600dpi (for the 2 nd SS and the 3 rd SS). In order to keep the focus length, as the distances of surface inside drilled hole with the scanning sensor are changeable, a pair of guide rings and scanner aperture mouth was established to support a stable rotational movement. The guide ring diameter is assumed 1mm smaller than inside borehole with the diameter of 24.5mm. The movement roller which interlocking a main body pipe and rotary encoder circuit is being stable as interlocking movement roller, and for movement distance data reading from encoder part is enabled to be confirmed without release it. In addition, a pair of guide rings that installed in encoder part and aperture mouth had made the scanner is possible to conduct a front and back movement for depth extension. Table 1. The specifications of SS model Generation The 1 st SS The 2 nd SS The 3 rd SS Mobile Instrument Note PC with OS Windows /2000/ME/XP Tablet PC with OS Windows /2000/ME/XP SD Card or USB Flash Disk without OS Power supply Via USB Via USB battery type AA (4 units) Resolution (dpi) Sensor type CIS (Contact Image Sensor) Sensor Length 120mm with reading size 105mm x 356mm The 3 rd International Conference of EACEF (European Asian Civil Engineering Forum) B - 23

4 Building materials Engineering 4. FIELD APPLICATIONS a. Inside deterioration assessment in concrete Before the use of stick scanner is started, an examination object (pier and abutment) is marked for indicating the rebar arrangement and location of inspection. From this inspection mark, the preliminary inspection hole is established by hammer drilling. The making process of inspection borehole is conducted in dry condition. After removing the emission of dust due to drilling work, the capturing process of inside surface concrete image from inspection borehole is ready to be conducted for general inspection. For carbonation depth inspection, the inside of inspection borehole must be sprayed by phenolphthalein solution, and dry conditioning process must be performed before capturing an image. It is clearly confirmation that from one inspection mark, various data of image can be captured. After all capturing image processes are finished, the segment restoration is conducted by inserting cement based material into the inspection borehole. The situation of image capturing by using the 2 nd generation of SS in is shown Figure 3a with the sample of image result is shown in Figure 3b. From this image, the analysis is conducted in photograph stage by using image processing software. The sample of final analysis image is shown in Figure 3c that provides plural information about inside deterioration in examination object such as crack width, crack depth and carbonation depth. From this information, the judgment for determining a grade of appearance is conducted by referring the standard specifications for concrete structures performance. a. The situation of image capturing c. Sample of final analysis image b. Sample of capturing image Figure 3. The 2 nd SS performance b. Interfacial de-bonding on concrete beam In 2008, the part of concrete beam of Bridge had been demolished due to significant environmental damage from salt water. From this part, it can be divided into several concrete beam segments with the length of 8,400mm and T-cross section. The interfacial de-bonding in concrete is investigated by conducting a four point bending test with load interval of 100kN from 0 to 800kN as shown in Figure 4a, and capturing the inside surface image of inspection borehole for each interval of load. The location of inspection borehole is determined by a black circle as shown in Figure 4b. This figure also shows a crack mapping and loading position for the examination concrete beam. B - 24 The 3 rd International Conference of EACEF (European Asian Civil Engineering Forum)

5 Building Materials Engineering a. Setup of four point bending test b. Location of inspection borehole Figure 4. The examination RC beam After all processes of inspection hole making were finished, the next stage is to capture an inside image from both inspection hole (south and north face) for each interval of load. The initial image is captured for 0kN load and determined as reference to measure a crack width and aggregate characteristic. The result of reference image that captured in initial stage of load is shown in Figure 5 for each face. a. South face b. North face Figure 5. Reference image of initial stage From this reference image, it can be useful for various analyze such as mortar thickness, rebar position, propagation of crack and segregation degree of concrete. By counting pixel number of captured image for each measurement position, this basic information of concrete beam segment for south face will be observed as shown in Figure 6. c. Crack propagation d. Segregation degree Figure 6. Basic information of RC beam segment For monitoring of interfacial re-bonding on concrete is conducted by measuring of crack width as shown in Figure 5 for each interval load. The results of measurement are shown in Table 2, and from these data can be drawn a graph to illustrate the revision trend of crack width for both faces of RC beam segment due to interval load as shown in Figure 7. The 3 rd International Conference of EACEF (European Asian Civil Engineering Forum) B - 25

6 Building materials Engineering Table 2. Revision of crack width South face North face Load c1 *) c2 c3 c4 c5 c1 c2 c3 c4 C5 (kn) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) *) c = crack width a. South face b. North face Figure 7. Trend of crack width revision 5. CONCLUSION Inspection by the SS using drilled hole has many advantages compare with conventional core method. This scanner makes the possibility for effective and secure working with a good precision to obtain plural information from one inspection mark of borehole. For continuing the use of existing deteriorated concrete structures, it is important to evaluate the degree of deterioration comprehensively. The scenario of maintaining and repairing can be proposed in selected part that indicated by a periodic inspection result below the minimum of requirements. The decision for extending or demolishing of existing concrete structures is depending on the comprehensive interpretation of inspection results. It was confirmed from the illustration of field application by using the developed inspection method that the actual strength of concrete can be estimated in a good accuracy and inside defect in concrete structures can be assessed in a rapid way as total time for one inspection mark as 30 minutes. 6. REFERENCES [1] Estes, A.C., & Frangopol, D.M., Updating Bridge Reliability Based on Bridge Management Systems Visual Inspection Results, Journal of Bridge Engineering, Vol. 8, 2003, pp [2] Chang, P.C. & Liu, S.C., Recent Research in Nondestructive Evaluation of Infrastructure, Journal of Material in Civil Engineering, Vol. 15, 2003, pp [3] Meola, C., Maio, R.D., Roberti, N., & Carlomagno, G.M., Application of Infrared Thermography and Geophysical Methods for Defect Detection in Architectural Structures, Engineering Failure Analysis, Vol. 12, 2005, pp [4] Zacoeb, A., Ishibashi, K., Ito, Y., Miyamoto, N., & Sogabe, M., Development of Advanced Inspection Device for Inside Concrete Structures, Proceedings of the 1 st European Asian Civil Engineering Forum, Jakarta, Indonesia, September 26-27, 2007, pp. D32-D39. [5] Graybeal, B.A., Phares, B.M., Rolander, D.D., Moore, M., & Washer, G., Visual Inspection of Highway Bridges, Journal of Nondestructive Evaluation, Vol. 21, 2002, pp [6] Tung, P.C., Hwang, Y.R., & Wu, M.C., The Development of a Mobile Manipulator Imaging System for Bridge Crack Inspection, Automation in Construction, Vol. 11, 2002, pp B - 26 The 3 rd International Conference of EACEF (European Asian Civil Engineering Forum)