AUTOMATED GEOMETRIC QUALITY INSPECTION OF REBAR LAYOUT USING RGBD DATA MAHSA SANEI*, XINXING YUAN†, FERNANDO MOREU‡, AND SREENIVAS ALAMPALLI§ ABSTRACT Quality control and quality assurance during construction is vital to ensure the structure is built as designed and durable. For reinforced concrete (RC) structures, rebar diameter, spacing, and concrete cover depth are critical in ensuring that the structure is designed for adequate strength and can maintain its service life without unplanned interventions. Once the rebar is laid out in the field, construction inspectors do the required quality control to ensure that the constructed rebar mat matches the design documents. The checks are made at finite points and thus can be improved with currently available technologies such as LiDAR, augmented reality (AR), and uncrewed aerial vehicles (UAVs). This paper summarizes the available technologies for such an effort and focuses on using Red Blue Green Depth (RGBD) cameras as a quality control tool for construction inspection of RC structures such as buildings and bridges. A study conducted using an RGBD camera for estimating rebar diameter is presented in this paper. Results show that RGBD cameras have a very high potential as a low-cost, efficient tool for quality control of RC structures during construction. RGBD cameras can potentially augment current visual inspections in assuring the structures are built as per design drawings, meeting the appropriate specifications with acceptable accuracy. KEYWORDS: RGBD camera, 3D scanning, structural health monitoring, construction inspection, quality control Introduction Recent initiatives for automated quantification of inspection and monitoring have demonstrated the promise for efficient management of construction projects (Zucchi 2015). The auto- mated quantification system increases the data collection quality and enables real-time data processing for managers (Gucunski et al. 2015). The concept of e-construction, which calls for gathering, examining, authorizing, and disseminat- ing highway construction contract documents without the use of paper, has also been gaining attention among owners. To design processes and store documentation in a paper- based system, a substantial amount of time and money is required (Cawley and Duval n.d.). This arrangement is quickly becoming outdated in an age of immediate communication, on-the-go information access, and a tech workforce. One advantage of using an automated quantification inspection platform is that it can also provide a permanent record of the construction throughout the service life of the structure. It would not be possible or easy to record this information manually. As a result, engineers can interpret the recorded inspection data, compare it at a different stage, incorporate it into the project design and schedule, and make informed deci- sions (Kopsida et al. 2015). Most of the quality control methods used on construction sites are not good at recognizing defects early in the construc- tion or maintenance stage. This is due to the data collection at a certain time and location (Almadhoun et al. 2016). Therefore, these new technologies allow inspectors to monitor the status of the structure as construction progresses. They generate appropriate digital data that describe the as-built condition when the data was collected (Memarzadeh and Pozzi 2016). To perform quality control, this digital data must be compared to the project’s quality requirements derived from specific design and construction specifications. Also, the result of past inspec- tions can be overlaid with the newly captured data to see how the structure condition has changed with time (Wang et al. 2015). To date, the efforts in automation in construction inspec- tion enable inspectors to compare data collected during con- struction as a reference for long-term structural inspection and maintenance (Boukamp and Akinci 2007). It would be of value if in addition to the long-term structural construction inspec- tion, the human in the loop can have access to the data at the site during the inspection. This paper outlines the proposed objective quality control methodology for practical implementation in reinforced concrete (RC) structures’ construction inspections that take advantage of low-cost automated global assessment technology * Department of Civil, Construction and Environmental Engineering, University of New Mexico, Albuquerque, NM 87131 msanei@unm.edu † Quiroga-Pfeiffer Engineering Corp. (QPEC), 4343 Pan American Fwy. NE, Albuquerque, NM 87107 xyuan@qpec.org ‡ Department of Civil, Construction and Environmental Engineering, University of New Mexico, Albuquerque, NM 87131 fmoreu@unm.edu § Stantec, 3 Columbia Circle, Albany, NY 12203 sreenivas.alampalli@stantec.com Materials Evaluation 81 (1): 46–54 https://doi.org/10.32548/2023.me-04307 ©2023 American Society for Nondestructive Testing ME | TECHNICALPAPER 46 M AT E R I A L S E V A L U AT I O N • J A N U A R Y 2 0 2 3 2301 ME Jan New.indd 46 12/20/22 8:15 AM

to improve construction quality. The focus is not on replac- ing construction inspectors but on enhancing their ability to conduct global assessments quickly and in a thorough fashion by combining low-cost technologies available in the market with an artificial intelligence framework. Specifically, this paper emphasizes using new low-cost technology to obtain the rebar size in reinforced concrete construction. This study in con- junction with work of other researchers in rebar spacing and cover estimation can automatize the rebar geometric inspec- tion. It can also be used as a general concept for inspection automation, where the collection of the data and its analysis can eventually inform the projected strength of the structure in real time. This also facilitates moving towards e-construc- tion, where quality construction is achieved using a paperless format while also creating a permanent record. Technology for Structure Inspection Traditional infrastructure inspections are performed by qual- ified inspectors who physically go to the field and perform inspections (Newman and Jain 1995). In the industrial, com- mercial, and civil sectors of the construction industry, the application of automation technologies has attracted attention in recent years. These technologies, such as uncrewed aerial vehicles (UAVs) or drones (Kuo et al. 2016), LiDAR (Wood and Mohammadi 2015), augmented reality (AR) (Wang et al. 2019), and RGBD cameras (Wójcik and Zarski . 2021) are being used for collecting 3D geometric information for inspection, renovation, and retrofit projects. Researchers use UAVs to reconstruct a 3D image of the structure using a camera and remote sensor (Chen et al. 2019 Perry et al. 2020 Ayele et al. 2020). UAVs can be used in areas that are hard to access, but they have a limitation of payload equipment, vibration, environmental condition, and cost. LiDAR is another instrument that researchers consider an inspection tool, and it has been used to automatically evaluate the rebar spacing before pouring concrete (Yuan et al. 2021a). In another study, they proposed a platform for mounting the LiDAR on the UAV to detect discontinuities of the structure (Nasrollahi et al. 2018). Despite the high accuracy of collected data from the LiDAR, it requires an expert to be familiar with the technology. Also, the setup time in the field is, in general, a concern for construction managers and structural engineers who need a quick quality control/quality assurance method to inform them in a short time on the rebar quality. AR is another new technology that has recently attracted researchers’ atten- tion. There are studies in which the authors used the AR-BIM platform for inspection of the bridge and locating defects (John Samuel et al. 2022). Also, the application of AR in infrastructure inspection and its capability have been examined in the past (Mascareñas et al. 2021). The rapid development of low-cost RGBD sensors has attracted the attention of researchers in various scientific and technological fields due to the advan- tages they offer. The RGBD sensor includes a color sensor and a depth sensor that captures color information and depth data by measuring the time between emitted and reflected light bouncing back to the visor (time of flight). An RGBD camera was used in the literature to detect the position of a target and its orientation on a bridge that was identified as damaged (Ivanovic et al. 2021). Additionally, other important factors such as spacing and cover of the rebar need to be controlled before pouring the concrete. A group of researchers used an RGBD camera to obtain the rebar spacing and cover in a rebar cage automatically to demonstrate the capability of a low-cost approach to assist in quantifying the quality of rebar place- ment. This method was tested on a rebar cage to calculate the spacing and the result was validated with tape measurement (Yuan et al. 2021b). In addition to the capability of measuring rebar spacing and clearance, it would be of value to explore if the proposed methodology would be able to measure the rebar diameter automatically. Each of these instruments has advantages and disad- vantages that make the engineer and owner use them based on the project’s specifications. However, there are important factors to consider for all inspectors as they can enhance the speed, cost, and quality of the inspection. Handheld, portable, low-cost instruments are among those capabilities that are worth considering. Inspection Industry Standards For more than a century, reinforced concrete has dominated the global construction industry, even though RC structures are frequently subject to a variety of deterioration and damage owing to various exposure factors. As a result, the require- ments of the building standards necessitate somewhat frequent inspections in many countries (Masoumi et al. 2013). The emphasis of the proposed method is on the inspection of rebar in RC structures, such as buildings or bridges. Rebar placement has a significant impact on the quality of RC structures (Qi et al. 2014). Rebar defects in concrete structures can induce struc- tural collapse, uneven strength capacity, and serious concrete degradation (Cusson 2009). Incorrect rebar placement or insufficient concrete cover might decrease structural strength. One of the main issues limiting the durability of old RC struc- tures is the rebar corrosion brought on when the concrete cover is not sufficient (Wilkie and Dyer 2022). Due to this, the concrete structure becomes less durable and is more suscepti- ble to chemical attacks (Chemrouk 2015). RC structures benefit from accurate rebar arrangements for the duration of their lives (Słowik 2019 Concrete Construction 2005). Rebar construction errors can be reduced to a minimum to avoid costly repairs, task deferrals, flaws in structural strength, and even save struc- tures from collapsing. Current Inspections Limitations Figure 1 shows the labor during rebar placement at a bridge deck construction project. Projects of this size can take several days to weeks for rebar placement. In tight construction sched- ules recognizing issues with placement as the project progresses is important in assuring that issues are addressed as soon as possible. Early detection of errors can accelerate construction. J A N U A R Y 2 0 2 3 • M AT E R I A L S E V A L U AT I O N 47 2301 ME Jan New.indd 47 12/20/22 8:15 AM