Visual inspections are performed to investigate cracks in concrete infrastructure. These activities require manpower or equipment such as articulated ladders. Additionally, there are health and safety issues because some structures have low accessibility. To deal with these problems, crack measurement with digital images and digital image processing (DIP) techniques have been adopted in various studies. The objective of this experimental study is to evaluate the optical limit of digital camera lenses as working distance increases. Three different lenses and two digital cameras were used to capture images of lines ranging from 0.1 to 0.5 mm in thickness. As a result of the experiments, it was found that many elements affect width measurement. However, crack width measurement is dependent on the measured pixel values. To accurately measure width, the measured pixel values must be in decimal units, but that is theoretically impossible. According to the results, in the case of 0.3 mm wide or wider cracks, a working distance of 1 m was secured when the focal length was 50 mm, and working distances of 3 m and 4 m were secured when the focal length was 100 mm and 135 mm, respectively. However, for cracks not wider than 0.1 mm, focal lengths of 100 mm and 135 mm showed measurability within 1 m, but a focal length of 50 mm was judged to hardly enable measurement except for certain working positions. Field measurement tests were conducted to verify measurement parameters identified by the results of the indoor experiment. The widths of actual cracks were measured through visual inspection and used for the analysis. From the evaluation, it was confirmed that the number of pixels corresponding to the working distance had a great influence on crack width measurement accuracy when using image processing. Therefore, the optimal distance and measurement guidelines required for the measurement of the size of certain objects was presented for the imaging equipment and optical equipment applied in this study.

Crack width estimation through remote imaging and digital image processing are the leading diagnostic technologies used for infrastructure. However, owing to limitations in the accuracy of these techniques, alternative methods to detect target crack widths larger than the diagnostic standard are being developed. In this study, the coordinates of fiducial markers were extracted using the Harris corner detector, and fine crack widths of approximately 0.3 mm or less were estimated using the ground sample distance, varied numbers of adjusted pixels, and varied focal lengths. The results of these examinations were compared with the measured values. As a result, it was confirmed that the number of pixels rather than the ground sample distance was the dominant factor affecting the accuracy of the estimated value, and the accuracy could be improved by adjusting the number of pixels, increasing the focal length, and ensuring an effective object distance. The results showed the feasibility of estimating fine crack widths with a high accuracy through the fiducial-marker-based method under the aforementioned conditions. In the future, if the number of crack samples is increased and more detailed focal length and object distance data are supported, this method may provide estimations with a higher accuracy.

Bonded natural stone pavement has been typically used in historical neighborhoods to satisfy functional and architectural aesthetic standards. Despite its advantages, it has been barely applied to places for heavy traffic volume or high travelling speed because of various structural failures in joints and bedding courses. Ultra-rapid-hardening mortar for natural stone pavement was considered as an alternative to minimize these failures. The objective of this study is to develop bound stone pavement using the ultra-rapid-hardening mortar for high traffic volume and evaluate throughout by carrying out material tests, plate load test, accelerated pavement test (APT), and falling weight deflectometer (FWD) test. For the tests, four types of pavements, asphalt, concrete block, and two bound stone pavements, were produced in a testing facility. The bearing capacity of the sub-base course, which was asphalt and concrete, showed values 1.62 and 2.64 times higher than deemed satisfactory. Additionally, rut depth was measured using a transverse profile logger during the APT test and the test was terminated at 1.97 million cumulative equivalent single axle loads (ESALs). In the rut depth measurements, the deepest deflection (16.0 mm) was made in the asphalt pavement and the depth of the concrete block pavement was 4.5 mm. Vertical displacements of 3.0 and 1.5 mm were obtained in stone pavements A and B, respectively. The maximum pavement vertical deflection response was recorded at 0, 0.4, and 1.97 million ESALs. The response results revealed that they were influenced by the material types of either bedding or sub-base courses. With these outcomes, it would be possible to apply the baseline data for designing rigid small element pavement for heavy traffic volume or high travelling speed roads.

A waterborne coating system for car park slab has recently gained interest as an alternative for solvent-based finishing materials due to environmental concerns and prolongation of service life. However, water-based finishers, regardless of their eco-friendly properties, have relatively lower hardness compared to traditional finishing systems. In order to overcome this obstacle, a hybrid technology was used to develop a substitute surface finisher for car park slab and its performance was evaluated according to the KS (Korean Standard) F 4937. Initially, the proper mix ratio of polyamide was found by comparing adhesion via pull-off-test results and other performance evaluation tests. From the test results, it was found that mixing polyamide with silicon acrylic finisher caused an increase in adhesion strength. Silicon acrylic with a 30% mix ratio of polyamide resin (SA+PR30%) was selected to perform the rest of the tests and the results satisfied the acceptance criteria of KS F 4937 and were compared with a recent water-based polyurethane finisher with cementitious powder (WPC). Finally, it was verified that the developed finisher could be an alternative finisher of urethane and epoxy finishers as it has good mechanical properties and emit less volatile organic compounds (VOC).

Due to the environmental concerns of solventborne coating systems, environmental directives have recently been promulgated in many countries. Additionally, integrated environmental policies have been pushed in many fields to minimise influences on the environment. Waterborne silicon acrylic finishers have gained much interest to replace the traditional finishing system. To satisfy the requirements, a waterborne finisher with polyamide was previously developed and its performance was determined. For further safety assessment, various tests were conducted, such as gas toxicity, heavy metals tests, chemical resistance test and chloride migration test, followed by equivalent standards. In the cases of gas toxicity and heavy metals evaluations, both results were acceptable considering their corresponding standards, e.g. KS F 2271, KS F 3888-2 and BS EN 71-3. Based on the evaluation, silicon acrylic with 30% mix ratio of polyamide resin (SA+PR30%) could be implemented as an environmentally friendly finisher for various applications. In the chemical resistance and chloride migration test results, the developed finisher showed a barrier effect in the chemical environment. Thus, the developed finisher could be an alternative finisher applicable for slabs in chemical industrial areas.