טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentLapiro Igor
SubjectAutomatic Crack Detection for Assessment of Structural
Durability using Combination of Light Beam and
Image Processing Techniques
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Konstantin Kovler
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

The service life of reinforced concrete structures depends on several factors, the main ones being environmental factors such as alkalinity, presence of chlorine ions, carbonation and temperature. All of these cause the corrosion process of the reinforcing steel to accelerate. At some point, the build-up of corrosion products leads to the formation of parallel cracks to the steel rebars. A 200-micron-wide crack is known to have a significant effect on the diffusion and permeability of concrete. Cracking of concrete increases the rate of corrosion and consequently the crack width increases. Today, there are several unconventional methods for identifying cracks, each of them has its own disadvantages and advantages. However, a uniform and reliable method for the consistent detection of parallel cracks for cores caused by corrosion has not yet been formulated. To develop an autonomous method for identifying corrosion-caused cracks the current research attempted to answer three key questions: (1) when will a crack form in a reinforced concrete structure; (2) where will it be created, and (3) what is the potential structural damage due to the corrosion-induced cracking.

For the qualitative and reliable detection of cracks formation, a method that combines a crack binary image processing algorithm with a light beam has been proposed. A combination of both makes the crack detection stage very reliable, this was demonstrated by examining the method first on a model of controlled size cracks in 3D printing and later on a model that simulates real crack behavior in a controlled crack model produced by an accelerated corrosion process. Most of the background noise obtained in binary image processing is usually derived from the concrete texture (pigmentation, roughness, voids, etc.). By illuminating the concrete surface with a light beam we get a checkpoint for the crack detection. In addition, by combining these methods, the width of the crack can be accurately measured, which allows determining the residual bond strength between concrete and steel rebars to evaluate the engineering conditions of the structure, answering the question what kind of damage occurs. Another advantage of the proposed method is that it does not require the development of special equipment and can be integrated into all existing digital platforms (different camera types, such as mobile cameras in quadcopters, stationary cameras installed in subway tunnels or other structural locations, or even cameras in mobile phone applications). To answer the question when the crack will occur, the model by Lu's, Liu and Jin (2010) for radial force development due to the formation of corrosion products, integrated with Faraday's law. In this work, through this combination, it is demonstrated that the crack formation time can be estimated as a function of electrical potential prevailing in the sample. Once the information about the crack formation time is available, the review execution times can be individually planned for a variety of concrete constructions, thereby significantly saving unnecessary work and thus also saving labor and time expenses.