Abstract
Concrete cracks have no specific shape and do not show linearity. Since the natural occurrences of concrete cracks make simulation identification difficult, rectangular step function and a dynamic geometry are used to define a concrete surface crack in the natural process. A novel interior crack expression is obtained by accepting the area between two curves as a crack filled by air in concrete and modeling this area like a Riemann integral domain. Taking the partition of this integral domain, the most realistic definition of the crack is made. Electromagnetic (EM) waves are utilized for numerical simulation after identifying the defects, cracks, rebars, and geometry of concrete. Three different simulation setups with complex geometries with two different surface cracks and one internal crack are simulated using a finite-difference time-domain (FDTD) method with Gaussian pulse wave excitation. Simulations are obtained using both transverse electric (TEz) waves and transverse magnetic (TMz) waves and the results are compared with each other. Air-dried concrete specimens are molded following simulation setups with surface cracks and measurements are made nondestructively with a Vivaldi antenna array in the frequency range of 0.4–4.0 GHz. The reflection and transmission coefficients are validated by comparing the data obtained using the measurement with the results obtained from numerical simulation.
Highlights
Detection of damage and cracks in concrete structures and infrastructures has great importance for public safety economic saves
Evaluations of changes in composites and concrete structures resulting from environmental factors such as temperature and moisture, including the effect of curing, are studies that can be done with microwave nondestructive testing (NDT)
In the finite-difference time-domain (FDTD) calculations, the dispersivity of the concrete samples is taken into account. e structures which have surface crack are measured with Vivaldi antenna array. e reflection and transmission coefficients obtained from the measurement results and FDTD calculations are compared
Summary
Detection of damage and cracks in concrete structures and infrastructures has great importance for public safety economic saves. Concrete to be examined can contain different types of cracks, rebar, delamination, void, and layered structures, so the computation domain becomes a complex geometry and analytical field solutions to Maxwell’s equations are very difficult to find. Instead of solving the wave equation for only electric field and magnetic field, a solution is obtained for the electric and magnetic fields by time and space discretization using Maxwell’s curl equations combined with the Yee algorithm As both E and H information are used to solve the problem, a better result is obtained in the arbitrarily shaped geometries [27, 28]. Measurement methods that provide information about the propagation of EM waves according to the dielectric properties of any material are parallel plate capacitor technique, free space technique, transmission line technique, and resonator/oscillator technique. In the FDTD calculations, the dispersivity of the concrete samples is taken into account. e structures which have surface crack are measured with Vivaldi antenna array. e reflection and transmission coefficients obtained from the measurement results and FDTD calculations are compared
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