Paper Title
IMAGE RECONSTRUCTION OF REINFORCED CONCRETES BY USING FILTERED BACK PROJECTION (FBP) ALGORITHM

Abstract
Reinforce concretes require frequent monitoring to ensure the concrete quality during its services life and for evaluation of in situ existing conditions. This paper describes the image reconstruction of reinforced concretes by using filtered back projection (FBP) algorithm. In this study, gamma ray transmission technique was used to measure the location of steel bars inside concretes. The samples were irradiated with gamma rays source from Cs-137 with activity of 370 kBq and the scattered photons were recorded by NaI (Tl) scintillation detector. The samples were rotated with 2.8125 intervals from 0 to 180 for the measurement. Experimental setup was prepared and measurementswere conducted with 64 projections by 64 degrees. The samples were measured with the parallel beam scanning method and the projection data were obtained. Scanning was achieved with the translational steps of 0.25 cm each to cover the whole sample. The image reconstruction problem was solved using filtered back projection (FBP) algorithm. Image reconstructions of these objects were performed by MATLAB program and performance improvements were investigated. In the MATLAB program, ‘v5cubic’ interpolation and ‘Hamming’ filter functions were chosen for the clearest images of reinforced concretes in image reconstruction. The results found that the reconstructed images of the concretes containing one rebar and two rebars could be observed clearly. The results in the reconstructed images form make it easier to be interpreted. Finally, the use of gamma ray tomography provided a potentially powerful non–destructive and accurate method for investigating the image of the steel bars inside the concretes. Keywords - Reinforced Concretes, Measurement, Gamma Ray, Image Reconstruction, MATLAB