Straight line reconstruction model is frequently used in concrete computerized tomography. It assumes the ray travels in a straight line between a sending transducer and a receiving transducer

which is valid for homogeneous medium. When there are defects in the medium

the ray will not travel in a straight line but in a spatial curve

and if still using straight line reconstruction model

error will be brought in. An improved algebraic reconstruction technique (ART)is put forward in the paper

and linear travel time interpolation (LTI)ray tracing is used during the iterations to obtain the real travel paths of rays. Firstly

defect meshes are ascertained by probability and mathematical statistic method

and then defect meshes and normal meshes are provided with different initial wave velocities. Secondly

the projection matrix is anew computed by LTI ray tracing before each iteration. And during each iteration

defect meshes and normal meshes are provided with different relaxation factors. The results of computer simulation and concrete model experiment show that the improved ART based on LTI ray tracing is effective to improve the accuracy of computation and the quality of image reconstruction on concrete，but takes more time.