In the construction industry, to prevent accidents, non-destructive tests are necessary and cost-effective. Electrical impedance tomography is a new technology in non-invasive imaging in which the image of the inner part of conductive bodies is reconstructed by the arrays of external electrodes that are connected on the periphery of the object. The equipment is cheap, fast, and edge compatible. In this imaging method, the image of electrical conductivity distribution (or its opposite; electrical impedance) of the internal parts of the target object is reconstructed. The image reconstruction process is performed by injecting a precise electric current to the peripheral boundaries of the object, measuring the peripheral voltages induced from it and processing the collected data. In an electrical impedance tomography system, the voltages measured in the peripheral boundaries have a non-linear equation with the electrical conductivity distribution. This paper presents a cheap EIT instrument for detecting impurities in the concrete. A voltage-controlled current source, a micro-controller, a set of multiplexers, a set of electrodes, and a personal computer constitute the structure of the system. The conducted tests on concrete with impurities show that the designed EIT system can reveal impurities with a good accuracy, in a reasonable time.