In this paper, the design, fabrication and testing of a two-port transmission line-based microwave sensor for the detection of various structural concrete bricks is presented. The microwave sensor is based on the complementary split-ring resonators (CSRRs). First, three dimensional small-scale concrete building bricks are modeled in CST microwave studio along with the design of the microwave CSRR sensor. Classical controlled concrete blocks along with concrete mixed with wood are also studied. The detection capability is then evaluated both numerically and experimentally. Good agreement between numerical and measured results are achieved. Based on the obtained results, the microwave CSRR sensor was sensitive enough to detect various concrete/reinforced concrete blocks with achieved sensitivity of maximum resonance shift of 350 MHz for concrete blocks, while a shift of 150 MHz was obtained for the case of reinforced concrete blocks. From the findings of this research study, the developed microwave CSRR sensor is a good candidate for pre-screening of structural buildings and classification of reinforced concrete samples in a controlled laboratory environment.INDEX TERMS Concrete, CSRR, microwave sensor, reinforced concrete, structural engineering.