No abstract

Conductive concrete is a construction material that can be utilized for a number of applications: in particular, electromagnetic shielding. In this research, the microwave shielding effectiveness of a carbon containing electrically conductive concrete was determined from both the real and the imaginary permittivities. Also, the permittivities and the shielding effectiveness of a normal concrete were determined for comparison purposes. It was shown that the permittivities of the conductive concrete were significantly higher than those of the normal concrete. The shielding abilities of both of the concretes were determined as a function of concrete thickness and temperature, and the conductive concrete had a superior shielding effectiveness. For the normal concrete, at room temperature and a frequency of 912 MHz, a shielding effectiveness of 30 dB was achieved for a thickness of about 400 cm. For the conductive concrete, under the same conditions, a thickness of only about 3 cm was required to achieve the same shielding effectiveness.

The microwave absorption characteristics of both powdered and rectangular blocks of an electrically conductive concrete were measured and compared to a normal Portland cement concrete in a multimode cavity. The variables investigated were: irradiation time, sample mass and incident power for the powdered samples and sample orientation, water additions and multiple irradiations for the block samples. The results were quantified in terms of the microwave absorption efficiency (η a ). The absorption efficiency of the electrically conductive concrete was significantly higher than the Portland cement control concrete. For both of the concretes, hot spot formation occurred in the vicinity of the corner of the block. For the electrically conductive concrete this phenomenon took place close to the surface and resulted in combustion of the carbon and disintegration of the concrete. For the normal Portland cement concrete, the hot spot formed below the surface where fracturing, degradation and melting occurred.