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A comparative analysis of the experimental results of the properties of fresh and hardened concrete with different replacement ratios of natural with recycled coarse aggregate is presented in the paper. Recycled aggregate was made by crushing the waste concrete of laboratory test cubes and precast concrete columns. Three types of concrete mixtures were tested: concrete made entirely with natural aggregate (NAC) as a control concrete and two types of concrete made with natural fine and recycled coarse aggregate (50% and 100% replacement of coarse recycled aggregate). Ninety-nine specimens were made for the testing of the basic properties of hardened concrete. Load testing of reinforced concrete beams made of the investigated concrete types is also presented in the paper. Regardless of the replacement ratio, recycled aggregate concrete (RAC) had a satisfactory performance, which did not differ significantly from the performance of control concrete in this experimental research. However, for this to be fulfilled, it is necessary to use quality recycled concrete coarse aggregate and to follow the specific rules for design and production of this new concrete type.

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This paper describes an innovative design of a wireless, passive LC sensor and its application for monitoring of water content in building materials. The sensor was embedded in test material samples so that the internal water content of the samples could be measured with an antenna by tracking the changes in the sensor’s resonant frequency. Since the dielectric constant of water was much higher compared with that of the test samples, the presence of water in the samples increased the capacitance of the LC circuit, thus decreasing the sensor’s resonant frequency. The sensor is made up of a printed circuit board in one metal layer and water content has been determined for clay brick and autoclaved aerated concrete block, both widely used construction materials. Measurements were conducted at room temperature using a HP-4194A Impedance/Gain-Phase Analyzer instrument.

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