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This paper presents a non-destructive system for assessing the curing quality of early-age concrete using the transmission of two frequency signals. The methodology involves transmitting signals to the concrete sample, measuring the reflected power signal, and then analyzing and comparing the responses to determine the concrete’s curing quality. The system consists of the transmitted and received parts. The transmitted part generates a signal by a high-frequency synthesizer and sends the signal through a directional coupler to patch the antenna prototype. The antenna serves to propagate signal power to the concrete sample and receives a reflected signal from the concrete sample backward to the received part. The reflected signal was detected by a directional coupler and converted to DC voltage by a linear power detector, converted to digital signal 10-bit by an ADC convertor, and then processed with microcontroller board. The voltage level from concrete measurement at an early age from 10 to 120 hours at 2.4 GHz was in the range of 0.844 to 0.94 V and 0.845 to 0.959 V, at 2.5 GHz was in the range of 0.871 to 0.876 V and 0.873 to 0.866 V, respectively. The voltage data measurement from two frequencies was calculated ratio of 2.4/2.5 GHz for the different wet curing and air curing concrete. In age below 54 hours, the ratio was different in the range of 0.969 to 1.009 and 0.968 to 1.045. In age between 65 and 120 hours, it was in the range of 1.026 to 1.123 and 1.073 to 1.183, respectively. Considering the absolute voltage ratio difference between wet and air curing, in age less than or equal to 37 hours it was slightly different when age increased 38 to 81 hours the absolute voltage ratio difference was 1.003±0.014 to 1.036±0.026 and most different when age in the range of 82 to 120 hours that was 1.076±0.032 to 1.114±0.031. The clear difference in ratio results in effective classifying of curing concrete quality.
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