Development of pot-cover effect apparatus with freezing-thawing cycles

‘Pot-cover effect’ refers to the phenomenon of moisture accumulation beneath the pavement under condensation or desublimation because the vapor transfer in the soil is blocked by the pavement. To study this phenomenon in the laboratory, we have developed the pot-cover effect apparatus with freezing-thawing cycles (PEAFC), which consists of three parts, namely, the vapor transfer system, the temperature control system, and the temperature and water content monitoring system. The major functions of this apparatus include: simulation of both vapor transfer and freezing-thawing cycling in the soil, real-time monitoring of the temperature and the water content in soil samples, and one-dimensional heat and moisture transfer in the samples. The FDR (frequency domain reflectometry) sensors of the apparatus are calibrated and a calibration formula is proposed to eliminate the water content measurement errors induced by temperature changes. Constant temperature difference tests and a freezing-thawing cycling test are conducted with the apparatus. Results indicate that the apparatus can control the water replenishment in the soil samples, monitor the vapor transfer in the samples in real time, and simulate the vapor transfer process under the condition of the freezing-thawing cycling in the soil. These tests verify the effectiveness and reliability of the apparatus, which indicates that the development purpose is achieved.