Thermal Diffusivity of Peat-Sand Mixtures with Different Peat and Sand Contents

The thermal diffusivity of screened quarry sand with a predominance of a fraction of 0.05–0.25 mm, lowland packed peat, and their mixtures was studied. Sand was mixed with peat in various proportions; the content of peat in mixtures ranged from 1 to 80% by dry weight. Metal cylinders 10 cm high and 3.8 cm in diameter were filled with sand, peat, and peat-sand mixtures. The thermal diffusivity was measured in the laboratory using the unsteady-state method with a working temperature range of 20–26°C. The heating rate of the packed samples was measured after the samples were placed in a liquid thermostat with a constant water temperature. For each sample, a series of measurements was carried out with a step-by-step change in water content from the maximum one after capillary saturation of the sample to the minimum one, corresponding to the air-dry state. The thermal diffusivity vs. water content dependence was almost linear for peat, and for sand it was a curve with a maximum. The lowest thermal diffusivity was obtained for peat and mixtures with low sand contents; the highest one – for pure sand. Within the studied range of water contents, the thermal diffusivity of different samples changed by a factor of 1.3–2.8. The non-linear character of the thermal diffusivity vs. peat content dependence was discovered. Small additions of peat to sand resulted in a noticeable decrease in the thermal diffusivity of the mixture; small additions of sand to peat had practically no effect on thermal diffusivity. The thermal diffusivity of the studied substrates increased with increasing sample bulk density and sand content; decreased with increasing organic matter content.