Study On Moisture And Heat Transport Perpormance For Block Portland Concrete And Foam Concrete Material

Moisture and heat transfer performance of porous materials is remarkably affected by temperature and water content. The variations of temperature and humidity in which indoor and outdoor will change temperature distribution and moisture distribution within wall materials, which makes corresponding alterations of moisture and heat transfer performance, and it impacts thermal insulation performance and durability of sandwish external wall further. In this paper, by implementing experiment scheme of moisture and heat transfer performance that block concrete and foam concrete, how water saturation degree influence moisture and heat transfer performance will be studied.Water permeability of block concrete and foam concrete is measured by indirect method in this paper, thus the relationship of water permeability and water saturation degree is studied. Under constant temperature, isothermal absorption test is conducted by unchanged relative humidity that is controlled by saturated salt solution method, Isothermal absorption test data is fitted regressively by GAB model and thereby the relationship of water saturation degree and relative humidity is determined; by employing water retention curve model proposed by Zhou Chunsheng to fit water retention curve data regressively, the relationship of capillary capacity function and water saturation degree is calculated; capillary water absorption of thick specimens within different water saturation degree is tested by capillary suction device. Based on theoretical relationship of capillary water absorption and initial water saturation degree when hydraulic diffusivity submits to exponential law, by fitting relationship of capillary water absorption and initial water saturation degree, shape parameter and initial hydraulic diffusivity is confirmed, then hydraulic diffusivity is calculated indirectly; according to capillary capacity function and hydraulic diffusivity, the relationship of hydraulic conductivity and water permeability respectively and water saturation degree is obtained further. The results indicate that, with the increase of water saturation degree, capillary water absorption and relative capillary water absorption are on a declining curve, hydraulic diffusivity, hydraulic conductivity and water permeability are rising exponentially.Combining isotherm absorption experiment and vacuum saturation experiment, thermal conductivity of block concrete and foam concrete under different water saturation degree and after saturated respectively is measured by thermal conductivity test equipment, the relationship of thermal conductivity and water saturation degree is derived. The results manifest that, as water saturation degree is gaining, the thermal conductivity of foam concrete is on linear increase slowly, linear upward trend of thermal conductivity of block concrete appears unconspicuous.Under the condition of constant temperature, moisture transmission within different relative humidity gradient is tested by employing cup method, water saturation degree of block concrete and foam concrete within different relative humidity and associated water vapor diffusivity is calculated by adopting Bazant method. The results show that, with water saturation degree increasing, water vapor diffusivity of block concrete and foam concrete presents a rising trend.