Thermophysical Properties of Cement Mortar Containing Waste Glass Powder

This study aims to provide a thermophysical characterization of a new economical and green mortar. This material is characterized by partially replacing the cement with recycled soda lime glass. The cement was partially substituted (10, 20, 30, 40, 50 and 60% in weight) by glass powder with a water/cement ratio of 0.4. The glass powder and four of the seven samples were analyzed using a scanning electron microscope (SEM). The thermophysical properties, such as thermal conductivity and volumetric specific heat, were experimentally measured in both dry and wet (water saturated) states. These properties were determined as a function of the glass powder percentage by using a CT-Meter at different temperatures (20 °C, 30 °C, 40 °C and 50 °C) in a temperature-controlled box. The results show that the thermophysical parameters decreased linearly when 60% glass powder was added to cement mortar: 37% for thermal conductivity, 18% for volumetric specific heat and 22% for thermal diffusivity. The density of the mortar also decreased by about 11% in dry state and 5% in wet state. The use of waste glass powder as a cement replacement affects the thermophysical properties of cement mortar due to its porosity as compared with the control mortar. The results indicate that thermal conductivity and volumetric specific heat increases with temperature increase and/or the substitution rate decrease. Therefore, the addition of waste glass powder can significantly affect the thermophysical properties of ordinary cement mortar.

Ideal thermophysical properties of building wall: Method based on impedance and interpretation mechanism

Thermal resistance is commonly defined as the ratio of the temperature difference to the heat flow, and it is only valid for one-dimensional, steady heat conduction without an internal source. This work extends the application scope of the thermal resistance to the multi-dimensional, unsteady conditions based on the entransy dissipation rate, which is called impedance. It provides an approach to optimize the heat transfer process of complex problems. For example, it can be used to analyse the unsteady heat transfer of building envelope: when the indoor and outdoor temperature difference is given, the extremum of building envelope thermal resistance is corresponding to the extremum of heat input to the interior from envelope, which is determined by the ideal volumetric specific heat distribution versus temperature of building envelope. Based on this, the relationship between thermal resistance and volumetric specific heat of building envelope is developed, and according to the extremum of thermal resistance, the ideal volumetric specific heat can be obtained. In this paper, applications are presented for active and passive conditions. The results show that, for active or passive condition, the ideal volumetric specific heat of the external wall should be a δ function in summer or winter.

THERMAL PROPERTIES OF MALAYSIAN COHESIVE SOILS

The thermal properties of soils surrounding energy piles are required for the efficient and optimal design of shallow geothermal energy pile systems. In this study, the thermal conductivity, thermal resistivity and volumetric specific heat of two types of Malaysian cohesive soil were obtained through a series of laboratory experiments using a thermal needle probe. This study was conducted to determine the effect of moisture content on the thermal conductivity, thermal resistivity and volumetric specific heat values of the cohesive soil at a given value of soil density. For soils with low to medium moisture content, a linear increase in the thermal conductivity and volumetric heat capacity was observed as the moisture content gradually increased, while the thermal resistivity values of the soil had decreased. Meanwhile, for soils with high moisture content, the thermal conductivity was observed to have decreased, and a marked increase was seen in the thermal resistivity. This is due to the disruption of the thermal flow continuity in the soil matrix with the presence of moisture in the soil which adversely affects the thermal conductivity