Thermophysical Properties of Porous Building Materials

Abstract

This dissertation was aimed to investigate the thermophysical properties of commercial building materials and lab-made bio-waste added fired clay bricks for sustainable energy conservation in buildings. The commercial bricks were intentionally saturated by NaCl solutions of different molar concentrations (0-5 M) for 10 days and then freeze-dried for halite crystallization. Lab-made bricks were prepared by addition of tea-waste, sawdust, and wheat straw in different proportions into the clay. The composite clay bricks were dried and then, sintered in an electric furnace at two different temperatures (500°C and 980°C). Different building stones were taken from market whereas limestones differing in elevation range were taken from a mountain. The thermal properties of building materials were measured by Transient Plane Source (TPS) technique and ASTM standards were followed for physical characterization of the brick samples. The proximate analysis, FTIR, SEM-EDS, XRD analysis, and SEM analysis were carried out to elaborate the chemical, mineral, structural and morphological properties of the samples. Results showed that the moisture and NaCl concentration significantly increased thermophysical properties of brick samples and this adverse effect was discussed by considering thermal properties of NaCl solutions, diffusion rate and saturation period. While thermophysical and mechanical properties of bio-waste added bricks were decreased due to change in mineral composition and porosity generation by inflammable nature of bio-waste. However, compressive strength of lab-made bricks were in the acceptable range specified by Pakistan Building Code (i.e. > 5 MPa). On comparison with commercial brick, 2-4 wt.% tea waste, 2-6 wt.% sawdust and 1-2 wt.% wheat straw addition were suitable for production of thermally insulated, mechanically strong, and environmentally friendly bricks. Thermophysical analysis of building stones showed graphical relations for the assessment of thermal conductivity from the physical properties. Experimental and predicted thermal conductivity of limestones at moist and dry states showed that in situ measurement is necessary for precise determination of thermal properties. The variations in thermal properties of limestones as a function of temperature were described by considering mineral compositions and heat transfer mechanism. The overall results suggest that the spinoff of this work is a helpful resource for up to date and accurate information about thermophysical properties of building materials and new fired clay bricks products for energy savings in buildings.