Thermal performance of unfired lightweight clay bricks with HDPE & PET waste plastics additives

Abstract

The main objective of this study is to investigate the effect of incorporation of wastes plastics additives in the thermal performance of unfired clay bricks. The low adhesion between the clay and polymer molecules, in general, is one of the major challenges faced while blending the two components. In this paper, an innovative brick preparation technique known as the melt compounding preparation is suggested to ensure a homogenous clay-polymer dispersion and a maximum polymerization intensity inside the brick matrix. Various proportions for both polymeric, High Density Polyethylene (HDPE) & Polyethylene Terephthalate (PET), plastics wastes additives, in three grain-size are added to the earth clay. Prepared samples were tested for thermal conductivity, specific heat capacity, time lag and decrement factor properties. Collected findings showed that thermal conductivity and specific heat capacity properties improved by 40% and 55%, respectively, with the incorporation the largest polymeric-grain additives (3 mm < δ ≤ 6 mm) compared to the smallest ones (δ ≤ 1 mm). This can be explained by the high porosity produced while using larger grain-size additives. Maxwell thermal-porosity mathematical model is also used to assess the theoretically predicted thermal properties of the brick samples and compare it the experimental findings. The computed Pearson Correlation Coefficient ‘R’ is found to be very close to 1; hence, reflecting a positive association between the experimental and theoretical results. Next, a dynamic thermal inertia via a thermal simulation of a 6 m × 5 m x 2 m reference house, with variable external wall thicknesses, is executed to analyze the time lag and decrement factor of the studied brick samples. The composition of the wall is based on the experimental results of the brick samples with the optimum compressive strength, deduced from previous work, and thermal performance, in the current study. An improvement in thermal stability, with increased time lag and decreased decrement factor, is observed with larger grain size additives and thicker external walls. As a matter of fact, for a 0.3 m thick external wall made of PET based samples, the recorded time lag and decrement factor was 13.50 h and 0.148, respectively, compared to 8.99 h and 0.346 for reference values. This represents very high gains in dynamic thermal inertia properties in the range of 50% and 57% for time lag and decrement factor, respectively, compared to reference values, meaning cutting the house's energy expenses in half.