THESIS ABSTRACT

Abstract

The energy requirements and environmental protection in buildings have been improved in line with the growing needs, thus placing the thermodynamic properties of building materials and fabrication of alternative walling products in centre stage as a cost effective and environmentally friendly material. Although conventional clay brick has a relatively poor thermal performance, high environmental damage during production phase, high economic cost, most people in Nepal still prefer it as the main walling materials. Aerated Concrete (AAC) shows a promising material because of the properties it offers related to its light weightness, thermal conductivity is low and less impact to the environment. This study aims to analyze the sustainability of the AAC blocks in building construction in Nepal considering their thermal performance, carbon emission and life cycle cost (LCC) along with conventional fired clay bricks. The research was carried out by utilizing experimental and analytical research methodology. The thermal performance had been tested in the lab that had been done following the Guarded Hot Plate Method (ASTM C177) and compared with the previous literature value and the tested thermal conductivity value for AAC blocks was obtained from accredited lab based on the principles of Guarded Hot Plate Method (ASTM C177). The average result of thermal conductivity shows that was AAC gives 0.18 W/m·K, while that of fired clay bricks was 0.81 W/m·K which denote a much lower thermal conductivity of AAC than fired clay bricks. However, the ACC block of 150 mm thickness is found to be thermally resistant as 0.83 m²·K/W as compared to brick wall of 100 mm thickness. The U- value was also much lower for AAC masonry which was 1.21 W/m²·K, compared with 8.13 W/m²·K for brick masonry. The temperature difference of 20°C created a heat flux of around 162.6 W/m² for brick masonry and 24.2 W/m2 for AAC masonry, it was found that there is a reduction of around 85% transfer of the heat flux. The above results indicate that use of AAC blocks offer significantly better insulation and can be used to slow down the heat transfer through the walls of a building. The environmental analysis for objective 2 did show a definite gap in the carbon emissions of the two walling products produced. As a result of the assessment, it was determined that the CO₂ produced from AAC production is around 270 kg CO₂/m3 while fired clay bricks produced an average of 649-1026kg CO₂/m3 depending on the type of kiln used. It is estimated from these results that the CO₂ reduction associated to block production with AAC bricks compared to fired clay bricks could range between approximately 58–74%. An economic study was also conducted for Objective 3 and indicated that AAC Masonry was more economical with estimated initial construction cost of NRs. 12,175.85/m³ compared with NRs. 17,721.08/m³ for brick masonry, which resulted in an initial cost savings of approximately 31%. Again Sensitivity analysis was conducted to see the behavior of energy savings per year on the change of the thickness of brick and AAC block, temperature difference below the blocks and temperature difference between the brick layers. The study reveals AAC blocks yield good thermal, cost and carbon emission performance compared to conventional fired clay bricks in overall. Thus AAC blocks may prove to be a viable and sustainable option to the Nepalese residential buildings.

Keywords

Autoclaved Aerated Concrete (AAC), Fired Clay Brick, Thermal Conductivity, Thermal Resistance, Overall Heat Transfer Coefficient, Heat Flux, Carbon Emissions Energy Efficiency, Sustainable Construction