Improving thermal performance of rammed earth walls using expanded clay aggregate

Abstract

The use of earth as a building material dates back to the beginning of our civilization. In the South of Portugal there is still a large number of buildings with rammed earth walls, but this technology has been falling into disuse since the middle of last century. The earth construction is highly sustainable since earth is a local material and is 100% reusable. The buildings with rammed earth walls have a high thermal inertia which, given the climate characteristics Portugal, improves its thermal behaviour. However, it is desirable that the thermal conductivity of the rammed earth were lower. Environmental concerns related to energy consumption associated with comfort in housing and construction, transportation and application of materials used in construction, has led us to seek new solutions in building typologies on earth. Considering these aspects and improving the energy efficiency in buildings, this paper presents the results of tests performed in the laboratory on building new solutions on earth. Geotechnical characterization of the soil used was made and various compositions prepared with the incorporation of expanded clay. The expanded clay was chosen as a thermal insulator made from raw materials available in the regions of Alentejo and Algarve (South of Portugal), which are the regions that are famous for using rammed earth in Portugal. Compositions were considered soil and expanded clay having the following percentages of expanded clay: 0%, 10%, 15%, 20% and 25%. In order to characterize the different compositions from the point of view of mechanical and thermal performance, cubes were produced with 10 cm edge and assayed in order to calculate its compression resistance and its thermal conductivity. The results showed that the use of this type of building typologies on earth with the incorporation of expanded clay allows to increase your performance by making it possible to adapt this typology needs of today, including the demands of the Portuguese legislation. The results of this research can be applied, with the appropriate adaptations, both in buildings in rammed earth and in buildings in adobe. Through the testing conducted, the value of the thermal conductivity of the soil sample was obtained and it equals to 1.08 W/m.°C. To a mixture of soil and expanded clay containing 25% expanded clay 2-4, we obtained thermal conductivity of 0.79 W/m.°C.