Thermal performance of plastered rice straw bales and walls: A case study

Abstract

Straw, as a fiber, has been used as part of building materials for several years. A carefully constructed strawbale building has excellent thermal performance because of the combination of the high isolative value of the bales and the thermal mass provided by the thick plaster coating of the interiors. This paper addresses the thermal performance of rice straw bales and walls plastered with different cement plaster mixes. The plaster mixes are applied on straw bales of thickness 45 cm. A fire resistance test is conducted for two complete h°urs on the bales using direct flame after which the flame was discontinued. According to the test results, the mix with equal parts of cement and lime showed acceptable mechanical properties. This mix is chosen to be applied on a prototype straw bale wall compartment with an aim to evaluate the thermal performance of the plastered straw bale walls in arid desert climate at the hottest month of the year in Egypt. The straw bale wall test is undertaken by collecting actual measurements on site. Thermal sensors are installed on both external and internal sides of the wall to record the heat transmission through the plastered walls. The results showed that all the plastered bales survived fire penetration for the life period of the test. Increasing the lime content and decreasing the cement content of the mix raises the possibility of weak areas in the plaster of straw bale walls causing cracks during direct fire exposure. Similar width and density of the bales for all the specimen mixes didn't affect the heat transmission through the bales, which did not exceed 5.3°C in all samples. The site readings on the straw bale walls showed high range of temperature fluctuation on the external wall sensor, while in the internal wall sensor the temperature fluctuation was kept to minimum values. It was concluded that due to their high thermal insulation, straw bale structures require comparatively less energy to sustain thermal comfort conditions. © 2011 WIT Press.