MECHANICAL BEHAVIOR OF STRAWBALES FOR USE IN CIVIL AND RURAL CONSTRUCTION

Over the last thirty years, the use of strawbales as a construction material has re-gained a lot of popularity for several reasons: baled straw has superior thermal insulation properties; buildings made with straw-bales are less expensive; straw is a by-product, hence its usage can help reduce the costs and emissions related to its disposal; structures built with strawbales can resist earthquakes better than those built according to traditional techniques. In the context of using materials and techniques sustainable for the environment, strawbale construction appears a more than promising choice establishing a strong link with the territory as well. Indeed, straw has been extensively used as a construction material since pre-history; more recently, strawbale houses were built in Nebraska at the end of the 19th century. The use of strawbales in construction returned popular in the late 80's (King, 2003); in some countries, this has been also supported by the development of design standards. In Italy, the lack of similar codes represents an obstacle; the procedure to have a design approved is tedious and discourages builders. In spite of this, however, strawbale houses have been and are currently being built. A deep understanding of the mechanical behavior of straw and of the material typically used in the rendering of strawbale walls is crucial for the development of construction techniques employing load-bearing strawbale walls. In the literature, studies on the mechanical properties of strawbales and strawbale assemblies have appeared since the rediscovery of this construction technique (Zhang, 2000; Vardy, 2009). Such studies report results of experimental tests conducted on single bales and on stacks of multiple bales, plastered or unplastered, loaded both on-edge and flat. However, very few of them provide some modeling to substantiate the results. In this paper, a review of the relevant literature regarding the mechanical properties of single unplastered straw bales is proposed and critically analyzed in order to provide guidance for future modeling; furthermore, the procedure for a comparative LCA between the options of building with conventional materials and with straw bales is sketched out and preliminary results of such an analysis are discussed.