Influence of sawdust and flax shives on the high temperature mechanical behavior of earthen materials

Abstract

Earthen materials have recently made headlines due to their high potential reuse in the construction industry. The growing request of earth-based materials is hampered by the lack of information on the fire behaviour of these materials, in particular for issues of instability. Vegetal additions are frequently used in earth construction because they stabilize the clay fraction’s shrinkage property and improve their insulating capacity. The current study focuses on the role the vegetal additions could play in their implementation inside earthen materials, specifically in terms of the latter's high temperature behavior. At various percentages, sawdust and flax shives were added to a raw earth mix. The percentages of those vegetal additions in the earthen matrix ranged between 0 and 7.5 percent of the dry weight of soil. The used additions were characterized before being mixed with soil that was itself characterized also. The manufactured specimens were therefore made up of a mix of raw earth soil mixed with water and vegetal additions, with the characteristics of each addition considered. The specimens were then heated to high temperatures in a furnace programmed to achieve target temperatures of 150 °C, 300 °C, 500 °C, 600 °C and 800 °C at a heating rate of 1 °C/min. The specimen’s residual mechanical properties were then examined. In the absence of vegetal additions, the compressive strength of the specimens increased with temperature. But, the addition of vegetal additions led to a decrease in strength between 150° and 300 °C, which is greater as the percentage of vegetal additions increased. For a lower mass percentage of vegetal additions (2.5%), the compressive strength increased again between 300 °C and 500 °C; and then between 600 °C and 800 °C for all the tested dosages. The comparison between the two types of vegetal additions illustrated the unfavourable influence of a larger size of additions on the residual properties of specimens. In terms of their contribution to the previously determined properties, the sawdust addition outperformed flax shives.