Re-baling straw for better insulation
Agricultural straw bales, produced as a co-product of cereal crops such as wheat and rice, have been used in construction worldwide for over 100 years, but despite their favourable low environmental impact, sustainable supply chain, and good thermal insulation properties their use has remained largely niche compared with other competing products. However, straw bales have remained sub-optimal for building performance or practically for construction. The current study seeks to improve the insulation qualities of straw by manufacturing bales specifically for construction applications, with the straw stems oriented to maximise available thermal resistance. Technical development and characterisation of an insulating material produced from wheat straw, for use in conjunction with typical timber-framed construction for example, is reported. The paper describes aspects of developing an insulating prototype made from wheat straw, where the thermal properties relative to the orientation of the straw are investigated. Straw orientations other than that produced by traditional baling equipment, and on a scale designed for ease in construction use, require modified equipment. The design and development of small-scale baling equipment for the laboratory is presented. A series of small-scale thermal conductivity tests demonstrate the potential for improved performance through consideration of various straw orientations. Controlling the orientation of the individual straws results in improved thermal resistance, allowing thinner walls than conventional agricultural bales. Straw needs to be baled to specific thicknesses to support uptake in wider construction. With the capability of re-baling the straw into desirable dimensions, the overall width and length of a straw bale can be designed to fit with standard construction. This research will enable greater uptake of a novel low embodied carbon bio-based material into mainstream construction.