Effects of the nature of atmosphere during thermal treatment on chemical compositions and properties of miscanthus. Application to miscanthus-filled concrete

Abstract

International audienceAmong the difficulties of preparation of ligno-cellulosic biomass-filled concrete are its hygroscopicity, its sensitivity to degradation in strong alkaline media and its probable low resistance to micro-organisms. Among the many methods have been explored and tested to solve these difficulties. We are reporting here the use of high temperature thermal treatment. We applied heat on miscanthus with the hope to reduce hygroscopicity, enhance alkali resistance and dimensional stability, without using any chemical treatment. The effects of heat treatment atmosphere on chemical modifications and behaviours of treated miscanthus were investigated. The parameters which were varied were atmospheres (vacuum and nitrogen), time and treatment temperature. Mass loss, with closely related to the degree of miscanthus modifications is the parameter used to control the treatment conditions. At the same treatment intensity, miscanthus treated under nitrogen has lower mass loss than those treated under vacuum. Under vacuum, volatile degraded products are continuously removed, which can help to stop their recondensation or cross linking reactions occurring on the surface of miscanthus stems. Reductions in water absorption and in mass loss in alkali medium with thermally treated Miscanthus are observed. The hydrophilicity of treated miscanthus is expected to decrease. The resulting products likely have an improvement in decay resistance due to the removal of hemicelluloses which are low stability and are mostly degraded during treatment. At elevated temperature, cellulose and lignin are also modified. After thermal treatment, miscanthus chips were used to prepare lightweight concrete blocks with a common Portland cement as a binder. The amount of sugars released during concrete preparation process, which can contribute to the inhibition of cement hydration or delay in cement setting time, was determined. The interactions between miscanthus chips and cement were characterised. We will evaluate the potential of this method for improving concrete preparation