Plant Biomass Used for Green Concrete: A Review of Treatment Methods

Abstract

Human activities require a growing need for raw materials. In order to contribute to sustainable development, many business sectors are focusing on biomass valorization. Whether from dedicated crops or first industrial processing, it generates materials with high potential that can be used in many fields. Non-food uses mainly concern the energy, chemical, and construction sectors. Whatever the intended application, a pre-treatment stage is essential to clean the material and/or to access a specific fraction. An additional modification may occur in order to endow the material with a new function thanks to a process known as functionalization. Uses of plant fractions (aggregates) in combination with cement offer advantages like low-density materials with attractive thermophysical properties for building. However, their development is limited by the compatibility of crop by-products with hydraulic binders such as Ordinary Portland Cement (OPC). This includes delays in setting time and hydrophilic character of vegetal components and their interaction with an alkaline environment. The aggregate/cement interfaces can therefore be strongly affected. In addition, the diversity of crop by-products and mineral binders increases the level of complexity. In order to overcome these drawbacks, the treatment of plant fractions before their use with mineral binders may result in significant benefits. In this way, various treatments have been tested, but the methods used at an industrial scale remain relatively under-researched. The purpose of this review is therefore to highlight the mechanisms involved in each specific process, thus justifying the operating conditions specific to each. This bibliography study aims to highlight potential treatments that could apply to biomass before their mixing with cementitious binders. According to the objective, a distinction can be made between extraction processes as hydrothermal or solvent treatments, assisted or not, and structural modification processes as surface treatments, impregnation, or grafting.