Earth as a building material is increasingly being studied for its low environmental impact and its availability. Plant aggregates and fibers have been incorporated into the earth matrix in the aim of enhancing performance for thousands of years but scientific studies began quite recently. The present paper reviews the state of the art of research on the influence of these various natural and renewable resources in unfired earth materials such as compressed earth blocks, plasters, and extruded and stabilized blocks. This review, based on 50 major studies, includes characterization of the particles and treatments, and recapitulative tables of the material compositions, and the physical, mechanical, hygrothermal and durability performances of earth-based materials. A lack of references on hygroscopic and durability properties was observed. Future research orientations are thus suggested to promote and develop this type of sustainable material, which provides a solution for saving energy and natural resources. Highlights Earth-based products with plant aggregates as a sustainable material are reviewed.  Physicochemical and mechanical properties of plant aggregates or fibers are reviewed.  Mechanical, hygrothermal and durability performances of the composites are reviewed.  Further investigations are needed to promote these materials.

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Expanding the use of low-environmental impact materials in the field of building materials is a major aim in a context of sustainable development. These alternative materials should be non-polluting, eventually recycled, and locally available. Bioresources are already used in some building materials but few studies have investigated their relevance in such applications. The aim of this paper is to evaluate the suitability of three kinds of vegetal aggregates: barley straw, hemp shiv and corn cob. The availability of these bioresources, extracted from a French database, is discussed, as are their physical properties and chemical compositions. Their microstructure is described with SEM images and their particle size distributions are provided through image analysis. Sorption-desorption isotherms are measured by a Dynamic Vapour Sorption system. Bulk density, thermal conductivity and water absorption are also quantified. The results highlight a tubular structure for the three different aggregates, with low bulk density and thermal conductivity (0.044, 0.051 and 0.096 W.m-1 .K-1 respectively for straw, hemp shiv and corn cob) and high water absorption, especially for barley straw and hemp shiv (414 and 380% vs. 123% for corn cob). Their hygric regulation capacity is also sufficiently good, with a water sorption of between 20 and 26% at 95% of relative humidity. These plant aggregates could therefore be used as additions in an earth matrix, or a hydraulic, pozzolanic, air lime or gypsum binder, or just as loose-fill insulation material. However, future research should focus on their resistance to fire and bacterial growth to validate this approach.

This recommendation is the outcome of research conducted by a working group within the RILEM Technical Committee 236-BBM 'Bio-aggregate-based building Materials'. The work of the group related to the study of construction materials made from plant particles. The major raw material utilised being renewable, recyclable and easily available plant particles. These particles are obtained from the processing of hemp, flax, miscanthus, pine, maize, sunflower, bamboo and other plants. In this report, the outcome of the Round Robin Testing is centred on hemp because hemp shiv is the bio-aggregate that is the most widely used in building materials and the most studied in the literature. The first round robin test of the TC-BBM published in the State of The Art Report of Technical Committee 236-BBM 'Bioaggregate-based building Materials' was carried out This recommendation was prepared by a working group within RILEM TC-236 coming from eight laboratories:

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. From the experimental characterization of the hygrothermal properties of straw-clay mixtures to the numerical assessment of their buffering potential. Building and Environment, Elsevier, 2016, 97, pp.69 -81. 10.1016/j.buildenv.2015 1 From the experimental characterization of the hygrothermal properties of straw-clay mixtures to the numerical assessment of their buffering potential ABSTRACTThe development of innovative materials has to respond to both environmental and energy concerns. Bio-based materials are relevant because they are made from renewable raw materials and are carbon neutral. Similarly, unprocessed earth has a very low embodied energy. In this paper, the basic hygrothermal properties of straw-clay samples provided by two French companies were determined. Mixes with densities lower than 450 kg.m -3 would be suitable for use as self-insulating material in current construction. In addition, the material showed a high sorption capacity and very high water vapour permeability. The measurements were then implemented in a numerical model in order to simulate the hygric response of a small room. The straw-clay mixture was found to have a moisture buffering effect of the same magnitude as walls made of hemp concrete and largely higher than conventional walls. The influence of various indoor finishing materials was investigated through additional simulations.

Effect of plant aggregates on the mechanical properties of earth bricks 25 26 ABSTRACT 27A building material is mainly characterized by its mechanical performance, which 28 provides proof of its quality. However, the measurement of the compressive or 29 flexural strength of an earth-based material with plant aggregates, which is very 30 ductile, is not fully standardised. The objective of this study is to determine the 31 compressive and flexural strengths of a composite made of earth and 0%, 3% or 32 6% of barley straw, hemp shiv or corn cob. Given the manufacturing processes 33 available, cylindrical compressed specimens were studied in compression 34 whereas extruded specimens were studied in flexion. Two protocols were tested 35 for compressive strength measurements: one with direct contact between the 36 specimen and the press, and the other with reduced friction. The test with 37 reduced friction engendered a huge decrease of the stress and a slight decrease 38 of the strain. For both compressive and flexural strengths, the specimens made 39 of earth alone were the most resistant, followed by composites containing straw. 40

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