Florence Collet

Bio-aggregates Based Building Materials

Global warming, energy savings, and life cycle analysis issues are the factors that have contributed to the rapid expansion of plant-based materials for buildings, which can be qualified as environmental-friendly, sustainable and efficient multifunctional materials. These materials are obtained from the processing of hemp, flax, miscanthus, pine, maize, sunflower and bamboo. The work of the Technical Committee (TC 236-BBM) was dedicated to the study of construction materials made from plant particles. Are concerned building materials containing as main raw material renewable, recyclable and easily available plant particles. However, the work was relatively 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. This state-of-the-art report reflects the current knowledge on the assessment of the chemical, physical and mechanical properties of bio-aggregate and vegetal concrete. It presents an overview on the several possibilities developed worldwide about the use of plant aggregate to design bio-based building materials. The first five chapters relate to the description of the vegetal aggregate. Then, hygrothermal properties, fire resistance, durability and finally the impact of the variability of the method of production of bio-based concrete are assessed on Chaps. 7-9.

Development and hygric and thermal characterization of hemp-clay composite

Abstract This study investigates the use of clay as binder in hemp composite and compares hemp–clay composite to hemp–lime concrete. The clay is produced from washing mud from gravels production site. Two clay drying temperature are used. The thermal properties are measured with a hot wire method and the hygric characterization is based on the measurement of Moisture Buffer Value. Performances obtained on clay blocks, hemp–clay composite and hemp–lime composite are compared. The results show that the two clay drying temperatures do not impact on the thermal conductivity nor on the moisture buffer value of clay blocks. Hygric and thermal performances of hemp–clay and hemp–lime composites with the same density are close. These materials act as excellent hygric regulators. Performances measured separately on hemp and clay underline an interesting synergetic effect in the case of hemp–clay composite leading to a higher ability to the moisture buffering. Such material can be advantageously used in buildings to moderate indoor humidity variations.

Influence of hysteresis on the transient hygrothermal response of a hemp concrete wall

Building envelopes with bio-materials like hemp concrete are currently undergoing an increasing development due to their low environmental impact and their interesting hygrothermal properties. This kind of hygroscopic material is characterized by a hysteretic behaviour. In this paper, the influence of such behaviour on the hygrothermal response of a building wall is discussed. An experimental facility is designed to measure temperature and relative humidity within a hemp concrete wall submitted to climatic variations. This facility provides a set of experimental data suited for benchmarking. Numerical simulations are performed with a hysteresis model implemented in a heat and moisture transfer model. Comparisons between numerical and experimental results show that hysteresis modelling is relevant to simulate the hygrothermal response of the wall. The discussion is extended to the influence of the initial moisture content.

Hygric and Thermal Properties of Bio-aggregate Based Building Materials

This chapter gives the state of the art of previous studies on hygric and thermal properties of bio-aggregate based building materials. Firstly, hygric characteristics such as sorption isotherms, water vapor permeability and moisture diffusivity are given. The ability of bio-aggregate based building materials to moderate ambient relative humidity may be valued using moisture buffer value. Then thermal properties (thermal conductivity, thermal diffusivity conductivity and specific heat capacity) are reported. Finally, concluding remarks on hygrothermal behavior with simultaneous heat and mass transfer are provided, they underline that considering only thermal conductivity and specific heat capacity is not sufficient to evaluate the energy performance of bio-aggregate based building materials. The results found in bibliography mainly concern wood-based and hemp-based materials.

Numerical Tool for the Evaluation of the Hygrothermal Performance of a Hemp-Lime Concrete

Hemp concrete is a non-loadbearing material used as filling material to form the building envelope. Hemp concrete is an hygroscopic bio-material characterized by a strong hysteretic hydric behavior and interesting thermal conductivity. A numerical tool able to model the hysteretic behavior of the hemp concrete sorption process is presented. The implementation of a suited hysteresis model in a heat and moisture transfer model allow evaluating and discussing the influence of this phenomenon in the transient hygrothermal response of hemp concrete to hydric loadings. The governing system of strongly coupled unsteady differential equations is implemented in Matlab with a finite differences method. Numerical transient hygrothermal responses of hemp concrete submitted to cyclic hydric isothermal loadings are then produced and compared with experimental results.