Characterization of Barley Straw, Hemp Shiv and Corn Cob as Resources for Bioaggregate Based Building Materials

Abstract

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.

Earth-based mortars for repair and protection of rammed earth walls. Stabilization with mineral binders and fibers

“…The wet bulk density of the fresh mortars is also reported in Table 4. The mortars with hemp fibers exhibit lower bulk density which is in accordance with the lower bulk density of these fibers in comparison with the other mortar materials (Arizzi et al, 2015;Laborel-Préneron et al, 2017).…”

Laboratory test to assess sensitivity of bio-based earth materials to fungal growth

“…Harper and Lynch [55] have shown that lignin is resistant to microbial attacks. According to a previous paper [56], a lignin content of 17.2% was determined for hemp shiv, while it was only 5.5 for barley straw. This high resistance of hemp to fungal growth was already observed by Sedlbauer et al [57], who showed that hemp had no risk of developing any mold at all below 95% of RH, whatever the temperature, while mold proliferation on straw was likely to occur from 70% RH.…”

Impact of Bio-Aggregates Properties on the Chemical Interactions with Mineral Binder, Application to Vegetal Concrete

“…230 000 tons of by-products were produced each year due to this agricultural crop. In comparison, only 17 000 t/year of hemp by-products are available (Laborel-Préneron et al 2018).…”