Characterization and comparison of hygric properties of rape straw concrete and hemp concrete M. Rahim ⇑ , O. Douzane, A.D. Tran Le, G. Promis, T. Langlet Laboratoire des Technologies Innovantes (LTI), University of Picardie Jules Verne, Avenue des Facultés – Le Bailly, 80 025 Amiens Cedex 1, France highlights  New bio-based material called ‘‘straw lime concrete” (SLC).  Experimental protocol validation (hemp lime concrete (HLC); the reference material).  Moisture properties characterization.  The both materials (SLC and HLC) exhibit an ‘‘excellent” moisture buffer capacity. article info Article history: Received 11 February 2015 Received in revised form 7 October 2015 Accepted 5 November 2015 Available online 13 November 2015 Keywords: Straw lime concrete Hemp lime concrete Hygric properties Moisture buffer capacity Moisture penetration depth abstract The use of plant particles as aggregates in construction materials provide a very good hygric performance, and offers a real contribution to sustainable buildings. This paper focuses on the hygric properties of a new bio-based material called ‘‘rape straw lime concrete” in comparison with a ‘‘hemp lime concrete” which is used to validate the experimental protocol of this work. The tests are conducted on the sorption isotherm, the water vapor permeability, the capillary water absorption and the moisture buffer capacity which is estimated from the moisture buffer value determined under equilibrium condition. The results showed that the materials have very interesting hygric properties and exhibit an excellent moisture buffer capacity. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction The building sector strongly affects the environment and gener- ates waste and emissions of pollutants acting on the environment and indoor air quality. In this context, there has been an increase in the use of vegetable particles as building material aggregates. Among them, different natural building materials have been stud- ied such as: straw-clay [1], flax shives [2,3], diss [4], cork [5], sug- arcane [6,7], straw bales [8,9]. Currently, hemp lime concrete (HLC) has been extensively studied in many researches [10–13]. This material suggests a low overall environmental impact [14,15]. The hemp concrete enables to store approximately 14–35 kg of CO 2 per square meter of wall built with a thickness of 25 cm over a period of 100 years [16]. Due to its insufficient mechanical performance [10,17], hemp concrete is mainly used to cover the walls of masonry or to fill the timber-framed structures in new and old buildings. Likewise, it can be used to isolate the roofs or floors. Compared to the stan- dard building materials, hemp concrete has a low conductivity (0.1 W/(mK)) which reduces heat diffusion and hence reduce energy consumption [17–19]. In addition, HLC has a good moisture buffer capacity [3,12,20,21], according to the classification pro- posed by the Nordtest project [22]. At the whole building level, numerical and experimental results showed that hemp concrete can reduce the indoor RH variation and leads to reduce energy con- sumption [23,24]. Regarding its thermal conductivity, this one depends on its den- sity, its formulation and its water content. The thermal conductiv- ity increases less than 15–20% in a wide range of relative humidity, and the water content has a lower effect on thermal conductivity than the density [18]. Referring to a study of Benfratello [25], the dry thermal conductivity increases from 0.09 to 0.14 W/(mK) – i.e. 55% – in a density range from 370 to 600 kg/m 3 at 15 °C. From the hygric point of view, hemp concrete has a high mois- ture diffusion coefficient; its water vapor permeability is approxi- mately 2.3  10 11 kg/(Pams) and is nearly constant for a low or middle relative humidity [3,11]. In addition, the hemp lime http://dx.doi.org/10.1016/j.conbuildmat.2015.11.021 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: mourad.rahim@u-picardie.fr (M. Rahim). Construction and Building Materials 102 (2016) 679–687 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat