Modeling and experimental characterization of effective transverse thermal properties of hemp insulation concrete. (20th November 2018)

• Record Type: Journal Article
• Authors: Somé, Saannibe Ciryle; Ben Fraj, Amor; Pavoine, Alexandre; Hajj Chehade, Mohamad
• Is Part Of: Construction & building materials. Volume 189(2018)
• Page Start: 384
• Page End: 396
• Publication Date: 2018-11-20
• Subjects: Hemp concrete -- Hot film method -- Thermal conductivity -- Homogenization; Building materials -- Periodicals; 624.18
• DOI: 10.1016/j.conbuildmat.2018.08.210
• Languages: English
• ISSNs: 0950-0618

Abstract

Graphical abstract: Highlights: An experimental setup for thermal properties characterization is developed. 4-phases self-consistent scheme is used to predict the thermal conductivity. Effects of shiv-to-binder ratio, curing condition and type of binder are studied through ANOVA. Abstract: Hemp concretes gain more and more interest in house building field because of their thermal properties. They are expected to be suitable and sustainable insulation materials. They are heterogeneous composite materials mainly produced with natural cement and hemp shivs. As insulation materials, their thermal properties characterization remains a challenge due to their high porosity which induces internal heat radiation and their low thermal conductivities which causes lateral heat loose in the experimental setups. This study presents an inexpensive and reliable experimental setup development, based on hot film method. It allows to determine the transverse conductivity of materials. Laplace integral transform and Green function solution methods have been used to determine analytic solutions of the heat conduction in the tested specimens. The thermal properties have been evaluated based on the asymptotic approximations of these solutions. Two binders noted "B" and "V" have been characterized by XRD and used to produce hemp concrete mixes. In addition, three shiv-to-binder ratios (S/B = 0.40, 0.50 and 0.67 by mass) have been considered in view of the thermal properties assessment. This variation of S/B ratio induces a variation of the densities and the air void contents of the concretes. The thermal properties have been evaluated after 90 days of curing at 20 °C and 50% RH. The results indicate that the thermal conductivity decreases by about 8% and 30% respectively when S/B increases from 0.40 to 0.5 and 0.67, whatever the binder. They also show that the mixes produced with lime based binder "B" (70% of natural lime, 30% of hydraulic lime and pozzoulane) have higher thermal conductivity than those produced with binder "V" (natural prompt cement and citric acid) by about 15%–20%. The specimens' thermal properties have been characterized before and after drying process. The results show a decrease by about 9%–16% of the thermal conductivity after drying. A self-consistent model widely used in the literature has been used to predict the thermal conductivity of the equivalent homogeneous hemp concrete. The comparison between the experiment data and the self-consistent model shows a relatively good agreement.