Durability of hemp concretes exposed to accelerated environmental aging

Abstract

This study examines the evolution of the functional properties of two hemp concretes formulated with two different binders over 2 years in different environmental conditions. Stable environmental conditions (50% RH -20°C) have been applied to hemp concretes to obtain the reference aging A REF .An accelerated aging process A WD is chosen, consisting of cycles of wetting and drying. In relation to the reference aging, no significant variation of the chemical, microstructural and functional properties is observed, whether in terms of the thermal, acoustic, hydric or mechanical behavior. During accelerated aging, variations of properties are observed: an increase of thermal conductivity, and water vapor sorption capacity for both binders and a decrease of acoustic performance for the limebased binder. No variation of mechanical properties is observed. These results are linked to alterations of the chemical and microstructural properties: hydration and carbonation of the binder, mineralization, swelling and shrinkage and consumption of vegetal walls by micro-organisms. By comparing these results with measurements carried out under real conditions, this work shows that the performance of hemp concretes should remain stable for several years. *Revised Manuscript Click here to view linked ReferencesA range of disorders have been observed in early hemp concrete constructions, such as binder powdering in the core of the material, development of micro-organisms, cracking of the renders applied on its surface, or delamination of renders [5]. These issues stem from an unsuitable implementation of materials, which causes high water content in the hemp concrete, due, for example, to insufficient drying, capillary rise or water infiltration. The validation of construction rules made it possible to greatly reduce the occurrence of these construction defects [6]. Today, with a view to increasing the use of these materials, the question of the evolution of their long-term performance arises. Indeed, the durability of hemp concretes is not yet known, and it is not possible to guarantee that a minimum level of thermal, hygrothermal and acoustic performances will be preserved for a given time. In this context, some reservations still remain that limit the use of these biobased insulating materials.The evolution of the properties of hemp concretes depends on the conditions of their use and the environment to which they are exposed. Parameters such as relative humidity, temperature, liquid water and UV radiation cause changes in chemical and microstructural properties, altering the functional properties. Previous studies have shown that water has many impacts on the properties of hemp concrete. As a matter of fact, as hemp shiv is hydrophilic, the presence of water leads to a swelling of the aggregates which increases the stresses at the interface between the vegetal particles and the binder [7], and can lessen the mechanical properties of hemp concrete. In addition, the presence of water and mineral binder causes a high pH within the m...

Accelerated Aging Effects on the Hygrothermal Behaviour of Hemp Concrete: Experimental and Numerical Investigations

“…Despite the long duration of this type of aging, we did not observe significant changes in the properties of the material after aging. These results are in line with the literature where authors have concluded that microstructural changes are not sufficient to lead to modifications in material properties during the first months of aging [27,28].…”

Thermal and hygroscopic study of hemp concrete in real ambient conditions

“…− 𝜆 𝛻𝑇 − 𝜌 𝑙 𝐿 𝑣 𝐷 𝑇,𝑣 𝛻𝑇 + 𝜌 𝑙 𝐿 𝑣 𝐷 𝜃,𝑣 𝛻𝜃 = ℎ 𝑇,L,0 (𝑇 𝑎,𝑒,𝑖 − 𝑇 𝑠,𝑒,𝑖 ) + 𝜌 𝑙 𝐿 𝑣 (𝜌𝑣 𝑎,𝑒,𝑖 − 𝜌𝑣 𝑠,𝑒,𝑖 ) + 𝜑 𝑟𝑎𝑑,𝑒,𝑖 (4) Where hT,L,0 is the convective heat transfer coefficient from external and internal sides, ρv,e,i is the air density, and φrad,e,i is a radiation term which is assumed negligible in our study.…”

“…The scientific community carried out several work in order to demonstrate the thermal and hygroscopic efficiency of bio-based material compared to classical insulation materials, and the advantages they offer in terms of energy needs [1], environmental impact [2], indoor air quality, durability [3], [4], [5], and thermal comfort [6].…”

Experimental investigations on water absorption and mechanical properties of expanded perlite mortar under accelerated and natural aging conditions

“…There are two common ways of aging of building materials-artificial accelerated aging (hereinafter referred to as 'artificial aging') and natural environmental aging (hereinafter termed as 'natural aging') [7]-with various specific methods and standards. Artificial aging involves simulating a certain temperature [8,9], humidity [10,11], drying-wetting changes [12,13], freeze-thaw cycles [14], ultraviolet radiations [15], and other conditions in the aging test box based on the characteristics of the service life environment of the studied material and the characteristics of the material itself. Natural aging is mostly to place the test specimen in a typical service life environment for a certain period to allow it to accept the aging effect of the environment that is most in line with the actual state to evaluate the material durability [16].…”