Biopolymers impact on hygrothermal properties of rammed earth: from material to building scale

Three biopolymers were tested as rammed earth (RE) stabilizers, evaluating their impact on the hygrothermal behavior from material to building scale. Hygrothermal characterization included the determination of sorption isotherm, water vapor permeability, thermal conductivity at different moisture content, and specific heat capacity. The hygrothermal data were used as input for the simulation at whole-building scale considering combined heat and moisture transfer. The results were evaluated by comparing heating demand, thermal comfort during summer, and the contribution of walls for passively controlling indoor humidity. The results show that hygric properties were only slightly affected by the use of stabilizers, while the thermal conductivity was 33% higher for RE stabilized with lignin, consequently increasing the heating demand at whole-building scale. All RE walls were effective in reducing temperature oscillations in summer. In the particular case of a canicular event, the indoor temperature was reduced by up to 10° compared with the outdoor value. The indoor humidity also benefited from the passive regulation by RE walls, regardless of whether a stablizer was used

Mechanical and Microstructural Characterization of Rammed Earth Stabilized with Five Biopolymers

This study aims to check the compatibility of a selection of waste and recycled biopolymers for rammed earth applications in order to replace the more common cement-based stabilization. Five formulations of stabilized rammed earth were prepared with different biopolymers: lignin sulfonate, tannin, sheep wool fibers, citrus pomace and grape-seed flour. The microstructure of the different formulations was characterized by investigating the interactions between earth and stabilizers through mercury intrusion porosimetry (MIP), nitrogen soprtion isotherm, powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The unconfined compressive strength (UCS) was also evaluated for all stabilized specimens. Three out of five biopolymers were considered suitable as rammed earth stabilizers. The use of wool increased the UCS by 6%, probably thanks to the combined effect of the length of the fibers and the roughness of their surfaces, which gives a contribution in binding clay particles higher than citrus and grape-seed flour. Lignin sulfonate and tannin increased the UCS by 38% and 13%, respectively, suggesting the additives’ ability to fill pores, coat soil grains and form aggregates; this capability is confirmed by the reduction in the specific surface area and the pore volume in the nano-and micropore zones

CYP72A67 catalyses a key oxidative step in Medicago truncatula hemolytic saponin biosynthesis

In the Medicago genus, triterpenic saponins are bioactive secondary metabolites constitutively synthesized in the aerial and subterranean parts of plants via the isoprenoid pathway. Exploitation of saponins as pharmaceutics, agrochemicals and in the food and cosmetic industries has raised interest in identifying the enzymes involved in their synthesis. We have identified a cytochrome P450 (CYP72A67) involved in hemolytic sapogenin biosynthesis by a reverse genetic TILLING approach in a Medicago truncatula ethylmethanesulfonate (EMS) mutagenized collection. Genetic and biochemical analyses, mutant complementation, and expression of the gene in a microsome yeast system showed that CYP72A67 is responsible for hydroxylation at the C-2 position downstreamof oleanolic acid synthesis. The affinity of CYP72A67 for substrates with different substitutions at multiple carbon positions was investigated in the same in vitro yeast system, and in relation to two other CYP450s (CYP72A68) responsible for the production of medicagenic acid, the main sapogenin in M. truncatula leaves and roots. Full sib mutant and wild-type plants were compared for their sapogenin profile, expression patterns of the genes involved in sapogenin synthesis, and response to inoculation with Sinorhizobium meliloti. The results obtained allowed us to revise the hemolytic sapogenin pathway in M. truncatula and contribute to highlighting the tissue specificities (leaves/roots) of sapogenin synthesis

Natural additives and biopolymers for raw earth construction stabilization – a review

The importance of earthen construction materials lies in their widespread availability combined with a low embodied energy. Chemical stabilizers are commonly used to improve their durability and mechanical performance. The main drawbacks are the high environmental impact of their production, the loss of recyclability, and the possible reduction of raw earth's hygrothermal properties. Historically stabilization was achieved by the use of different kinds of fibers, agricultural wastes, and biopolymers incorporated into the earthen matrix. The purpose of the present study is to review the state of the art of investigations on the influence of natural additives for raw earthen materials, to promote and facilitate future research in this field. More than 50 independent studies have been considered, including different types of raw earth constructions: plasters, adobe, compressed earth blocks and rammed earth. To enlarge the opportunity of investigating the use of biopolymers as stabilizers, some studies about soil stabilization have been included in the review. Results show that the use of recycled and waste material as a natural additive is promising direction for future research as it can provide a sustainable alternative to chemical stabilization

Comparative Life Cycle Assessment of Rammed Earth Stabilized with Different Biopolymers

Rammed Earth (RE) is a traditional technique based on the compaction of local soil, avoiding long-distance transportation and carbon emissions processes typical of concrete production. Nevertheless, RE presents limited mechanical performances and low resistance against water. Cement is usually added to improve RE properties to comply with the construction standards. Consequently, the environmental impacts increase and the recyclability of the soil at the end of life is lost. In the present study, some biopolymers were considered for RE stabilization: lignin sulfonate, tannins, and sheep wool fibers. These additives were found to be effective to improve the unconfined compressive strength of the RE in a previous study by Losini et al. [1]. In this study, the analysis focuses on the environmental impacts of the production phase of a stabilized rammed earth (RE) wall via Life Cycle Assessment (LCA). Through a comparative LCA from cradle to gate, the environmental impacts generated by the construction phase of the RE wall stabilized with three natural additives, is performed on a functional unit equal to 1m2 wall with a thickness of 30 cm. The unstabilized RE is then compared with the stabilized materials, both in terms of improvements of compressive strength and LCA environmental indicators. As a result, lignin and sheep wool fibers stabilized walls show almost negligible differences in terms of environmental impact while improving the mechanical properties up to +38% and +6% respectively. Despite the relatively high enhancement of the mechanical strength by +13%, the tannins stabilizer performs around +95% rise in all environmental indicators compared to the unstabilized material

Hygrothermal behaviour of hemp-lime walls: the effect of binder carbonation over time

Bio-based building materials are produced by recovering agricultural biomasses which are used as vegetal aggregate to replace traditional ones and realize more sustainable building materials. This study focuses on hemp-lime that is made by mixing a lime-based binder with hemp shives i.e. the waste of industrial hemp cultivation. The work aims to evaluate the effect of the maturation of hemp-lime on its hygrothermal performances. Specifically, the binder undergoes carbonation reaction through which the strength of the material and its hygrothermal properties develop. With this aim, two experimental campaigns were carried out on an experimental wall built using prefabricated hemp-lime blocks: the first few months after the construction and the second one after 3 years. The wall, equipped with hygrothermal sensors, was subjected to cycles at varying relative humidity values and fixed temperatures applied with the help of a climatic chamber. The cycles were performed at 23 °C and 35 °C to focus on the performances of the material in conditions comparable to those of the Mediterranean climate. The results prove that hygrothermal performances improve with maturation, which could be due to the carbonation of the binder and to the reduction of the initial moisture content. Numerical simulations of the experimental tests were implemented using the software WUFI® aiming at confirming the experimental methodology and also the possibility of simulating the behavior of such innovative material in dynamic regime. The proceeding of carbonation was proved through X-ray diffraction (XRD) and thermogravimetric (TG-DTG) analyses of samples having different maturation times

Evaluation of different raw earthen plasters stabilized with lime for bio-building exploitation

The building sector generates around 5-8% of greenhouse gas emissions (GHG)1 and the disposal of C&D waste at the end-of-life is a high environmental cost. The raw earth is a sustainable construction material with low embedded energy, available locally. It is the most ancient technique of construction, studied in recent years to reduce the environmental life cycle impact of buildings. Clay is responsible for the earth plastic behaviour and represents the binder that keeps together silt and sand grains. Earth sets through drying without chemical reactions, so it could be reinserted into the nature. At the same time, earthen constructions do not withstand weathering and develop lower mechanical performances compared with those which exploit hydraulic binders. We investigated the possibility of improving these characteristics by stabilizing earthen products with the addition of small amounts of lime preserving clay as eco-friendly binder and the full end-of-life recyclability. Four earths with different binder properties – two kaolin clays, one illite clay and a smectite – were characterized and analysed at the lab scale. The change of the Atterberg limits on adding lime was determined. The clay modification and potential pozzolanic reactions with lime were measured by X-ray diffraction. Two earths were selected to be tested as plasters, adding sand and lime in order to reduce shrinkage and increase water resistance. Cracking and adhesion tests were run for all mixtures. The results show decreasing performances for all the plasters mixtures stabilized with lime, especially in the presence of an expandable clay fraction. The water resistance is improved for the stabilized mixtures that require less sand to reduce cracking and swelling. Lime is better used as a surface finish and plaster, not as stabilizer, because reacting with clay it increases the plastic limit and raises the water demand to obtain a plastic and workable mixture