© N. Amarone et al., Published by EDP Sciences, 2023

1 Introduction

The use of natural materials in the building sector can contribute to climate change mitigation, biodiversity conservation and sustainable economic development. These are just some of the reasons that encourage to study a plant with a huge range of possible uses: Arundo donax L. (ADL). This natural species belongs to the botanical family of “Poaceae” [1], the same as bamboo. The plant presents an underground part composed by a complex system of rhizomes able to store large quantities of nutrients, and an aboveground part, characterized by tall and lignified culms, which may reach heights from 4 to 8 m [2]. Depending on the level of maturity it can be used for different purposes (Fig. 1, 2, 3). It is native of the Middle East, but thanks to the autonomous reproduction, it easily reached the Mediterranean basin, as well as America and Australia [2]. The large diffusion was possible for the ability of ADL to be cultivated on different types of soil, as wet soils and dry fields, but also for the adaptability to the most varied climatic conditions. ADL has no fertile seeds, so that the vegetative propagation, through fragments' propagation or layering, remains the only spreading strategy. For these reasons, ADL is often classified as an invasive species [2]. Its spreading all over the world often caused serious problems to the native flora, to anthropized areas and, especially in warmer seasons, it can cause fires because of the high flammability. Solutions can be appropriate cutting and weeding measures. The plant extraction allows to use it for the most varied purposes. Indeed, this species has advantageous features which guarantee its utilization in different sectors. Hereafter all the possibilities of use in the field of constructions are analysed, studying existing architectures. Therefore the benefits as sustainable building material are assessed through the analysis of the Lyfe cycle and an energy performance analysis of different constructive components made of ADL.

2 Arundo donax as building material

Arundo donax offers a lot of possibilities of usage especially in buildings thanks to numerous properties, like good resistance to water actions, durability and flexibility, efficiency as insulator, low labour intensity and skills. The use of ADL as a building material can be traced back to the first manifestations of architecture, but it is also used today as an expression of vernacular architectures [4].

ADL is characterized by a simple building technique, which does not require complex manuals. Over the centuries different assembly solutions have been applied, allowing to obtain constructive elements assuming both structural and non-structural functions. For example, in Mediterranean countries, especially in rural buildings, giant reeds are traditionally employed in roofs for the creation of false ceilings, in order protect the structure in case of fire and to increase thermal and acoustic insulation by reducing the height and containing the heat dispersion [1]. This material is also used for the construction of internal or external walls, generally characterized by a timber frame that supports panels of ADL, created arranging reeds in a regular disposition, or mats generated by intertwined reeds [5]. Also bundles of reeds, tied together, realize structural elements used as columns and beams.

3 Arundo donax as sustainable material

3.1 Sustainable vernacular architectures

A vernacular architecture is the main expression of traditional buildings, which represent a response to both environmental and climatic constraints, as well as to the socio-economic and cultural characters of societies. This type of architecture normally presents a good climate adaptation and supplies good thermal comfort due to the choice of natural materials adapted to the environment [30]. Numerous architectures placed around the world involves Arundo donax as building material. They are classified in relation to their characteristics in lightweight structures, earthquake resistant systems and roof shaped design, following the categories defined by the Project VERSUS [7].

Lightweight structures are the Mudhif in Iraq [8], the Sardinian barracas [9] and the floating huts from the Titicaca lake, in Bolivia [10]. The sustainability of vernacular lightweight structures lies in the low weight and, indirectly, in the materials and techniques used to the assembly. The lightweight framework ensures good indoor environmental quality, since it allows buildings to have large openings; this is particularly useful to provide ventilation and shade in hot wet climates [30]. In cold climates, the internal environment is protected by insulating layers. Another advantage is the use of local available materials, combined with dry, low-rate processing, and low-energy consuming techniques [7].

Earthquake resistant systems are the quincha and the pau-a-pique techniques [11], diffused both in South America. This category also involves the most modern Peruvian technique of the domocaña [12]. The benefits of employing local materials and low-tech solution may regard energy saving, transports and pollution reduction [30]. In socio-economic terms, such seismic resistant structure are not expensive. Indeed, in case of earthquakes, damage mostly affects the secondary structures, while the main structure is preserved, making them easily repairable, both financially and technically [7].

Rural architectures characterized by sloped roofs are diffused especially in Mediterranean countries. Spain, Italy and France offer several examples of roof shaped design. In Italy examples are the traditional casoni of the Venetian marshes [13] or the Sardinian hut, called pinnetta [9], while examples in Spain are the barracks from Valencia or Orihuela [5]. The use of local resources for building roofs meets several principles of sustainability: integration into the site, recycling of local natural materials, reduction of the use of industrial materials and pollution. Sloped roofs contribute also to increase the inertia of buildings. The use of local resources contributes to save the energy and also to increase green and floral surfaces, reducing the level of air pollution. Economy also concerns the transportation energy, since materials are collected on-site and only transported over short distances [7].

3.2 Lyfe cycle advantages for the circular green economy

The main advantage of using Arundo donax in buildings is the low environmental impact, related to all the phases of the life cycle: from the choice of the construction site to the design, from the construction to maintenance and, finally, to the deconstruction [1,30].

With regards to the production, ADL is a perennial species and for this reason it gives an important contribution to reduce CO₂ emissions, since it captures atmospheric CO₂ and stores it in its tissues (the ability to absorb CO₂ of perennial crops is 20–30 times greater than annual species). The cultivation does not demand particular care or specific water resources. Indeed, the plant grows in autonomy. If required, the plant can be easily cultivated, using traditional cultivation techniques and agricultural equipments, with a final annual cultivation cost of about 700 Euro/ha [3].

The positive impact also involves the construction phase because, being a natural high-quality material, it does not require transformation processes. This aspect allows to reduce the energy consumption and limits the use of heavy machines in site, since reeds can be handled by voluntary operators without specific knowledges. Moreover, most of times ADL is accompanied by natural materials (as natural fibres ropes, clay, natural lime, wood), so that the overall final product is totally sustainable. With regards to the constructions costs, ADL is a low-cost material especially in terms of supplying and management costs, thanks to the high availability and to extreme lightness, which reduce the costs of collection and transport.

In terms of maintenance, this material has a great durability: it lasts about 50 years without treatments and does not require specific actions to improve its preservation. Moreover, thanks to the excellent thermal properties of the material, the energy requested during the life cycle of the building is very low. Sustainability also concerns the disposal phase, in fact the high quantity of waste material can be recycled and reused to create new constructive elements or to produce biomass.

3.3 Thermal performance of Arundo constructive elements

Thanks to its low thermal conductivity coefficient (0.063 W/mK [5]), Arundo donax can be used to realize insulating panels that increase the thermal performance of buildings, also reducing in summer seasons the overheating effect and preserving in winter the internal microclimate. Moreover, ADL is breathable, it promotes the diffusion of steam, it does not contain toxic substances, it reduces the presence of moisture and plays a hygroscopic balance [1]. Insulating panels can be used for external walls, internal partitions or roofs. These panels are created arranging reeds in sequence and tying them with galvanized iron, nylon, or ropes, in a way to leave intact the inner cavities of the cane. Other types of insulating products can use ADL fibres. Once extracted, fibres are mixed with a hydraulic binder, creating eco-sustainable products specifically designed for a better thermo-acoustic behaviour of the building. Fibres can be used as the main aggregate of natural limes or as reinforcement for bricks or fibreboards. According to their thickness and composition, these products may have different thermal performance, as summarized in the following table.

4 Energy performance simulation of building components

A building is a complex thermodynamic system influenced by a wide range of parameters, such as geometry, building envelope and climatic conditions. In order to study the interaction between the building and the environment, an energy performance simulation through specific softwares as the Grasshopper's plug-ins Ladybug and Honeybee is carried out [30]. The main goal is to simulate the behaviour of a simple building equipped with different insulating panels, identifying the solution that meets at the most of insulation requirements and optimizes the performance of the building.

The simulation has different inputs which define the main performance parameters, regarding local weather, building geometry, occupancy, energy ventilation system specifications and building envelope. Table 2 resumes the general input parameters applied to the building, together with the site parameters .

One of the main input data refers to the building envelope. The simulation is carried out on four different constructive systems and for each system different insulating products have been tested (Fig. 4 and Tab. 3). The latter are selected assuming the limits of thermal transmittance for opaque surfaces fixed by the Italian standard DM 26/06/2015 [20] that for buildings placed in climatic zone C [19] is 0.34 W/m²K, as well as on the bases of technical data sheets (Tab. 3), providing different solutions in terms of walls thickness and composition of the insulating product.

Insulating products include Arundo donax L. as canes panels [16], fibres-boards [14] and fibres reinforced bricks [14]. In order to certify the economic and environmental benefits related to the use of ADL as insulating material, also traditional insulating products, such as mineral wool [23], hemp fibre-reinforced bricks [14] and straw bricks, are considered for the sake of comparison. For each product roughness, thickness, thermal conductivity, density and specific heat have been set, according to literature and technical data sheets.

The performance parameters are the yearly energy demand and thermal performance, which costs and environmental impacts have been added to, in order to provide a comprehensive evaluation of the most cost-effective solution (Table 1). An overall dimensionless performance parameter P that integrates all these factors has been also defined. Hereafter the performance parameters are introduced.

Fig. 1 Main parts of the Arundo Donax L. plant: (a) rhizome, (b) culm, (c) leaves, (d) flowers [3].

Fig. 2 Main applications of ADL in buildings: (a) false ceilings [5], (b) wall [1], (c) bundle [6].

Fig. 3 Lightweight structures: (a) Mudhif [8], (b) barracas [9], (c) floating huts [10]; Earthquake resistant systems: (d) Quincha [11], (e) Pau-a-pique [11], (f) Domocaña [12]; Roof shaped design: (g) Casoni [13], (h) Pinnetta [9], (i) Spanish barrack [5].

Fig. 4 Constructive systems and insulating products tested for each system.

4.1 Yearly energy demand

Energy demand describes the consumption of energy by human activities. The simulation quantifies the energy requested by each system during a whole year, providing the total energy demand, the energy request per total building area and the energy demand for each sector (heating, cooling, light, equipment) to maintain an internal temperature within the fixed range (21–25 °C).

4.2 Thermal performance

The thermal performance takes account of several parameters, such as internal thermal comfort, thermal inertia, heat emissions and thermal transmittance. In particular, the simulation provides the heat emissions related to each surface and the thermal transmittance. The transmittance is evaluated through the U-Factor, which is the flow of average heat that passes through a wall that divides two environments at different temperatures. This value is a key point for figuring out thermal losses and also for determining the insulating power of a wall: lower is the U value, higher is the insulating power. To evaluate the feasibility of Arundo donax in terms of thermal performance, the limit values of 0.34 W/m²K [16] has been considered.

4.3 Costs

In order to assess the convenience of the insulating solutions, the cost of each product, which varies according to type and thickness of the panels, is considered. Thus, the final cost of each wall will differ case by case according to the different type and thickness of insulating product used.

4.4 Environmental impact

The Life Cycle analysis is conducted through the Ecoindicator99 method [25], in order to assess the environmental benefits or negative impacts derived from using Arundo donax [26], hemp [27] and mineral wool [28]. Three main damage categories are considered: human health (DALY, disability-adjusted life year), which correspond to the number and duration of diseases and loss of life-years owing to deaths caused by environmental degradation; ecosystem quality (PDF · m²· year, potentially disappeared fraction of species, calculated as percentage of species extinct in a given area in a year), which accounts for the impact on species diversity, acidification, eco-toxicity, and land use; and resources (MJ surplus), which represents the depletion of raw materials and energy resources, it being measured in terms of the surplus energy required in the future to extract lower-quality energy and minerals.

4.5 Performance parameter

The overall dimensionless performance parameter P incorporates transmittance, heat emissions, energy demand, costs and environmental impact. Each dimensionless parameter has been obtained through the ratio between the values related to ADL products and the ones related to mineral wool, hemp and straw. It is defined through the following equation:

where: U^¯ is the dimensionless transmittance; H^¯ is the dimensionless heat emissions; E^¯ is the dimensionless energy demand; I^¯ is the dimensionless environmental impact, divided in the categories human health, ecosystem and resources; C^¯ is the dimensionless cost. If the performance parameter is <1, the ADL performance is better than that of traditional products (Tab. 4).

From the analysis of the results, it is apparent that Arundo products offer a good performance, both in terms of energy and environmental impact. If compared to mineral wool, ADL has higher transmittance, which implies lower thermal performance and higher costs. However in terms of environmental impact ADL products is much more convenient than mineral wool. If compared to hemp, ADL has very similar performances, but it is advantageous in terms of costs, since hemp requires necessarily to be imported and is characterized by a greater manufacture demand. If compared to straw, Arundo donax is better in terms of thermal transmittance and energy demand. However, in this case, the lack of information about the LCA of straw does not allow to calculate the final parameter.

In synthesis the material that mostly has negative effects on the environment is the mineral wool. In particular, the high impact is related to the human health category, since this material may release thin particles that are harmful to humans. Another disadvantage is the hard disposal: according to the European Waste Catalogue (EWC) [29], mineral wool is classified as special no-hazardous waste and requires to be disposed by specialized workers. Contrary, ADL and hemp both feature a low environmental impact, especially in terms of human health, since they are responsible for a high amount of CO₂ absorption from the environment during the growth. At the same time the ADL is more favourable than hemp due to the lower land use and lower exploitation of resources of the giant reed thanks to the high natural availability.

5 Conclusive remarks

The paper illustrates different possible uses of Arundo donax L. in the field of construction and shows the contribution that this material gives to traditional architectures in terms of sustainability. Starting from the vernacular architecture, the material has been revalued and proposed in a modern key, in order to find innovative, natural and sustainable architectural solutions. The analysis on existing buildings, using ADL is an important background for the design of new sustainable buildings identifying aspects to be improved and new steps forward to take. The tool adopted for the evaluation is the energy performance simulation, which allows to define the most convenient solution among a wide range of possible techniques. Indeed, the preliminary investigation presented has shown that Arundo donax has several advantages, related to the sustainability, as respect to traditional materials like mineral wool, but also as respect to other natural materials like hemp. Definitely, considering the numerous benefits that Arundo donax L. generates, this study can be a starting point for further comprehensive and detailed investigations on the application of this versatile building material.

References

All Tables

All Figures

	Fig. 1 Main parts of the Arundo Donax L. plant: (a) rhizome, (b) culm, (c) leaves, (d) flowers [3].
In the text

	Fig. 2 Main applications of ADL in buildings: (a) false ceilings [5], (b) wall [1], (c) bundle [6].
In the text

	Fig. 3 Lightweight structures: (a) Mudhif [8], (b) barracas [9], (c) floating huts [10]; Earthquake resistant systems: (d) Quincha [11], (e) Pau-a-pique [11], (f) Domocaña [12]; Roof shaped design: (g) Casoni [13], (h) Pinnetta [9], (i) Spanish barrack [5].
In the text

	Fig. 4 Constructive systems and insulating products tested for each system.
In the text