Environmental analysis of the use of plant fiber blocks in building construction
Graphical abstract
Introduction
The impact of civilization on the environment is increasing, fundamentally due to constant population growth and greater energy consumption. It is becoming increasingly necessary to change such patterns in order to find a more sustainable way of life.
The construction sector is one of the highest energy consumers (Gil-Lopez, 2020). It is responsible for about one-third of the energy consumed in the world and 39% of all carbon emissions. Of that 39%, 28% can be attributed to operational emissions, i.e. those that occur when heating, cooling or lighting buildings. The remaining 11% comes from carbon emissions that are associated with building materials and processes (WGBW, 2019).
On the other hand, the construction and use of buildings represents approximately half of the materials extracted, and around a third of the water consumed and waste produced in the European Union. As such, it is becoming increasingly important to use sustainable materials which reduce the environmental impacts of construction (Manso et al., 2018).
It is therefore urgent to propose new materials for the construction of buildings to reduce the consumption of resources and the environmental impact.
Life Cycle Assessment (LCA) is a tool that is widely used in the construction sector to quantify the environmental impacts of a material throughout its life (Soust-Verdaguer et al., 2017; Xing et al., 2008). There are different LCA modeling methodologies. The LCA's own characteristics cause the different methodologies to suffer in terms of comparability and consistency (Huijbregts, 1998). Although standardized procedures exist, as specified in ISO 14040 (European Committee for Standardization, 2006a) as well as others which are more specific to construction products, such as EN 15804 (British Standard, 2019), they do not prevent uncertainties in model options or scenarios. Various research projects propose using methods to circumvent these uncertainties, such as studies on specific buildings (Aktas and Bilec, 2012), on building materials (Noshadravan et al., 2013; Silvestre et al., 2014), and even on the parameters of the model (Wang and Shen, 2013).
In order to determine the impact of a specific building material, all of the stages in the life of a building must be taken into account: design, construction, use and demolition. The assessment of the environmental aspects in the design phase may help to reduce the use of resources and the environmental impacts during the building's entire life cycle (Schlegl et al., 2019; Sanz Requena et al., 2011).
It is at this stage that the materials for a construction are chosen. A study carried out at the University of Belgium shows that architects should focus on choosing the best materials, in ecological terms (Liu and Mi, 2017).
Among all the materials used in the construction of a building, those that form the building envelope are those that generate the greatest impact (García-Ceballos et al., 2018; Gil-Lopez and Gimenez-Molina, 2013a, Gil-Lopez and Gimenez-Molina, 2013b). The results of the research carried out by Audenaert et al. indicate that the choice of insulating materials has a significant impact on the design's ecological score, especially those of natural origin (Audenaert et al., 2012).
Among the insulating materials used in construction, straw is considered to be one of the oldest materials, it having been used mixed with mud for thousands of years, going by the name of cob. However, its use in construction as a bale or block is relatively modern and dates back to the end of the nineteenth century, which is when the baler was invented. Today, the packaging process has improved, achieving an improvement of its properties and greater durability.
The plant fiber block (PFB) consists of a compressed straw block, a by-product of growing cereal in the case of wheat straw, barley straw, rice straw and rye straw, which has been used as feed for livestock or bedding for animals (Revuelta Aramburu, 2017). Properties featuring PFB as a building material have been evaluated by means of studies and tests, applying the international regulations which govern building materials.
Studies such as that by Chaussinand have been found, which evaluated its conductivity and heat capacity, concluding that straw bales may provide a sustainable solution for the future of construction due to their low embodied energy and their excellent thermal behavior (Chaussinand, 2015). With regard to sound insulation, as it is a natural material composed of straw, it has a high absorption coefficient (Gil-Lopez et al., 2017).
Where fire resistance is concerned, PFB provides excellent flame resistance as was proven by the tests performed in Germany in 2003, by the FASBA, the German Association of Straw Bale Construction (FASBA, 2003). Bearing in mind that the minimum requirements in the basic fire protection document of the technical building code indicate that structural elements must have a resistance of at least 30 min, it has been proven that the plant fiber block wall complies with these requirements perfectly (CTE DB-SI, 2019).
Where its load capacity is concerned, numerous compression tests have been performed to verify the load capacity of a wall made from plant fiber blocks, such as many of the tests led by Minke, which have shown that a PFB wall can support loads of >1000 kg/m2 as a load bearing wall (Minke, 2012).
In addition, the use of straw as a building material does not carry this environmental burden, since combustion is not required for such use (Osman et al., 2019).
Several research projects have been carried out into the LCA of materials used in construction (Asif et al., 2007; Blengini and Di Carlo, 2010; Esin, 2007). Some of them even carry out a detailed study of a particular material such as those carried out by Ximenes and Grant on wood (Ximenes and Grant, 2013) or Wu et al. on bamboo (Wu et al., 2005). However, no research has been performed on the PFB encompassing the extraction of the raw material, the transport to the factory and the manufacturing process. As it is a material that is not widely studied at the level of environmental impact, it is not included in most international databases on building materials.
The present research analyzes the environmental impact associated with the production of PFB as a building material, using the Life Cycle Assessment methodology. In addition to looking at the sustainability of this material, it also compares it with other conventional building materials. To this end, a full-scale prototype has been built with the aim of identifying the substances or processes that cause the highest impact on the environment. In this way, more precise corrective measures can be defined through the implementation of environmental policies. In addition, the intention is to provide information to complete databases with reference to the PFB as a building material.
Section snippets
Technical characteristics of the plant fiber block
Given that the plant fiber block is a material of variable composition, the characteristics of the material used in this research are defined below (Table 1).
These technical characteristics make the plant fiber block an extremely advantageous building material due to its excellent physicochemical properties and the fact that it is easy to use as a result of its low weight compared to other conventional materials.
Definition of the study prototype
A full-scale prototype has been built, with a useful area of 6.60 × 4.40m2 and a
Calculation of the impact on global warming of the products used
To obtain the impact on global warming associated with the products used to obtain 1 kg of straw, the emission factors associated with production and transport have been added (Table 2).
To obtain the emission factor associated with production, the quantity of each of the products used (seeds, fertilizers, herbicides, urea and polypropylene) has been multiplied by the production emission factor of each of them. The sum of all these values determines the emission factor associated with the
Conclusions
The construction sector generates a significant environmental impact, due to both the materials and processes used. If we seek to reduce the impact produced by a specific material, it is essential to be able to measure the impacts produced in each of the construction phases quantitatively, reliably and accurately.
During this research, the environmental impact produced when manufacturing a plant fiber block was analyzed, given that this is a material which, due to its insulating properties, easy
CRediT authorship contribution statement
Marta Revuelta-Aramburu:Conceptualization, Methodology, Validation, Investigation, Resources, Writing - original draft, Writing - review & editing.Amparo Verdú-Vázquez:Methodology, Writing - original draft, Writing - review & editing, Visualization, Supervision.Tomás Gil-López:Validation, Formal analysis, Writing - original draft, Writing - review & editing, Visualization, Supervision.Carlos Morales-Polo:Conceptualization, Methodology, Formal analysis, Investigation, Resources, Writing - review
Declaration of competing interest
The authors have no conflicts of interest to declare.
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