1. Introduction
Climate change and the degradation of ecosystems significantly impact people and their health (Huss et al., 2022). This paper presents a literature review to understand the ideal processes for vegetation growth in building materials. It analyses the ideal chemical conditions for its development and identifies the different applications of vegetation in urban centres to obtain more sustainable solutions and minimise the damage that the use of these solutions can bring to buildings. Evapotranspiration, which is characterised by the transpiration of the building material with the vegetation to reduce thermal condensation, was used to analyse the degree of hydration of the materials (Juras and Durica, 2022).
The European Commission is trying to tackle the high demand for CO2 through cost-effective measures that provide environmental, social and economic benefits at the same time, thus contributing to more sustainable development, with the adoption of the Green Deal. (“The European Green Deal,” 2019). These solutions aim to bring more diverse natural resources to cities, landscapes and marine areas through locally adapted, resource-efficient and systemic interventions (Ascione et al., 2020a, Ascione et al., 2020b).
With the growth of cities, the land cover has changed, directly influencing the urban microclimate through landscape consumption and displacement of nature. Many local effects in cities (Smith et al., 2020), the integration of vegetation, have significant impacts on temperature regulation (Lehmann, 2014).
There is a new trend toward restructuring cities into green spaces; even existing somewhat degraded areas can be taken advantage of (Smith et al., 2020). And a new awareness for the use of resources of energy, land, water, green spaces and materials, called green urbanism (Santos et al., 2021).
Many exemplary projects have demonstrated that Nature-Based Solutions (NBS) can contribute to climate improvements, but now the challenge is to scale up their use; natural elements of vegetation and trees are the key to reducing CO2emissions. These NBS solutions, in urban centres, are applied on roofs, walls of buildings and even degraded pavement areas, thus extending the vegetation in urban parks, bringing as benefits the mitigation of heat, the reduction of runoff, carbon storage, an increase in biodiversity and visual aesthetics. In addition, one of the essential roles of vegetation is to be a biological filter capable of renewing the air by retaining particles and improving breathing capacities in society, thus acting as a prophylactic measure, especially in urban centres. The lack of vegetation in cities contributes to the increase of respiratory diseases (Cortinovis et al., 2022).
This study encompasses using these materials to minimise the global production sector's environmental impact and climate change to reduce the waste produced by industries so that it can be reused, as a new product, re-entering the circular economy (van Capelleveen et al., 2021). This is a promising and eco-innovative approach because the reuse of this waste is used with primary inputs for the new industrial processes, thus generating a new product (Rautiainen et al., 2018).
New approaches currently contributing to the concept of eco-innovation are based on cooperative production, whereby secondary products from one industry are used as primary inputs for the production processes of another industry (Rautiainen et al., 2018).
Several studies have shown that these materials bring sustainable improvements to the environment, thus providing an economically better quality of life while simultaneously lowering CO2 emissions (European Commissionbib_European_Commission_, 2019.).
Several examples in the literature studied in the introduction of waste for concrete and mortar preparation (Rautiainen et al., 2018). For example, the introduction of steel slag waste instead of Portland cement and phosphogypsum in the manufacture of mortars influences the porous structure, with very good mechanical strengths (Shen et al., 2020). The biomass waste and solid products are derived from its thermochemical transformation (Giglio, 2013). The use of biochar and fly ash in mortars for carbon dioxide sequestration purposes (Gupta et al., 2021). The introduction of phosphogypsum waste in the manufacture of mortars influences the porous structure.
Climate change adaptation can be integrated into urban and regional planning. This requires efficient infrastructures that are integrated through urban planning.
For these reasons, the approach that is intended with this review becomes even more justified, namely detailing the studies related to the development of cladding materials for the exterior and identifying construction methods and materials, all bearing in mind the use of an approach of bio construction with vegetation (Jovanović et al., 2018).
The various existing studies are limited to the analysis and comparison of the development of exterior cladding materials that incorporate maintenance-free vegetation. This literature review identifies and classifies the type of plants, substrate, and possible irrigation conditions in exterior cladding construction materials. It also studies nutrients from waste to develop a bio-construction approach with vegetation (Cuce, 2017). In this sense, it aims to understand the ideal processes and the most suitable materials for vegetation growth by analysing the ideal chemical conditions for its development to obtain a more sustainable solution.
2. Methodology
The Scopus platform was accessed to develop this review, and a search using specific keywords was carried out. This platform was chosen because it has a higher number of scientific journals and magazines with higher citations. In an embryonic stage, a search was carried out with the following short phrases: “Green Wall Systems”, “Plant-covered Wall”, “Vegetation Solutions in Green Roof”, and “Ideal Plant Nutrients” arrive at the need to make the study of the present topic.
Fig. 1 shows the search methodology regarding the topic. It started with the keywords “green roof” or “green wall” filter one was added in engineering, material sciences, and environment, where 8978 documents were obtained.
Fig. 1. Structure diagram applied.A filter two was added with the following keywords “green roof” or “green wall” and “vegetation solution”, where a total of 160 documents were obtained.
A filter three was added; this was subdivided into three parts: Filter 3.1 keywords “green roof” or “green wall” and “vegetation solution” and “waste” with 7 documents. Filter 3.2 key words green roof” or “green wall” and “vegetation solution” and “nutrient” with 9 papers. And lastly the, filter 3.3 key words green roof” or “green wall” and “vegetation solution” and “plant” with 66 documents.
The selected articles have information on types of plants and substrate composition/irrigation of building elements. And also have information on nutrients from waste. The articles that do not present content for the present study were left out of the study.
The search for the articles on each topic was limited, and those published before 2017 were not considered.
The remaining articles studied according to the keywords described that did not fit into the studies after being read were not considered for this analysis and comparison. The abstracts were analysed to select the articles for this review to verify if the article would fit the theme under study.
All articles have been analysed, in a detailed way, namely regarding the type of plant used, type of substrate, technologies of implementing vegetation growth (e.g. types of nutrients and irrigation cycles) and building systems of vegetation coupled materials and their use in construction. This study also covers the information found, mainly, each material's characteristics that contribute to vegetation growth, or building system, to the applications and appropriation of each material or building system used. For these reasons, this review article's result will help improve the investigated methods further and provide ideas for more sustainable civil engineering and building applications.
3. Vegetation growth coupled with construction materials
A first analysis of the articles about the different methods and applications of materials that allow vegetation growth in constructions showed that there is a particular concern among researchers regarding the minimization of CO2emissions to the environment and that the use of vegetation and trees is a natural and a low-cost priority measure that helps to reduce the carbon footprint.
There are currently several vegetal coating and ecological elements on buildings, namely on walls and roofs. There are preliminary studies by authors who use waste, detailing its chemical composition, as a potential nutrient. Fig. 2shows the fields of research in which vegetation is being used in building materials.
Fig. 2. Outline of the sear harried out for the type of plants and the type of substrate/irrigation.3.1. Types of building solutions and substrate
The substrate is the name given to the material through which the plant feeds and develops, supporting its roots. There are diverse substrates containing mixtures of minerals and organic materials and providing vegetation with the ideal conditions for its development. Knowing their chemical and physical composition is essential to understanding their properties better.
In a natural environment, the material resulting from the erosion of rocks, which is a slow process and through which the release of the rock nutrients occurs, combined with the decomposition of organic materials present in the ecosystem, results in a fertile substrate for plants. In addition to stimulating plant growth, this substrate provides the ideal nutrients for their development and root fixation. It serves as a water retention reservoir due to its porous structure.
In the scope of this study, Table 1 presents a list of the studies carried out for each type of substrate versus where they are applied in construction.
Table 1. List of articles and substrates/composition versus the place of application of the different building elements and irrigation information.
| Ref. | Building elements | Substrate Composition | Irrigation Information |
|---|---|---|---|
| (Ascione et al., 2020a, Ascione et al., 2020b; Charoenkit and Yiemwattana, 2017) | Green walls | A mixture of plant residues, husk, coconut fibre and cow manure |
Watering twice/day and fertilizer twice/year |
| (Ascione et al., 2020a, Ascione et al., 2020b; He et al., 2017) | Green walls |
Peat soil, powdered perlite, vermiculite and organic fertilizer |
Watering once a day |
| (Ascione et al., 2020a, Ascione et al., 2020b; Manso and Castro-Gomes, 2016) | Green walls | Mix: 60% organic and 40% inorganic materials in contact with sandwich panels with XPS, and paint | Watering every other day |
| (Ascione et al., 2020a, Ascione et al., 2020b; Mårtensson et al., 2014) | Green walls | Rockwool panel system in contact with masonry wall | Watering three times a day |
| (Ascione et al., 2020a, Ascione et al., 2020b; Coma et al., 2017) | Green walls | Coconut fibres | |
| (Ascione et al., 2020a, Ascione et al., 2020b; Cuce, 2017) | Green walls | Vegetation growth of climber on brick | |
| (Ascione et al., 2020a, Ascione et al., 2020b; Susorova et al., 2014) | Green walls | Vegetation growth of climber on plaster, limestone and brick | |
| (Ascione et al., 2020a, Ascione et al., 2020b; Mazzali et al., 2013; Manso and Castro-Gomes, 2015) | Green walls | Geotextile felts and soil | Flexible pipe irrigation with a flow rate of 2.1 l/h |
| (Ascione et al., 2020a, Ascione et al., 2020b; Lacasta et al., 2016) | Green walls | Mix compost and coconut fibres in contact with mortar-coated block concrete | Irrigation made with two pipes through an injection system |
| (Ascione et al., 2020a, Ascione et al., 2020b) | Green walls | Vegetation growth on clay bricks | |
| (Ascione et al., 2020a, Ascione et al., 2020b; Perini et al., 2011, Perini et al., 2011b) | Green walls | Geotextile felts in contact with XPS | Drip irrigation system |
| (Ascione et al., 2020a, Ascione et al., 2020b; Razzaghmanesh and Razzaghmanesh, 2017) | Green walls | A mixture of scoria and clay in contact with brick | Drip irrigation system |
| (Ascione et al., 2020a, Ascione et al., 2020b; Ottelé et al., 2011) | Green walls | Soil in contact with bricks, mineral wool and limestone | |
| (Ascione et al., 2020a, Ascione et al., 2020b; Martensson et al., 2015) | Green walls | Rockwool panels in contact with masonry wall | Watering three times/per day |
| (Manso and Castro-Gomes, 2015; Hoffmeyer et al., 2016; Perini et al., 2011; Pérez et al., 2011; Perini et al., 2011) | Green walls | Ground soil or pots filled with substrate in contact with stainless steel, galvanised steel, wood, plastic, fibreglass cables, ropes, nets, trellis | Drip irrigation system |
| (Manso and Castro-Gomes, 2015; Wall et al., 2011) | Green walls | Geotextile felts and soil | Drip irrigation system |
| (Perini et al., 2011; Wall et al., 2011; Ortega, 2010; Examiner and Mansen, 2009) | Green walls | A mixture of organic and inorganic substrates | Drip irrigation system |
| (Kontoleon and Eumorfopoulou, 2009; Zampini et al., 2020) | Green wall, green roofs, eco-restoration | Porous substrate made with a binder of aluminosilicates minerals (pozzolanic) from blast furnace slag and aggregate origin silica and limestone, and construction and demolition waste, quartz (waste glass) with a Hoagland solution | |
| (Pettit et al., 2018) | Green wall | Artificial soil (AgroSci 2018), Biofilter, and pyrolysis-activated carbon and shale | Drip irrigation system |
| (Assimakopoulos et al., 2020) | Green wall | Geotextile, peat, pumice stone, expanded perlite, coconut shell clays, organic fertilisers | Intelligent; suspends when it detects saturated ground |
| (Köhler and Kaiser, 2021) | Green roofs |
Mix 1: with 50% optimum culture soil and 50% expanded clay Mix 2: with 50% optimum culture soil and 50% Zinc Mix 3: crushed expanded clay with recycled product (pyroplastic) without nutrition |
Mix 1 and Mix 2 irrigation according to FLL2018 Mix 3: without irrigation, has a good water storage capacity |
| (Rocha et al., 2021) | Green roofs | Commercial green roof substrate, 71% fine organic matter and remaining medium-grained LECA (Expanded Clay) with 25 mm polyethylene drainage filter with water retention cavities and geotextile layer | Without irrigation |
| (Bortolini et al., 2020) | Green roofs |
Mix 1: preformed layer in recycled HDPE (plastic) and an expanded perlite mineral layer Mix 2: medium layers of growth serving as recycled brick substrate and volcanic substrate |
Start daily irrigations to ensure normal plant growth. And supplementary irrigations during the first two years in case of strong wilting symptoms. Afterwards, without irrigation. |
| (Antoszewski et al., 2020) | Green roofs | Porous soil substrate and plants | Regular |
| (Jauni et al., 2020a) | Green roofs | Crushed concrete (alkaline) + compost (recycled materials - fir shells, clay aggregate and animal waste) and fertiliser with reduced phosphorus (P) content | Irrigation, according to the rainfall zone, hence the use of indigenous plant species is recommended |
| (Tello and Vilar, 2020) | Green roofs | A porous substrate containing minerals and organic matter. | It does not require permanent irrigation |
| (Grullón – Penkova et al., 2020) | Green roofs | Mix: crushed bricks, expanded clay and/or loamy-clay soil; in addition, the mixture may contain animal manure and green waste | Minimal maintenance over the years; it took more irrigation and fertilisation in the first year. |
| (Vanstockem et al., 2019) | Green roofs | Mix: Organic soil, mineral, fertilizer, pig manure, wood chips and lava grains | |
| (Liu et al., 2022) | Green roofs | Mix: vermiculite aggregate (30%), peat moss soil (30%), ceramsite (30%), and organic matter (10%) | Irrigation |
| (Mitchell et al., 2021) | Green roofs | Mix: crushed lava, natural calcareous soil, clay and peat | |
| (Monteiro et al., 2017) | Green roofs | Expanded clay and granulated cork, in combination with organic matter and crushed eggshell | Nitrogen-fixing bacteria and thus contribute to the natural fertilization, regular irrigation |
| (Kuoppamäki and Lehvävirta, 2016) | Green roofs | Crushed brick and biochar | Irrigation, without any fertilisers |
| (Ntoulas et al., 2013) | Green roofs | Sandy loam soil 8 pumice:4 perlite:4 compost:1 zeolite (by volume)] and a commercially available substrate based on crushed tiles | Irrigation 3 times a day. Nitrogen fertilization |
| (Thomaidi et al., 2022) | Green roofs | Perlite, vermiculite and LECA used in the experiment are commercially available agricultural products with the brand name: Geoflor | Greywater treatment |
| (Bianco et al., 2016) | Green roofs |
Comercial substrate (coconut fibre, Hydroretentors, mycorrhizae) Comercial substrate and shredded felt |
Irrigation system |
| (Liu et al., 2022) | Green roofs | Powdered vermiculite aggregate (30%), peat moss soil (30%), ceramsite (30%), and organic matter (10%) | Substrate capable of storing rainwater and drainage functions. With a duration of 20 days |
| (Williams et al., 2021) | Green roofs | Roof tile, crushed brick, crushed concrete and bottom ash from coal-fired power stations | Rainwater |
| (Meetam et al., 2020) | Green roofs | potting compost and 20% rice husk and 20% chopped coconut shell | Rainwater, Natural fertilizer |
Based on the analysis of Table 1, it can be seen that in many of the articles studied, the concerns of the researchers are the use of wastes that are part of the composition of the substrates, the function of these wastes as a source of nutrition for the plant or the ability to obtain a substrate with a more porous structure, to the plant to retain more nutrients and water.
However, vegetable soil is still used in construction elements, and this soil is deposited in pots of various sizes depending on the construction element. Ready for cultivation soils can be marketed, having their chemical information as an advantage. The structure of vegetable soil consists of a mixture of inorganic and organic parts. According to the table analysis, perlite, vermiculite, rock wool, quartz, clay, pumice, aluminosiliceous minerals, silica, and limestone contribute to the inorganic part. The organic part can be from vegetable and wood waste, coconut shells and fibres, pyrolysis coal, pyroplastic, and abedo shells.
Studies show that the vegetation adapts to an alkaline environment with crushed concrete waste (construction and demolition waste) and does not resist an acidic environment (Jauni et al., 2020a).
For a good water and mineral storage capacity, the composition of the substrate, such as the existence of clay materials (Bortolini et al., 2020), can be considered. It will contribute to the degree of hydration of the material, thus considering the concept of evapotranspiration and the transpiration of the building material, which is done through the substrate and the existing vegetation. With the increase of water in the substrate, thermal condensation in the materials decreases (Antoszewski et al., 2020).
The material's hydration level is characterized by the ability to retain water through the substrate. Based on the bibliography studied, each element that constitutes the substrate has a different porosity and present distribution of particles in function of each component. These pores can store water and nutrients where the root fixes the vegetation and where it feeds itself. As indicated in the table, the substrates with peat, perlite, vermiculite fertilizer, rock wool, perlite and geotextile, and the waste belonging to the composition of the substrates were irrigated, and the animal manure, the shell and coconut fibre fertilizer were added. With this irrigation and depending on the area where it was applied and the type of substrate and vegetation, the substrate reached the ideal hydration level. As already mentioned, the water storage is related to the substrate composition. The table indicates substrates with a successful rate of vegetation development, most of them belonging to the Bryophyte type (moss), without any irrigation. The porous substrate is made with a binder of aluminosilicious minerals (pozzolanic) of silica-rich blast furnace slag and limestone of aggregate origin, and construction and demolition waste, quartz (waste glass) with a degree of hydration using a Hoagland solution (Zampini et al., 2020), a mixture of crushed expanded clay with the recycled pyroplastic product, also presents a good water storage capacity (Bortolini et al., 2020). The commercial green roof substrate, with fine organic matter and remaining medium grain LECA (expanded clay) with 25 mm polyethylene drainage filter with water retention capacities and geotextile layer, does not need irrigation (Rocha et al., 2021). Most of the mentioned substrates that do not require irrigation for vegetation development to succeed, as mentioned in Table 2, belong to the Bryophytes classification group, moss.
Table 2. Synthesis of nutrients for plants obtained from waste, soil types and other sources.
| Combination | Sample Description | Characteristics | Nutrients for plants | Ref. |
|---|---|---|---|---|
| A | A mixture of pyrolysis eucalyptus charcoal, polyethene pyrolysis, talc and clay soil | Both eucalyptus coal and polyethene pyrolysis increase alkalinity and have carbon sequestration capacity. Coal has a good porous capacity. | Na, K, Ca, Mg | Vanapalli et al. (2021) |
| B | A mixture of waste: Industrial Sewage Sludge, Lignite Ash, Sawdust in various proportions, and Ammonium and Potassium Phosphate were added as additives | Residues with high carbon and calcium content. In acid soils, it reduces the degree of acidification, thus increasing organic matter. | And several ionic bonds were analysed, K:Mg; K:Ca; K: (Ca + Mg); Ca:Mg; Ca:P; N:S | Mozdzer and Jałoszyński (2019) |
| C | Combustion mixture of waste from auto workshops, cattle manure, human iodine waste | For cereal crops, good development within acceptable parameters and good fertilizer potential were recorded. | H + Al, P, K, Ca, Mg2, Ag3, KCl, Zn | Neiva Júnior et al. (2019) |
| D | Silty soil mixture with cellulose industry ash and lime | Porous structure | C, O, Mg, Al, Si, K, Ca, Ti, Fe | Erbs and Lima (2020) |
| E | A mixture of phosphogypsum and coffee husk (rich in potassium) | Increase in Ca and Mg and a decrease in Al | Ca, Mg, K, P, Al | Voltolini et al. (2020) |
| F | A carbonate mixture of crushed powdered steel slag and phosphogypsum. | Porous structure, plant germination capacity. | CaO, SiO2, FeO, Fe2O3, Al2O3, MgO, F, SO3 | (Shen et al., 2020) |
3.2. The use of waste as a nutrient for vegetation
Recent studies have focused on the combination of waste to verify the capacity to retain water and nutrients to develop vegetation with the possibility of obtaining a porous and water-pervious materials skeleton and identifying the influence of the nature of the nutrients on vegetation growth. It has been found that there are several possibilities of obtaining nutrients from waste, such as Na, K, Ca, Mg, K, P N. Reducing the application of traditional fertilizers by replacing them with nutrients from waste also contributes to sustainable development. Table 2 summarises the literature on the main studies related to the existence and supply of nutrients for plants using indifferent waste, soil types and other sources.
The results of Table 3 were grouped into six main combinations and are presented in Table 2.
Table 3. Mix combinations A to F of Table 3.
|
Combinations |
A | B | C | D | E | F |
|---|---|---|---|---|---|---|
| Waste | Eucalyptus wood charcoal | Industrial Sewage Sludge | Cotton Yarn (with automotive repair residues) | Cellulose waste | Phosphogypsum | Phosphogypsum |
| Polyethene | Lignite Ash | Cattle Manure | Lime | Coffee Bark | Steel Slag | |
| Talc | Sawdust | Iodine | ||||
| CaCO3 | ||||||
| Soil | Clay | Silt | ||||
| Additives | Ammonium phosphate | |||||
| Salt Potassium |
According to Table 2, Table 3, it is evident that there is a possibility of obtaining nutrients from industrial and domestic waste. These studies identify ideal nutrients for a plant to germinate and develop: Na, K, Ca, Mg, P and N.
Table 3 shows that a mixture of pyrolysis eucalyptus charcoal, polyethene pyrolysis, talc (CaCO3) and clay soil provide suitable nutrients for the plants. Besides, it may enable the obtainment of a porous materials skeleton with carbon capture capacity due to the presence of waste obtained due to pyrolysis in the mixtures (Zampini et al., 2020).
In combination B, the waste contains industrial sewage sludge, lignite ash, sawdust in various proportions, and ammonium and potassium phosphate as additives. The waste used is waste with high carbon and calcium content. In acid soils, it reduces the degree of acidification, thus increasing organic matter.
The mixture combination C focused on the study of combustion of auto garage waste, bovine manure and human iodine waste and showed promising results in terms of vegetation development; this mixture also serves as an alternative fertilizer.
In combination D, silty soil was mixed with ashes from the pulp and lime industry, and a porous structure was observed.
Mixture E contains phosphogypsum and coffee husk, which is rich in potassium.
Lastly, mixture F is a carbonate mixture of steel slag (powder and aggregate) and phosphogypsum powder (Zampini et al., 2020). This mixture was used to study the CO2 sequestration capacity with phosphogypsum waste and water retention in the materials due to its porosity (Pettit et al., 2018). A very positive aspect of the studies carried out with this carbonate element is the development of vegetation when in contact with soil and fertilizer containing Nitrogen (N), Phosphorus (P) and Potassium (K) (Fig. 3). This way, it was possible to verify the interaction with the ideal nutrients for the growth and development of vegetation (Razzaghmanesh and Razzaghmanesh, 2017).
Fig. 3. Vegetation development on a carbonaceous sample (Shen et al., 2020).Moreover, it is necessary to consider a balance between water, nutrients and porosity for the survival of vegetation, in terms of its resistance in dry environments, to produce a similar effect to that of igneous and carbonate rocks. So that the structure of the material development contains a reservoir of water and nutrients for the survival of plants. Magnesium provides plants with good resistance to droughts, which, together with potassium (K), has better behaviour when the calcium (Ca) concentration is increased (Bortolini et al., 2020).
3.3. Types of plants
Plants can be classified through different methods, which have changed over the last years. The classification varies according to the morphological characteristics of the plants. The present item classifies plants as avascular and vascular according to the presence of conducting tissues. Besides this, the presence of flowers, seeds and fruits are other criteria used. This allowed grouping of plants into four classification groups named Bryophytes, Pteridophytes, Gymnosperms and Angiosperms.
Fig. 4 shows the four groups of plants, from those with a more straightforward structure to the most complex ones. The Bryophytes do not have sap-conducting vessels and do not have flowers (for example, mosses and lichens); the Pteridophytes have sap-conducting vessels (for instance, avenca and ferns); Gymnosperms are more complex due to the presence of flowers and seeds (pine trees and cypress); lastly, Angiosperms which differ from the Gymnosperms due to the presence of fruit (orange and almond trees, for example).
Fig. 4. Classification of the types of plants.The present review covers the study of the different types of plants versus where they are applied in the building elements, as shown in Table 4.
Table 4. List of publications and plans/classification versus a place of application in the different construction elements.