The chapter delves into the valorisation of polyurethane waste in gypsum mortar, addressing the growing concern of plastic waste in the construction industry. It examines the feasibility of incorporating recycled polyurethane waste into gypsum mortar, evaluating the impact on bulk density, mechanical properties, and environmental performance. The study highlights the potential for reducing waste and enhancing the circular economy while meeting regulatory standards. The analysis includes a detailed Life Cycle Assessment, revealing the environmental benefits and drawbacks of different polyurethane waste types. This research offers valuable insights into sustainable construction materials, encouraging further advancements in waste management and recycling practices.
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Abstract
The study of the behaviour of polymeric waste in building materials is of great interest. Both sectors are important and have a significant impact on the environment, so more sustainable alternatives that drive the circular economy are needed. A multi-criteria assessment on gypsum mortar with polyurethane waste from eight different industries has been carried out to analyse in depth the influence of this polymer on building materials. The methodology used studies the physico-mechanical properties of the mixtures. A “cradle to gate” Life Cycle Assessment at laboratory level is also included to evaluate and compare their environmental performance. The dosage evaluated is the one that recovers the greatest amount of waste possible while maintaining its performance above the values established in the regulation. The results of the study show that the incorporation of polyurethane waste in gypsum mortars decreases their bulk density by 2–22% in the fresh state and 7–24% in the hardened state, while flexural and compressive strengths are reduced by about one third. The environmental impact assessment of the innovative materials shows that some samples are 15–22% more environmentally friendly than the conventional one. It is concluded that the incorporation of polyurethane waste in gypsum mortar products is a viable alternative to landfill disposal or incineration, given its good technical and environmental performance.
1 Introduction
Nowadays, plastic is a material that is highly present in our economy and daily life, so that the use of traditional materials such as wood, metal, glass, stone and leather, among others, has been displaced [1]. However, numerous studies have demonstrated the serious negative effects of polymeric waste on the environment and on the health of living beings [2]. Therefore, in 2018, the European Union (EU) approved a strategic action plan with the aim of eliminating plastic pollution and accelerating the circularity of its economy, while improving the efficiency of these resources [3].
Global plastic production has reached 391 million tonnes in 2021 [4]. Polyurethane represents 5,5% of this total production, it is the 6th most demanded polymer and, within this type of plastic, polyurethane foams represent 67% of the total consumed [4, 5]. The sectors with the highest consumption of this thermoset polymer are construction and automotive [6].
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The volume of plastic waste generated each year stands at 250 million tonnes of which only 20% is recovered, the remaining 80% is sent to incineration, landfill, leakage or improper disposal [7]. Existing data on the management of polyurethane foam waste show a similar trend, with only 23.8% being recycled after reaching its end-of-life [8].
Recent studies have demonstrated the feasibility of building materials including polymeric wastes such as gypsum mortars that include recycled polypropylene [9], polycarbonate waste [10], recycled polystyrene [11] and polyethylene waste [12], among others.
This research line develops gypsum mortars that include recycled polyurethane waste in their composition. This helps, at the same, to reduce the amount of natural resources used in the manufacture of this construction material and to extend the life of this plastic waste. In order to improve its circularity, the waste is subjected to a mechanical shredding process. Bulk density, mechanical properties of flexural and compressive strength and environmental impact of the different samples, with an in-depth study of reusing the PUW, are analysed in this paper.
2 Materials and Methods
The raw materials, gypsum mortar mixtures and methodology used in this research are described in this section.
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2.1 Raw Materials and Mixtures
The polymer-gypsum mortars developed are made of:
Gypsum binder (type A), as per UNE-EN 13279–1 [13], with a density of 879 kg/m3.
Crushed polyurethane from industrial waste with a density between 40 and 142 kg/m3, depending on the type. The different PUW are type I, type B, type P, type A, type AT, type SG, type BU and type ES.
Water from the municipal network.
Glass fibre with a linear density of 2400 tex and fibre diameter of 24 µm.
Fluidifying additive.
Polymer-gypsum mortars have been designed with eight different samples of PUW (Table 1). The incorporation of polyurethane waste implies a reduction in the amount of resources (gypsum and water) used in the mix, however, it also requires a pre-crushing process.
The ideal dosage has been set up by previous research, taking into consideration the one with the highest amount of polymer valorized while maintaining the technical performance above the established standards [14]. The ratio consists of 1.5 parts of polyurethane waste (PUW) to 1 part of gypsum (by volume). The nomenclature used, G+1.5I2 as an example, refers to one part of gypsum (G) plus one and a half parts of polyurethane residue type I (by volume) with particle size less than 2 mm (1.5I2). In addition, a reference gypsum mortar has been included in order to assess the performance of the new products under study.
Table 1.
Gypsum mortar mixtures by weight (g).
Sample
Gypsum (g)
Polyurethane waste (g)
Water (g)
Glass Fibre (g)
Fluidifying additive (g)
G
1000.00
–
950.00
10.00
5.00
G+1.5I2
1000.00
97.50
1042.70
10.00
5.00
G+1.5B2
1000.00
83.00
1029.00
10.00
5.00
G+1.5P2
1000.00
271.00
1207.00
10.00
5.00
G+1.5A2
1000.00
236.00
1174.00
10.00
5.00
G+1.5AT4
1000.00
197.00
1017.00
–
5.00
G+1.5SG2
1000.00
167.50
1109.00
10.00
5.00
G+1.5BU2
1000.00
83.10
1029.00
10.00
5.00
G+1.5ES2
1000.00
1033.00
1931.40
10.00
5.00
The water-conglomerate ratio (w/c ratio) is set at 0.95, which guarantees a good workability and a suitable setting time, with the exception of the G+1.5AT4 mix, which has a ratio of 0.85 and no glass fibre, due to the specific characteristics of this type of PUW. The amount of glass fibre and additive is 1% and 0.5%, respectively, of the gypsum weight.
2.2 Characterisation
Bulk density in fresh state is determined according to standard UNE 102042 [15]. Bulk density in hardened state is obtained by dividing the mass of the samples by the known volume.
Mechanical properties are evaluated following the indications in the UNE-EN 13279–2 [16]. First, flexural strength is determined by applying a specific load in the center of the samples until failure. Compression test is then carried out on each of the specimen halves.
The environmental performance of the samples is examined using the methodology of Life Cycle Assessment (LCA). Principles, framework, requirements and guidelines are set up in the standards ISO 14040 and ISO 14044 [17, 18].
Fig. 1.
System boundary for the LCA of polymeric-gypsum mortars.
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The system boundaries are “cradle to gate”, which includes the raw materials acquisition phase, the transport phase and the construction phase (Fig. 1). All other stages have been excluded as the products are at a research and development stage.
The functional unit is 1 m2 of 15 mm thick gypsum mortar coating. The inventory data are obtained from the real laboratory practice with the help of the Ecoinvent database. The LCA analysis is carried out with the software SimaPro. EN 15804 + A2 Method is the calculation methodology used to get the results. The impact categories assessed are climate change (CC) (kg CO2 eq), photochemical ozone formation (POF) (kg NMVOC eq), particulate matter (PM) (disease inc.), acidification (A) (mol H+ eq), freshwater ecotoxicity (EF) (CTUe), fossils resource use (RUF) (MJ) and minerals and metals resource use (RUMM) (kg Sb eq).
3 Results and Discussion
3.1 Bulk Density in Fresh and Hardened State
The determination of the bulk density in fresh and hardened state of gypsum mortars is included. The results given by tests are displayed in Fig. 2.
Fig. 2.
Bulk density in fresh and hardened state of polymeric-gypsum mortars.
×
The incorporation of PUW in gypsum mortars leads to a generalised decrease in their density. In the fresh state, the density drops by 14.49% ± 9.85%; whereas in the hardened state, it falls by 15.77% ± 8.42%, with the exception of the AT4 sample whose density is 10.03% higher than the reference mortar.
Looking at the results for both states, all mortars report a loss in density from fresh to hardened state of around 39.75% ± 1.99%; with the exception of AT4 specimen which experiences a 30.39%, even if it is the only sample with a lower w/c ratio.
3.2 Flexural Strength and Compressive Strength
The data provided by the mechanical tests of the studied materials are represented in Fig. 3.
Fig. 3.
Flexural strength and compressive strength of polymeric-gypsum mortars.
×
The polymeric-gypsum mortars experience a severe reduction in their mechanical properties. Flexural strength is reduced by 33.62% ± 4.63%, without taking into account the specimens P2, AT4 and ES2, which show a high dispersion with regard to the rest of the data. The AT4 sample improve its performance by 32.25%, while samples P2 and ES2 do not meet or are close to not meeting the minimum requirements of the standard (1 N/mm2). Compressive strength of the developed mortars compared to the traditional one also goes down by 28.50% ± 4.18%, without considering the samples P2, BU2 and ES2, which are below or close to the limit of the regulatory requirements (2 N/mm2).
3.3 Life Cycle Assessment
The results of the different impact categories studied for each specimen are shown in Fig. 4. The data are presented as a percentage in order to identify the specimens with the best performance in each environmental aspect. The smaller the percentage, the lower the impact. Samples G+1.5ES2 and G+1.5P2 have not been taken into account in this evaluation due to the low mechanical properties shown in the previous tests.
The G+1.5SG2 sample has the highest score in 6 of the 7 impact categories analysed, this is due to the high amount of energy required for this polyurethane waste to be shredded and the distance for transport. Specimens G+1.5A2, G+1.5B2 and G+1.5I2 have a similar performance and a slightly higher environmental impact than the reference product, because of the combination of the impact of average processing times and the relative transport distances. The mixes G+1.5AT4 and G+1.5BU2 give the best outcomes, in comparison with the reference mortar. Although the processing time of AT4 waste is high, the non-inclusion of glass fibre in its composition offsets the environmental impacts. Waste BU2 meets the ideal conditions with a low processing time and short transport distance.
Fig. 4.
Contribution of each sample to the impact categories analysed.
×
In order to obtain an overall assessment of the environmental performance of each specimen, all impact categories are unified. This process is known as weighting and the resulting impact category is single score (µPt). The outcomes are displayed in Fig. 5.
Fig. 5.
Single Score of polymeric-gypsum mortars.
×
The single score supports the data previously discussed. In a global computation, mixtures G+1.5BU2 and G+1.5AT4 show a decrease in the overall environmental impact of 22% and 15%, respectively, compared to the reference one, while samples G+1.5A2, G+1.5B2 and G+1.5I2 are slightly above (2%, 7% and 6%, accordingly). However, the inclusion of polyurethane waste type SG2 in gypsum mortars implies an increase in environmental damage of 77%.
It has been noticed that the impact categories with the greatest weight in the single score are climate change and fossils resource use.
4 Conclusions
The current study, focused on the valorisation of polyurethane waste in gypsum mortars, concludes that:
The manufacture of gypsum mortars with polymeric waste is feasible.
In general, the addition of PUW in the mixtures leads to a decrease in the bulk density of the materials of between 7% and 24%.
The mechanical properties are reduced by one third compared to the reference material, but the values are still above the normative standards.
The environmental improvement depends on the time of processing and the distance of acquisition of the polyurethane waste. Nevertheless, samples with PUW type BU2 and AT4 show a damage reduction of 22% and 15%, respectively.
Climate change and fossils resource use are the two environmental impact categories in which this kind of specimens cause the most damage.
Acknowledgements
The authors would like to thank the European Regional Development Fund (FEDER) (UE) (project BU070P20), the Consejería de Educación de la Junta de Castilla y León (Spain) and the European Social Fund (EU), and the Consejo General de la Arquitectura Técnica de España (CGATE) for funding the study.
This work has also been supported by the Regional Government of Castilla y León (Junta de Castilla y León) and by the Ministry of Science and Innovation MICIN and the European Union NextGeneration EU / PRTR.
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