Recycling waste plastics in cementitious composites is a potential solution that can address the challenges in both concrete- and plastic industry. The purpose of this master thesis is to estimate the environmental impacts of incorporating recycled PET bottles as fine aggregate into concrete.
This life cycle assessment (LCA) study follows the ISO 14040/44 methodology. The functional unit is determined as one cubic meter of concrete and the system boundary is considered as cradle to gate, limited to the production of fresh concrete and does not include the use phase and end of life disposal of concrete. The results from an existing experimental investigation are analyzed carefully to provide reliable data for the LCA work. Four different concrete mixes containing 0%, 14%, 47% and 58% of recycled PET aggregates (RPA) as fine aggregate with compressive strength equivalent to 30 MPa are considered for comparative LCA study in nine impact categories.
Results and discussion
The results of this study are discussed based on the consideration of credit from the elimination of incineration process due to using RPA in concrete. This study reveals that the main advantage of this method of using RPA in concrete when the credit from incineration is not considered, is reducing environmental impacts in the land use category, and the other selected categories have higher impacts compared to the reference concrete with 0% RPA. However, if this recycling method is considered as an alternative to incineration of waste plastics and the credit from elimination of incineration process is considered for this product, significant advantages in different impact categories will be observed.
By considering the credit, the impacts on climate change and human toxicity- non cancer effect categories are reduced considerably. Where increasing the RPA percentage to 47% and 58% will result in negative impacts. The environmental impacts on human toxicity- cancer effects, terrestrial eutrophication and land use categories decreases by increasing the portion of RPA when the credit is considered. However, there is a slight jump from 47% RPA to 58% RPA and it is due to the increase in cement content while the RPA content is not increased considerably when compared to the difference between concrete containing 14% and 47% RPA. Considering the credit also reduced the impacts on ozone depletion, particulate matters and acidification categories, but the results show that using RPA in concrete in case of consideration of credit still had higher impacts compared to the reference concrete. Water resource depletion was the only impact category that had slightly higher impacts in the four mix designs when considering the credit and this is due to negative impact of incineration process on water resource depletion category.
This evaluation gives an understanding of the effect of this method of recycling. Using RPA in concrete resulted in considerable advantages in different impact categories by considering the credit from elimination of incineration process.
In order to increase environmental benefits of incorporating RPA into concrete, measures such as enhancing mechanical properties of recycled plastic aggregates, improving properties of the interface between cement and the aggregates, modification of composition of the cementitious binder as well as optimizing the washing process of waste PET bottles and natural aggregates can be taken.
Furthermore, targeting cement-based composites that do not demand high compressive strength such as separation walls, insulation boards or decorative elements as well as recycling concrete containing waste plastics into new products without re-melting the plastics would also be some approaches beneficial for the environment. The results can be a motivation for producing cement-based composites containing recycled plastic aggregates from other types of waste plastics such as mixed plastics, which are mainly incinerated in different countries including Norway.||