Date of Award

2024

Degree Type

Thesis

Degree Name

Master of Science in Civil Engineering (MSCE)

Department

Civil and Environmental Engineering

First Advisor

Vinka Oyanedel-Craver

Abstract

Plastic production is projected to increase in the coming decades. Combined with the mismanagement of plastic waste, this makes implementing sustainable plastic recycling practices vital. Designing an alternative to fired- clay bricks by combining recycled plastic and sand not only provides a new recycling method for waste plastic but also establishes a brick production process that requires lower temperatures.

Before this study examines the environmental impact of various proportions of recycled plastic and sand for bricks using Life Cycle Assessment (LCA), a comprehensive literature review is conducted. This review focuses on potential applications, characteristics and existing LCAs of plastic waste bricks. To identify major contributors and key areas of concern throughout the entire life cycle, a contribution analysis is performed. Finally, the uncertainty of the results is assessed using a Monte Carlo simulation in conjunction with a discernibility analysis. The examined compositions consist of sand proportions ranging from 60% to 90% and plastic contents between 10% and 40%. The three types of plastic, PET (Polyethylene Terephthalate), HDPE (High-Density Polyethylene) and LDPE (Low-Density Polyethylene), are incorporated in varying ratios between 0% and 40%. The percentages change in increments of 10%.

For all compositions, the results indicate that the raw material supply and manufacturing of the bricks account for the largest share of the environmental impacts. Depending on the composition, the raw material supply constitutes between 13.36% and 51% of the total impact, while the manufacturing process accounts for 40.85% to 77.17%. Transportation, construction, and use stage have a smaller impact, ranging between 0.05% and 2.58%. On the other hand, the end-of-life stages, recycling and incineration, contribute to environmental benefits, however, demolition contributed to the overall harm associated with the bricks. Recycling the waste bricks provides environmental benefits ranging from 0.37% to 0.72%. In contrast, the portion of waste bricks ending up in incinerators and their demolition contributes between 3.66% and 7.15% to environmental harm. Finally, a composition of 90% sand and 10% recycled plastic results in the lowest environmental impact, primarily due to the relatively low impact associated with the raw material supply of sand.

For 13 out of 18 impact categories, over 90% of the environmental impact from the raw material supply is attributed to the processing of waste plastic. Regarding the remaining five categories, the processing of waste plastic still contributes at least 50% to the environmental impact from the raw material supply. Heat production is a major contributing process throughout the entire life cycle, occurring in most activities considered in this LCA. It accounts for over 8% of the processes needed in raw material supply, manufacturing, recycling and incineration - the most impactful stages.

Finally, increasing the sand content is likely to significantly decrease the environmental impacts associated with raw material supply and manufacturing. However, the environmental allowances generated from recycling and incineration are likely to decrease which can be explained by the smaller amount of waste plastic removed from the environment.

In conclusion, this LCA suggests that bricks composed of 90% sand and 10% PET result in the lowest environmental harm. However, to determine the optimal composition, the amount of waste plastic incorporated should also be considered. The further investigations are needed to minimize environmental harm while maximizing the recycling waste plastic and ensuring the necessary structural characteristics of these bricks.

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Available for download on Saturday, September 12, 2026

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