Biomineralization of Plastic Waste to Improve the Strength of Plastic-Reinforced Cement Mortar.

Seth Kane,Chelsea Heveran,Cecily Ryan,Kendra Lunday,Abby Thane,Hakan Armağan,Adrienne Phillips,Michael Espinal

doi:10.3390/ma14081949

Abstract

The development of methods to reuse large volumes of plastic waste is essential to curb the environmental impact of plastic pollution. Plastic-reinforced cementitious materials (PRCs), such as plastic-reinforced mortar (PRM), may be potential avenues to productively use large quantities of low-value plastic waste. However, poor bonding between the plastic and cement matrix reduces the strength of PRCs, limiting its viable applications. In this study, calcium carbonate biomineralization techniques were applied to coat plastic waste and improved the compressive strength of PRM. Two biomineralization treatments were examined: enzymatically induced calcium carbonate precipitation (EICP) and microbially induced calcium carbonate precipitation (MICP). MICP treatment of polyethylene terephthalate (PET) resulted in PRMs with compressive strengths similar to that of plastic-free mortar and higher than the compressive strengths of PRMs with untreated or EICP-treated PET. Based on the results of this study, MICP was used to treat hard-to-recycle types 3–7 plastic waste. No plastics investigated in this study inhibited the MICP process. PRM samples with 5% MICP-treated polyvinyl chloride (PVC) and mixed type 3–7 plastic had compressive strengths similar to plastic-free mortar. These results indicate that MICP treatment can improve PRM strength and that MICP-treated PRM shows promise as a method to reuse plastic waste.

Highlights

Plastic is one of the world’s largest and fastest-growing waste streams, with 368 million tons of plastic waste generated in 2019 [1]
In the first study comparing enzymatically induced calcium carbonate precipitation (EICP) and microbially induced calcium carbonate precipitation (MICP) treatment, polyethylene terephthalate (PET) did not impair the growth of S. pasteurii in a flask culture
The compressive strengths measured in this study demonstrate that, for PET and polyvinyl chloride (PVC) plastic, MICP treatment can produce a significant increase in plastic-reinforced mortar (PRM) compressive strength while, in other plastic types, little change in compressive strength was seen with mineralization

Summary

Introduction

Plastic is one of the world’s largest and fastest-growing waste streams, with 368 million tons of plastic waste generated in 2019 [1]. The amount of plastic recycled is economically limited by the low cost of virgin plastic and the high costs associated with recycling processes such as transportation, sorting, cleaning, and extrusion. This limitation leads to low-value type 3–7 plastics typically being routed to the landfill or being improperly managed, thereby contaminating the environment. The addition of waste materials to concrete has the potential to reuse large volumes of diverse waste streams including glass, plastic, and industrial waste [3,4,5,6]. The addition of waste to concrete provides the dual benefits of redirecting waste away from the landfill and reducing greenhouse gas emissions associated with cement production. Plastic-reinforced cementitious materials (PRCs), such as plastic-reinforced mortar (PRM), may allow for the repurposing of mixed-type plastic waste of varying geometries, eliminating the costly sorting process required for conventional plastic recycling [3,7,8,9,10,11,12,13,14,15]

Methods

Results

Conclusion