A group of researchers from Montana State University (MSU) has published a study on the biomineralization of plastic waste to improve the strength of plastic-reinforced cement mortar.
The application of plastic-reinforced cementitious material (PRC) is presently limited due to its low strength in comparison to conventional concrete. The MSU research enhances the strength of PRC by improving the interfacial strength via the deposition of calcium carbonate (CaCO3) onto the surface of the plastic.
Biomineralization is a method for depositing calcium carbonate onto plastic. The study evaluates calcium carbonate biomineralization techniques applied to coat plastic waste and improve the compressive strength of plastic-reinforced mortar (PRM), a type of PRC.
The research examined two biomineralization treatments: enzymatically induced calcium carbonate precipitation (EICP) and microbially induced calcium carbonate precipitation (MICP).
In the MICP process, the urease enzyme is produced by microorganisms, like the soil bacterium S. pasteurii (Sporosarcina pasteurii), while in the EICP process, the urease enzymes are instead sourced from Canavalia ensiformis (i.e., jack bean).
When polyethylene terephthalate (PET) was subjected to MICP treatment, it resulted in PRMs with compressive strengths similar to that of plastic-free mortar, whereas EICP-treated PET demonstrated weaker strength than that of MICP.
The MICP treatment affects the compressive strength of PRM in various types of plastics differently. Though the research requires further work to understand the impact of MICP treatment on interfacial strength, the results indicate that MICP treatment can improve PRM strength and that MICP-treated PRM is a promising method to reuse plastic waste.
However, a deeper knowledge of this mechanism can lead to the application of biomineralized PRC as a high-volume method to reuse plastic waste.
The study found that none of the examined plastics (PET, PVC, LDPE, PP, PS, or ABS) inhibited S. pasteurii growth under the tested biomineralization conditions. MICP treatment deposited more CaCO₃ on the surface of PET plastic than EICP treatment, resulting in PRM with 5% MICP-treated PET having 88% of the compressive strength of the plastic-free mortar.
Particularly, PRM reinforced with 5% MICP-treated PET, PVC, and mixed type 3–7 plastics had strengths similar to that of plastic-free mortar and showed sufficient strength for application in engineering structures.
You can read the complete research paper here.