A Life Cycle Assessment of HDPE Plastic Milk Bottle Waste Within Concrete Composites and Their Potential in Residential Building and Construction Applications

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Plastic waste management is an important global problem. Therefore, the integration of plastic waste into concrete is a relevant area for reducing waste and increasing the cost-effectiveness of building materials production. The paper analyzed the mechanical strength of plastic milk bottle waste granules as a partial replacement for cement, assessed the life cycle impact on the environment, and conducted a sensitivity analysis to assess the variability of greenhouse gas emissions from transport and energy use. The effect of additives on the strength and other characteristics of concrete was also assessed. Despite the relevance and significance of the study, the work has a number of shortcomings. Thus, the authors propose to use plastic milk bottles, while nothing is said about the possibility of using other plastic containers, which significantly narrows the topic of the study. In the literature review of the work, I would like to see more studies of works related to the use of various types of waste in the field of concrete production. A study similar in approach and structure was carried out by the authors of the following works. It is recommended to indicate the following works in the literature review: 1) Kuz'min, M.P., Larionov, L.M., Kuz'mina, M.Yu., Kuz'mina, A.S., Ran, J.Q., Burdonov, A.E., Zenkov, E.V. Production of portland cement using fluorine gypsum – hydrofluoric acid waste // Magazine of Civil Engineering. – 2022. – V. 111 (3). – Article No. 11113. 2) Kuz'min M.P., Larionov L.M., Kondratiev V.V., Kuz'mina M.Yu., Grigoriev V.G., Kuz'mina A.S. Use of the burnt rock of coal deposits slag heaps in the concrete products manufacturing // Construction and Building Materials. – 2018. – V. 179 – P. 117–124. The work contains quite a large number of figures, many of which are redundant (for example, figure 7). In many places, the sources are not identified - "Error! Reference source not found." In general, the work is done at a high level and, if the noted shortcomings are corrected, it can be published in the journal.

Author Response

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Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript presents an interesting topic that is worth studying. However, the technical contents and quality need to be improved significantly. Below are some comments for reference and consideration.

1.There are a large number of literature citation format errors in this manuscript, which need to be improved as a whole.

2.The innovation of the article is not obvious enough, and the alternative mechanism of plastic milk bottles is not analyzed in detail, or whether the improvement of cement strength can be considered to come from materials such as SF.

3.Although the waste milk bottle is treated by this method, whether the author has considered that the plastic will produce a large amount of microplastics in the long-term service environment, which will cause irreversible damage to the environment such as groundwater.

4.The charts should include a clear description of the data sources (e.g., "Global Warming Potential 100-year (GWP100) based on IPCC 2013 baseline").

5. In the Results and Discussion, technical feasibility (e.g., compressive strength ≥ 40 MPa) should be clearly differentiated from economic feasibility (e.g., cost-effectiveness analysis). It is necessary to distinguish between technical feasibility and economic feasibility, and it is suggested to supplement the policy sensitivity analysis to facilitate readers to better understand.

6. A control group design must be included to establish a performance benchmark for plain cement-based materials.  

Author Response

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Reviewer 3 Report

Comments and Suggestions for Authors

The core content of this article is to study how to use discarded plastic milk bottles (PMB) as part of concrete composite materials for residential buildings and construction applications, and evaluate their environmental impact and sustainability potential. The feasibility and environmental benefits of this new type of concrete composite material are analyzed through mechanical performance testing, life cycle assessment (LCA), and Monte Carlo simulation. This study not only provides a new way to dispose of discarded plastic milk bottles, but also offers a possible sustainable material choice for the construction industry, which can help reduce dependence on traditional cement, lower the carbon footprint of the construction industry, and promote the development of a circular economy. But there are still several aspects of the article that need improvement:

(1) The study assumes that the service life of all concrete mix proportions is the same as that of traditional concrete, and does not take into account the durability differences of different mix proportions in practical applications. Furthermore, assuming that the transportation distance and energy consumption of all materials are fixed, this may not be consistent with the actual situation, especially in projects of different regions or scales.

(2) In the study, it was found that although the SFMKPMB ratio performed the best in GWP, there was an increase in HTP and FDP due to the use of metakaolin. This indicates that pursuing improvement in one environmental indicator may have a negative impact on other indicators.

(3) The study did not evaluate the economic feasibility of using waste plastic milk bottles as concrete raw materials. Although this alternative solution has potential from an environmental perspective, its economic costs (such as the collection, treatment, and modification costs of waste plastics) may affect its practical application. It is recommended to increase discussion in this area, which is the main reason for using this material in this article.

(4) Triangular distributions are used in Monte Carlo simulations to evaluate the uncertainty of transportation and energy demand, but this distribution may not fully reflect the complexity of actual situations. For example, the actual distribution of transportation distance and energy consumption may be more complex, leading to deviations in simulation results.

Author Response

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Reviewer 4 Report

Comments and Suggestions for Authors

This paper presented the research on the life cycle assessment of plastic milk bottle waste within concrete composites and their potential in residential building and construction applications. The potential of waste plastic milk bottles (PMB) in residential concrete was evaluated by assessing their mechanical strength, environmental impact, and variability in greenhouse gas (GHG) emissions. Replacing up to 10% of cement with silica fume modified plastic milk bottle (SFPMB) waste granules preserved comparable compressive strength to traditional concrete, together with the addition of metakaolin to the SFPMB mix design (SFMKPMB) further improving the materials’ strength. Also, the life cycle assessment (LCA) results were analysed on their effects on the global warming potential (GWP), human toxicity potential (HTP), and fossil depletion potential (FDP). Meanwhile, Monte Carlo simulations were conducted. The presented results were genuine, initiative, extensive and practically useful, and the discussion was comprehensive, sound and convincing with decent conclusions. The paper was well prepared, including tables and figures. The paper provides much new and useful information so it is worthwhile to publish after review. There are some technical, editorial and grammatical errors, in particular missing quotations of references in the text and wrong formats and incomplete information of References, which need to be corrected before the paper can be finally published. I have marked my comments and suggestions in the PDF file submitted by the authors. The authors should pay attention to each of these and mark the revisions clearly in a different colour in the revised manuscript for re-review.

Comments for author File: Comments.pdf

Author Response

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Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The article has been carefully revised and meets the requirements for publication.

Comments on the Quality of English Language

The article has been carefully revised and meets the requirements for publication.