Carbon Emission Reduction Evaluation of End-of-Life Buildings Based on Multiple Recycling Strategies

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper covers the topic of carbon savings in case of different types of buildings and different strategies concerning the end-of-life management.

 

The conclusions are very interesting. It appears that it is not ecologicly beneficial to wait for the building to be exploited for 70 years, but it is better to end its life after 50 years when the parts of the buildng can be used in new ones. Considering the carbon emissions this strategy is good, but the question remains if it is economically reasonable. The designed service life of a building is specified at 50 years, but it is well known that the buildings are not demolished after that period of time. The conclusions are quite reasonable, but is it really more environmentally friendly to conduct the deconstruction after 50 years of buildings' life or to improve the buildings' maintenance to lengthen its life? The paper is very well prepared and conclusions are consistent. 

Author Response

Reviewer #1

The paper covers the topic of carbon savings in case of different types of buildings and different strategies concerning the end-of-life management.

The conclusions are very interesting. It appears that it is not ecologicly beneficial to wait for the building to be exploited for 70 years, but it is better to end its life after 50 years when the parts of the building can be used in new ones. Considering the carbon emissions this strategy is good, but the question remains if it is economically reasonable. The designed service life of a building is specified at 50 years, but it is well known that the buildings are not demolished after that period of time. The conclusions are quite reasonable, but is it really more environmentally friendly to conduct the deconstruction after 50 years of buildings' life or to improve the buildings' maintenance to lengthen its life? The paper is very well prepared and conclusions are consistent.

Reply: There are also literature analysis of the economic benefits of building deconstruction, indicating that some deconstruction scenarios do present economic advantages [20] (Coelho, A. (2013). Conventional demolition versus deconstruction techniques in managing construction and demolition waste (CDW). In Handbook of recycled concrete and demolition waste (pp. 141-185). Woodhead Publishing. While this paper mainly analyzes the study of carbon saving benefits at the end of building life, that is, the evaluation of environmental benefits. It is possible to extend the life of the building after 50 years through maintenance to achieve a more environmentally friendly effect. However, the article discusses the life of the building at demolition in order to obtain the maximum recovery rate and carbon reduction effect of the building demolition waste. With the life span of a building increasing from 50 years to 70 years, the CSP of the building decreases because of the increased replacement of cement, mortar, and sand with a low recycling rate and high abandonment rate. Buildings show the greatest CSP when the life span is 50 years.

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors

The following issue I am concerned
1. What is the type of article? Is it a "review article"?
2. What are the criteria for choosing "school, residential, commercial, and office buildings"? Please provide relevant references with logical reasoning.
3. The idea of the research is promising. However, the type of buildings is comprehensive.

For example, there are different types of school buildings. So, the definition of school building must be addressed. It is better to consider the same matter as the other three types of buildings.

In general, the building consists of several types of materials, and it also depends on the purpose of the building owner and designer, which makes this study's design concept impractical.

For further study, I suggest considering the CSP for more specific buildings, and the building plan might be provided to be more reasonable while studying their CSP and lifespan.

Author Response

Reviewer #2

Dear Authors

The following issue I am concerned

Comment 1: What is the type of article? Is it a "review article"?

Reply: Thank you for your suggestion. This paper is a research article which explores the carbon saving benefits under different management strategies at the end of building life based on the life cycle assessment method.

Comment 2: What are the criteria for choosing "school, residential, commercial, and office buildings"? Please provide relevant references with logical reasoning.

Reply: Considering that the material consumption per unit building area of residential, office, commercial and school buildings is quite different, the corresponding embodied carbon and carbon saving benefits will show great differences, which is helpful to compare the carbon-saving potential differences of different types of buildings. Therefore, this paper selects these four types of buildings.

Comment 3: The idea of the research is promising. However, the type of buildings is comprehensive. For example, there are different types of school buildings. So, the definition of school building must be addressed. It is better to consider the same matter as the other three types of buildings.

Reply: Thank you for your suggestion. The relevant explanations will be added in the article. The function of each type of building is different, then the amount of various materials per unit area is different. The material composition per square meter of school buildings and the other three types of buildings is the statistical result from the large database of Shenzhen Sware Budget Platform, which counts the material consumption of a large number of different buildings.

Comment 4: In general, the building consists of several types of materials, and it also depends on the purpose of the building owner and designer, which makes this study's design concept impractical.

Reply: Thank you for your suggestion. The material types of the four buildings listed in this paper are the material types of the statistically completed buildings. The purpose of this paper is to analyze the impact on the carbon-saving potential of these four types of buildings with different functions due to the different management strategies, such as recycling, remanufacturing, and reuse, the large difference in material consumption and embodied carbon per unit area.

Comment 5: For further study, I suggest considering the CSP for more specific buildings, and the building plan might be provided to be more reasonable while studying their CSP and lifespan.

Reply: Thank you for your suggestion. We will analyze the carbon saving benefits of the three different management strategies (e.g.: recycling, remanufacturing and reuse) and their impact on life span for specific engineering cases in further studies.

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript addresses an important topic on carbon-saving strategies in the construction sector, but it requires major revisions to improve its structure, results presentation, and overall clarity. Addressing these issues will significantly enhance the quality and impact of the research.

 

Please add a discussion part and provide a comprehensive analysis of the findings, comparing them to existing literature and explaining the implications of the results. The manuscript should address questions such as why certain building materials contribute more to carbon savings and what factors drive the observed variations in CSP among different building types.

 

 The language used in the manuscript needs improvement. There are grammatical issues, awkward phrasing, and unclear sentences that need revision to enhance readability and comprehension.

 

Briefly describe the current state of sustainability efforts in the buildings and construction sector to establish the relevance of the study.

 

Emphasize the broader implications of the findings in terms of environmental impact and sustainability.

 

Line 115, improve and extend the significance of your work's novelty in a broader range. The current format is not acceptable.

 

 What were the major differences in CSP among different building types?

 

Were sensitivity analyses conducted to assess the robustness of the findings in response to variations in key parameters or assumptions?

 

After applying the above revision to your manuscript, I will perform the second review of your work in the next round.

Comments on the Quality of English Language

Moderate editing of the English language required

Author Response

Reviewer #3

The manuscript addresses an important topic on carbon-saving strategies in the construction sector, but it requires major revisions to improve its structure, results presentation, and overall clarity. Addressing these issues will significantly enhance the quality and impact of the research.

Comment 1: Please add a discussion part and provide a comprehensive analysis of the findings, comparing them to existing literature and explaining the implications of the results. The manuscript should address questions such as why certain building materials contribute more to carbon savings and what factors drive the observed variations in CSP among different building types.

Reply: We added the discussion part in section 4 of the revised manuscript. It was found that 32.3%, 69.1% and 81.3% of the total embodied energy consumption could be saved if all the building materials were reused after deconstructing the concrete structure, prefabricated steel structure and wood structure at the end of the building life.(L. Aye, Ngo, R. H. Crawford, R. Gammampila, P. Mendis, Life cycle greenhouse gas emissions and energy analysis of prefabricated reusable building modules) The material table 1 shows that compared with other buildings, the school building has the largest content of structural steel. The carbon-saving potential of school buildings under the integrated management strategy is 64.01%, which is consistent with the literature. The amount of building materials used in different structures, the embodied carbon of materials, and the processing carbon emissions of materials adopted by management strategies lead to the difference in the carbon-saving benefits of materials among various buildings and different management strategies.

Comment 2: The language used in the manuscript needs improvement. There are grammatical issues, awkward phrasing, and unclear sentences that need revision to enhance readability and comprehension.

Reply: Thank you for your suggestion. We have improved the language and English expression in the manuscript as much as possible.

Comment 3: Briefly describe the current state of sustainability efforts in the buildings and construction sector to establish the relevance of the study.

Reply: Thank you for your suggestion. Reference [14] (Evaluation of Sustainable Environmental Flows Based on the Valuation of Ecosystem Services: A Case Study for the Baiyangdian Wetland, China.) has been added. Over the past decade, the principle of sustainability has become a fundamental requirement for modern building projects [14]. The conversion of waste into resources is one of the elements within the framework of the circular economy system. Thus, special attention must be paid to innovation in building recycling, reuse of materials and waste management.

Comment 4: Emphasize the broader implications of the findings in terms of environmental impact and sustainability.

Reply: Thank you for your suggestion. The relevant information has been added at the end of the discussion: In this paper, three different management strategies are adopted to improve the recovery rate of construction and demolition wastes, avoid the accumulation of construction and demolition wastes, and replace natural resources to avoid the environmental impact brought by the use of natural resources. The recycling, remanufacturing and recycling of construction and demolition wastes will reduce the impact on the natural environment to the lowest possible degree in order to obtain the best technical, environmental benefits and social sustainability.

Comment 5: Line 115, improve and extend the significance of your work's novelty in a broader range. The current format is not acceptable.

Reply: Thanks for the comment. Current studies on management strategies at the EoL stage of a building mainly focus on energy savings. As mentioned in the last paragraph of Introduction, the main novelty of this paper is to study the management strategies (e.g., recycling, remanufactur-ing, and reuse) and carbon saving benefits of four types of buildings at the end of life (e.g., residential, office, commercial, and school buildings), obtain the carbon saving potential (CSP) of different types of buildings and building materials, and then determine the building types and materials with the greatest CSP at the end life of a building. The results of the study will help reduce environmental impacts and have broad positive implications in terms of sustainable construction.

Comment 6: What were the major differences in CSP among different building types?

Reply: Thank you for your suggestion. Line 429-431: Among the four types of buildings, school buildings have the highest CSP (57.18%-64.01%), followed by residential buildings (48.74%-51.03%), commercial buildings (48.66%-51.14%), and office buildings (43.70%-47.41%). Among the four types of buildings, school buildings have the greatest carbon saving benefits, whereas commercial buildings have the least carbon saving benefits. Because the consumption of structural steel in school buildings is about 5-10 times those of other types of buildings and the reuse rate of structural steel is high under the integrated management strategy, school buildings have the greatest carbon saving benefits, whereas the consumption of concrete and structural steel in commercial buildings is lower than those of the other types of buildings. Hence, commercial buildings have the least carbon saving benefits.

Comment 7: Were sensitivity analyses conducted to assess the robustness of the findings in response to variations in key parameters or assumptions?

Reply: Thank you for your suggestion. Although we did not conduct sensitivity analysis, our data selection was based on multiple literature data [27] [46-47] [42] [44], and the data reliability was good.

Comment 8: After applying the above revision to your manuscript, I will perform the second review of your work in the next round.

Reply: I hope the above reply will satisfy you, and thank you for your review.

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

I have diligently examined the updated iteration of your article. While a number of alterations have been made, I believe that further revisions are necessary. Therefore, I kindly request your consideration of the following comments.

1) Line 150, the paper discusses the system boundaries, particularly in the context of carbon savings from recycling Construction and Demolition Waste (C&DW). Could you provide more details on the specific parameters considered within these boundaries? For instance, are there distinctions made between different types of C&DW materials and their respective environmental impacts?

 

2) The promotion of sustainability in the buildings and construction sector is intrinsically linked to broader environmental considerations, especially those related to carbon emissions and resource management. As such, the identification and assessment of carbon saving strategies in the end-of-life (EoL) phase of buildings has garnered increasing attention within the global context. Several key references offer valuable insights that align with the core objectives of this study, and they are introduced below to provide a comprehensive framework for your research:

 

(a) "Large-scale ecosystem carbon stocks and their driving factors across Loess Plateau" delves into the significant role that ecosystem carbon stocks play in regional carbon balance, highlighting the critical importance of understanding carbon dynamics within specific landscapes. This reference underscores the importance of considering ecosystem-level factors when assessing carbon savings in various contexts.

 

(b) "The Tapio Decoupling Principle and Key Strategies for Changing Factors of Chinese Urban Carbon Footprint Based on Cloud Computing" presents innovative strategies for addressing the carbon footprint of urban areas, offering a compelling perspective on carbon reduction strategies within a complex urban environment. The application of cloud computing to analyze and manage carbon footprints mirrors the cutting-edge methodologies employed in this study.

 

(c) "Life cycle carbon emissions from road infrastructure in China: A region-level analysis" provides a region-level analysis of carbon emissions associated with road infrastructure, akin to you region-specific approach in assessing carbon savings within the context of building end-of-life management strategies. This reference exemplifies the significance of life cycle assessment (LCA) for carbon-related investigations.

 

(d) "Have carbon emission trading pilot policy improved urban innovation capacity? Evidence from a quasi-natural experiment in China" investigates the relationship between carbon emission trading policies and urban innovation capacity, emphasizing the potential effects of environmental policies on broader innovation within urban settings. This reference is pertinent to understanding the multifaceted impacts of carbon-saving strategies in different sectors.

 

By establishing connections to these references, your study aims to contribute to the broader discourse on carbon savings in the construction sector, taking inspiration from and aligning with the insights provided by these significant works. It is within this context that you focus attention on the life cycle assessment (LCA) and the carbon-saving benefits of various end-of-life management strategies for different types of buildings.

Author Response

I have diligently examined the updated iteration of your article. While a number of alterations have been made, I believe that further revisions are necessary. Therefore, I kindly request your consideration of the following comments.

Comment 1:  Line 150, the paper discusses the system boundaries, particularly in the context of carbon savings from recycling Construction and Demolition Waste (C&DW). Could you provide more details on the specific parameters considered within these boundaries? For instance, are there distinctions made between different types of C&DW materials and their respective environmental impacts?

 Reply: Thank you for your review. The material consumption of different types of buildings is different, which produces different quantities of C&DW materials, such as concrete, reinforcing bar, structural steel, and so on, The specific parameters corresponding to different types of C&DW are different in the boundaries, including carbon emissions in the recycling process, carbon emissions in remanufacturing process  (e.g. recycling, remanufacturing, reuse and landfill), embodied carbon of building materials, life span of building materials, and proportional distribution of different management strategies. The respective environmental impacts of different types of C&DW materials will be discussed in the following chapter.

Comment 2: The promotion of sustainability in the buildings and construction sector is intrinsically linked to broader environmental considerations, especially those related to carbon emissions and resource management. As such, the identification and assessment of carbon saving strategies in the end-of-life (EoL) phase of buildings has garnered increasing attention within the global context. Several key references offer valuable insights that align with the core objectives of this study, and they are introduced below to provide a comprehensive framework for your research:

...

By establishing connections to these references, your study aims to contribute to the broader discourse on carbon savings in the construction sector, taking inspiration from and aligning with the insights provided by these significant works. It is within this context that you focus attention on the life cycle assessment (LCA) and the carbon-saving benefits of various end-of-life management strategies for different types of buildings.

Reply: Thank you for suggesting the above 4 references, and we have added these references to the Introduction section ( see Lines 45-54).

 

Round 3

Reviewer 3 Report

Comments and Suggestions for Authors

Your paper is confirmed to be accepted in the current format.