Life Cycle Assessment (LCA) in Earth Construction: A Systematic Literature Review Considering Five Construction Techniques
Round 1
Reviewer 1 Report
This study through an appreciable system analytic literature review based on prisma methodology assess how LCA has been applied to earth construction over the past six years.
Though the literature review this paper “brings insights for improving LCA methodological aspects applied to earth construction”.
Nevertheless, the main goal of the paper, unfortunately, has not been achieved.
According to the authors, “this study aims to bring insights for a more sustainable design of the evaluated constructive techniques and presents environmental benchmarks at the unit, wall and building scales” and “environmental guidelines can help designers, builders, researchers, and other stakeholders such as designers, builders, researchers, etc. that use earth-based materials and want to evaluate the environmental performance of the chosen technique”
The mismatch between goals and results depends on:
a) environmental performance obtained by LCA from cradle to gate, from cradle to grave, etc, are not comparable;
b) even more significant is the fact that, in the building sector, the environmental guidelines with only the data of the environmental performance (related to materials or techniques) but without the data of the technical performance, are almost useless.
As there are no values in the guidelines (at least) for thermal, mechanical and fire resistance, water resistance; it is not possible to make a conscious choice that takes into account both - environmental and technical performance - at the same time.
Without this information, the designer and other parties involved cannot deal with the specific technical regulations of the context in which they work.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper requires a more detailed discussion about the results, and in particular, relating to the impacts shown in Figure 12. My suggestion is to divide the results for the functional unit and consider the additional following aspects:
1- same system boundaries -it is necessary to compare and discuss the results based on system boundaries and techniques.
This means to compare the GWP indicator for example A1-A3 of 1 m2 of the solutions for Adobe-RE-SC etc.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
This is a very good review article.
A number of papers were critically reviewed.
The approach to search and locate papers is robust.
The existing body of knowledge on earth work is critically analyzed.
Some minor points:
please consider the broader contribution of LCA of earth work beyond the traditional boundary of buildings.
please consider propose a future research agenda.
Line 295, please check the reference and correct it.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Affirm that:
It is outside of the scope of this review to provide a deeper discus- 707 sion by comparing the technical data and embodied carbon or embodied energy…
it is not shareable
And not even that:
291 However, it is essential to highlight that some of the publications only show the adopted 292 unit (mass or wall system) but do not clearly indicate …
768 . In addition, the values of embodied carbon and energy may serve as initial the specific function of the product bench- 769 marks for researchers, builders, and designers that work with earth-based construction 770 techniques...
LCAs processed without the specific function of product are incorrect. This approach only weakens the value of an LCA; It eliminates the possibility of making it decisive in the choice of products
It is not even correct to say that:
…since 708 there is no quantitative data for each technical feature combined with the LCA data that 709 allow visualizing the benchmarks..
In the references selected there are certainly technical data: Why not put them in a table together with the environmental ones?
With a further effort you could indicate in a table a range of variability for at least one technical performance, proceeding in the same way as you did in:
The here gathered results for embodied carbon and embodied energy are both not 739 available at the scales mentioned above. However, it is possible to visualize initial bench- 740 marks considering the adopted unities. 741 For embodied carbon at the unit (mass) scale, the values are under 1 kg CO2 eq/kg of 742 material. On the wall scale, it increases by 102 kg CO2 eq/m2 , and at the building scale, 743 embodied carbon increases by 103 kg CO2 eq/m2 . Regarding the embodied energy, the val- 744 ues begin around 10-3 MJ/kg (unit scale), increasing 105 MJ until reaching values at 102 745 MJ/m2 (wall scale). At the building scale, embodied energy values reach 103 MJ, perform- 746 ing a range of 107 MJ/unit.
Perhaps these technical data could be added in Appendix A.
Fro example, in:
a Arrigoni: doi:10.1016/j.conbuildmat.2017.03.066.
This paper rates the relevance of two acknowledged durability tests (accelerated erosion due to sprayed water and mass loss due to wire brushing) and relates outcomes to the strength and the environmental impact of several SRE mixes. The environmental impact of each mix was estimated using attributional and consequential life cycle assessment (LCA) approaches as well as an assessment of cumulative energy demand. Results demonstrated that it is possible to have durable SRE mixes without paying the cost of using environmentally-expensive stabilisers.
There are technical data and not just environmental ones
In 31. Elahi, T.E.; Shahriar, A.R.; Islam, M.S. Engineering Characteristics of Compressed Earth Blocks Stabilized with Cement 877 and Fly Ash. Constr Build Mater 2021, 277, doi:10.1016/j.conbuildmat.2021.122367.
The abstract indicates that:
...strength characteristics of CSEBs have been evaluated in terms of compressive, split tensile, flexural and shear strength. For durability, accumulated loss of mass due to cyclic drying-wetting test, wet strengths, submersion and efflorescence test have been performed.
in 45. Nouri, H.; Safehian, M.; Mir Mohammad Hosseini, S.M. Life Cycle Assessment of Earthen Materials for Low-Cost Hous- 912 ing a Comparison between Rammed Earth and Fired Clay Bricks. International Journal of Building Pathology and Adaptation 913 2021, doi:10.1108/IJBPA-02-2021-0021.
There should also be technical data
Instead, reference 42 Brambilla, A.; Bonvin, J.; Flourentzou, F.; Jusselme, T. Life Cycle Efficiency Ratio: A New Performance Indicator for a 904 Life Cycle Driven Approach to Evaluate the Potential of Ventilative Cooling and Thermal Inertia. Energy Build 2018, 163, 905 doi:10.1016/j.enbuild.2017.12.010.
does not seem to be pertinent to this study.
Finally, table 4 as it is now contains very general, almost trivial suggestions. Again, the recommendations without the link with the technical characteristics are not useful, except maybe the last one: Use bio-based materi[1]als as reinforcement.
Author Response
To fulfill the suggestions made for the reviewer, topics 3.3 and 3.4 were substantially modified to improve the discussion. During the review, the product function was taken into consideration and presented in the Supplementary Material (S1).
1) LCAs processed without the specific function of product are incorrect. This approach only weakens the value of an LCA; It eliminates the possibility of making it decisive in the choice of products
Previously the 3.4 topic was presenting “extra” technical features presented for authors to improve the LCA study, or to assess the choice of stabilizers (e.g. Arrigoni: doi:10.1016/j.conbuildmat.2017.03.066. and Elahi In 31. Elahi, T.E.; Shahriar, A.R.; Islam, M.S. Engineering Characteristics of Compressed Earth Blocks Stabilized with Cement 877 and Fly Ash. Constr Build Mater 2021, 277, doi:10.1016/j.conbuildmat.2021.122367). In other words, the topic was presenting other studied technical features that were not part of the function unit or product function. In addition, a Figure (“Fig. 16 - Rammed Earth m2 exterior wall values for Embodied Energy and UCS results gathered in SLR”) was added in order to exemplify the influence of compressive strength in terms of embodied energy and energy-mechanical efficiency of rammed earth technique.
2) In the references selected there are certainly technical data: Why not put them in a table together with the environmental ones?
With a further effort you could indicate in a table a range of variability for at least one technical performance,
Since it has been miss interpreted, we have changed the structure and gathered all the technical features in the 3.4 topic discussion. Indeed, it would be really interesting to put in a table the ranges of variability for each technical performance. However, since the authors use different technical features to characterize the product function, we have opted to put an inline table with all the data in the Supplementary Material (S1) for all the references. The same data is also available per construction technique (S1).
S1 now presents a table with product function, unit, mix designs, LCA indicators, and the technical features approached in the studies gathered in this review. They are grouped as Mechanical, Durability assessment tests, Hygroscopic, Thermal and Microstructural. The Mechanical group tests include unconfined compressive strength, flexural strength, and tensile strength. The Durability tests comprise the Accelerated Erosion Test (AET), Wire Brush Test and Modified Wire brush test, the Cyclic Dry Wet tests, and also the submersion and efflorescence assessment. The Thermal Properties group includes the thermal transmittance (U-Value), thermal resistance (R-Value), and the specific heat capacity. The microstructure comprises the porosity assessment. Therefore, besides the reviewer´s suggestion of adding the technical data in Appendix A1, the technical data was added in the Supplementary Material (S1), along with embodied carbon and embodied energy values when available.
3)Finally, table 4 as it is now contains very general, almost trivial suggestions. Again, the recommendations without the link with the technical characteristics are not useful, except maybe the last one
In terms of Table 4, “Recommendations for environmental performance improvement based on hotspots” we preferer to maintain it as it is because we believe that it can help earthen construction actors, especially those who are starting to study these techniques, and the other reviewers do not criticize.
The research limitations and conclusions also suffer modifications after this new version taking into account the proposed changes.
Thank you for your time and valuable suggestions.
Reviewer 2 Report
The new version of the documents includes my suggestions. It is necessary to review the editing of the figures
Author Response
The figures editing were reviewed as recommended.
Thank you for your time and valuable suggestions.
Round 3
Reviewer 1 Report
Dear Authors,
your work after the modifications and integrations appears to be of medium-high level and a valid reference for those who wish to replicate LCAs of earth construction techniques (and improvement with new data) or for these who need a scientific approach to make informed choices.
These important additions should be highlighted also in the abstract, for example with two lines (almost at the end of it):
…”Environmental guidelines and technical features that were presented in the LCA studies are discussed for Adobe, Cob, Rammed Earth 20 (RE), Compressed Earth Block (CEB) and Light Straw Clay (LSC).”…
Author Response
Dear Reviewer,
We thank you for the valuable suggestions that helped us to improve this work. As you suggested in this review:
These important additions should be highlighted also in the abstract, for example with two lines (almost at the end of it):
…” Environmental guidelines and technical features that were presented in the LCA studies are discussed for Adobe, Cob, Rammed Earth 20 (RE), Compressed Earth Block (CEB) and Light Straw Clay (LSC).”…
We have added to the abstract our additions, as follows (line 20 in the manuscript):
"(...) Environmental guidelines and technical features that were presented in the LCA studies are discussed for Adobe, Cob, Rammed Earth (RE), Compressed Earth Block (CEB) and Light Straw Clay (LSC). This study presents environmental benchmarks at the unit, wall and building scales aiming to encourage LCA methodology applied to earth construction techniques and fostering the discussion of earth construction sustainability."
Thank you for your time and all the suggestions.
