Influence of Magnesium Oxide on Carbonation of Cement Paste Containing Limestone and Metakaolin
Round 1
Reviewer 1 Report
This study investigated the Influence of MgO on carbonation of ternary Portland cement limestone-metakaolin cement? Nevertheless, there are some questions about this paper, and answers are required for publication.
- The title of this research must be change to reflect better to the paper presentation??
- The need for this study was not highlighted in the introduction for example deep in literature review and motivation of research last will be research objective??
- Create table for section 2 from line 85-90, authors can make easier for any reader to follow the paper sequence.
- Extend the literature review Geopolymers (Metakaolin) field by checking those valuable sources.
- https://doi.org/10.1016/j.jmrt.2021.09.045
- https://doi.org/10.3390/su13063330
- Please carefully check all abbreviations for this manuscript?
- Extend the conclusion length its seems not fully discussed the contain in your manuscript?
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper investigated the use of MgO in the LC3. However, the author(s) are suggested to improve the writeup on the research novelty of the paper, as in the conclusions, it seem that the research contribution of adding MgO in LC3 is limited due to insignificant strength enhancement but higher CH in the LC3 produced.
Also, there is a major comment on the results in Section 3.2 (Conclusion 2) and Section 3.3 (Conclusion 3). It was mentioned that CH contents remain relatively higher in the LC3 with MgO relative to the control mix. However, how can the author(s) can obtain the results that carbonation resistance can be improved with the addition of MgO? Carbonation is directly related to the CH in the concrete as CH reacts with CO2 to form carbonate.
Other comments are given as follows:
- Introduction (line 69): It was mentioned that “little work regarding the influence of reactive MgO addition on the reaction and carbonation of LC3 systems has been documented in the literature”. The statement brings the meaning that there had been past researches on the use of MgO in the LC3. Thus it is highly recommended that the author(s) should elaborate these literature and discuss on the research gaps of these literature and which gap(s) that this study was trying to fill up. The writeup of the research contribution on this paper remains weak if the author(s) only mention that limited studies available on the use of MgO in LC3 without discussing the research gaps.
- Section 2
- line 81: please explain what is meant by “by powder mass”. Conventional way to express the material addition/replacement is either by mass or by volume. Or the author(s) meant “by the binder mass”?
- Line 86-89: suggest to report the XRD compositional analyses in the form of table.
- Line 99 and 114: any reference/standard that the author(s) referred for the preparation of 40 mm cube specimens for both compressive strength and carbonation characterizations?
- Section 3.1:
- There is no discussions on LC3-2.5M which showed lower strength than the control and other LC3 mixes.
- Also, if LC3-2.5M showed lower strengths in all ages, thus the statement within the line 126-134 became inappropriate, for instance,
- the LC3 pastes, in general, show lower strength at 1 day 127 but then surpass at 7 days, but LC3-2.5M did not surpass after day 7.
- the addition of MgO has an insignificant impact on the later age compressive strength of LC3 pastes, but LC3-2.5M produced at least 10% lower strength than the control LC3 and OPC mixes.
- Line 156 and Figure 3: The author(s) did not label the 3 TGA curves in the Figure 3 and in the discussions (Line 156-163), the discussions did not guide the readers on which TGA curves to refer to. There is no detailed explanations on the observations/variations of the TGA curves and the author(s) directly jump to the conclusions(s).
Similar comment to Figure 6.
- Line 192: Please explain how can the MH content can be quantified in the XRD analysis which is capable to measure only the degree of crystallinity of the specimen?
- Conclusions 3: the discussions only suggest that MH can uptake CO2 to some extent but conclusion 3 concluded that the formed brucite can uptake CO2, but at a much slower rate
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
This article draws conclusions from the tests of compressive strength and carbonation resistance of cement paste made with LC3 and calcined clay, as reference and with addition of MgO. It would be better if the tests were performed on more specimens. The article should be considered for publication after some minor corrections.
L10 - Please write 3 as superscript (LC3), here and at other places in the paper.
L19 - Please write 2 as subscript (CO2).
L36 - cqueoncrete
L38 - questionquestionqueabundant
L157 - moss loss... maybe mass?
L198 and L199 - Please include labels at right ordinates of diagrams 1, 2 and 3.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
It can be accept in current shape with checking extensive whole the paper by English expert.
Author Response
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Author Response File: Author Response.pdf
Reviewer 2 Report
Most of comments had been addressed compared to the previous version. However, the following comments are given for further clarifications:
- Responses 2, the author(s) responded that "This is because MgO affects LC3 hydration, forming more CH. Also, MgO can bind some CO2 by itself". There is no discussions given in the manuscript on this statement. Without detailed discussions with support of reference citations or mechanism proposal, this statement remains as speculation.
- In Response 5, the author(s) mentioned that non-quantitative analysis was performed but in response 9, the author(s) mentioned that Rietveld quantitative phase analysis is the measure of relative proportion of elemental constituents or phases using X-ray diffraction (XRD) patterns. Both are contradictual and I am confused that whether the XRD can measure the constituents quantitatively or not? Also, the methodology of : Rietveld quantitative phase analysis was not given in Section 2.
- Response 7: It seem that the author(s) failed to explain my comment that LC3-2.5M showed lower strengths in all ages and LC3-2.5M did not surpass after day 7 but only gave the response that "Further investigation is need to understand its mechanical behaviors". It shows that the author(s) did not address my comment and simply put this as a recommendation for future study but leaving this new research gap (that why LC3-2.5M showed different observations than other mixes) unanswered and undiscussed.
- Response 10: It seem that the author(s) did not understand my comment. My previous comment 10 was commented on the different conclusion made. In the discussion, it was about the MH can take CO2 up to some extend (this means amount) but the author(s) concluded that MH can take CO2 at a slower rate (this is about the rate), but no prior discussions in Section 3 on the rate of CO2 to be taken by the MH.
Author Response
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Author Response File: Author Response.pdf
Round 3
Reviewer 2 Report
The author(s) still failed to explain my comment that LC3-2.5M showed lower strengths in all ages and LC3-2.5M did not surpass after day 7. Although the author(s) explained the incorporating percentages of MgO increases from 2.5% to 7.5%, w/b ratio may dominate the strength development of hardened pastes, resulting in comparable strength as the reference mixture (line 155-159). But the author(s) still did not explain why a different trend/observation was observed on the mix of LC3-2.5M, while the author(s) only explained the observations beyond 2.5%.
New comment: the new conclusions should be concised as it contains slightly too much discussions.
Author Response
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Round 4
Reviewer 2 Report
The author(s) now addressed the previous comment by including the observation that LC3_2.5M mix produced lower strength than the control mix after 7 days. However, in order to achieve the research contributions, the author(s) are suggested to, at least, provide the possible explanation for why this observation is obtained, with proper literature citations, along with the statement for future study recommendation. Providing only the observations without scientific proof does not achieve the research merit of an ISI journal.
Author Response
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