Utilization of Basic Oxygen Furnace Slag in Geopolymeric Coating for Passive Radiative Cooling Application

Round 1

Reviewer 1 Report

See the attachment

Comments for author File: Comments.pdf

Author Response

Revised Version from Reviewer 1.

1. First of all the purpose of the research was not clearly stated.

In the Abstract: "The key intention of this research work is to develop a new way to reutilize BOF slag due to ...". (I have my doubts: what percentage of slag can be utilized for the production of thin coatings if "BOFs is produced in the steelmaking process in quantities of 100-150 kg slag per ton of steel". Does it have any practical significance?)

Ans: The concept of the circular economy aims at eliminating waste and the continual use of resources. As the diversified development, the new utilization of BOFs in coating is proposed in this study. This preliminary tests are focus on the feasibility and possibility. Honestly, there are still lots of problems need to face, such as the basic characteristic- working ability, durability, and storage ability. This research is still in process. After the better results is shown, we must take into account this constructive idea. Some parts of abstract is revised.

In the Section 2.1.: "The purpose of this study is trying to make the PRC coating by geopolymer powder with the alkaline solution as a binder to stick PRC powder." So what is the purpose of the work? These sentences are contradictory. A clearly defined research　purpose should be set in the Introduction. You should also think about whether the title of the work　corresponds to this purpose. Change it if necessary.

Ans: Revised. The section 2.1 is revised and rewritten.

2. It is not clearly written how the authors came to the proposed solutions, for example:

– the authors claim that the properties of double-layer coatings are better than those of single layer coatings. In what sense is this a new solution? Is it due to previous tests, if so, what were the results? (In the Introduction, the authors refer to the literature "Combined with the other white geopolymeric coating as a reflection layer, this double-layer method can reach a better effect on PRC [26].")

Ans: Revised. The idea of the double-layer structure comes from the reference [18]. In this study, we used different powders for reflection layer and PRC layer.

– how did the authors reach the coating composition presented in the article? Is this the optimal solution to the problem, if so, on what basis do the authors claim this? Were any preliminary tests performed?

Ans: Yes, we have preliminary tests. The reference [28] has been attached.

– what is 510 powder? Why 510?

Ans: In fact, “51” means the 51^st development for white coating. “0” stands for the original composition. The 511, 512, 513, 514 are also exploited due to modifying. In this study, the supplementary explanation for 510 and BOF has already added. Please see page 2 line 74-76.

3. The test description provided in the Section 2 is disordered. Some information has to be guessed from the results presented later.

For example, there is no information that authors’ coatings were compared with commercial ones -this only appears in the results of research.

Ans: Revised. Please see page 3 line 93-95.

Another example: in the Section 2 there is no information about studies on the impact of the percentage of BOFs on the emissivity of the BOF coating - this also only appears in the test results.

Ans: Revised. Please see page 2 line 65-67.

After all, this study probably served to determine the optimal composition of the BOF coating and in my opinion should be presented first.

Ans: Revised. Please see page 14 line 286-289.

In addition, I see inconsistencies between the "Overall experiment procedure" (Fig. 1) and the test results presented below. For example, for which coatings "Emission test" and "FT-IR" have been carried out? I have the impression that sometimes authors confuse the terms powder/coating. So put the description in order, that is, write in turn what was done and for what purpose.

Ans: Figure 1, Overall experiment procedure, has been redrawn.

In Section the 3, the results and discussion of studies should be given in the same order.

Ans: Revised.

4. The data in Tables 2 and 3 are not clearly presented. Where is the border between Powders and Solutions. What does "Addition to powder" mean? The results in the table rows do not add up to 100%.

Ans: Revised. Please see page 2 line 71-79.

5. Lines 105-107: "Figure 4 clearly shows the higher emissivity following with the increasing amount of BOFs until around 55% -70%. It means that the addition of 55% BOFs is closing to the upper limit." Is it true?

Ans: Revised. We made mistake. Partly sentence is deleted.

6. In the Figures 2, 3 and 5 some emissivity values are greater than 1. Please explain this.

Ans: Some emissivity values were greater than 1 due to the difference between blackbody in the FTIR and standard blackbody.

7. Figure 2 shows that the emissivity of 510 powder in the range of 8~13 μm is 0.8-1.0. Figure 4shows that the reflectivity of 510 powder in the range of 8~13 μm is 0.5-0.75. Is A + R = 1? Please explain this.

Ans: Revised. We made mistake so Figure 4 was redrawn. The emissivity of 510 powder in the range of 8~13 μm is 0.8-1.0, thus, the A ≈ 0.85. The reflectivity of 510 powder in the range of 8~13 μm was around 0.15, thus, R ≈ 0.15. Therefore, A +R = 1.

8. Please explain in more detail to what extent "Wooden box simulation temperature test" reflects the actual conditions in the building. If the test was carried out in the basement, how was radiation cooling simulated.

Ans: The purpose of testing in the basement is to decrease the weather disruption. Although placed in the basement, the radiation cooling is still in process whenever and wherever. It does not be limited by the surroundings. With regard to the radiation across the sky window, it cannot go to the sky directly and easily absorbed by other thing. However, it did not have a great effect on the experiment related to temperature.

9. Each symbol should be explained the first time it is used. In Figures 7-12 there are several symbols that should be explained in detail in the text: T0, T300, T, etc.

Ans: Revised.

10. Line 196-199 "Based on the above-mentioned results, the double-layer coating, which has great PRC effect, can cool down concrete surface 5° C and bottom about 6.2° C, with a low heating rate and high cooling rate. Therefore, choosing double-layer comparisons to commercial painting is the followup test." This text does not match the rest of the paragraph.

Ans: Revised. Please see page 9 line 214-220.

11. Figure 14 is unclear to me, poorly described in the text, no value on the vertical axis. Are these your own research? What is the meaning of these results?

Ans: Revised. Please see page 13 line 276-281 and Figure 14.

12. In the chemical formulas, the authors do not use sub- and superscripts at all. I think it should be:Ca(OH)2, Si4+, etc.

Ans: Revised.

13. The Conclusions should be largely rewritten. The Conclusions should assess the extent to which the purpose of the work has been achieved, present the most important research results, describe the advantages and disadvantages of the proposed solution and provide perspectives for its application. The innovation of the proposed solutions should be prominent. This was partly done, but the authors did not avoid, especially in the second part of the Conclusions, certain grandiloquent wording, which was not confirmed in the results of the research and in my opinion did not describe reality objectively.

Ans: The conclusion has already rewritten.

Author Response File: Author Response.docx

Reviewer 2 Report

This paper studies the validity of a geopolymeric double-layer coating made with Basic Oxygen Furnace slag (BOFS). The study deals with a novel subject and it is of interest. It is valuable to be published if the following considerations are taken into account:

• Although the introduction clearly addresses the topic of this article, from the point of view of this reviewer it should be developed in detail. In the 22 lines of the introduction, the explanation of the existing research is very scarce, when there are enough references, indicated in the introduction in groups of three in parenthesis, that can be developed, to provide a broader vision and to allow a better understanding of the approach to the problem. Please provide a more detailed introduction.
• There is a formatting mistake in the title in the word “oxygen”
• Indicating the quantities of the components of the mixture in section 2.1 would help to better understanding the behavior of the slurry tested.
• In section 3.1., the 510 powder is profusely cited. It is convenient to introduce a more detailed explanation of what it is, mainly for those potential readers who are not familiar with it.
• Figure 5 should be placed after being quoted in the text, i.e. after line 138.
• Figures 8(a), 9(a), 11(a) and 12(a) need to be improved, as it is not possible to distinguish the four lines from each other. The thickness can be increased, for example, as in Figure 7(a) or 10(a).
• In sections 3.3.1 and 3.3.2, at the end, it would be interesting to introduce a comparison between the temperature variations obtained at the surface of the coating and inside the wooden box. In this way, the efficiency of each of the options (510, BOF and 510-BOF) would be analyzed in terms of the relative efficiency of heat emission and of preventing its entry into the house.
• In the chemical notation, please observe the corresponding superscripts and subscripts.
• The paragraph of conclusions should be restructured so that all conclusions are perfectly identifiable, for example, by means of bullet points.
• In the conclusion of the adhesion, it should also be noted that the behavior of the double-layer geopolymeric coating is worse than that of commercial paintings when tested on steel surfaces. This is a fundamental aspect from this reviewer's point of view, since it would be detrimental to clearly define the limitations of use of this geopolymeric double-layer coating

In addition, this reviewer is not a native speaker, but there are a few obvious mistakes in the language style (line 16, difficulty; line 17, have; conclusions…) that make a language revision advisable, in some sections.

Author Response

Revised Version from Reviewer 2.

• Although the introduction clearly addresses the topic of this article, from the point of view of this reviewer it should be developed in detail. In the 22 lines of the introduction, the explanation of the existing research is very scarce, when there are enough references, indicated in the introduction in groups of three in parenthesis, that can be developed, to provide a broader vision and to allow a better understanding of the approach to the problem. Please provide a more detailed introduction.

Ans: The detailed information related to PRC coating has been revised at the second paragraph of Introduction. Please see revised manuscript page 2, line 45-50.

• There is a formatting mistake in the title in the word “oxygen”

Ans: Revised.

• Indicating the quantities of the components of the mixture in section 2.1 would help to better understanding the behavior of the slurry tested.

Ans: The description of section 2.1 has already rewritten with more detail. Please see page 2 line 63 to page 3 line 95.

• In section 3.1., the 510 powder is profusely cited. It is convenient to introduce a more detailed explanation of what it is, mainly for those potential readers who are not familiar with it.

Ans: Revised. Please see page 2 line 74-75.

• Figure 5 should be placed after being quoted in the text, i.e. after line 138.

Ans: Revised.

• Figures 8(a), 9(a), 11(a) and 12(a) need to be improved, as it is not possible to distinguish the four lines from each other. The thickness can be increased, for example, as in Figure 7(a) or 10(a).

Ans: All figures have revised.

• In sections 3.3.1 and 3.3.2, at the end, it would be interesting to introduce a comparison between the temperature variations obtained at the surface of the coating and inside the wooden box. In this way, the efficiency of each of the options (510, BOF and 510-BOF) would be analyzed in terms of the relative efficiency of heat emission and of preventing its entry into the house.
• Ans: Revised. Please see page 9 line 222-229.

• In the chemical notation, please observe the corresponding superscripts and subscripts.

Ans: Revised.

• The paragraph of conclusions should be restructured so that all conclusions are perfectly identifiable, for example, by means of bullet points.

Ans: Revised.

• In the conclusion of the adhesion, it should also be noted that the behavior of the double-layer geopolymeric coating is worse than that of commercial paintings when tested on steel surfaces. This is a fundamental aspect from this reviewer's point of view, since it would be detrimental to clearly define the limitations of use of this geopolymeric double-layer coating

Ans: Revised.

• In addition, this reviewer is not a native speaker, but there are a few obvious mistakes in the language style (line 16, difficulty; line 17, have; conclusions…) that make a language revision advisable, in some sections.

Ans: Revised.

Author Response File: Author Response.docx