Self-Cleaning Mortar Façades with Addition of Anatase and Rutile Titanium Dioxide for Cool Façades

Round 1

Reviewer 1 Report

In the present work, the author analysed the addition of different types of titanium dioxide, anatase, and rutile, in cement tiles for building façades. 

The following issues have to be addressed:

• At Introduction, line 57, authors mention “several chemical constituents”. Specify these constituents.

• At Introduction, line 60, authors mention “other construction materials”. Specify these materials.

• At chapter 2, line 112, authors mention “made by national and international manufacturers”. Specify manufacturers.

• At chapter 2.1, authors mention “manufacturer” (lines 116, 127). Specify manufacturer.

• At chapter 3.1. Photocatalysis analysis, authors present the results for day zero exposure to the last day exposure (49). Present the results also for other days to observed the colour variation.  

• At chapter 3.1.2. Evaluation of the superficial tension through contact angle, authors present the results regarding the contact angles and their wetting classification in Table 9. Present also the profiles of contact angles of a water drop on the surface of a cement tile, before and after application of UVA light.

Author Response

Dear reviewer,

Thank you for giving us the opportunity to submit a revised draft of my manuscript titled “Self-Cleaning Mortar Façades with Addition of Titanium Dioxide - Anatase and Rutile for Cool Façades” to Energies - Smart and Innovative Solutions for Adaptive Facade Systems. We appreciate the time and effort that you and the reviewers have dedicated to providing your valuable feedback on our manuscript. We are grateful to the reviewers for their insightful comments on our paper. We have been able to incorporate changes to reflect most of the suggestions provided by the reviewers. We have highlighted the changes within the manuscript.

Here is a point-by-point response to the reviewers’ comments and concerns.

In the present work, the author analysed the addition of different types of titanium dioxide, anatase, and rutile, in cement tiles for building façades.  The following issues have to be addressed:

• Comment 1: At Introduction, line 57, authors mention “several chemical constituents”. Specify these constituents.

Response: We have rewritten the aforementioned excerpt specifying the chemical constituents (such as metal oxides and sulfides) with reference to the consulted source (line 60).

• Comment 2: At Introduction, line 60, authors mention “other construction materials”. Specify these materials.

Response: As in comment 1, we have rewritten the excerpt mentioned above, specifying other material (coatings) with reference to the source consulted (line 64).

• Comment 3: At chapter 2, line 112, authors mention “made by national and international manufacturers”. Specify manufacturers.

Response: The manufacturers whose technical catalogs were consulted in this study were cited in the rewritten paragraph (line 125).

• Comment 4: At chapter 2.1, authors mention “manufacturer” (lines 116, 127). Specify manufacturer.

Response: You raised an important point here. However, we believe that the brands/manufacturers of the products used in the study should not be disclosed in order to preserve them.

• Comment 5: At chapter 3.1. Photocatalysis analysis, authors present the results for day zero exposure to the last day exposure (49). Present the results also for other days to observed the colour variation.

Response: We agree with this and have incorporated your suggestion with a new table 5 (currently table 6) is presented in the article with images of days 0, 3, 7, 14, 21, 18, 35, 42, and 49, to enable a comparison of color variations.

• Comment 6: At chapter 3.1.2. Evaluation of the superficial tension through contact angle, authors present the results regarding the contact angles and their wetting classification in Table 9. Present also the profiles of contact angles of a water drop on the surface of a cement tile, before and after application of UVA light.

Response: Thank you for pointing this out. Thereby, we have edited the table 9 (table 10) with drop-wetting images for better visualization of the behavior of surfaces.

We look forward to hearing from you in due time regarding our submission and to respond to any further questions and comments you may have.

Sincerely,

Eduardo Linhares Qualharini

Reviewer 2 Report

This manuscript reported the addition of commercial TiO₂ samples, both anatase and rutile in cement tiles for building façades and their application as a self-cleaning material in regulating the temperature within buildings from remaining higher reflection of sunlight. By introducing TiO₂ into cement tiles, the materials with 5% of TiO₂ give out kind of better performance forward color removement from photocatalysis effects. However, the materials characterization is not strong enough to support the conclusion. Here are some suggestions for authors to be considered for the improvement needed.

 

1) The introduction part is not informative enough to clarify the design of the experiment. More content about the photocatalysis process and mechanism with TiO₂ should be provided.

 

2) For sample preparation. More careful analysis and details should be provided, like SEM, EDS etc to confirm the real exist of TiO₂. Also, how is the dispersity of TiO₂ on cement tiles, since the bulk one will not be able to contribute to photocatalysis?

 

3) Long-term stability experiment data should be provided since it’s very important for real application. What about the leakage issues under high temperature?

 

4) The authors should seriously organize data and figure captions over the manuscript.

 

Figure 6 is not readable. What’s the unit of Y axis and what’s the X? How did that give out the colour variation information over time?

 

Scale bar for Figure 3, 4 and 5 should be added, otherwise, it not readable at all.

 

5) The diagram of Figure 1 is too simple and cannot clarify the whole experiment and design. More details about the self-cleaning photocatalysis mechanisms should be added in.

 

6) The p-factors in Table 3 are too accurate with up to 5 sig figures, is that possible?

The same questions to Table 4, 6 and 7?

 

 

 

 

Author Response

Dear reviewer,

Thank you for giving us the opportunity to submit a revised draft of my manuscript titled “Self-Cleaning Mortar Façades with Addition of Titanium Dioxide - Anatase and Rutile for Cool Façades” to Energies - Smart and Innovative Solutions for Adaptive Facade Systems. We appreciate the time and effort that you and the reviewers have dedicated to providing your valuable feedback on our manuscript. We are grateful to the reviewers for their insightful comments on our paper. We have been able to incorporate changes to reflect most of the suggestions provided by the reviewers. We have highlighted the changes within the manuscript.

Here is a point-by-point response to the reviewers’ comments and concerns.

This manuscript reported the addition of commercial TiO₂ samples, both anatase and rutile in cement tiles for building façades and their application as a self-cleaning material in regulating the temperature within buildings from remaining higher reflection of sunlight. By introducing TiO₂ into cement tiles, the materials with 5% of TiO₂ give out kind of better performance forward color removement from photocatalysis effects. However, the materials characterization is not strong enough to support the conclusion. Here are some suggestions for authors to be considered for the improvement needed.

• Comment 1: The introduction part is not informative enough to clarify the design of the experiment. More content about the photocatalysis process and mechanism with TiO₂should be provided.

Response: More information about the photocatalysis process involving titanium dioxide was inserted in the introduction of the article (line 52-59).

• Comment 2: For sample preparation. More careful analysis and details should be provided, like SEM, EDS etc to confirm the real exist of TiO2. Also, how is the dispersity of TiO2 on cement tiles, since the bulk one will not be able to contribute to photocatalysis?

Response: TiO2 was added in the laboratory by the researchers during the cement tiles production. So, the TiO2 was added carefully intending to disperse in all cement matrices, as cited in paper methodology “the titanium dioxide was mixed with water and kept in constant movement until its use”. It was added to the article in the last lines of the methodology (line 241-244): “For a visual qualitative analysis of the distribution of TiO2 in the cementitious matrix and aiming to analyze the interaction of the paste with the fibers and the behavior of the composite as a whole, images of scanning electronic microscopy were performed, using a JEOL JSM-6510LV equipment.” Some results of SEM are presented in figure 7.

• Comment 3: Long-term stability experiment data should be provided since it’s very important for real application. What about the leakage issues under high temperature?

Response: The present study focused on staining and the mechanism of photocatalysis. No tests were carried out over time for the dimensional characteristics of the tiles, only for the dry and saturated tiles, as required by Brazilian standards. For the same reason presented above, the cement boards were evaluated in terms of qualitative permeability, water absorption, and flexural tensile strength. We understand that more studies on performance are necessary to apply facades in the long term, which would not fit in just one scientific article. Thus, we reiterate that the present study’s focus was the evaluation of staining and photocatalysis of cementitious plates produced with rutile TiO2 and anatase in their composition at different levels. They were submitted to two different curing environments: UVA radiation and urban environment. With these controllable factors, important results regarding the behavior of these plates were obtained, so more properties should be obtained in future studies aiming to complement them.

• Comment 4: The authors should seriously organize data and figure captions over the manuscript. Figure 6 is not readable. What’s the unit of Y axis and what’s the X? How did that give out the colour variation information over time? Scale bar for Figure 3, 4 and 5 should be added, otherwise, it not readable at all.

Response: The figure 6 was remade using bigger letters. ΔE (Y axis) indicates the difference between the stains obtained with L x a x b at two different times. Figure 3 presents the scale bar for one cement tile. Figures 4, and 5 are representations of the same cement tile presented in figure 3 but positioned side by side. The authors believe that the scale of figures 4, and 5 are valuable to figure 3 dimensions. All figures’ resolutions were improved.

• Comment 5: The diagram of Figure 1 is too simple and cannot clarify the whole experiment and design. More details about the self-cleaning photocatalysis mechanisms should be added in.

Response: A new diagram composition is proposed in Figure 1, including the photocatalysis mechanism.

• Comment 6: The p-factors in Table 3 are too accurate with up to 5 sig figures, is that possible? The same questions to Table 4, 6 and 7?

Response: The p-factor is automatically calculated by Statistica Software, through a multiple variance analysis with 95% of confidence, we can obtain both the p-factor and the presented graphics. It reflects the variation of color (ΔE) values added in the software obtained by the spectrophotometer.

We look forward to hearing from you in due time regarding our submission and to respond to any further questions and comments you may have.

Sincerely,

Eduardo Linhares Qualharini

Reviewer 3 Report

The manuscript title: Self-Cleaning Mortar Façades with Addition of Titanium Dioxide - Anatase and Rutile for Cool Façades.

The author needs to take into consideration the following comments to improve the manuscript:

1. Abstract should contain objectives, methodology, key findings, and conclusion. The authors performed mechanical strength, absorption, and permeability, but their outcomes are not reported, and the conclusion was drawn by avoiding those properties. Therefore, the abstract need to be written considering them. ANOVA was performed but not reported.

2. In Line 21: What do authors want to declare by “plus an admixture of 0.3% polypropylene fibre”? Please write it differently to understand the reader better.

3. Keywords do not match the findings and objectives; please consider changing and adding according to the study objectives. 

4. The literature review in the introduction is not designed appropriately, e.g., only 12 papers have been addressed, and some do not match the study's objectives. Only 26 articles have been used, which is quite low. It was found that Line 74-81 is the summary of one paper, which is relatively high. Please add recent relevant information by reviewing more papers, highlighting the gap in the literature, and the aim of the present study thus can fill the gap of the literature.

5. Chemical and mineral composition of white Portland cement and titanium dioxide need to be added and discussed. 

6. In Lines 114-116: Compressive strength of white Portland cement at 28 days greater than or equal to 60 MPa. Indeed, though it was given by the manufacturer, this property needs to be verified in the lab using proper testing guidelines as it is one of the key parameters, or please add the proper references to support this.

7. In Line 121: Please add the selection of the geometry of the polypropylene fiber and add any reference to support the purpose of this geometry. Indeed, many information was used in Section 2.1, which was not performed in the lab, and the name of the manufacturer, testing guidelines, and a proper citation was not reported. Please consider all of these and improve the section.

8. Give a proper name for Section 2.2. Many tests (flexural tensile strength, water absorption, permeability, and dimensional variation) were performed where the testing guidelines, size of the specimens, and testing methods were not discussed properly. Please consider all of these

9. Line 153-154: The testing age was 30 days instead of 28 days; please explain why. As only flexural strength was performed, replace the mechanical strength with flexural strength in the entire manuscript.

10. In Table 2, permeability was assessed as qualitative; why not quantitative? Please justify this and what scientific justification can be drawn for the durability of tiles. What represent "Not present"? Is the deflection during the flexural test monitored?

11. Instead of summing up all parameters, the authors need to add a proper discussion of each result with a proper mechanism to discuss the results in different sections.

 

12. The study's conclusions need to be reported based on key findings accordingly.

Author Response

Dear reviewer,

Thank you for giving us the opportunity to submit a revised draft of my manuscript titled “Self-Cleaning Mortar Façades with Addition of Titanium Dioxide - Anatase and Rutile for Cool Façades” to Energies - Smart and Innovative Solutions for Adaptive Facade Systems. We appreciate the time and effort that you and the reviewers have dedicated to providing your valuable feedback on our manuscript. We are grateful to the reviewers for their insightful comments on our paper. We have been able to incorporate changes to reflect most of the suggestions provided by the reviewers. We have highlighted the changes within the manuscript.

Here is a point-by-point response to the reviewers’ comments and concerns.

The autor needs to take into consideration the following comments to improve the manuscript:

• Comment 1: Abstract should contain objectives, methodology, key findings, and conclusion. The authors performed mechanical strength, absorption, and permeability, but their outcomes are not reported, and the conclusion was drawn by avoiding those properties. Therefore, the abstract need to be written considering them. ANOVA was performed but not reported.

Response: Thanks for pointing this out. We agree with your comment. However, we opted for a more concise section in the abstract informing the reader that with the addition of titanium dioxide, cementitious tiles maintain the characteristics imposed by normative criteria, thus making the reading more fluid. Regarding the ANOVA, the following sentence was added to the methodology (line 238-240): “The analysis of results was performed using analysis of variance, in the Statistica software, version 10, with 95% reliability, in order to assess whether the response variables were statistically influenced by the controllable variables.”

• Comment 2: In Line 21: What do authors want to declare by “plus an admixture of 0.3% polypropylene fibre”? Please write it differently to understand the reader better.

Response: We have rewritten the aforementioned section on line 21 to make it easier to understand.

• Comment 3: Keywords do not match the findings and objectives; please consider changing and adding according to the study objectives.

Response: Keywords were modified according to the findings and objectives presented in this manuscript.

• Comment 4: The literature review in the introduction is not designed appropriately, e.g., only 12 papers have been addressed, and some do not match the study's objectives. Only 26 articles have been used, which is quite low. It was found that Line 74-81 is the summary of one paper, which is relatively high. Please add recent relevant information by reviewing more papers, highlighting the gap in the literature, and the aim of the present study thus can fill the gap of the literature.

Response: Thanks for the suggestion. The quoted excerpt has been modified, as well as a few more sources have been added to the work. The existing gap in the literature and our objective in approaching the subject were also inserted (line 84-93).

• Comment 5: Chemical and mineral composition of white Portland cement and titanium dioxide need to be added and discussed.

Response: The properties of Anatase and Rutile titanium dioxide are shown in Table 2. No further chemical analyzes were performed on these materials. Table 1 was added to the paper, with some properties of white Portland cement.

• Comment 6: In Lines 114-116: Compressive strength of white Portland cement at 28 days greater than or equal to 60 MPa. Indeed, though it was given by the manufacturer, this property needs to be verified in the lab using proper testing guidelines as it is one of the key parameters, or please add the proper references to support this.

Response: In this work, the compressive strength of the cement was not performed. It is believed that the values obtained for the flexural tensile strength of the plates were satisfactory since the compressive strength corresponds to approximately 10x the tensile strength values. Of course, it must be considered that the tests were carried out on specimens with fibers, which influences the results. As for referencing the manufacturers, the authors chose not to mention the names of manufacturers in order to preserve them.

• Comment 7: In Line 121: Please add the selection of the geometry of the polypropylene fiber and add any reference to support the purpose of this geometry. Indeed, many information was used in Section 2.1, which was not performed in the lab, and the name of the manufacturer, testing guidelines, and a proper citation was not reported. Please consider all of these and improve the section.

Response: Figure 2 was added to the paper to show the dimensions and visual appearance of the polypropylene fiber used in the study. In this work, the names of the manufacturers will not be disclosed in order to preserve the manufacturers.

• Comment 8: Give a proper name for Section 2.2. Many tests (flexural tensile strength, water absorption, permeability, and dimensional variation) were performed where the testing guidelines, size of the specimens, and testing methods were not discussed properly. Please consider all of these.

Response: The name of 2.2 section was changed to: “Methodology of tests performed”.

The following sentence was added to section 2.2 (line 168-171): “The dimensions of the specimens followed the determinations of current regulations: 60x10x1cm³ for permeability, 22x10x1cm³ for flexural strength, and 10x10x1cm³ for the other ones.”

As the tests were carried out in accordance with regulations, the methodologies were not described in detail, since the article would be too extensive. The authors believe that citing the referred regulations is enough for the reader to seek the necessary information if they wish to reproduce the experimental program executed here. However, if the reviewer wishes, the tests can be explained in detail.

• Comment 9: Line 153-154: The testing age was 30 days instead of 28 days; please explain why. As only flexural strength was performed, replace the mechanical strength with flexural strength in the entire manuscript.

Response: It was included the information in the sentence (line 175-177): “The tests carried out in accordance with this standard were: flexural tensile strength, water absorption, permeability, and dimensional variation, all at 30 days of age, due to the availability of equipment for its realization.” The suggestion was accepted and the modifications were made.

• Comment 10: In Table 2, permeability was assessed as qualitative; why not quantitative? Please justify this and what scientific justification can be drawn for the durability of tiles. What represent "Not present"? Is the deflection during the flexural test monitored?

Response: The permeability test for cementitious slabs was carried out in accordance with NBR 15498 (ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS, 2021). The specimens were placed away from the support base and an adapted box completely sealed with silicone was positioned over them, which was filled with water and maintained at a minimum height of 20 mm. for 24 hours. The result of the test corresponds to the analysis of the underside of the plates after 24 hours, for positive results the plates must not show drop formation and may show signs of moisture. Thus, not present, means that the plate did not show drops or spots of moisture.

In the article, the following sentence is presented after the permeability results (line 259-264): “The permeability test is carried out by analysing the underside of the tile exposed to a layer of water, which, for positive results, must not show drop formation, but may show signs of moisture. All cement tiles were approved in terms of permeability, so that none showed drop formation (“not present”). Only the reference tile, without the TiO₂ admixture, showed “moisture” marks on the side opposite to contact with water, indicating the improvement in the efficiency of the tiles with the admixture, in terms of their tightness.” The deflection during the flexural test was not monitored.

• Comment 11: Instead of summing up all parameters, the authors need to add a proper discussion of each result with a proper mechanism to discuss the results in different sections.

Response: Some new sentences, figures, tables, and information about the results were added to the paper for making the discussion more profound and interesting.

• Comment 12: The study's conclusions need to be reported based on key findings accordingly.

Response: While we appreciate reviewer feedback, we understand that the conclusion points out the main findings in the study in an objective way.

We look forward to hearing from you in due time regarding our submission and to respond to any further questions and comments you may have.

Sincerely,

Eduardo Linhares Qualharini

Round 2

Reviewer 1 Report

Dear Sirs,

The manuscript was improved and it can be published in this form.

Reviewer 2 Report

This revised manuscript reported the modified cement tiles of building façades and their application as a self-cleaning material. By introducing TiO₂ into cement tiles, the materials likely showed better performance forward color movement under UV light irradiation. After this sufficient improvement, it should be able to publish in Energies.