Review Reports - Assessment of the Wettability and Mechanical Properties of Stearic-Acid-Modified Hydrophobic Cementitious Materials

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1. Abbreviations should be defined when they first appear in the manuscript. In the abstract, what does STA stands for? Include its full name.

2. The abstract is weak and does not include the most important information from the manuscript. More insights from the results should be included in the abstract, where more numbers, percentages are presented.

3. The following sentence in the introduction section needs a reference: "To prevent salt solutions and moisture from penetrating into the concrete structure and causing damage, a common method is to reduce the water-cement ratio or add additional cementitious materials to the cement-based materials, thereby improving the density and reducing the porosity". Cite the following paper, which contains the same information: https://doi.org/10.1002/suco.202100198

4. In the introduction part, include a critical discussion of limitations in existing hydrophobic modifications and how your methods address them.

5. Specify the selection criteria for the STA content percentages and w/c ratios.

6. The rationale behind the use of ethanol in dissolving STA needs more discussion.

7. How were the contact angle measurements validated for consistency?

8. At the end of the conclusions section, provide a brief mention of future research directions, such as investigating the long-term performance of these materials.

Author Response

RESPONSE: We sincerely appreciate your valuable comments, we have carefully explained all issues you raised and marked them up in the manuscript. All comments have been addressed and marked in BLUE the manuscript.

Comments 1: Abbreviations should be defined when they first appear in the manuscript. In the abstract, what does STA stands for? Include its full name.

RESPONSE 1: Thank you immensely for your invaluable suggestion. STA refers to stearic acid, and we have made the necessary correction on Line 15 of the text. We sincerely apologize for our oversight.

Comments 2: The abstract is weak and does not include the most important information from the manuscript. More insights from the results should be included in the abstract, where more numbers, percentages are presented.

RESPONSE 2: Thank you for your suggestion. We've added more insights from the results in the summary. (Line 24-28)

Comments 3: The following sentence in the introduction section needs a reference: "To prevent salt solutions and moisture from penetrating into the concrete structure and causing damage, a common method is to reduce the water-cement ratio or add additional cementitious materials to the cement-based materials, thereby improving the density and reducing the porosity". Cite the following paper, which contains the same information: https://doi.org/10.1002/suco.202100198

RESPONSE 3: Thank you for your suggestion. This reference is highly relevant to the sentence and has been incorporated at the corresponding position in the text.(Line 40)

Comments 4: In the introduction part, include a critical discussion of limitations in existing hydrophobic modifications and how your methods address them.

RESPONSE 4: Thank you for your suggestion; we have incorporated the necessary additions into the text.(Line 85-104)

Comments 5: Specify the selection criteria for the STA content percentages and w/c ratios.

RESPONSE 5: A substantial body of research indicates that the incorporation of hydrophobic agents often leads to a reduction in the mechanical strength of concrete. Thus, it is imperative to determine an optimal dosage of STA that achieves effective hydrophobicity without excessively compromising the mechanical properties of the concrete. Moreover, the w/c ratio serves as a critical indicator of the compactness of mortar structures, significantly influencing both the wettability and mechanical performance of the material. Drawing upon the foundational insights provided by our manuscript literature, our team conducted extensive preliminary experiments, ultimately establishing the STA content and w/c ratio presented in this study. These findings not only advance the development of superhydrophobic concrete but also align with the principles of environmental protection and sustainable development. As one of our core research pursuits, this study offers valuable guidance for future investigations in this field and holds substantial engineering applicability and practical significance.

Comments 6: The rationale behind the use of ethanol in dissolving STA needs more discussion.

RESPONSE 6: Firstly, due to the substantial hydrocarbon chain in stearic acid, it remains insoluble in water under normal temperature conditions. Consequently, it tends to agglomerate in aqueous solutions, leading to poor dispersion and uneven distribution in cement-based materials. The fundamental principle underlying the dissolution of stearic acid in ethanol primarily revolves around molecular interactions between the solvent and the solute. Below are some key points:

Polarity Compatibility: Ethanol is a mildly polar organic solvent, while stearic acid is a long-chain fatty acid composed of a nonpolar hydrocarbon chain and a polar carboxyl group. The polarity of ethanol is sufficient to dissolve the polar carboxyl group of stearic acid, while its nonpolar hydrocarbon chain can also engage in interactions with ethanol's nonpolar components.
Hydrogen Bonding: Ethanol can interact with the carboxyl group of stearic acid through hydrogen bonding, thereby enhancing the solubility of stearic acid in ethanol. The carboxyl group in stearic acid serves as a hydrogen bond acceptor, while the hydroxyl (-OH) group in ethanol provides both hydrogen bond donors and acceptors.
Nonpolar Solvent Interaction: Although the long hydrocarbon chain of stearic acid is nonpolar, ethanol, as an organic solvent, creates a favorable nonpolar environment. This allows the nonpolar chain of stearic acid to interact effectively with the nonpolar regions of ethanol, thereby improving its solubility.

Our preliminary literature review indicates that at room temperature, approximately 1 gram of stearic acid dissolves in 16.6 grams of anhydrous ethanol, with solubility increasing as the temperature rises. For instance, literature reference 23 in this study employed ethanol to dissolve stearic acid, aiming to enhance the dispersion of stearic acid in mortar compositions. In summary, ethanol's ability to dissolve stearic acid is attributed to its dual polar and nonpolar characteristics, which enable effective interaction with both the polar and nonpolar components of stearic acid. Based on your suggestions, we have incorporated these details into the corresponding sections of the text. Thank you very much for your valuable suggestion.(Line 137-141)

Comments 7: How were the contact angle measurements validated for consistency?

RESPONSE 7: Each group is provided with three contact angle test specimens, and upon completing the tests, the mean value of the three specimens is calculated to represent the contact angle for that particular group experiment.

Comments 8: At the end of the conclusions section, provide a brief mention of future research directions, such as investigating the long-term performance of these materials.

RESPONSE 8: Thank you for your suggestion, we have added it in the corresponding place in our manuscript.(Line 741-748)

Reviewer 2 Report

Comments and Suggestions for Authors

The paper “Assessment of the Wettability and Mechanical Properties of Stearic Acid-Modified Hydrophobic Cementitious Materials” reports a research work about the evaluation of the wettability and of the main mechanical properties of Stearic Acid-Modified Hydrophobic Cementitious Materials. In particular, the authors have investigated the effects of STA content, water-cement ratio, cement-sand ratio, the replacement rate and addition method of TP and MTP on the wettability (contact angle and sorptivity) and compressive strength of the mortar. In general, the topic of the manuscript is interesting and the manuscript appears well-written and well-organized in its different Sections. Furthermore, the tests performed, useful for the evaluation of the chemical and mechanical properties of the different mortar mixes design, are clearly described in the text with the related obtained results. For these reasons, it is opinion of this reviewer that the manuscript can be considered for publication in Coatings after the following corrections/improvements:

- Abstract: the meaning of the acronym STA must be indicated the first time it is mentioned in the text.

- lines 29-31: consider as reported in 10.1016/j.engfailanal.2022.106546 for the influence of corrosion phenomena on the load-bearing capacity of concrete structures.

- line 98: the correct reference is Table 3 and not Table 4.

- Figures 1, 2, and 3: why doesn't the graph start from 0?

- line 184: replace “sorotivity” with “sorptivity”.

- Figure 5a: the trend shown is not clear. Why is the sorptivity, obtained at 28 days, higher for a STA content equal to 1.5%?

- Delete “Figure 1. This is a figure. Schemes follow the same formatting.” in line 563.

- Table 8: The trend of the compressive strength obtained for 0.4-MTP replacement does not appear as function of the STA content (see the result obtained for 0.9% STA content). How do the authors explain this aspect?

- Table 9: Also in this case, the trend of compressive strength does not appear as function of MTP additional rate. Better clarify this aspect.

Author Response

RESPONSE: First of all, thank you very much for your positive feedback on this paper. The comments have important guiding significance for the revision and improvement of the paper. We have carefully revised according to your feedback and marked them in RED in the manuscript.

Comments 1: Abstract: the meaning of the acronym STA must be indicated the first time it is mentioned in the text.

Comments 2: lines 29-31: consider as reported in 10.1016/j.engfailanal.2022.106546 for the influence of corrosion phenomena on the load-bearing capacity of concrete structures.

RESPONSE 2: Thank you for your suggestion. This reference is highly relevant to the sentence and has been incorporated at the corresponding position in the text.(Line 36)

Comments 3: line 98: the correct reference is Table 3 and not Table 4.

RESPONSE 3: Thanks for the suggestion. We have already made the revisions at the corresponding position in the manuscript. We are very sorry for our mistake！(Line 126)

Comments 4: Figures 1, 2, and 3: why doesn't the graph start from 0?

RESPONSE 4: In the course of our writing, we referred to the template provided by your esteemed journal, wherein the numbering begins from 1. Consequently, the numbering of our images also starts from 1. However, should your journal have specific requirements, we are more than willing to make the necessary adjustments.

Comments 5: line 184: replace “sorotivity” with “sorptivity”.

RESPONSE 5: Thank you for your suggestion. We have already changed the word in our manuscript. We are very sorry for our mistake！(Line 215)

Comments 6: Figure 5a: the trend shown is not clear. Why is the sorptivity, obtained at 28 days, higher for a STA content equal to 1.5%?

RESPONSE 6: Thanks for the suggestion. When the STA content increases further, the reaction between hydroxyl groups in the mortar and STA produces compounds that contain water, resulting in a higher amount of free water within the mortar. This, in turn, leads to greater porosity. While the addition of STA can enhance impermeability, excessive porosity facilitates water penetration, ultimately causing an increase in sorptivity. Therefore, the STA content should not be overly high. We have given an explanation at the corresponding place in the manuscript.(Line 292-303)

Comments 7: Delete “Figure 1. This is a figure. Schemes follow the same formatting.” in line 563.

RESPONSE 7: We have deleted this sentence. Once again, we sincerely thank you for your suggestion and offer our deepest apologies for our mistake.

Comments 8: Table 8: The trend of the compressive strength obtained for 0.4-MTP replacement does not appear as function of the STA content (see the result obtained for 0.9% STA content). How do the authors explain this aspect?

RESPONSE 8: For the sorptivity, STA demonstrates a certain capacity to enhance the impermeability of mortar. By forming a hydrophobic film that envelops the surface of particles within the mortar, it effectively impedes the penetration of water. Consequently, as the substitution rate of MTP increases, the corresponding STA content rises proportionally, leading to a reduction in sorptivity. However, regarding compressive strength, when the STA content reaches 0.9%, corresponding to a 30% replacement rate of MTP, an excessive reduction in cementitious materials occurs. This results in a decline in compressive strength. Therefore, The trend of the compressive strength obtained for 0.4-MTP replacement does not appear as function of the STA content. We have added to the corresponding position in the previous article.(Line 510-514)

Comments 9: Table 9: Also in this case, the trend of compressive strength does not appear as function of MTP additional rate. Better clarify this aspect.

RESPONSE 9: Similarly, sorptivity decreases with increasing MTP content and will not be repeated here. As for compressive strength, a higher content of MTP does not necessarily yield better results. Excessive MTP can disrupt the optimal compact packing structure of the mortar or cause the cement-sand ratio to deviate from its ideal value, thereby hindering the development of mortar strength. In this experiment, MTP additional rate of 10% and 20% at the 28-day curing stage enhanced the mortar's strength, whereas a content of 30% led to a pronounced negative effect, resulting in a decline in compressive strength.