Optimizing Mechanical and Thermal Properties of Slag-Based Geopolymer Fiber Boards via Fiber Pretreatment and Reinforcement Type

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript entitled “Optimizing Mechanical and Thermal Properties of Slag-Based Geopolymer Fiber Boards via Fiber Pretreatment and Reinforcement Type” is in line with the topics presented in the JCS journal. This article is based on original research. The topic is up-to-date and strictly connected with composite materials. The article has a composition typical of a research article, but before being considered for publication, it requires significant changes and supplementation. The areas that have to be corrected are as follows:

• Affiliations: Supplement according to journal requirements.
• Abstract: Add measurable results.
• Abstract: Verify line 14. According to information given in the article, the pine wood was used as a primary reinforcement. The sentence requires clarification.
• Introduction (line 52): Many works introduce the term “geopolymers” before this date. Please verified. The term was introduced in 70ties. XX century.
• Introduction: Compare lines 57 and 67. However, each of these pieces of information is true, there is a lack of logical bonding between them. They required more in-depth clarification.
• Introduction: Line 74, what about the problem with the shrinkage? What's a common problem for slag-based GP? What is a mechanism to prevent this phenomenon in the fibre?
• Introduction: Please also look at the previous investigations with wood fibre, for example: 10.1080/15440478.2019.1621792. What is an exact research gap that you may have formulated?
• Introduction (last paragraph): the novelty aspect should be presented.
• Chapter 2.1: line 100 – reference to this literature is needed.
• Chapter 2.1: What kind of research method was applied to measuring Blaine fineness and specific gravity? All the used methods should be presented in the methodological part.
• Chapter 2.2: If possible, add the photos of used fibres.
• Chapter 2.2: A lack of information about the dimensions and amount of added pinewood fibres.
• Chapter 2.3: Could you explain in more detail the adverse effect of hemicellulose?
• Chapter 2.4.2.: What was the exact proportion of the composites? If possible, please introduce the table with a sample composition. It is not clear whether the reference sample pure geopolymer or one with untreated pine fibres.
• Table 3.2. The composition of the samples is not clear. Please supplement the information about composition in Point 2.4.2. Also, add information on what kind of % are used – by mass or volume?
• Chapter 3.4: Explain the amorphous structure. Normally, after the geopolymerization process, the crystalline structure is obtained, please see: https://doi.org/10.1016/j.ceramint.2024.07.024. Moreover, the presented XRD patterns have visible peaks in Figure 7. These results should be analysed again.
• Conclusion: Supplement about the measurable data.

Author Response

Comments 1: Affiliations: Supplement according to journal requirements. Response 1: Thank you for noticing this. We have updated the affiliation section with the full details (Department, University, City, Country) as required.

Comments 2: Abstract: Add measurable results. Response 2: You are right, the abstract was a bit vague. We added the specific numbers now: MOR (10.05 N/mm²), Internal Bond (1.32 N/mm²), and the thermal conductivity values (0.10 W/m·K) so readers can see the main results immediately.

Comments 3: Abstract: Verify line 14. According to information given in the article, the pine wood was used as a primary reinforcement. The sentence requires clarification. Response 3: We apologize for the confusion there. We rewrote that sentence to be very clear: Pine fibers are the "primary reinforcement matrix," and the others (glass/hemp) are secondary additives.

Comments 4: Introduction (line 52): Many works introduce the term “geopolymers” before this date. Please verified. The term was introduced in 70ties. XX century. Response 4: You are absolutely correct. We fixed the date to the 1970s and updated the reference to Davidovits (1979).

Comments 5: Introduction: Compare lines 57 and 67. However, each of these pieces of information is true, there is a lack of logical bonding between them... Introduction: Line 74, what about the problem with the shrinkage? Response 5: We re-read the introduction and agreed the flow was disconnected. We reorganized those paragraphs to connect the ideas better. We also added a specific mention that slag-based geopolymers often suffer from high drying shrinkage, which explains why we are using fibers in the first place.

Comments 6: Introduction: Please also look at the previous investigations with wood fibre... What is an exact research gap? Response 6: We refined the "research gap" statement. We clarified that while wood fibers have been studied before, the specific gap we are addressing is the "optimization of pretreatment severity" specifically for 100% slag-based systems, which react differently than fly ash systems.

Comments 7: Chapter 2.1: line 100 – reference to this literature is needed. Response 7: Added. We included the reference (Davidovits, 2008) regarding the Silica Modulus.

Comments 8: Chapter 2.1: What kind of research method was applied to measuring Blaine fineness and specific gravity? Response 8: We added the standard codes we used: ASTM C204 for Blaine fineness and ASTM C188 for specific gravity.

Comments 9: Chapter 2.2: If possible, add the photos of used fibres. A lack of information about the dimensions... Response 9: We referenced Figure 1 (SEM) and Figure 2 (Hemp) for the visuals. We also added the missing dimensions for the pine fibers (length 0.5–1 mm; diameter ~34–37 µm) to the text.

Comments 10: Chapter 2.3: Could you explain in more detail the adverse effect of hemicellulose? Response 10: We added a brief explanation. Basically, hemicellulose is hydrophilic and unstable in high-alkali environments, which hurts the bonding. We made sure this is clear in the text now.

Comments 11: Chapter 2.4.2.: What was the exact proportion of the composites? ... It is not clear whether the reference sample pure geopolymer or one with untreated pine fibres. Response 11: We clarified this in Table 1. The Control group (G) is the binder plus untreated pine fibers (1:9 ratio). We made sure the table clearly shows the composition for every group.

Comments 12: Chapter 3.4: Explain the amorphous structure... Moreover, the presented XRD patterns have visible peaks in Figure 7. Response 12: We revised the explanation in the XRD section. We clarified that the "hump" is the geopolymer gel, while the sharp peaks are just residual impurities (like calcite) or the cellulose from the fibers itself, not new geopolymer crystals.

Comments 13: Conclusion: Supplement about the measurable data. Response 13: We updated the Conclusion to include the key numbers (strength and insulation values) so the takeaways are concrete.

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript presents a well-performed experimental study on geopolymer fibre boards, focusing on effects of fibre treatment and secondary reinforcement type. Overall the problem investigated in this manuscript is interesting and potentially valuable to the literature. However, at the current state, the manuscript requires a major revision before it can be accepted for publication. Please find my comments below:

1) First issue, the manuscript is excessively long, making it challenging to read and focus. A lot of the results are just repeatedly restated across the text and figures/tables. Please remove the data repetitions, and provide more in-depth analysis of the data instead.

2) While the experimental work is solid, the manuscript needs to highly and demonstrate better the main novelty and contribution of this manuscript. Currently the key takeaways are already known in the literature, that fibre hybridisation improves strength, and excessive fibre pretreatment can degrade the fibres. If the focus is on 'waste-derived', please do more analysis/discussion on the waste and how the learning can be applicable for other types of fibres/waste too.

3) The current literature review on fibre pretreatment is not sufficient, given its importance in this manuscript. Only line 66 to 70 is too short. More literature review and discussions needed. How about fibre treatment improving mechanical properties and minimising water absorption? How to optimise fibre treatment? I recommend this reference to help in writing this: (https://doi.org/10.1080/15440478.2024.2356697)

4) I would not discuss about 'fibre minineralisation' here in this manuscript. While it is a small possibility, the authors did not do any test to verify it (such as EDS at fibre walls after treatment). As it does not add much value but speculation, i suggest removing it and reframing the discussion, the ref suggested earlier could help too.

5) The conclusion section needs major revision. While excessive alkaline treatment plus alkaline geopolymer matrix would definitely impact the fibre performance, the alkaline concentration and treatment durations were not optimised in this study. At the optimised alkaline concentration and duration, the treatment will help clean contamination and roughen the fibre surface, helping matrix bonding for sure. Consider reframing that.

6) Line 641 to 648, these takeaways are already known in the literature. Instead, the authors should either provide more in-depth discussion of why, or based on current results, suggest future research direction.

Author Response

Comments 1: The manuscript is excessively long... Please remove the data repetitions, and provide more in-depth analysis. Response 1: We agree, it was a bit repetitive. We went through the text and removed the parts where we just repeated numbers that were already in the tables. We focused the text more on why the results happened (mechanisms) rather than just listing values.

Comments 2: The manuscript needs to highly and demonstrate better the main novelty... If the focus is on 'waste-derived', please do more analysis. Response 2: We rewrote parts of the Introduction and Conclusion to highlight the novelty better. The main point is finding the "limit" of fiber treatment in these high-calcium systems. We also emphasized the value of using both industrial slag and agricultural waste together.

Comments 3: The current literature review on fibre pretreatment is not sufficient... I recommend this reference: (https://doi.org/10.1080/15440478.2024.2356697) Response 3: Thank you for the suggestion. We read that paper (Ladaci et al., 2024) and found it very relevant, especially regarding water uptake. We have cited it and added it to our discussion.

Comments 4: I would not discuss about 'fibre minineralisation' here... I suggest removing it. Response 4: Good point. Since we didn't do specific tests (like EDS on fiber walls) to prove mineralization, we removed that part to avoid speculation. We stuck to what our data clearly showed.

Comments 5: The conclusion section needs major revision... At the optimised alkaline concentration... treatment will help clean contamination. Response 5: We revised the Conclusion to be more nuanced. We acknowledge that alkali treatment can be good, but in our specific case (1% NaOH with this specific slag matrix), it was too aggressive. We framed this as a finding about the sensitivity of these fibers, rather than saying alkali treatment is always bad.

Comments 6: Line 641 to 648, these takeaways are already known in the literature. Response 6: We rewrote the conclusion to be more specific to our findings. Instead of general statements, we focused on the specific trade-off we found: you can tailor this specific waste-based material for either strength (glass) or insulation (hemp), but getting both at the same time is the challenge

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors adequately addressed my comments.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have revised the manuscript well, especially on addressing the overclaim of fibre mineralisation. I can now recommend manuscript acceptance.