Bonding Characteristics of CLT Made from Silver Birch (Betula pendula Roth.), European Aspen (Populus tremula L.) and Norway Spruce (Picea abies (L.) H. Karst.) Wood
, Sumanta Das 1, Tomáš Kytka 1, Elham Karami 1,*, Mohsen Bahmani 2,* and Martin Sviták 1
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsPeer Review Report on the Research Article: „Bonding characteristics of CLT made from Silver birch (Betula 2 pendula Roth.) and European aspen (Populus tremula L.) wood 3 as an alternative to the Norway spruce (Picea abies (L.) H. 4 Karst.) wood CLT“
The topic of the article is timely as it explores the properties of cross-laminated timber (CLT) joints made from alternative wood species (birch and poplar) as opposed to the traditionally used spruce. CLT is a crucial building material in the context of sustainable construction, and the search for new wood species for its production has significant practical and theoretical implications. Given the evolving forestry policies and the increased interest in using hardwoods in construction, the topic is highly relevant.
The authors employed standard and validated methods to assess delamination, shear strength, and wood failure percentage according to relevant standards (EN 16531, FprEN 14732). The use of statistical analysis (ANOVA) is appropriate for comparing results and determining the statistical significance of findings. The methodological approach is consistent and aligns with the research objectives.
The article offers new insights into the suitability of birch and poplar in CLT as alternatives to spruce. The results indicate that CLT made from birch and poplar has higher shear strength than CLT from spruce; however, these alternative wood species do not meet the optimal delamination resistance according to current standards. This conclusion is crucial for future research and development of adhesives or process modifications to fully utilize the potential of these wood species.
The research objective – evaluating the suitability of birch and poplar for CLT production and comparing them with traditionally used spruce – has been fulfilled. The authors clearly presented the results and offered relevant conclusions regarding the usability of these wood species in building constructions.
The article represents a quality piece of research that contributes to the field of civil engineering and wood technology. The authors provided a detailed analysis of the properties of CLT made from alternative wood species and offered new insights that could be valuable for further research and industrial application.
Comments on the Article:
- Consideration of Further Testing: It could be beneficial to supplement the study with tests using different types of adhesives or surface treatments that could improve delamination resistance.
- Discussion of Practical Applications: The article could expand on the discussion of the practical applications of the results in the industry and potential limitations.
- More Detailed Comparison with Other Studies: A more detailed comparison of the results with other existing studies in the field would be welcomed, as it would help place the findings in a broader research context.
The language quality of the article is high. The text is clearly formulated, and technical terms are used correctly and in context. The text is free of grammatical errors or ambiguities that could hinder understanding.
Author Response
Comments on the Article:
- Consideration of Further Testing: It could be beneficial to supplement the study with tests using different types of adhesives or surface treatments that could improve delamination resistance.
It may seem that the results are not complete, but we adhered to the required properties prescribed by the EN 16351 (2015) standard for CLT. For this reason, total and maximum delamination, bond shear strength, and wood failure were selected. From a practical point of view, PUR adhesive was also chosen because it is the most used adhesive for creating glued load-bearing structural elements from wood (Kestopur 1010 type is directly intended for glulam and CLT by the manufacturer). Unfortunately, our research is not yet completed, so additional data cannot be added to the manuscript. At present, we do not yet have completed parts of the experiment where other adhesives (e.g., melamine-based adhesive) are also tested. We did not consider surface modification because we wanted to use the most used conditions from practical production of CLT.
- Discussion of Practical Applications: The article could expand on the discussion of the practical applications of the results in the industry and potential limitations.
The discussion was significantly expanded, and a total of 13 new sources were added to the references.
- More Detailed Comparison with Other Studies: A more detailed comparison of the results with other existing studies in the field would be welcomed, as it would help place the findings in a broader research context.
In the Results and Discussion chapter, additional sources (authors) were added for comparison of results for both delamination and bond shear strength.
Comments on the Quality of English Language
The language quality of the article is high. The text is clearly formulated, and technical terms are used correctly and in context. The text is free of grammatical errors or ambiguities that could hinder understanding.
All newly added or changed/fixed issues in revised version of manuscript are highlighted in red text.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsComments are reported in the attached file.
Comments for author File: Comments.pdf
Author Response
See attached pdf review.
All responses to the reviewer’s questions or comments are provided directly in the PDF file at the specific comments.
All newly added or changed/fixed issues in revised version of manuscript are highlighted in red text.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsDear Authors
Iam glad to reviewe this paper about CLT. This paer aimed to search an alternative to replace CLT made of spruce by birch and aspen. The bonding characteristics were measured to evaluate three types of CLT. However, in my point of view, the novelty of paper is not clear and enough for a scentific paper. Additionaly, the the criterion used to comprare three wood species CLT is not enough to get a conclusion if the birch and aspen are qualified to replace Spruce. Some details are proposed for your reference.
1) Title, Bonding characteristics are not a qualified criterion to evaluate if the birch and aspen can be regarded as an alternative. More criteria must be added according to the usage of CLT.
2) Abstract, It it not clear if one do not read the full text. Does the CLT be made of by a pure wood species or two wood species together. Thus, declare your experimental design clearly at the beginning.
3) Introduction, More criteria used to evaluate strength of CLT should be added in the references, such as bolt bearing strength, compression strength, etc. These criteria are commonly used. See-- Bolt-bearing yield strength of three-layered cross-laminated timber treated with phenol formaldehyde resin.
4) Line 89-90, The aim should be in detail. Which area does the CLT be utilized?
5) Line 106, the unit should be mm2;
6) Section 2.2, the third order subtitles should be added, such as 2.2.1, 2.2.2'
7) Table. The captions of Table 1 and 2 are identical. Please double check it. According to your test , it should be total and maximum delamination. If so, please combine them in one table.
8) Figrue 3 and 4. The Y axis it too large to read. It should be set according to the data range.
9) Conclusion, the last point, As mentioned at the beginning, only bonding characteristics are not qualified to judge if birch and aspen can be regarded as an alternative of spruce. More criteria must be added.
Author Response
1) Title, Bonding characteristics are not a qualified criterion to evaluate if the birch and aspen can be regarded as an alternative. More criteria must be added according to the usage of CLT.
It may seem that the results are not complete, but we adhered to the all required properties prescribed by basic European standard EN 16351 (2015) for CLT. For this reason, total and maximum delamination, bond shear strength, and wood failure were selected. Unfortunately, our research is not yet completed, so additional data cannot be added to the manuscript. At present, we do not yet have completed parts of the experiment where other adhesives (e.g., melamine-based adhesive) are also tested.
However, title and abstract were modified.
2) Abstract, It it not clear if one do not read the full text. Does the CLT be made of by a pure wood species or two wood species together. Thus, declare your experimental design clearly at the beginning.
The text has been edited to make it clear that only single-species CLTs were always used.
3) Introduction, More criteria used to evaluate strength of CLT should be added in the references, such as bolt bearing strength, compression strength, etc. These criteria are commonly used. See-- Bolt-bearing yield strength of three-layered cross-laminated timber treated with phenol formaldehyde resin.
Indeed, bolt-bearing strength (BBS) or in general, dowel-bearing strength (DBS) is an important property for CLT constructions, but it is differently focused than our research. DBS does not evaluate the composition of CLT in terms of strength relationships between individual layers, the adhesive used, and the effect of adhesion. Dowel-bearing strength is focused on the strength of connecting CLT panels using fasteners (dowels, bolts, screws etc.) in many ways.
But we have supplemented the Introduction with information that not only bond shear strength and delamination are important. Therefore, bolt-bearing strength is now mentioned in the Introduction as another important strength property when certain construction elements made of CLTs are joined together and simultaneously loaded in building or house structures.
4) Line 89-90, The aim should be in detail. Which area does the CLT be utilized?
The area of application is the same as for conventional CLT currently being produced. The goal was not to create CLT from hardwoods for specific constructions or buildings, but to find a suitable hardwood (from the perspective of suitable properties) that could match the currently the most used softwood - spruce.
5) Line 106, the unit should be mm2;
If the reviewer is referring to the unit for glue spread (line 106), we disagree with the change. The necessary amount of glue (as well as for surface/finishing treatment substances such as paint, lacquer, or varnish) is always given per basic unit area of the surface to which it is applied, i.e., m2. This is also how adhesive manufacturers state it in their product sheets, i.e. g/m2 or kg/m2.
6) Section 2.2, the third order subtitles should be added, such as 2.2.1, 2.2.2.
Subtitles were corrected in revised version.
7) Table. The captions of Table 1 and 2 are identical. Please double check it. According to your test , it should be total and maximum delamination. If so, please combine them in one table.
You are right, both captions were identical. Captions of both tables were corrected in revised version. However, for better clarity, the tables remained separated.
8) Figure 3 and 4. The Y axis it too large to read. It should be set according to the data range.
The range of the Y-axis is set to 0 - 100%, which corresponds to the possible occurrence of both delaminations or wood failure.
9) Conclusion, the last point, As mentioned at the beginning, only bonding characteristics are not qualified to judge if birch and aspen can be regarded as an alternative of spruce. More criteria must be added.
This point in the conclusion was edited and expanded.
All newly added or changed/fixed issues in revised version of manuscript are highlighted in red text.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsDear Authors
Based on the revised version, the paper has been much improved. I think this version can be accepted.
Best
Reviewer
Author Response
Thank you very much for your valuable comments. We have revised the text according to your comments.
let me know whether you have further questions.
Best,
Author Response File: 
Author Response.docx
