The Recycling and Reuse of Natural Materials: Sound Absorbing Box Patterns That Use Waste from Olive Tree Pruning
Round 1
Reviewer 1 Report
The paper aims to promote the use of waste from pruning olive trees in sound absorbing structures. It investigates the random absorption coefficients obtained with various distributions of olive tree waste in plywood frames regarding aesthetic or decorative appeal as well sound absorption. The influence of two ways of confining the loose waste material is investigated also.
While the development of more sustainable materials as sound absorbers is to be welcomed, and this paper makes a useful contribution in this respect, it contains very little science and, unfortunately, in many places, the use of English either obscures or creates confusion about the authors’ meaning, so it is important that it be improved.
The authors should consider the following detailed points.
1. A more elegant and informative title would be ‘Sound absorbing box patterns using waste from olive tree pruning’
2. Abstract line 7: I suggest replacing ‘a plywood formwork’ by ‘plywood frames’, and the use of ‘frames’ rather than ‘formwork’ throughout the text.
3. Introduction, last paragraph on page 2: I suggest replacing “focuses on reuse agricultural by-products from olive tree pruning including branches and leaves without distinction to demonstrate how, instead of being disposed of with no secondary purpose, burned or composted, they can be reused to produce key components for the building sector, with a focus on acoustic performance, so as to direct the olive sector toward a unique circular economy model” by ‘investigates the reuse of olive tree branches and leaves from pruning in sound absorbing structures thereby contributing to a circular economy [15]’.
4. It would be helpful to have more information about the ‘chips’ produced from the pruning wastes. In section 1.1 on page 3 it is stated “olive wood pruning scraps, in the form of chips of different sizes”. In section 2.1 on page 3 it is stated “Pruned branches and leaves have been transformed, by means of a tractor-driven chipper with an autonomous motor, into the intermediate product consisting of variable size chips” and that these are sieved to remove the coarser fraction. To what extent do olive tree leaves contribute to these ‘chips’ after the sieving? If they do, what is their proportion by weight? Do the stated range of dimensions of between 40 mm and 100 mm refer to the largest dimensions of the ‘chips’? What is ‘d’ in Table 1?
5. Introduction last sentence: I suggest a rewrite of “Moreover, it is of great interest for the acoustic community to also assess the acoustic effects at the scale of the environment based on location and extension of the acoustic materials [19,20]” Perhaps this means ‘Moreover, the acoustics community should be interested in another sustainable decorative type of sound absorber [19,20].’
6. In the caption for Figure 4, what is the meaning of “In red the maximum dimension by decomposition”? Does this refer to the ‘sub-modules’?
7. After Figure 5 on Page 6, I suggest replacing 'Defining a basis total area of 0.27 m2' by 'With sides enclosing a base area of 0.27 m2'. I suggest replacing ‘reflective’ by ‘acoustically hard’.
8. The nomenclatures ‘FULL’ and ‘EMPTY’ in Figure 6 and in the text are strange, since ‘EMPTY’ refers to the case where, as well as the ‘BASE’ module sides, there are the sides of sub-modules, and modules D and E are ‘fuller’ than ‘FULL’.
9. In section 2.2.2 second paragraph I suggest replacing “final effect of the sound-absorbing” by ‘sound-absorbing configuration’.
1- The vertical labels in Figures 12 to 14 should be ‘Random Incidence Sound Absorption Coefficient’. Alternatively use this description in the captions. Why does the ‘EMPTY’ configuration results in greater absorption than the ‘BASE’ configuration above 1300 Hz?
1- In describing the absorption spectra, please replace ‘maximum peaks’ by ‘maxima’ and replace ‘minimum peak’ or ‘peak minimum’ by ‘minimum’.
1- Please discuss whether the peaks in the absorption spectra are related to quarter wavelength resonances of the sound waves inside the hard-backed porous materials.
1- In addition to the further work mentioned on page 14, it would be interesting to conduct systematic measurements of flow resistivity and tortuosity of the olive tree waste derived materials with a view to establishing a bespoke model for the absorption of such a material.
Author Response
Please see attached file.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The paper is interesting, especially for the designers and the overall community for considering as the driving force for the study the concept of sustainability and the reduction of carbon footprint. It is well written, follows a correct methodological order, is duly supported by an extensive evaluation of the state-of-art, the figures are clear in content, the references are up to date, and the conclusions are supported by the obtained results.
However, some clarifications are needed:
1. In the abstract is referred the acronym TNT. The abstract is the first text a reader reads, so that I suggest putting in brackets (Tissue-Non-Tissue) as it is in the middle of the paper.
2. The authors say in the second paragraph of the Introduction that there are few studies on natural fibres. This seems to be in contradiction to the several examples cited, and on the references consulted. Some clarification is needed.
3. In legend of Figure 1, a) is referred to Production pruning. Should be as such, for what we see are only olive trees?
4. In Figure 2, as we usually read from left to right and the modelling as something that comes after a real thing to effectively represent it, the a) and the b) should be interchanged, let's say on the left the real configuration and on the right the modelling.
5. It is said that the void content was obtained using image techniques as the Figure 3 shows. But the images on figure 3 only shows a surface. A clarification is needed to understand how the void content has been obtained considering the sample thickness.
6. IN Figure 4, the mentioned colors are not readable. Maybe it will be in the final printable version...?
7. After Figure 5, it is said "Pattern B was chosen". Nothing is referred to support that choice. Is it the most representative? Or flexible to get other sub-modules? A clarification is needed.
8. What is conceptually the difference between Pattern D and Module E?
9. In Figure 8 c), it is referred "TNT in detail". It is not easy to see it in a better detail than in the other images of the same figure. Maybe a more refined focusing or other presentation could be envisaged. The same applies to Figure 10 c).
10. In Section 2.3, 2 line of page 9, it is said that the temperature and humidity influencing the absorption were measured. Is this relevant when considering the SSRR dimensions?
11. In Section 3, the authors say that the weighted absorption is relevant and fundamental for architects. Is it really. The parameter is very tricky for agglutinates in one simple value a behavior of a global spectra. And normally the designers (the good ones) to make an effective project should consider the overall spectra and not the composed value. Concerning this, maybe some particular considerations should be added to clarify the scope of this parameter, which could be considered relevant just for comparative evaluations. And the disturbances the tests show (see figures) within the global spectra are a proof of this.
12. In Figure 12, nothing is said about the peak at 1600 Hz and the drop of 3150 Hz, for the situations of empty and full. Some explanation could be added.
13. In the Conclusions Chapter is referred that "From 800 Hz onwards.... between 0.1 and 1". This range is obviously evident almost for all materials, for all this part of the spectra, and sometimes for the lower part of it (in certain cases the values are below 0.1, but this happens rarely). So, being too evident should it be included in the conclusions section?
14. In the conclusions, a reference to the peaks and drops is done. However, no explanation is presented.
15. Last one: Why the authors haven't done any test using the requirements and procedures of EN ISO 354, using more appropriate values of exposed surface areas (10 m2), even though, in two or three samples, in order to get a more suitable comparison between the overall set of samples? In fact, the use of small-scale procedures is more academic but nor sufficiently "real". And the sample dimensions used are very small. It seems the uncertainty of the procedure is quite large, and that's why the EN354 requires rooms with 200 m3 volume and samples of 10 m2 at the minimum, where the cut-off frequency is lower than in the SSRR, making the process more stochastic.
Author Response
Please see attached file.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The authors have responded to the review comments, criticisms and questions and made revisions including arranging for a check by a native English speaker of their use of English. As a result the paper has been improved considerably. However, there are four places in which use of English could cause lack of clarity and confusion for the reader. So, I request that the authors consider making the further revisions suggested below.
1. On page 3 the sub heading ‘1.1. The valorization of loose natural fibers’ doesn’t make sense and is not needed. So, I suggest that it be deleted.
2. In the caption for Figure 2, what does ‘real’ mean? The context suggests that Figure 2(a) is a photograph of the chips prepared from pruning waste without being confined by a frame.
Similarly I suggest replacing ‘3D modelling and rendering of the plywood frames made of birch plywood and olive tree pruning chips.’ by ‘3D image of a frame containing loose chips’
3. In Section 2.2.1 I suggest replacing the first sentence by ‘Sixteen differently shaped sub modules were made using the same material and with the same frame thickness and have been used in different configurations inside the frame of the basic module.’.
4. I suggest replacing the Figure 3 caption by ‘2D images of the sub module frames. Those with maximum base dimensions of 200 mm by 200 mm are shown in gray and those with maximum base dimensions of 100 mm by 100 mm are shown in white.’
Author Response
Please see attached file.
Author Response File: Author Response.docx
Reviewer 2 Report
I thank the authors for taking good note of the recommendations and suggestions raised.
For me the paper is fine in its last version. I just suggest moving part of the legend of Figure 3 to the main text (the legend is too long).
Author Response
Please see attached file.
Author Response File: Author Response.docx
