Elucidation of Microstructural and Mechanical Properties of Coconut Husk Mortar as a Sustainable Building Material for Ferrocement

Round 1

Reviewer 1 Report

Authors are required to replace given photos (Fig 1) with close up photos of both (a) and (b), so readers understand properly.  

Figs 3, 4, 5 and 6 are very common work, so it is suggested to remove.

Section 6.1: suggestion to add sample preparation for each test.

Fig 7. Suggestion to mark pores in Fig 7(c) and 7(d).

Author Response

Comment 1: Authors are required to replace given photos (Fig 1) with close-up photos of both (a) and (b) so readers understand correctly.  

Response 1: As suggested by the Reviewer (Figure 1) both (a) and (b) are replaced with close-up photos in the revised manuscript.

Comment 2: Figs 3, 4, 5, and 6 are very common to work, so it is suggested to remove.

Response 2: As suggested by the Reviewer, Figs 3, 4, 5, and 6 are removed and hence other Figures are re-numbered.

Comment 3: Section 6.1: suggestion to add sample preparation for each test.

Response 3: As suggested by the Reviewer, added one paragraph for sample preparation for each test. The newly added paragraph detail is given here for the Reviewer’s reference. Please note that the other Reviewer also suggested including the same and also to add information on the XRD test (test parameters and device information), as well as the method which was used to analyze the XRD results and what database was used, hence included as given below:

The sample preparation of microstructural studies is furnished for the benefit of the readers. At the end of the curing periods, core samples of mortar prisms of approximately 10 mm square cut from samples using a mortar cutting machine are used for SEM and EDX analysis. Initially, the sample was flooded with acetone to stop the hydration process before it was subjected to gold sputtering to make it conductive. Electron beams from the SEM interact with the sample and produce images that can be used to determine the chemical composition and phase distribution. X-ray diffraction is a technique for the identification of the mineral content of powdered samples or the determination of the chemical structure of crystalline materials and phase identification. The principle that is used in this XRD is the production of spectra consist of several components has different wave lengths and the specific wavelengths are characteristic of the target material (generally, copper Cu). Then the X-rays are collimated and directed onto the sample. That is, the process involves directing X-ray beams on the powdered sample, and diffracted x-rays are recorded as a characteristic of the crystalline phases of the specimen. As the sample and detector are rotated, the intensity of the reflected X-rays is recorded the peaks in intensity occurs. A detector records and processes this X-ray signal and converts the signal to a count rate which is then output to a device such as a printer or computer monitor. The geometry of an X-ray diffractometer is such that the sample rotates in the path of the collimated X-ray beam at an angle θ while the X-ray detector is mounted on an arm to collect the diffracted X-rays and rotates at an angle of 2θ. The results are interpreted by comparing the peaks with standards available to identify phases present in the sample. For this analysis, mortar samples were ground to a fine powder of less than 63µm. X-mineralogical analysis was carried out using PANnalytical X’ - X’per PRO with source CuK radiation (2.2 kW maximum).

Comment 4: Fig 7. Suggestion to mark pores in Fig 7(c) and 7(d).

Response 4: Since the Reviewer suggested to some of the Figures (comment 2), Fig 7. Is now renumbered as Figure 3, and in that pores are marked in Fig 3(c) and 3(d).

In general, the black spots in SEM images are considered pores present in them. As suggested by the Reviewer, sample black spots are identified and marked in Fig 3 (c) and 3 (d), and the same was given here for the Reviewer’s Reference.

*****

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript under the title: “Elucidation of microstructural and mechanical properties of coconut husk mortar as a sustainable building material for ferrocement”  is relevant for the Sustainability Journal (ISSN 2071-1050). The author’s work on up-to-date topics contributes to sustainable development goals. The goal of the manuscript was to determine whether coconut shell waste could find use as a sustainable building material in ferrocement applications. The authors examined the microstructural and mechanical properties of four different types of cement mortars that used coconut shells as a fine aggregate. The paper presents a number of research results widely supported by literature reports. The organization of the article is appropriate. The conclusions presented in the paper are consistent with the evidence and arguments presented and address the main research question posed. The research part of the work is preceded by a theoretical introduction justifying the undertaken subject matter of the work. The bibliography of the work is based on current scientific articles.

Overall, the paper is well prepared, but needs some improvements, which are listed below:

- the abstract – please add information about the test of mechanical properties test (compressive, split tensile, flexural strength, and impact strength resistance),

- Line 343-345 – please correct the sentence - it is unfinished,

- Mortar Mix Proportions – I suggest adding a table showing the exact percentage composition of the tested mixes along with the water-cement ratio,

- add information on the devices used for the test,

- add information on the XRD test (test parameters and device information), as well as the method which was used to analyze the XRD results and what database was used,

- Editing - please check your work for the use of proper spacing between text and photos, interlineation, and the presence of double spaces in the text.

Author Response

REVIEWER 2

Comment 1: The abstract – please add information about the test of mechanical properties test (compressive, split tensile, flexural strength, and impact strength resistance).

Response 1: As suggested by the Reviewer, in the abstract, added information about the test of mechanical properties tests (compressive, split tensile, flexural strength, and impact strength resistance). Since the other Reviewer suggested revising the abstract, hence completely revised in the revised manuscript.  

Abstract: The main objective of this study is to use coconut husk to produce mortar for ferrocement. Mortar mix proportions are selected per ACI codes’ recommendation and the WRD Handbook. Four types of mortars: Cement and River Sand mortar (CSM), Cement, River Sand and Steel fibre mortar (CSSFM), Cement and Coconut Husk mortar (CCHM), and Cement, River Sand (60%), Coconut Husk (40%), and Steel fibre mortar (CSCHSFM) are used for this study Microstructural studies like SEM, EDX, XRD, and FTIR analysis on cement mortar constituents and mortar mixes are studied and reported. At 3, 7, and 28 days tests of hardened mortar, such as compressive, split tensile, flexural strength, and impact strength resistance, were studied. Test results revealed that the coconut husk is innovative and sustainable and could be an alternative fine aggregate that can be utilized in place of river sand, which in turn can be used for mortar production. Since it has a lesser density which proves to be an advantage for developing lightweight mortar, it can be used for ferrocement applications.

Comment 2: Line 343-345 – please correct the sentence - it is unfinished,

The findings of the XRD experiment provided more evidence that the sample contained a mixture of CSM, CSSFM, CCHM, and CSCHSFM.

Response 2: As suggested by the Reviewer, Lines 343-345 sentences corrected.

We thank the Reviewer for this notification of an incomplete sentence. We want to inform the Reviewer that this sentence does not have meaning here and was copied and pasted in error; hence, this sentence is removed in the revised manuscript. We hope that the Reviewer will accept, and we regret the inconvenience caused in this regard. 

Comment 3: Mortar Mix Proportions – I suggest adding a table showing the exact percentage composition of the tested mixes along with the water-cement ratio.

Response 3: As suggested by the Reviewer, added Table 2 in the revised manuscript and showed the percentage composition of the tested mixes along with the water-cement ratio.

Table 2 shows a mix proportion (1:3 by volume) of different mixes and the corresponding percentage composition of constituents used, and the same was given here for the Reviewer’s Reference.

Table 2 Mix proportions and percentage composition of constituents

Comment 4: Add information on the XRD test (test parameters and device information), as well as the method which was used to analyze the XRD results and what database was used.

Response 4: As suggested by the Reviewer, information was added to the XRD (test parameters and device information), the method used to analyze the XRD results, and the database used. Please note that the other Reviewer also suggested including the same differently, like adding sample preparation for each test, hence added as given below:

The sample preparation of microstructural studies is furnished for the benefit of the readers. At the end of the curing periods, core samples of mortar prisms of approximately 10 mm square cut from samples using a mortar cutting machine are used for SEM and EDX analysis. Initially, the sample was flooded with acetone to stop the hydration process before it was subjected to gold sputtering to make it conductive. Electron beams from the SEM interact with the sample and produce images that can be used to determine the chemical composition and phase distribution. X-ray diffraction is a technique for identifying the mineral content of powdered samples or determining the chemical structure of crystalline materials and phase identification. The principle used in this XRD is the production of spectra consisting of several components with different wavelengths. The specific wavelengths are characteristic of the target material (generally, copper Cu). Then the X-rays are collimated and directed onto the sample. That is, the process involves directing X-ray beams on the powdered sample, and diffracted x-rays are recorded as a characteristic of the crystalline phases of the specimen. As the sample and detector are rotated, the intensity of the reflected X-rays has recorded the peaks in intensity. A detector records and processes this X-ray signal and converts the signal to a count rate which is then output to a device such as a printer or a computer monitor. The geometry of an X-ray diffractometer is such that the sample rotates in the path of the collimated X-ray beam at an angle θ while the X-ray detector is mounted on the arm to collect the diffracted X-rays and rotates at an angle of 2θ. The results are interpreted by comparing the peaks with standards available to identify phases present in the sample. For this analysis, mortar samples were ground to a fine powder of less than 63µm. X-mineralogical analysis was carried out using PANnalytical X’ - X’per PRO with source CuK radiation (2.2 kW maximum).

Comment 5: Editing - please check your work for proper spacing between text and photos, interlineation, and the presence of double spaces in the text.

Response 5: As suggested by the Reviewer, edited the use of proper spacing between text and photos, interlineation, and double spacing in the text.

*****

Reviewer 3 Report

The authors hoped to identify the properties that make coconut husk waste, an ideal material for use as a sustainable building material for ferrocement applications. It is very interesting for researchers. Before the paper can be accepted, there are some questiones the authors should be answer.

1. The abstract should be revised and gives more specific conclusions.

2. How about the grain composition of the coconut and workability of the fresh mortar?

3. Have you considered the durability of the coconut?

4. What is the mean of the WRD in line 20?

5. The secion of 3. Mortar Mix Proportions is chaos. The research objective should be cleared out. Why the steel fibre is used?

6. In line 170, To determine the workability of cement mortar mixtures, slump and flow table tests were performed. But there is no results and analysis. How about the workability? The figure of the fresh mortar should be added in the paper.

7. In seciton 5. Experimental Programme, the experiments should be expressed in orderliness.

8. Could you please remove the black background of the EDX analysis result? If it must be shown in this style, it can not be revised.

Author Response

REVIEWER 3

Comment 1: The abstract should be revised and give more specific conclusions.

Response 1: As suggested by the Reviewer, the abstract was completely revised and given a more specific conclusion as given below:

Abstract: The main objective of this study is to use coconut husk to produce mortar for ferrocement. Mortar mix proportions are selected per ACI codes’ recommendation and the WRD Handbook. Four types of mortars: Cement and River Sand mortar (CSM), Cement, River Sand and Steel fibre mortar (CSSFM), Cement and Coconut Husk mortar (CCHM), and Cement, River Sand (60%), Coconut Husk (40%), and Steel fibre mortar (CSCHSFM) are used for this study Microstructural studies like SEM, EDX, XRD, and FTIR analysis on cement mortar constituents and mortar mixes are studied and reported. At 3, 7, and 28 days tests of hardened mortar, such as compressive, split tensile, flexural strength, and impact strength resistance, were studied. Test results revealed that the coconut husk is innovative and sustainable and could be an alternative fine aggregate that can be utilized in place of river sand, which in turn can be used for mortar production. Since it has a lesser density which proves to be an advantage for developing lightweight mortar, it can be used for ferrocement applications.

Comment 2: How about the grain composition of the coconut and the workability of the fresh mortar?

Response 2:

Grain composition of the coconut husk:

Thanks to the Reviewer for raising this query. Since 2010 onwards, we have been researching coconut shells as coarse aggregate and constructed a structure using coconut shell concrete. During that time, we studied all significant aspects in connection with the physical, chemical, and durability studies of both coconut shell and coconut shell concrete. We published many SCI-indexed and Scopus-indexed journal papers (a few examples references are given here for the Reviewer information) and produced 6 Ph.D. scholars in this area. Now, we have taken another by-product, coconut husk, from crushing the coconut shells to use as mortar replacing the river sand. Hence, from the works carried out and published article, we would like to inform that the grain composition of coconut husk in terms of chemicals is: Glucose (1.90%); Fructose (2.88%); Sucrose (14.80%); Reducing sugar (7.5%); Total Phenols (5.08%); Ash (0.50 to 0.60%); Cellulose (32.36%); and pH (6.00 to 6.40). In terms of physical grain composition, it is almost similar to conventional fine aggregate with a maximum size of 4.75 mm and other grains, including micro grains, shown in Figure 2.

1. Compatibility studies on the coconut shell cement composites, National Journal of Indian Concrete Institute, 11, 2010.
2. Study on Properties of Coconut Shell as an aggregate for concrete, National Journal of Indian Concrete Institute, 2011, Vol.12, Issue.2, pp. 27-33.
3. Long-term study on compressive and bond strength of coconut shell aggregate concrete, International Journal of Construction and Building Materials, 28(2012), pp 208-215.
4. Plastic shrinkage and deflection characteristics of coconut shell concrete slab", International Journal of Construction and Building Materials, 43(2013), pp 203-207.

5. All-in-one about a momentous review study on coconut shell as coarse aggregate in concrete. International Journal of Civil Engineering and Technology, 8 (3), March 2017, pp. 1049-1060, 2017.
6. Mix design and rheological properties of self-compacting coconut shell aggregate concrete. ARPN Journal of Engineering and Applied Sciences. Volume 13, Issue 4, page 1465-1475, 2018.

Workability of fresh mortar:

Since the main of the study is to develop a mortar using coconut husk for ferrocement applications, and the most important design criterion for ferrocement mortars is maintaining plasticity, the mortar mix should be as stiff as feasible, the mortar should not be in the form of fluid since the pressure techniques are used in ferrocement mortar applications; hence workability is not a primary concern here. In general, the slump of fresh mortar should not exceed 50 mm. In this investigation, no workability concerns were experienced in the case of both conventional materials and CH mortar; the slump values were found to be less than 50 mm in CSM, CSSFM, CCHM, and CSCHSFM mixes. However, significant details are furnished in the original manuscript section 6.3 Fresh mortar properties.

Comment 3: Have you considered the durability of the coconut?

Response 3: Again, as mentioned in the previous comments’ response, we have conducted many durability studies on coconut shell concrete earlier (a few example references are given here for the Reviewer’s information). Since coconut husk is a by-product of crushed coconut shells, durability is also not a significant concern here since we have already constructed a structure and many other non-structural elements like Flooring tiles; pipe; hollow blocks; paver blocks; and manhole cover slabs.  

1. A study on some durability properties of coconut shell concrete, International Journal of Materials and Structures, 48 (5): 2015, pp 1253-1264.

2. Experimental study on strength and durability properties of self-compacting coconut shell aggregate concrete blended with fly ash. ARPN Journal of Engineering and Applied Sciences. 13(23), PP. 8983-8993, 2018.
3. Study on the durability properties of coconut shell concrete with granite powder. International Journal of Recent Technology and Engineering (IJRTE) ISSN: 2277-3878, 7(6), S4, pp.:70-74, 2019.
4. Durability properties of hybrid fibers in Coconut shell concrete. International Journal of Innovative Technology and Exploring Engineering (IJITEE)’, ISSN: 2278–3075 (Online), 8(7), pp. 2606-2610, 2019.
5. Study on Durability Properties of Coconut Shell Concrete with Coconut Fiber, Buildings 2019, 9 (5), 107; doi: 10.3390/buildings9050107.
6. Study on some durability properties of coconut shell concrete with quarry dust, European Journal of Environmental and Civil Engineering, 24 (6), pp. 709-723, 2020. DOI: 10.1080/19648189.2017.1418435, (2020).
7. Study on coconut shell concrete hollow blocks and the shrinkage, durability and bond properties of mixes used, European Journal of Environmental and Civil Engineering, 25:1, 73-89, 2021, https://doi.org/10.1080/19648189.2018.1516165.
8. Study for the relevance of coconut shell aggregate concrete flooring tiles. International Journal of Civil Engineering and Technology, 8 (6), June 2017, pp. 370-379, 2017.
9. Study for the relevance of coconut shell aggregate concrete non-pressure pipe. Ain Shams Engineering Journal, 8(4), December 2017, pp. 523-530, 2017.

1. Study for the relevance of coconut shell aggregate concrete paver blocks. Materials Today: Proceedings (Ref. MATPR8007), 14, pp.368-378, 2019.
2. Study on the reinforced manhole cover slab using coconut shell aggregate concrete. Materials Today: Proceedings (Ref. MATPR8009), 14, pp.386-394, 2019.

Comment 4: What is the mean of the WRD in line 20?

Response 4: WRD: Water Resource Department – Maharashtra Engineering Research Institute developed a handbook for “Ferrocement Technology.” For the information of the Reviewer, the link is given here for any ready future reference (line 14 and 15 in the revised manuscript)

https://wrd.maharashtra.gov.in/Upload/PDF/WRD-01%20Ferrocement%20Technology.pdf

Comment 5: The section 3. Mortar mix Proportions is chaos. The research objective should be cleared out. Why the steel fibre is used?

Response 5: As the other Reviewer also raised the same and suggested adding a Table to show the mix proportions and exact percentage composition, Table 2 is given to overcome mortar mix proportions chaos in the revised manuscript. The research objective was made clear in the revised manuscript.

The reason for the use of steel fibre:

            WRD handbook recommended that the mortar for ferrocement applications have a minimum strength of 35 N/mm². Achieved this from conventional mortar with river sand. But, we failed to achieve the same when the river sand was replaced with coconut husk; hence we tried for partial replacement, but it also not succeed, and hence finally, we decided to add steel fiber and achieved that minimum strength of 35 N/mm². This is the reason why we used steel fibre.

Comment 6: In line 170, To determine the workability of cement mortar mixtures, slump, and flow table tests were performed. But there is no results and analysis. How about the workability? The figure of the fresh mortar should be added in the paper.

Response 6: This is to inform the reviewer that the details mentioned in line 170 (Original manuscript) results and analysis are given ((line 177 in the revised manuscript) in section 6.3 as:

True slump patterns were obtained for all the mixes and do not experience any segregation; hence, using coconut husk in place of river sand results in cohesive mixes. Slump values of 30 mm for the CSM mix, 10 mm for the CSSFM mix, 40 mm for the CCHM mix, and 20 mm for the CSCHSFM mix were measured. The values from the flow table test were measured as 101.67% for the CSM mix, and 101.3% for the CCHM mix, which is near to the requirement of IS 4031(Part 7)-1988 [59] (i.e) 110±5%. However, these values are 64.3% for the CSSFM mix, and 27.7% for the CSCHSFM mix, which did not satisfy the requirement of IS 4031(Part 7)-1988 [59]. Since this IS code recommendation is meant for conventional mortar and fibre-added mortar, it cannot be taken for comparison and validation of the results. In general, from these results, the degree of workability of mortar mixes can be stated as a medium degree of workability, when the flow value is considered [60-61].

About the workability:

As the reviewer asked in comment 2 also the same, and hence about the workability, we would like to say the same over here also as:

Since the main of the study is to develop a mortar using coconut husk for ferrocement applications, and the most important design criterion for ferrocement mortars is maintaining plasticity, the mortar mix should be as stiff as feasible, the mortar should not be in the form of fluid since the pressure techniques are used in ferrocement mortar applications; hence workability is not a primary concern here. In general, the slump of fresh mortar should not exceed 50 mm. In this investigation, no workability concerns were experienced in the case of both conventional materials and CH mortar; the slump values were found to be less than 50 mm in CSM, CSSFM, CCHM, and CSCHSFM mixes. However, significant details are furnished in the original manuscript section 6.3 Fresh mortar properties.

The figure of the fresh mortar

            As suggested by the Reviewer, fresh mortar in which coconut husks are used is added in Figure 30 (a) for CCHM and (b) for CSCHSFM mixes.

Comment 7: In section 5. Experimental Programme, the experiments should be expressed in orderliness.

Response 7: We thank the Reviewer for this notification. As suggested in section 5, experimental programme, the experiments are expressed in orderliness.

Comment 8: Could you please remove the black background of the EDX analysis result? If it must be shown in this style, it cannot be revised.

Response 8: As suggested by the Reviewer, we tried to remove the black background of the EDX result, but we could not do it, and we came to know that with the help of the source file, only it can be done. Since the labs and resource persons are on a very tight schedule, we could not be able to stress them within the given time for revision. Hence, we request the Reviewer to consider showing it in the same style, please.

*****

Round 2

Reviewer 3 Report

The paper can be accepted.