Enhancing Compressive Strength in Cementitious Composites through Effective Use of Wasted Oyster Shells and Admixtures

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

For this paper, an algebraic approach to the design of resource-efficient carbon-reinforced concrete structures is presented. Interdisciplinary research in the fields of mathematics and algebra on the one hand and civil engineering and concrete structures on the other can lead to fruitful interactions and can contribute to the development of resource-efficient and sustainable concrete structures. Textile-reinforced concrete (TRC) using non-crimp fabric carbon-reinforcement enables very thin and  light-weight constructions and thus requires new construction strategies and new manufacturing methods. I found that the manuscript is very informative and presents the useful results of the experiment.

 

General comment
1. The title is clear and focuses to output research.
2. Suitable keyword for the paper.
3. Well written for the abstract.
4. The contribution of this work to solve the limitation/problems is clearly highlighted.

However, I would like the authors please correct and explain some comments and questions as followings.

1. Recheck the minor English spelling errors.                                                                                                                        
2. The authors should manage the order of descriptions in all Tables and Figures.
3. Explanation of any figures and tables should be placed as close as possible.                                                        

 4. Conclusions are weak and not supported by comparisons with previous studies.

Comments on the Quality of English Language

It should be improved

Author Response

The authors would like to thank the reviewer for the comments and suggestions, which helped us improve the quality of our paper. The reviewer’s comments have been fully incorporated into the revised version of this paper, as detailed below:

Q1. Recheck the minor English spelling errors.  

A1. To avoid confusion, English spelling errors have been modified in the manuscript. Moreover, All English text in the paper was proofread by an expert.(Location: All manuscript)

Q2. The authors should manage the order of descriptions in all Tables and Figures.

A2. All figures and tables have been modified in the manuscript, as recommended by the reviewer.(Location: All manuscript)

Q3. Explanation of any figures and tables should be placed as close as possible.

A3. Explanations of figures and tables have been carefully checked and revised. As advised by the reviewer, some sentences have been added(Location: All manuscript)

• Table 1 lists the mix proportions of the specimens. Ordinary Portland cement was used for cement and silica sand no. 6 (sand size:0.35–0.7 mm) for sand. OSs from the southern coast of Korea were used, and OS powder was produced using a rock crusher.(Location: Last paragraph of page 3)

Q4. Conclusions are weak and not supported by comparisons with previous studies.

A4. As suggested by the reviewer, the purpose of the research has been corrected and the conclusions have been added in the text:

• Previous investigations failed to demonstrate that cementitious composite incorporating WOS exhibited a compressive strength exceeding 40 MPa. Moreover, the introduction of WOS resulted in a decline in the compressive strength of the cementitious composite. reduced the compressive strength of the cementitious composite. Thus, this study fabricated cementitious composites by replacing sand with WOS. An admixture was also used to improve the compressive strength of the cementitious composites. The composites were prepared by varying the WOS content, presence or absence of the admixture added for strength improvement, and admixture type. The admixtures used included silica fume, blast furnace slag, and an air-entraining water-reducing agent (AE). The experimental parameters were composed of cementitious composites with no admixture, those mixed with silica fume and AE, and those mixed with blast furnace slag and AE (OS-Slag). The prepared specimens were cured for 7 and 28 days to analyze compressive strength and internal structure. To discern the cause of changes in the compressive strengths of the cementitious composites that used WOS, a field emission scanning electron microscope (FE-SEM), X-ray diffractometer (XRD), and thermogravimetric analyzer (TGA) were used in the internal structure analysis.(Location: Second paragraph of page 3)
• 1) The compressive strength of the cementitious composite containing only OS powder tended to decrease as the OS powder content increased. The compressive strength of OS-100 was approximately 18% lower than that of OS-0 after 7 days and 13% lower after 28 days. The cement composite containing OS powder developed an average compressive strength of more than 40 MPa even without sand. Therefore, OSs are expected to be used as a new construction material that can replace sand.(Location: Conclusion 1 of page 11)

Reviewer 2 Report

Comments and Suggestions for Authors

This paper discusses an interesting topic of an algebraic approach to the design of resource-efficient carbon-reinforced concrete structures. This paper's authors pursue a modular approach to construct new interlocking blocks by combining different Platonic and Archimedian solids. The study is sufficient in terms of literature. The manuscript is exceptionally well-structured. The language structure of the study is understandable. I believe that it would be appropriate to publish the study in this form.

Author Response

The authors would like to thank the reviewer for the comments and suggestions, which helped us improve the quality of our paper. 

Reviewer 3 Report

Comments and Suggestions for Authors

The recycling of OS in concrete is a good ideal, however, this work did not perform a deep study in this topic.

The compressive strength of concrete containing OS was decreasing with the increase of OS, please explain the reason. In addition, after adding slag, the strength of OS-SLAG increases, please explain.

More SEM should be included.

Only compressive strength is insufficient, at least the bending text should be conduced. To my best knowledge, the concrete specification in every country requires the bending strength. As a feasibility study, the evaluation of performances should include a large range of test items.

It is still unclear that the role of OS in concrete performance, there is a lot of previous studied reported, please identify the novelty of this work.

 

Author Response

The authors would like to thank the reviewer for the comments and suggestions, which helped us improve the quality of our paper. The reviewer’s comments have been fully incorporated into the revised version of this paper, as detailed below.

Q1. The compressive strength of concrete containing OS was decreasing with the increase of OS, please explain the reason. In addition, after adding slag, the strength of OS-SLAG increases, please explain. 

A1. As recommended by the reviewer, some sentences were added in the text as follows:

• The decrease in compressive strength of was observed with an increase in OS powder content. This can be attributed to the substitution of OS powder for silica sand in the cementitious composite, resulting in a reduction of SiO2 content within the silica sand. As a consequence, the formation of calcium-silicate-hydrate (C-S-H) compounds in the cementitious composite was diminished, ultimately leading to a decrease in compressive strength. (Location : First paragraph of page 7)
• In contrast, similar to OS-SF, OS-Slag exhibited induced C-S-H reactions, resulting in an enhancement of compressive strength. However, note that the increase in compressive strength observed in OS-Slag was relatively low when compared with OS-SF under similar conditions. This phenomenon can be attributed to the lower SiO₂ content in the blast furnace slag of OS-Slag in contrast with the high SiO₂ content present in the silica fume of OS-SF, which subsequently led to fewer C-S-H hydration reactions in OS-Slag.(Location : Second paragraph of page 8)

Q2. More SEM should be included.

A2. Figure 8 has been modified, and two SEM image were added in the text as recommended by the reviewer:

• As shown in Figure 8(a), a large amount of C-S-H generated via the addition of silica fume filled the voids between OS powder and sand. More voids than those in Figure 8(a) can be observed in Figure 8(b) because the blast furnace slag caused fewer C-S-H reactions than silica fume. Further, the C-S-H compounds can be observed to significantly decrease in Figure 8(b) compared with those in Figure 8(a). Because silica fume generates more C-S-H hydrates than blast furnace slag and fills voids, the compressive strength of OS-SF improved more significantly than that of OS-Slag.  (Location: Last paragraph of page 9, Figure 8 of page 10)

Q3. Only compressive strength is insufficient, at least the bending text should be conducted. To my best knowledge, the concrete specification in every country requires the bending strength. As a feasibility study, the evaluation of performances should include a large range of test items.

A3. This study primarily addresses the compressive strength of cement composites incorporating wasted oyster shells. In response to the reviewer's feedback, the authors intend to explore the bending performance and durability in our forthcoming research. Additional details regarding these aspects have been be included in the conclusion section.

• Based on this observed increase in compressive strength, future research endeavors will focus on investigating the flexural characteristics of cementitious composites incorporating wasted OSs and assessing their durability under environmental conditions.(Location: Conclusion 2 of page 11)

Q4. It is still unclear that the role of OS in concrete performance, there is a lot of previous studied reported, please identify the novelty of this work.

A4. 

In this study, cementitious composites were fabricated using oyster shells as a sand substitute. Previous research has demonstrated a consistent trend of reduced compressive strength when incorporating wasted oyster shells into cement composites. However, this study successfully achieved a high-strength cement composite with a compressive strength exceeding 40 MPa, even with the inclusion of wasted oyster shells. Moreover, the incorporation of various admixtures and wasted oyster shells into the cement composite enabled us to attain compressive strengths exceeding 80 MPa. In addition, internal structure analyses (SEM, XRD, and TGA) were conducted to provide engineering basis for this. In response to the reviewer's feedback, the authors have revised the objectives and conclusions of this study to better align with the reviewer's input.

• Previous investigations failed to demonstrate that cementitious composite incorporating WOS exhibited a compressive strength exceeding 40 MPa. Moreover, the introduction of WOS resulted in a decline in the compressive strength of the cementitious composite Thus, this study fabricated cementitious composites by replacing sand with WOS. An admixture was also used to improve the compressive strength of the cementitious composites. The composites were prepared by varying the WOS content, presence or absence of the admixture added for strength improvement, and admixture type. The admixtures used included silica fume, blast furnace slag, and an air-entraining water-reducing agent (AE). The experimental parameters were composed of cementitious composites with no admixture, those mixed with silica fume and AE, and those mixed with blast furnace slag and AE (OS-Slag). The prepared specimens were cured for 7 and 28 days to analyze compressive strength and internal structure. To discern the cause of changes in the compressive strengths of the cementitious composites that used WOS, a field emission scanning electron microscope (FE-SEM), X-ray diffractometer (XRD), and thermogravimetric analyzer (TGA) were used in the internal structure analysis.(Location: Second paragraph of page 3)
• The compressive strength of the cementitious composite containing only OS powder tended to decrease as the OS powder content increased. The compressive strength of OS-100 was approximately 18% lower than that of OS-0 after 7 days and 13% lower after 28 days. The cement composite containing OS powder developed an average compressive strength of more than 40 MPa even without sand. Therefore, OSs are expected to be used as a new construction material that can replace sand.(Location: Conclusion 1 of page 11)

 

Reviewer 4 Report

Comments and Suggestions for Authors

Dear authors you have done a good study, but I have some comments:

- please enhance the quality of figures. They are too small.

- please describe the used software

- describe how you have verified and validate your models.

- Describe how your blocks can be put in practice to obtain building structures

 

Author Response

The authors would like to thank the reviewer for the comments and suggestions, which helped us improve the quality of our paper. The reviewer’s comments have been fully incorporated into the revised version of this paper, as detailed below.

Q1. Please enhance the quality of figures. They are too small.

A1. As recommended by the reviewer, figure quality has been enhanced in the manuscript.(Location: All Figures)

Q2. Please describe the used software.

A2. Software information has been added in text, as advised by the reviewer. This study involved the use of compressive strength testing. The compressive strength tests were conducted in accordance with ASTM regulations using a universal testing machine (UTM).

• In the experiment, the specimens were prepared with a size of 50ⅹ50ⅹ50 ㎣ in accordance with ASTM C109 [29] to test the compressive strength.(Location: Last paragraph of page 4)

Q3. Describe how you have verified and validate your models.

A3. As recommended by the reviewer, some sentences were added in the text:

• FE-SEM analysis was conducted in accordance with ISO 19749:2021 [32], as shown in Figure 4(b) (Liu et al. [33]). The specimen surface was observed at high magnification using the secondary electrons and the backscattered electrons generated by electron beam irradiation to the sample with FE-SEM. Figure 4(c) shows the XRD test setup. XRD was used in accordance with ASTM E915-96 [34] [35-37]. In the XRD analysis, when the X-ray collides with a crystal, a portion of it is diffracted. Because the generated diffraction angle and strength are the unique values of the material structure, the types and quantities of the crystalline materials contained in the sample can be analyzed using the X-rays. Figure 4(d) shows the TGA, which is an analyzer to observe the weight fluctuations caused by the heat-induced chemical and physical changes of the sample according to time and temperature. TGA was used in accordance with ASTM C1872 [38].(Location: First paragraph of page 6)

Q4. Describe how your blocks can be put in practice to obtain building structures.

A4. As suggested by the reviewer, some sentences have been added in the conclusion section as follows:

• The compressive strength of the cementitious composite containing only OS powder tended to decrease as the OS powder content increased. The compressive strength of OS-100 was approximately 18% lower than that of OS-0 after 7 days and 13% lower after 28 days. The cement composite containing OS powder developed an average compressive strength of more than 40 MPa even without sand. Therefore, OSs are expected to be used as a new construction material that can replace sand.(Location: Conclusion 1 of page 11)

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

I can see authors have carefully revised their work to a good state, there is no further comments from my side.