Study on the Characteristics of Composite Recycled Aggregate Concrete Based on Box–Behnken Design Response Surface Model
Round 1
Reviewer 1 Report
[Major Comments]
This manuscript has various analyses and results. However, this manuscript is tough to read and hard to evaluate. A significant revision is required. Also, the novelty of this study should be emphasized. The literature review and the main content of this manuscript are not closely related. The literature review content should be related to the research with similar technical approaches. This manuscript begins with a literature review related to eco-friendly literature. This manuscript has enough potential to publish in this journal. But many revisions are necessary before it goes through insightful reviews.
[Minor Comments]
l Line numbers should be added.
l Punctuation marks should be consistent. For example, 20%-30% and 0.075mm~4.75mm are different.
l There are many kinds of research related to the characteristics of concrete using Box-Behnken design. What are the differences between the existing studies and this study? A literature review must be included.
l The purpose of this study is not closely related to the existing studies presented in the literature review.
l Enough explanations associated with tests are required with photos.
l A section on results and discussions is required before the conclusions. Discussions are not enough to provide the insightfulness of this study.
l The designs of Tables should be consistent.
l There are other ways to evaluate and verify the established models. Please, provide the reasons why ANOVA was selected.
l The research objective and problem statements of the previous studies are unclear. Please, provide them before the experimental section.
l The content of the recycled coarse aggregate process should be emphasized.
l In every table, the upper case and lower case should be consistent.
l Please, check the font size of the sentence under Table 2.
l In the main text, the words Table and Figure should be started with an upper case.
l Please, provide how to perform the X-ray spectrum in detail.
l Please, check the space between numbers and punctuation marks. It should be consistent. For example, 70 % and 70% must be matched.
l Please, check the English of every title in the manuscript. For example, upper case and lower case.
l Please, check the font size of the model establishment section.
l Conclusions are not strong enough to close this manuscript.
English must be checked and punctuation marks must be consistent.
Author Response
Response to Referee 1
This manuscript has various analyses and results. However, this manuscript is tough to read and hard to evaluate. A significant revision is required. Also, the novelty of this study should be emphasized. The literature review and the main content of this manuscript are not closely related. The literature review content should be related to the research with similar technical approaches. This manuscript begins with a literature review related to eco-friendly literature. This manuscript has enough potential to publish in this journal. But many revisions are necessary before it goes through insightful reviews.
3 There are many kinds of research related to the characteristics of concrete using Box-Behnken design. What are the differences between the existing studies and this study? A literature review must be included.
4 The purpose of this study is not closely related to the existing studies presented in the literature review.
Response: In response to the aforementioned issues, the introduction section of this paper has been revised to include a discussion on the current state of research and literature regarding the utilization of the Box-Behnken design method. The modified version is presented below:（Line85-Line121）
Based on the current research status mentioned above, the utilization of waste particles with a diameter smaller than 4.75mm remains a bottleneck in the harmless disposal of concrete. There are several factors that can influence the compressive strength of concrete with recycled fine aggregates. The most important factors include the content of WCP, the water-cement ratio, and the content of recycled fine aggregates. Considering all these fac-tors and their interactions requires a significant number of experiments to be conducted. Moreover, experimental errors can affect the accuracy of the conclusions. To overcome these issues, experimental design methods are needed. In some studies, advanced design methods have been used for the optimal mixture design of concrete materials. For example, Kumar R utilized response surface methodology to design structural grade lightweight cellular concrete containing micro fines stone sludge[22]. Sharaky I A constructed a cube strength equation for concrete using Central Composite Design and Box Behnken Design, accurately predicting the effects of steel fiber content, high content of kaolin clay, and cur-ing time on compressive strength[23]. Shaheen N optimized the formulation of microor-ganisms cementitious composite using the Taguchi approach of experimental design, con-sidering factors such as water-cement ratio, type of cement, and effective microorganisms technology[24]. Zhang Q optimized the mix proportion of recycled aggregate pervious concrete using response surface methodology and established the response of void content for different gradations of recycled aggregates using simplex centroid design[25]. To ad-dress the two major issues of fully utilizing fine aggregates and harmless disposal of WCP, this study replaces the fine aggregates with particles ranging from 0.075mm to 4.75mm, which are obtained by crushing waste concrete. The WCP below 0.075mm are used as inert fillers to prepare recycled aggregate concrete. The Box-Behnken method is employed to de-sign and assess the effects of three factors, namely the content of WCP, water-cement ratio, and content of recycled fine aggregates, on the compressive strength of concrete. The in-teractions among these three factors are evaluated. Using the aforementioned factors as independent variables, response models for the compressive strength of concrete at 3 days, 28 days, and 90 days are constructed. The models are evaluated and validated using variance analysis and R2. By plotting three-dimensional response surfaces, the optimal mixture conditions for achieving the highest strength in recycled concrete are determined. Finally, the changes in concrete strength due to the addition of WCP and recycled fine aggregates are quantitatively described from a microscopic perspective through the characterization of morphological features and calculation of fractal dimensions based on SEM micrographs. This reveals the mechanisms through which each factor affects the strength. These findings provide a basis for further enhancing the utilization efficiency of recycled micro powder, as well as expanding its functionality and application scenarios.
[22] Kumar R. Effects of high volume dolomite sludge on the properties of eco-efficient lightweight concrete: Microstructure, statis-tical modeling, multi-attribute optimization through Derringer's desirability function, and life cycle assessment[J]. Journal of Cleaner Production, 2021, 307: 127107.
[23] Sharaky I A, Ghoneim S S M, Aziz B H A, et al. Experimental and theoretical study on the compressive strength of the high strength concrete incorporating steel fiber and metakaolin[C]//Structures. Elsevier, 2021, 31: 57-67.
[24] Shaheen N, Rizwan S A, Khushnood R A, et al. Mechanical and energy performance of variably cured effective microorgan-isms cementitious composite designed via Taguchi[J]. Journal of Cleaner Production, 2021, 310: 127350.
[25] Zhang Q, Feng X, Chen X, et al. Mix design for recycled aggregate pervious concrete based on response surface methodolo-gy[J]. Construction and Building Materials, 2020, 259: 119776.
1 Line numbers should be added.
2 Punctuation marks should be consistent. For example, 20%-30% and 0.075mm~4.75mm are different.
7 The designs of Tables should be consistent.
11 In every table, the upper case and lower case should be consistent
12 Please, check the font size of the sentence under Table 2.
13 In the main text, the words Table and Figure should be started with an upper case.
15 Please, check the space between numbers and punctuation marks. It should be consistent. For example, 70 % and 70% must be matched.
16 Please, check the English of every title in the manuscript. For example, upper case and lower case.
17 Please, check the font size of the model establishment section.
Response: The formatting issues mentioned above have been thoroughly addressed and revised throughout the entire manuscript. The modified sections are highlighted in red within the manuscript.
5 Enough explanations associated with tests are required with photos.
Response:
The compressive strength test pictures are shown in the Figure 4.
Figure 4. Pictures of compressive strength tests
The SEM test pictures are shown in the Figure 5.
Figure 5. SEM test picture
6 A section on results and discussions is required before the conclusions. Discussions are not enough to provide the insightfulness of this study.
Response:
Results and discussion were not integrated into a separate section at the end of each set of trials. (Line376-Line409)
8 There are other ways to evaluate and verify the established models. Please, provide the reasons why ANOVA was selected.
Response: (Line297-Line302)
The response surface model essentially represents the implicit functional relationship between the independent variables and the response variable. To address the question of whether there exists a statistically significant relationship between the independent variables and the response variable, it is necessary to conduct significance tests, analysis of variance, and precision tests on the model designed in this study. These tests aim to determine the goodness of fit of the regression results.
9 The research objective and problem statements of the previous studies are unclear. Please, provide them before the experimental section.
Response: (Line178-Line186)
2.3. Experimental design and Methods
In previous studies, the impact of variations in a single factor on compressive strength was often considered. However, in reality, changes in one factor can simultane-ously induce changes in other factors, and the interaction effects may influence the indi-cators of compressive strength. This is known as "response effect". Based on this, this study utilizes the compressive strength indicators at 3 d, 28 d, and 90 d to evaluate the early, middle, and long-term strength of concrete. The response surface methodology is employed to analyze the significant effects of both single and interaction factors on the evaluation indicators.
10 The content of the recycled coarse aggregate process should be emphasized.
Response:
The experimental investigation in this study focused solely on the use of recycled fine aggregate and waste concrete powder, without considering the utilization of recycled coarse aggregate. The coarse aggregate used in the experiments was entirely composed of natural aggregate.
14 Please, provide how to perform the X-ray spectrum in detail.
Response: (Line167-Line171)
To investigate the oxide content in the raw material of WCP, a semi-quantitative (qualitative) analysis of the samples was performed using X-ray spectroscopy. A loose sample of 50 mg of WCP was taken and dried at a constant temperature of 60°C for 48 hours in a vacuum drying oven. The oxide content was measured using the X-ray fluores-cence spectrometer model Brook S2 RANGER.
18 Conclusions are not strong enough to close this manuscript.
Response: (Line581-Line606)
- Conclusions:
Results of an experimental study examining the strength of concrete with single in-corporation of recycled fine aggregate, dual incorporation of RFA, and incorporation of WCP are presented. The interactive effects of the amount of WCP, water-cement ratio, and replacement rate of RFA were investigated using the Box-Behnken design method to de-termine the optimal mix proportion. Microscopic test images were subjected to layered grayscale binarization processing, and fractal analysis of the product morphology was performed at different levels. The following conclusions can be drawn:
(1) Based on the response surface experimental analysis of compressive strength, it was found that an appropriate amount of WCP is beneficial for improving the early, standard, and long-term strength of concrete. The optimal dosage is 15 % by mass of the fine aggregate.
(2) The water-cement ratio has a significant impact on the compressive strength of concrete. According to the experimental process used in this study, the optimal wa-ter-cement ratio is 0.43.
(3) The replacement of 33 % by mass of natural aggregate with RFA does not have a significant effect on compressive strength. This can serve as a guideline for the application of RFA as a substitute for natural aggregate.
(4) Grayscale binarization processing of the concrete matrix revealed that the concrete with single incorporation of fine aggregate has the largest pore area, while the concrete with dual incorporation of RFA has the smallest pore area. The fractal dimension of the pores is negatively correlated with compressive strength.
(5) Fractal analysis of the hydration products at three levels demonstrated a positive correlation between the fractal dimension of the hydrated calcium silicate gel and com-pressive strength. The layered fractal model shows superiority in evaluating the compres-sive strength of concrete.
19 Comments on the Quality of English Language
20 English must be checked and punctuation marks must be consistent.
Response: The language has been polished by a professional team
Author Response File: 
Author Response.docx
Reviewer 2 Report
The paper presents an useful study regarding the effects of recycled and concrete waste on the compressive strength of concrete.
The entire paper is well written, following a logical line. The introduction has enough references to justify the present study, although the novelty is not so clearly presented.
All the mehodes and experimental tests are described and explained sufficiently. The results are clearly presented and explained by the authors and they are inline with the present literature and practical applications.
- in the abstract and in the main part of the paper, 3d, 28d and 90d were considered for testing the concrete specimens... in the introduction, 7d is mentioned for response models of compressive strength... please explaine;
- how many samples were tested for each concrete mixture?
- along table 4, some comarative charts showing the values for compressive strength (at different ages) could help.
The microstructure analysis based on SEM images is a good addition, improving the entire paper and validating the fractal model.
The conclusions can be improved by adding some personal opinion on the results, future research based on the present findings and some practical applications.
There are some corrections to be made:
- different font size and alignment of the paragraphs;
- reference no 38 is missing;
The entire paper should be revised:
- there are many paragraphs in which the subject or predicate is missing, making them difficult to understand; these paragraphs need to be revised;
- there are many missing spaces between words, paragraphs, tables or figures;
- unnecessary punctuation marks (figure 4. shows... ), unnecessary capital letters or different use of them for the same word ("Residual" and "residual"), etc.
Author Response
Response to Referee 2
Comments and Suggestions for Authors. The paper presents an useful study regarding the effects of recycled and concrete waste on the compressive strength of concrete. The entire paper is well written, following a logical line. The introduction has enough references to justify the present study, although the novelty is not so clearly presented. All the mehodes and experimental tests are described and explained sufficiently. The results are clearly presented and explained by the authors and they are inline with the present literature and practical.
1 in the abstract and in the main part of the paper, 3d, 28d and 90d were considered for testing the concrete specimens... in the introduction, 7d is mentioned for response models of compressive strength... please explaine;
Response: (Line14-Line15)
The notation "7 d" was a typographical error and has been corrected.14-15
2 how many samples were tested for each concrete mixture?
Response: (Line226-Line227)
The average value of the compressive strength was calculated from three specimens for each mix proportion.
Figure 4. Pictures of compressive strength tests
Figure 5. SEM test picture
3 along table 4, some comarative charts showing the values for compressive strength (at different ages) could help.
Response: (Line231-Line232)
Figure 4. The resuilts of compressive strength tests
4 The conclusions can be improved by adding some personal opinion on the results, future research based on the present findings and some practical applications.
Response: (Line581-Line606)
- Conclusions:
Results of an experimental study examining the strength of concrete with single in-corporation of recycled fine aggregate, dual incorporation of RFA, and incorporation of WCP are presented. The interactive effects of the amount of WCP, water-cement ratio, and replacement rate of RFA were investigated using the Box-Behnken design method to de-termine the optimal mix proportion. Microscopic test images were subjected to layered grayscale binarization processing, and fractal analysis of the product morphology was performed at different levels. The following conclusions can be drawn:
(1) Based on the response surface experimental analysis of compressive strength, it was found that an appropriate amount of WCP is beneficial for improving the early, standard, and long-term strength of concrete. The optimal dosage is 15 % by mass of the fine aggregate.
(2) The water-cement ratio has a significant impact on the compressive strength of concrete. According to the experimental process used in this study, the optimal wa-ter-cement ratio is 0.43.
(3) The replacement of 33 % by mass of natural aggregate with RFA does not have a significant effect on compressive strength. This can serve as a guideline for the application of RFA as a substitute for natural aggregate.
(4) Grayscale binarization processing of the concrete matrix revealed that the concrete with single incorporation of fine aggregate has the largest pore area, while the concrete with dual incorporation of RFA has the smallest pore area. The fractal dimension of the pores is negatively correlated with compressive strength.
(5) Fractal analysis of the hydration products at three levels demonstrated a positive correlation between the fractal dimension of the hydrated calcium silicate gel and com-pressive strength. The layered fractal model shows superiority in evaluating the compres-sive strength of concrete.
6 different font size and alignment of the paragraphs;
7 reference no 38 is missing;
8 Comments on the Quality of English Language
9 The entire paper should be revised: there are many paragraphs in which the subject or predicate is missing, making them difficult to understand; these paragraphs need to be revised; there are many missing spaces between words, paragraphs, tables or figures; unnecessary punctuation marks (figure 4. shows... ), unnecessary capital letters or different use of them for the same word ("Residual" and "residual"), etc.
Response: The formatting issues mentioned above have been thoroughly addressed and revised throughout the entire manuscript. The modified sections are highlighted in red within the manuscript.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Thank you very much for this great improvement!
This manuscript had a high potential to publish in this journal.
But, now, this manuscript is strong enough publish in this publish.
That is all.
Thank you very much for all the authors' hard works.
This reviewer very interestingly read this manuscript.
Just in case, it will be awesome if a native English speaker checks typos or grammers one more time before it is published online.
