Experimental Study on the Strength and Stress–Strain Properties of Waste Concrete Fine Aggregate and Cement-Solidified Sludge
Round 1
Reviewer 1 Report
In this manuscript, the authors have studied the effect of fine aggregate content, particle size, cement content and curing time on the waste concrete fine aggregate-cement solidified sludge (WCSS)’s strength, and the stress-strain properties of WCSS were analyzed, to prove the feasibility of using waste concrete fine aggregate and cement to solidify sludge. The relevant research results provide the reference for applying the WCSS in practical engineering. The manuscript has provided sufficient details and is written well. However, some comments need to be considered to improve the quality of the paper. These comments are listed below:
1. How does the excess waste concrete fine aggregate affect the strength of WCSS?
2. The fitting formula in Section 3.2.3 of the paper adopts the power function form of the stress-strain fitting of cement soil in Tang's paper, and why the fitting form is adopted？
3. In section 3.1.4, the unconfined compressive strength of WCSS is fitted with the waste concrete fine aggregate content, curing time and cement content. Why multiple linear regression analysis is selected? In table 5, What is the Durbin-Watson coefficient of 5 indicates?
4. The form of some E50 in Section 3.3.2 needs to be modified.
Author Response
Point 1: How does the excess waste concrete fine aggregate affect the strength of WCSS?
Response 1: Too much fine aggregates will damage the skeleton which already formed in the soil. When the force is exerted, the excess fine aggregates will cause friction and collision to the formed skeleton. The surface of waste concrete fine aggregate is rough and porous, which will absorb water. Therefore, these redundant fine aggregates absorb the moisture which should have the hydrolysis and hydration reaction with cement and affect the production of cementation. Excess fine aggregates also hinder the connection of cementation between soil particles, as well as the connection between soil particles and skeleton. As a result, it negatively affects the strength of WCSS.
Point 2: The fitting formula in Section 3.2.3 of the paper adopts the power function form of the stress-strain fitting of cement soil in Tang's paper, and why the fitting form is adopted？
Response 2: First of all, the fine aggregate of waste concrete is not directly involved in the curing reaction of cement. According to the experimental data, the addition of fine aggregate will not affect the rapid increase of WCSS’s early strength, and it also shows the strain hardening characteristics of cement soil in the later stage of curing, so it will not change the original properties of cement soil. In the case of appropriate content, compared with the original cement soil, the strength will be improved to a certain extent, so the formula proposed by Tang is used for fitting.
Point 3: In section 3.1.4, the unconfined compressive strength of WCSS is fitted with the waste concrete fine aggregate content, curing time and cement content. Why multiple linear regression analysis is selected? In table 5, What is the Durbin-Watson coefficient of 5 indicates?
Response 3: First of all, the strength of WCSS is related to many factors such as cement content, and the optimal combination of multiple independent variables to predict or estimate the dependent variable is more effective and more realistic than using only one independent variable to predict or estimate. Therefore, this paper uses multiple linear regression analysis. Ma [1] used waste concrete particles with a particle size of 0-2mm to reinforce cement soil, and obtained a high fitting relationship through multiple linear regression analysis. The particle size of waste concrete particles used in this paper is in the range of 0-4.75mm, which belongs to the fine aggregate. Therefore, multiple linear regression is also used to analyze each dosage. Durbin-Watson coefficient is the most commonly used method to test autocorrelation currently. In general, the Durbin-Watson coefficient in the range of 1.5-2.5, indicating that the autocorrelation of each variable is not high, the multiple linear regression equation is highly accurate and practical. The Durbin-Watson coefficient obtained in this paper is 1.712, indicating that the equation (1) has high fitting degree and practicability.
- Ma, X.; Chen, S. L.; Hou, R. Mechanical Properties of Composite Cement Soil Mixed In Wasted Concrete Particle. Bulletin of The Chinese Ceramic Society. 2018, 37, 1010-1016. DOI:10.16552/j.cnki.issn1001-1625.2018.03.042
Point 4: The form of some E50 in Section 3.3.2 needs to be modified.
Response 4: Thanks for pointing this mistake out, we made a stupid mistake. We will modify this.
Reviewer 2 Report
This manuscript explores the “Experimental study of strength and stress-strain properties of waste concrete fine aggregate-cement solidified sludge”. The manuscript is concisely described and contextualized with the help of previous and present theoretical background and empirical research. Are all the references cited are relevant to this area of research and also adequate. The methods are clearly stated. The result and discussion of the research are coherent and balanced. The conclusions are supported by the results. However, some minor corrections need to be addressed before the acceptance the Manuscript.
1.What is the need for waste concrete fine aggregate-cement solidified sludge? Mention it in the abstract.
2. Arrange the key words in alphabetical order.
3. Cite the sentence “Cement can generate cementation products with considerable strength through a series of chemical reactions, so many scholars have researched using cement as a curing agent to solidify sludge” in the introduction section.
4.In what way this research differs from past research of solidification of dredged sludge?
5. Present the novelty of the current research at the end of introduction.
6. How did you arrived the chemical composition of cement?
7. Mention the relevant standards/guidelines of various test performed in this study.
8. Present the test setup images if available with author.
9. Remove the numbers (1), (2) used in the section 3.1.2. Instead you can use bulletin. It confuses with chapter number.
10. Show the graph of Multiple Linear Regression Analysis using SPSS software.
Author Response
Point 1: What is the need for waste concrete fine aggregate-cement solidified sludge? Mention it in the abstract.
Response 1: Thank you for your good suggestion. In this study, waste concrete fine aggregate of waste concrete is used to solidify dredge sludge with cement to achieve the purpose of reusing waste concrete and forming solidified soil with a good mechanical property. We will mention it in the abstract.
Point 2: Arrange the key words in alphabetical order.
Response 2:
Before revised: waste concrete fine aggregate; solidification; unconfined compression strength; stress-strain properties; deformation modulus
After revised: deformation modulus; solidification; stress-strain properties; unconfined compression strength; waste concrete fine aggregate
Point 3: Cite the sentence “Cement can generate cementation products with considerable strength through a series of chemical reactions, so many scholars have researched using cement as a curing agent to solidify sludge” in the introduction section.
Response 3: I am sorry that the expression in this sentence is not clear enough. We will modify.
Before revised: Cement can generate cementation products with considerable strength through a series of chemical reactions, so many scholars have researched using cement as a curing agent to solidify sludge
After revised: Cement can generate cementation products, namely CAH and CSH, through a series of chemical reactions, which can bond soil particles and form clusters. Thus, cement has been extensively used as a curing agent to solidify sludge [1].
[1] Omid, A.; Mojtaba, G. Laboratory study of the effects of using magnesium slag on the geotechnical properties of cement stabilized soil. Construction and Building Materials. 2019, 223, 409-420. DOI: 10.1016/j.conbuildmat.2019.07.011
Point 4: In what way this research differs from past research of solidification of dredged sludge?
Response 4: The idea of this study is the same as that of using composite curing agent to solidify sludge in the past. For example, Zhang et al. [2] added cement and ethylene-vinyl acetate copolymer to loess as the soil curing agent. The results showed that, the addition of ethylene-vinyl acetate copolymer significantly improved the performance of cement stabilized loess; However, compared with most previous studies, the construction waste is used as an additive, and the fine aggregate with a particle size of 0-4.75mm is obtained by treating the waste concrete in this research. Solidifying dredged sludge with waste concrete fine aggregate and cement to achieve better solidification effect while reusing resources.
[2] Zhang, B. W.; Jiang, W.; Xu, Q. Z.; Yuan, D. D.; Shan, J. H.; Lu, R. Experimental feasibility study of ethylene-vinyl acetate copolymer (EVA) as cement stabilized soil curing agent. Road Materials and Pavement Design. 2020, 23, 617-638. Doi:10.1080/14680629.2020.1834442
Point 5: Present the novelty of the current research at the end of introduction.
Response 5: Thank you for your good suggestion. We will modify the end of the introduction.
Before revised: Therefore, this paper proposes using waste concrete fine aggregate and cement to solidify dredged sludge. Based on the data of UCS, researching the effect of fine aggregate content, particle size, cement content and curing time on the waste concrete fine aggregate-cement solidified sludge (WCSS)’s strength, and the stress-strain properties of WCSS were analyzed, to prove the feasibility of using waste concrete fine aggregate and cement to solidify sludge.
After revised: Therefore, this study uses the fine aggregate with a particle size of 0-4.75 mm obtained from waste concrete treatment as an additive to solidify the dredged sludge together with cement. While reusing construction waste resources, the dredged sludge can also achieve an excellent solidification effect. Based on the UCS test data, the effects of fine aggregate content, particle size, cement content, and curing time on the strength of waste concrete fine aggregate-cement solidified sludge (WCSS) were investigated. The stress-strain characteristics of WCSS were analyzed, and the feasibility of WCSS was proved.
Point 6: How did you arrived the chemical composition of cement?
Response 6: The cement used in the test is P.O42.5 ordinary portland cement produced by Huaxin cement (Ezhou) Co., LTD. The chemical compositions of the cement are determined by XRF analysis.
Point 7: Mention the relevant standards/guidelines of various test performed in this study.
Response 7: Thanks for your suggestion. The main test used in this study is the unconfined compressive strength test. We carried out the test according to the steps in the geotechnical test specification GBT 50123-2019. We will add this in the text.
Ministry of Water Resources of the People 's Republic of China.
GBT50123-2019.Soil Test Method Standard. Beijing: China Plan Press, 2019.
Point 8: Present the test setup images if available with author.
Response 8: Here are the pictures taken during the experiment. Fig.2(a) is TSZ-1A automatic triaxial apparatus ; Fig. 2(b) is the unconfined compressive strength specimen.
Fig. 2 (a) TSZ-1A automatic triaxial apparatus
Fig. 2 (b) Waste concrete fine aggregate-cement solidified sludge (WCSS) samples
Point 9: Remove the numbers (1), (2) used in the section 3.1.2. Instead you can use bulletin. It confuses with chapter number.
Response 9: Thank you for your suggestion, we will modify this part according to the standard of the journal.
Point 10: Show the graph of Multiple Linear Regression Analysis using SPSS software.
Response 10: The table obtained by using SPSS software for multiple linear regression analysis is the key to show the fitting model. The figures obtained in multiple linear regression analysis are mostly standardized residual histograms and normal P-P graph of regression standardized residuals. The meaning of these two figures is: if the residual is randomly scattered distribution, indicating that the standardized residual histogram in accordance with the normal distribution, then the residual and the data is matched. The model fits better. If the points in the P-P diagram are distributed around the asymptote, it can be shown that the residuals are randomly scattered.
It can be seen from Figure 3 and Figure 4 (exported from SPSS), the points in the P-P diagram are roughly distributed around the asymptote, so it can be considered that the histogram is roughly in accordance with the normal distribution, and the established fitting model is good.
However, the focus of this study is on the WCSS’s strength and stress-strain properties. The main work of this section is also to establish the appropriate model between strength and factors. Standardized residual histogram and P-P diagram are only methods to study the accuracy of the model, which is secondary. And the two graphs will not have a great impact on the fitting results. Therefore, the SPSS fitting diagram is not the key to analyzing the model, and we do not recommend displaying the SPSS diagram in the article.
Figure. 3 Standardized residual histograms
Figure. 4 P-p graph of regression standardized residuals
Author Response File: 
Author Response.docx
Reviewer 3 Report
General comments：
The objective of this study is to analyze the effect of four main factors, including fine aggregate content, particle size, cement content and curing time, on the strength of WCSS. Tests and analyses were performed for the relationship between unconfined compressive strength and stress-strain. However, the analysis of the intrinsic mechanism is insufficient and the experimental analysis at the microscopic level is also lacking. Moreover, this paper lacks some novelty in experimental design. Therefore, all aspects of this paper, from experimental design to results analysis, need to be improved.
The following suggestions are shared for authors:
INTRODUCTION:
The introduction section mentions the two parts of CO2 generation and additives that have led to the tendency to use additives to reduce the amount of cement, and does not present whether there are previous studies using fine aggregates to assist in curing. If not, the relevant studies should be presented in detail to justify the research. Therefore a more focused presentation of the background of the study would have been better.
EXPERIMENTAL PROGRAM:
-In the context of the study, many studies tend to use additives to enhance the curing effect, while the following uses waste concrete fine aggregate as an additive and no other auxiliary additives, please describe carefully the reasons for this and the possible effects.
-Please provide as much detail as possible on the basis for determining the waste concrete particle content and cement content in the experimental design grouping. And whether it is consistent with the actual application in the engineering.
-Curing temperature of 30℃ is used, which is higher than the normal curing temperature. Is there any basis for the temperature selection if it is only to speed up the reaction? How is the temperature selected to ensure that the concrete curing effect is better? Should ensure that the experiment is representative.
RESULTS AND DISCUSSION:
-Fig 3 and fig 4 are duplicated only by replacing the axes. It is suggested to change to a better presentation.
-Section 3.2.2 is titled the effect of maintenance time, but the conclusion is the effect of fine aggregate admixture. Why the effect of fine aggregate admixture is not studied, but can reach a conclusive conclusion, is it lack of rigor?
-Section 3.2.3 and 3.3 are more descriptive of the phenomenon, but not enough analysis of the inner mechanism. And the adverse effect on the skeleton, when the fine aggregate content is high, is not clear as described in the previous paper. It should be added in the analysis section.
-Please proofread the paper to correct grammatical errors.
-The abstract lacks the necessary terminology, please add the relevant information.
-What is the basis for the development of the test regime for the curing temperature of 30°C? Please explain its representativeness for the reader's reference.
-Fig 3 and fig 4 are duplicated, please consider the form of presentation.
-In the section of results and discussion, most of the theoretical content is present, but the micromechanism analysis is lacking. Please add supporting information for the discussion.
-Please analyze the practical value of the research and make suggestions, taking into account the experimental results and the engineering.
Author Response
Point 1: The introduction section mentions the two parts of CO2 generation and additives that have led to the tendency to use additives to reduce the amount of cement and does not present whether there are previous studies using fine aggregates to assist in curing. If not, the relevant studies should be presented in detail to justify the research. Therefore, a more focused presentation of the background of the study would have been better.
Response 1: Thanks for your suggestions.
At present, recycled waste concrete fine aggregate is mainly used for the manufacture of recycled mortar. Rebeca [1] used fine aggregate in the manufacture of cement-based mortar and tested the mechanical properties of cement mortar with Fine recycled concrete aggregates. However, there are few studies on using waste concrete fine aggregate to solidify sludge. On the one hand, waste concrete fine aggregate is a kind of artificial aggregate with complex composition, low hydration activity and high permeability [2]. On the other hand, waste concrete fine aggregate will not react with silt, so the effect of using waste concrete fine aggregate alone to solidify silt is not obvious. However, the waste concrete fine aggregate itself has a certain strength. When it interacts with other curing agents which can generate cementation products, the generated cementation products can make the soil particles attach to the skeleton formed by the waste concrete fine aggregate, which can absorb excess water and improve the strength of the sample to a certain extent. Ma [3] has used wasted concrete particle with a particle size of 0-2mm and cement to reinforce soft soil, but it does not include all fine aggregates (0-4.75mm). The analysis of the factors affecting the strength of solidified soil is not complete, and the stress and strain properties of solidified soil are not studied in depth. Therefore, this paper selects waste concrete fine aggregate and cement solidify sludge, analyzes the factors affecting the strength, and researches the stress-strain and deformation modulus of the solidified sample.
The following will be added to the introduction section: This is mainly because waste concrete fine aggregate does not react with sludge directly, and the effect of using waste concrete fine aggregate alone to solidify sludge is not obvious. However, the waste concrete fine aggregate has a certain strength. When it interacts with other curing agents capable of generating cementation products, the generated cementation products can make soil particles attach to the skeleton formed by the aggregate. Moreover, fine aggregate can also absorb excess water and improve the strength of the sample to a certain extent.
[1] Rebeca Martínez-García.; María Isabel Sánchez de Rojas;Julia Mª. Morán-del Pozo;Fernando J. Fraile-Fernández;Andrés Juan-Valdés. Evaluation of Mechanical Characteristics of Cement Mortar with Fine Recycled Concrete Aggregates (FRCA) . Sustainability. ; 2021, 13, 414. Doi:10.3390/su13010414
[2] Ai, W. B.; Liu, H. M; Zhang, J.; Lv, S. S; Xu, Q.; Li, H. H . Research on crushing and recycling of waste concrete. IOP Conference Series: Earth and Environmental Science.2020, 446, 032069. Doi:10.1088/1755-1315/446/3/032069
[3] Ma,X.; Chen, S. L.; Hou, R. Mechanical Properties of Composite Cement Soil Mixed In Wasted Concrete Particle. Bulletin of The Chinese Ceramic Society. 2018, 37, 1010-1016. DOI:10.16552/j.cnki.issn1001-1625.2018.03.042
Point 2: In the context of the study, many studies tend to use additives to enhance the curing effect, while the following uses waste concrete fine aggregate as an additive and no other auxiliary additives, please describe carefully the reasons for this and the possible effects.
Response 2: In this study, waste concrete fine aggregate is used as an additive to solidify sludge with cement. The fine aggregate of waste concrete does not react directly with sludge, and the effect of using fine aggregate alone to solidify sludge is not ideal.
Point 3: Please provide as much detail as possible on the basis for determining the waste concrete particle content and cement content in the experimental design grouping. And whether it is consistent with the actual application in the engineering.
Response 3: First of all, our research group used Wenzhou sludge in previous studies [4]. In the study, it was found that the unconfined compressive strength of solidified sludge increased most significantly when the cement content was 12%-16%. From the previous study on solidification of soft soil and sludge by the curing agent, it can be known that the liquid and plastic limit of soil is one of the main factors determining the curing agent content. The Wenzhou sludge belongs to high liquid limit clay according to the standard [5]. Referring to previous studies, Zhang [6] used magnesium phosphate cement to solidify lead-contaminated soils the liquid limit and the plastic limit of the soil are 41.6% and 21.8%, respectively. The curing agent content was set to 30%, 40%, 50%, 60%, and 70% of the dry soil mass, respectively. Dahal [7] also chose to use a curing agent to treat marine clay with high water content. The cement content was set to 5%, 10%, 15%, and 20% of the dry soil mass in his research. The results show that the unconfined compressive strength and residual strength of marine clay increase with cement content. Therefore, we set the cement content range as 10%-16% in this study. For the selection of content of waste concrete fine aggregate, we believe that the waste concrete fine aggregate should be used as much as possible to maximize the resource utilization. Secondly, due to the lack of research on the use of waste concrete fine aggregate and cement to solidify sludge, therefore, this paper uses the fine aggregate of this dosage range.
- Bian, X. Y.; Cheng, Y. X. Study on Strength and Strain Characteristics of Low Cement Content Solidified Sea Mud.Journal of Wuhan Institute of Technology. 2021, 43, 76-80 (in Chinese)
[5] GB/T50145-2007. Soil classification standards. Ministry of Water Resources of the People’s Republic of China. 1991.
[6] Zhang, T.T.; Li, J. S.; Wang, P.; Li, Z. Z. Experimental study of stress-strain properties of lead-contaminated soils treated by magnesium phosphate cement.Rock and Soil Mechanics. 2016, 37, 215-225. (in Chinese)
[7] Dahal, B.K.; Zheng, J.J.; Zhang, R.J.; Song,D.B. Enhancing the mechanical properties of marine clay using cement solidification, Marine. Georesources & Geotechnology. 2018, 37, 755-764. DOI: 10.1080/1064119X.2018.1484532
Point 4: Curing temperature of 30℃ is used, which is higher than the normal curing temperature. Is there any basis for the temperature selection if it is only to speed up the reaction?
Point 5: How is the temperature selected to ensure that the concrete curing effect is better? Should ensure that the experiment is representative.
Point 11: What is the basis for the development of the test regime for the curing temperature of 30°C? Please explain its representativeness for the reader's reference.
Response 4, 5, 11: On the one hand, considering that the large amount of dredged sludge produced every year will cause a lot of economic burden to the project if it is not handled in time. The temperatures in many parts of China are above 20°C throughout the year, and the temperature is close to or even more than 30 °C for half a year. Taking Wuhan as an example, Wuhan 's summer lasts for four to five months, and the summer temperature is high. Most of the time in summer, the temperature will exceed 30℃. Therefore, this study considers the treatment of solidified sludge of engineering in summer, so the curing temperature is set to 30℃, which is closer to the summer curing temperature. On the other hand, according to the conclusion obtained by Zhang in the research [8]. High curing temperature can accelerate the rate of hydration reaction, which will significantly improve the early strength of cement soil development rate. Higher curing temperature can also make cement produce more pozzolanic reaction products, which also improve the late strength of cement soil. At present, we believe that the selection of temperature in the test should be based on the time and season of the local project and consider the difference between the actual curing temperature and the laboratory standard curing temperature, which is of great significance to control the total cost of the project.
[8] Zhang, R. J.; Zheng J. J.; Cheng, Y. S.; Dong, R. Experimental investigation on effect of curing temperature on strength development of cement stabilized clay. Rock and Soil Mechanics. 2016, 37, 3463-3471.
Point 6: Fig 3 and fig 4 are duplicated only by replacing the axes. It is suggested to change to a better presentation.
Point 12: Fig 3 and fig 4 are duplicated, please consider the form of presentation.
Response 6, 12: Thank you for your advice. The new orders in the text are Figure 4 and 5. Firstly, Figure 4 and Figure 5 are different. Figure 4 is the variation of WCSS’s strength with the increase of fine aggregate content at three different curing times. It can be seen from the figure that with the increase of fine aggregate content, the strength of WCSS appears inflection point.
|
(a) Curing for 7d |
(b) Curing for 14d |
|
(c) Curing for 28d |
|
Figure 4. Variation of strength with fine aggregate content
Fig.5 shows the variation of WCSS’s strength with the increase of cement content at three curing time. In the figure, the strength of WCSS is almost linearly increased, and there is no inflection point. And because the strength of WCSS will increase significantly with the curing age. Therefore, we believe that this expression can more intuitively express the specific changes of the strength with each content.
|
(a) 7d |
(b) 14d |
|
(c) 28d |
|
Figure 5. Variation of strength with cement content
Point 7: Section 3.2.2 is titled the effect of maintenance time, but the conclusion is the effect of fine aggregate admixture. Why the effect of fine aggregate admixture is not studied, but can reach a conclusive conclusion, is it lack of rigor?
Response 7: Thank you for pointing this out. I' m sorry that my expression is not clear enough here. Here we mainly want to express in the short-term maintenance, WCSS’ s strength can be rapid growth and show strain hardening. We will modify this part.
Before revised: The results show that the incorporation of waste concrete fine aggregate does not change the rapid growth in the early strength of cement soil, and the strain property.
After revised: The UCS of cement soil could be enhanced rapidly with curing time due to its early hydrolysis and hydration reaction. WCSS also showed this property, whose hydrolysis and hydration reaction enabled the UCS to increase rapidly with curing time. In addition, WCSS could show strain hardening properties similar to cement soil with curing time. Curing time was an important factor for strength improvement and strain hardening of WCSS. This also reflected that the incorporation of waste concrete fine aggregate did not change the properties of cement soil.
Point 8: Section 3.2.3 and 3.3 are more descriptive of the phenomenon, but not enough analysis of the inner mechanism. And the adverse effect on the skeleton, when the fine aggregate content is high, is not clear as described in the previous paper. It should be added in the analysis section.
Response 8: Thank you for your suggestions, in Section 3.2.3 and Section 3.3，we will further analyze the internal mechanism , and give a more detailed description of the adverse effect on the skeleton when fine aggregate content is higher content
Point 9: Please proofread the paper to correct grammatical errors.
Response 9: Thanks for your recommendation. We made comprehensive adjustments to the language and logic of the full text according to the opinions of experts, and finally asked a professional language polishing company to process the language of the manuscript.
The file “English editing certificate” is attached to my submission, which is about a certification of the polished work about our manuscript entitled “Experimental study of strength and stress-strain properties of waste concrete fine aggregate-cement solidified sludge”.
We have the confidence that the quality of our revision manuscript in the aspect of language has significantly improved by the dedicated work of my team and the effective help from a professional language polish company. We all hope the revision work can satisfy your requirements.
Point 10: The abstract lacks the necessary terminology, please add the relevant information.
Response 10: Thank you for your suggestion. Here is the structure of the abstract section of this paper.
This part is the purpose of this study: In this study, waste concrete fine aggregate and cement are applied to sludge solidification and resource recycling.
This part is the research methods and ideas of this study: The unconfined compressive strength (UCS) test is performed to investigate the variation in the strength and stress-strain properties of the solidified sludge with the content and particle size of waste concrete fine aggregate, cement content, and curing time.
This part is the result of this study: The results show that incorporating waste concrete fine aggregate can improve the UCS of cement solidified sludge, which can achieve the optimum effect when the fine aggregate content ranges from 12% to 15%. However, compared with the fine aggregate content, the cement content and curing time are the main factors in improving the strength of waste concrete fine aggregate-cement solidified sludge (WCSS). The stress-strain curves of WCSS comprise four stages. The failure strain εf of WCSS with four fine aggregate contents decreases in a power function with the increase of qu, and εf is mostly distributed when the content is 1.1%-2.1%. A linear relationship is observed between E50 and qu.
This part is the conclusion of this study: This study attempts to promote the recycling of waste concrete fine aggregate and obtain solidified sludge with excellent mechanical properties, providing some reference for practical engineering applications.
Point 13: In the section of results and discussion, most of the theoretical content is present, but the micro-mechanism analysis is lacking. Please add supporting information for the discussion.
Response 13: You are right, this paper focuses on the analysis of the phenomenon, and fitting the stress-strain parameters of WCSS, to determine the practical engineering meaningful parameters, such as fine aggregate content. However, combined with previous studies, it is not difficult to obtain the microscopic mechanism of WCSS. An innovative approach mixing cement and brick waste fine aggregate is proposed to stabilize the high water content clay (called as double mixing stabilized clay, DMSC) by Duan [9]. He pointed out in the paper that brick waste fine aggregate can be used as skeleton to improve the strength of solidified clay. Estabragh [10] added nylon fiber to cement soil. Through microscopic experiments, it was found that the cementation products generated by cement enabled soil particles to adhere to nylon fiber, and the generated cementation products could also fill the pores in solidified soil. Nylon fiber is not directly involved in some chemical reactions of soil in curing engineering. Therefore, we can analyze the microscopic mechanism of WCSS based on previous studies.
However, the microscopic experiment of WCSS is of great significance, so we will further improve the microscopic mechanism of WCSS. For the opinions of reviewer, we will carry out a micro study of WCSS in the next experiment.
[9] Duan, K.; Bian, X. Y.; Chen, J. L.; Bai, J. L. Experimental investigation on clay stabilized by cement and waste brick fine aggregate. Chinese Journal of Geotechnical Engineering. 2021, 43, 174-177. (in Chinese)
[10] Estabragh, A. R.; Namdar, P.; Javadi, A. A. Behavior of cement-stabilized clay reinforced with nylon fiber. Geosynthetics International. 2012, 19, 85-92. Doi:10.1680/gein.2012.19.1. .85
Point 14: Please analyze the practical value of the research and make suggestions, taking into account the experimental results and the engineering.
Response 14: First of all, the study can solidify the idle dredged silt and achieve the purpose of reuse of waste concrete fine aggregate resources. This study confirms that waste concrete fine aggregate and cement solidified sludge have better effects than pure cement solidified sludge. It is necessary to determine the optimal dosage of curing agent for many studies using curing agent to solidify soil. For example, when Wen [11] studied the effect of pumice powder on the cement soil’s strength, he proposed that when the cement content was 16% and the pumice powder content was 8%, the curing effect was the best. Zhang [12] also did a lot of research on the optimal dosage of curing agent when using flocculation-solidification method to reinforce soft soil. According to the conclusions of this paper, if waste concrete fine aggregate and cement are used to solidify sludge in practical engineering, it can be selected in the fine aggregate content of 12%-15%. The formula proposed in section 3.1.4 can be used in practical engineering to estimate the strength of solidified sludge according to the fine aggregate content, cement content and curing time. In the stress-strain analysis, the strain is concentrated between 1.1% and 2.1%, indicating that within the bearing capacity range of WCSS, its deformation is small and has good engineering performance. The deformation modulus reflects the ability of the material to resist elastic-plastic deformation. In the practical projects, the deformation modulus is the main parameter [13]. Therefore, the study of deformation modulus of WCSS has certain engineering significance. When considering the ability of WCSS to resist elastic-plastic deformation, the E50 of WCSS can be estimated according to formula (7), which can provide corresponding parameter guidance for engineering. Because cement solidified sludge technology has been widely used in engineering and achieved good results. For example, Japan Ishinomaki reclamation project [14,15], Singapore Tekong island reclamation project [16,17], so we have reason to believe that WCSS which has better engineering performance should have certain engineering value.
[11] Wen, Y. Q.; Feng, X. Y.; Shen, X. D.; Cui, Y. P. Microscopic Mechanism Study on the Strength Effects of Pumice Powder to Cement Soil. Advanced Materials Research. 2013. 834-836, 776-783. doi:10.4028/www.scientific.net/AMR.834-836.776
[12] Zhang, R. J.; Dong, C. Q.; Lu, Z.; Pu, K. F. Strength characteristics of hydraulically dredged mud slurry treated by flocculation-solidification combined method. Construction and Building Materials.2019.228,116742. Doi.org/10.1016/j.co
Nbuildmat.2019.116742
[13] Zhang, T. T.; Li, J. S.; Wang, P.; Li, Z. Z. Experimental study of stress-strain properties of lead-contaminated soils treated by magnesium phosphate cement. Rock and Soil Mechanics. 2016, 37, 215-225. (in Chinese)
[14] Porbaha A, Hanzawa H, Shima H. Technology of air-transported stabilized dredged fill [J]. Part i: Pilot study. Ground Improvement, 1999, (3): 49-58.
[15] Sakamoto A. Cement and soft mud mixing technique using compressed air-mixture pipeline: Efficient solidification at a disposal site [J]. Terra et Aqua Journal, 1998, 73: 11-22.
[16] Tan T S, Karthikeyan M, Loh Y H. Beneficial use of dredged sediments [J]. International Symposium on Sediment Management, Lille, France, 2008: 69-78.
[17] Tan T S, Lu Y T, Phoon K K, et al. Innovative approaches to land reclamation in Singapore [J]. Advances in Ground Technology and Geo-Information, Singapore, 2011: 85-102.
Author Response File: Author Response.docx
Reviewer 4 Report
The article is very difficult to read, so extensive editing of the English language and style is required.
Comments for author File: 
Comments.pdf
Author Response
Point 1: The article is very difficult to read, so extensive editing of the English language and style is required.
Response 1: Thanks for your recommendation. We made comprehensive adjustments to the language and logic of the full text according to the opinions of experts, and finally asked a professional language polishing company to process the language of the manuscript.
The file “English editing certificate” is attached to my submission, which is about a certification of the polished work about our manuscript entitled “Experimental study of strength and stress-strain properties of waste concrete fine aggregate-cement solidified sludge”.
We have the confidence that the quality of our revision manuscript in the aspect of language has significantly improved by the dedicated work of my team and the effective help from a professional language polish company. We all hope the revision work can satisfy your requirements.
Author Response File: Author Response.docx
Round 2
Reviewer 3 Report
Thanks to the authors for their efforts to respond to my questions and recommandations.
