Effects of pH and Fineness of Phosphogypsum on Mechanical Performance of Cement–Phosphogypsum-Stabilized Soil and Classification for Road-Used Phosphogypsum

Round 1

Reviewer 1 Report

The paper is very well written and contains valuable research for future studies. The below issues should be considered before publication

1-"This study is also favorable to establish or supplement criterion about road usage PG considering the conventional standard barely give specification for road usage PG." Revise this sentence. 

2-experimental section is too long. try to reduce it.

3-ınformation should be provided for soil. characterization of soil, physical and chemical properties is missing

4-provide more explanation on "inhibiting mechanism"

5-"The UCS values under different PG particle fineness are graphically presented in Figure 2." revise this sentence. check the others. ın my opinion, "under" should be replaced with appropriate one.

Author Response

Response to Reviewer

Ms. Ref. No.: coatings-960241

Title: Effects of pH and Fineness of phosphogypsum on Mechanical Performance of Cement-phosphogypsum-stabilized Soil and Classification for Road-used Phosphogypsum

Correspondence Author: Zhongchang Yang

Dear Prof. Yolanda Guo and Reviewer, 

We would like to take this opportunity to thank your acceptance and comments concerning our manuscript entitled “Effects of pH and Fineness of phosphogypsum on Mechanical Performance of Cement-phosphogypsum-stabilized Soil and Classification for Road-used Phosphogypsum (Ms. Ref. No.: coatings-960241)”. Meanwhile, these comments are all valuable and very helpful for refining our paper, as well as the important guiding significance to our researches. We have carefully revised our manuscript in light of your kind comments. Revised portions regarding your comments are marked in red in the revised paper. Once again, we earnestly appreciate for Prof. Yolanda Guo and reviewer for warm work, and hope that the revised version of our manuscript can meet with approval. If you have any question about this paper, please don’t hesitate to let us know. Enclosed please find our point-by-point responses to your comments as follow.

Thank you and best regards.

Yours Sincerely,

Zhongchang Yang* (E-mail: [email protected])

¨ Responses to the comments from Reviewer:

1. "This study is also favorable to establish or supplement criterion about road usage PG considering the conventional standard barely give specification for road usage PG." Revise this sentence.

Many thanks for reviewer’s kind advice. This sentence has been revised as follow: “This study is also helpful to establish or supplement a standard for PG used in road, considering that this standard is barely given in the current specification”. The details can be found in the revised paper, i.e., lines 83-85.

2. Experimental section is too long. try to reduce it.

Experimental section has been reduced in the revised paper. The details are can be found in lines 144-156.

3. Information should be provided for soil. characterization of soil, physical and chemical properties is missing.

Physical and chemical properties of soil have been provided in the revised paper. The details are presented in Tables 3 and 4, can be also found in lines 107-108.

Table 3.Physical properties of loess.

Table 4. Chemical properties of loess.

4. Provide more explanation on "inhibiting mechanism"

 More explanation on "inhibiting mechanism" is provided in this article. The possible reasons for this can be contributed to that the larger fineness of PG particles led to a smaller specific surface area for PG particles. The reaction between calcium sulfate dihydrate crystals in PG and soil particles mainly occurs on the surface; therefore, the speed and extent of the reaction between calcium sulfate dihydrate crystals and soil particles and cement decreased with increased fineness, which caused an increase in the unconfined compressive strength of cement–PG-stabilized soil. Additionally, there are differences in the content of impurities in different particle size ranges. Purities like soluble phosphorus, organic matter, and F- mainly exist in the surface of PG particles, so the content of purities increased with decreased PG fineness, which goes against to the strength-forming process of cement–PG-stabilized soil. The details can be found in lines 205-207, lines 251-258 and lines 278-285.

5. "The UCS values under different PG particle fineness are graphically presented in Figure 2." revise this sentence. check the others. ın my opinion, "under" should be replaced with appropriate one.

We are very grateful for the reviewer’s kind advice. This sentence has been revised as follow: “The UCS values with different PG particle fineness are graphically presented in Figure 2”, and all the words “under” have been also changed to “with” in the revised paper. The details can be found in line 244 and 270.

Author Response File: Author Response.docx

Reviewer 2 Report

The article is interesting for the interest in new building materials with better properties, and with the possibility of using a by-product or waste. But it has some shortcomings or inconsistencies, such as:

Are needed to explain the aims of the research, clearly. I just do not understand what they are trying to do with this research

The introduction mentions that phosphogypsum PG, causes harmful radon emissions, which can be dangerous to human health, so how is it proposed to use PG as building materials considering the dangerous emissions of radon that can produce?

It should be clarified that means Fineness, is it particle diameter?

Line 88, what means Loess?

In table 1, explain the meaning of W_L, W_P and I_P

Point 2.2.2. Is needed to define each variable in equations the final statement (lines 188,199) is not understood.

Line 138: What is p-l curve? Clarify

What is CPCM? And difference with Cement-stabilized soil, Explain deeply this point

Tables 6,7,8 are not understood the results in them, and specially in Table 6, how you have obtained the results and what information gives about your research

How you determine pH and how you can modify

You can add a resume Table in order to provide all the key information from the application conclusions in your research.

In line 209: P2O5 , how do you know these impurities appears?, and ¿why did appears?

How do you change the fineness and pH in the samples?

Finally according with the standards, what samples and with variable (pH,…) could be used and improved the actual construction materials?, and ¿specifically in which applications?

Author Response

Response to Reviewer

Ms. Ref. No.: coatings-960241

Title: Effects of pH and Fineness of phosphogypsum on Mechanical Performance of Cement-phosphogypsum-stabilized Soil and Classification for Road-used Phosphogypsum

Correspondence Author: Zhongchang Yang

Dear Prof. Yolanda Guo and Reviewer, 

We would like to take this opportunity to thank your acceptance and comments concerning our manuscript entitled “Effects of pH and Fineness of phosphogypsum on Mechanical Performance of Cement-phosphogypsum-stabilized Soil and Classification for Road-used Phosphogypsum (Ms. Ref. No.: coatings-960241)”. Meanwhile, these comments are all valuable and very helpful for refining our paper, as well as the important guiding significance to our researches. We have carefully revised our manuscript in light of your kind comments. Revised portions regarding your comments are marked in red in the revised paper. Once again, we earnestly appreciate for Prof. Yolanda Guo and reviewer for warm work, and hope that the revised version of our manuscript can meet with approval. If you have any question about this paper, please don’t hesitate to let us know. Enclosed please find our point-by-point responses to your comments as follow.

Thank you and best regards.

Yours Sincerely,

Zhongchang Yang* (E-mail: [email protected])

¨ Responses to the comments from Reviewer:

1. Are needed to explain the aims of the research, clearly. I just do not understand what they are trying to do with this research.

Many thanks for reviewer’s comments. PG is a kind of production waste of the phosphoric acid production. This research focuses on the utilization of PG in subgrade soil to recycle waste PG and facilitate its utilization in road engineering. It is confirmed that PG can be used in subgrade to stabilize soil with cement based on the mechanical analysis. In this research, the effects of pH and fineness of PG on the mechanical properties of cement-PG stabilized materials are systematically investigated. Moreover, this research also establishes a standard for PG used in road, so it is helpful to choose or disposal PG in road engineering.

2. The introduction mentions that phosphogypsum PG, causes harmful radon emissions, which can be dangerous to human health, so how is it proposed to use PG as building materials considering the dangerous emissions of radon that can produce?

According to reviewer’s comments, we would like to make the following statements regarding the questions.

The underground water and soil will be polluted when both a large amount of PG stacked in the open air and rainwater infiltration are simultaneously occurred, while human health is be adversely affected. However, the maximum PG content used in this paper is 12%, so the PG with this content hardly causes the pollution to the natural environment. Additionally, it is also hard for the rainwater to infiltrate into the subgrade, so the PG do not contaminate the natural environment and pose a threat to human health when it is used in subgrade soil. It is therefore safe to the application of PG in subgrade soil.

3. It should be clarified that means Fineness, is it particle diameter?

We are very grateful for the reviewer’s kind advice. Yes. Fineness refers to the size of particle diameter.  The explanation of fineness has been added into the revised paper, and the details can be found in line 119.

4. Line 88, what means Loess?

Loess is a kind of soil, and it refers to the yellow powdery soil with columnar formed in dry climate. Loess can be used as the subgrade soil when it is treated with cement or other stabilization materials. The explanation of loess has been added into the revised paper, and the details can be found in lines 92–93.

5. In table 1, explain the meaning of W_L, W_P and I_P.

W_L, W_P and I_P have been defined in the Table 3. Furthermore, W_L, W_P and I_P refer to liquid limit, plastic limit and plasticity index, respectively. The meaning of W_L is as follow: liquid limit refers to the limit moisture content between the plastic state and the fluid state of the cohesive soil, i.e., the upper limit moisture content of the cohesive soil in the plastic state; the moisture content of the soil is too high and the soil can even flow like a liquid when the moisture content of the soil is larger than the liquid limit. The meaning of WP is as follow: plastic limit refers to the limit moisture content between the plastic state and the semi-solid state of the cohesive soil, i.e., the lower limit moisture content of the cohesive soil in the plastic state; the moisture content of the soil is greatly low, and the soil changes from the plastic state to the semi-solid state and loses its plasticity when the moisture content of the soil is less than the plastic limit. The meaning of IP is as follow: the plasticity index is an important index characterizing the mechanical and deformation properties of the soil; the value of plasticity index is equal to the difference between liquid limit and plastic limit, i.e., I_P = W_L-W_P. W_L, WP and IP are the significant parameters of soil properties. We have added these statements regarding W_L, W_P and I_P into the revised paper and the details can be found lines 94-104.

6. Point 2.2.2. Is needed to define each variable in equations the final statement (lines 188,199) is not understood.

Many thanks for reviewer’s comments. All the variables in equations have been defined in the revised paper. And the related statement (lines 127-143) has been revised, which also can be seen as followed:

(1) Set reference sequence {Y₀(k)} and comparison sequences {Y_i(k)}.

(2) Average {Y_i(k)} and {Y₀(k)} according to Eq. (1), signed as average sequences {X_i(k)}. Actually, {X_i(k)} can be seen as a mapping to {Y_i(k)}.

(3) Sequences formed by absolute differences between {X₀(k)} and {X_i(k)} are signed as {Δ_i(k)}, Δ_i(k)=|X₀(k)-X_i(k)|. The correlation coefficient sequence {ξ_i(k)} can be calculated using Eq. (2), where Δmin indicates the minimum element of sequences {Δ_i(k)} and Δmax indicates the maximum element of sequences {Δ_i(k)}. The distinguishing coefficient ρ in the formula is generally set as 0.5, and thus, ρ was assigned a value of 0.5 in this paper.

(4) The Grey correlation degree γ_i is expressed as:

(5) Because the data were subjected to absolute value processing when calculating the sequences Δ_i(k), relational polarity of the Grey correlation degree is difficult to confirm. Thus, relational polarity is determined using Eqs. (4) and (5). When sgn(Q_i/Q_k) equals sgn(Q₀/Q_k), the relational polarity is positive. For the opposite, relational polarity is negative.

The correlation degree is used to characterize the relation between particle size and UCS when GRA is used to analysis this relation. The absolute correlation degree with larger value means that the relation between the particle size and UCS is more significant. And when the correlation degree is positive, it means that the corresponding particle size has positive effect on UCS. However, when the correlation degree is negative, it means that the effect is negative. From Table 8, when the particle size was larger than 200, it can be seen that correlation degree is negative, which indicates that the particle smaller than 200 goes against the formation of UCS. And it also can be seen that the absolute value of correlation degree increased with the decrease in particle size, it means that the inhibition effect of USC enhanced with decreased particle size. The details can be found in the revised paper, i.e., lines 201-207.

7. Line 138: What is p-l curve? Clarify.

The relationship between pressure (P, kPa) and penetration (l, mm) can be obtained by the CBR test. And the p-l curve refers to the curve containing the X axis corresponding to P and Y axis corresponding to l. The CBR value can be therefore calculated by the Equation 6. The details can be found in the lines 153-156.

     8.What is CPCM? And difference with Cement-stabilized soil, Explain deeply this point.

Many thanks for reviewer’s comments. CPCM refers to cement-PG cementitious material, and it is formed by PG, cement and water. The results of unconfined compressive strength test or CBR test of CPCM can directly reflect the mechanical properties of cement and PG. It is favorable to understand the basic mechanical properties of PG with different pH value or fineness. The comparison of CPCM and cement-PG-stabilized soil indicates that soil is added into the cement-PG-stabilized soil. Cement-PG-stabilized soil means that cement, PG, water and soil are mixed in a certain proportion. Both CPCM and cement-PG-stabilized soil are important type of mixture to study the mechanical properties of cement stabilized materials. The statements have been added into the revised paper, and the details can be found in lines 163-168.

9. Tables 6,7,8 are not understood the results in them, and specially in Table 6, how you have obtained the results and what information gives about your research.

Many thanks for reviewer’s comments. The values of X₁-X₈ in Table 6 are calculated by the average progress of {Yi(k)} according to Eq. (1). {Xi(k)} can be seen as a mapping to {Yi(k)}. After that, the correlation coefficient sequence {ξi(k)} can be calculated using Eq. (2) to reflect the relation between different sequences, as shown in Table 7. And then the grey correlation degree, which determines the degree of correlation, can be calculated by Eq. (3) and documented in Table 8. It is conducive to understand the analysis of the Grey Relational Analysis. The details can be found in lines 130-143.

10. How you determine pH and how you can modify.

We mixing PG and water in a 1:10 mass ratio, stirring uniformly, and then letting the mixture stand for 10 min before testing. PG pH refers to the pH value of the supernatant liquid of solution. To modify the pH value of PG, mixing PG and water in a test tube, and then adding solutions of calcium hydroxide (Ca(OH)₂) or sulfate (H₂SO₄) into the tube to adjust the pH value until the PG pH value reached expected value. The statements have been added into the revised paper, and the details can be found in lines 111-118.

11. You can add a resume Table in order to provide all the key information from the application conclusions in your research.

Many thanks for reviewer’s kind advice. All the key information from the application conclusions in this research has been provide in Appendix. The details can be found in lines 346-347.

12. In line 209: P2O5 , how do you know these impurities appears? and why did appears?

Many thanks for reviewer’s comments. Phosphogypsum (PG), an industrial byproduct of the phosphoric acid production, mainly comprises calcium sulfate dihydrate (CaSO4•2H2O), though it also contains impurities such as soluble phosphorus, eutectic phosphorus, insoluble phosphorus, fluoride, and organic compounds because of the imperfection of the technology. The details can be found in lines 44-50.

13. How do you change the fineness and pH in the samples?

We change the fineness by grinding the PG at different times. By controlling the grinding time at 0, 5, 10, 15, 20, 25 minutes, we can get six groups of different fineness PG. And we change the pH value of PG by using solutions of calcium hydroxide (Ca(OH)₂) or sulfate (H₂SO₄). After mixing water and PG in a test tube, using above solutions to adjust basicity or acidity until the pH value reached expected value. The statements have been added into the revised paper, and the details can be found in lines 97-104 and 111-118 and 172-174.

14. Finally according with the standards, what samples and with variable (pH,…) could be used and improved the actual construction materials? and specifically in which applications?

Many thanks for reviewer’s comments. According with the standards, PG can be defined as the I grade PG when the following four conditions are satisfied simultaneously: pH value of PG is larger than 5, fineness of PG is less than 20%, the CaSO₄·2H₂O content of PG is larger than 90% and adherent moisture content of PG is larger than 15%. The mechanical properties of cement-stabilized soil can be improved significantly when the I grade PG is used in the stabilization of subgrade soil. The details can be found in lines 303-307.

Author Response File: Author Response.docx

Reviewer 3 Report

This manuscript presents an interesting subjected on the effects of phosphogypsum (PG) pH and particle fineness on the mechanical properties of cement–PG-stabilized soil.

In general, the manuscript presents figures and tables which are supported the findings and conclusions of this study. The manuscript is written and organized well. However, the authors should improve their manuscript by following the below comments:

• Lines 15: The authors should define some chemicals when they are appeared for first time such as; Ca(OH)2 and H2SO4.
• Lines 31 and 35: In Introduction section, the authors missing some of important articles about lime and cement stabilizations. Below are some examples that could the authors used them:
• Mutter, G. M., Al-Madhhachi, A. T., and Rashed, R. R. (2017). Influence of soil stabilizing materials on lead polluted soils using Jet Erosion Tests. International Journal of Integrated Engineering, 9(1), 28-38.
• Al-Madhhachi, A.T., Mutter, G. M., and Hasan, M. B. (2019). Predicting Mechanistic Detachment Model due to Lead-Contaminated Soil Treated with Iraqi Stabilizers. KSCE Journal of Civil Engineering, 23(7): pp 2898–2907. DOI: 10.1007/s12205-019-2312-3.   
• Lines 64-69: The authors should explain the methods of testing soil stabilizations that treated with cement. The above mentioned references are obtained some new techniques. A separate paragraph should be provided by the authors to briefly provide the previous techniques of testing soil stabilizations that treated with cement.  
• Lines 92 and Table 3: The W_L, W_P, and I_P are not defined in the Table 3 or in text.  
• Lines 114-118: The parameters in Eqs. 1 through 5 should be defined. Also, the authors should provide the references for these equations.
• Line 146: It is preferred to separate the discussion section from the results section. The authors should discuss their results in details in separate section.

Author Response

Response to Reviewer

Ms. Ref. No.: coatings-960241

Title: Effects of pH and Fineness of phosphogypsum on Mechanical Performance of Cement-phosphogypsum-stabilized Soil and Classification for Road-used Phosphogypsum

Correspondence Author: Zhongchang Yang

Dear Prof. Yolanda Guo and Reviewer, 

We would like to take this opportunity to thank your acceptance and comments concerning our manuscript entitled “Effects of pH and Fineness of phosphogypsum on Mechanical Performance of Cement-phosphogypsum-stabilized Soil and Classification for Road-used Phosphogypsum (Ms. Ref. No.: coatings-960241)”. Meanwhile, these comments are all valuable and very helpful for refining our paper, as well as the important guiding significance to our researches. We have carefully revised our manuscript in light of your kind comments. Revised portions regarding your comments are marked in red in the revised paper. Once again, we earnestly appreciate for Prof. Yolanda Guo and reviewer for warm work, and hope that the revised version of our manuscript can meet with approval. If you have any question about this paper, please don’t hesitate to let us know. Enclosed please find our point-by-point responses to your comments as follow.

Thank you and best regards.

Yours Sincerely,

Zhongchang Yang* (E-mail:[email protected])

 ¨ Responses to the comments from Reviewer:

1. Lines 15: The authors should define some chemicals when they are appeared for first time such as; Ca(OH)2 and H2SO4.

We are very grateful for the reviewer’s kind advice. All the chemicals have been defined when they are appeared for the first time. Such as:  Using solutions of calcium hydroxide (Ca(OH)₂) and sulfate (H₂SO₄) to adjust pH value of PG from 2 to 8. The details can be found in the revised paper, i.e., lines 14-16.

2. Lines 31 and 35: In Introduction section, the authors missing some of important articles about lime and cement stabilizations. Below are some examples that could the authors used them:

Mutter, G. M., Al-Madhhachi, A. T., and Rashed, R. R. (2017). Influence of soil stabilizing materials on lead polluted soils using Jet Erosion Tests. International Journal of Integrated Engineering, 9(1), 28-38.

Al-Madhhachi, A.T., Mutter, G. M., and Hasan, M. B. (2019). Predicting Mechanistic Detachment Model due to Lead-Contaminated Soil Treated with Iraqi Stabilizers. KSCE Journal of Civil Engineering, 23(7): pp 2898–2907. DOI: 10.1007/s12205-019-2312-3.

We appreciate the reviewer’s kind advice very much. We have cited these important articles in introduction section. The details can be found in the revised paper, i.e., lines 34-35

3. Lines 64-69: The authors should explain the methods of testing soil stabilizations that treated with cement. The above mentioned references are obtained some new techniques. A separate paragraph should be provided by the authors to briefly provide the previous techniques of testing soil stabilizations that treated with cement.  

We appreciate the reviewer’s kind advice very much. The introduction has been revised as followed:

To ensure sufficient subgrade strength and bearing capacity of pavement, original subgrade soils with poor performance are sometimes subjected to certain technical treatments during road construction. Chemical stabilization is a very common disposal measure of technical treatments, it involves the modification of soil properties to improve engineering performance. Ghazi M found that cement can improve soil properties of Pb-contaminated soil and using JET device can consume testing time and conserving energy. Researchers also proposed formulas to mathematically predict the influence of different stabilizer on the mechanistic erodibility parameters[1,2]. The two most commonly used chemical stabilization methods are lime stabilization and cement stabilization.

The details can be found in lines 34-38.

4. Lines 92 and Table 3: The WL, WP, and IP are not defined in the Table 3 or in text.

WL, WP and IP have been defined in the Table 3. Furthermore, WL, WP and IP refer to liquid limit, plastic limit and plasticity index, respectively. The meaning of WL is as follow: liquid limit refers to the limit moisture content between the plastic state and the fluid state of the cohesive soil, i.e., the upper limit moisture content of the cohesive soil in the plastic state; the moisture content of the soil is too high and the soil can even flow like a liquid when the moisture content of the soil is larger than the liquid limit. The meaning of WP is as follow: plastic limit refers to the limit moisture content between the plastic state and the semi-solid state of the cohesive soil, i.e., the lower limit moisture content of the cohesive soil in the plastic state; the moisture content of the soil is greatly low, and the soil changes from the plastic state to the semi-solid state and loses its plasticity when the moisture content of the soil is less than the plastic limit. The meaning of IP is as follow: the plasticity index is an important index characterizing the mechanical and deformation properties of the soil; the value of plasticity index is equal to the difference between liquid limit and plastic limit, i.e., IP = WL-WP. WL, WP and IP are the significant parameters of soil properties. We have added these statements regarding WL, WP and IP into the revised paper and the details can be found lines 94-104.

5. Lines 114-118: The parameters in Eqs. 1 through 5 should be defined. Also, the authors should provide the references for these equations.

Many thanks for reviewer’s kind advice. All the parameters in Eqs.1 through 5 have been defined, and the related references for these equations have been cited in the revised paper. The details can be found in lines. Many thanks for reviewer’s comments. All the variables in equations have been defined in the revised paper in lines 127-143, which also can be seen as followed:

(1) Set reference sequence {Y₀(k)} and comparison sequences {Y_i(k)}.

(2) Average {Y_i(k)} and {Y₀(k)} according to Eq. (1), signed as average sequences {X_i(k)}. Actually, {X_i(k)} can be seen as a mapping to {Y_i(k)}.

(3) Sequences formed by absolute differences between {X₀(k)} and {X_i(k)} are signed as {Δ_i(k)}, Δ_i(k)=|X₀(k)-X_i(k)|. The correlation coefficient sequence {ξ_i(k)} can be calculated using Eq. (2), where Δmin indicates the minimum element of sequences {Δ_i(k)} and Δmax indicates the maximum element of sequences {Δ_i(k)}. The distinguishing coefficient ρ in the formula is generally set as 0.5, and thus, ρ was assigned a value of 0.5 in this paper.

(4) The Grey correlation degree γ_i is expressed as:

(5) Because the data were subjected to absolute value processing when calculating the sequences Δ_i(k), relational polarity of the Grey correlation degree is difficult to confirm. Thus, relational polarity is determined using Eqs. (4) and (5). When sgn(Q_i/Q_k) equals sgn(Q₀/Q_k), the relational polarity is positive. For the opposite, relational polarity is negative.

6. Line 146: It is preferred to separate the discussion section from the results section. The authors should discuss their results in details in separate section

Many thanks for reviewer’s kind advice. The above comment is extremely valuable to this article. Authors tried to discuss the results in separate section, but it seems that discussing the results in one section is more helpful to readers to understand this article. Because there are more than one test results in a results section. Taking the UCS test as example, the results of UCS contain both the effect of pH and fineness of PG on the specimen at the same time. It is helpful to understand the effect of PG of on the specimen if the discussion of PG pH follows the results of it directly. However, the relationship between results and discussion might be difficult to correspond if they are separated into two sections. Considering the , all the discussion sections are in a separate paragraph in this article. The details can be found in lines 198-199, 250-251 and 277-278.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The article has improved substantially, the authors have resolved
many of the doubts and comments raised by the reviewer,
however some point on what is in doubt has yet to be resolved
or some point needs to be corrected.
It is needed to add that article is interesting for the audience because
stablish the possibility to use a byproduct as a construction material.

Author Response

Response to Reviewer

Ms. Ref. No.: coatings-960241

Title: Effects of pH and Fineness of phosphogypsum on Mechanical Performance of Cement-phosphogypsum-stabilized Soil and Classification for Road-used Phosphogypsum

Correspondence Author: Zhongchang Yang

Dear Prof. Yolanda Guo and Reviewer, 

We would like to take this opportunity to thank your acceptance and comments concerning our manuscript entitled “Effects of pH and Fineness of phosphogypsum on Mechanical Performance of Cement-phosphogypsum-stabilized Soil and Classification for Road-used Phosphogypsum (Ms. Ref. No.: coatings-960241)”. Meanwhile, these comments are all valuable and very helpful for refining our paper, as well as the important guiding significance to our researches. We have carefully revised our manuscript in light of your kind comments. Revised portions regarding your comments are marked in red in the revised paper. Once again, we earnestly appreciate for Prof. Yolanda Guo and reviewer for warm work, and hope that the revised version of our manuscript can meet with approval. If you have any question about this paper, please don’t hesitate to let us know. Enclosed please find our point-by-point responses to your comments as follow.

Thank you and best regards.

Yours Sincerely,

Zhongchang Yang* (E-mail:[email protected])

¨ Responses to the comments from Reviewer:

1. The article has improved substantially, the authors have resolved many of the doubts and comments raised by the reviewer, however some point on what is in doubt has yet to be resolved or some point needs to be corrected.

It is needed to add that article is interesting for the audience because stablish the possibility to use a byproduct as a construction material.

Many thanks for reviewer’s comments. The possibility to use a by-product as a construction material has been provided in the introduction of revised article. The details can be seen in lines 56-73 and 83-88 or as follows:

This indicates that PG can used in building materials, but if PG can also be widely used in road construction engineering, the problems of stacking PG and contamination of cement and lime can be simultaneously solved.

The utilization of PG in highway engineering has been extensively studied. When mixed with cement and class-C fly ash, PG can stabilize expansive or non-expansive soils. Using PG for construction, rather than disposing it, is favorable for both economic and environmental reasons when considering the high cost of cement [17]. Strydom [18] demonstrated that PG can successfully replace natural gypsum as a retardant for both ordinary Portland cement and fly ash Portland cement; however, minor impurities in PG affect early strength of cement. Kumar [19] found that a mixture of lime, fly ash, and PG can be applied to the road based on unconfined compressive strength and unconsolidated undrained triaxial tests. It has been confirmed that self-leveling underlayments can be produced using heated PG as the main binder, but the handling time is short, requiring the use of retarders [20]. Additionally, a lime, fly ash, and PG mixture can be used to improve behavior of problematic soils based on an index experiment of unconfined compressive strength, indirect tensile strength, and California bearing rate [21]. Another study confirmed that steel slag–fly ash–PG solidified material can be used for a roadbed [22]. The use of cement-stabilized PG has been recently studied, and it has been found that PG can be used in soil stabilization when stabilized with class-C fly ash and cement [23,24].

This study confirms that PG which is an industrial waste of the phosphoric acid production can be used in subgrade to stabilize soil with cement based on the mechanical analysis. Thus, the environmental problem caused by PG can be resolved, and the resources can be recycled to improve the properties of subgrade soil. And the research is also helpful to establish or supplement a standard for PG used in road, considering that this standard is barely given in the current specification.

Author Response File: Author Response.docx

Reviewer 3 Report

The authors addressed well all comments by the reviewers. I recommended publishing this article. 

Author Response

Response to Reviewer

Ms. Ref. No.: coatings-960241

Title: Effects of pH and Fineness of phosphogypsum on Mechanical Performance of Cement-phosphogypsum-stabilized Soil and Classification for Road-used Phosphogypsum

Correspondence Author: Zhongchang Yang

Dear Prof. Yolanda Guo and Reviewer, 

We would like to take this opportunity to thank your acceptance and comments concerning our manuscript entitled “Effects of pH and Fineness of phosphogypsum on Mechanical Performance of Cement-phosphogypsum-stabilized Soil and Classification for Road-used Phosphogypsum (Ms. Ref. No.: coatings-960241)”. Meanwhile, these comments are all valuable and very helpful for refining our paper, as well as the important guiding significance to our researches. We have carefully revised our manuscript in light of your kind comments. Revised portions regarding your comments are marked in red in the revised paper. Once again, we earnestly appreciate for Prof. Yolanda Guo and reviewer for warm work, and hope that the revised version of our manuscript can meet with approval. If you have any question about this paper, please don’t hesitate to let us know. Enclosed please find our point-by-point responses to your comments as follow.

Thank you and best regards.

Yours Sincerely,

Zhongchang Yang* (E-mail:[email protected])

 ¨ Responses to the comments from Reviewer:

1. The authors addressed well all comments by the reviewers. I recommended publishing this article.

We are very grateful for the reviewer’s kind comments.

Author Response File: Author Response.docx