Stabilization of Soft Soil by a Sustainable Binder Comprises Ground Granulated Blast Slag (GGBS) and Cement Kiln Dust (CKD)

Response to Editor’s and other general comments

General comment:

[Recycling] Manuscript ID: recycling-2048250 - Major Revisions

Please revise the manuscript according to the referees' comments and upload the revised file within 10 days.

The authors wish to commend the reviewers’ diligent work on the manuscript. Moreover, we reiterated our willingness to revise the manuscript by affecting all the editor and reviewers’ observations and corrections and resubmitting within the stipulated time frame. We are glad that our manuscript is found worthy of publication.

Respond to comments (reviewer #1)

Comments/Remarks

Response

General:

The overarching aim of this manuscript is to investigate the improvements in the physical and mechanical properties of soft soil after stabilization with both ground granulated blast slag (GGBS) and cement kiln dust (CKD).

We appreciate the precious time spared to critique our manuscript and the opportunity to improve its quality.

The sentence on Line 64 should be rewritten as Cement and lime are the most common binders used in chemical soil stabilization.

Thank you for your comment.

The amendments have been done according to the reviewer comments.

In Lines 64 – 72, the authors are recommended to extend their literature review on the gains instrength and physical properties of soil after being stabilized with cement. This is important to benchmark the gains in strength and physical properties of soil after stabilization with GGBS and CKD to those after stabilization with cement

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The amendments have been done according to the reviewer comments.

This sentence has been included in the revised manuscript:

“There are two main stages in the hydration of cement-treated soil. It could take a few minutes to many hours for the initial stage of cement hydration. This stage is connected to the complex chemical system of cement's dissolution and precipitation, which leads to the development of various hydrate compounds (calcium silicate hydrate gel (C-S-H) and calcium hydroxide (hydrated lime Ca(OH)2) which is called Portlandite) [8-11]. This stage is accountable for the early strength of stabilized soil development and helps to improve the plasticity index and workability. The silica and alumina of the clay minerals in the treated soil or from other cement minerals react with the excess hydrated lime (Portlandite) from the first phase of cement hydration to form the second phase of the cement treated soil hydration, which is known as the pozzolanic reaction. This reaction only takes place in the presence of water. The pH of the surrounding environment, the availability of silicate and aluminate compounds, and time are all factors that affect the pozzolanic process. Additional C-S-H or calcium aluminate hydrated (C-A-H) compounds are created as a result of this reaction [9,12].

The following notable references present the improvements in soil's physical and mechanical properties after cement stabilization. The authors can also use these references to justify their choice of UCS for evaluating the strength of stabilized soil.

https://doi.org/10.1016/j.trgeo.2022.100864

https://doi.org/10.1061/(ASCE)MT.1943-5533.0004250

Thank you for your comment.

The authors are grateful for such valuable references.

The amendments have been done according to the reviewer comments.

Section 2.2, Lines 160 – 161, the authors mentioned that GGBS was mixed with the soft soil in 0%, 3%, 6%, 9%, and 12% (by dry weight of the soil). What is the rationale behind these specific proportions?

 Thank you for your comment.

The first stage of the experiments comprised the optimization of the binder content using the GGBS alone as a binder. This stage was

dependant on the results of the UCS tests which were conducted on specimens of soil treated with different percentages of GGBS (0, 3,

6, 9, and 12 by the dry mass).

This was based on the work of Jafer et al (2018)

https://doi.org/10.1016/j.jclepro.2017.10.233

In addition, these percentages were chosen because they cover almost the whole range of dosage of conventional soil stabilizing agents

Lines 162 – 163, please correct the sentence in these two lines as Secondly, the optimum GGBS was used in a binary blendedsystem with CKD by (0, 25, 50, 75, and 100) % (by dry weight ofGGBS) (see Table 5).

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The amendments have been done according to the reviewer comments.

Lines 164 – 166, the authors limited their experimental protocol to Atterberg limits, compaction and UCS testing. What is the rationale behind these specific tests? And why didn’t they include more advanced performance testing, such as the Cyclic Triaxial Test,which is more suitable for studying soil shear resistance undercyclic traffic loads?

Thank you for your comment.

Indeed numerous exploratory tests for evaluating performance are available. These include but are not limited to Atterberg limits, compaction and UCS testing. However, the study was constrained to the limited available equipment in the School of Civil Engineering and Built Environment, Liverpool John Moores University, UK. Nonetheless, this study’s exploration tests align with the typical tests on soil stabilization.

We are optimistic that these laboratory tests suffice in judging the performance of soil stabilization.

Lines 167 – 168, the authors stated that the curing adopted forUCS and SEM was for 7 and 28 days. The authors are recommended to provide more details on the curing condition, whether it was dry, wet or a combination of the two. They should also provide details on other curing parameters, such as temperature, humidity…etc.

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This sentence has been included in the revised manuscript:

“The UCS and SEM test specimens were taken out of the mould, weighed, covered in cling film, labeled, put in tightly sealed plastic bags, and kept at room temperature (20 ± 2 ^οC) for curing.”

Table 5, the name of the fourth field should change to 25%GGBS+75%CKD. Soil designation in this field should change to 25G-75C.

Thank you for your comment.

We apologize for the silly mistake. It is

appropriately corrected now.

Lines 219 - 220, the authors should correct the sentence on these lines as The pattern is the opposite after 9 percent, with the MDD falling and the OMC rising.

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The amendments have been done according to the reviewer comments.

Lines 278 – 279, the authors should correct the sentence on these lines as Nevertheless, the trend became the opposite as GGBSwas replaced by CKD since both the plastic limit and liquid limit increased while the plastic index decreased.

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The amendments have been done according to the reviewer comments.

Lines 321 – 323, the authors should correct the sentence on these lines as: The increase in the MDD in the 6G sample can be attributed to the coarse particles of GGBS, while the decrease inthe OMC was due to a decrease in the fine fractions of the soilupon the substitution of GGBS [40].

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The amendments have been done according to the reviewer comments.

Line 335, replace a increase with an increase.

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The amendments have been done according to the reviewer comments.

Lines 353, 358 and 359, the authors mentioned earlier that the binary blending of 25% CKD and 75% GGBS (75G-25C) increased the UCS at 7 days by 2.5 times and 3.2 times at 28 days. Then, later on, they wrote after 7 days and 28 days, the UCS of the 25G-75C was 3.3 times and 5.5 times greater than U, respectively. Which rises in UCS are the right ones, the former or the latter ones?

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The amendments have been done according to the reviewer comments.

Section 3.2.3, the authors should discuss the reasons for the reduction in UCS upon the transition from 25G-75C to 6C.

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The amendments have been done according to the reviewer comment.

This sentence has been included in the revised manuscript:

“The slower rate of strength development of the CKD in comparison to the (25G-75C) binder especially after 28 days may be due to the presence of more Ca(OH)₂ than was required for the pozzolanic reaction. The unreacted Ca(OH)₂ that is still present weakens the matrix [35].”

Section 3.2.4, the authors should compare Figure 8d to Figure 8f and Figure 8e to Figure 8g to justify the drop in UCS upon the transition from 25G-75C to 6C.

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The amendments have been done according to the reviewer comment.

This sentence has been included in the revised manuscript:

Although the application of CKD had an impact on improving soil strength, in the 25G-75G stabilized soil, the clay became denser and stiffer due to the intercrossing of ettringite crystals with CSH and clay clusters as well as the CSH fabric filling in the pore space between clay particles. It was reported that the stabilized clay's strength might rise as a result of the CKD and its hydration products [65]. However, the combination of CKD and other pozzolanic materials like slag and fly ash may be more advantageous because of their mechanical properties [69-71].

Response to Editor’s and other general comments

General comment:

[Recycling] Manuscript ID: recycling-2048250 - Major Revisions

Please revise the manuscript according to the referees' comments and upload the revised file within 10 days.

The authors wish to commend the reviewers’ diligent work on the manuscript. Moreover, we reiterated our willingness to revise the manuscript by affecting all the editor and reviewers’ observations and corrections and resubmitting within the stipulated time frame. We are glad that our manuscript is found worthy of publication.

Respond to comments (reviewer #2)

The present work investigated the engineering properties ofmixtures between a soft soil and different contents of ground granulated blast slag (GGBS) and cement kiln dust (CKD). The literature review is limited. Many experimental methods were not provided. Microstructural analyses of the mixtures was very poor because only scanning electron microscopy (SEM) was used. Moreover, many technical mistakes were identified in the SEM analyses.

The following problems were identified in this work:

We appreciate the applause from Reviewer #2 for recognizing our study’s importance. Moreover, the concerns raised by Reviewer #1 are addressed, and the opportunity accorded to us to improve our manuscript through the invaluable comments is appreciated. Thank you for your valuable time and advice.

Title: the title of the manuscript could clarify that groundgranulated blast slag (GGBS) and cement kiln dust (CKD) were used as sustainable binders.

Thank you for your priceless comment.

We appreciate the critique towards the improvement of our manuscript.

The amendments have been done according to the reviewer comment.

Section 1: the content of lines 73-78 should be supported with citation of relevant literature

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The amendments have been done according to the reviewer comments.

Section 1: although the authors stated that cement, line, GGBS,CCR and CKD improved the engineering properties of soils in previous works, they did not provide any example of quantitative improvements. Section 1 should be complemented with percentage changes in different soil properties (e.g.,strength, permeability, compressibility, etc) provided by the stabilization with the stabilizer agents mentioned in this section.

The highest improvements and optimal dosages of GGBS and CKD could be also stated, as these sustainable binders were used in the present study.

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The amendments have been done according to the reviewer comments.

Section 1: in line 98, the authors should indicate if the contents of stabilizing agents (2% cement and 30% cement kiln dust) were provided in terms of mass (or volume) of dry soil (or total composite).

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The amendments have been done according to the reviewer comment.

This sentence has been included in the revised manuscript:

“by the dry weight of such soil”

Section 2: The abbreviation “NWC” used in the second column of Table 1 should be replaced by “NMC”, as indicated in the note of this table.

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The amendments have been done according to the reviewer comment.

Section 2: The meaning of many abbreviations used in Table 1 were not provided in the note of the table (e.g., “γd max”, “PI”,“UCS”, “OMC”).

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The amendments have been done according to the reviewer comment.

Section 2: More than one specimen (various replicates) were probably used to determine the average values of the parameters presented in Table 1. Then, the standard deviation (or coefficient of variation) associated with each average value should be also indicated in Table 1, in order to clarify the natural variability of the experimental data.

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The amendments have been done according to the reviewer comment.

Generally, five specimens were prepared and tested to represent each single test result with a standard deviation as shown in Table 1.

Section 2: Test methods and equipment used to determine the chemical composition of GGBS and CKD (Tables 2 and 3) should be provided. Did you use X-ray fluorescence analyses?

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The amendments have been done according to the reviewer comment.

This sentence has been included in the revised manuscript:

“Shimadzu's EDX-720 Energy Dispersive X-Ray Fluorescence analyzer was used to conduct the X-Ray fluorescence spectrometry (XRF) analysis to determine the oxide contents.”

Section 2: Table 3 should indicate if the numbers presented in this table are percentage values

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The amendments have been done according to the reviewer comment.

Section 2: The authors should clarify the reasons for choosing only some specific samples for SEM analyses

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By comparing SEM images of unstabilized and stabilized samples, the changes made in the structure of the samples can be associated with the production of cementitious products and the creation of bonds between particles

The SEM of the untreated soil (U), unary 6% GGBS soil (6G), soil with 6% binder (25% GGBS and 75% CKD) (25G-75C), and soil with unary 6% CKD binder (6C) was carried out in the study at curing of 7 and 28 days. This is to make a comparison between the reference samples and the improved sample (based on USC test).

Section 2: The fourth column of Table 5 presents incorrect information. In this column, the terms “75%GGBS+75%CKD”should be replaced by “25%GGBS+75%CKD”. In addition, the designation "75G-25C” should be replaced by “25G-75C”.

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The amendments have been done according to the reviewer comment.

Section 2: Caption of Table 5 should specify if the percentage values were provided in terms of mass or volume of stabilizing agents

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Percentage values were provided in terms of mass of stabilizing agents

Section 2: Number of replicates used in experimental tests described in Sections 2.2.1, 2.2.2 and 2.2.3 could be reported.

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Percentage values were provided in terms of the mass of stabilizing agents.

For each dose of additives, three specimens were prepared.

Section 2: The text of lines 200-205 is technically confusing.UCS tests provide compressive strength, rather than shear strength. UCS tests are uniaxial tests, rather than triaxial tests

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The amendments have been done according to the reviewer comment.

The sentence has been amended as:

“A computerized and motorized triaxial machine was used for this test, although there was no lateral load applied in the triaxial cell.”

Section 2: Sample preparation methods for SEM analyses were not explained. Where did the samples come from? Are they intern fragments of a specimen after failure? The surface of the specimen? Some undamaged sample casted specifically for microstructural evaluation? How was the preparation of the surface of the samples? Have you used a sputter coater tocover the surface of samples with gold? Did you polish the surface of the samples?

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The amendments have been done according to the reviewer comment.

The following sentence has been added:

“Before performing the SEM imaging, the samples of the hydrated pastes were allowed to cure for 7 and 28 days. These studies were performed on soil-treated samples as well as pastes made from the optimum binder mixture. The specimens were coated to increase visibility before the SEM imaging with a thin layer of Palladium using a sputter coater.”

Section 3: Caption of Figure 2 is incorrect. OMC should be replaced by MDD and vice versa

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The amendments have been done according to the reviewer comment.

Section 3: Error bars that represent values of standard deviation should be added to all graphs (e.g., Figure 3, 4, 6, 7),in order to represent the natural variability of the experimental data.

Thank you for your comment.

The amendments have been done according to the reviewer comment.

Error bars have been added to all graphs (e.g., Figures ( 3, 4, 6, 7).

Section 3: The authors did not discuss their results based on some different mechanisms that also ensure the improvements in mechanical properties of stabilized soils, according to previous research (e.g.,

Montenegro et al. - DOI:10.1061/(ASCE)MT.1943-5533.0000642;

Lopes et al. DOI:10.1080/10298436.2021.1990289;

Cikmit et al. - DOI:10.1016/j.sandf.2019.06.013;

Manso et al. DOI:10.1016/j.conbuildmat.2012.09.079).

For example: pozzolanicactivity, filler effects, changes in diffused double layers of clayey particles, anchoring between aggregate particles, etc.

Thank you for your comment.

The amendments have been done according to the reviewer comment.

The research has been included in the revised version.

Section 3: the authors discussed porosity in Section 3.2.4 based on images of soil fragments without using quantitative techniques for evaluation of SEM analyses, which is technically incorrect. The microstructure of the materials investigated in the present work is very heterogeneous. Without systematic quantitative techniques, the authors could find locally spots that could approve or reject any hypothesis. Therefore, most of the statements of Section 3.2.4 are not technically reliable, such as"discontinuous structure with well-observed voids", "occurrence of agglomeration in association with compactness", "Despite the decrease in the size of the pores, some pores are still available"“highly compacted and ense structure with very low  available, highly compacted and dense structure with very lowpores”, “the compactness of the soil structure increasedsignificantly with relatively few pores”, “becomes highly denseand very compacted with relatively no voids”, etc.

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The amendments have been done according to the reviewer comment.

The SEM section has been improved based on the reviewer comment.

Section 3: the authors were not able to identify in Figure 8 the cementation compounds mentioned in the text of Section 3.2.4, such as the flocculated or fibrous structures of C-S-H, plate-like crystals of portlandite or needle-like crystals of ettringite

Thank you for your comment.

The amendments have been done according to the reviewer comment.

Figure 8 has been updated according to the reviewer comment.

Section 3: the engineering properties of the stabilized soils were not supported by detailed microstructural analyses. Proofs of development of cementitious or pozzolanic reactions and porosity assessment should be provided with results of different microscale evaluations of the different mixtures, such as X-ray diffraction (XRD), thermogravimetric analysis (TGA), Raman spectroscopy, mercury intrusion porosimetry (MIP), Fouriertrans form infrared spectroscopy (FTIR), and other traditional techniques

Thank you for your comment.

The study was constrained to the limited available equipment in the School of Civil Engineering and Built Environment, Liverpool John Moores University, UK.

This sentence has been included in the revised manuscript for the recommended further work.

“In addition, further research is needed, especially to increase the knowledge of treated soil mixture behavior based on X-ray diffraction (XRD), thermogravimetric analysis (TGA), Raman spectroscopy, mercury intrusion porosimetry (MIP), and Fouriertrans form infrared spectroscopy (FTIR).”

Furthermore, the same technique used in this study has been used previously by using SEM to support the engineering properties of the stabilized soils. Please see:

https://doi.org/10.1016/j.jclepro.2017.10.233

https://doi.org/10.1007/s10064-022-02816-7

http://dx.doi.org/10.1016/j.clay.2017.02.028

Section 4: A brief summary of the aims of the present work could be provided at the beginning of the conclusion section

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The amendments have been done according to the reviewer comment.

Section 4: based on the previous comments, all conclusions should be corrected (especially conclusion #4).

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The amendments have been done according to the reviewer comment.

Section 4: limitations of the present work and recommendations for future studies were not provided at the end of the manuscript

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The amendments have been done according to the reviewer comment.

Limitations and recommendations are as follow:

“The results of this research are limited to the particular stabilized soil type, the particular geotechnical qualities that were examined and the particular waste materials employed to create the cementitious binder. In addition, the findings of the liquid limit and plastic limit tests in this research should also be viewed as a restriction because the ability to conduct these tests depends largely on the skills and experience of the person performing these tests.

Since not all of the stabilized soil's geotechnical characteristics have been discussed in this research. It is therefore advised to investigate how the produced binder affects the other geotechnical characteristics of the stabilized soil, such as the hydraulic conductivity, California bearing ratio (CBR), and resilient modulus of elasticity.”

There are some English mistakes in the text such as “Cement and lime represent are the most”; “to flow beneath its eight is”;“and changes to the microstructure”. In addition, many typo issues were identified in this manuscript. For example, some“PH” terms should be replaced by “pH"; “gm/cm^3” should be replaced by “g/cm³”.

Thank you for your comment.

The amendments have been done according to the reviewer comment.

Response to Editor’s and other general comments

General comment:

[Recycling] Manuscript ID: recycling-2048250 - Major Revisions

Please revise the manuscript according to the referees' comments.

The authors wish to commend the reviewers’ diligent work on the manuscript. Moreover, we reiterated our willingness to revise the manuscript by affecting all the editor and reviewers’ observations and corrections and resubmitting within the stipulated time frame. We are glad that our manuscript is found worthy of publication.

Respond to comments (reviewer #2)

Comments/Remarks

Response

General:

The authors successfully corrected various problems in the first version of the paper. However, the following problems need to be solved before recommendation for publication:

We appreciate the precious time spared to critique our manuscript and the opportunity to improve its quality.

1.         In response to comment #3 of the first review round, the authors did not indicate if the contents of admixtures (e.g., 60% CCR, 40% RHA, 100% CCR, 2% cement, 5% slag, 1% sodium silicate) were provided in terms of mass (or volume) of dry soil (or total composite).

Thank you for your comment.

The amendments have been done according to the reviewer comments.

2.         Response to comment #6 of this reviewer is incomplete because the meaning of some abbreviations used in Table 1 were not provided in the note of the table (e.g., “UCS”, “OMC”). In addition, this table did not indicate if the clay content was provided as a percentage (%) value, as indicated in the case of Sand % and Silt %.

Thank you for your comment.

The amendments have been done according to the reviewer comments.

The reason that the authors have not included them previously because the meaning of these abbreviations were available in the introduction section. However, they are now provided in the note of the table as per the reviewer comment.

3.         Response to comment #7 of this reviewer can be improved by adding to Table 1 the number of specimens (replicates) tested to determine each different parameter of this table.

Thank you for your comment.

The amendments have been done according to the reviewer comments.

4.         Response to comment #15 is confusing. Section 2.2.4 should provide details about the difference between the composition of the “hydrated pastes” and the “soil-treated samples” subjected to SEM analyses.

 Thank you for your comment.

The amendments have been done according to the reviewer comments.

We apologize for the mistake. It is

appropriately corrected now. The SEM investigations have been done only on soil-treated samples.

5.         Incorrect abbreviation was used in Figure 2. The vertical axis of the first graph of Figure 2 should be “OMC (%)” rather than “OMM (%)”. In addition, this figure did not indicate which graph is (a) and which graph is (b).

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The amendments have been done according to the reviewer comments.

6.         If Figure 4 shows the values of Atterberg limits, it seems that the vertical axis “Moisture content (%)” does not make sense.

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The amendments have been done according to the reviewer comments.

7.         The identification of some hydrates (CH, C-S-H, AFt) in the SEM images is not appropriate. Arrows should be added to all figures, according to all citations of the text of Section 3.2.4. In addition, did you use SEM/EDS to support the identification of these hydrates, based on their chemical composition? The authors did not cite and compare the size of the compounds indicated in the figures with those typically observed in CH, C-S-H, AFt, etc. The book “Concrete: Microstructure, Properties, and Materials” of Mehta and Monteiro describes the size and shape of cement hydrates, which can help the authors to solve the problems.

Thank you for your comment.

The amendments have been done according to the reviewer comments.

The authors have divided Figure 8 into two Figures (8 and 9) and they introduced new SEM images for the binary binder (25%GGBS, 75%CKD) (25G-75C) at 7 days and 28 days.

The authors follow the procedures of below articles in the SEM observation:

http://dx.doi.org/10.1016/j.conbuildmat.2014.08.011

https://doi.org/10.1016/j.conbuildmat.2020.118126

http://dx.doi.org/10.1016/j.sandf.2016.02.004

http://dx.doi.org/10.28991/cej-2020-03091533

https://doi.org/10.1016/j.jclepro.2017.10.233

https://doi.org/10.1007/s10064-022-02816-7

The authors are grateful to the reviewer for guiding them to such a valuable book (Concrete: Microstructure, Properties, and Materials) which has been cited in the manuscript.

8.         Response to comment #20 is not convincing. Quality of the SEM images is very poor. It is hard to see the flocculated structures typically observed in C-S-H and needle-like crystals typical of ettringite (AFt) in the yellow arrows of Figure 8. The authors need to improve the quality of these images. After that, it will be possible to identify C-S-H, CH, AFt, etc.

Thank you for your comment.

The amendments have been done according to the reviewer comments.

The authors introduced new SEM images for the binary binder (25%GGBS, 75%CKD) (25G-75C) at 7 days and 28 days.

9.         In Section 4, the terms “Fouriertrans form infrared spectroscopy” should be replaced by “Fourier-transform infrared spectroscopy”.

Thank you for your comment.

The amendments have been done according to the reviewer comments.

10.     English writing needs to be improved. The revised version of the paper still presents many grammar and punctuation mistakes such as: “a Sustainable Binder Comprises Ground Granulated”, “This study amis at the”, “A modification (…) have been achieved”, “elasticity.” In addition,”, “MDD (gm/cm^3)”, etc.

Thank you for your comment.

The amendments have been done according to the reviewer comments.