Effect of Alkali Concentration on the Activation of Carbonate-High Illite Clay

Round 1

Reviewer 1 Report

Overall I would recommend publication of this research with some revision. See my comments below:

1. Terminology: the authors should introduce full name when the acronym is first presented e.g. C-A-S-H gel & N-A-S-H gel. 
2. Abstract: Before reading the full paper, abstract is difficult to understand. For instance instead of stating 2d and 28d samples, the authors should give more description, such as samples stored for 2 days and 28 days. In this sense, I suggest the authors rewrite the abstract to help the readers understand it better
3. Sample names: I notice the authors did not use the same sample name throughout the manuscript. Most of the times they refer samples as 2d and 28d, often they refer as 2 days and 28 days samples as seen in Figure 1. Try to be consistent over sample naming
4. XRD (Figure 3): I do not see amorphous region at 20 and 40 2 theta. How do the authors define amorphous region? I believe it could be from background scattering.
5. EDX (Figure 7): EDX is not the most accurate method to identify chemical composition. I would suggest the authors to compare results with ICP-OES or other elemental analysis to confirm results shown in Figure 7. 

Author Response

The authors wish to thank the reviewers for their comments and suggestions to which we respond below. The authors believe that such comments have helped to improve the quality of the final paper. All recommendations have been taking into account and a reviewed Manuscript has been sent again. We trust that changes completed address the Reviewer requirements.

Reviewer 1

Overall I would recommend publication of this research with some revision. See my comments below:

1. Terminology: the authors should introduce full name when the acronym is first presented e.g. C-A-S-H gel & N-A-S-H gel. 

Ok, included

1. Abstract: Before reading the full paper, abstract is difficult to understand. For instance instead of stating 2d and 28d samples, the authors should give more description, such as samples stored for 2 days and 28 days. In this sense, I suggest the authors rewrite the abstract to help the readers understand it better

All right. A new abstract has been written

1. Sample names: I notice the authors did not use the same sample name throughout the manuscript. Most of the times they refer samples as 2d and 28d, often they refer as 2 days and 28 days samples as seen in Figure 1. Try to be consistent over sample naming

All right. Sample names are now homogeneus

1. XRD (Figure 3): I do not see amorphous region at 20 and 40 2 theta. How do the authors define amorphous region? I believe it could be from background scattering.

Actually, we mean that XRD patterns show a hump (quite evident) in the region 20 – 40 2theta. This hump is attribute to some amorphous fraction of the material.

1. EDX (Figure 7): EDX is not the most accurate method to identify chemical composition. I would suggest the authors to compare results with ICP-OES or other elemental analysis to confirm results shown in Figure 7. 

The authors agree with the reviewer that the SEM analyzes are not completely accurate when determining the quantitative chemical composition.
In this work as in many others published by these authors and by many other authors, the results of SEM / EDX are used only qualitatively in order to observe behaviors in the composition of the gels formed in the cementitious materials.
The authors use a set of analytical tools to confirm each and every one of the conclusions drawn in the paper; that is, we only interpret results when they are supported by more than one analytical technique.

Reviewer 2 Report

Figure 1. Why there is a vertical line in the figure at particle size equal to about 30 microns?

Figure 2. Caption or in the text discussing the results: please indicate the number of samples used to determine the standard deviations.

L118-120: Please specify if the water-to-binder ratio, age and curing conditions in the literature mentioned (refs 25, 26 and 19) are the same or not. Also, sample geometry and size may conduct to variability in strength measurements.

L144. Please add a “.” Before 5H20  for gaylussite.

L165. Ref 40 is not a hyperlink

L175. Is there any evidence from the literature of a dissolution of Si4+?

Figure 5. the x-axis cannot be read in the EDX spectra.

Line 202 What was the criterion to evaluate a “more compact” matrix? Visual assessment of the micrographs only?

The paragraph starting at line 266: I believe that other factors could also explain the differences in the strength than only a larger DOR. For instance: differences in the total porosity per se (not necessarily always associated with a higher DOR), presence of finer porosity (for heterogeneous materials with the same porosity, larger porosity = more larger defects = lower strength), strength of gels (the composition of the gel is known to affect its mechanical strength e.g ref below; the morphology could also play a role). The authors should comment on each of these factors and discuss they are not relevant to explain the differences observed in the strength

Bauchy M, Laubie H, Abdolhosseini Qomi MJ, et al (2015) Fracture toughness of calcium–silicate–hydrate from molecular dynamics simulations. Journal of Non-Crystalline Solids 419:58–64.

References: please remove the jumps in the lines 306, 310, 324, 327 etc…

Author Response

The authors wish to thank the reviewers for their comments and suggestions to which we respond below. The authors believe that such comments have helped to improve the quality of the final paper. All recommendations have been taking into account and a reviewed Manuscript has been sent again. We trust that changes completed address the Reviewer requirements.

Comments and Suggestions for Authors

Figure 1. Why there is a vertical line in the figure at particle size equal to about 30 microns?

It is a mistake; the line has been removed

Figure 2. Caption or in the text discussing the results: please indicate the number of samples used to determine the standard deviations.

Included  (Six specimens per test age and material were tested)

L118-120: Please specify if the water-to-binder ratio, age and curing conditions in the literature mentioned (refs 25, 26 and 19) are the same or not. Also, sample geometry and size may conduct to variability in strength measurements.

The compressive strength values recorded here were higher than reported by other authors, who worked with thermally treated alkali-activated illite/smectite clay with CaO contents of <5 %. Buchwald et al. [25] found compressive strength values of around 13 MPa with 6 M NaOH, (solution/solid ratio= 0.41, curing 20 hours at 20 °C in sealed moulds avoiding drying out, after demoulding; 7 days at 60 °C in 100% relative humidity (RH), 3 hours at 80 °C in 100% RH and drying over 24 hours at 40 °C). Essaidi et al. [26], using a potassium silicate solution, observed strength of 25 MPa (initial curing in an opened polystyrene sealed mold, 48 hours at 70°C, subsquently, the mold was closed into oven at 70°C for 2 hours; after demoulding ambient air (25°C, 40 % RH) during 21 days). Seiffarth et al. [19] obtained values of <10 MPa with sodium silicate molar ratio of SiO₂/Na₂O=0.31 (initial curing in wet conditions, 7 days, 25 °C and  85% RH, followed by curing in dry conditions: 3 days, 40 °C, 55% RH).

L144. Please add a “.” Before 5H20  for gaylussite.

 All right

L165. Ref 40 is not a hyperlink...... all right

L175. Is there any evidence from the literature of a dissolution of Si4+?

Modified

Figure 5. the x-axis cannot be read in the EDX spectra. Modified

Line 202 What was the criterion to evaluate a “more compact” matrix? Visual assessment of the micrographs only?

 Yes visual assessment

The paragraph starting at line 266: I believe that other factors could also explain the differences in the strength than only a larger DOR. For instance: differences in the total porosity per se (not necessarily always associated with a higher DOR), presence of finer porosity (for heterogeneous materials with the same porosity, larger porosity = more larger defects = lower strength), strength of gels (the composition of the gel is known to affect its mechanical strength e.g ref below; the morphology could also play a role). The authors should comment on each of these factors and discuss they are not relevant to explain the differences observed in the strength

Bauchy M, Laubie H, Abdolhosseini Qomi MJ, et al (2015) Fracture toughness of calcium–silicate–hydrate from molecular dynamics simulations. Journal of Non-Crystalline Solids 419:58–64.

 The reference and an additional paragraph have been included

References: please remove the jumps in the lines 306, 310, 324, 327 etc…

All right

Reviewer 3 Report

The manuscript is interesting and well written. 

I can recommend the acceptance of this manuscript and have no particular comments. But regarding mechanical strength, I would like to see more results.

Regarding the formatting, in the references section, the style is not homogeneous. For example, some are separated by a line and others not. The authors must fix this section. 

Author Response

The authors wish to thank the reviewers for their comments and suggestions to which we respond below. The authors believe that such comments have helped to improve the quality of the final paper. All recommendations have been taking into account and a reviewed Manuscript has been sent again. We trust that changes completed address the Reviewer requirements.

Comments and Suggestions for Authors

The manuscript is interesting and well written. 

I can recommend the acceptance of this manuscript and have no particular comments. But regarding mechanical strength, I would like to see more results.

Some additional comments have been included

Regarding the formatting, in the references section, the style is not homogeneous. For example, some are separated by a line and others not. The authors must fix this section. 

References have been homogenized

Round 2

Reviewer 2 Report

I recommend the following minor modifications:

1) Abstract: please modify the words on capital letters in "At 2 days and 28 days, compressive mechanical strength WAS determined, and the reaction products were characterized by XRPD, FTIR and BSEM / EDX. Results obtained SHOWED that..."

2) Remove the last ")" in "partially replaced by calcium (N,C)-A-S-H) "

3)  remove the "," before N-A-S-H in "alkaline aluminosilicate hydrate gel (Na2O-Al2O3-SiO2-H2O) commonly named as, N-A-S-H " and C-A-S-H in "commonly named as, C-A-S-H "

4) Figure 5. the x-axis is still too small (the font size should be similar to that of the figure caption) . Actually I can perceive any modifications...

Author Response

The authors wish to thank the reviewer for their comments and suggestions to which we respond below.

I recommend the following minor modifications:

• Abstract: please modify the words on capital letters in "At 2 days and 28 days, compressive mechanical strength WAS determined, and the reaction products were characterized by XRPD, FTIR and BSEM / EDX. Results obtained SHOWED that..."

Agreement, modified

• Remove the last ")" in "partially replaced by calcium (N,C)-A-S-H) "

Agreement, modified

• remove the "," before N-A-S-H in "alkaline aluminosilicate hydrate gel (Na2O-Al2O3-SiO2-H2O) commonly named as, N-A-S-H " and C-A-S-H in "commonly named as, C-A-S-H "

Agreement, modified

4) Figure 5. the x-axis is still too small (the font size should be similar to that of the figure caption) . Actually I can perceive any modifications...

Agreement, modified