Low-Carbon Binder for Cemented Paste Backfill: Flowability, Strength and Leaching Characteristics
Round 1
Reviewer 1 Report
The paper reports interesting results on a timely important topic. The data are well documented and support the conclusions.
On the scientific levels I have two important remarks.
The first concerns the appropriateness of the reported zeta potential measurements. By measuring the zeta potential in MilliQ water, the authors change the ionc concentration in contact with the solid and thus change the surface potential. The measured zeta potential bears no relation with the surface state in the real system. Moreover the authors probably observe a severe sedimentation of the measuring system, preventing meaningful results. All this prevents any correlation between the zeta potential data and the fluidity of the samples.
The second concerns the explanation that the authors give of the role of gypsum abundance in the formulation of the binder (lines 164-165-166). What the authors write is entirely speculative. If they suspect a role of flocculation induced by ettringite they should prove it at least indirectly. To prove it the authors should experimentally measure the cohesivity of the binder paste, e.g. by small-amplitude oscillation rheometry.
The paper needs a complete editorial revision, starting from the mis-numbering of the tables.
I have plenty of more comments which are included in the file attached.
Comments for author File: 
Comments.pdf
Author Response
Point 1: The first concerns the appropriateness of the reported zeta potential measurements. By measuring the zeta potential in MilliQ water, the authors change the ionic concentration in contact with the solid and thus change the surface potential. The measured zeta potential bears no relation with the surface state in the real system. Moreover, the authors probably observe a severe sedimentation of the measuring system, preventing meaningful results. All this prevents any correlation between the zeta potential data and the fluidity of the samples.
Response 1: A ZetaProbe analyzer was used to measure the zeta potential (ζ, mV) of selected samples. 0.1g sample and 1L water were used to prepare the suspension . Each zeta potential measurement was performed at least three times to verify the reproducibility of the results.
Point 2: The second concerns the explanation that the authors give of the role of gypsum abundance in the formulation of the binder (lines 164-165-166). What the authors write is entirely speculative. If they suspect a role of flocculation induced by ettringite they should prove it at least indirectly. To prove it the authors should experimentally measure the cohesivity of the binder paste, e.g. by small-amplitude oscillation rheometer.
Response 2: There is no condition to measure the cohesivity of the binder paste, e.g. by small-amplitude oscillation rheometer at present. So, we just speculate according to the studies reported in references [1,2]. Higher dosage of gypsum can lead to the excessive growth of crystals in the pore, and then expansive cracking or large voids will generate. This can decrease the compressive strength of samples. On the other hand, some unreacted gypsum can remain in the matrix and result in a lower strength of the hardened matrix [1].
Other comments including in the file attached have been rectified in the file.
References
[1] Park H, Jeong Y, Jun Y, Jeong J-H, Oh JE. Strength enhancement and pore-size refinement in clinker-free CaO-activated GGBFS systems through substitution with gypsum. Cement and Concrete Composites 2016;68:57–65.
[2] Neto AAM, Cincotto MA, Repette W. Mechanical properties, drying and autogenous shrinkage of blast furnace slag activated with hydrated lime and gypsum. Cement and Concrete Composites 2010;32(4):312–8.
Author Response File: Author Response.pdf
Reviewer 2 Report
This paper deals with investigation of properties of composite binder for cemented pasted backfill. The optimum conditions for the preparation of binder based on alkali activated slag using orthogonal tests have been found. The results are interesting, and the paper can be accepted after the authors address these issues.
The chemical composition of gypsum and specific surface area or particle size distribution of the mine tailings should be provided in ‘Materials’ section. On p. 3 there are two different Tables with the same number 2. Please describe the water film thickness determination. Please define what “solid content” is in Tables 4 and 5. What was the concentration of the NaOH solution used to prepare the samples and what was water to cement (w/c) ratio? The authors do not take into account the effect of the w/c ratio on compressive strength of the samples. Please provide the standard errors for the coefficients of fitting equations (Table 6). In Fig. 2 leaching concentration of Pb are presented incorrectly. There are some typos and grammar issues. Authors should carefully check them throughout this paper.Author Response
Point 1: The chemical composition of gypsum and specific surface area or particle size distribution of the mine tailings should be provided in ‘Materials’ section.
Response 1: The particle size distribution of MT could be found in the Figure S1 in supplementary materials.
Chemical composition of gypsum could be found in Table 1.
Figure S1. Particle size distribution of tailings.
Point 2: On p. 3 there are two different Tables with the same number 2.
Response 2: Table numbers have been changed.
Point 3: Please describe the water film thickness determination.
Response 3: The WFT around particles in fresh CPB slurry can be obtained from the following equations
where is the water ratio of the CPB mix (the ratio of the volume of water to the solid volume of all the particles). The voids ratio us can be obtained as , where is the packing density of all the particles. is the specific surface area of all the solid particles.
Point 4: What was the concentration of the NaOH solution used to prepare the samples and what was water to cement (w/c) ratio?
Response 4: The liquid to solid ratio (L/S) was fixed at 0.5 for all mixtures, and it needs to be emphasized that the NaOH includes in the binders as solid matter when calculating the L/S.
Point 5: Please provide the standard errors for the coefficients of fitting equations (Table 7).
Response 5:
|
Curing period (d) |
Fitting equation |
Standard errors |
Correlation coefficient (R2) |
|
3 |
y1=27.5665-19.2973x12+50.6791x22-24.0004x1-75.1738x2+45.9925x1x2 |
0.1368 |
0.9016 |
|
7 |
y2=60.3656-27.5251x12+105.9263x22-53.7166x1-160.9699x2+94.3906x1x2 |
0.1428 |
0.9578 |
|
14 |
y3=100.3304-112.6050x12+192.4251x22+5.1676x1-282.8351x2+64.1722x1x2 |
0.1807 |
0.9614 |
|
28 |
y4=151.7099-129.9277x12+280.8141x22-27.3326x1-418.3366x2+119.5032x1x2 |
0.2525 |
0.9549 |
Pointe 6: In Fig. 2 leaching concentration of Pb are presented incorrectly.
Response 6: We have changed the leaching concentration of Pb in the manuscripts.
Author Response File: Author Response.pdf
Reviewer 3 Report
The present work is on the performance of CLSM mixture based on localized cementless binder.
The organization of the paper and the discussion of the results is good enough.
If the authors can reflecting following inquiry, the paper could be published.
1. There is no novelty on topic of paper.
Some papers with similar topic has been reported:
- Lee, N. K., Kim, H. K., Park, I. S., & Lee, H. K. (2013). Alkali-activated, cementless, controlled low-strength materials (CLSM) utilizing industrial by-products. Construction and Building Materials, 49, 738-746.
- Kim, Y. S., Do, T. M., Kim, M. J., Kim, B. J., & Kim, H. K. (2018). Utilization of by-product in controlled low-strength material for geothermal systems: Engineering performances, environmental impact, and cost analysis. Journal of cleaner production, 172, 909-920.
- Kim, B. J., Jang, J. G., Park, C. Y., Han, O. H., & Kim, H. K. (2016). Recycling of arsenic-rich mine tailings in controlled low-strength materials. Journal of cleaner production, 118, 151-161.
These papers contained the similar information:
1) slag-based alkali activate materials could be used for binder system in CLSM.
2) Local mine tailing could be use as filler or fine aggregate for CLSM.
3) There is low leaching potential of heavy metals from CLSM with AAM binders.
These are also contained in the present manuscript. What point is different with other papers.
Author Response
For one thing, although alkali activated materials have been used in controlled low-strength materials (CLSM) in recent year, it has to admit the fact that the properties of the prepared alkali activated materilas varied due to the various combination of the raw materials as well as the alkali activators. For another, in the present study, we introduced WFT to explain the flow ability of the CPB slurry and used multivariate analysis and sensitivity analysis to analyze the compressive strength of CPB samples. Besides, we also obtained a predictive model to predict the compressive strength of samples. All these were not reported in the references mentioned above.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The paper still needs revisions. The authors should concentrate on the important results results of their work, and not speculate on the interpretation of the results.
The zeta potential data should be omitted. Not only they do not represent the surface potential during hydration because of the different ionic concentration of the suspending medium during hydration and during measurement, but they are also not necessary to explain the results being reported. The fluidity and the yield stress is explained quite well by the surface area and maximum packing density of the CPB slurries, represented by the WFT. The speculations about the role of NaOH dosage on mechanical strength at lines 158-161 are doubtful and do not add to the paper. They should be omitted. The same holds for the role of gypsum at lines 174-177 At lines 178 and 347 the optimal combination of binder is A1B1C3 and not A1B1C1. The discussion on the mechanisms of immobilization at lines 308-334 is not supported by experimental data. No quantification of phase abundance is reported and the authors cannot speculate if the heavy metal capture occurs onto C-S-H, Aft, AFm or any other phase. Finally the English wording still needs revision.
Further minor comments are as follows:
line 40: the majority of CO2 emission from clinker production comes from limestone decomposition and not from the burning of fuels in the kiln line 57: the conjugation of "using" is incorrect. The sentence shall be revised line 94: The wording "To preparation" is incorrect. lines 101-102: what does it mean "For samples used for the optimal decision, specimens were prepared without MT."? Are we not dealing of the binder paste samples? They are obviously without MT. line 115: the wording "resulted paste" is incorrect line 122: the acronym WFT has not been explained first line 140: the wording "mechanical rheological and properties" is incorrect line 267: use "variables" or "levels" instead of "things" line 275: what does it mean "dimensionless processing"?
Author Response
Thanks for your comments for the manuscript, and we have made some resvison according to your advice.
Author Response File: Author Response.pdf
Reviewer 2 Report
The manuscript has been improved; however throughout the paper there are still typing errors and inconsistencies, for example:
Line 88: “Table 3” should be replaced by “Table 4”. Lines 295-301: “Pd” should be replaced by “Pb”. The positions of columns in Fig. 2 (left) do not correspond to the binder content (12%, 16% and 20%).Author Response
Point 1: Line 88: “Table 3” should be replaced by “Table 4”. Lines 295-301: “Pd” should be replaced by “Pb”. The positions of columns in Fig. 2 (left) do not correspond to the binder content (12%, 16% and 20%).
Response 1: The typing errors in Line 88 and 295-301 have been corrected.
As for Figure 2 (a), no Pb leaching was found using 12% binder content at 7d, so the concentration of Pb in the picture is 0.
Reviewer 3 Report
In reviewer's opinion, this paper could be published in the journal.
Author Response
Thanks for your advice on the manuscript.
Round 3
Reviewer 1 Report
Line 97: The authors state that the samples have been prepared by mixing BFS, OPC, gypsum and MT. They shall specify the amount of MT introduced in th samples.
Line 132: The authors state that the weakest impact is the ratio of gypsum. Form Table 4 it appears that the weakest impact is the one of NaOH dosage. Please clarify.
Line 173: The authors state that the best gypsum dosage is 6. From Table 4 it appears that the best gypsum dosage is 4. Please clarify.
Line 176: Table 5, not Table 4.
Line 203: Table 5, not Table 4.
Lines 237-238: Table 7, not Table 6.
Line 239: Table 7, not Table 6.
Lines 280-281: Table 9, not Table 8.
Lines 244-245: On line 173 the authors state that the best gypsum dosage is 6%. Please clarify.
Author Response
Responds to review 1:
We have added the related content. the weakest impact is the one of NaOH dosage, we have corrected it. the best gypsum dosage is 4, we have corrected it. We have corrected the Table number We have corrected the Table number We have corrected the Table number We have corrected the Table number We have corrected the Table number the best gypsum dosage is 4, we have corrected it.
Author Response File: Author Response.pdf
