Characterization and Leachability Behaviour of Geopolymer Cement Synthesised from Municipal Solid Waste Incinerator Fly Ash and Volcanic Ash Blends
Round 1
Reviewer 1 Report
The article by Tome et al entitled “Characterization and leachability behaviour of alkali-activated cement synthesised from Municipal solid waste incinerator fly ash and volcanic ash blends” provides an experimental research on the effects of incorporating volcanic ash (VA) and municipal solid waste incinerator fly ash (MSW-FA) in eco-friendly cements (alkali-activated). VA was added to compensate de low content of alumina and silica.
The background is adequate, and the work is both well structured and written. Besides, the manuscript matches the aims and scope of the journal (use of recycled materials). The performed tests provide valuable information (especially those of Sections 3.2.1, 3.2.2, 3.2.3 and 3,2.4). However, taking into account that the raw materials are used in cement-based compounds, additional analyses and experimental tests are required to provide a complete, useful and coherent research. The following changes and/or additional work are required:
· Line 11, the acronym of municipal solid waste incinerator fly ash is MSW-FA. However, in the text MSWI-FA is used. Please, correct.
· Line 58, please explain the terms “hearth” and “patios”.
· Typos must be corrected (e.g. line 65, 69, etc).
· In the XRD analyses, which are the step size and the seconds per step? The answer must be included within the text.
· In the mechanical tests, which is the velocity loading? What standard has been followed? The answers must be included within the text.
· The effect of adding MSW-FA and VA in workability and consistency must be analysed. The effect of the MSW-FA particle size must be analysed. Is required more water content? The quantity of water is acceptable?
· The effect of adding MSW-FA and VA in setting times must be analysed.
· The effect of adding MSW-FA and VA in drying shrinkage must be analysed.
· Has the insoluble residuum been obtained? The answer must be clearly specified within the text.
· Are the researchers planning to analyse the feasibility of using MSW-bottom ash in future works?
· Line 300-301, why using hardened samples at 28-d is a limitation?
· Line 300-301, if the sample size is 25 mm3, it is possible to extrapolate to standardized dimensions. Please, analyse.
· The resistance to chloride, sulfate and carbonation are key factors for the durability in cement compounds. An analysis on durability must be provided.
Author Response
Dear reviewer find below and rebuttal to comments
Point 1: Line 11, the acronym of municipal solid waste incinerator fly ash is MSW-FA. However, in the text MSWI-FA is used. Please, correct.
Answer
MSW-FA was replaced by MSWI-FA in the revised manuscript
Point 2: Line 58, please explain the terms “hearth” and “patios”.
Answer
They are materials used for non-structural applications. Hearth is the floor of a fireplace and patios is a paved outdoor area adjoining a house. we included the explanations in bracket after every term.
Point 3: Typos must be corrected (e.g. line 65, 69, etc).
Answer
The typos errors were spaces between some words and paragraphs. we corrected them in line 37, 40, 64, 77, 80, 135, 141, 173, 175, 192, 197, 261, 270, 310, 389
Point 4: In the XRD analyses, which are the step size and the seconds per step? The answer must be included within the text.
Answer
It has been included them in revised manuscript.
Point 5: In the mechanical tests, which is the velocity loading? What standard has been followed? The answers must be included within the text.
Answer
The mechanical tests were done as per Indian Standards IS 4031. However the sample size of 25mm is lower than the prescribed sample size of 70mm. This sample size was used due to low quantity of samples carried from Cameroon to India. A few results of compressive strength was compared with 70mm size and found to be within ±10 % deviation.
The velocity loading rate has been included in the manuscript.
Point 6: The effect of adding MSW-FA and VA in workability and consistency must be analysed. The effect of the MSW-FA particle size must be analysed. Is required more water content? The quantity of water is acceptable?
Answer
The paste made only with MSWI-FA required high amount of alkaline solution (ratio liquid/solid=0.75) to have good workability, which is not match with the ratio required in construction (range of L/S =0.45- 0.6). But, when 50% of MSWI-FA is substituted by volcanic ash, the ratio became 0.5 and good workability is achieved. This can be explaining by the difference of bulk density (0.71 g/cm3 and 1.51 g/cm3 for MSWI-FA and VA, respectively) and specific surface area (7.5 m2/g and 3.6 m2/g for MSWI-FA and VA, respectively) of these materials. We included this paragraph in the manuscript as the first of the results and discussion section.
Point 7: The effect of adding MSW-FA and VA in setting times must be analysed.
Answer
Setting time is an important parameter for Portland cement but many times not applicable in geopolymer cement as initial and final setting occurs concurrently. The paste made only with MSWI-FA took 6 minutes to set and when VA was added; the paste took 8, 11 minutes to set for 70%MSWI-FA-30%VA and 50%MSWI-FA-50%VA, respectively.
Point 8: The effect of adding MSW-FA and VA in drying shrinkage must be analysed.
Answer
A few samples have been tested for shrinkage using Autoclave method. No notable shrinkage or expansion is observed so not mentioned in the study. This has been now mentioned in revised manuscript.
Point 9: Has the insoluble residuum been obtained? The answer must be clearly specified within the text.
Answer
This has been now mentioned in revised manuscript.
Point 10: Are the researchers planning to analyse the feasibility of using MSW-bottom ash in future works?
Answer
Yes, we planned to analyse the feasibility of using MSW-bottom ash in future works. This has been mentioned in conclusion section.
Point 11: Line 300-301, why using hardened samples at 28-d is a limitation?
Answer
Based on the literature review, the mains expected reactions (alkalinization and geopolymerization) already took place with significant yield.
Point 12: Line 300-301, if the sample size is 25 mm3, it is possible to extrapolate to standardized dimensions. Please, analyse.
Answer
Already answered in Answer 5
Point 13: The resistance to chloride, sulfate and carbonation are key factors for the durability in cement compounds. An analysis on durability must be provided.
Answer
Durability is not in the scope of present study but is part of our future study. We mentioned in conclusion that to use the cement we have to study the durability.
Reviewer 2 Report
This is an interesting paper, and I think it is worth to be published after some minor revisions.
In all equations, please notice the subscripts should be placed in the correct format.
For researchers in this area, we concern the modulus [SiO2]/[Na2O], please provide this information although one can calculate it from the data.
Since the compressive strength is too low to meet the engineering application, I think the main purpose of this study is to solidify the MSW-FA. I suggest the authors emphasize this in the conclusions.
After all these points are revised, it is my pleasure to recommend its acceptance.
Author Response
Dear reviewer
Find below the responses and rebuttal to comments
Point 1: In all equations, please notice the subscripts should be placed in the correct format.
Answer
This was done in revised manuscript
Point 2: For researchers in this area, we concern the modulus [SiO2]/[Na2O], please provide this information although one can calculate it from the data.
Answer
We calculated the modulus [SiO2]/[Na2O]. We obtained Ms=0.66, 0.56 and 0.36 for 6M, 8M and 10M, respectively. This was included in the revised manuscript (preparation of geopolymer samples section line118).
Point 3: Since the compressive strength is too low to meet the engineering application, I think the main purpose of this study is to solidify the MSW-FA. I suggest the authors emphasize this in the conclusions.
Answer
This was done in revised manuscript
Reviewer 3 Report
The authors should be commended for producing a very interesting manuscript. The reviewer has only three relatively minor comments:
Figure 6 – When displaying an electron micrograph, only a scale bar should be presented. The reader does not need to see the entire databar, since most of that information is irrelevant and may be hiding something interesting. Further, as the vertical height of peaks in EDS spectra are arbitrary, including the peaks as figures would only be necessary if the authors were trying to argue that they had identified the presence of an unexpected element. Since the presence of these elements are not surprising, the EDS data can be cut from this figure. In addition to these comments about how to present figures, they authors should make sure that they note more explicitly in the text that they are trying to draw semi-quantitative results from purely qualitative data. Individual SEM images really do not serve as a good basis for drawing conclusions about density, microstructure, etc. For example, the low-pressure vacuum inside the SEM can cause cracking in otherwise sound materials.
The reader would benefit from the inclusion of standard deviation data in Table 4 and error bars in figure 7.
The conclusions section should be rewritten. Right now it is a summary of the results that the reader just read. The reader would be much more interested in the author’s analysis of what these results mean to industry, the state of science, etc.
Author Response
Dear Reviewer
Find below the responses and rebuttal to comments
Point 1: Figure 6 – When displaying an electron micrograph, only a scale bar should be presented. The reader does not need to see the entire databar, since most of that information is irrelevant and may be hiding something interesting. Further, as the vertical height of peaks in EDS spectra are arbitrary, including the peaks as figures would only be necessary if the authors were trying to argue that they had identified the presence of an unexpected element. Since the presence of these elements are not surprising, the EDS data can be cut from this figure. In addition to these comments about how to present figures, they authors should make sure that they note more explicitly in the text that they are trying to draw semi-quantitative results from purely qualitative data. Individual SEM images really do not serve as a good basis for drawing conclusions about density, microstructure, etc. For example, the low-pressure vacuum inside the SEM can cause cracking in otherwise sound materials.
Answer
I deleted the entire databar and the EDS spectra in the revised manuscript.
Point 2: The reader would benefit from the inclusion of standard deviation data in Table 4 and error bars in figure 7.
Answer
The error bars were added.
Point 3: The conclusions section should be rewritten. Right now it is a summary of the results that the reader just read. The reader would be much more interested in the author’s analysis of what these results mean to industry, the state of science, etc.
Answer
This was done in revised manuscript
Round 2
Reviewer 1 Report
Please, revise English grammar and style in the new version (e.g. line 138, 268).
Author Response
Dear Reviewer
The manuscript was revised by two native English speakers.
