Properties and Mechanism of Hydration of Fly Ash Belite Cement Prepared from Low-Quality Fly Ash
Round 1
Reviewer 1 Report
The paper analyses properties and mechanism of hydration of fly ash belite cement (FABC) prepared from low-quality fly ash. It gives interesting and useful details on FABC such as optimal production parameters, compressive strength, microstructure, heat evolution, pore size distributions etc. The paper is of interest to material scientists working with cements and additionally it is of practical usefulness. One can note that the fly ash finds specific interest as cement or geopolymer raw component of nuclear wasteforms, see for example the works published within the Special issue of MDPI journal “Materials” dedicated to Materials for nuclear waste immobilisation https://0-www-mdpi-com.brum.beds.ac.uk/journal/materials/special_issues/MNWI where alkali activated cements (geopolymers) found practical utilisation in the immobilisation of liquid radioactive waste.
The paper can be published subject to several amendments. The following questions shall be resolved:
Line 74: Notation for CaO is just C, not CA.
Line 83 -explain the reason of noting NaOH as AR.
Chapter 2.1 mises data on gypsum used as the line 92 specifies just “gypsum (Analytical Reagent)”.
Table 1: Is the P·I 42.5 cement the same as the RC? If yes, then write that explicitly. If not, then give data for RC.
Table 1and lines 90, 91, 96: What is the reason of indicating “clinkers” rather than “clinker”? The Table1 and Figure 1 gives data of just one clinker not many clinkers.
Line 91: It is specified that “the density of clinkers was 2.82 kg/m3” which however is unlikely to be true because 1 cubic metre of clinker cannot be so light weighting under 3 kg.
Line 96 and Figure 1: The claim “The phase composition of clinkers under different preparation conditions” is not supported by data because the Figure 1 shows just one XRD pattern. Moreover, the conditions are not specified even in this case. That shall be done. How many clinkers were used? How they differ from each other? Please specify.
Lines 107-115: The text is inconsistent with Figure 2, it uses “clinkers” whereas Figure 2 gives the image of just one clinker.
Figure 2: Explain what is meant under “particles” and powders. How these were selected from original clinker obtained? If these were both present in the clinker, then it is needed to add a figure that would show them or to write about that.
Lines 246-247: Figure 8 does not show the total porosity whereas the text claims on some integral figures. Please also specify whether the “the porosity of FABC pastes hydrated” refers to the total porosity or to something else (effective porosity etc.) and how the integral data on porosity were found.
Author Response
Response to Reviewer 1 Comments
Point 1: Line 74: Notation for CaO is just C, not CA.
Response 1: Line 77: calcium oxide (CaO) ,CA has been corrected to CaO
Point 2: Line 83: explain the reason of noting NaOH as AR.
Response 2: Analytical Reagent NaOH was used as an activator, and AR is abbreviated notion of Analytical Reagent, we have revised “AR” as “Analytical Reagent, NaOH≥96.0%”. Please see the highlighted text in the line 86-87.
Point 3: Chapter 2.1 mises data on gypsum used as the line 92 specifies just “gypsum (Analytical Reagent)”.
Response 3: Thanks for your attention, We have added a content of CaSO4·2H2O. Please see the highlighted text in the line 95.
Point 4: Table 1: Is the P·I 42.5 cement the same as the RC? If yes, then write that explicitly. If not, then give data for RC.
Response 4: Yes, the P·I 42.5 cement the same as the RC, it has been explained in the line 96.
Point 5: Table 1and lines 90, 91, 96: What is the reason of indicating “clinkers” rather than “clinker”? The Table1 and Figure 1 gives data of just one clinker not many clinkers.
Response 5: Thanks for the suggestion, “clinkers” should be corrected to “clinker”, because there is only one type of clinker in this work.
Point 6:Line 91: It is specified that “the density of clinkers was 2.82 kg/m3” which however is unlikely to be true because 1 cubic metre of clinker cannot be so light weighting under 3 kg.
Response 6: It is ture, the density of portland cement clinker is more than 3kg, but the new cement of FABC clinker has a lower density, beacuse the density of fly ash is lower than 2.9 kg/m3. The 2.82 kg/m3 is tested by Micromeritics AccuPyc 1330.
Point 7:Line 96 and Figure 1: The claim “The phase composition of clinkers under different preparation conditions” is not supported by data because the Figure 1 shows just one XRD pattern. Moreover, the conditions are not specified even in this case. That shall be done. How many clinkers were used? How they differ from each other? Please specify.
Response 7: Thanks for the suggestion, we have revised as “The phase composition of clinker under the above preparation conditions is shown in Figure 1”. please see the the highlighted text in the line 100. The preparation conditions have been shown in the line 87-94. The preparation steps of FABC were shown as follows. First, FA, pure lime with 99 wt.% CaO, and Na2O at a ratio of 70:30:1 were mixed uniformly. Second, the mixtures were wound into a ball with the diameter ranging from 8 to 12 mm through a small disk granulator. Third, these granule specimens were hydrothermally treated at 90–100℃ for at least 12 h. Finally, all dried precursors were burned in a furnace in the following parameter settings: rate of temperature rise, 10℃/min; final temperature, 800℃; holding time, 1–1.5 h, and rapid cooling.
Point 8: Lines 107-115: The text is inconsistent with Figure 2, it uses “clinkers” whereas Figure 2 gives the image of just one clinker.
Response 8:The reviewer is correct, “clinkers” should be corrected to “clinker”.
Point 9:Figure 2: Explain what is meant under “particles” and powders. How these were selected from original clinker obtained? If these were both present in the clinker, then it is needed to add a figure that would show them or to write about that.
Response 9: After rapid cooling, we only get spherical particles from 8 to 12 mm , then the particles should be ground to powders.
Point 10:Lines 246-247: Figure 8 does not show the total porosity whereas the text claims on some integral figures. Please also specify whether the “the porosity of FABC pastes hydrated” refers to the total porosity or to something else (effective porosity etc.) and how the integral data on porosity were found.
Response 10: Thanks for the suggestion, we have added the total porosity on the figure 8(a). all the integral data on porosity were found by MIP (Premaster 60GT).
Author Response File: 
Author Response.pdf
Reviewer 2 Report
- Intoduction: why the issue is important and for whom, what is the main aim of the study?
- It is not clear how authors could obtain the information given in Table 1. Is there any specific measurement technique applied?
- Line 102 please add unit to 900.
- Point 2.2. what kind of sand and what diameter was used? How many samples were made? According to which standard the compressive and flexural strength were tested? Have the scale effect of the samples been taken into account and the results compared with the standard value for Portland cement? Please add this information in paper.
- Line 144-145 the authors refer to the results of Portland cement, which are not included in table 2. Please add results for RC specimen.
- Figures 5,6 and 8 are blurry.
- The discussion did not refer to the specific results of other authors, the work looks more like a research report. Have other authors carried out studies that can be referred to quantitatively?
- Conclusions: Why are our results important and valuable (what were the limitations at work)?
What are the future lines of research and what else needs to be done?
What is the meaning, application of the described methods and results?
Have our results influenced the development of a specific field of knowledge?
What do we know now that we did not know before?
Was the assumed work goal achieved and how? Conclusions should be expanded
Author Response
Response to Reviewer 2 Comments
Point 1: Intoduction: why the issue is important and for whom, what is the main aim of the study?
Response 1: Thanks for your attention, Low-quality fly ash has been stockpiled due to its coarse particles, high carbon content, and low pozzolanic activity. Though we have focused on the technology for preparing FABC, the hydration mechanism and characteristics of FABC are still rarely reported. By this research article, we can better understand the hydration mechanism of FABC. The research results will increase utilization and improve applictaion of low-quality fly ash. The main aim of the study is to explore compressive strength, microstructure, heat evolution, pore size distributions of FABC.
Point 2: It is not clear how authors could obtain the information given in Table 1. Is there any specific measurement technique applied?
Response 2: Chemical composition was tested by XRF ( X-ray fluorescence method) , Density was tested by Micromeritics AccuPyc 1330, Blaine specific area was tested by FBT-9 (Full Automation Instrument Testing Specific Surace).
Point 3: Line 102 please add unit to 900.
Response 3: The reviewer is correct, we has revised as “900℃”.Please see the highlighted text in the line 106.
Point 4: Point 2.2. what kind of sand and what diameter was used? How many samples were made? According to which standard the compressive and flexural strength were tested? Have the scale effect of the samples been taken into account and the results compared with the standard value for Portland cement? Please add this information in paper.
Response 4: Thanks for the suggestion, ISO679-standard sands were used for testing the strength of cement mortars. The sentence was shown in line 96. Setting time, water requirement, compressive and flexural strength were tested from GB/T1346-2011 and GB/T17671-1999. Please see the highlighted text in the line 130-131.
Point 5: Line 144-145 the authors refer to the results of Portland cement, which are not included in table 2. Please add results for RC specimen.
Response 5: 28 day compressive strength of P·I 42.5 mortars is higher than 42.5 MPa, so FABC mortars is compared with 42.5 MPa, we have added “the water requirement of RC was 28.6%. Please see the highlighted text in the line 150.
Point 6: Figures 5,6 and 8 are blurry.
Response 6: Thanks for the suggestion, we has used bold lines in Figures 5,6 and 8.
Point 7: The discussion did not refer to the specific results of other authors, the work looks more like a research report. Have other authors carried out studies that can be referred to quantitatively?
Response 7: We have cited ref 21 to 26, they studied the effect of C2S and C12A7 on portland cement, and some chinese researchers also studied, we did not cited these chinese research articles, but we can provide doi as follows.
- doi:3321/j.issn:0454-5648.2004.04.025
- doi:10.3321/j.issn:0454-5648.2003.02.018
- doi:3969/j.issn.1001-702X.2017.05.012
Point 8: Conclusions: Why are our results important and valuable (what were the limitations at work)?
Response 8: We have found hydration properties of FABC clinker, the long-term strength development, the low content of Ca(OH)2 , the low heat and high porosity have been found in this paper, these results provide guidance and reference for future research.
Point 9: What are the future lines of research and what else needs to be done?
Response 9: We will compound FABC and Portland cement, the composite cement can be used to prepare mortars and concrete. We will research the working performance, mechanics performance and durability of mortars and concrete. The correlation mechanisms between the synergistic hydration of composite cement will to be revealed.
Point 10: What is the meaning, application of the described methods and results?
Response 10: The ultimate aim is to give a theoretical foundation and technological support for the application of the new cementitious material made of low quality fly ash.
Point 11: Have our results influenced the development of a specific field of knowledge?
Response 11: Yes, Although fly ash is widely used in cement and concrete, the low quality fly ash is stockpiled. Our research results can provide a way of low carbon cement production and low-quality fly ash utilization.
Point 12: What do we know now that we did not know before?
Response 12: Through this paper, we can find appropriate gypsum content, no Ca(OH)2 , low heat, higher porosity in FABC hydration productions. The strength is growing rapidly during 3 day to 28 day.
Point 13: Was the assumed work goal achieved and how? Conclusions should be expanded
Response 13: Thanks for the suggestion, we have revised our conclusions, Please see the highlighted text in the line 325-332.
Author Response File: Author Response.pdf
Reviewer 3 Report
The paper deals with an experimental activity regarding the investigation of the hydration and mechanical properties of cement mixtures prepared by using low-quality fly ash.
The topic is innovative, interesting and suitable for the scope of the Journal. The results are presented and argued properly. However, English language and style need a revision, possibly by a native English speaker.
The Introductory part is fairly exhaustive, even though it can be enlarged by expanding a bit the findings of [19-20] and other papers specifically dealing with the hydration properties and the peculiarities of FABC.
Before being suitable for publication, the Authors should make an effort to improve their manuscript since it lacks scientific rigour for several reasons, which I try to detail hereafter.
The abstract should be completely rearranged, because it must be self-standing and provide the reader with a complete and concise view of the problem, the topic of the paper and finally some (brief) insights about the findings. Too many details are given in the first version of the abstract, which are not relevant in that position.
Moreover, all the acronyms and chemical symbols must be disclosed at their first use.
Section 2.1 should be limited to the mere description of the raw materials. All the analyses reported in Fig.1 and 2 and herein discussed must be moved to the "Results" section. The description of the FABC preparation should be moved in the subsection 2.2. In addition, the Authors mention the preparation of mortar and concrete specimens. Which sand/aggregates was/were used? Please add the grain size/chemical composition of the sand or, alternatively, openly declare which ISO standards were followed for the sand (Line 93). The “Materials and Methods” section should be exhaustive so that the experiments can be easily replicated by all the interested readers.
Section 2.2 should be enriched by adding a more exhaustive explanation of the experimental program, possibly by using a table. The number of repetitions for each test should be declared. Accordingly, bar-charts in Fig.3 must be provided with the relevant standard deviation bands. Data fluctuation is a very important parameter in the intepretation of the experimental results and should be considered thoroughly. No mention about the tested gypsum contents is provided in the specimens manufacturing section.
Was the curing protocol retrieved from particular guidelines (Lines 123-126)?
Other notes are the following:
- Line 60: The Authors mention "Rheobuild 1000". Commercial names should be avoided, or if necessary, a description of the product should be disclosed
- Lines 72-77: The Authors refer to several experimental results without reporting the relevant sources
- Line 91: 2.82 kg/m3: is it a typo?
- Lines 110-112: is this evidence endorsed in the literature? Please refer to existing results, if available.
The "Conclusions" section is quite elementary and should be improved.
Author Response
Response to Reviewer 3 Comments
Point 1: The abstract should be completely rearranged, because it must be self-standing and provide the reader with a complete and concise view of the problem, the topic of the paper and finally some (brief) insights about the findings. Too many details are given in the first version of the abstract, which are not relevant in that position.
Response 1: Thanks for your suggestion, we have revisied our abstract. Please see the highlighted text in the line 11-28.
Point 2: Moreover, all the acronyms and chemical symbols must be disclosed at their first use.
Response 2: The reviewer is correct, we have added some abbreviation in the abstract. Please see the highlighted text in the line 11.
Point 3: Section 2.1 should be limited to the mere description of the raw materials. All the analyses reported in Fig.1 and 2 and herein discussed must be moved to the "Results" section. The description of the FABC preparation should be moved in the subsection 2.2. In addition, the Authors mention the preparation of mortar and concrete specimens. Which sand/aggregates was/were used? Please add the grain size/chemical composition of the sand or, alternatively, openly declare which ISO standards were followed for the sand (Line 93). The “Materials and Methods” section should be exhaustive so that the experiments can be easily replicated by all the interested readers.
Response 3: Thanks for your suggestion, we use chinese ISO standard sands according to ISO 679:1989. beacuse FABC is a new cementitious material, the preparation of FABC has been reported in another article doi: 10.1016/j.conbuildmat.2016.02.043. So we arranged the the analyses of FABC in the Section 2.1, we should let readers understand the basic properties of the new cementitious material, in order to read more clearly. Please forgive us for this arrangement.
Point 4: Section 2.2 should be enriched by adding a more exhaustive explanation of the experimental program, possibly by using a table. The number of repetitions for each test should be declared. Accordingly, bar-charts in Fig.3 must be provided with the relevant standard deviation bands. Data fluctuation is a very important parameter in the intepretation of the experimental results and should be considered thoroughly. No mention about the tested gypsum contents is provided in the specimens manufacturing section.
Response 4: Thanks for the suggestion, some mix proportion were shown in table 2, we also have revised Section 2.2, The test method is shown according to GB/T1346-2011 and GB/T17671-1999. Please see the highlighted text in the line 130-131. The errors of all test values were below 15% according to GB/T17671-1999, so we have added standard deviation bands in figure 3 according to reviewer comments, Please see the highlighted text in the line 177.
Point 5: Was the curing protocol retrieved from particular guidelines (Lines 123-126)?
Response 5: Curing protocol was arranged from GB/T17671-1999.
Point 6: Line 60: The Authors mention "Rheobuild 1000". Commercial names should be avoided, or if necessary, a description of the product should be disclosed.
Response 6: Thanks for the suggestion, we have delete Rheobuild 1000 and revised as naphthalene water reducer. Please see the highlighted text in the line 63.
Point 7: Lines 72-77: The Authors refer to several experimental results without reporting the relevant sources
Response 7: Thanks for the suggestion, We have cited ref 6 and 12 in the line 75
Point 8: Line 91: 2.82 kg/m3: is it a typo?
Response 8: It is ture, the density of portland cement clinker is more than 3kg, but the new cement of FABC clinker has a lower density, beacuse the density of fly ash is lower than 2.9 kg/m3. The 2.82 kg/m3 is tested by Micromeritics AccuPyc 1330.
Point 9: Lines 110-112: is this evidence endorsed in the literature? Please refer to existing results, if available.
Response 9: Current thinking suggests that C2S prepared at a high temperature have lower activity, we can provide references doi as follows.
- 1007/s10973-018-7251-6
- 3969/j.issn.1007-9629.2011.02.001
Point 10: The "Conclusions" section is quite elementary and should be improved.
Response 10:Thanks for the suggestion, we have revised Conclusions, please the highlighted text in the line325-332.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
I accept in present form.
