The Influence of FA Content on the Mechanical and Hydration Properties of Alkali-Activated Ground Granulated Blast Furnace Slag Cement
, Zhenbo Fu 2,†, Xihao Yang 1, Yimeng Zhao 2, Binghan Li 2, Da Xu 2, Shige Yu 3, Zhiyu Yao 4, Zhibin Sun 4, Zhilu Zhen 4, Xinfeng Ouyang 1, Yangyang Zong 1, Wendi Tian 1, Hai Yu 5, Shuli Zhao 2, Yen Wei 6,* and Kangmin Niu 1,*Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsDear Authors
The work is interesting, the authors have done well work.
Author Response
Thank you very much for your recognition of our work！
Reviewer 2 Report
Comments and Suggestions for Authors1. The authors mentioned the gap in previous research in the last paragraph of the introduction part. Also, they have mentioned a short description of the methodology in the same paragraph. However, this paragraph should also contain the novelty and the objectives of the current study. Please elaborate.
2. The first sentence in the introduction part needs a reference. The same mentioned information can be found in the following article: https://doi.org/10.3390/su13094949... Cite it at the end of the sentence.
3. In section 2.3.2 mention the type and model of the used device (isothermal calorimetry).
4. There is an obvious anomaly in the compressive and flexural strength results (Figure 3). For instance, in figure 3d, the strength decreases FA-10 the increases for FA-20, then start to decrease again. Why? What is the reason?
5. Section 3.2: in the pre-induction Stage, what about the role of C2S in hydration?
6. In the induction stage, how did you know for sure that Ca2+ has been adsorbed on the surface of FA?
7. In Figure 10, isn't there a high distribution of ettringite ??? Please check and explain the reason for its abundant presence.
8. Include the observations from SEM in the conclusion part.
Author Response
Comments1:The authors mentioned the gap in previous research in the last paragraph of the introduction part. Also, they have mentioned a short description of the methodology in the same paragraph. However, this paragraph should also contain the novelty and the objectives of the current study. Please elaborate.
Response1:
Thank you for pointing this out.
novelty: This study aims to reveal the correlation between the hydration performance and compressive strength of AAGC under varying FA content.
Objective: This study investigates the trends and differences in compressive strength and flexural strength of AAGC from 3 to 28 days under varying OPC and FA content, while also exploring the differences in hydration performance of AAGC with changes in OPC and FA content.
Comments2:The first sentence in the introduction part needs a reference. The same mentioned information can be found in the following article: https://doi.org/10.3390/su13094949... Cite it at the end of the sentence.
Response2:Thank you for pointing this out.
I apologize for the oversight and omission in not citing that reference during my literature review. I have now added the citation in the revised version of the manuscript.
Comments3:In section 2.3.2 mention the type and model of the used device (isothermal calorimetry).
Response 3:
Thank you for pointing out the omission of the testing equipment details in the research methodology. The equipment used in this study is from Jingqiang (Tianjin) Test Instrument Technology, model SHR-16. This information has been added in the corresponding section of the revised manuscript.
Comments4:There is an obvious anomaly in the compressive and flexural strength results (Figure 3). For instance, in figure 3d, the strength decreases FA-10 the increases for FA-20, then start to decrease again. Why? What is the reason?
Response4:
Thank you very much for pointing out the explanatory omission in this study. Based on your guidance regarding the 3-day strength of AAGC and the results of this research, the following explanation is provided:
Alkali-activated GBFS cementitious materials exhibit relatively high shrinkage [6], leading to the formation of numerous microcracks in the paste. In the 28-day paste of FA-0 in this literature, there were a significant number of microcracks. Additionally, due to the low pozzolanic activity of fly ash, it primarily plays a filling role and improves the pore structure of the cementitious material at an early age [7]. This results in FA-10 having the highest compressive strength at 3 days. However, as the FA content increases, the strength of the cementitious material decreases. Similar experimental results have been observed in related studies [7,8].
Comments 5:Section 3.2: in the pre-induction Stage, what about the role of C2S in hydration?
Response 5:The hydration rate of C2S is particularly slow, approximately one-twentieth of the hydration rate of C3S, and therefore, C2S mainly contributes to the hydration heat release rate of OPC at later stages [1].
Comments 6:In the induction stage, how did you know for sure that Ca2+ has been adsorbed on the surface of FA?
Response 6:We sincerely apologize for the insufficient explanation due to our oversight. The research results regarding Ca2+ adsorption on the surface of FA are derived from reference [9], and the citation has been added in the revised version of the manuscript. However, the original reference did not provide an explanation for this conclusion. We conducted further literature research and found in reference [10] that the surface of fly ash contains a large number of Si-O-Si bonds, which, after interacting with water, generate a significant amount of hydroxyl groups on the particle surface. Due to electrostatic adsorption between positive and negative charges, Ca2+ is adsorbed onto the surface of the fly ash. This citation has also been added in the revised version of the manuscript.
Comments 7:In Figure 10, isn't there a high distribution of ettringite ??? Please check and explain the reason for its abundant presence.
Response 7:To facilitate your observation of the SEM images, please note that the images cited in this paragraph are in a larger format, and we apologize for any inconvenience this may cause.
Fig. 1 shows SEM images of different areas of the same paste, taken under the same magnification. It can be observed that both images in Fig. 1 are filled with network-like hydration gel products, which are not ettringite. Similar network-like hydration gel products have been reported in related literature on alkali-activated GGBFS cements [2-4]. In alkali-activated GGBFS cements with flue gas desulfurization gypsum, ettringite formation is accompanied, and in SEM images of the paste, ettringite appears as needle-like structures scattered throughout the paste [5]. In this study, the network-like hydration gel products in alkali-activated GGBFS cements with fly ash resemble the appearance of ettringite, but careful observation reveals significant differences, and the distribution patterns of the two hydration products are not the same.
Comments 8:Include the observations from SEM in the conclusion part.
Response 8:
Based on your feedback, the observation results of the SEM images in the paste have been added to conclusion 4.
In the 28-day SEM images of AAGC paste, unhydrated FA and GBFS were observed. As the FA content increases, the porosity in the paste increases, leading to a higher cumulative pore volume (<100 µm), which results in lower compressive and flexural strengths for AAGC with high FA content. The SEM image of the FA-0 paste at 28 days shows a dense structure, but with numerous cracks. The high early hydration heat release rate of low FA content causes microcracks to form within the paste, and as the curing age increases, the number of microcracks grows, leading to a reduction in compressive strength for FA-0 and FA-10.
Author Response File: 
Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe paper describe how the mechanical properties and hydration performance change using ground granulated blast furnace slag (GGBFS) and fly ash (FA) in various contents of geopolymer paste.
The introduction describes how the materials used for geopolymer paste react according the alkali-activation and other ways that produced.
Some comments or mistakes that found are:
1. In the results (paragraph 3.1) the description write about the decreasing trend of compressive and flexural strength with the incerase of FA content. It would more preferable to describe that samples of 3d and 7d increase the strength with content of FA from 0 to 10% and then the decreasing.
The lines 330-341 describe again, as conclusion of paragraph, the same results in a better way.
2. In figure 6(d) missing a d in the legend of second peak.
3. In llines 531, 535, 536 is writing M0, M1, M2, M3, M5, M6. What are these? I suppose that are FA-0, etc., but you have to correct or explain!
4. In figure 13 is written "hate" instead of "heat" explaining in the text (line 553). It is written in legends, axis of figures and line 552.
5. In abstract and conclusions it is used the term of AAGC for the cements that contents FA and GGBFS. In the rest of manuscript it is used the term of GGBFS, That may confuse some readers. It could be used the one term "AAGC" as it is done OPC for portland cement.
Author Response
Comments1: In the results (paragraph 3.1) the description write about the decreasing trend of compressive and flexural strength with the incerase of FA content. It would more preferable to describe that samples of 3d and 7d increase the strength with content of FA from 0 to 10% and then the decreasing.
Response1:Thank you for pointing this out.We have taken your suggestion into consideration and corrected it in the revised version of this article.
Comments2: In figure 6(d) missing a d in the legend of second peak.
Response2:
Thank you for pointing this out.
I apologize for my oversight and have updated Figure 6d in the revised version of this article.
Comments3:In llines 531, 535, 536 is writing M0, M1, M2, M3, M5, M6. What are these? I suppose that are FA-0, etc., but you have to correct or explain!
Response3:
Thank you for pointing this out.I am deeply sorry for my negligence.
In the revised version of this article, all M0, M1, M2, M3, M4, M5, and M6 have been corrected to FA-0, FA-1, FA-2, FA-3, FA-4, FA-5, and FA-6.
Comments4:In figure 13 is written "hate" instead of "heat" explaining in the text (line 553). It is written in legends, axis of figures and line 552.
Response4:
Thank you for pointing this out.I apologize for my oversight.
I have changed "hate" to "heat" in the figures and paragraphs of this revised version.
Comments5:In abstract and conclusions it is used the term of AAGC for the cements that contents FA and GGBFS. In the rest of manuscript it is used the term of GGBFS, That may confuse some readers. It could be used the one term "AAGC" as it is done OPC for portland cement.
Response5:
Thank you for pointing this out.According to your comments, some changes have been made in the revised manuscript of this article, such as changing alkali-activated GGBFS cements to AAGC.
Author Response File: Author Response.pdf
