Suitability of Clinker Replacement by a Calcined Common Clay in Self-Consolidating Mortar—Impact on Rheology and Early Age Properties

Round 1

Reviewer 1 Report

The manuscript is about the use of calcined clay in replacement of clinker.
In general, the structure of the manuscript is well organized, the methods are well described, and the procedures are well conducted. The results sound and the conclusions are based on the experimental data.
Comments on the manuscript:
A list of acronyms/abbreviations is needed.
Give the reference for the chemical composition of the raw materials in Tab.1. The total amount of oxides do not sum 100%.
Give references for the characterization shown in Tab.2 and Fig.1. Otherwise, give the techniques, methods, equipment, and procedures for all characterizations.
l.204: I believe that alumina crucibles were used, not aluminum ones.
l.219: The equipment and loading rate should be given for the compressive strength test.
Fig.2: Error bars are missing. The same for all figures. Statistical analysis!

Author Response

Thank you very much for your fruitful and pertinent comments on our manuscript. Please find below the answers to the comments.

A list of acronyms/abbreviations is needed. Thanks for the suggestion. Since the text is not that long and most abbreviations are commonly used in other papers we preferred to introduce all acronyms used were they occur the first time in the text.
Give the reference for the chemical composition of the raw materials in Tab.1. The total amount of oxides do not sum 100%. Thanks for your comment. References were added where available. The chemical composition was provided by the supplier. The composition of CC was re-evaluated and the missing quantity to sum up to 100 % belongs to elements which cannot be measured by the methods used. The deviation is within the range reported by other researchers.
Give references for the characterization shown in Tab.2 and Fig.1. Otherwise, give the techniques, methods, equipment, and procedures for all characterizations. References were added.
l.204: I believe that alumina crucibles were used, not aluminum ones. Corrected.
l.219: The equipment and loading rate should be given for the compressive strength test. The information was added.
Fig.2: Error bars are missing. The same for all figures. Statistical analysis! This was added to the graphs where applicable. However, a statistical analysis yielding more than the mean value (which is provided) is not meaningful with three repetitions according to the authors’ opinion.

Reviewer 2 Report

The study presents some interesting results on the clay calcined at 750 °C as a 40 % substitution of clinker in self consolidating mortar. The study is nicely written, contains a great portion of useful results and presents a great work done. However, there are some points possible to improve, as follows.

1. The last paragraph in the Introduction section should contain the short review of what is done in this study, what is novel compared to the previous publications, and which are the main conclusions.
2. In Table 1, use OPC rather than “cement”. Also, change “CaO2” to “CaO”.
3. Materials and methods section is supposed to present all the methodologies implemented to test the products, experimental conditions and instrumentation. Also, provide references for the standardized tests.
4. Please discuss in which way the large portion of the amorphous phase from calcined clay helps self-consolidation? Why is this clay called “common”? It is intentionally produced to contained high amount of amorphous matter, which is not common for other applications of clay.
5. Some lines need to be deleted, such as 111-112, 196-197, 239, but there is more.
6. Please revise particle size distribution of the fine aggregate. Is the X axis supposed to be in mm?
7. The title of the section 3.1. is suggested to be “Flow behavior of the studied binders”.
8. The calcined clays are studied and patented before; the novelty of this work is not clear. Possibly, the results from other studies should be more intensively compared to this one.

Author Response

Thanks for your nice words. You will find our response below.

1. The last paragraph in the Introduction section should contain the short review of what is done in this study, what is novel compared to the previous publications, and which are the main conclusions. Done.
2. In Table 1, use OPC rather than “cement”. Also, change “CaO2” to “CaO”. Corrected.
3. Materials and methods section is supposed to present all the methodologies implemented to test the products, experimental conditions and instrumentation. Also, provide references for the standardized tests. References were added.
4. Please discuss in which way the large portion of the amorphous phase from calcined clay helps self-consolidation? Why is this clay called “common”? It is intentionally produced to contained high amount of amorphous matter, which is not common for other applications of clay. The amorphous content of the calcined clay affects less the workability, but plays a major role with respect to the reactivity. Thus it is intended to achieve a high amount of amorphous content and avoid the formation of new crystalline phases as it would be intended in brick or tile production. Workability is affected mainly by the specific surface area and, particle shape. The designation “common clay” is used by several researches indication a natural clay mix containing various constituents (e.g. kaolinite, illite, quartz, mica, hematite…) which are common in natural clays.
5. Some lines need to be deleted, such as 111-112, 196-197, 239, but there is more. Removed.
6. Please revise particle size distribution of the fine aggregate. Is the X axis supposed to be in mm? The particle size distribution graph was checked.
7. The title of the section 3.1. is suggested to be “Flow behavior of the studied binders”. Corrected.
8. The calcined clays are studied and patented before; the novelty of this work is not clear. Possibly, the results from other studies should be more intensively compared to this one. You are right that calcined clays are well-studied. The patents we are aware of are related to production techniques. The focus of our paper is not on the calcined clay itself, but on the use of low-grade kaolinitic clay in self-compacting concrete at high substitution levels. We are well aware of the existing literature in the field of calcined clays and their application.

Reviewer 3 Report

This paper describes mix designs of self-consolidating mortars based on OPC clinker and a common, low kaolin calcined clay. Its rheological, hydration and mechanical properties are comprehensively described. The paper is structured very clearly, the methods are presented in a way that all experiments could re repeated, the conclusions are sound and extensive literature is included which confirms the overall competence of the authors. I enjoyed reading this excellent paper and have only a few remarks to bring the manuscript into a printable form:

1. Apparently, the superplasticizer (I assume it was a PCE) is of paramount importance to achieve self-consolidating properties, but no information at all is provided. Please, specify the product name, chemical identity, solid content of the liquid, manufacturer / supplier etc. Authors should expressly state that all results reported here are specific for this very SP, and that other SPs may produce different results e.g. on dosage hike, impact on hydration etc.
2. Table 1 shows oxide compositions, not chemical compositions. Chemical composition would be C₃S, C₂S, C₃A …etc. contents. Please clarify.
3. Fig. 2: Do you have any explanation for the non-linear increase, especially from 30 to 40 % substitution ratio? One would expect a linear relationship here.
4. Table 4: provide range of SP addition to different systems.
5. Can you explain why the specific pore volume reverses from 20 % replacement (decrease by 4 %) to 40 % replacement (increase by 18 %)? This result is surprising.
6. Did you measure the air content in the fresh mortars? Consider that PCEs often introduce air, especially at the elevated dosages which you have used, unless a defoamer is used. Did your PCE contain a defoamer?

Once all points are clarified the paper can be considered for publication.

Author Response

Thanks for your nice words. You will find our response to your remarks below.

1. Apparently, the superplasticizer (I assume it was a PCE) is of paramount importance to achieve self-consolidating properties, but no information at all is provided. Please, specify the product name, chemical identity, solid content of the liquid, manufacturer / supplier etc. Authors should expressly state that all results reported here are specific for this very SP, and that other SPs may produce different results e.g. on dosage hike, impact on hydration etc. Done and the information was added.
2. Table 1 shows oxide compositions, not chemical compositions. Chemical composition would be C₃S, C₂S, C₃A …etc. contents. Please clarify. Corrected
3. Fig. 2: Do you have any explanation for the non-linear increase, especially from 30 to 40 % substitution ratio? One would expect a linear relationship here. You are right that there should be a linear relationship, especially as the water demand of the binder increases linear as well. However, it is assumed that beside the established parameters of the CC itself, such as water demand, BET specific surface area and particle size, the packing density is significantly altered with increasing proportions of CC. In previous investigations, we saw sometimes non linear trends as well.
4. Table 4: provide range of SP addition to different systems. Done.
5. Can you explain why the specific pore volume reverses from 20 % replacement (decrease by 4 %) to 40 % replacement (increase by 18 %)? This result is surprising. The decrease at 20 % replacement level is assumed to be within the deviation range of MIP measurements and hence the reference (0 % CC) and 20 % CC have a comparable total, accessible porosity. Further, total porosity increases, while pore size refinement occurs with higher proportions of calcined clays, as stated e.g. by Beuntner [1] or Tironi et al. [2].
6. Did you measure the air content in the fresh mortars? Consider that PCEs often introduce air, especially at the elevated dosages which you have used, unless a defoamer is used. Did your PCE contain a defoamer? Thanks for this question! This could be an interesting information but it was not measured. The supplier of the PCE did not mention if it contains a defoamer. However, we didn’t notice any “bubbles” on the surface while producing the mortar.

1. Beuntner, N., Zur Eignung und Wirkungsweise calcinierter Tone als reaktive Bindemittelkomponente in Zement (On the suitability and mode of action of calcined clays as reactive binder components in cement), in Fakultät für Bauingenieurwesen und Umweltwissenschaften. 2017, Universität der Bundeswehr München: Neubiberg. p. 207.
2. Tironi, A., C.C. Castellano, V.L. Bonavetti, M.A. Trezza, A.N. Scian, and E.F. Irassar, Kaolinitic calcined clays – Portland cement system: Hydration and properties. Construction and Building Materials, 2014. 64: p. 215-221.