Evaluation of Concrete Strength Made with Recycled Aggregate

Round 1

Reviewer 1 Report

The article presents the results of investigations of parameters of High Strength Concrete made on recycled aggregates (RA). To make concrete mixes conventional additives such as fly ash and micro silica were also used. This manuscript analyzes properties of concretes such as: compressive strength, tensile strength, modulus of elasticity and rapid chloride permeability.

In general, the quality of the paper is totally satisfied with requirement of the journal. However, it is recommended that the paper be revised before publication. The specific amendments are as follows:

(1) Fly ash and micro silica are important modifiers of the cementitious matrix. Therefore, the keyword section should be supplemented with these 2 terms.

(2) The article presents the results of tests of HSC concretes, whose composition is modified both in the area of the aggregates and the matrix. Therefore, Introduction section should be devided into 2 parts. The first part should cover issues concerning the use of recycle aggregates in concretes, whereas the second part should contain information on the use of the binder substitutes in composites.

The article presents the results of testing HSC concretes made with addition two of the many Supplementary cementitious materials (SCMs). Therefore, in the Introduction section of the article, it would be necessary to characterize and discuss all groups of SCMs used as substitutes for concrete. For this purpose, one can use a quotation of an article in which all these materials are divided into special groups:

 

“An assessment of microcracks in the Interfacial Transition Zone of durable concrete composites with fly ash additives”, Composite Structures, 2018.

(3) Please provide more details of experimental program. There is a need to provide the photo of the specimen during fabrication and mixing. These information are needed for other researchers to repeat and validate the study in the future.

(4) It would also be useful to show pictures of the RA, used for the studies.

(5) Please explain exactly why the same amount of micro silica and the variable amount of fly ash was used. The addition of fly ash has a significant impact on the concrete parameters. In order to accurately estimate the impact of the applied RA, a better solution would be to select the same amount of fly ash addition in all mixtures.

(6) Figures: 2,3,4,6,7,9 with results of investigations should contain error bars. This will allow to evaluate the convergence of test results.

(7) It should be noted that use of the RA in concrete and substitution of cement in the composites with other materials is part of the concept of sustainable concrete, or otherwise, green concrete. This topic has already been the subject of publication in the journals from MDPI Database and in other journals.

 It is therefore required that the authors comment on the results of previous papers. In the Introduction section, the following articles should be discussed and cited:

 

“Generalized fracture toughness and compressive strength of sustainable concrete including low calcium fly ash”, Materials, 2017.

 

“Green concrete composite incorporating fly ash with high strength and fracture toughness”, Journal of Cleaner Production, 2018.

Author Response

Dear Reviewer,

Greetings !

We value your time and comments on our paper, it has significantly improved our paper. Thank you very much. 

Almost all your comments have been answered and implemented in the new version of the paper. 

Please note that we have answered all reviewer's comments in one single document that is attached. 

It showed the details of the comments received from each reviewer and how they were addressed. 

Thanks again !

Kind regards,

Adil Tamimi,

Professor of Civil Engineering

The American University of Sharjah

Dubai, UAE. 

Author Response File: Author Response.docx

Reviewer 2 Report

This paper presents an experimental investigation of the production and evaluation of high strength recycled concrete. The following comments are suggested:

1.    The authors should cite more recent publications in their literature review.

2.    Although the academic definition of high-strength concrete is inconsistent, what is the definition of strength concrete in this study? The author should clearly explain.

3.   The length of the first chapter should be moderately reduced.

4.  Although the concrete mix design has been added with a superplasticizer, it can be seen from Table 3 that the slump of the poured concrete is only about 5 cm. What is the reason?

5. The fresh properties of concrete are listed in Table 3, so Figures 2-4 are redundant and can be omitted.

6.  At 7 days of age, RA20 should have the highest compressive strength due to its lowest fly ash content. However, the test results show that the compressive strength of RA50 is large. The author should provide more explanation for this.

7.   At 28 days of age, RA50 has the highest compressive strength and splitting strength, but its elastic modulus is the lowest. Authors should give more explanations for this.

8.   At 56 days of age, RA80 has the highest compressive strength, and because of its highest fly ash content. Is there a 56-day test result in terms of splitting strength and elastic modulus?

9.   In Figure 8, the Equations (2)-(4) listed should be corrected to Equations (1)-(3).

10.  In lines 315-316: “Comparison of the modulus of elasticity values with the predicted equations are illustrated in Figure 8 and Table 4, all results are represented as GPa.”. However, there is no Table 4 in the article. Authors should give more explanations for this.

11.  The abbreviation for a phrase should be defined at its first appearance and thus it can be used throughout the text and tables.

12.   Reference should follow the style of this journal.

Author Response

Dear reviewer,

Greetings from the American University of Sharjah, Dubai, UAE.

 

We would like to thank you for your time and valued comments on our paper. It has significantly enhanced our paper. Thank you very much.

Almost all comments have been addressed in the attached document. It includes answers to all reviewer’s comments in details.

 

Thanks again.

 

Kind regards,

 

Adil Tamimi

Professor of Civil Engineering

American University of Sharjah

Dubai, UAE

Author Response File: Author Response.docx

Reviewer 3 Report

The reviewed article deals with important and current issues - the use of recycled materials for concrete. The object of interest is the use of recycled aggregates as a substitute for natural aggregate for HPC concretes. Topic is interesting but the article in its present form does not bring much new to it. Most important critical remarks:

 

·         The title does not reflect the content of the article well

·         The introduction contains a lot of detailed literature information, but without any attempt to synthesize and analyze it. As a consequence, the purpose and significance of the research undertaken are unclear (the purpose of the research in the introduction and the conclusions are different). What new information of a general nature was intended to be obtained (and obtained)?

·         The scope of the research is very narrow and does not allow for generalization. Any generalization makes it difficult to change the amount of RA aggregate and fly ash FA simultaneously. The authors pay a lot of attention to the number of samples tested. However, it should be remembered that only four concretes were tested.·         Characteristics of the materials is not complete: no information about the properties and origin of OPC, FA, CSF and natural aggregate. Lack of information on the method of obtaining (production) of RA aggregates and comparison of properties RA with natural aggregate.·         The obtained test results are given with too high accuracy. Authors really are able to measure the slump with an accuracy of 0.1 mm?·         Confusing results were obtained, in eg: the introduction of RA and the simultaneous change in the cement and FA content in mix do not affect the consistency, for such low w / c concretes are characterized by low strength·         The discussion of the results is usually carried out in terms of the amount of RA, although in the research the amount of FA and cement is significantly changed, which seems to have an at least equally significant impact on the tested properties. Numerous publications are referred to in the discussion of results, but without any deeper attempt to synthesize and analyze in the context of own research results.·         Authors conclude: „Recycled aggregate concrete is a good solution to reduce waste concrete ruble” this is not a conclusion from the research, but a fact known universally (although you can discuss the details),·         Authors conclude: “There is improvement in the workability of concrete made with recycled aggregate.” From the presented research results it does not follow·         Authors conclude: “The compressive strength of concrete made with 80% recycled aggregate showed high compressive strength of 60 MPa at 28 days and 77 MPa at 56 days - OK and the results of this is…?·         Authors conclude: “The pozzolans were highly effective in resisting the chloride ions. It reduced the  permeability of the concrete with recycled aggregate” - this effect of pozzolans is well known and, as the Authors have previously noticed, is not associated with the presence of RA (effect of RA is main topic of research). Authors did not tested permeability, thus the conclusion is not from the research.·         Authors conclude: “Based on the experimental results, concrete with 80% of recycled aggregate produced good  results and can be used in the construction projects” - it is a bold statement on such narrow research. How does this relate to the current state of knowledge? To standards and other reference documents? Is this conclusion general or does it only apply to investigated RA and concrete?·         Authors conclude: “Based on the experimental results, concrete with 80% of recycled aggregate produced good  results and can be used in the construction projects” - it is a bold statement on such narrow research. How does this relate to the current state of knowledge? To standards and other reference documents? Is this conclusion general or does it only apply to investigated RA and concrete?

 

The presented research covers a very narrow scope, they concern specific materials with properties not described by the authors. Research has been incorrectly planned in a way that makes it impossible to clearly determine the effects of RA. Research does not contribute much to the current state of knowledge. Therefore, I do not recommend the article for publication in an international journal.

Author Response

Dear reviewer,

Greetings from the American University of Sharjah, Dubai, UAE.

 

We would like to thank you for your time and valued comments on our paper. It has significantly enhanced our paper. Thank you very much.

Almost all comments have been addressed in the attached document. It includes answers to all reviewer’s comments in details.

 

Thanks again.

 

Kind regards,

 

Adil Tamimi

Professor of Civil Engineering

American University of Sharjah

Dubai, UAE

Author Response File: Author Response.docx

Reviewer 4 Report

The manuscript presents an experimental work aimed at fresh and hardened properties of the concrete containing recycled aggregate. No theoretical or numerical approach is proposed to check the experimental results. There are following questions:

1.      In the full text, the standard format should be written consistently. Ex. ASTM C231-10 or ASTM C231.

2.      Please describe the physical properties of fine aggregate.

3.      The fresh properties of RA concrete should be discussed in depth.

4.      What is the blending ratio of RA1 and RA2? Does the gradation comply with the relevant specifications?

5.      In Fig.4, Vertical coordinate unit is incorrect.

6.      In Fig.8, the legend is incorrect.

7.      Los angles abrasion of RA is as high as 77%, why can the compressive strength of 80% RA concrete be as high as 60 MPa? Is it only the pozzolanic reaction of fly ash? Please explain the mechanism.

8.      Why is the elastic modulus of RA50 different from the prediction formula?

9.      Conclusion 2, from the data, I don't think RA concrete has good workability.

Author Response

Dear reviewer,

Greetings from the American University of Sharjah, Dubai, UAE.

 

We would like to thank you for your time and valued comments on our paper. It has significantly enhanced our paper. Thank you very much.

Almost all comments have been addressed in the attached document. It includes answers to all reviewer’s comments in details.

 

Thanks again.

 

Kind regards,

 

Adil Tamimi

Professor of Civil Engineering

American University of Sharjah

Dubai, UAE

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have revised the manuscript obeying the review comments.

The manuscript can be accepted. 

Reviewer 2 Report

Overall, the paper has been revised in accordance with the reviewer’s comments.

 

Reviewer 3 Report

The authors partially took into account my previous remarks, especially regarding the conclusions. However, in my opinion the main problem is the narrow scope of research and the lack of new knowlege on influent of material farctors on the properties of concrete. The authors also did not refer to other comments in the text. The authors must clearly indicate what is new in their research, and demonstrate that tests performed to such extent entitle to be of a general nature.

Reviewer 4 Report

The previous comments from this reviewer were carefully considered and nicely addressed, therefore, this reviewer has no further comments.