Coefficient of Thermal Expansion of RCA Concrete Made by Equivalent Mortar Volume

Round 1

Reviewer 1 Report

Author Response

Thank you so much for your valuable comments and encouragements. This manuscript has been revised in response to other reviewers’ comments. 

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript presents the results of Authors' study on the coefficient of thermal expansion of RCA concrete. Two types of such material are investigated together with a conventional one. Generally, the paper is well-written. Some minor remarks are listed below referring to a specific section.

Featured Application

Rephrase this sentence. Split it into several shorter ones. In the present form, it is unreadable.

Abstract

Shorter sentences are highly recommended to make this paragraph more readable.

Introduction

General comment to this section: can you refer to any numerical analyses carried out to predict the effective COTE of RCA concrete?

Specific remarks are listed below.

Line 14: "verify if" is suggested.

Line 22: correct "by in".

Line 47: correct "are have ended".

Line 57: is this observation of practical meaning? The concrete pavement performance is analyzed in much larger time periods than 4 hours or even 1 day.

Line 93: correct "the COTE value of mortar or RM are higher".

Experimental Program

Can you specify the age and exposure conditions of the structures used for RCA production?

Line 144: "the same source" - namely, the PC culverts?

Line 149: the abbreviation "NCA" should be explained here (instead of the line 152).

Table 1: its description presented in Section 2.2 is not complete and inconsistent. 

Line  265: "inserted" fits better than "substituted".

Line 176: "3,380" - comma is not consistent with the format used for rest of the numbers.

Experimental Tests

Line 212: specify, if the value 100 mm refers to the diameter of the cylinder base.

Test Results

Table 3: what is "cv"?

Line 262: correct to "mortar specimens.

Line 270 and the forthcoming lines: how the error is defined?

Figure 5a: the unit is not consistent with the one used in tables and in the text.

Figure 9: see my previous comment

Line 395: how "X" is practically assessed?

Figure 10: not referred to in the text + inconsistency of the unit.

The so-called composite equation used to determine the effective COTE is very simple. In the future work, I would suggest to compare the experimental results with various (possibly multiscale) numerical approaches.

Conclusions

How the findings of this study can be generalized to other RCA concrete types (i.e., using RCA from other sources / having different parameters and exposure conditions)? I find the research, in its present form, rather a kind of a case study.

Line 435: use "results" instead of "data".

Author Response

Featured Application

1)Rephrase this sentence. Split it into several shorter ones. In the present form, it is unreadable.

 → As suggested, Featured Application was rewritten as follows:

Recycled aggregate concrete is not harmful even for concrete pavement which is greatly influenced by thermal movements since the COTE of recycled aggregate concrete made by equivalent mortar volume method leads to comparable to the referenced natural aggregate concrete. "Coefficient of thermal expansion of RCA concrete prepared by the equivalent mortar volume mix design was over 6-7% lower than that of RCA concrete by conventional mix design, at the same RCA replacement ratio. And it was similar to or 1-2% lower than that of the natural coarse aggregate concrete."

Abstract

2)Shorter sentences are highly recommended to make this paragraph more readable.

→ As suggested, Abstract was rewritten with shorter sentences as follows:

"The present study was conducted to experimentally verify that if the coefficient of thermal expansion (COTE) of recycled concrete aggregate (RCA) concrete is proportional to the volume of the original virgin aggregate in the total RCA concrete mix. Three types of RCA were crushed from: (one crushed from railroad concrete sleepers; one crushed from precast (PC) culverts; and one obtained from a commercial recycling plant.) RCA concretes were mixed using two concrete mixing methods: (conventional mix method and equivalent mortar volume (EMV) method.) Aand by varying the replacement ratio, relative to that of natural coarse aggregate, which was used as a reference. The experiment was performed in three test series were made. The Test results showed that at the same RCA replacement ratio of 68%, the COTE of RCA concrete prepared by in the EMV mix design was over 6-7% lower than that of RCA concrete prepared by made with the conventional mix method., and iIt was also similar to or 1-2% lower than that of the reference natural coarse aggregate concrete. This may be because the conventional mix method does not take into account the residual mortar content attached to RCA., and thus This results in the decrease in the volumetric ratio of the original virgin aggregate decreases and a relative increase in the volumetric ratio that of the mortar (or cement paste) relatively increases."

Introduction

3)General comment to this section: can you refer to any numerical analyses carried out to predict the effective COTE of RCA concrete?

→ I know some journals for COTE numerical analysis on concrete or mortar mixed with natural coarse aggregate. I searched numerical analysis papers dealing RCA concretes by using 'ScienceDirect.com', 'MDPI Journals, ' etc. But I have not found one yet.

Specific remarks are listed below.

4)Line 14: "verify if" is suggested.

→ As suggested, 'verify that' was changed to 'verify that.’

5)Line 22: correct "by in".

→ As pointed out, 'in' was deleted.

6)Line 47: correct "are have ended".

→ As pointed out, 'are' was deleted.

7)Line 57: is this observation of practical meaning? The concrete pavement performance is analyzed in much larger time periods than 4 hours or even 1 day.

 → I entirely agreed with you. As pointed out, the following sentence was deleted. Comparison of the COTE between specimens 4 hours after their preparation and after 1 day showed that the COTE values were about 7 times different from each other and then gradually converged [9].

8)Line 93: correct "the COTE value of mortar or RM are higher".

 → As pointed out, 'are' was changed to 'is.'

Experimental Program

9)Can you specify the age and exposure conditions of the structures used for RCA production?

 → As requested, the age and expose conditions of the structures used for RCA production were described.

“It should be noted that the old railway PC sleepers were used about for 20 years, while the old PC culverts were laid out in the open area at best for a year and old concrete structures for ‘RA’ more than 20 years.“

10)Line 144: "the same source" - namely, the PC culverts?

 → As requested, the original coarse aggregate sources of old railway sleepers and PC culverts were added in the text as follows:

“The original coarse aggregate sources of the old railway sleepers and the old PC culverts were granite.”

11)Line 149: the abbreviation "NCA" should be explained here (instead of the line 152).

 → As pointed out, the abbreviation 'NCA’ was explained before.

12)Table 1: its description presented in Section 2.2 is not complete and inconsistent. 

“Table 1 shows the specific gravity, and water absorption and residual mortar content (RMC) of fine aggregate in 3 types of RCA and, 2 types of natural coarse aggregate (NCA)., and 2 types of fine aggregate. The specific gravity and the water absorption of the RR produced from concrete sleepers were 2.48 and 4.53%, respectively, and those of the RP, produced from concrete culvert, were 2.60 and 2.62%, respectively, and those of the RA, produced from a plant, were 2.52 and 3.82%, respectively.

Crushed granite was used as natural coarse aggregate (NCA); its specific gravity and water absorption were 2.65 and 0.70%, respectively, in test series 1, and 2.60 and 0.95%, respectively, in test series 2. River sand was used as fine aggregate; its specific gravity and water absorption were 2.56, 2.60 and 1.10, 0.95 respectively for fine aggregate 1 and fine aggregate 2. Table 2 provides details of the test series.“

13)Line 265: "inserted" fits better than "substituted".

 → As suggested, 'substituted' was changed to 'inserted.'

14)Line 176: "3,380" - comma is not consistent with the format used for rest of the numbers.

  → As suggested, '3,380' was changed to '3380' without comma.

Experimental Tests

15)Line 212: specify, if the value 100 mm refers to the diameter of the cylinder base.

→ As suggested, a base diameter 100 mm was specified with a height 200 mm.

”100x200 mm a base diameter of 100 mm and a height of 200 mm.”

Test Results

16)Table 3: what is "cv"?

 → As pointed out, 'cv' was changed to 'Coefficient of Variation.'

17)Line 262: correct to "mortar specimens.

 → As suggested, 'mortars specimens' was changed to 'mortar specimens.'

18)Line 270 and the forthcoming lines: how the error is defined?

→ As pointed out, the description on error bar graph was modified. In the error bar graph, (the maximum value minus the mean value) as well as (the minimum value minus the mean value) is represented by the errors in each data group.

“The error bar graph in Figure 5(a) represents the mean values of the individual specimens with the errors.“

19)Figure 5a: the unit is not consistent with the one used in tables and in the text.

→ As suggested, the unit of the COTE’ value was consistently represented by '10^-6 /' in figures, tables and in the text.

20)Figure 9: see my previous comment

→ As requested, the unit of the COTE’ value was consistently represented by '10^-6 /' in figures.

21)Line 395: how "X" is practically assessed?

→ I found a research paper which deals with the composite equation for the concrete COTE, where the value of X was suggested as follows:

 “The value of 0.4 was used in this study based on the numerous experiences in the CoTE testing and analysis performed by the authors.“

15. Jeong, D. Zollinger, J. Lim, J. Park, Age and Moisture Effects on Thermal Expansion of Concrete Pavement Slabs, Journal of Materials in Civil Engineering, ASCE, 2012, pp. 8-15.

22)Figure 10: not referred to in the text + inconsistency of the unit.

→ As requested, comments on Figure 10 were provided in the text and the unit of the COTE’ value was consistently represented by '10^-6 /' in Figure 10.

“Figures 10(a) and 10(c) show that the predicted COTE values fit well to the measured COTE values with determination coefficient of 0.85 and 0.86, respectively by linear relationships in Mix 1 and Mix 3. However, the determination coefficient was lower in mix series 2 than in mix series 1 or 3, because RCA replacement ratios were 33% and 68% in mix series 1 and 25% and 50% in mix series 2. As a result, the distribution of the total coarse aggregate ratio, represented by the x-axis of the plot shown in Figure 9, is closer among the specimens in mix series 2 than in mix series 1. Although the measured COTEs and the predicted COTEs are slightly different, the coefficient of determination (R²) was the same as the value obtained in the procedure described in 2) above.“

23)The so-called composite equation used to determine the effective COTE is very simple. In the future work, I would suggest to compare the experimental results with various (possibly multiscale) numerical approaches.

 → Thank you for your suggestions. I will definitely consider reviewer’s valuable comments.

Conclusions

24)How the findings of this study can be generalized to other RCA concrete types (i.e., using RCA from other sources / having different parameters and exposure conditions)? I find the research, in its present form, rather a kind of a case study.

→ As suggested, Reviewer’s comments were added in Conclusions for future works as follows:

“It should be noted that because of limited test variables and test numbers in this study, further study is needed for the findings of this study to be generalized to other RCA concrete types (i.e., using RCA from other sources, or having different parameters and exposure conditions).“

25)Line 435: use "results" instead of "data".

 → As suggested, data' was changed to results.'

Author Response File: Author Response.docx

Reviewer 3 Report

Dear authors,
Thank you very much for this practical and useful scientific article on the preparation and evaluation of RCA concrete mixes.

The article is prepared quite well, but several things need to be added and improved.

The title and abstract are well written.

The introductory paragraph contains a lot of valuable basic information, but it lacks a broader overview and justification - even if you are talking about global warming and the impact of this on concrete, it is necessary to add some information related to the sustainability of recycled and new concrete, etc. For example by:
10.1016 / j.gete.2021.100253
10.3390 / app11114964
10.1016 / j.jclepro.2021.126129

The hypotheses and justifications are well written.

I would appreciate a broader and more detailed description of the aggregate preparation - the type of crushing used, etc.

The description of the applied test is austere but probably sufficient - it could be enough for an attentive reader.

I appreciate the description of mixtures - you should add a specific name and manufacturer of admixtures.

Please explain the different W / C - respectively, what is your opinion on influencing the results in terms of W / C?

The description of the COTE measurement is sufficient.

337 and 384 contain incorrect numbering.

It can be seen in Figures 9 and 10 that the regression will not be linear but logarithmic, exponential or quadratic.
You describe the correlation, but in the pictures, you have a linear regression and evaluation of the coefficient of determination - if you want to prove the correlation, use one of the known methods. Please note here - R2 is not a correlation coefficient.

Line 407 contains the word "table" but you mean "figure".

The conclusions are consistent with your findings but pay attention to the evaluation of correlation (regression), etc. I recommend studying this information more.

comment:
- make figures 1, 9, 10 larger,
- the tables and formatting of the article will need to be modified so that they are not split into two pages,

Regards,

Author Response

1)The introductory paragraph contains a lot of valuable basic information, but it lacks a broader overview and justification - even if you are talking about global warming and the impact of this on concrete, it is necessary to add some information related to the sustainability of recycled and new concrete, etc. For example by:
10.1016 / j.gete.2021.100253
10.3390 / app11114964
10.1016 / j.jclepro.2021.126129

 → As requested, one more paragraph was added in 1. Introduction which is related to the sustainability of recycled and new concrete as follows: And 3 references were added.

“In other aspect, global warming problems led some researchers to consider sustainability including environmental benefits and innovative new materials and construction methods incorporating various other eco-friendly supplementary cementitious materials [7-9]. Heat energy was harvested from geothermal pavement constructed with construction and demolition waste materials [7]. The solar radiation can be absorbed by placing pipes in the pavement systems and circulating water in the pipes to collect the heat energy, to maximize the sustainability and energy efficiency of the infrastructures [7]. Feasibility of using demolished concrete block (DCB) was explored in a continued effort of material recycling [8]. The DCBs were used with self-compacting concrete (SCC) to produce DCB-filled-concrete since SCC can easily fill up the voids between DCBs. In addition to the traditional material testing properties such as mechanical strength and durability properties, the importance of the sustainability indicator which is a function of strength, resilience, ecology and economy has been emphasized [9].”

7. Arulrajah, A.; Ghorbani, B.; Narsilio, G.; Horpibulsuk, S.; Leong, M. Thermal performance of geothermal pavements constructed with demolition wastes, Geomechanics for Energy and the Environment, 2021, 28, 100253, 1-11.
8. Li, J.; Zhang, J.; Ni, S.; Liu, L.; Walubita, L. Mechanical performance and environmental impacts of self-compacting concrete with recycled demolished concrete blocks, J. Clean. Prod., 2021, 293, 126129, 1-13.
9. Hraboa, K.; Lehner, P.; Ghosh, P.; Konecny, P.; Teply, B. Sustainability levels in comparison with mechanical properties and durability of pumice high-performance concrete, Appl. Sci., 2021, 11, 4964, 1-13.

2)I would appreciate a broader and more detailed description of the aggregate preparation - the type of crushing used, etc.

 → As requested, detailed description of the aggregate preparation was provided as follows:

“Old concrete structures were crushed using a hydraulic breaker, and foreign materials such as rail pads and wires in the railway PC sleepers and reinforcing rebars in the PC culverts and other structures were collected by separation. Ton bags of initially crushed RCA were then transported to the recycling plant and treated by four, six, and three additional crushing process steps (combinations of jaw crusher and impact crusher) for 'RR', 'RP', 'RA,' respectively. Finally, RCA products were obtained.”

3)The description of the applied test is austere but probably sufficient - it could be enough for an attentive reader. I appreciate the description of mixtures - you should add a specific name and manufacturer of admixtures.

 → As pointed out, the specific name and manufacturer were given for the chemical admixtures.

“The chemical admixture used in the present experiment was an a polycarboxylate-based air-entraining agent and a water-reducing agent from a S. Korean vendor (Econex Co.).”

4)Please explain the different W / C - respectively, what is your opinion on influencing the results in terms of W / C?

→ Mix 1 and Mix 2 are typical concrete mix designs adopted in the industry targeted for manufacturing railway PC sleepers and PC culverts, respectively. The w/c ratio for mix 1 is 0.39 and the w/c ratio for mix 2 is 0.36. Literature reviews (fourth paragraph in 1. Introduction in our paper) reveal that the COTE of concrete is dependent on the concrete mixes, ages, humidity conditions, temperature cycles and types of aggregate. Especially in concrete mix designs, the COTE of concrete is affected by volume of paste or volume of aggregate. With a limited study, our authors hesitate to say that the COTE is slightly influenced by different w/c ratios.

5) 337 and 384 contain incorrect numbering.

 → As pointed out, subtitle numbers '2)' and '3)' was changed to '1)' and '2)', respectively.

6)It can be seen in Figures 9 and 10 that the regression will not be linear but logarithmic, exponential or quadratic. You describe the correlation, but in the pictures, you have a linear regression and evaluation of the coefficient of determination - if you want to prove the correlation, use one of the known methods. Please note here - R2 is not a correlation coefficient.

7)Line 407 contains the word "table" but you mean "figure".

 → As pointed out, 'Table' was changed to 'Fig.'

8)The conclusions are consistent with your findings but pay attention to the evaluation of correlation (regression), etc. I recommend studying this information more.

 → As pointed out, in Conclusions, one more concluding remark was added and 'correlation' was changed to 'determination' as follows:

(3) The COTE of RCA concrete is represented in terms of the volumetric ratio of coarse aggregate of the individual mixes by the best fit quadratic curves. However, further study is needed to verify if the COTE value of concrete is linear or nonlinear to the volume ratio of total coarse aggregate.

(3) (4) Finally, the predicted COTE obtained by applying the composite series model was slightly higher than the measured COTE, but the correlation determination coefficient was higher than usual, indicating that experimental results obtained in this study are reliable. 

9)comment: make figures 1, 9, 10 larger.

 → As requested, figures 1, 9, 10 were made larger.

10) comment: the tables and formatting of the article will need to be modified so that they are not split into two pages.

 → As requested, tables and figures were rearranged not to be placed into two pages.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

Dear authors,
thank you for the detailed answers and responses.
Your edits have taken the article to the next level.
I can't deal with some things, but I accept your opinion.
Regards