Bond to Bar Reinforcement of PET-Modified Concrete Containing Natural or Recycled Coarse Aggregates

Round 1

Reviewer 1 Report

This paper presents a comparison test study on the performance of polyethylene terephthalate (PET) wastes-modified concrete between using natural and recycled coarse aggregates. The research findings are helpful and significant to improve the recycling of post-consumed plastics. The overall work is good and well-written. Some suggestions are given as below,

(i) PET-wastes are added between 0 and 4.5%. Please explain the consideration for this selection.

(ii) The critical parallel test data is recommended to list, and some tables are better illustrated in Figures for increasing readability of test results.

(iii) From Figure 8, the R2 is 0.52, which is difficult to say ‘higher slips 411 are associated with mixtures exhibiting higher bond stresses’. Please check it.

(iv) From the materials, the shredded pieces had irregular shapes with varying sizes between 1 to 6 mm, which could significantly increase the variability of test results due to the change of the shredded piece size even still controlled between 1 and 6 mm. Please explain it to make this research repeatable.

(v) The title of Table 1 has been duplicated. Please check the language mistakes and all expressions to meet the requirements of academic writing.

Author Response

Bond to bar reinforcement of PET-modified concrete containing natural or recycled coarse aggregates

Joseph J. Assaad, Jamal Khatib, and Rawan Ghanem

The authors would like to thank the reviewers for taking the time and read the submitted manuscript, while providing valuable comments and suggestions to enhance its quality. Below are the authors reply to various queries, point-by-point:

Reviewer #1:

This paper presents a comparison test study on the performance of polyethylene terephthalate (PET) wastes-modified concrete between using natural and recycled coarse aggregates. The research findings are helpful and significant to improve the recycling of post-consumed plastics. The overall work is good and well-written. Some suggestions are given as below,

(i) PET-wastes are added between 0 and 4.5%. Please explain the consideration for this selection.

Thanks for the comment. In fact, the preliminary test results have shown that additional PET dosages exceeding 4.5% will lead to dramatic drop in the concrete strength, which would be very difficult/impossible to compensate such drop by reducing w/c or adding fibers or polymers. This is why and how the 4.5% rate was chosen. This information was added in the revised version, in lines 157-158.

(ii) The critical parallel test data is recommended to list, and some tables are better illustrated in Figures for increasing readability of test results.

Indeed, the authors did particular attention to run several parallel tests to evaluate the repeatability of data. In this context, the 3% PET-modified concrete was tested 3 to 5 times, as noted in lines 233-235.

(iii) From Figure 8, the R2 is 0.52, which is difficult to say ‘higher slips 411 are associated with mixtures exhibiting higher bond stresses’. Please check it.

Thanks for the remark. The sentence was re-written to read: “Moderate relationship with R² of 0.52 exists between  and slip at failure (Fig. 8); hence, mixtures possessing higher bond strengths exhibited higher slips at failure.” Please, refer to lines 358-359.

(iv) From the materials, the shredded pieces had irregular shapes with varying sizes between 1 to 6 mm, which could significantly increase the variability of test results due to the change of the shredded piece size even still controlled between 1 and 6 mm. Please explain it to make this research repeatable.

The authors fully agree with the reviewer. The following sentence was added when assessing the repeatability of tests, in lines 240-242. “Additionally, the shredded PET pieces had irregular shapes with varying sizes between 1 to 6 mm, which could significantly increase the variability of test results.”

(v) The title of Table 1 has been duplicated. Please check the language mistakes and all expressions to meet the requirements of academic writing.

The title of Table 1 was adjusted, while the paper was double-checked for English writing. Thanks a lot for the useful comments.

Author Response File: Author Response.docx

Reviewer 2 Report

This article aimed to assess the bond performance of mixtures containing polyethylene terephthalate (PET) additions. Two concrete series prepared with natural coarse aggregate (NCA) or 100% recycled concrete aggregate (RCA) replacement were investigated, with PET wastes added between 0% and 4.5% by volume. The paper is interesting and useful for the practicing engineers. The following comments are suggested:

1. This study planed two series of concrete, one was to use natural aggregates, and the other was to use 100% recycled aggregates. In the two series of concrete, different volume percentages of PET were added. RCA was used to NCA. It can be seen from Table 1 that the number of aggregates of the two series of concrete was different. Please explain the purpose of adding PET.
2. This study considered three methods (ie, w/c reduction and adding SBR or SF) to reduce the impact of PET on concrete properties. Are these methods feasible in actual engineering applications?
3. On page 4, the title of Table 1 appears twice, please correct it.
4. The elastic modulus (E) of concrete was derived by UPV using the conventional equation of wave propagation in solid rock. How accurate is it?
5. The length of the embedded steel bar in the direct bond testing specimen of this study was 50 mm (that is, 5 times the diameter of the steel bar). Please explain the reason.
6. The effect of adding PET on the mechanical properties of the two series of concrete should be drawn on the same graph to facilitate the comparison of their differences.
7. The effect of adding PET on the sorptivity of the two series of concrete should be drawn on the same graph to facilitate the comparison of their differences.
8. The variations in drying shrinkage of the two series of concrete should be drawn on the same graph to facilitate the comparison of their differences.

Author Response

Bond to bar reinforcement of PET-modified concrete containing natural or recycled coarse aggregates

Joseph J. Assaad, Jamal Khatib, and Rawan Ghanem

The authors would like to thank the reviewers for taking the time and read the submitted manuscript, while providing valuable comments and suggestions to enhance its quality. Below are the authors reply to various queries, point-by-point:

Reviewer #2:

This article aimed to assess the bond performance of mixtures containing polyethylene terephthalate (PET) additions. Two concrete series prepared with natural coarse aggregate (NCA) or 100% recycled concrete aggregate (RCA) replacement were investigated, with PET wastes added between 0% and 4.5% by volume. The paper is interesting and useful for the practicing engineers. The following comments are suggested:

Thanks for the positive feedback.

1. This study planed two series of concrete, one was to use natural aggregates, and the other was to use 100% recycled aggregates. In the two series of concrete, different volume percentages of PET were added. RCA was used to NCA. It can be seen from Table 1 that the number of aggregates of the two series of concrete was different. Please explain the purpose of adding PET.

Thanks for the question. In fact, the specific gravity of the natural aggregates vs. recycled aggregates is different, thus the concrete proportions were adjusted to maintain a relative yield of 1.0. Also, the control mix was made without PET, whereby the fine and coarse aggregates were slightly increased to compensate for the presence of PET. Please, refer to lines 122-124 and lines 130-131.

2. This study considered three methods (ie, w/c reduction and adding SBR or SF) to reduce the impact of PET on concrete properties. Are these methods feasible in actual engineering applications?

Sure, the authors selected those 3 methods to compensate the drop in strength due to PET additions, as these are feasible in practice. For example, reducing w/c is the least expensive, however, this approach considerably increased the mixture cohesiveness, which could alter pumpability and casting procedures on site (Please, refer to lines 162-166). From the other hand, the addition of fibers and polymers is very common for structural applications, as noted in lines 167-172.

3. On page 4, the title of Table 1 appears twice, please correct it.

Ok, thanks. Done

4. The elastic modulus (E) of concrete was derived by UPV using the conventional equation of wave propagation in solid rock. How accurate is it?

Thanks for the comment. Indeed, the E value was deducted from the UPV measurement, which in its turn, was measured as per ASTM C597 test method. This later standard is commonly used in the industry to deduct the E values. It is worth noting from the repeatability tests have shown that the COV of UPV values varied within 8.5%, reflecting acceptable repeatability (especially since the E is deducted using the same equation).

5. The length of the embedded steel bar in the direct bond testing specimen of this study was 50 mm (that is, 5 times the diameter of the steel bar). Please explain the reason.

The embedded length of 5 times d_b is based on the RILEM/CEB/FIB recommendations, as noted in line 215-218.

6. The effect of adding PET on the mechanical properties of the two series of concrete should be drawn on the same graph to facilitate the comparison of their differences.

Indeed, the effect of PET on the mechanical properties for NCA and RCA concrete is plotted in Fig. 3 and 4. The authors have tried combining both figures, however, it appeared that such act would make the figure too congested and difficult to understand. Actually, this is why the authors thought of using the Δ(f’c, ft, and E) values, where the scale in percent of Fig. 3 and 4 would be useful to facilitate the comparison between both concrete series.

7. The effect of adding PET on the sorptivity of the two series of concrete should be drawn on the same graph to facilitate the comparison of their differences.

Regarding the sorptivity, the authors only plotted the NCA concrete mixtures (so that the number of figures would not excessively increase). Rather, the discussion of both series was realized during the text and discussion of results. Thanks very much for the comment.

8. The variations in drying shrinkage of the two series of concrete should be drawn on the same graph to facilitate the comparison of their differences.

Thanks for the remark. However, as shown in Table 2, the drying shrinkage was not measured for the RCA concrete during this experimental program. As a matter of fact, the main objective of this study is to assess the bond behavior of PET concrete to embedded steel reinforcement. The other mechanical properties including the drying shrinkage are well documented in the literature, and this is why the authors did not attribute much importance on those measurements.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

I have completely checked the revised manuscript, and all of what I was concerned can be found in the authors’ response. Just one suggestion is that the first current conclusion, the threshold PET rate was equal to 4.5%, however, the true threshold value should be drawn from a sufficient test sample size. This research did not do that, so suggest authors consider adjusting the related expression. Except for this, I do not have any other suggestions, and I think the authors did a nice job for the revision which has met the requirements of this Journal.