A Brief Review: Application of Recycled Polyethylene Terephthalate in Asphalt Pavement Reinforcement

Reviewer 1

Comment (1)

It would be helpful to see images of fatigue and rutting deformation before and after asphalt modifications.

Response

Thank you for your comment.

Results from laboratory test related to fatigue and rutting deformation for PET modified bitumen were included. But for the images before and after asphalt modifications were not included as none was found in the literatures.

Comment (2)

The legend notations in figures 7, 8 and 9 need clear explanations provided in the figure captions.

Response

Thank you for meaningful comment.

For all figures the legends notation is amended and also has been fitted with the caption to be more clear. Please refer to captions of figure 7 in line (229-230), 8 in line (232-233) and 9 in line (234 to 236).

Comment (3)

Scientifically speaking, there is no point in fitting a curve to the data (as done in Figure 12) if its representing equation is not mentioned.

Response

Thank you for meaningful comment.

Both graphs describe the constant stress of asphalt mixtures under dynamic static loads. As you mentioned, there is no point in not having the curve in case the equation is not mentioned in the graphs and graphs are amended accordingly. Please refer to line number (287)

Comment (4)

Some recommendations for future work could be added

Response

We thank you for this comment as this convinced us to modify the manuscript to further strengthen it.

The recommendation section has been added to the manuscript in line (372 to 382).

There is very limited work done so far on the chemical interaction between PET and bitumen which need to be analysed further in detail to proven the true compatibility of material. The wet process can be further evaluated with the various gradation to analyse the performance of mixture as dry process has been followed so far. The dynamic rheological properties of the binder could be evaluated in accordance with the Strategic Highway Research Program (SHRP) to better understanding of PET material. The modified binder can also be tested with short term ageing and long-term ageing. The development of proper modification method is needed to get optimum results for road construction as well as for industrial scale production. The nano sized PET is recommended to use in asphalt mixture as wet or dry process to further analysed the mechanical performance of asphalt mixture.

Reviewer 2

Comment (1)

This paper briefly reviews the Application of Recycled Polyethylene Terephthalate in Asphalt Pavement Reinforcement. The covered aspects are very limited. The interaction mechanism between PET and asphalt is missing.

Response

Thank you for drawing our attention to this very interesting possible research work. Currently most of the research being published are related to the performance of PET modified asphalt mixture (i.e. performance of mixtures as a whole).

Your suggestions to look into the interaction mechanisms between PET and asphalt will be put into considerations of next scope of study. 

Comment (2)

There is less value for readers to get a sort of understanding for future research and practice.

Response

We thank you for this comment as this convinced us to modify the manuscript to further strengthen it. The recommendation section has been added to the manuscript in line (372 to 382).

There is very limited work done so far on the chemical interaction between PET and bitumen which need to be analysed further in detail to proven the true compatibility of material. The wet process can be further evaluated with the various gradation to analyse the performance of mixture as dry process has been followed so far. The dynamic rheological properties of the binder could be evaluated in accordance with the Strategic Highway Research Program (SHRP) to better understanding of PET material. The modified binder can also be tested with short term ageing and long-term ageing. The development of proper modification method is needed to get optimum results for road construction as well as for industrial scale production. The nano sized PET is recommended to use in asphalt mixture as wet or dry process to further analysed the mechanical performance of asphalt mixture.

Reviewer 3

Comment (1)

The first and second paragraph of the introduction is not related to the topic of the review, the authors could list some data about waste plastic generated annually, PET generation and recycling percentage.

Response

The first and second paragraphs are removed from the introduction according to your suggestion, and two new paragraphs are added related to plastic material describing its most significant characterisations and some percentages of the main applications plastic manufacturing.

Also, this section mentions current rapid growth production of plastics and the prediction in the future around the world. Also the percentage of production and recycled  plastic that could be reused again in different fields are highlighted in red (first and second paragraphs and in line (29 to 52)). In addition, a section showing the amount of PET production in 2014 with an expected growth by 2020 is added together with some percentages in different manufacturer countries around the world as highlighted in red (third paragraph in line (60 to 63)).

Further details are included in the manuscript.

Comment (2)

The authors could add one section before the conclusion part to discuss the future applications and expectations about the application of PET on asphalt mixtures.

Response

We thank you for this comment as this convinced us to modify the manuscript to further strengthen it. The recommendation section has been added to the manuscript in line (372 to 382).

There is very limited work done so far on the chemical interaction between PET and bitumen which need to be analysed further in detail to proven the true compatibility of material. The wet process can be further evaluated with the various gradation to analyse the performance of mixture as dry process has been followed so far. The dynamic rheological properties of the binder could be evaluated in accordance with the Strategic Highway Research Program (SHRP) to better understanding of PET material. The modified binder can also be tested with short term ageing and long-term ageing. The development of proper modification method is needed to get optimum results for road construction as well as for industrial scale production. The nano sized PET is recommended to use in asphalt mixture as wet or dry process to further analysed the mechanical performance of asphalt mixture.

Comment (3)

Please change the data in figure 3 with plastic or PET data.

Response

Thank you for the comment.

We’ve already removed this figure and replaced it with another illustrates the accumulated amount of waste plastic generation and disposal from 1950 to 2015 and also mentioned the expected quantity by 2050 as mentioned in line (86 to 88).

Comment (4)

The title 2 and title 3 are the same.

Response

We agreed with the reviewer with this comment and titles have been modified accordingly to mitigate any further confusion. The titles are amended and highlighted in red as 2. The performance of PET modified asphalt binder and 4. PET waste as an additive in asphalt mixtures, and  Please refer to the line (121) and line (169).

Comment (5)

It is recommended to add one section to describe the application of PET on asphalt binder. The section 2.1 could be replaced with PET modified asphalt binder 

Response

Thank you for the comment. The new section 2. The performance of PET modified asphalt binder has been added to manuscript and highlighted in red and please refer to line (121 to 149).

There is very limited work done so far on describing the application of PET on asphalt binder which need to be analysed further. there is one limited study conducting on using micronized PET as a modifier for asphalt binder and provided better homogenous by the addition of this size compared with bigger PET particle. The result showed an improvement in the physical properties of asphalt binder in the consistency of the binder and increased its elastic behaviour. However, the increase in viscosity of modified binder leads to higher mixing and compaction temperatures.

Comment (6)

The sentence in line 142 is not correct, please modify.

Response

Thank you. It has been modified according to your advice and highlighted in red and please refer to line (127-128)

Comment (7)

In line 164-171, the authors mentioned that both the dry process and the wet process is not applicable.

Response

Thank you for your comment.

Previously it was mis-written that both dry and wet process method will not applicable. However, in the revised manuscript it has been amended that dry processes is already proven in various studies to be effective for mixture modification. On the other hand, wet process has some limitation due to its high melting temperature which has been discussed in the section highlighted in red line (158 to 162).

Comment (8)

More detailed information could be included in section 2.2 to explain the process differences.

Response

Thank you for your comment, as in response of previous comment number 7, it was revised accordingly to clearly mention the differences in the process and was amended where necessarily need. Please for your kind reference see section 3. Design Methods in line (150 to 167)

Comment (9)

Please describe more detailed information about the reference cited in line 195-197.

Response

More details has been discussed in the revised manuscript and amended accordingly line (178 to 194).

Several factors affect fatigue life behaviour, such as asphalt binder type, filler content, stiffness, air-void percentage and asphalt content. Additional factors that also have been noted to affect fatigue performance of some mixtures include the angularity and gradation of aggregate and temperature of construction.

The lack of adequate cohesion between two different pavement layers causes layer interface separation. This inadequate bonding contributes to not homogeneous structural movement, which inevitably shortens the life cycle of the asphalt pavement due to surface slippage and cracking from the bottom of the upper separated asphalt pavement layer.

Comment (10)

Please use the full term for the first time use "ITFT" in line 198.

Response

Thank you. It has been amended accordingly as Indirect Tensile Fatigue Test (ITFT) accordingly line (197)

Comment (11)

In the end of section 3.1, 3.2, and 3.3, please summarize recommendations on how to improve the fatigue, rutting, and moisture damage resistance of PET modified asphalt mixture.

Response

Summary has been included at the end of each section together with the possible recommendations which is now revised as highlighted in red line (237 to 242) for section 4.1, and line (301 to 311) for section 4.2, and line (364 to 371) for section 4.