Waste Cooking Oil as a Sustainable Bio Modifier for Asphalt Modification: A Review

Comment (1)

The authors thoroughly reviewed the basic background of waste cooking oil (WCO), available technologies to mitigate the effect of free fatty acid (FFA) and water content, and the adverse impact of the quality of WCO on asphalt binder. The work is interesting. It provides constructive analysis through summary and recommendations. The authors are highly encouraged to take the following comments into consideration and revise the manuscript accordingly.

Response

Thank you for your encouraging comments.

Comment (2)

Use colon instead of the full stop to separate the main and subtitle of the manuscript, like “Waste cooking oil as a sustainable bio modifier for asphalt modification: A Review”

Response

Thank you for your comment. The Title has amended with colon instead of full stop.

Comment (3)

Provide the full description of every acronym and abbreviations before using it in the text.

Response

The GTR in the abstract has been revised as ground tire rubber and DSR is replaced with dynamic shear rheometer as it is only used once in the manuscript. Please refer to the page number 1 line 27 and page 15 line 463 respectively and highlighted in yellow.

Comment (4)

Omit full tops at the end of every section titles.

Response

All the full stops from title, sections and subsection have been removed and amended accordingly.

Comment (5)

Line 56, provide a space between than and 10 …“…less than10 wt.% by…”

Response

Thanks for your comment. The space has been removed please refer to the revised manuscript page 2 and line 60 and also highlighted in yellow in revised manuscript.

Comment (6)

Line 69, provide the missed reference.

Response

The missed cross reference has been amended in the revised manuscript. Please refer page 2 line 73.

Comment (7)

Line 72, merge references. Apply the same if it exists somewhere else.

Response

Agreed with a reviewer and the references have been merged. Please refer to page 2 line 76 and highlighted in yellow in revised manuscript and highlighted in yellow.

Comment (8)

Table 1, use superscript for the unit density (g/cm3).

Response

Thank you for the comment. The density unit has been modified as advised.

Comment (9)

Table 9, the last column is not fully visible.

Response

Agreed with the reviewer. The table layout has been adjusted accordingly for the clearer vision.

Comment (10)

Some of the figures are poor e.g. Figure 16, enhances all poor quality of figures.

Response

Thank you for your comment.

The figure quality and visibility has been enhanced please refer to the revised manuscript page 24.

Comment (11)

 Some sentences do not have full stops at the end e.g., line 793, 802. Apply full stops to all the missed parts.   

Response

Thank you for your comment. The manuscript has been revised and amended accordingly and also has checked and corrected for any missing full stops.

Comment (1)

-can the proposed method be applied on an industrial scale or are these only theoretical considerations based on laboratory scale experiments?  

Response

The waste cooking oil studies for the asphalt modification has grown recently past half decades and researchers are putting efforts to utilize the cooking in the pavement industry. Initially the only filtered oil was incorporated for the modification which has caused some negative effects on the performance of the binder. However, in the later phase recently some of the research did pre-treatments to enhance the quality of the waste cooking oil in term of its acidity which may be measure with its free fatty acids presence within the oil matrix. The treatment certainly showed some improvement in bitumen grade which ultimately will performs better in the field as well. The study is in the empirical stage of the development so far according to the authors knowledge no industrial scale works has been initiated for waste cooking oil modified asphalt.  

Comment (2)

-has similar activities with the use of similar oil (more or less processed / used) already introduced into industrial production?

Response

Thank you for your comment.

The similar activities which authors understands is the treatments processes. So far, the waste cooking oil improvement in its chemical perspective was done with transesterification and esterification for many other perspectives in the industrial scale to reduce the fatty acid. However, the same product after the treatment has not been fully utilized for the asphalt modification as it was already known that the free fatty acids directly affect the binder performance. Beside the treatment for the reduction in the free fatty acid the authors contributed and suggested few other treatments together with the transesterification likewise the moisture reduction, distillation, and few others. Please refer to the section number 3 to 6 for further understanding of the processed procedures and available technologies.

Comment (3)

what is the estimated cost of producing e.g. 1 ton of asphalt modified with used cooking oil compared to the production of 1 ton of asphalt modified with classic plasticizers and improvers?

Response

Thank you for your comment.

As per authors knowledge the commercially available improvers such as SBS price is high compared to waste cooking oil. The average price of SBS is approximately 1600USD/Ton however the price of waste cooking is 400USD/Ton, and the price of 60/70 grade bitumen is almost 300USD/Ton. According to this scenario, SBS cost 64USD and waste cooking oil cost 16USD for production of modified binder.  The overall cost reduction in oil modified binder will be approximately 75% compared to the improvers.

Comment (4)

-is the Authors known to the effect of processed cooking oil on the durability of the asphalt mix?  

Response

Thank you for your comment.

The studies indicated that the performance of the processed cooking oil is better compared to the non-processed waster cooking oil into the asphalt mix. The reason behind is that the non-polar group in the non-processed waste cooking oil converts into a polar group, and polar attraction between processed WCO molecules and polar aggregate surface improves adhesion bonding thus, will resulting in improved rutting resistance performance in asphalt mixture. However, the performance of the non-processed oil is marginal in comparison to the any asphalt mixture without any oil modification. Furthermore, the for the better and more enhanced performance the processed waste cooking oil with minimum free fatty acid together with some other additional additives may performs far better in a conjunction manner. The details on the performance of the asphalt mix have been further explained in the section 13 of the revised manuscript.

Comment (5)

-on what size of samples the tests were carried out on the physico-chemical properties of the mixture modified with cooking oil and whether, in the Authors' opinion, these results are reliable and whether these results are not affected by the scale effect, which in this particular case may give values ​​that put asphalt modified with cooking oil in a better light than classic asphalt?   

Response

Thank you for your comment. As per authors understandings and reviewed literature the physio-chemical properties of the asphalt mixture have not been analysed. However, the physical and chemical properties of waste cooking oil before and after treatment was analysed in majority of the reviewed literature for the better understanding of the chemical changes in the oil. The standard procedure was mainly followed for the determination of the properties i.e., the viscosity of oil, density, and water content. On the other hand, in term of chemical evaluation the oil composition and its acid value test were conducted before and after treatment.  Also, the modified bitumen with the oil has been analysed for chemical reaction by FTIR testing and for GC-MS for the function group determination. The physical, rheological and mixture analysis has been done with all standard procedures and with standard sample quantity or any size desired for testing purpose. In authors point of view there will be only marginal differences in term of the scale effect.

Comment (6)

 -for what applications is the proposed asphalt modified with used cooking oil possible? - what is the maximum thickness of an asphalt rug for which we can use cooking oil-modified asphalt?

Response

The typical application of waste cooking oil as a modifier in the pavement industry initiated few years back. There are many applications we can accommodate the waste cooking oil for pavement application. The oil basically can be worked as a rejuvenator for the aged bitumen’s as it can reduces the viscosity and hardness of the aged bitumen for the recycling. However, the paper concern is the waste cooking oil as a modifier for the pavement applications. In this way the many studies suggested the only and non-processed waste cooking oil modified asphalt for the low and intermediate temperature where it can work within the limits of the standard performance. Whereas the high temperature performance might be compromise due to excessive oily nature of the waste cooking oil which may be marginally enhanced by the pre-processing of waste cooking oil to reduce the free fatty acid which may affects less as compared to the non-processed waste cooking oil. Moreover, the researchers also suggested the additional modifier in conjunction with the waste cooking oil to balance the high temperature performance of the pavement. In response to the second part of the question, the thickness of the asphalt will not be affected by the utilization of the processed waste cooking oil. However, in any case if the grading of the bitumen will improve with waste cooking oil the thickness might be reduce due to the improvement in the grading of bitumen.

Comment (7)

   - at what maximum speed can motor vehicles travel on an asphalt surface made of asphalt modified with processed cooking oil? 

Response

Thank for your comment. The vehicle speed mainly causes the failures in the pavements. However, according to the reviewed literature and understanding of the authors the processed cooking oil has improved the one grade of the bitumen as to PG70. Since the grade has improved while utilizing the waste cooking oil so it can accommodate the high speed easily in fact it can also resist the greater slow speed vehicles stress better in comparison to grade lower than the PG70. It was also suggested the processed cooking oil together with the other waste material likewise crumb rubber, or waste plastic can accommodate more stresses variation of vehicle speeds.

Comment (8)

 - how the use of the modifier in the form of processed cooking oil changes the acoustic parameters,.

Response

Thank for your comment. The acoustic parameters mainly depend on the aggregate type, gradation, bitumen type, air voids and density of mixture.  Hence, the waste cooking oil modified asphalt mixture does not have enough ability to reduce the noise of pavement. The reason behind is that the waste cooking oil cannot highly increase the viscosity of the bitumen. However, it is recommended to use waste cooking oil in conjunction with the co modifiers such as SBS and crumb rubber to reduce the acoustic parameters. So far none of the studies has been conducted on the acoustic parameters of the waste cooking oil modified asphalt.

Comment (9)

- this type of surface is quieter or louder than the classic asphalt surface

Response

As described earlier the waste cooking oil have limited ability to increase the viscosity of the bitumen. so, in authors point of view the performance may remains the same as classic surface in term of the noise of pavement. However, its performance in noise reduction might increase when processed cooking oil incorporated together with the other co modifier such as SBS, tire rubber.

Comment (10)

- at what minimum and what maximum levels it is possible to make the pavement using the material described above

Response

The processed waste cooking oil for the better performance of binder should not be greater than 4% wt. of original binder. However, its percentage may vary or increase when used in conjunction with the other co modifiers.