Contribution to the Research on the Application of Bio-Ash as a Filler in Asphalt Mixtures
Round 1
Reviewer 1 Report
The paper report the environmental effects and material properties of HMA when using bio-ash as a replacement of mineral filler. The paper is well written. The topic is of interests. Specific comments:
1. The literature indicates that a 50% replacement of the mineral filler by the bio-ash can improve the performance of the HMA. In this case, the objective of the current study need to be further discussed, to indicate the contribution of the current study (if it has already been proved, why we still need a new study?)
2. The authors indicated that the bio-ash considerably varies as to its composition and properties, depending on the origin of biomass, biomass handling, and combustion technology and temperature. How this variation affect the usage of the bio-ash in HMA? Does the finding of the current study a coincidence of the specific composition or they are more general findings? This needs to be discussed in the paper, such as in the conclusion.
3. The experiment design is limited in terms of types of HMA mixture design, sources of bio-ash, and HMA performance evaluation (such as cracking resistance, aging ect.). Although the comparison of the rutting test results of the mixture with BA, without BA but the same mixture design, and other 8 different mixtures is meaning full, but since we don’t know the effect of BA for the other 8 different mixtures, still the findings of this study in terms of the effects of BA can not be generalized. This should be discussed in the paper.
4. Line 516: “carried out examined…” need to be revised.
Author Response
ANSWERS TO REVIEWER 1
The paper reports the environmental effects and material properties of HMA when using bio-ash as a replacement of mineral filler. The paper is well written. The topic is of interests. Specific comments:
Dear Reviewer, thank you for the introductory comment regarding the work and topic, below are the answers to your constructive comments (1-4).
Remark: all addition and explanation in the text based on Reviewer comments and suggestions are highlighted in yellow.
- The literature indicates that a 50% replacement of the mineral filler by the bio-ash can improve the performance of the HMA. In this case, the objective of the current study needs to be further discussed, to indicate the contribution of the current study (if it has already been proved, why we still need a new study?)
Answer: Many researchers confirmed improvement of asphalt properties with bio ash, that is a fact. And also, is known that the physical and chemical properties of wood bio ash (BA) depend on many things: the origin of the biomass and the part of the plant from which it is made, the quantity of mineral impurities, the location of the source of the biomass, the way in which the biomass is collected and pro-cessed, and the technology and temperature of combustion. So, every type of wood ash is uniqe and has different properties and needs to be detailed investigated. It is important to determine how much the improvement in the asphalt properties is. In Croatia, research on application of wood ash has only started to be carried out in recent years, initiated by the large quantities of bioash produced in newly built power plants so every research and new results are important for possible usage.
- The authors indicated that the bio-ash considerably varies as to its composition and properties, depending on the origin of biomass, biomass handling, and combustion technology and temperature. How this variation affects the usage of the bio-ash in HMA? Does the finding of the current study a coincidence of the specific composition or they are more general findings? This needs to be discussed in the paper, such as in the conclusion.
Answer: One part of answer on this question is above. We are aware of the variability and uniqueness of each WA type but we believe that this research can be a contribution to previous researches on confirmation of wood ash from any specific local source, as a material for sustainable pavements.
According to your recommendation, we added in Conclusion next facts:
On the end, it should be mentioned that the variability of the WA composition should always be considered and the possibility of application confirmed with full laboratory tests. For the type of asphalt for which a recipe with bioash was created in the laboratory at the asphalt plant, bioash from the same power plant/heating plant or from more than one should be used if the same biomass is used as energy source.
- The experiment design is limited in terms of types of HMA mixture design, sources of bio-ash, and HMA performance evaluation (such as cracking resistance, aging ect.). Although the comparison of the rutting test results of the mixture with BA, without BA but the same mixture design, and other 8 different mixtures is meaning full, but since we don’t know the effect of BA for the other 8 different mixtures, still the findings of this study in terms of the effects of BA cannot be generalized. This should be discussed in the paper.
Answer: The authors agree that the effects of BA in HMA should not be generalized but viewed from the aspect of ecological benefits that result in economic effects, therefore a sentence was added in the conclusion: It is important that the addition of bioash does not worsen the resistance of the asphalt mixture to the occurrence of plastic deformations, and multiple is used for environmental protection, which also results in positive economic indicators.
- Line 516: “carried out examined…” need to be revised.
Thanks for the suggestion, "carried out examined ..." has been revised to: has ....
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This paper investigated the possibility of using wood bio-ash (BA) as a filler in asphalt mixtures and determined its amount through tests of physical and mechanical properties, the paper is generally well written, and the topic is somewhat interesting in regard to the utilization of waste. However, the test asphalt samples seem not enough when conducting rutting process, I suggest to add the test numbers to provide more solid results. Except this, some literature that discussing the influences of mixtures in to asphalt or concrete should be included in the introduction part, e.g., A review on durability of alkali-activated system from sustainable construction materials to infrastructure, 2019; Embedded piezoelectric transducers based early-age hydration monitoring of cement concrete added with accelerator/retarder admixtures, 2020.
The English could be improved.
Author Response
ANSWERS TO REVIEWER 2
This paper investigated the possibility of using wood bio-ash (BA) as a filler in asphalt mixtures and determined its amount through tests of physical and mechanical properties, the paper is generally well written, and the topic is somewhat interesting in regard to the utilization of waste.
Dear Reviewer, thank you for the positive introductory comment on the work, below are our answers.
However, the test asphalt samples seem not enough when conducting rutting process, I suggest to add the test numbers to provide more solid results.
Answer: Rutting test samples were carried out on comparable asphalt mixtures of the same type, similar in composition and with acceptable deviations in physical and mechanical properties, with the aim of being representative. Thank you for your suggestion, unfortunately at that time when we conducted this research, we were limited by the research budget but we hope it will be opportunity in the future for expand research.
Except this, some literature that discussing the influences of mixtures in to asphalt or concrete should be included in the introduction part, e.g., A review on durability of alkali-activated system from sustainable construction materials to infrastructure, 2019; Embedded piezoelectric transducers based early-age hydration monitoring of cement concrete added with accelerator/retarder admixtures, 2020.
Answer: The authors have studied the proposed literature and we agree that it is an interesting topic related to sustainable construction materials in infrastructure and monitoring the hydration of cement concrete and we will include them in our further similar research but cannot now when subject is about asphalt mixes and wood ash.
Based on comments and suggestions as part of the reviews, a corrected paper is attached (highlighted in green end highlighted in yellow.).
Author Response File: Author Response.pdf
Reviewer 3 Report
The main objective of this work is to study the incorporation of wood bio-ash as a constituent material of asphalt pavements focused on environmental analysis, permanent deformation and water sensitivity. The manuscript is well written needing just some adjustments:
Please include more information about the asphalt binder used: which type, penetration, softening point, RTFOT, PAV, viscosity, rheology etc.
Why din't the authors perform the fatigue test?
Discussion on the environmental analysis may be improved (topic 6.1.).
The Equation of ITS and ITSR (Equation 1) must be presented at the section Test Methods not in results. These results are better showed in form of column graphs (Table 10).
In Figures 5 to 7, please replace the numbers to the name of the samples.
In general, the discussions of the results must be improved to argue the conclusions.
Please, avoid using vague terms, for example, very good. It can be seen many times in the text, including in the Conclusions.
Please, use technical and scientific language.
Author Response
ANSWERS TO REVIEWER 3
Dear Reviewer, Thank you for your affirmative, constructive comments and suggestions as part of your review.
Remark: all addition and explanation in the text based on Reviewer comments and suggestions are highlighted in green.
The main objective of this work is to study the incorporation of wood bio-ash as a constituent material of asphalt pavements focused on environmental analysis, permanent deformation and water sensitivity. The manuscript is well written needing just some adjustments:
Please include more information about the asphalt binder used: which type, penetration, softening point, RTFOT, PAV, viscosity, rheology etc.
Answer: New Table 3. Properties of road construction bitumen 50/70
Why din't the authors perform the fatigue test?
Answer: Thank you for your suggestion, we agree that fatigue test is important for asphalt mixtures. Unfortunately, at that time when we conducted this research, we were limited by the research budget but we hope it will be opportunity to perform the fatigue test in the next stages of research.
Discussion on the environmental analysis may be improved (topic 6.1.).
Answer: It was added: The test established that bioash as a filler in the asphalt mixture does not release harmful ingredients that endanger the environment and confirms its usability in asphalt layers of road construction.
The Equation of ITS and ITSR (Equation 1) must be presented at the section Test Methods not in results.
Answer: Thanks for the comment, equation 1) shown in 5.2.
These results are better showed in form of column graphs (Table 10).
Answer: New Figure 4 is instead of Table 10.
In Figures 5 to 7, please replace the numbers to the name of the samples.
Answer: Sorry, we are not sure what reviewer mean with this request?
In general, the discussions of the results must be improved to argue the conclusions.
Answer: Thank you for your comment, the results are discussed in more detail in the conclusion.
Please, avoid using vague terms, for example, very good. It can be seen many times in the text, including in the Conclusions.
Answer: We accepted your suggestion and deleted “very” in text, including in Conclusion.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
The authors have improved the manuscript according to the recommendations.
No issues.
