Effect of Bagasse and Coconut Peat Fillers on Asphalt Mixture Workability

Round 1

Reviewer 1 Report

In general, I think this manuscript is well-written and easy to follow. I only have few comments.

1. What are the diameters of the bagasse, coconut peat and the limestone mineral filler? I believe the diameters of these materials affects a lot on the workability.
2. This study only employed the rotational viscosity to investigate the effects of different fillers on the workability of asphalt mixture. However, the limitations of rotational viscosity have been reported by various studies. If possible, please discuss more about the motivation in using the rotational viscometer.
3. What are the suggestions or recommendations from authors? Do you recommend to replace the natural mineral filler by the coconut peat or bagasse?

Author Response

Thank you very much for your comments. Here are the responses for each of your comment. 

1. What are the diameters of the bagasse, coconut peat and the limestone mineral filler? I believe the diameters of these materials affects a lot on the workability.

• Please find the additions at line 124-128 and 394-395

Table 2. The Estimated surface area through SEM image.

From Table 2, it is shown that the SEM surface area of Limestone, Bagasse and Coconut peat fillers (i.e. 3,437, 3,494 and 3,973 µm² respectively) are among the similar sizes which yield higher values than that of granite filler (i.e. 2,253 µm² ).

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... Also, this result can be addressed from the SEM surface area in which the viscosities correspond to the SEM surface area for each filler.

1. This study only employed the rotational viscosity to investigate the effects of different fillers on the workability of asphalt mixture. However, the limitations of rotational viscosity have been reported by various studies. If possible, please discuss more about the motivation in using the rotational viscometer.

• Please find the revised at line 164-166 and the analysis from line 224-237

In this study, preliminary asphalt mastics viscosities display a Newtonian behavior between the shear stress and shear rate as their filler concentration was low, thus the rotational viscometer was adopted to use for determining the asphalt mastic viscosities.

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To confirm that the asphalt mastics with low filler concentration show Newtonian behavior, the mastic viscosities were performed in different shear rate.

Figure 4. the relationship of asphalt mastic (a) viscosity and shear rate, and (b) shear stress and shear rate at 150°C and 170°C

               Figures 4 display the relationship of mastic viscosity and shear rate, and shear stress and shear rate at 150°C and 170°C. When applying different shear rates, mastic viscosities displayed constant values through the same temperature. Likewise, the relation between shear stress and shear rate show a linear mastic viscous behavior. This is to confirm that the mastics with low filler concentration exhibit Newtonian behavior.

1. What are the suggestions or recommendations from authors? Do you recommend to replace the natural mineral filler by the coconut peat or bagasse?

• Further research is needed to verify, as this is the preliminary results on the workability and some results on performances. Future research is needed to focus more on many factors on materials and suitable testing for range of filler concentration.
• Added the recommendations at line 415-419

Further studies on different factors such as binder type, aggregate type and aggregate gradation should be considered to verify the performance of using waste natural fillers as alternative in asphalt mixture. Other failure performance tests for testing the mixtures of bagasse or coconut peat fillers should be considered for future work. The Non-Newtonian behavior for the high concentration of fillers needs to be considered.

Author Response File: Author Response.docx

Reviewer 2 Report

Thank you for your effort to contribute journal.

The title is Effect of Bagasse and Coconut Peat Fillers on Asphalt Mixture Workability. But there is no result of workability.

This paper is similar with technical report. For example TSR result, bagasse can be alternative filler replacing mineral filler for moisture damage resistance. Why dose not coconut satisfy the TSR ? What mechanisim is effect this result ?

This paper is requred more analysis the test results.

Author Response

Thank you very much for your comments. Here are the responses for your comments.

1. This study only employed the rotational viscosity to investigate the effects of different fillers on the workability of asphalt mixture. However, the limitations of rotational viscosity have been reported by various studies. If possible, please discuss more about the motivation in using the rotational viscometer.

• Please find the revised at line 164-166 and the analysis from line 224-237

In this study, preliminary asphalt mastics viscosities display a Newtonian behavior between the shear stress and shear rate as their filler concentration was low, thus the rotational viscometer was adopted to use for determining the asphalt mastic viscosities.

.

.

.

To confirm that the asphalt mastics with low filler concentration show Newtonian behavior, the mastic viscosities were performed in different shear rate.

Figure 4. the relationship of asphalt mastic (a) viscosity and shear rate, and (b) shear stress and shear rate at 150°C and 170°C

               Figures 4 display the relationship of mastic viscosity and shear rate, and shear stress and shear rate at 150°C and 170°C. When applying different shear rates, mastic viscosities displayed constant values through the same temperature. Likewise, the relation between shear stress and shear rate show a linear mastic viscous behavior. This is to confirm that the mastics with low filler concentration exhibit Newtonian behavior.

Author Response File: Author Response.docx

Reviewer 3 Report

Dear Editor,

I have read the manuscript and here are my impressions;  

The topic is very interesting, but due to the low density of the waste natural fillers, I have many doubts on their possibility for practical use in real industrial process. In my experience, it is not easy to use fibers directly in dry process. There are some lacking elements that seem to be important, you can find my comments in the following:

1. In "Materials" please describe better bitumen and the aggregates. The importance of the interaction between bitumen and filler is well known and for this reason, the authors could add more information about aggregates (i.e. X-rays) and bitumen (i.e. SARA).
2. Please indicate the source of the bitumen.
3. Information about the experimental instruments (Marshall, SEM, Viscometer, etc) are completely missing in the manuscript.
4. Add more information about the sample preparation, in particular of the mastic samples preparation and the mixing process of asphalt.
5. The authors have performed SEM analysis on the filler, I suggest they calculate the size distribution of the filler and compare them.

Author Response

Thank you very much for your comments. Here are the responses for your comments.

In "Materials" please describe better bitumen and the aggregates. The importance of the interaction between bitumen and filler is well known and for this reason, the authors could add more information about aggregates (i.e. X-rays) and bitumen (i.e. SARA).

Please indicate the source of the bitumen.

• Please find the source at line 92

Two waste natural fillers were separated by the grinding machine: Coconut peat (Figure 1a) and Bagasse (Figure 1b). They were subsequently sieved to obtain fillers with a sieve number of 200 (0.075 mm).  The asphalt binder AC 60-70 used in this analysis was obtained from TIPCO Asphalt PCL

Information about the experimental instruments (Marshall, SEM, Viscometer, etc) are completely missing in the manuscript.

• Please find the additions from line 110-114, 164-189, and 201-204

The four fillers' surface micro morphological characteristics were observed with FEI Quanta 250 Scanning electron microscope (SEM) used for structural and chemical analysis of metallographic specimens with magnification up to x1,000,000 and down to a resolution of 3 nm as shown in Figure 3. SEM operational parameters were 20kV accelerating voltage, 15 mm working distance, and stage tilt angles of 8°.

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In this study, preliminary asphalt mastics viscosities display a Newtonian behavior between the shear stress and shear rate as their filler concentration was low, thus the rotational viscometer was adopted to use for determining the asphalt mastic viscosities. A standard viscosity (or Brookfield) viscometer (RV) was used in the viscosity test, in accordance with the AASHTO T316 standard, or with standard ASTM D4402 [36]. With precision of ±1 percent and repeatability of ±0.2 percent, the Viscometer system measures viscosities between 100 and 40 million cP. The device is compatible with a wide range of spindles including an integrated temperature resistance detector to measure samples from 9 °C to 260 °C. The rotational viscometer used in this study. Viscometer measures the torque as the spindle rotates at constant speed through an asphalt tube.  The dynamic viscosity is proportional to the torque of the rotational viscosity. The RV criterion for calculating non-newton viscosity fluids is prevalently used in the chemical and food industry. RV can be tested at high temperatures and suited for non-newton fluids (such as asphalt binder, and modified asphalt binder). RV is used in asphalt technology primarily to measure asphalt binder viscosity; however, some studies have used RV to assess asphalt mastic viscosity [37]. In a straightforward way, such a viscometer consists of a cylindrical chamber that controls temperatures, in which the test fluid is inserted and a 27-size spindle that is operated by a power motor. While the spindle is spinning, a calibrated spring, attached to the dial, records the fluid resistance to rotation. Although viscosity (measured by the rotational viscometer) is not an absolute feature of bituminous binders as it can often show non-Newtonian behavior, it can be used for comparative purposes where, as with the present analysis, temperatures, share rate, torque, etc. Therefore, through the entire investigation, the shear rate kept at 20 rpm and the torque at 100%±3%. The shear rate of 20 rpm was used since the shear rate in binder experiments is the most widely used. Several experiments to determine the effect of shear rate on the viscosity of mastics have been performed. While shear dependent on the mastic was found, the relative classification of the mastics did not change according to the shear rate covered in the test. Viscosity tests were performed with a Spindle of SC4-27 and a sample of 10 ± 0.5 g. 

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…Marshall stability and IDT tests specified in ASTM D6927-15 and AASHTO T283, respectively. The Marshall stability and IDT results obtained from Humboldt HM-5120A including the load capacity of 50 kN, speed range of 50.8 mm/min., platen size of 254 mm./100 mm., and 1,000 tests and up to 3,000 readings per test data storage.

Add more information about the sample preparation, in particular of the mastic samples preparation and the mixing process of asphalt.

• Please find the added information at line 90-93, 136-143 and 152-156

. Two waste natural fillers were separated by the grinding machine: Coconut peat (Figure 1a) and Bagasse (Figure 1b). They were subsequently sieved to obtain fillers with a sieve number of 200 (0.075 mm).  The asphalt binder AC 60-70 used in this analysis was obtained from TIPCO Asphalt PCL.

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In accordance with ASTM D6926 (ASTM 2010a), every material was prepared. The aggregates were heated overnight at 100 ° C to insure moisture-free conditions. Due to increasing viscosity of the asphalt mastic and a constant temperature of 150 °C, the mixture samples were heated over 2 hours. For compacting specimens measuring 101.6 mm in diameter and 65-75 mm in height, the Marshall hammer compaction (2 x 75 blows) was used. For all specimens’ volumetric measurements were performed after a 24-hour curing time for the Marshall specimens. Following the required conditioning, the Marshall stability test was carried out in accordance with ASTM D6927-15. The specimens were then tested Indirect Tensile Strength (ITS) according to the AASHTO T283.

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The asphalt mastics were blended using laboratory devices including a heating mental and a vertical blender with a spindle. The blending process for the asphalt mastics consist of the following steps: heating of the asphalt into the heating mental up to the mixing temperature (i.e. 155 ^◦C); placing the spindle in the center of the asphalt, then blending with an addition of filler with the rotational speed of 1000 rpm for 1 h.

The authors have performed SEM analysis on the filler, I suggest they calculate the size distribution of the filler and compare them.

• Please find the additions at line 124-128 and 394-395

Table 2. The Estimated surface area through SEM image.

From Table 2, it is shown that the SEM surface area of Limestone, Bagasse and Coconut peat fillers (i.e. 3,437, 3,494 and 3,973 µm² respectively) are among the similar sizes which yield higher values than that of granite filler (i.e. 2,253 µm² ).

.

.

.

... Also, this result can be addressed from the SEM surface area in which the viscosities correspond to the SEM surface area for each filler.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

dear Editor,

The paper can be published in the current form. Please correct the lines 153 and 155: "Heating mental" should be substituted by "heating mantle".