Acoustic Emission Wave Velocity Measurement of Asphalt Mixture by Arbitrary Wave Method

Round 1

Reviewer 1 Report

The paper deals with acoustic emission wave velocity measurement. In particular, it proposes a novel method based on arbitrary waves.

An experimental campaign has been realized for comparing the proposed method with two methods available in literature. As a result of this analysis, the proposed method shows very good repeatability, and the signal test used for it is less subjected to attenuation.

The presentation style is good even if typos are present. As a consequence, I suggest reviewing the manuscript in order to remove them.

Remarks:

• Figure 9 reports the frequency spectrum of the AW. Analyzing the plot it is possible to highlight that the frequency of the waveform is lower than the nominal frequency (150 kHz). Can you explain why? Which is the frequency resolution of the analysis?
• In paragraph 4.3 the number of tests carried out is not specified even if it is possible to understand that the number is 10.
• In the same paragraph, the following sentence is not very clear "The emission type of AW is equal interval emission, and the interval time is 1000 ms". Please clarify it.
• Figure 10 (a) shows the results of the three wave velocity measurement methods. Analyzing it, we can see that the number of measurements is 16. But previously you mentioned that 10 tests have been carried out. Can you better explain this aspect?

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

In this paper, the results of PLB, AST and AW methods for the determination of acoustic emission wave velocity of asphalt mixture are analyzed and studied clearly, and the advantages of AW method are verified by comparison. This is a paper containing interesting results which merit publication. But I still have the following questions:

1. I have clearly understood the advantages of AW, what are the innovations reflected in the new method?
2. How to accurately measure the time when AE signal arrive at the receiving sensor? How to judge whether the signal has reached the sensor? In other words, what is the sign that the signal has reached the sensor?
3. What is the actual AE wave velocity of the specimen? How accurate is each method?
4. It is mentioned in 3.3, the AW method is to design and write arbitrary waveform data by computer, and modulate the AW signal generated by the data. In the following experiments, the modulation signal is sinusoidal signal. Are other forms of waves used for verification?
5. Are (a) and (b) in Figure 12 reversed?

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

This is a paper containing interesting results which merit publication. But I still have the following questions:

1. "Three AE sensors are arranged on the upper surface of asphalt mixture beam" is mentioned in the paper, but the result measured by this operation seems to be the wave velocity of surface waves. Can this method be used to measure the bulk wave velocity?
2. How is the threshold adjustment value specifically set and selected?

Author Response

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Author Response File: Author Response.docx