Review Reports - Experimental Investigation of the Influence of Freeze–Thaw Mode on Damage Characteristics of Sandstone

Round 1

Reviewer 1 Report

In this manuscript, the authors investigated the damage behavior of cultural stone relics under varying modes of freezing and thawing, namely immersion, capillary and periodic saturation. Using macro and micrographic tests, the authors analyzed the morphology of sandstone under these freeze-thaw cycles in addition to several tests evaluating the existence of porosity, water content, wave velocity and surface hardness.

In the opinion of the reviewer, the paper can be recommended for publication in Journal of applied sciences after revisions listed below:

- Line 137. The authors should clarify the reason for the choice of temperature range: are these the same natural conditions, or extreme conditions that may exceed what actually occurs in nature?

- Also, is the freeze-thaw cycle shown in Figure 3 a normalized cycle or one that mimics what actually happens? If it is a normalized cycle, authors should specify if there is a norm or a standard and they need to write its reference.

- Analysis of Figure 5. As stated by the authors, the rock samples are damaged on the edges and corners, but this damage is only on the top part of the rock, while no damage is noticed on the other part. The authors should clarify the reason for this.

- Figure 6: please add a description for the red circles on the microscopic rock morphology: what is the type of damage on each circle?

- Figure 7. Is that any reason for the similarity between the evolutions of open porosity changes of rock samples under capillary freeze-thaw and periodic saturated freeze-thaw?

- Looking at Figure 15, this similarity has disappeared and there is a remarkable difference between the two modes; however, there is a correlation between the appearance of cracks, porosities and the variation in damage.

Author Response

Response to Reviewers

First of all, thank you for allowing me to improve the quality of the study, the authors sincerely appreciate the editors and the reviewers for their work to review the manuscript again. Based on the valuable comments, the authors revised some of the text as well as the figures, though the essence of the manuscript keeps unchanged. Now the authors are sure that the revised manuscript is much better than the original, and they would appreciate it very much if the editors and reviewers could point out further comments toward the publication.

The authors respond to all the comments one-by-one in the following. They also prepared the detailed revision note as a separate file.

Reviewer 1:

In the opinion of the reviewer, the paper can be recommended for publication in Journal of applied sciences after revisions listed below:

Line 137. The authors should clarify the reason for the choice of temperature range: are these the same natural conditions, or extreme conditions that may exceed what actually occurs in nature?Also, is the freeze-thaw cycle shown in Figure 3 a normalized cycle or one that mimics what actually happens? If it is a normalized cycle, authors should specify if there is a norm or a standard and they need to write its reference.

The authors have elaborated on the basis of the test setup in the article as follows:

According to meteorological data of the North Grottoes in Qingyang, Gansu, the climatic temperature in the region in recent 10 years is 30°C at the highest and -20°C at the lowest. The surface temperature of the caves in summer afternoon is around 40°C and in the winter the surface temperature is close to -25°C, with a moderate increase on the basis of the historical true temperature. The annual trend of seasonal relative temperature in the Qingyang shows that the time period of below and above 0°C is about 6 months. The present study investigates the failure characteristics and variation rules of rock mass under extreme temperature conditions.

Analysis of Figure 5. As stated by the authors, the rock samples are damaged on the edges and corners, but this damage is only on the top part of the rock, while no damage is noticed on the other part. The authors should clarify the reason for this.

All rock parts are damaged to varying degrees by freeze-thaw. The edges and corners are the most severely damaged and the most significant in terms of apparent morphological deterioration.

Figure 6: please add a description for the red circles on the microscopic rock morphology: what is the type of damage on each circle?

Overall, as the number of cycles increases, the cracks of sandstone particles continue to expand, the pores in the rock sample gradually increase, and the pore size becomes larger. In addition, the pores continue to expand and extend, and gradually form the connected cracks, and typical variations are shown in the red circle area.

Figure 7. Is that any reason for the similarity between the evolutions of open porosity changes of rock samples under capillary freeze-thaw and periodic saturated freeze-thaw?

The trend of open pore porosity damage is the same for all three freeze-thaw methods, and the process can be fitted with the function φ=ae^(-n/b)+c (φ is the open pore porosity; n is the number of cycles, a, b and c represent constants). The difference in magnitude between the capillary freeze-thaw and cyclic saturated freeze-thaw samples is not significant, and therefore the curves shown in the graphs are similar.

Looking at Figure 15, this similarity has disappeared and there is a remarkable difference between the two modes; however, there is a correlation between the appearance of cracks, porosities and the variation in damage.

In this paper, I assess the degree of weathering by means of wave velocity damage variables and intensity damage variables, which are only two means of analysing the degree of weathering of rocks. For a single damage variable, the damage factors of the rock samples undergoing different freeze-thawing methods follow the same trend, which is due to the continuous development and enlargement of the rock pores and fractures under the freeze-thawing action.

Author Response File: Author Response.docx

Reviewer 2 Report

Attached

Comments for author File: Comments.pdf

Author Response

Response to Reviewers

The authors respond to all the comments one-by-one in the following. They also prepared the detailed revision note as a separate file.

Reviewer 2:

The abstract must contain the methodology. Also, in existing position, the abstract iscomparatively lengthy (read the instructions for the authors). The revised abstract mustinclude the problem statement/research gap, methodology, and results along with concise background.

Thank you for your advice.The article abstract has been rewritten as follows:

Freeze-thaw is one of the most important factors of stone cultural relics weathering in northern China. Due to the large size of the immovable caves, there are significant differences in the environments in which different parts of the caves are located, and they are damaged to different degrees from the same freeze-thaw action. In this paper, three kinds of typical freeze-thaw cycle tests of sandstone were designed, namely, immersion test, capillary action test, and periodic saturation test. The macroscopic and microscopic morphologies of rock samples under different freeze-thaw cycles were analyzed,, and weathering indexes such as porosity, water content, wave velocity, and surface hardness were tested. Uniaxial compressive strength was taken as a reference index of mechanical properties. The variation rules of weathering indexes and mechanical properties under different freeze-thaw cycles were obtained, and the quantitative relationship among the indexes was further analyzed. The results show that under different freeze-thaw conditions, the morphologic characteristics of rock samples are significantly different, and the variation trend of each weathering index is similar, but the change rate is different. The water content of rock has a great influence on the wave velocity test results, but a slight influence on the surface hardness. The functional relationship between nondestructive testing indexes and mechanical strength was similar under different freeze-thaw methods, but the fitting parameters were different. Finally, the strength and wave velocity damage factors were used to quantitatively evaluate the weathering degree of rock under different freeze-thaw modes, in which the immersion freeze-thaw damage degree was the highest, the periodic saturation freeze-thaw damage degree was the second, and the damaging effect of capillary freeze-thaw was the least. The conclusion of this paper can provide a reference for the detection of stone cultural relics and the scientific basis for the protection of stone cultural relics against weathering.

Details map of the samples location.

The authors add a map of rock sampling locations to the article as follows:

Fig. 1 Rock sampling site - Qingyang, Gansu, China

Temperature record of the area, from where the samples are collected. Is this taken as the

maximum and minimum temperature in the experiments.

The background is discussed comprehensively, but how about the freezing and thawing

duration. On what basis the authors selected the temperature and their duration (Figure 3).Discuss comprehensively.

The authors explain questions 3 and 4 as follows:

Show the experimental setup.

The freeze-thaw test is carried out in the humid heat chamber with rapid temperature change. The temperature control range is from -40°C to +120°C, and the allowable error is ±1°C. The heating and cooling rates are up to 10℃/min, which meets the requirements of the test, the test chamber is shown in Figure 4.

Fig. 4 Rapid temperature to humidity test chamber

Avoid the slash (/) between the symbol and unit. Some other minor linguistic mistakes are

present in the manuscript (For example line 19, 189).

Thank you for your correction. Some minor linguistic mistakes have been amended in the article.

Discuss the results. For example, Figure 6 need discussion.

Thank you for your advice. The authors have reanalysed the results as follows:

In terms of the change law of micromorphology,the phenological deterioration rate of rock samples under different freeze-thaw modes is different, but the change law of rock samples under the three freeze-thaw conditions is similar.The sample with periodic saturated freeze-thaw cycles is taken as an example, and its micromorphology is shown in Figure 9. At the beginning of the test (FIG. 9a), the particles were closely arranged, the pores and cracks were small, and the cement was filled between the particles. After 10 cycles (FIG. 9b), the sample was in a state of "rapid metamorphic". Compared with the initial compact arrangement, microcracks between grains gradually developed, and some cements were affected by hydrolysis and developed more internal cracks. Small particles such as calcite can be seen attached; During the 10 cycles (FIG. 9c), on the one hand, the mass loss of cement leads to the formation of pores and the connection of fractures; on the other hand, feldspar and dolomite particles are broken under the influence of hydrolysis, and new fractures are generated on the surface. Finally, at the time of failure (FIG. 9d ~f), the cracks have been completely connected, and the particles are scattered and cut by them. Some particles also develop internally, and some particles also develop cracks within and become fragments. In general, with the increase of the number of cycles, the cracks of sandstone particles continue to expand, and the pores in rock samples gradually increase and the pore size becomes larger. In addition, the pores continue to expand and extend, and gradually form the connected cracks, typical variations in rock micromorphology are shown in the red circle area.


a. 5 cycles	b. 10 cycles	c. 20 cycles

d. 40 cycles	e. 60 cycles	f. 80 cycles

Fig. 9 Microscopic morphology changes of rock samples with capillary freeze-thaw cycles

The authors have plotted the results, but how about the trend in literature betweendifferent parameters. Discuss your results with existing literature. The following paper canenhance the literature; Development of Predictive Models for Determination of the Extent of Damage in Granite Caused by Thermal Treatment and Cooling Conditions Using Artificial Intelligence.

Thank you for your advice. The authors have quoted the article as follows:

Khan N et al. developed three models for predicting the degree of flint thermal response damage based on density, wave velocity and porosity. The results showed that the prediction model similar to the neural network was more accurate than MLR and ANFIS, and the damage factor based on porosity was more effective than that based on elastic modulus.

How about the results relation with filed (real time deterioration)? Discuss.

Figure 8 shows the current state of weathering on the façade of the North Grottoes in Qingyang, Gansu, China. It can be seen that, under the influence of freeze-thaw action and cave building environment, the bottom and interior of the cave are seriously damaged by seepage erosion, and the cave deteriorates obviously. There are many longitudinal and transverse pore cracks in the surface layer. In the severely weathered area, part of the surface layer has spalled off. The upper part of the cave, the middle part and the Buddha in the cave are affected by capillity, the particle loss is serious, and the surface has white crystal precipitation. The appearance of the cavity is similar to the test results, with obvious discoloration and longitudinal and transverse cracks.


a. Significant fissures at the base and upper areas of the cave	b. White crystals precipitating from the upper and middle surfaces of the cave body	c. Blurring of the Buddha's face

Fig. 8 Weathering characteristics of North Grottoes in Qingyang, China under freeze-thaw action

Conclusion must be concise and must be based on the study results. Avoid discussion in theconclusion.

Thank you for your advice. The conclusion has been modified.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

1. Figure 1 must be readable.

2. Reference style must be as per journal format.

3. Concise the abstract according to the journal format.

Author Response

Dear reviewer, the manuscript has been revised as required. Please see the attachment.

Author Response File: Author Response.docx