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Study on the corrosion behavior and mechanical response of weakly cemented sandstone in alkaline solutions
Zhang Jie Resources Writing – original draft Writing – review & editing 1
https://orcid.org/0000-0002-2128-0852
Zhuo Qingsong Data curation Methodology Resources Software Writing – original draft Writing – review & editing 1 *
Zheng Qian Data curation Investigation Methodology Resources 2
Wang Bin Methodology 1
Zhang Mingang Data curation Investigation Methodology Software 3
Zhao Xiaoyu Data curation Investigation Methodology Software 3
Geng Jigang Data curation Formal analysis Methodology Software 3
Li Xiaoshi Conceptualization Data curation Investigation Software 3
Bao Ruoyu Data curation Formal analysis Investigation Resources 4
1 College of Energy, Xi’an University of Science and Technology, Xi’an, China
2 College of Intelligent Manufacturing and Information Engineering, Shaanxi Energy Institute, Xianyang, China
3 Department of Medical Imaging, Xi’an Daxing Hospital, Xi’an, China
4 Information Institute of the Ministry of Emergency Management of the PRC, Beijing, China
Marrocchino Elena Editor
University of Ferrara: Universita degli Studi di Ferrara, ITALY
Competing Interests: The authors have declared that no competing interests exist.

* E-mail: zhuo_simon@163.com
4 9 2024
2024
19 9 e03095441 2 2024
13 8 2024
© 2024 Zhang et al
2024
Zhang et al
https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

This study examines the corrosion characteristics of weakly cemented sandstone under alkaline conditions, evaluating the effects of varying pH levels on its macroscopic degradation, micro-porosity, and mechanical properties, notably uniaxial compressive strength. Findings reveal that heightened alkalinity exacerbates rock damage, although a temporary alleviation in mass loss occurs between pH 9 and 11 due to pore clogging by complexes formed from cations like Ca2+ and Mg2+.Increased alkalinity induces marked changes in pore features, with an observed rise in pore numbers, transformation of pore shapes from elongated to more spherical, and adjustments in porosity, pore size, and roundness. Furthermore, the study confirms a decline in both the rock’s compressive strength and elastic modulus as pH rises. These revelations shed light on the role of pH in the corrosion behavior of weakly cemented sandstone under alkaline conditions, providing a fresh perspective for understanding its corrosion mechanisms in such environments.

The author(s) received no specific funding for this work. Data AvailabilityAll relevant data are within the manuscript and its Supporting information files.
Data Availability

All relevant data are within the manuscript and its Supporting information files.
==== Body
pmcIntroduction

Rocks, as major components of the Earth’s crust, have a decisive impact on the stability of geotechnical engineering due to their physical and mechanical properties. Although most rocks exhibit high strength and compactness, their internal microstructures are particularly sensitive to chemical corrosion, largely due to natural defects and microfractures, potentially weakening their macroscopic mechanical capabilities [1–3]. The mechanisms of rock damage under the influence of chemical solutions is a broadly concerned issue, encompassing theories such as the change in pH values at the tips of rock cracks proposed by Wiederhorn [4], analyses by Feucht and others on the impact on the mechanical strength of sandstone [5], research by M.G. Karfakis and colleagues using fracture mechanics to investigate the intrinsic mechanisms of changes in rock properties [6], and studies by T. Critelli and others on the dissolution rates of rock bodies [7, 8]. Wang and colleagues utilized two-dimensional (2D) micro-computed tomography combined with three-dimensional (3D) volume reconstruction methodologies to scrutinize the dispersion of pores and fractures within sandstones from a microscopic viewpoint, which in turn guides the understanding of macroscopic characteristics [9]. The research on the deformation and failure mechanisms of rocks under the coupled action of chemical solutions has also attracted attention from scholars both domestically and internationally, including Feng Xiaoting and Ding Wuxiu [10–12], and the rock damage models established by Chen Sili, Qiao Liping, and others [13–15]. Tan Xianjun et al. analyzed the deterioration phenomena of rock mass by examining parameters such as strength, deformation characteristics, elastic modulus, and cohesive strength through uniaxial and triaxial experiments [16], while Chen Wei and others have analyzed from macro to micro the corrosion mechanisms of acidic groundwater on coal and rock bodies [17]. Yang Xiurong and others have used SEM to analyze the damage mechanisms of the micro-structure of sandstone [18, 19], and Fang Xinyu and others have studied the mechanical characteristics of yellow sandstone under chemical corrosion and freeze-thaw conditions [20–22]. Li Xinping introduced a model for the evolution of sandstone damage [23–25], and Hao Li and others proposed and validated a damage model for rock bodies under cyclic loading [26]. Lin Yun and others established a statistical damage constitutive model describing the damage evolution pattern of sandstone [27, 28]. In studies exploring the impact of chemical corrosion on the dynamic fracture mechanics of limestone, Yu Liyuan and others found significant effects on the microstructure and mineral elements of rock bodies [2, 29, 30]. Su Xuexue and colleagues investigated the influence and micro-mechanisms of pH on the disintegration of red-layer mudstone on the slopes of the Three Gorges Reservoir [31], and Huang Ming and others developed theoretical models for the disintegration experiments of shale under various acidic and alkaline solutions [32]. Feng Xuezhi and others focused on the impact of chemical solution corrosion and freeze-thaw cycles on rock body damage mechanisms [33]. In the mining areas of Western China, weakly cemented rock bodies such as mudstone, sandstone, and interbedded mud-sandstone may undergo significant changes under the action of water [34, 35], especially in areas with unique hydrogeological conditions where groundwater is predominantly alkaline, leading to a reduction in rock strength [36]. Global research has intensively investigated the mechanisms of rock degradation induced by chemical corrosion, with a particular focus on its pivotal role in geotechnical stability. These inquiries span theories on pH fluctuations at fracture tips, the impact of chemical corrosion on sandstone strength, the evolution of rock properties from a fracture mechanics perspective, and the rates of rock dissolution, among other aspects. The application of advanced imaging techniques has refined our understanding of rock macro-behavior, while numerous scholars have made significant contributions to elucidating the deformation and failure mechanisms of rocks under chemical attack, the pH-dependent variations in mechanical properties, micro-corrosion processes, and theoretical models of rock erosion in varied media. Despite extensive studies conducted in major engineering projects and exceptional geological settings, research specifically addressing the mechanical properties of weakly cemented sandstone in alkaline environments, as in the Shaanbei mining region, remains scarce. Therefore, this paper, building upon previous research, systematically conducts mechanical property tests on weakly cemented sandstone in the Shaanbei mining area under alkaline water corrosion. The objective is to thoroughly analyze the impact of alkaline solutions on the mechanical properties of rocks and investigate their corrosion mechanisms, providing theoretical and experimental support for the development of rock mechanics constitutive models.

Experimental materials, equipment, and methods

Rock specimens and experimental equipment

The weakly cemented sandstone samples required for this experiment were collected from the roof rock layer of the 30208 belt conveyor roadway in Longhua Coal Mine, Sunjiacha Town, Yushenfu mining area in Northern Shaanxi. The cores were taken from the roof according to the distribution and structural characteristics of the coal seams in the mine field, and all selected cores were from the same location within the roadway. After meticulous classification and identification, the cores were processed in the laboratory into standard cylindrical specimens with diameters of 50 mm and heights of 100 mm (for compression), 25 mm (for tension), and 50 mm (for shear) according to the national “Standard for Test Methods of Rock” (GB/T 50218–2014). All specimens were precision machined to ensure that their end face perpendicularity, parallelism, and flatness met the precision required by national standards. After removing any visible defects, the average density of the specimens in their natural water-containing state was 2.66 g/cm3. Mechanical property testing was completed at the MTS laboratory of Xi’an University of Science and Technology, using an HCT series microcomputer controlled electro-hydraulic servo universal testing machine. This machine is equipped with an advanced electro-hydraulic servo control system, which can achieve closed-loop control of load and displacement to ensure high precision of the experiments. During the immersion of rock samples in chemical solutions, the pH was measured using a high-precision pH meter provided by Lichen Technology, with a highly sensitive probe and three-point calibration function ensuring measurement accuracy to 0.01. The mass change of the rock specimens was monitored by a Mengchuang electronic scale with an accuracy of 0.1 g. SEM scanning analysis was conducted using an Axio Scope. A1 polarized light microscope to investigate the microstructural characteristics of weakly cemented sandstone under various alkaline immersion conditions. The operational parameters of the microscope comprised a principal voltage of 100V, power consumption of 140W, with specimen dimensions required to be at least 30mm×60mm×90mm. Additionally, a thin section slicing thickness of 0.03mm was adopted to guarantee clear observation and meticulous analysis of the intricate structures. Concurrently, through the application of pseudocolor enhancement technology, the visual quality of SEM images was improved, enabling a more intuitive analysis and description of the microscale damage and corrosion in the rock mass. Fig 1 displays the processing and testing equipment for the rock specimens.

10.1371/journal.pone.0309544.g001 Fig 1 Rock specimens and testing equipment.

(A) Processed specimen. (B) Pressure testing machine. (C) pH testing pen. (D) Electronic scale. (E) Polarized light microscope.

Preparation of chemical solutions

To verify the types of groundwater in the mining areas of Northern Shaanxi, this study selected the seepage water from the roof of the 3−1 coal seam in Longhua Mine, Shenmu City for chemical composition analysis. Field measurements indicated that the average annual temperature in the 3−1 coal seam roadway is approximately 20.8°C, with relative humidity ranging from 93% to 95%. When collecting water samples, 500 mL plastic bottles, rinsed three to four times with the raw water and corresponding samples, were used. The pH value of the water samples was determined using an onsite water quality monitor and preserved under sealed conditions at temperatures between 0 to 4°C. Sample filtration was conducted using a microporous filter membrane with a diameter of 0.45μm for cation testing. The samples were treated with dilute nitric acid in the laboratory, and the concentrations of anions (SO42−,Cl-) were determined by ion chromatography, while the concentration of HCO3− was measured by titration; cation concentrations (Ca2+, Na+, Mg2+) were tested using an inductively coupled plasma emission spectrometer. To ensure the accuracy of the tests, an ion conservation analysis was conducted. If the ratio of ion concentration was within a 5% range, it was considered conserved; otherwise, the measurement was retaken. Table 1 is a statistical table of the groundwater chemical characteristics for the 3−1 coal seam at the Longhua Mine. The groundwater is slightly alkaline, with an average pH value of 8.75 for the 3−1 coal seam. The groundwater exhibited a slightly alkaline nature, with an average pH value of 8.75 for the 3−1 coal seam. The ion concentration test results indicated a high degree of mineralization, primarily characterized by high contents of Ca2+, Na+, Mg2+, Cl-, SO42−, and HCO3−, with the water chemistry type being predominantly HCO3−-Ca-Na type.

10.1371/journal.pone.0309544.t001 Table 1 Chemical characteristics of groundwater in the Longhua Mine’s 3−1 coal seam.

pH value and ion concentration	3−1 coal seam	
pH	8.75	
K+	mg/l	61.01	
Na+	mg/l	416.92	
Ca2+	mg/l	101.18	
Mg2+	mg/l	93.79	
SO42−	mg/l	590.64	
Cl-	mg/l	1728	
HCO3−	mg/l	673.39	
NO3−	mg/l	66.04	
NO2−	mg/l	20.21	

To simulate the impact of the alkaline hydrochemical environment of shallow coal seams on the mechanical properties of surrounding rocks, solutions with varying ion concentrations and pH levels were prepared, taking into consideration the primary cations (K+, Na+, Ca2+, Mg2+) and anions (Cl-, SO42−,HCO3−) present in the percolating water of the 3−1 coal seam roof. The solution preparation scheme for the water chemistry is shown in Table 2. Solutions with pH values of 7, 9, and 11 were prepared by adding corresponding salts, including anhydrous calcium chloride, sodium chloride, magnesium chloride, and potassium sulfate. These solutions were used to immerse the surrounding rock samples, aiming to observe changes in rock mechanical properties under different alkaline conditions. Deionized distilled water was prepared using the advanced ultrapure water production system at Xi’an University of Science and Technology’s laboratory. The equipment used for immersing the samples was a DZF-1 vacuum drying oven. Fig 2 illustrates the drying process of the immersed samples.

10.1371/journal.pone.0309544.g002 Fig 2 Soaking materials and drying equipment.

(A) Ion concentration preparation chemicals. (B) Ultrapure water manufacturing equipment. (C) Soaked rock specimens. (D) DZF vacuum drying oven.

10.1371/journal.pone.0309544.t002 Table 2 Preparation scheme of water chemical solutions.

Solution type	Solution components	Solution pH value	Solution concentration (mg/l)	
Hydrogen ion concentration of 7 solution	K2SO4, CaCl2, NaCl, MgCl2	7	0.1	
Hydrogen ion concentration of 9 solution	K2SO4, CaCl2, NaCl, MgCl2	9	0.1	
Hydrogen ion concentration of 11 solution	K2SO4, CaCl2, NaCl, MgCl2	11	0.1	

Experimental method

Regarding the experimental procedure, rock samples were placed in open PPS acid-base immersion tanks to ensure continuous contact between the solution and the external environment. Air conditioning was employed to control the indoor temperature. During the immersion process, regular records of the mass variation (Δm) of the samples were maintained, and data changes were monitored. The pH value of the immersion solution was measured using a pH meter, and the trend of pH changes was recorded. After immersion, the rock samples underwent drying and polishing treatments to ensure that the end faces and side surfaces met testing standards and maintained a smooth and vertical appearance. Prior to conducting uniaxial compression tests on the rock samples, a uniform application of Vaseline was applied to both the upper and lower ends of the samples to minimize friction’s influence on the test results. The testing employed a displacement loading method, with the upper loading device kept stable, and a lower loading rate of 0.06 millimeters per minute was applied. Throughout this process, the axial load and axial displacement of the rock sample were monitored in real-time, and deformation and failure processes were recorded. Data changes and numerical variations were also concurrently documented and analyzed.

Analysis of chemical damage mechanisms under alkaline corrosion

Weakly cemented sandstone primarily consists of a framework composed of quartz and feldspar, with pore-filling materials dominated by clay minerals. These two components collectively determine its structural characteristics. Quartz is chemically composed of SiO2, and the chemical formula for potassium feldspar is KAlSi3O8. Clay minerals include kaolinite (Al2[Si2O5](OH)4), montmorillonite (Na0.33(Al,Mg)2Si4O10(OH)2), and others. As the solution’s alkalinity increases, changes in these mineral components indicate their involvement in hydrochemical reactions. The specific chemical reactions are as follows:

In a neutral solution with a pH value of 7, the framework and pore-filling materials of the rock primarily undergo hydrolysis reactions, slowly releasing trace amounts of metal ions such as aluminum and magnesium. These ions subsequently form aluminate ions in the solution. This process may result in minor mineral alteration, although the basic structure of the rock is preserved, long-term exposure may lead to slight changes in its physical and chemical properties. KAlSi3O8+H++4H2O→K++Al3++3H4SiO4 (1)

When the pH value is raised to 9, the release rate of aluminum, magnesium, and other ions from potassium feldspar and clay minerals accelerates, particularly that of magnesium ions. This accelerated release may lead to partial loosening of mineral structures. The dissolution of aluminum and the subsequent formation of aluminum hydroxide ions may attach to the surface of clay minerals, disrupting the lattice structure of potassium feldspar and reducing its physical mechanical strength. In this environment, kaolinite and montmorillonite may transform into silicates and other new compounds, as shown in Eq (3). KAlSi3O8+8H2O→K++AlOH4−+3H4SiO4 (2)

NaAlSi3O8+8H2O→Na++AlOH4−+3H4SiO4 (3)

In a strongly alkaline solution with a pH value of 11, the stability of the rock mass is severely threatened. A large and rapid release of potassium, magnesium, and aluminum ions leads to rapid mineral degradation. Under strong alkaline conditions, kaolinite first undergoes dehydroxylation reactions, while SiO2 in the strongly alkaline environment undergoes hydrolysis to produce a large amount of silicate ions (SiO32−). Aluminum also forms aluminum salts under alkaline conditions. Montmorillonite, a 2:1 layered silicate mineral with a negative charge, undergoes ion exchange with cations such as calcium ions in alkaline aqueous solutions. Along with the dissolution of silicon, aluminum, and magnesium, this results in the formation of corresponding silicate ions, aluminum salts, and magnesium salts. These reactions severely disrupt the framework structure of the rock, leading to a significant reduction in the structural performance of weakly cemented sandstone. At the micro and meso levels, these changes manifest as the development of pores and cracks, while at the macro level, they result in damage to the mechanical properties of the rock. KAl3Si3O10OH2+2OH−+10H2O→K++3AlOH4−+3H4SiO4 (4)

Al2Si2O4OH4+4OH−→2AlOH4−+2SiO32-+2H2O (5)

Na0.33Al,Mg2Si4O10OH2+6OH−→2AlOH4−+2SiO32-+2MgOH42−+0.3Na+ (6)

Results analysis

Analysis of mass damage to rocks in alkaline solutions

Immersing specimens in alkaline solutions inevitably leads to chemical reactions that cause mineral components to leach out, affecting the mass of the rock before and after corrosion. The extent of mass change varies among specimens with different degrees of corrosion. Prior to measurement, surface moisture is removed until no obvious droplets remain, followed by drying and weighing on an electronic scale. The relative mass change (Δm) of a sample in various hydrated chemical solutions is recorded over time, revealing the process of water-rock chemical action. Table 3 lists the mass values of the samples before and after stabilization of the chemical action, while Fig 3 shows the curve of mass damage to rock samples in different pH solutions over time.

10.1371/journal.pone.0309544.g003 Fig 3 Pattern of rock mass loss under hydrochemical action over corrosion time.

(A) Mass difference of pH = 11 specimen. (B) Mass difference of pH = 9 specimen. (C) Mass difference of pH = 7 specimen. (D) Fitting curve.

10.1371/journal.pone.0309544.t003 Table 3 Mass loss Δm (g) of corrosion specimens in different pH solutions.

Solution pH	Corrosion time (days)	
Sample No	1d	7d	14d	21d	28d	35d	42d	49d	
pH = 7	1	0.72	0.97	0.91	0.92	0.96	0.98	0.98	0.97	
2	0.61	0.86	0.86	0.86	0.87	0.91	0.88	0.87	
3	0.49	0.82	0.81	0.81	0.83	0.83	0.84	0.83	
Average		0.60	0.87	0.86	0.88	0.89	0.90	0.90	0.89	
pH = 9	1	0.88	1.60	1.62	1.62	1.63	1.63	1.64	1.63	
2	0.85	1.51	1.56	1.55	1.59	1.57	1.57	1.57	
3	0.81	1.49	1.51	1.53	1.49	1.51	1.52	1.51	
Average		0.85	1.53	1.56	1.57	1.57	1.57	1.58	1.57	
pH = 11	1	1.39	1.69	1.71	1.70	1.69	1.67	1.66	1.66	
2	1.33	1.60	1.63	1.63	1.61	1.59	1.60	1.61	
3	1.29	1.59	1.59	1.57	1.57	1.58	1.56	1.54	
Average		1.34	1.60	1.64	1.63	1.62	1.61	1.60	1.60	

Trend analysis from Fig 3 indicates: (1) With increasing corrosion time, mass loss in all alkaline solutions tends to increase, especially significant in strong and medium alkaline solutions, while the impact of neutral solution is relatively minimal. (2) Initially, the mass change (Δm) is substantial, stabilizing after 6 days, indicating intense water-chemical reactions initially, weakening later. (3) After 50 days of corrosion, the impact of different pH solutions on rock mass is distinct, with the average mass loss in pH = 11 solution being the greatest at 1.60g, equating to a daily loss rate of 3.2×10-2g; loss in pH = 9 solution is slightly lower, and the rate in pH = 7 solution is the lowest.

For varying corrosion times, fitting the mass loss Δm of specimens in different pH chemical solutions yields the curve as shown in Fig 3. The formulae derived for mass loss Δm over time x in various corrosion states are: Δm=m0+A1(1−epxx/t1)+A2(1−epxx/t2) (7)

Eqs (7), (8), (9) and (10) detail these relationships.

Δm=2.796+1.25(1−epxx/0.04)+0.37(1−epx−x/2.70)R2=0.998 (8)

Δm=−0.016+0.79(1−exp−x/2.30)+0.79(1−exp−x/2.30)R2=0.981 (9)

Δm=−0.002+0.09(1−exp−x/25.15)+0.84(1−exp−x/1.52)R2=0.995 (10)

Through fitting analysis of the relationship between mass loss Δm in different pH solutions and corrosion time, we find these variations can be approximately described using a Boltzmann function, showing a high correlation between Δm and the pH of the chemical solution. The main component of quartz is SiO2, an alkaline oxide. Under the action of a pH = 7 solution, due to the presence of abundant Ca2+ in the solution, hydrolysis reactions of calcite and calcium substances are inhibited, and clay minerals in weakly cemented sandstone adsorb Ca2+, clogging pores and fractures, impeding migration, thereby reducing the solubility of SiO2.

Reactions in various pH solutions are detailed in Eqs (11) to (14).

2Rn-+nCa2+→R2Can (11)

When the aqueous solution is at pH = 7, the solubility of SiO2 is very low, and the dissolution reaction of SiO2 can be written as: SiO2+2H2O→H4SiO4 (12)

When the pH of the solution is ≥9, SiO2 undergoes hydrolysis to form H4SiO4. H4SiO4 further decomposes and can be broken down into H3SiO4− and H2SiO42− through the following reactions, which can be represented by the chemical Eq as: H4SiO4→H3SiO4−+H+ (13)

H4SiO4→H3SiO42−+H+ (14)

After 49 days, X-ray diffraction tests show significant changes in the composition of rock specimens, with quartz’s mass percentage dropping from 34.4% to 28.1%, a 20% decrease. SiO2 precipitation increases significantly, and the alkaline solution corrodes the rock specimens, reducing their mass. Over the same period, specimen mass Δm shows pH = 11 > pH = 9 > pH = 7.

Analysis of the pore development patterns in weakly cemented sandstone

In the previous section, the mass damage to rocks by different alkaline solutions was analyzed. This section builds upon the last, employing microscopic methods to analyze the distribution of pores and fractures in weakly cemented sandstone under various alkaline aqueous environments. The approach used here includes analyzing parameters such as the rock’s pore size, porosity, roundness, and orientation frequency.

Porosity: This refers to the ratio of the area of all pores to the total area in SEM images, characterized by the average area of pores within each pore size range.

Pore size: Defined as the longest chord through a pore, representing the size of the pore.

Roundness: R = P2/4πA, where P is the perimeter of the pore and A is its area. Roundness characterizes the shape variation and roundness of pores, representing the shape factor of pores. The larger the shape factor, the more elongated the pore.

Using AVIZO software for domain value segmentation of SEM images of weakly cemented sandstone, appropriate domain values were selected that encompass the pores on the rock surface. Small spots in the images were excluded, and the blue areas represent the distribution of pores in the weakly cemented sandstone under different alkaline water conditions, with other areas indicating undamaged rock base, as shown in Fig 4.

10.1371/journal.pone.0309544.g004 Fig 4 Analysis of porosity in weakly cemented sandstone under different alkaline soaking conditions.

(A) Deionized distilled water. (B) 0.01mol/L CaCl2 pH = 7. (C) 0.01mol/L CaCl2 pH = 9. (D) 0.01mol/L CaCl2 pH = 11.

Table 4 provides the statistics on the micro-pore distribution of weakly cemented sandstone under various alkaline water conditions. The distribution of microscopic pores in weakly cemented sandstone under different alkaline water conditions was statistically analyzed, with the following patterns observed:

Under deionized distilled water soaking conditions, the rock surface exhibited extensive micropores and microcavities, with a surface porosity of 29.09%. The pore diameters ranged from 6.03e-6 to 0.0008 μm, with an average of 2.05e-5 μm and a variance of 8.16e-10. The average pore area was 2.15e-10 μm2. The roundness of the pores ranged from 0.97 to 1094.45, with an average roundness of 6.74 and a variance of 663.

Under 0.01 mol/L CaCl2 pH = 7 soaking conditions, the surface porosity increased to 31.91%, representing a 9.69% increase compared to deionized distilled water. The pore diameters ranged from 8.20e-6 to 0.0011 μm, with an average of 2.43e-5 μm and a variance of 1.25e-9, indicating uniformity in pore sizes. The average pore area was 2.55e-10 μm2. The roundness of the pores ranged from 0.95 to 925.00, with an average roundness of 4.89 and a variance of 607.

Under 0.01 mol/L CaCl2 pH = 9 soaking conditions, there was a further increase in micropores and microcavities on the rock surface. The surface porosity was 33.62%. The pore diameters ranged from 1.03e-6 to 0.0013 μm, with an average of 2.64e-5 μm and a variance of 1.94e-9. The average pore area was 3.06e-10 μm2. The roundness of the pores ranged from 0.91 to 763.00, with an average roundness of 4.59 and a variance of 530, indicating further dispersion in roundness data.

Under 0.01 mol/L CaCl2 pH = 11 soaking conditions, the surface porosity reached 40.39%, representing a 38.84% increase relative to deionized distilled water and a 20.14% increase compared to 0.01 mol/L CaCl2 pH = 9 soaking conditions. The pore diameters ranged from 1.58e-6 to 0.0023 μm, with an average of 3.31e-5 μm and a variance of 6.89e-9. The average pore area was 3.58e-10 μm2. The roundness of the pores ranged from 0.86 to 613.00, with an average roundness of 4.08.

10.1371/journal.pone.0309544.t004 Table 4 Statistical distribution of microscopic pores in weakly cemented sandstone under different alkaline water conditions.

Parameter	Deionized water	0.01mol/L CaCl2 pH = 7 Solution	0.01mol/L CaCl2 pH = 9 Solution	0.01mol/L CaCl2 pH = 11 Solution	
Porosity (%)	29.09	31.91	33.62	40.39	
Pore size (um)	Mean	2.05e-5	2.43e-5	2.64e-5	3.31e-5	
Minimum	6.03e-6	8.20e-6	1.03e-6	1.58e-6	
Maximum	0.0008	0.0011	0.0013	0.0023	
Median	1.36e-6	4.10e-6	5.15e-6	7.90e-6	
Variance	8.16e-10	1.25e-9	1.94e-9	6.89e-9	
Pore area (um2)	2.16e-10	2.55e-10	3.06e-10	3.58e-10	
Roundness	Mean	6.73	4.89	4.59	4.08	
Minimum	0.97	0.95	0.91	0.86	
Maximum	1094.45	925.00	763.00	613.00	
Variance	663	607	530	487	

To better understand the impact of porosity on pore characteristics, we analyzed the correlations between porosity and various parameters such as pore diameter, pore area, and roundness. The relationships are illustrated in Fig 5.

As porosity increases, the average pore diameter also increases. This indicates that as porosity grows, the size of the pores tends to become larger. Specifically, at higher porosity levels, the distribution of pore sizes is broader, and the mean value significantly rises. This trend suggests that the expansion of pores in an alkaline environment may promote the formation of larger pores.

There is a positive correlation between porosity and average pore area; the higher the porosity, the larger the average pore area. As porosity increases, the distribution of pore areas also tends to expand. This is because the alkaline environment promotes the expansion and connection of pores, increasing the area of individual pores. This finding is consistent with the increase in pore diameter, further indicating changes in pore structure under alkaline conditions.

As porosity increases, pore roundness tends to decrease. This suggests that as porosity grows, the shape of the pores becomes more elongated and less circular. Pores with higher porosity are closer to a circular shape, indicating that the alkaline environment may make the pore boundaries more uniform and smooth. This change in shape could be due to the intensified chemical reactions in the alkaline environment, leading to further erosion and adjustment of the pore boundaries.

10.1371/journal.pone.0309544.g005 Fig 5 The relationships between porosity and pore diameter, pore area, and roundness.

(A) The Relationship between Porosity and Pore Diameter. (B) The Relationship between Porosity and Pore Area. (C) The Relationship between Porosity and Roundness.

Through the design of an equivalent factor formula, the number of elongated and round pores could be determined. Shape factors greater than 5 were considered elongated pores, while those less than 2 were considered round. In image processing, equivalent diameter is used to describe the size of irregular objects, so pore size distribution under different alkaline water conditions could be represented by a histogram of the equivalent radius of pores.

From Fig 6, it is evident that with increasing pH of the alkaline water, the number of elongated pores gradually decreases, while the number of round pores slowly increases. Under deionized water conditions, the equivalent diameter of pores ranged from 5.05e-6 to 3.69e-4 um, with an average of 1.04e-5 um. Under 0.01mol/L CaCl2 pH = 7, the range was 2.02e-6 to 8.11e-6 um, with an average of 4.24e-6 um. Under pH = 9, it ranged from 5.05e-7 to 3.51e-5 um, averaging 1.36e-6 um, and under pH = 11, from 1.01e-6 to 7.39e-5 um, averaging 2.69e-6 um.

10.1371/journal.pone.0309544.g006 Fig 6 Distribution of equivalent diameter of pores in weakly cemented sandstone under different alkaline soaking conditions.

(A) Deionized distilled water. (B) 0.01mol/L CaCl2 pH = 7. (C) 0.01mol/L CaCl2 pH = 9. (D) 0.01mol/L CaCl2 pH = 11.

In summary, an enhancement in the alkalinity of solutions fosters a more intricate pore distribution within rocks, thereby progressively elevating the porosity of the rock mass [37, 38]. The mean pore diameter fluctuates in accordance with variations in the alkaline aqueous milieu, concurrently witnessing a reduction in the variance of pore sizes, indicative of an augmented uniformity in pore dimensions as the solution’s alkalinity intensifies. This progression is accompanied by modifications in pore areas and circularity, underscoring a systematic transformation in pore morphology as alkalinity escalates.

A shift in pore shape factors occurs, manifesting a transformation in pore geometries; primitive elongated pores, subsequent to exposure to alkaline conditions, tend to transmute into elliptical and circular configurations. These observations highlight the pivotal role of alkaline fluids in mediating chemical reactions that bolster the stability of the rock structure, instigating structural alterations, mineral dissolution, and the genesis of novel clay minerals-collectively exemplifying a synergistic interplay between mineral dissolution and precipitation processes. Furthermore, an upsurge in the pH of alkaline waters promotes the development of both primary and secondary porosities, augmenting porosity levels and prompting a morphological transition of pore shapes from elongated to elliptical and, ultimately, circular. Concomitantly, there is a diminution in the equivalent pore diameters, while circularity broadly exhibits a declining tendency, altogether emphasizing the profound and transformative influence of heightened alkalinity on the evolutionary trajectory of pore architectures within the lithic fabric.

Changes in the pH of hydrochemical solutions

While analyzing the impact of alkaline solutions on rock mass damage, this study also explored the soaking effect of deionized distilled water, including four different pH hydrochemical solutions. During the experiment, the dynamic changes in the pH of the solutions were regularly measured and recorded using a pH pen. Fig 7 shows that the pH of the four solutions changed differently over time:

For pH = 9 and 11 hydrochemical solutions, their pH decreased over time and eventually stabilized, reflecting the gradual consumption of alkaline components due to chemical reactions with the minerals in the rock, particularly the consumption of hydroxide ions in the solution. By contrast, the pH of deionized distilled water and pH = 7 initially increased, peaked, then gradually decreased, slowly stabilizing. This was due to initial chemical exchanges and reactions with the rock surface, but over time, the reactions balanced.

In the early soaking stage, the pH of deionized distilled water and pH = 7 solution fluctuated significantly within the first 48 hours, especially rising sharply in the first 24 hours to 9.22 and 9.17, respectively. The pH of pH = 9 solution initially decreased significantly in the first 48 hours, then gradually stabilized. These three solutions showed minor pH changes during the mid-soaking stage. For pH = 11 solution, although the pH continued to fluctuate, it remained within a stable range overall.

By 120 hours of soaking, the pH changes in the four solutions were minimal, maintaining a stable state. This was due to minerals such as quartz (SiO2) and glauconite (KAl3Si3O10(OH)2) in the solution undergoing hydrochemical reactions, producing K+ and Al+ ions that caused the original mineral structures to dissociate and release into the solution, binding with OH- ions, thus consuming a large amount of OH- ions and shifting the solution’s pH towards weak alkalinity.

After 150 hours of soaking, due to the increased ion exchange and solubility between the weakly cemented sandstone and the hydrochemical solution, the decomposition of minerals like quartz consumed more OH- ions, causing the pH of the solution to decrease. Continuing to soak until 180 hours, as the ion exchange and hydrolysis reactions between the rock and solution neared completion, the solution’s pH stabilized and no longer exhibited significant changes.

10.1371/journal.pone.0309544.g007 Fig 7 Changes in pH over time in different hydrochemical solutions.

Uniaxial compression test results and analysis

Failure modes of weakly cemented sandstone

Rock specimens soaked in 0.01mol/L CaCl2 solution were used for rock mechanics experimental analysis. Prior to the experiments, the rock specimens that had been soaked were categorized and numbered for ease of subsequent testing and analysis, as shown in Table 5.

10.1371/journal.pone.0309544.t005 Table 5 Soaking conditions of rock specimens under different conditions.

Serial Number	pH Value	Sample Number	Number of Specimen	Remarks	
1	No corrosion	n-1	3	Standard Specimen	
2	n-2	
3	n-3	
4	7	7–1	3	Deionized Water	
5	7–2	
6	7–3	
7	9	9–1	3		
8	9–2	
9	9–3	
10	11	11–1	3		
11	11–2	
12	11–3	

Subjected to external influences, the evolution of pores and fissures within rocks can significantly affect their mechanical properties and the underlying rules governing macroscopic damage, deformation, and failure behavior [39]. During uniaxial compression, the rock specimens exhibited three representative failure modes: conjugate oblique shear failure, single oblique shear failure, and tensile failure. Similarly, unsoaked specimens and those soaked in pH = 7, pH = 9, and pH = 11 solutions demonstrated these failure modes during uniaxial compression tests, as shown in Fig 8.

10.1371/journal.pone.0309544.g008 Fig 8 Shapes and schematic diagrams of uniaxial compression test specimens under stress.

(A) Conjugate oblique shear failure. (B) Single oblique shear failure. (C) Tensile failure.

X-shaped Conjugate Shear Failure Mode: As illustrated in the figure, this failure mode is particularly prominent in an alkaline aqueous immersion environment. The alkaline medium accelerates the dissolution of bonding materials within the rock, thereby exacerbating variations in its microstructure. In this process, two intersecting fracture planes form, creating an oblique angle with respect to the direction of applied load, directly illustrating the outcome where shear stress surpasses the rock’s bearing threshold. With sustained external loading, microcracks within the rock gradually extend and interconnect, culminating in the characteristic X-shaped fracture pattern. This evolution underscores the complex interplay between shear forces and changes in the rock’s internal structure.

The rock samples display a propensity for plastic flow behavior, evidenced by a rise in internal plastic deformation that, in turn, diminishes the rock’s comprehensive strength. Initiation of the failure progression is gradual and continuous, departing from typical brittle fracture modes and exhibiting heightened plastic deformation traits. Under these circumstances, crack propagation assumes a more complex and refined pattern, indicative of sophisticated fracturing dynamics.

Single-plane Shear Failure Mode: Under identical alkaline water soaking conditions, this failure mode exhibits its distinctiveness, characterized by the presence of a single dominant shear fracture plane. This type of failure arises from the accumulation of shear stress on a specific plane exceeding the rock’s shear strength limit, embodying the classic shear failure mechanism. Of note, the maximum resistance before shear failure is not only dependent on the magnitude of shear stress but is also intricately linked to the normal stress acting on that plane, reflecting an adjustment of the rock’s shear strength under the combined influence of normal and shear stresses. Thus, it can also be regarded as a form of combined compressive-shear failure. Unlike the X-shaped conjugate shear, this mode highlights scenarios where stress in a single direction overwhelms the rock’s shear resistance.

Tensile Failure Mode: In the single-axis compression testing under alkaline water conditions, the tensile failure of rocks is equally remarkable. Transverse tensile stress induced by axial pressure, when surpassing the rock’s tensile strength, leads to prominent radial fractures. The alteration of the rock’s internal structure due to alkaline immersion enhances its susceptibility to lateral stress, facilitating the occurrence of tensile failure. This phenomenon emphasizes how environmental factors, by altering the internal stress state of the rock, facilitate the development of specific failure mechanisms.

Through these systematic descriptions, our understanding of rock failure modes under specific environmental loads is not only enhanced but also provides a firmer theoretical foundation for subsequent mechanical analyses and predictions.

Analysis of the failure process of weakly cemented sandstone

Unsoaked specimens and those soaked in pH = 7, pH = 9, and pH = 11 solutions were subjected to uniaxial compression tests to analyze the mechanical properties of the rock at various stages, as shown in Fig 9. In each hydrochemical environment, the rock’s stress-strain curve can be divided into four stages: compaction, elasticity, yield, and post-yield.

10.1371/journal.pone.0309544.g009 Fig 9 Stress-strain curves of rock specimens under uniaxial compression in different soaking conditions.

(A) Dry state. (B) pH = 7 CaCl2 soaking solution. (C) pH = 9 CaCl2 soaking solution. (D) pH = 11 CaCl2 soaking solution.

Compaction Stage: Under axial pressure, the rock’s original open structural planes and microcracks gradually close, causing compaction. In this stage, strain increases rapidly, while stress growth is relatively slower. As the soaking environment’s pH increases, the duration of the rock’s uniaxial compression compaction stage tends to extend. This is due to the dissolution of minerals and changes in cementing material properties caused by alkaline water, expanding the rock’s pore structure and forming more cracks and holes, affecting the rate of internal structure closure.

Elastic Stage: The curve is almost linear, with stress and strain growing linearly and uniformly. Microcracks continue to close, and due to the reduction of cementing substances, new microcracks easily form, leading to fracture. The increasing pH of alkaline water significantly affects the amount of stress and strain change in this stage, reducing the amount of stress change. The slope, representing the modulus of elasticity, shows Dry (4.7GPa) > pH = 7 (4.4GPa) > pH = 9 (3.8GPa) > pH = 11 (3.1GPa).

Yield Stage: The rock specimens enter an irreversible stage, exhibiting plastic deformation and crack expansion. The stress-strain curve shows non-linear characteristics. With increasing pH of alkaline water, the rock’s strain values correspondingly increase. Peak strength is Dry (38.8MPa) > pH = 7 (30.1MPa) > pH = 9 (28.7MPa) > pH = 11 (26.7MPa), while peak strain values follow the order of Dry < pH = 7 < pH = 9 < pH = 11.

Post-Yield Stage: After the rock specimens reach peak strength, their internal structure is damaged, but they largely maintain their overall shape. Due to stress concentration and deformation, existing cracks in the rock further expand, forming along existing microcracks or in new areas, further damaging the rock’s internal structure. Under alkaline water soaking, changes in the properties of cementing substances weaken the bond between rock particles, leading to displacement and relative motion of micro-particles, and eventually particle fragmentation. As cracks expand and particle fragmentation increases, the rock’s overall structure gradually becomes unstable, leading to a decline in strength, but not to zero, indicating that fractured rock still has some load-bearing capacity.

Microstructural changes in the elastic modulus of weakly cemented sandstone in alkaline environments

The modulus of elasticity is a key indicator of a rock’s resistance to deformation, directly reflecting its internal structure’s rigidity [40, 41]. In alkaline environments, changes in the microstructural porosity and fracture structure due to chemical solutions’ action are crucially important to the modulus of elasticity. With increasing pH of the solution, the microstructure of weakly cemented sandstone specimens undergoes disintegration, with cementing materials like silicates and carbonates dissolving faster in alkaline water solutions with pH greater than 9, leading to a decrease in the degree of cementation. This process not only increases the number and volume of pores but may also induce the formation of new microcracks or the expansion of existing ones, thereby weakening the rock’s cohesion and structural integrity.

Under neutral conditions (pH = 7), the cementing materials of weakly cemented sandstone are relatively stable, with minimal impact on pores and fractures, thus maintaining a higher modulus of elasticity. However, with increasing alkalinity of the solution, especially when the pH exceeds 9, the dissolution of cementing materials leads to significant changes in the pore structure, increasing the number and connectivity of microcracks, reducing the rock’s load transfer ability, thereby decreasing its resistance to compressive forces, as reflected in the reduced modulus of elasticity. In summary, as the pH of the solution increases, the modulus of elasticity of weakly cemented sandstone specimens gradually decreases, as shown in Fig 10.

10.1371/journal.pone.0309544.g010 Fig 10 Analysis of rock modulus of elasticity under different soaking conditions.

Conclusion

This study has thoroughly investigated the impact of alkaline solutions on the mass damage and mechanical properties of weakly cemented sandstone. The primary findings of this research are as follows:(1) The experiments indicate that as the alkalinity (pH value) of the soaking solution increases, the degree of mass damage to the rock significantly escalates. Particularly when the pH value reaches or exceeds 9, complexes composed of cations like Ca2+ and Mg2+ can block the pores and fractures in the rock. The protective layers formed by these complexes effectively prevent further infiltration of moisture and chemicals, thereby significantly slowing down additional mass damage to the rock. This discovery highlights the crucial role of cations in maintaining rock structural stability in alkaline environments.(2) The microscopic pore analysis indicates that as the alkalinity of the solution increases, there is a continuous increase in porosity and a corresponding decrease in the variance of pore sizes, leading to a greater uniformity among the pore sizes. The original elongated pores at the edges lose their cementation, altering their shape towards more elliptical and circular forms. The primary pores continue to expand slowly, while new pores further develop. The evolution of pores is increasingly away from elongated forms, progressing towards elliptical and even circular shapes.(3) The study found that the pH of the alkaline solution exhibits a decreasing trend over time due to the consumption of alkaline components in the solution. In contrast, the pH of deionized distilled water and solutions with a pH of 7 initially rises, then gradually decreases, and eventually stabilizes. This change indicates that the reaction between the alkaline solution and minerals leads to the consumption of hydroxide ions, and this reaction stabilizes over time.(4) After hydrochemical corrosion, the uniaxial compressive strength of weakly cemented sandstone specimens decreases with increasing pH of the alkaline solution, while the modulus of elasticity shows an increasing trend with increasing pH. This trend reflects the complex response of rock structures to alkaline solutions and reveals the intricate impact of alkaline solutions on the corrosion of rock minerals and internal fracture changes. These studies not only enhance our understanding of the mechanical behavior of rocks in alkaline environments but also provide important guidance for engineering practice management in related fields.

Supporting information

S1 File (DOCX)

The authors would like to thank the staff of the Radiology Department at Daxing Hospital.

10.1371/journal.pone.0309544.r001
Decision Letter 0
Marrocchino Elena Academic Editor
© 2024 Elena Marrocchino
2024
Elena Marrocchino
https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Submission Version0
26 Jun 2024

PONE-D-24-04355Study on the corrosion behavior and mechanical response of weakly cemented sandstone in alkaline solutionsPLOS ONE

Dear Dr. Zhuo,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands.

Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

The topic of your paper is within the scope of PONE, and it is generally well written and well organized, with experimental facilities and methods well described.

More in detail,

The research is particularly relevant to the fields of mining and geotechnical engineering. By focusing on weakly cemented sandstone from a specific mining area, the study offers practical insights that can be directly applied to similar geological settings.

The study examines the corrosion behavior and mechanical reaction of weakly cemented sandstone in alkaline solutions using a thorough and organized technique that includes a variety of experiments and analysis.. This includes mass damage analysis, pore characteristics assessment, uniaxial compressive strength tests, and microstructural analysis using SEM.

The preparation of rock specimens, the creation of alkaline solutions, and the precise measurement techniques (e.g., pH meter, electronic scale, SEM) are thoroughly documented.

The findings are strengthened by the results, which are presented with sufficient statistical support and are examined using statistical techniques to assess data such as porosity, pore size, and roundness..

Figures and tables effectively visualize the data and help in understanding the trends observed in the experiments.

Anyway

Chemical reactions and their impacts on mineral composition are inferred based on observed data. To get a more precise picture of the precise molecular changes occurring, direct chemical examination (such as spectroscopy) of the rock composition before and after exposure to alkaline solutions could be helpful..

While the study presents significant findings, the discussion on their practical applications in engineering scenarios is limited. A more detailed exploration of how these insights can influence mining practices, construction methods, or material selection would enhance the practical value of the research.

The authors should ensure that their references are accessible internationally.

References to comparable rock structures in other parts of the world should be included and compared.

In summary, this study is relevant providing valuable insights. However, direct chemical analysis, such as spectroscopy, before and after exposure to alkaline solutions, would provide a more precise understanding of molecular-level changes. Additionally, a more detailed discussion on the practical applications of these findings in engineering scenarios would enhance the research's practical value. Ensuring that references are internationally accessible and comparing findings with similar rock structures globally would further strengthen the study.

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Comments to the Author

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Reviewer #1: Yes

Reviewer #2: Yes

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: No

Reviewer #2: Yes

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Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: In this paper, the corrosion behavior and mechanical response of weakly cemented sandstone in alkaline solutions are studied. It is an original and technical work, which is valuable for the research in related fields. But the paper needs very significant improvements before it can be accepted for publication. My detailed comments are as follows:

1.Please check the logic of the abstract. It should clearly describe the research background, the method used to conduct the research, the main content of the manuscript, the results, and the expected effect. The current version should be carefully simplified.

2.The introduction listed many references that are mainly related to the corrosion behavior and mechanical response of weakly cemented sandstone in alkaline solutions. If the authors would like to keep these references, some discussions on the relevance of these refs to the present research are needed. A review of the directly relevant refs will be more helpful for the reader.

3. The scanning electron microscope (SEM) analysis method utilized in this paper is particularly effective for corrosive environments. On the other hand, this SEM analysis technique is well-established. However, the study does not provide details such as the equipment model and other parameters. The current research represents a direct application of this method, yet it fails to adequately describe the microscopic morphology and structure of the rock texture. The existing descriptions are solely based on the structure of the magnified rock texture, without a specific quantification process.

4.In the analysis of failure patterns in uniaxial compression tests on weakly cemented sandstone, the characterization of the stress-induced failure modes for rock samples needs enhancement. The details within this section should be further elaborated upon.

5.It is noted that your manuscript needs careful editing, particularly attention to English grammar, spelling, and sentence structure so that the goals and results of the study are clear to the reader. It is strongly recommended that simple and precise sentences be used to convey the study's findings.

Once the above concerns are fully addressed, the manuscript can be further evaluated for publication in the journal.

Reviewer #2: Summary of paper

This is an experimental study to assess the impact of varying alkaline pH levels on macroscopic mass damage, microscopic pore characteristics, and uniaxial compressive strength of weakly cemented sandstone. This work fills a gap in studies on weakly cemented sandstone in the Shaanbei mining area.

The results indicate that as the alkalinity of the solution increases, the mass damage to the rock intensifies. However, in the pH range of 9 to 11, the mass loss rate is mitigated due to the clogging of pores by complexes formed by cations such as Ca2+ and Mg2+. Microstructural analysis reveals that porosity, pore size, and roundness undergo changes with increasing alkalinity; native pores increase, secondary pores develop, and the roundness of the pores shows a declining trend, with pore shapes evolving from elongated to elliptical and even spherical. Moreover, both the uniaxial compressive strength and elastic modulus of the rock exhibit a downward trend with increasing pH values.

Comments

The topic is within the scope of PONE.

The paper is generally well written, the level of English is good.

The experimental facilities and methods are well described.

The authors propose various chemical pathways that could explain the results.

The authors focus mostly on recording the mass variation (Δm) in the rock samples over a long period of time -- 55 days, e.g. figure 3. However, it is also customary to present and analyze correlations as a function of porosity, see Qi Ping et al. Applied Science 2022, 12, 7635; Yun Lin et al. Hindawi Geofluids 2019, 7320536. Although the authors mention the pdf of porosity, e.g. Table 4, they do not present any correlations against porosity or discussion. Hence, this part of the paper is weak.

Why did the authors not consider the effects of acidic solutions? That would complete the whole range of pH, and presumably could be done in a relatively straight forward manner given that they already have the setup.

About 90% of the references are studies in China published in Chinese journals; I have found these references difficult to access, many I could not access at all. It is important that references, particularly those containing data, in an internationally renowned journal such as PONE should be readily accessible to the international community. The authors should make sure that their references are accessible internationally.

Along the same lines as above, references to other comparable rock structures in other parts of the world should also be made compared and conclusions drawn. How do their findings compare with other similar rocks from around the world? Are the results predictable, or is there anything radically different or surprising?

Summary and recommendation

This paper is essentially about characterizing the development of corrosion and failure in weakly cemented sandstone form the Shaanbei mining area. Unfortunately, many deficiencies in the paper compel me to recommend rejection for publication in PONE:

A comparison with similar studies worldwide is lacking.

A plots/figures of correlations against porosity and discussion is lacking.

References and comparison with similar rock structures from other parts of the world is lacking.

References to readily accessible internationally peer reviewed journals must be made.

**********

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Reviewer #1: No

Reviewer #2: No

**********

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Attachment Submitted filename: PONE-D-24-04355-Review.docx

10.1371/journal.pone.0309544.r002
Author response to Decision Letter 0
Submission Version1
4 Jul 2024

Dear editors and reviewers:

I am delighted to receive your response and am deeply appreciative of the effort and diligent approach you have demonstrated in reviewing my article. Moving forward, I intend to address each question raised by the reviewing experts systematically. In accordance with your suggestions, I have meticulously revised the manuscript, and herein, I provide responses to your comments for your review and verification.

Response to Reviewer 1 Comments

Point 1: Please check the logic of the abstract. It should clearly describe the research background, the method used to conduct the research, the main content of the manuscript, the results, and the expected effect. The current version should be carefully simplified.

Response 1: I deeply appreciate your constructive feedback on the abstract. In line with your suggestion, I have meticulously reviewed and revised the abstract to clearly lay out the research background, explicitly detail the methodologies used, accurately summarize the manuscript's core contents, plainly present the attained results, and succinctly communicate the anticipated outcomes.

Point 2: The introduction listed many references that are mainly related to the corrosion behavior and mechanical response of weakly cemented sandstone in alkaline solutions. If the authors would like to keep these references, some discussions on the relevance of these refs to the present research are needed. A review of the directly relevant refs will be more helpful for the reader.

Response 2: Thank you for highlighting the need for a more nuanced discussion of the references cited in the introduction. I understand the importance of demonstrating the relevance of each reference to our present work. Consequently, I have critically reviewed the list and augmented the introductory section with a concise discourse on how each of the selected references connects to our study objectives, methodologies, and anticipated findings. This additional context should enhance readability and clarify the rationale behind the inclusion of these references, thereby offering readers a more coherent understanding of the research landscape within which our work is situated.

Point 3: The scanning electron microscope (SEM) analysis method utilized in this paper is particularly effective for corrosive environments. On the other hand, this SEM analysis technique is well-established. However, the study does not provide details such as the equipment model and other parameters. The current research represents a direct application of this method, yet it fails to adequately describe the microscopic morphology and structure of the rock texture. The existing descriptions are solely based on the structure of the magnified rock texture, without a specific quantification process.

Response 3: I appreciate the reviewer's comment concerning the SEM analysis method. In addressing this, I have included detailed specifics about the SEM equipment model, operational voltage levels, and magnification configurations employed in my experiments within the Materials and Methods section. Furthermore, I have enhanced the depiction of the rock texture's microscopic morphology and structure by integrating quantitative measures, such as analyses of pore size distribution and surface roughness, facilitated by image processing techniques. These improvements are aimed at furnishing a more holistic and scientifically rigorous portrayal of the SEM analysis outcomes.

Point 4: In the analysis of failure patterns in uniaxial compression tests on weakly cemented sandstone, the characterization of the stress-induced failure modes for rock samples needs enhancement. The details within this section should be further elaborated upon.

Response 4: I am genuinely appreciative of the reviewer's astute recommendation emphasizing the need for a more exhaustive depiction of stress-induced failure mechanisms in my uniaxial compression experiments concerning weakly cemented sandstone samples. In light of this guidance, I have comprehensively enhanced the explication of the complex breakdown processes triggered by loading in the course of conducting uniaxial compression tests on these weakly consolidated sandstone specimens.

Point 5: It is noted that your manuscript needs careful editing, particularly attention to English grammar, spelling, and sentence structure so that the goals and results of the study are clear to the reader. It is strongly recommended that simple and precise sentences be used to convey the study's findings.

Response 5: I am deeply grateful for the reviewer's meticulous scrutiny of linguistic clarity and the constructive criticism offered. Special attention has been devoted to ensuring grammatical precision, rectifying spelling mistakes, and simplifying sentence structures for improved readability. Consequently, I have reformulated several sections, adopting simpler and more succinct sentences, with the aim of conveying our study's aims, methodology, results, and implications more lucidly. I am assured that these modifications will markedly enhance the manuscript's clarity and efficacy in communicating our research to the targeted readership.

Response to Reviewer 2 Comments

Point 1: The authors focus mostly on recording the mass variation () in the rock samples over a long period of time -- 55 days, e.g. figure 3. However, it is also customary to present and analyze correlations as a function of porosity, see Qi Ping et al. Applied Science 2022, 12, 7635; Yun Lin et al. Hindawi Geofluids 2019, 7320536. Although the authors mention the pdf of porosity, e.g. Table 4, they do not present any correlations against porosity or discussion.

Response 1: I am deeply grateful to the reviewer for suggesting a more in-depth analysis regarding the correlation with porosity. In response to this feedback, I have conducted additional statistical evaluations, referencing and citing the similar approaches employed by Qi Ping et al. (Applied Science, 2022, 12, 7635) and Yun Lin et al. (Hindawi Geofluids, 2019, 7320536). This detailed analysis encompasses considerations such as the transformation of pore shape factors, effects of mineral dissolution and precipitation, thereby enriching the discussion on this topic.

Point 2: Why did the authors not consider the effects of acidic solutions? That would complete the whole range of pH, and presumably relatively straight forward given that they already have the setup.

Response 2: The reviewer poses a relevant question about the omission of acidic solutions in my study. My initial emphasis rested on elucidating corrosion characteristics in alkaline environments, given their predominance in the targeted geological context. Nonetheless, I acknowledge the importance of broadening my inquiry to cover the complete pH spectrum. In light of this realization, I intend to conduct further experiments incorporating acidic solutions in a subsequent study. These additional investigations will serve to augment the present results and facilitate a holistic comprehension of the rock's behavior throughout the entire pH range. I am thankful for the reviewer's insight, which has significantly expanded the horizon of my impending research efforts.

Point 3: About 90% of the references are studies in China published in Chinese journals; I have found these difficult to access, many I could not access at all. It is important that references, particularly those containing data, in an internationally renowned journal such as PONE should be readily accessible to the international community. The authors should make sure that their references are accessible internationally.

Response 3: I am exceedingly grateful for your insightful comments on the accessibility of references in my paper, particularly highlighting the challenges that referencing Chinese journals might impose on an international audience. Your observation has both inspired me and proved vital in informing necessary enhancements to my work.

In line with your guidance, I have taken the following actions: I have meticulously verified and corrected the URLs for the Chinese references to ensure seamless linking and accessibility. Furthermore, I have expanded the bibliography to incorporate a greater number of foreign language references relevant to the study, thereby elevating the paper's international scope and perspective.

Point 4: Along the same lines as above, references to other comparable rock structures in other parts of the world should also be made compared and conclusions drawn. How do their findings compare with other similar rocks from around the world? Are the results predictable, or is there anything radically different or surprising?

Response 4: Sincere gratitude for emphasizing the importance of positioning my research findings within a global context. Heeding your invaluable advice, I have integrated the following enhancements into the manuscript, thereby augmenting its depth and breadth through the inclusion of a comparative analysis with analogous geological structures worldwide.I have broadened the scope of the literature review to encompass pivotal global studies that concentrate on geological formations resembling my rock layers. These studies meticulously compare and contrast similarities and differences in geological attributes, formation processes, and observable behaviors.

I am immensely grateful to the editors and reviewers for their invaluable advice, which has enabled me to meticulously revise the manuscript, restructure its content, and enhance both the academic rigor and readability of the paper. I extend my sincere thanks once again to the editorial team and reviewers for their diligent efforts. Each of your comments has proven to be immensely valuable and instrumental in refining and improving our work. I remain hopeful that our paper will soon gain full recognition and be published.

Dr. Qingsong Zhuo

Xi'an City, Shaanxi Province, China

Jul. 3, 2024

Attachment Submitted filename: Response to Reviewers.docx

10.1371/journal.pone.0309544.r003
Decision Letter 1
Marrocchino Elena Academic Editor
© 2024 Elena Marrocchino
2024
Elena Marrocchino
https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Submission Version1
2 Aug 2024

PONE-D-24-04355R1Study on the corrosion behavior and mechanical response of weakly cemented sandstone in alkaline solutionsPLOS ONE

Dear Dr. Zhuo,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

==============================

ACADEMIC EDITOR: Dear Authors,

the following issues need attention:

<ol><li> 

Porosity Correlations: Include analysis and plots correlating results with porosity, as this is customary in similar studies (e.g., Qi Ping et al., 2022; Yun Lin et al., 2019).<li> 

Figure Adjustments:

Figure 3: Consolidate panels A-D into a single figure with fits and increase font sizes for readability.

All Figures: Ensure font sizes are clear and consistent across all figures.

<li> 

References Accessibility:

Ensure all references are internationally accessible. Many current references are difficult to access, and some links (e.g., references 38-42) are incorrect. Verify all references are correctly linked and accessible.

 

Please address these points to improve the manuscript

==============================

Please submit your revised manuscript by Sep 16 2024 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

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Elena Marrocchino

Academic Editor

PLOS ONE

Journal Requirements:

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

Additional Editor Comments:

Dear Authors,

The manuscript "Study on the Corrosion Behavior and Mechanical Response of Weakly Cemented Sandstone in Alkaline Solutions" (PONE-D-24-04355R1) was reviewed by two expert peer reviewers. While one reviewer has recommended acceptance, the other reviewer has requested further revisions to improve the manuscript.

Please carefully consider the comments and suggestions provided by the reviewer and make the necessary revisions. Once you have addressed these points, please submit the revised manuscript for further evaluation.

Thank you for your attention to this matter.

Best regards,

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: (No Response)

********** 

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

********** 

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: No

********** 

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Reviewer #1: Yes

Reviewer #2: Yes

********** 

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Reviewer #1: Yes

Reviewer #2: Yes

********** 

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The authors have diligently addressed all reviewer comments and concerns, resulting in a significantly improved manuscript. The revised manuscript now presents a well-structured and informative analysis of the impact of seepage force on the mechanical characteristics of filling bodies. The proposed constitutive model demonstrates good agreement with the experimental results, showcasing its potential application in analyzing the mechanical behavior of filling bodies under various seepage conditions. I am confident that this revised work will be of significant interest to researchers in the field of geotechnical engineering and recommend its acceptance for publication.

Reviewer #2: Some of my concerns have been addressed and satisfied. Below, I summaries my remaining concerns:

[1] “The authors focus mostly on recording the mass variation (Δm) in the rock samples over a long period of time -- 55 days, e.g. figure 3. However, it is also customary to present and analyze correlations as a function of porosity, see Qi Ping et al. Applied Science 2022, 12, 7635; Yun Lin et al. Hindawi Geofluids 2019, 7320536. Although the authors mention the pdf of porosity, e.g. Table 4, they do not present any correlations against porosity or discussion.”

Although the authors have updated the review section, what I really wanted was actual plots of variable against the porosity such as those appearing in the cited references. Please address this point with more analysis and correlations against porosity.

[2] Figure 3: (D) is simply a repeat of A-C with fits added. Please reduce this to a single figure3D=figure 3.

Figure 3: make the axes and table insert fonts bigger (or put the table into the main text) – they are not clearly visible.

All figures: increase the axes font size for the same reason as above.

[3] “About 90% of the references are studies in China published in Chinese journals; I have found these difficult to access, many I could not access at all. It is important that references, particularly those containing data, in an internationally renowned journal such as PONE should be readily accessible to the international community. The authors should make sure that their references are accessible internationally.”

The two references that I suggested were just examples. The authors should find more similar references.

Although the authors have referenced more international journals, there are still some that are difficult to access e.g. references 16. Furthermore, some of the web links are spurious – for example, the links in references 38-42 seem to be wrong. I do not have the time to go through all the references – the authors should make sure that all 42 references are readily accessible internationally and are properly linked.

********** 

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Reviewer #1: No

Reviewer #2: No

**********

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Attachment Submitted filename: PONE-D-24-04355-R2.pdf

10.1371/journal.pone.0309544.r004
Author response to Decision Letter 1
Submission Version2
5 Aug 2024

Dear editors and reviewers:

I am delighted to receive your response and am deeply appreciative of the effort and diligent approach you have demonstrated in reviewing my article. Moving forward, I intend to address each question raised by the reviewing experts systematically. In accordance with your suggestions, I have meticulously revised the manuscript, and herein, I provide responses to your comments for your review and verification.

Response to Reviewer Comments

Point 1: “The authors focus mostly on recording the mass variation (Δm) in the rock samples over a long period of time -- 55 days, e.g. figure 3. However, it is also customary to present and analyze correlations as a function of porosity, see Qi Ping et al. Applied Science 2022, 12, 7635; Yun Lin et al. Hindawi Geofluids 2019, 7320536. Although the authors mention the pdf of porosity, e.g. Table 4, they do not present any correlations against porosity or discussion.”

Although the authors have updated the review section, what I really wanted was actual plots of variable against the porosity such as those appearing in the cited references. Please address this point with more analysis and correlations against porosity.

Response 1: Thank you for your valuable feedback on our manuscript. We have addressed your comments as follows:We recognize the importance of presenting and analyzing correlations with porosity. We have provided detailed scatter plots illustrating the relationship between porosity and various parameters, such as pore diameter, pore area, and circularity. These plots were inspired by the methodology employed in the references you cited (Qi Ping et al., Applied Science 2022, 12, 7635; Yun Lin et al., Hindawi Geofluids 2019, 7320536). We have expanded the discussion section to include a comprehensive analysis of these correlations. We have provided interpretations for the observed trends and their implications for the structural changes in the rock samples under different immersion conditions. This detailed discussion, as you requested, addresses the need for a more thorough analysis and correlation with porosity.

We are grateful for your valuable feedback. We look forward to your further comments and suggestions.

Point 2: Figure 3: (D) is simply a repeat of A-C with fits added. Please reduce this to a single figure3D=figure 3.Figure 3: make the axes and table insert fonts bigger (or put the table into the main text) – they are not clearly visible. All figures: increase the axes font size for the same reason as above.

Response 2: Thank you for your suggestion. I have enlarged and standardized the font size in all figures throughout the paper to ensure clarity and consistency for reader accessibility.

Point 3: “About 90% of the references are studies in China published in Chinese journals; I have found these difficult to access, many I could not access at all. It is important that references, particularly those containing data, in an internationally renowned journal such as PONE should be readily accessible to the international community. The authors should make sure that their references are accessible internationally.”

The two references that I suggested were just examples. The authors should find more similar references. Although the authors have referenced more international journals, there are still some that are difficult to access e.g. references 16. Furthermore, some of the web links are spurious – for example, the links in references 38-42 seem to be wrong. I do not have the time to go through all the references – the authors should make sure that all 42 references are readily accessible internationally and are properly linked.

Response 3: I have carefully checked and revised all references to guarantee that they are correctly formatted, hyperlinked, and lead to the correct online sources.

I am immensely grateful to the editors and reviewers for their invaluable advice, which has enabled me to meticulously revise the manuscript, restructure its content, and enhance both the academic rigor and readability of the paper. I extend my sincere thanks once again to the editorial team and reviewers for their diligent efforts. Each of your comments has proven to be immensely valuable and instrumental in refining and improving our work. I remain hopeful that our paper will soon gain full recognition and be published.

Dr. Qingsong Zhuo

Xi'an City, Shaanxi Province, China

Aug. 5, 2024

Attachment Submitted filename: Response to Reviewers.docx

10.1371/journal.pone.0309544.r005
Decision Letter 2
Marrocchino Elena Academic Editor
© 2024 Elena Marrocchino
2024
Elena Marrocchino
https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Submission Version2
14 Aug 2024

Study on the corrosion behavior and mechanical response of weakly cemented sandstone in alkaline solutions

PONE-D-24-04355R2

Dear Dr. Zhuo,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice will be generated when your article is formally accepted. Please note, if your institution has a publishing partnership with PLOS and your article meets the relevant criteria, all or part of your publication costs will be covered. Please make sure your user information is up-to-date by logging into Editorial Manager at Editorial Manager® and clicking the ‘Update My Information' link at the top of the page. If you have any questions relating to publication charges, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Elena Marrocchino

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

10.1371/journal.pone.0309544.r006
Acceptance letter
Marrocchino Elena Academic Editor
© 2024 Elena Marrocchino
2024
Elena Marrocchino
https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
23 Aug 2024

PONE-D-24-04355R2

PLOS ONE

Dear Dr. Zhuo,

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now being handed over to our production team.

At this stage, our production department will prepare your paper for publication. This includes ensuring the following:

* All references, tables, and figures are properly cited

* All relevant supporting information is included in the manuscript submission,

* There are no issues that prevent the paper from being properly typeset

If revisions are needed, the production department will contact you directly to resolve them. If no revisions are needed, you will receive an email when the publication date has been set. At this time, we do not offer pre-publication proofs to authors during production of the accepted work. Please keep in mind that we are working through a large volume of accepted articles, so please give us a few weeks to review your paper and let you know the next and final steps.

Lastly, if your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

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on behalf of

Dr. Elena Marrocchino

Academic Editor

PLOS ONE
==== Refs
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