Combined effects of salt, cyclic wetting and drying cycles on the physical and mechanical properties of sandstone

Accepted Manuscript Combined effects of salt, cyclic wetting and drying cycles on the physical and mechanical properties of sandstone

Qiang Sun, Yuliang Zhang PII: DOI: Reference:

S0013-7952(18)30841-X https://doi.org/10.1016/j.enggeo.2018.11.009 ENGEO 4995

To appear in:

Engineering Geology

Received date: Revised date: Accepted date:

22 May 2018 19 November 2018 20 November 2018

Please cite this article as: Qiang Sun, Yuliang Zhang , Combined effects of salt, cyclic wetting and drying cycles on the physical and mechanical properties of sandstone. Engeo (2018), https://doi.org/10.1016/j.enggeo.2018.11.009

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

Combined effects of salt, cyclic wetting and drying cycles on the physical and mechanical properties of sandstone Qiang Sun1,2, Yuliang Zhang1,3,* 1. School of Resources and Geosciences, China University of Mining and Technology, Xuzhou,

PT

Jiangsu Province 221116, P.R. China

RI

2. Geological Research Institute for Coal Green Mining, Xi’an University of Science and

SC

Technology, Xi’an 710054, P.R. China

*Corresponding author: [email protected]

NU

3. School of Civil Engineering, Tianjin University, Tianjin 300072, P.R. China

MA

Abstract: Salt weathering has considerable effects, and it has recently become the subject of interest among researchers and engineers, especially in terms of sandstone heritage buildings and

PT E

D

sandstone monuments. However, the impacts of salt weathering on sandstone after wetting-drying cycles have been neglected in the literature. Under the conditions of the long-term or gradual

CE

underground seepage of water into sandstone heritage buildings and monuments, salt accumulation and recrystallization occur in sandstone when the rate of evaporation is sufficiently high, and they

AC

reduce rock stability. In view of this problem, experiments subjecting sandstone to up to 50 wetting-drying cycles were conducted using water and solutions containing concentrations of 4%, 6% or 8% magnesium sulfate (MgSO4). The physical and mechanical properties were tested after different wetting-drying cycles. The results show that the wetting-drying cycles impacted the sandstone samples soaked in a salt solution more than the samples that were soaked in only water. Thirty cycles is the threshold number in terms of changes in P-wave velocity, thermal conductivity

ACCEPTED MANUSCRIPT

and tensile strength. A correlation analysis was conducted, and it showed that both color lightness and thermal conductivity are good parameters for evaluating tensile strength. The results contribute to the evaluation process and protection of sandstone heritage buildings and monuments against salt weathering.

PT

Keywords: salt weathering; sandstone heritage buildings; sandstone monuments; tensile strength;

RI

thermal conductivity; P-wave velocity

SC

1. Introduction

NU

Sandstone, a common sedimentary rock, is widely distributed on the earth’s surface, and it is also a material used in heritage buildings due to not only the high degree of cementation as a calcareous or

MA

siliceous material but also its local availability. Hence, many buildings and monuments in the past have used sandstone, as evidenced by the many sandstone heritage buildings and sandstone

PT E

D

monuments. These include, for example, the Schloss Johannisburg (a château) in the Renaissance period in Germany (Siedel et al., 2003), the Corbii de Piatra church in Romania (Barzoi and Luca,

CE

2013), the Museum of Contemporary Art in Sydney (Franklin et al., 2014), the San Gimignano towers with Tuscany architecture in Italy (Andreotti et al., 2018) and the Angkor temples in

AC

Cambodia (Xu et al., 2018).

However, deterioration and even damage to heritage buildings and monuments due to salt weathering are detrimental because these structures have historic value and are irreplaceable. For example, the Great Sphinx in Egypt, which is made of limestone, is losing the intensity of the color of its face after thousands of years of weathering, and the exquisitely carved serpent tail and beard have already disappeared (Tanimoto et al., 1993). Therefore, the protection of such cultural relics is

ACCEPTED MANUSCRIPT

essential, and it has become a topic examined by many researchers with important results. For example, Smith (2009) systematically analyzed the weathering of desert rock due to temperature, moisture, salt, and chemical and biochemical reactions. Steiger et al. (2009) provided an introduction on the weathering of architectural stone due to the mechanical properties of stone,

PT

thermal cycling, hydric swelling, crystal growth, chemical reactions, salt and crystallization.

RI

Marszałek et al. (2014) presented the mineralogical and chemical characteristics of sandstone

SC

weathering crusts exposed to various air pollution conditions. Hua et al. (2016, 2017) studied the

NU

fracture toughness of sandstone after cyclic wetting and drying. Others in the literature also studied rock weathering in terms of solutional weathering processes (Wray and Sauro, 2017),

MA

wetting-drying cycles (Loubser, 2013), and salt recrystallization (Lindström et al., 2016; Özşen et al., 2017) or by using elastic waves to differentiate the level of weathering in rocks (Lee and Yoon,

PT E

D

2017). In saline environments, salt weathering plays a dominant role in rock weathering (Jutson, 1917; Wellman and Wilson, 1965; Mottershead, 2013; Ludovico-Marques and Chastre, 2016;

CE

Menéndez and Petráňová, 2016). Although the origin of honeycomb weathering is not fully understood, it is strongly influenced by salt availability and the frequency of wetting and drying

AC

(McBride and Picard, 2004; Bruthans et al., 2018). These studies show that salt has a significant impact on rock weathering; therefore, investigating the role of salt on rock deterioration is important. To date, studies on rock weathering, especially sandstone, due to salt-related damage have focused on two interrelated aspects: 1) salt recrystallization and growth and 2) wetting-drying cycles. Table 1 provides a summary of the relevant studies in the literature. They provide the basic foundation for a better understanding of salt

ACCEPTED MANUSCRIPT

weathering of rocks; however, in reality, there is a universal problem of salt recrystallization and growth after many wetting-drying cycles. This issue often emerges from groundwater seepage or saline environments. With the seepage of groundwater through rock, the salt dissolved in water recrystallizes within cracks in sandstone by evaporation. When the pressure of recrystallization

PT

exceeds the strength of rock, rock fails. Few studies in the literature have examined the effect of

RI

recrystallization cycles on rock weathering. Based on this consideration, laboratory experiments on

SC

cyclic salt recrystallization in sandstone were conducted to examine its influence on sandstone

NU

heritage buildings and sandstone monuments. 2. Experiment

MA

2.1. Preparation and test principle

The sandstone rock originated from the city of Linyi city Shandong Province, China. The main

PT E

D

cemented grains of the sandstone are albite and quartz in the size range of 0.1 – 2 mm. These grains are bound by calcite, which results in a relatively high strength of the sandstone.

CE

Eighty sandstone samples were cut into cylinders of Φ25×50 mm (diameter × height). A standard testing method recommended by the International Society for Rock Mechanics and Rock

AC

Engineering (ISRM) was used in which the difference in the distance between the top and bottom surfaces is less than 0.5 mm and the surface evenness is less than 0.1 mm. The samples were divided into 10 groups (8 samples in each group). Each group was divided into 4 subgroups and used for different cycles. Each subgroup was used for different MgSO4 concentrations. 2.2. Mineral and quantitative analyses of the sandstone

ACCEPTED MANUSCRIPT

The sandstone sample was ground into a powder finer than 400 mesh to undergo XRD, which was conducted using a D8 ADVANCE X-ray diffractometer. The voltage used was 40 kV, and the current was 30 mA using a copper (Cu) anode and nickel (Ni) filter. The radius of the measuring circle was 250 mm, the divergent slit (DS) was 0.6 mm, the scattering slit (SS) was 8 mm, the

PT

detector opening was 2.82°, the primary and secondary Soller slits were both 2.5°, the scanning

RI

speed was 0.2 s/step and the sampling interval was 0.01945°. The Rieveld-RIR method (Gualtieri

NU

2.3. Wetting-drying cycles conducted on sandstone

SC

and Artioli, 1995; Gualtieri, 1996) was used to calculate the mineral composition.

The sandstone samples were subjected to 5, 10, 15, 20, 25, 30, 35, 40, 45 and 50 cycles of wetting

MA

and drying. In the real world there are many conditions of varying salt combinations, solution concentrations and evaporation rates. All of these factors have a great impact on salt weathering. To

PT E

D

determine the effect of salt on sandstone weathering, a wetting-drying experiment was designed and conducted in a laboratory. A blank group experiment was also set without salt. In these experiments,

CE

MgSO4 was selected as the only salt due to its common exist in nature, and the elevated temperature was used to accelerate the experimental process. Based on these rationales, each cycle consisted of

AC

soaking the samples for 2 h in water or solutions that contain a concentration of 4%, 6%, or 8% MgSO4. They were then dried for 2 h in an oven at 80ºC. 2.4. Color changes The color changes of the sandstone samples after the wetting-drying cycles were examined using a TES-135A color meter, which checks the differences in colors between samples and displays them using three parameters of the CIE-L*a*b* system. The CIE-L*a*b* color space

ACCEPTED MANUSCRIPT

mathematically describes all perceivable colors in absolute values with three dimensions: L* for lightness and a* and b* for the color components of green–red and blue–yellow, respectively. The vertical axis is L*; L* has a scale of 0-100, in which 0 denotes black and 100 denotes white. The horizontal axes are a* and b*; a* and b* are the color channels in which +a* denotes the red

PT

spectrum, -a* denotes the green spectrum, +b* denotes the yellow spectrum and -b* denotes the

SC

differences were based on their unique color-space position.

RI

blue spectrum. Therefore, colors were identified through these L*a*b* coordinates, and their

NU

2.5. P-wave velocity test

The P-wave velocity test is a method for predicting the properties of materials by measuring the

MA

travel time of acoustic pulses. In this study, the properties of the sandstone samples were tested using an RSM-SY6 acoustic wave detector. In the testing process, the sample was placed between

PT E

D

two transducers. To minimize wave attenuation, Vaseline petroleum jelly was smeared as a medium onto the transducer and the surface of the sample for maximizing acoustic coupling.

CE

2.6. Thermal conductivity test

Measurements of the thermal conductivity of the sandstone samples were performed using a

AC

transient plane source technique. A DRE-2C thermal conductivity tester was used to measure the thermal conductivity of the samples along with a communication port host, a computer and a hot disk. The hot disk is a nickel metal wire constructed in a double-spiral formation with polyimide (Kapton) (0.025 mm) as the protective outer layer, which provides the hot disk with good electrical insulation. This formation is embedded between dielectric insulation layers. It is a heat source as well as a temperature sensor. In the testing, the hot disk sensor was sandwiched between two

ACCEPTED MANUSCRIPT

samples, which have a smooth surface. The sensor generated a series of impulse currents, which results in a temperature increase. The thermal conductivity was measured by recording the temperature and response time of the hot disk sensor. 2.7. Tensile strength test

PT

The tensile strength test was conducted on an MTS Model 815 rock mechanics test system using the

RI

Brazilian disc test (BD) (ISRM 1978) by the loading speed of 0.5 mm/min. Each condition (same

SC

wetting-drying cycle and same concentration of MgSO4) was used to test two samples. Before

NU

calculation, the initiation of a crack in the BD test was checked to ensure its validity. If the crack does not initiate from the center of the BD disc, the test result is invalid for the BD test (Wong et al.,

MA

2014; Zhou et al., 2018; Zhou et al., 2018). The tensile strength was calculated using the following: 2𝑃

𝜎𝑡 = 𝜋𝐷𝛿

(1)

PT E

D

where 𝜎𝑡 denotes the tensile strength; 𝑃 is the peak load; D denotes the diameter of the sample; and 𝛿 is the thickness of the sample.

CE

3. Results

3.1. Composition of minerals

AC

Fig. 1 shows the XRD pattern of the studied sandstone. The result shows that the mineral composition of the sandstone is quartz (14.3 wt%), albite (67.4 wt%), calcite (5.7 wt%) and laumontite (12.7 wt%). 3.2. Surface properties Fig. 2 shows the mesoscopic images of the samples soaked in water and MgSO4 solution from 0 to 45 wetting-drying cycles (0% denotes water; 4%, 6% and 8% denote solutions that contain a

ACCEPTED MANUSCRIPT

concentration of 4%, 6% and 8% MgSO4, respectively). All of the samples soaked in water had a similar surface property with no cracks. However, the samples that were soaked in MgSO4 solution showed cracks on their surface after 40 ~ 45 wetting-drying cycles. Moreover, after 40 ~ 45 cycles the samples soaked in MgSO4 solutions presented a rough surface due to detached grains, and those

PT

soaked in a higher concentration of MgSO4 solution (that is, 8% MgSO4) presented a very rough

RI

surface.

SC

Fig. 3 shows the color of the sandstone samples after different wetting-drying cycles. The MgSO4

NU

solution had a significant effect on the color as shown by the changes in the L* (Fig. 3(a)), a* (Fig. 3(b)), and b* (Fig. 3(c)) values.

MA

The L* value decreased with an increase in the number of cycles, but the changes in the samples soaked in water differed from those soaked in MgSO4 solution. The L* value was reduced slightly

PT E

D

from ~28.5 to ~26 in the samples that were soaked in water, but it decreased substantially from ~28 to ~15 in the samples that were soaked in the solutions containing MgSO4.

CE

The a* value increased with the number of low cycles. At the same number of wetting-drying cycles, the a* value of the samples soaked in MgSO4 solution was larger than that of the samples

AC

soaked in water. Despite different initial values, all of the samples had nearly the same increase ratio, namely, there is a trend of parallel increase. Notably, it remained nearly constant after 35 cycles for the samples soaked in MgSO4 solution. The changes in the samples soaked in MgSO4 solution differed from those soaked in water. With fewer wetting-drying cycles (less than 15 cycles), the b* value of the samples soaked in MgSO4 solution was higher than that of the samples soaked in water. In contrast, with more than 45

ACCEPTED MANUSCRIPT

wetting-drying cycles the b* value of the MgSO4-soaked samples was less than that of the water-soaked group due to the rapid increase in the b* value of the latter samples. 3.3. P-wave velocity Fig. 4 shows the P-wave velocity of the sandstone samples after different numbers of

PT

wetting-drying cycles. In general, the P-wave velocity decreased with the increasing number of

RI

cycles, but differences were found with the solutions that had different concentrations of MgSO4.

SC

The P-wave velocity of the samples soaked in water was nearly constant at ~2.0 km/s, whereas that

NU

in the MgSO4 solutions decreased with the number of cycles; however, the extent and changes due to the reduction were different. A decrease in the P-wave velocity of the sample with a

MA

concentration of 6% MgSO4 occurred at the 25th cycle, and that for the solution containing a concentration of 8% MgSO4 occurred at the 10th cycle. The samples soaked in water and in

PT E

D

solutions of 4% and 6% MgSO4 had lower P-wave velocities than those soaked in a solution of 8% MgSO4, which has a P-wave velocity of approximately 2.6 km/s at the 5th cycle and 2.2 km/s from

CE

the 20th to the 30th cycles. The P-wave velocity showed a slight increase from the 30th to 35th

MgSO4.

AC

cycles, especially for the samples soaked in solutions that contained a concentration of 6% and 8%

3.4. Thermal conductivity The thermal conductivity decreased with the increasing number of wetting-drying cycles, as shown in Fig. 5(a). The thermal conductivity was ~1.95 W/mK at 5 cycles for the samples soaked in solutions that contained a concentration of 4% and 6% MgSO4 and water and ~2.3 W/mK for the samples soaked in a solution containing 8% MgSO4. Additionally, the thermal conductivity was 1.2

ACCEPTED MANUSCRIPT

to 1.8 W/mK at 50 cycles for the samples soaked in both the MgSO4 solutions and water. Of these reductions in thermal conductivity, the most substantial reduction was found in the samples soaked in water and those soaked in the solution containing 8% MgSO4, which were reduced by 15% and 40%, respectively. Fig. 5(b) presents the relationship between thermal conductivity and the number

PT

of cycles. All the fitted lines show a good linear relationship, among which the slope of the samples

RI

soaked in 8% MgSO4 is the steepest. This indicates that greater concentrations of MgSO4 result in a

SC

clear reduction in the thermal conductivity.

NU

3.5. Tensile strength

Fig. 6 shows the tensile strength of the samples after undergoing the wetting-drying cycles. With

MA

more cycles, the tensile strength decreases. The tensile strength of the samples soaked in water slowly decreased with more cycles, ranging from ~3.6 to 3.2 MPa, while that of the samples soaked

PT E

D

in the solution with MgSO4 quickly decreased with more cycles from the initial ~3.6 to ~2.0 MPa. The most substantial decrease in tensile strength was found in the samples soaked in the solution

CE

with a concentration of 4% MgSO4. After 30 cycles, the tensile strength of all samples soaked in an MgSO4 solution was substantially reduced.

AC

Fig. 7 shows the failure of the samples soaked in water and MgSO4 solution after 10 to 45 wetting-drying cycles. All of the samples soaked in water showed the same type of failure with a relatively straight fracture. For the samples soaked in a solution with 4% MgSO4, the fracture was also straight similar to the samples soaked in water for the first 30 cycles. After that, the fractures were irregular, similar to those of the other samples soaked in the solutions with 6% and 8% MgSO4.

ACCEPTED MANUSCRIPT

The irregularity of the fracture increases with a higher concentration of MgSO4 or more wetting-drying cycles. 3.6. Correlation analysis of parameters Fig. 8 shows the relationships between the tensile strength and color lightness, the P-wave velocity

PT

and thermal conductivity, and the tensile strength and thermal conductivity. Figs. 8(a) and 8(c) show

RI

that the tensile strength has a relatively good linear relationship with color lightness and thermal

SC

conductivity as determined with Eqs. (2a) and (2b). However, the tensile strength and P-wave

NU

velocity have different linear relationships in different MgSO4 concentrations (Fig. 8(b)) as determined with Eqs. (2c) and (2d):

R2=0.65

(2a)

𝜎𝑡 = −4.48 + 4.01𝜆,

R2=0.66

(2b)

𝜎𝑡 = −7.03 + 5.14𝑢,

R2=0.50

(2c)

R2=0.57

(2d)

PT E

D

MA

𝜎𝑡 = 0.36 + 0.11𝐿∗ ,

𝜎𝑡 = 0.79 + 1.00𝑢,

CE

where 𝜎𝑡 denotes the tensile strength; 𝐿∗ denotes the color lightness; 𝜆 denotes the thermal conductivity; and u donates the P-wave velocity.

AC

4. Discussion

Salt weathering has substantially destructive effects in porous materials such as sandstone, which is found in heritage buildings and monuments. To explore the effects of salt weathering on these sandstone structures, the physical and mechanical properties of the sandstone samples were examined after a wetting-drying process.

ACCEPTED MANUSCRIPT

In comparing the results of the samples soaked in water and the samples soaked in a solution with MgSO4, MgSO4 was found to have a significant influence on the structure of sandstone due to the pressure of salt recrystallization. The generated pressure (∆𝑝) due to recrystallization is calculated by (Wellman and Wilson, 1968): 1

1

PT

∆𝑝 = 2𝜎(𝑅 − 𝑟 )

(3)

RI

where 𝜎 is the tension between the interface of the sample soaked in the solution with MgSO4 and

SC

MgSO4 crystals and R is the radius of the large pores that are connected by the small pores with a

NU

radius r.

According to the theory in Wellman and Wilson (1968), recrystallization always occurs in large

MA

pores. In this experiment, an increased number of wetting-drying cycles means that the MgSO4 crystals continue to grow in the large pores due to the constant addition of solution to the salt load

PT E

D

in each cycle, and then the pressure induced from crystallization onto the pore walls increases. When this pressure exceeds the tensile strength of the sandstone, cracks appear. This explains why

CE

the tensile strength decreases with more wetting-drying cycles. The results obtained by the color meter showed that the changes in the L* of the samples that

AC

were soaked in a solution with MgSO4 differed from those soaked in water (Fig. 3(a)) due to the dissolution and recrystallization of MgSO4 which change the surface property of the samples. This is evident in the mesoscopic images shown in Fig. 2. The samples soaked in a solution of MgSO 4 after 35 wetting-drying cycles present an obviously rough surface. The changes in the surface properties are due to two factors: MgSO4 crystals and reduced cementation. The latter, a result of the recrystallization of MgSO4, is considered to be the main reason for the reduction in L* and

ACCEPTED MANUSCRIPT

lower P-wave velocity as well as for the reduced thermal conductivity and tensile strength. The L* increases in the range of 45-50 cycles, reflecting the increasing concentration of MgSO4. Indeed, the substantially increasing concentration of MgSO4 starts at 35 cycles (Fig. 3(b)). The lower P-wave velocity and reduced thermal conductivity and tensile strength of sandstone

PT

due to salt weathering begins even before the 10th wetting-drying cycle as shown by the plotted

RI

P-wave velocities in Fig. 4. The P-wave velocity is sensitive to changes in the rock structure,

SC

especially cracks. P-waves travel through the solid-fluid-gas phases of sandstone, of which wave

NU

propagation through solids is the most rapid. If cracks emerge in sandstone, they impede the propagation of the P-waves, thus resulting in a reduced P-wave velocity. Fig. 4 shows that the

MA

P-wave velocity decreased at the 10th cycle of wetting-drying for the samples soaked in a solution with a concentration of 8% MgSO4 while remaining nearly constant for those soaked in water. Even

PT E

D

though visual cracks only appeared after 40 cycles (Fig. 2), the reduction in P-wave velocity shows that microcracks have developed with fewer cycles. An unusual increase in P-wave velocity is

CE

observed in Fig. 4 after 30 cycles; this is due to the recrystallization of MgSO 4 filling the sandstone pores, thus resulting in the local failure in sandstone. Furthermore, a decrease in tensile strength

AC

occurs (Fig. 6). The high concentration of MgSO4 caused the slow reduction in tensile strength at high number of cycles, which resulted from three reasons. With the increase in cycle number, the grain contact-cementation weakens, resulting in the decrease in tensile strength. The surface roughness of the samples becomes larger, causing the stress concentration at the contact region between the sample and machine. Due to the deterioration of the sample’s surface, a big deformation occurs in this contact region, and then contact area increases and causes the calculated

ACCEPTED MANUSCRIPT

tensile strength to increase, especially at high cycles and high MgSO4 concentrations. Therefore, the tensile strength of the samples at high cycles (more than 35 cycle number) cannot be tested by the Brazilian disc test. Thermal conductivity can also be used to show crack emergence in sandstone after the

PT

wetting-drying cycles occur. Fig. 5 shows that the thermal conductivity of the samples soaked in a

RI

solution with MgSO4 is reduced with the increasing number of cycles. Therefore, thermal

SC

conductivity is a parameter that can denote the thermal transmission efficiency of sandstone. The thermal transmission in porous media can be determined by (Huang, 1971): 𝑛 1−

𝑛 

NU

−

𝜆𝑠 + (𝑒

−

+

2 𝐻()

𝑛

− (1−𝑒  )

)(𝜆𝑓 + 𝜆𝑟 )

(4)

MA

𝜆𝑝 = (1 − )𝑒

where 𝜆𝑝 is the effective thermal conductivity of the porous media; 𝜆𝑓 is the thermal conductivity

D

of the fluid phase; 𝜆𝑟 is the radiant or convection thermal conductivity of the gas phase; 𝜆𝑠 is the

PT E

thermal conductivity of the solid phase;  denotes porosity; n denotes the geometric factor of the pores; and H() is the portion of the pore space in the solid-fluid phases in the series configuration.

CE

According to Eq. (4), the effective thermal conductivity of the porous media is determined by the

AC

solid, fluid and gas phases. In the wetting-drying cycles of the sandstone in this study, all of the sample surfaces were dried, so the fluid phase was not present in the samples. Moreover, the thermal conductivity of gas is much less than that of a solid. Therefore, the solid phase plays a decisive role in heat transmission in the sandstone samples. However, the emergence of micro-cracks inhibits efficient heat transfer, and hence the thermal conductivity decreases with the increasing number of wetting-drying cycles.

ACCEPTED MANUSCRIPT

In comparing the P-wave velocity and thermal conductivity, no increase in thermal conductivity with more wetting-drying cycles was found. This is because heat transfer needs adequate space, whereas the P-wave propagation only requires connectivity of the solid. After the wetting-drying cycles occur, numerous cracks appeared inside the sandstone, and some of them may be filled with

PT

MgSO4 crystals after more wetting-drying cycles occur. The MgSO4 crystals are a medium for the

RI

propagation of P-waves, but they are insufficient for heat transfer because there are limitations in

SC

space. This process is illustrated in Fig. 9.

NU

The emergence of cracks with more wetting-drying cycles reduces the tensile strength of sandstone. Two phases were determined by the decreased ratio of tensile strength. A substantial

reduction of cementation of sandstone.

MA

reduction in tensile strength commenced at the 30th cycle. This is the threshold cycle due to the

PT E

D

The relationships between the parameters in this study can be used as a new means to assess the status of sandstone heritage buildings and sandstone monuments. Fig. 8 shows that color lightness

CE

and thermal conductivity can be used to evaluate the tensile strength, which is important for rock stability. However, tensile strength and P-wave velocity do not have a linear relationship due to the

AC

higher P-wave velocities after 30 cycles of wetting and drying resulting from the recrystallization of MgSO4; therefore, P-wave velocity is not recommended for use in assessing the tensile strength of sandstone heritage buildings and sandstone monuments. 5. Conclusions

ACCEPTED MANUSCRIPT

Laboratory experiments involving cycles of wetting and drying were conducted. The color, P-wave velocity, thermal conductivity and tensile strength were tested after drying with different salt concentrations. The main conclusions are provided as follows. (1) After the samples soaked in a solution with MgSO4 were subjected to the wetting-drying

PT

cycles, the L* value of the samples gradually decreased with more cycles. The a* and b* values

RI

slightly increased with more cycles. After the samples soaked in water were subjected to the

SC

wetting-drying cycles, the L* value was nearly constant and the a* and b* values increased slightly

NU

with more cycles. The greatest difference that salt weathering has on sandstone color is the change in L*.

MA

(2) After the samples soaked in a solution with MgSO4 were subjected to wetting-drying cycles, the P-wave velocity was gradually reduced up to 30 cycles and then increased after 30 cycles. The

PT E

D

P-wave velocity of the samples soaked in a solution with 8% MgSO4 showed the greatest changes. The P-wave velocity of the samples soaked in water was nearly constant after the wetting-drying

CE

cycles.

(3) The thermal conductivity was gradually reduced in the samples with more wetting-drying

AC

cycles, with a good linear relationship between thermal conductivity and the number of cycles. The decreasing ratio of thermal conductivity of the sample soaked in a solution with MgSO4 was higher than that of the samples soaked in water. Furthermore, a higher concentration of MgSO4 showed a sharply decreasing ratio of thermal conductivity. (4) After the samples soaked in a solution with MgSO4 were subjected to wetting-drying cycles, their tensile strength decreased gradually up to 30 cycles and then decreased drastically after 30

ACCEPTED MANUSCRIPT

cycles. The tensile strength of the samples soaked in water and subjected to the wetting-drying cycles decreased slightly with more cycles. (5) Thirty cycles is the threshold after which the sandstone begins to deteriorate. The recrystallization of MgSO4 is considered to be the primary reason for the reduction in color

PT

lightness and lower P-wave velocity, thermal conductivity and tensile strength as well as higher

RI

P-wave velocity after 30 cycles.

SC

(6) The correlation analysis of the parameters showed that color lightness and thermal

NU

conductivity are two useful parameters for the evaluation of tensile strength, one of the key factors for rock stability. The results show that both have a good linear relationship with tensile strength.

MA

Acknowledgement

This research was supported by “the Fundamental Research Funds for the Central Universities” (No.

PT E

D

2017XKZD07). References

CE

Andreotti, S., Franzoni, E., Fabbri, P., 2018. Poly (hydroxyalkanoate) s-based hydrophobic coatings for the protection of stone in cultural heritage. Materials 11 (1), 165.

AC

Angeli, M., Bigas, J.P., Menendez, B., Hébert, R., David C., 2006. Influence of capillary properties and evaporation on salt weathering of sedimentary rocks. Heritage Weathering and Conservation, Taylor & Francis, Balkema. 1, 253-259. Barzoi, S.C., Luca, A.C., 2013. Significance of studying the petrography and mineralogy of the geological environment of old rupestrian churches to prevent their deterioration. A case study from the South Carpathians. J. Cult. Herit. 14 (2), 163-168.

ACCEPTED MANUSCRIPT

Benavente, D., Martínez-Martínez, J., Cueto, N., García-del-Cura, M.A., 2007. Salt weathering in dual-porosity building dolostones. Eng. Geol. 94 (3-4), 215-226. Bruthans, J., Filippi, M., Slavík, M., Svobodová, E., 2018. Origin of honeycombs: Testing the hydraulic and case hardening hypotheses. Geomorphology 303, 68-83.

PT

Cardell, C., Rivas, T., Mosquer,a M.J., Birginie, J.M., Moropoulou, A., Prieto, B., Silva, B., Van

RI

Grieken, R., 2003. Patterns of damage in igneous and sedimentary rocks under conditions

SC

simulating sea‐salt weathering. Earth. Surf. Proc. Land. 28 (1), 1-14.

NU

Dragovich, D., Egan, M., 2011. Salt weathering and experimental desalination treatment of building sandstone, Sydney (Australia). Environ. Earth. Sci. 62 (2), 277-288.

MA

Franklin, B.J., Young, J.F., Powell, R., 2014. Testing of Sydney dimension sandstone for use in the conservation of heritage buildings. Aust. J. Earth. Sci. 61 (3), 351-362.

PT E

D

Gualtieri, A., Artioli, G., 1995. Quantitative determination of chrysotile asbestos in bulk materials by combined Rietveld and RIR methods. Powder Diffraction 10 (4), 269-277.

CE

Gualtieri, A., 1996. Modal analysis of pyroclastic rocks by combined Rietveld and RIR methods. Powder Diffraction 11 (2), 97-106.

AC

Hua, W., Dong, S., Peng, F., Li, K., Wang, Q., 2017. Experimental investigation on the effect of wetting-drying cycles on mixed mode fracture toughness of sandstone. Int. J. Rock Mech. Min. Sci. (93), 242-249. Hua, W., Dong, S., Li, Y., Wang, Q., 2016. Effect of cyclic wetting and drying on the pure mode II fracture toughness of sandstone. Eng. Fract. Mech. 153, 143-150.

ACCEPTED MANUSCRIPT

Huang, J.H., 1971. Effective thermal conductivity of porous rocks. J. Geophys. Res. 76 (26), 6420-6427. The International Society for Rock Mechanics and Rock Engineering (ISRM). 1978. Suggested methods for determining tensile strength of rock materials. Int. J. Rock. Mech. Min. Sci.

PT

Geomech. Abstr. 15, 99–103.

RI

Jenkins, K.A., Smith, B.J., 1990. Daytime rock surface temperature variability and its implications

SC

for mechanical rock weathering: Tenerife, Canary Islands. Catena 17 (4-5), 449-459.

NU

Jutson, J.T., 1917. Erosion and the resulting land forms in sub-arid Western Australia, including the origin and growth of the dry lakes. The Geographical Journal 50 (6), 418-434.

MA

Lee, J.S., Yoon, H.K., 2017. Characterization of rock weathering using elastic waves: A Laboratory-scale experimental study. J. Appl. Geophys. 140, 24-33.

PT E

D

Lindström, N., Talreja, T., Linnow, K., Stahlbuhk, A., Steiger, M., 2016. Crystallization behavior of Na2SO4–MgSO4 salt mixtures in sandstone and comparison to single salt behavior. Appl.

CE

Geochem. 69, 50-70.

Loubser, M.J., 2013. Weathering of basalt and sandstone by wetting and drying: A process isolation

AC

study. Geogr. Ann. A 95 (4), 295-304. Ludovico-Marques, M., Chastre, C., 2016. Effect of artificial accelerated salt weathering on physical and mechanical behavior of sandstone samples from surface reservoirs. Handbook of Materials Failure Analysis with Case Studies from the Oil and Gas Industry 215-233.

ACCEPTED MANUSCRIPT Marszałek, M., Alexandrowicz, Z., Rzepa, G., 2014. Composition of weathering crusts on sandstones from natural outcrops and architectonic elements in an urban environment. Environ. Sci. Pollut. R. 21 (24), 14023-14036. McBride, E.F., Picard, M.D., 2004. Origin of honeycombs and related weathering forms in

PT

Oligocene Macigno Sandstone, Tuscan coast near Livorno, Italy. Earth Surf. Proc. Land. 29 (6),

RI

713-735.

SC

Menéndez, B., Petráňová, V., 2016. Effect of mixed vs single brine composition on salt weathering

NU

in porous carbonate building stones for different environmental conditions. Eng. Geol. 210, 124-139.

MA

Mottershead, D., 2013. Coastal weathering. Treatise on geomorphology. Volume 4, Weathering and soils geomorphology. Elsevier, p228-244.

PT E

D

Özşen, H., Bozdağ, A., İnce, İ., 2017. Effect of salt crystallization on weathering of pyroclastic rocks from Cappadocia, Turkey. Arab. J. Geosci. 10 (12), 258.

CE

Peel, R.F., 1974. Insolation weathering: Some measurements of diurnal temperature changes in exposed rocks in the Tibesti region, central Sahara. Z. Geomorph. NF, Suppl. 21, 19-28.

AC

Přikryl, R., Melounová, L., Vařilová, Z., Weishauptová, Z., 2007. Spatial relationships of salt distribution and related physical changes of underlying rocks on naturally weathered sandstone exposures (Bohemian Switzerland National Park, Czech Republic). Environ. Geol. 52 (2), 409-420. Rodriguez‐Navarro, C., Doehne, E., 1999. Salt weathering: influence of evaporation rate, supersaturation and crystallization pattern. Earth surf. Proc. Land. 24 (3), 191-209.

ACCEPTED MANUSCRIPT

Ruedrich, J., Siegesmund, S., 2007. Salt and ice crystallisation in porous sandstones. Environ. Geol. 52 (2), 225-249. Smith, B.J., 1977. Rock temperature measurements from the northwest Sahara and their implications for rock weathering. Catena 4 (1-2), 41-63.

PT

Smith, B.J., 2009. Weathering processes and forms. Geomorphology of desert environments.

RI

Springer, Dordrecht. 39-63.

SC

Steiger, M., Charola, A.E., Sterflinger, K., 2011. Weathering and deterioration. Stone in architecture.

NU

Springer, Berlin Heidelberg. 227-316.

Siedel, H., Neumeister, K., Sobott, R.J.G., 2003. Laser cleaning as a part of the restoration process:

MA

Removal of aged oil paints from a Renaissance sandstone portal in Dresden, Germany. J. Cult. Herit. 4, 11-16.

PT E

D

Tanimoto, C., Yoshimura, S., Kondo, J., 1993. Long term stability of the underground cavern for the Pharaoh and the deterioration of the Great Sphinx. Int. J. Rock Mech. Min. Sci. & Geomechanics

CE

Abstracts. Pergamon 30 (7), 1545-1551. Xu, H.B., Tsukuda, M., Takahara, Y., Sato, T., Gu, J.D., Katayama, Y., 2018. Lithoautotrophical

AC

oxidation of elemental sulfur by fungi including Fusarium solani isolated from sandstone Angkor temples. International Biodeterioration & Biodegradation 126, 95-102. Wedekind, W., Ruedrich, J., 2006. Salt-weathering, conservation techniques and strategies to protect the rock cut facades in Petra/Jordan. Heritage, Weathering and Conservation. Proceedings of the International Heritage, Weathering and Conservation Conference, Taylor & Francis, London. 261-268.

ACCEPTED MANUSCRIPT

Wellman, H.W., Wilson, A.T., 1965. Salt weathering, a neglected geological erosive agent in coastal and arid environments. Nature 205 (4976), 1097. Wellman, H.W., Wilson, A.T., 1968. Salt weathering or fretting. In: Geomorphology. Encyclopedia of Earth Science. Springer, Berlin, Heidelberg. 968-970.

PT

Wray, R.A.L., Sauro, F., 2017. An updated global review of solutional weathering processes and

RI

forms in quartz sandstones and quartzites. Earth-Sci Rev. 171, 520-557.

SC

Wong, L.N.Y., Ming, C.J., 2014. Water Saturation Effects on the Brazilian Tensile Strength of

NU

Gypsum and Assessment of Cracking Processes Using High-Speed Video. Rock Mech. Rock Eng. 47 (4), 1103-1115.

MA

Zhao, Z., Yang, J., Zhang, D., Peng, H., 2017. Effects of wetting and cyclic wetting–drying on tensile strength of sandstone with a low clay mineral content. Rock Mech. Rock Eng. 50 (2),

PT E

D

485-491.

Zhou, Z., Cai, X., Chen, L., Cao, W., Zhao, Y., Xiong, C., 2017. Influence of cyclic wetting and

CE

drying on physical and dynamic compressive properties of sandstone. Eng. Geol. 220, 1-12. Zhou, Z., Cai, X., Ma, D., Cao, W., Chen, L., Zhou, J., 2018. Effects of water content on fracture

47-65.

AC

and mechanical behavior of sandstone with a low clay mineral content. Eng. Fract. Mech. 193,

Zhou, Z., Cai, X., Ma, D., Chen, L., Wang, S., Tan, L., 2018. Dynamic tensile properties of sandstone subjected to wetting and drying cycles. Constr. Build. Mater. 182, 215-232.

ACCEPTED MANUSCRIPT

Table 1 Literature related to salt weathering of rock or cyclic wetting-drying of rock. No. Rock

Main

studied

contribution

parameters

by study

of Site

Condition

Reference cycle s

Salt recrystallization

‐Navarro

under different

SC

RI

Rodriguez

Limeston e

MA

relative humidities

-

D PT E

-

Evaporation effect on rate

Doehne

recrystallizati

1999

on. Salt

Wellman

Coastal and arid

Evaporation rate has major

and

NU

UK

PT

type

Rocks

Tested or

recrystallizati

and

Recrystallizati

on plays

Wilson

on

important role

-

CE

environment

1968

in rock

AC

weathering. Ionic diffusion and Angeli et

Stones

-

-

Recrystallizati

-

dissolution of al. 2006

on pre-existent salts are not

ACCEPTED MANUSCRIPT

efficient enough to imply

RI

PT

supersaturatio

Petra in -

distribution and hygric Pore swelling are distribution;

-

Jordan

probably Ruedrich

hygric responsible

D

e

and

PT E

2006

swelling for sandstone

CE

sensitivity in salt

AC

weathering. Wetting

Chongqin Sandston

reduces Wetting-drying

g in e

Zhao et

Tensile

0-15 cycles

China

The bimodal pore radii

SC NU Sandston

MA

Wedekind

n.

tensile al. 2017

strength strength. Wetting-dryin

ACCEPTED MANUSCRIPT

g does not change tensile strength for 0

D

Wetting-drying

in China

P-wave velocity and dynamic

Density, water elastic absorption, modulus decrease with

Zhou et

P-wave

0-50

cycling

Density,

porosity,

more al. 2017

velocity, wetting-dryin dynamic g cycles, elastic

CE

e

Kunming

PT E

Sandston

MA

NU

SC

RI

PT

to 14 cycles.

while porosity modulus

AC

increases with more wetting-dryin g cycles.

Sandston

Salt wetting-drying -

e

Ruedrich 0-20

cycles

When salt Weight

and

wetting-dryin

ACCEPTED MANUSCRIPT

Siegesmu

g cycles

nd 2007

exceed a specific

SC

RI

PT

number of

NU

The solute

MA

concentration at

D ming and poulticing

Australia

AC

e

reduced

the surface of

PT E

CE

Sydney,

weight is

drastically.

sandstone Dragovic

washing-and-vacuu Sandston

cycles, rock

from the h and

Solute

0-5

Sydney Egan

treatments

concentration Hospital and

2011 Australian Museum is increased through desalination

ACCEPTED MANUSCRIPT

treatments. In the limestone, the

Calcareo

Apulia in

0-336

Italy

0

was added to distribution,

al. 2003

the effect ion content caused by the pressure

PT E

D

exerted by salt

CE

crystallization . Weight loss

AC Doloston

results when Benavent

Salt wetting-drying -

e

cement

Pore

MA

us rock

calcareous

dissolution

Cardell et

NU

Saline spray

SC

RI

PT

effect of

0-15

Dry weight

crystallization

loss

pressure

e et al.

cycles 2003

exceeds rock cohesion

ACCEPTED MANUSCRIPT

threshold. Bohemian

Salt

Salt

Switzerla

concentration,

concentration

nd

porosity,

is correlated

microporosity,

to changes in

moisture

physical

Přikryl et

Naturally weathered National

e

exposed sandstone

al. 2007

RI

Park in

PT

Sandston

SC

Czech

AC

CE

PT E

D

MA

NU

Republic

content,

properties of

absorption

sandstone.

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

AC

CE

PT E

Fig. 1. XRD patterns of the sandstone.

ACCEPTED MANUSCRIPT

0%

T P

I R

C S U

N A

4%

D E

T P E

A

C C

M

ACCEPTED MANUSCRIPT

6%

T P

I R

C S U

N A

8%

D E

M

T P E

C C

A (a) 10 cycles

(b) 25 cycles

(c) 30 cycles

(d) 35 cycles

(e) 40 cycles

(f) 45

cycles Fig. 2. Mesoscopic images of samples (surface properties) after wetting-drying cycles. All the pictures have a same scale: 5.8×3.2 mm.

ACCEPTED MANUSCRIPT

T P

I R

C S U

N A

D E

T P E

A

C C

M

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

D

Fig. 3. Changes in color of sandstone after wetting-drying cycles. (a) L* refers to light; (b) a* refers

PT E

to blue-red component; (c) b* refers to yellow-green component. Each parameter was obtained from

AC

CE

3 samples and more than 6 data for same cycles were tested.

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

PT E

Fig. 4. P-wave velocity of sandstone samples after different wetting-drying cycles. P-wave velocity

AC

CE

was obtained from 3 samples and more than 6 data for same cycles were tested.

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT

Fig. 5. Changes in thermal conductivity with number of cycles after wetting-drying process. Thermal conductivity was obtained from 3 samples and more than 4 data for same cycles were

AC

CE

PT E

D

MA

NU

SC

RI

PT

tested.

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

PT E

Fig. 6. Changes in tensile strength with number of wetting-drying cycles. Sample number: 3 for

AC

CE

each cycle and MgSO4 concentration. Samples soaked in solution with MgSO4 were not tested after 35 cycles due to partial damage.

ACCEPTED MANUSCRIPT

0%

T P

I R

C S U

4%

N A

D E

6%

M

T P E

C C

A

8%

(a) 10 cycles cycles

(b) 25 cycles

(c) 30 cycles

(d) 35 cycles

(e) 40 cycles

(f) 45

ACCEPTED MANUSCRIPT Fig. 7. Failure of samples. All the pictures have a same diameter: ∅=5mm.

T P

I R

C S U

N A

D E

T P E

A

C C

M

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

PT E

Fig. 8. Relationship between parameters: (a) Tensile strength and color lightness, (b) tensile strength and P-wave velocity and (c) tensile strength and thermal conductivity. The regression function was

AC

CE

determined without considering the discrete point in picture (b).

ACCEPTED MANUSCRIPT

Heat or wave in (a) Heat or wave Heat or wave

Heat or wave

Pore

RI

PT

Mineral particle

Heat or wave in

NU

(b)

SC

Heat or wave out

Heat or wave

Heat or wave out

Heat or wave in

CE

PT E

D

MA

Crack

(c)

AC

Heat or wave Wave

Wave

Crack MgSO4

Heat or wave out

Wave

ACCEPTED MANUSCRIPT

Fig. 9. Heat transfer and P-wave propagation in porous sandstone: (a) initial condition, (b) generation of cracks with fewer wetting-drying cycles, and (c) recrystallization of MgSO4 with

AC

CE

PT E

D

MA

NU

SC

RI

PT

more wetting-drying cycles.

ACCEPTED MANUSCRIPT

Research highlights 

A combined experiment was designed and conducted for studying salt weathering of sandstone heritage. Cyclic wetting and drying cycles substantially accelerate the weathering process.



Thirty cycles is the threshold in our results after which the sandstone begins to deteriorate.



Color and thermal conductivity were introduced for evaluating tensile strength.

AC

CE

PT E

D

MA

NU

SC

RI

PT

