MechanicalPropertiesofWeatheredFeldsparSandstoneafter...

Research ArticleMechanical Properties of Weathered Feldspar Sandstone afterExperiencing Dry-Wet Cycles

Wen-bo An 1 Laigui Wang1 and He Chen 2

1College of Mechanics and Engineering Liaoning Technical University Fuxin 123000 China2College of Civil and Engineering Liaoning Technical University Fuxin 123000 China

Correspondence should be addressed to Wen-bo An wb_an1992163com

Received 15 February 2020 Accepted 12 March 2020 Published 31 March 2020

Academic Editor Raffaele Sepe

Copyright copy 2020 Wen-bo An et al is is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Weathering is one of the important geological hazards to many stone cultural relics carved on feldspar sandstone (such as theDatong Yungang Grottoes) To study the mechanical properties of the weathered Yungang Grottoes feldspar sandstone wassubjected to comparative dry-wet cycle tests with water-rock interaction (Group A) and salt-rock interaction (Group B) evariation patterns of the macroscopic physical and mechanical parameters as well as the micromesoscopic structures of the twogroups of feldspar sandstone with the number of dry-wet cycles were measured e results showed that for the Group A andGroup B sandstones as the number of dry-wet cycles increased the saturated water absorption and the longitudinal wave velocityincreased with the maximum variation rates reaching 2802 3698 1620 and 3327 e peak strength and elasticmodulus gradually decreased with the maximum variation rate reaching 4853 7344 2661 and 7239e surface heightdeviation increased by as much as 106 μm and 334 μm e mechanism of weathering for the water-rock interaction includedthree effects namely the hydrolysis of the K-Na feldspar the water swelling of the clay minerals such as kaolinite and thedissolution of the soluble minerals e mechanism of weathering for the salt-rock interaction included salt crystallization in thepores or fissures and chemical reactions between the minerals (such as feldspar and calcite) and sulfate in addition to the abovethree effects erefore the crystallization stress of the salt exerted the most notable effect on the deterioration of the feldsparsandstone e results are expected to provide a reference for the stability evaluation and protection of the rock mass ofthe Grottoes

1 Introduction

e Yungang Grottoes in Datong Shanxi are famous fortheir spectacular scenery and they hold a pivotal positionamong the cultural relics of China After thousands of yearsmost of the temples in the Yungang Grottoes have beendestroyed and some of the painted sculptures and muralshave disappeared due to the impact of the natural envi-ronment Over time the Yungang Grottoes have been af-fected by both natural weathering and manmade sabotagee weathering of the grottoes has been increasingly severeleading to enormous consequences [1 2] It was found fromthe field investigation that the Yungang Grottoes werescattered in huge lens-like feldspar sandstone (also known asYungang Stone Buddha feldspar sandstone) e analysis ofthe weathering of grottoes no 2 3 and 12 showed that the

severely weathered parts of the grottoes were generally atspots where there was abundant water or a water outlet Forexample the weathering of the rock faces near the groundsurface was more severe than the weathering farther awayfrom the ground surface Additionally the rock faces nearthe ground surface were relatively moist with the salt pre-cipitated at part of the other areas and the feldspar sand-stone far from the ground surface was relatively wellpreserved Over more than a thousand years the seasonaland diurnal changes have caused the water in the Grottoes tostay in different states In summer the daytime temperatureis high so the water evaporates quickly and the Grottoesappear dry but the nighttime temperature is low so theGrottoes are in a moist state In winter the water is mostly ina liquid state during the day when the evaporation is in-significant and it freezes at night when the temperature is

HindawiAdvances in Materials Science and EngineeringVolume 2020 Article ID 6268945 15 pageshttpsdoiorg10115520206268945

lowerefore the water (salt) and temperature are the mainfactors affecting the weathering of the Grottoes

To protect these stone cultural relics from weatheringthe Yungang Grottoes Research Institute among otherorganizations has also implemented a large scale of pro-tection work including protection measures such as seepageprevention dehumidification in the Grottoes and drainageAlthough these measures have had a protective effect theproblem of weathering has not been solved Yan et al andQin et al studied the weathering characteristics of theYungang Grottoes and conducted tests on the soluble saltweathering in the Grottoes e results show that the de-struction of the Yungang Grottoes sandstone resulted fromthe combination of physical and chemical weathering ewater salt solution and temperature were the main influ-encing factors and salt could aggravate the deterioration ofthe grotto structure [3ndash5] Yao et al investigated the me-chanical properties of sandstone after dry-wet cycles [6]eresults showed that the mechanical indexes of the rock afterdry-wet cycles decreased to varying extents Coombes andNaylor obtained the weathering mechanism of rock throughdry-wet cycle tests on limestone granite and concretematerials [7] Torres-Suarez et al examined the physical andmechanical properties of mudstone after dry-wet cycles [8]e results showed that the main destruction mechanism ofthe layered mudstone started with microscopic scale fissurecoalescence and it manifested as physical and chemicaldeterioration ere have been numerous studies on thephysical and mechanical properties of feldspar sandstoneand ordinary sandstone such as those above-mentioned[9ndash13] However there have been few studies on the damagemechanism of feldspar sandstone after dry-wet cycles fromthe perspective of chemical damage

erefore for this study feldspar sandstone of the samestratum and with similar lithology as that of feldsparsandstone where the Yungang Grottoes are scattered wasselected An experimental method was used that combinedlaboratory dry-wet cycle tests and macro-micromesoscopicobservation to obtain the macroscopic physical and me-chanical properties (eg saturated water absorption lon-gitudinal wave velocity strength elastic modulus anddeformation) as well as the variation patterns of the mi-crostructure and the mesoscopic roughness of feldsparsandstone after wet-wet cycles Based on this the mechanicalproperties and the weathering mechanisms of feldsparsandstone after dry-wet cycles were analyzed

2 Material and Methods

21 Preparation of the Materials

211 Preparation of the Feldspar Sandstone Given thehistorical value of the Yungang Grottoes the relevant de-partment in this scenic area disallowed the collection of alarge number of rock samples erefore feldspar sandstonein the same stratum as that of the Yungang Grottoes wasselected for the tests e mineral composition and theaverage relative content of this feldspar sandstone and thestatues of the Yungang Grottoes were compared and

analyzed by X-ray diffraction (XRD) e results are shownin Figure 1 and Table 1 In the figure Q is quartz P is K-Nafeldspar K is kaolinite and I is illite It can be seen that thefeldspar sandstone used in the experiment had similar li-thology to that of the sandstone of the Yungang Grottoes soit could represent the sandstone of the Yungang Grottoes Inthe laboratory the rock pieces of the feldspar sandstone wereprocessed using a JKZS-100 automatic coring machine and aYBDQ-4 rock cutter according to the specifications (SL264-2001 GBT50266-99) After the processes of core drillingcutting polishing grinding cleaning and drying a standardsample of feldspar sandstone with a size of φ50mmtimes 100mm was finally obtained as shown in Figure 2

212 Preparation of the Erosion Solution According to thefield investigation the weathered grotto faces within 1mfrom the ground are often moist and a large amount ofwhite salt appears in the dry season Extensive researchrevealed that the white salt was sulfate [14 15] erefore inthe tests the crystal salt of Na2SO4 (Glauberrsquos salt) was usedas the solute to prepare the saturated Na2SO4 solution as theerosion solution and distilled water was used as a controle standard samples were immersed in the preparederosion solution to carry out the dry-wet cycle tests withwater-rock interaction (Group A) and salt-rock interaction(Group B)

22 Multiscale Experimental Techniques

221 Dry-Wet Cycle Test e dry-wet cycle test was con-ducted in reference to the requirements of the free im-mersion method in the specification (GBT50266-99) estandard sample of feldspar sandstone was immersed in theerosion solution for 12 h e water level was first controlledat one-fourth of the height of the feldspar sandstone andthen the erosion solution was added after 2 h and 4 h to reachone-half and three-fourths of the height of the sample re-spectively After 6 h the sample was completely immersed inthe erosion solution until the end of the immersion durationNext the sample was taken out and dried in the oven for12 h with the drying temperature set to 50degC in consider-ation of the maximum temperature of around 60degC at thesurface of the Grottoes in summer en all of the sampleswere taken out and cooled to room temperature thuscompleting a dry-wet cycle of feldspar sandstone enumbers of cycles were set to six levels (0 5 10 15 20 and25 times T) After the dry-wet cycle test was completed at alevel the corresponding feldspar sandstone samples wereremoved to perform the subsequent tests

222 Experimental Study of the Physical Properties ofFeldspar Sandstone After the test at each level was com-pleted the mass and the saturated water absorption of thefeldspar sandstone were determined using an electronicbalance (accuracy 001 g) e longitudinal wave velocity ofthe feldspar sandstone was measured by an NM-4B-600nonmetal ultrasonic detector Before the measurement the

2 Advances in Materials Science and Engineering

detector was calibrated with a standard aluminum block toensure the stability of its transmitted signal During themeasurement a small amount of Vaseline was applied be-tween the feldspar sandstone and the probe to ensure a closecontact and a 30-Hz probe was used for the ultrasonictransducer

223 Experimental Study of the Mechanical Properties ofFeldspar Sandstone After the test at each gradient wascompleted a uniaxial compression test was carried out onthe dry feldspar sandstone sample At the same timespeckles were prefabricated on the relatively smooth lateralsurface of the feldspar sandstone and the evolution of thelateral deformation field of the feldspar sandstone under theload was observed e mechanical properties of the dryfeldspar sandstone were tested by a YAW-2000 hydraulicservo-tester e uniaxial compression test adopted a dis-placement control loading mode with a loading rate set to

0005mms e lateral deformation field of the feldsparsandstone was observed by a digital speckle observationsystem which mainly included a charge coupled device(CCD) camera an analog -to -digital (AD) converter and acomputer (PC) end e resolution of the CCD camera was1630 pixelstimes 1224 pixels the object surface resolution of thetest was 00347mmpixel the image acquisition rate was 2framess and the field of view was selected to be30mmtimes 80mm e loading system and the optical mea-surement system had to be performed synchronously

224 MicroMesoscopic Observation of Feldspar Sandstonee feldspar sandstone was scanned with a Hitachi S-3400Nscanning electron microscope (SEM) to determine its ap-parent morphology and microstructure Before the scan-ning the feldspar sandstone (a cube with sides ofapproximately 10mm) was fixed on the stage with fixingglue and the surface was sprayed with a gold coating of5ndash10 nm e accelerating voltage was 20 kV

e mineral composition and the relative content of thefeldspar sandstone were determined by a Shimadzu XRD-6100 X-ray diffractometer Before the test the feldsparsandstone fragments were ground into powder (less than 200mesh) in an agate mortar e light source was X-ray Cutarget radiation (λ 0154056 nm) An accelerating voltageof 20 kV a current of 30mA a scanning speed of 3degmm anda scan range of 10deg to 80deg were used

e surface roughness of the feldspar sandstone wasdetermined by laser confocal scanning microscopy (LCSM)

Table 1 Average relative content of the minerals of the feldspar sandstones

Feldspar sandstonesAverage relative content of minerals ()

Quartz Potassium sodium feldspar Kaolinite IlliteYungang Grotto statue 51 41 5 3Experimental samples 51 40 7 2

Figure 2 Standard feldspar sandstone samples

10 20 30 40 50 60 70 80

2500

0

2θ (deg)

2000

0

Diff

ract

ion

inte

nsity

(CPS

)

Diff

ract

ion

inte

nsity

(CPS

)

Feldspar sandstone of theYungang Grotto statueFeldspar sandstone ofthe experiment

lowast

lowast lowastlowast

lowast

lowast

PQlowast

IK

Figure 1 X-ray diffraction pattern

Advances in Materials Science and Engineering 3

Each sample was measured by surface scanning its threeareas with a scan area of 128mmtimes 128mm e mea-surement parameters included an XYZ fine scanning modean image pixel size of 1024times1024 an image size of1280times1280 an object lens MPLFLN10times and a zoom 1times

3 Results and Analysis

31 Comparative Analysis of the Apparent Properties ofFeldspar Sandstone e apparent properties of feldsparsandstone after the dry-wet cycle could directly reveal thedegree of surface deterioration of the feldspar sandstoneFigures 3 and 4 show the apparent properties of the feldsparsandstone after a dry-wet cycle with water-rock interaction(Group A) and a salt-rock dry-wet cycle (Group B) It can beseen that apparent deterioration of the Group A feldsparsandstone was not notable in appearance from the outsidewhile the apparent deterioration of the Group B feldsparsandstone was very pronounced In the early stage of thedry-wet cycle during salt-rock interaction (0 to 5 T) theGroup B feldspar sandstone was angular and it had asmooth surface As the number of cycles increased to enterthe middle stage of the dry-wet cycle (5 to 20 T) the feldsparsandstone was rounded and the surface became rough Inthe late stage of the dry-wet cycle (20 to 25 T) this phe-nomenon of the feldspar sandstone increased with a largeamount of white crystals precipitated on the surface and alarge amount of quartz particles spalling is is mainlybecause the feldspar sandstone was primarily subjected towater softening and dissolution during the dry-wet cycle ofwater while the feldspar sandstone was subjected to not onlywater softening-dissolution but also salt crystallizationduring the dry-wet cycle of the salt solution

32 Comparative Analysis of the Physical Properties of Feld-spar Sandstone From the changes in the apparent prop-erties of the feldspar sandstones in Groups A and B inSection 31 it can be seen that the water and salt solutioncould cause a certain degree of damage to feldspar sand-stone e effects of the dry-wet cycles on the physicalproperties of the feldspar sandstone are discussed in thefollowing sections

321 Comparative Analysis of the Saturated Water Ab-sorption of Feldspar Sandstone e saturated water ab-sorption of the feldspar sandstone could be used tocharacterize the amount of internal pores or fissuresAccording to the specification (DLT5368-2007) the satu-rated water absorption of feldspar sandstone is defined as

ws mz minus md

md

times 100 (1)

where ws is the saturated water absorption of the feldsparsandstone mz is the saturated water mass of the feldsparsandstone andmd is the dry mass of the feldspar sandstone

To obtain the complete variation pattern of the saturatedwater absorption of the feldspar sandstone in 0 to 25 dry-wetcycles three samples at the level of 25 dry-wet cycles in the

Group A and Group B feldspar sandstones were selected foranalysis e average saturated water absorption of thefeldspar sandstone after the dry-wet cycles was calculatedusing formula (1)e results are shown in Figure 5 It can beseen that as the number of dry-wet cycles increased thesaturated water absorption of the Group A and Group Bfeldspar sandstones gradually increased reaching themaximums of 594 and 626 respectively erefore thedry-wet cycle could promote the expansion of pores andfissures in the feldspar sandstone and the salt-rock inter-action was more pronounced than the water-rockinteraction

322 Comparative Analysis of the Longitudinal Wave Ve-locity of Feldspar Sandstone Longitudinal wave velocity isone of the important indicators for evaluating materialdamage Because ultrasonic waves have different propaga-tion velocities in different media longitudinal wave velocitycan characterize the development of the internal pores orfissures of rock As described in this section the NM-4Bnonmetal ultrasonic detection analyzer was used to measurethe longitudinal wave velocities of the Group A and Group Bfeldspar sandstone after different numbers of dry-wet cyclesTo avoid the error of the experimental results due to thedifference between the individual feldspar sandstone sam-ples the change rate of the longitudinal wave velocity wasused as an evaluation indicator e results are shown inFigure 6 e change rate of the longitudinal wave velocityR is defined as

R v0 minus vn

v0times 100 (2)

where v0 is the initial longitudinal wave velocity of thefeldspar sandstone and vn is the longitudinal wave velocity ofthe feldspar sandstone after n dry-wet cycles

It can be seen from Figure 6 that as the number of dry-wet cycles increased the longitudinal wave velocities of theGroup A and Group B feldspar sandstones gradually de-creased and the change rates of the wave velocity graduallyincreased reaching the maximum values of 1620 and3327e decrease in wave velocity indicated that the dry-wet cycle could promote the development of pores or fissuresin the feldspar sandstone In other words the developmentwas improved with the increase in the number of dry-wetcycles e change rate of the wave velocity of Group A waslower than that of Group B indicating that the salt crys-tallization had a great effect on the pores or fissures in thefeldspar sandstone consistent with the results corre-sponding to the saturated water absorption

33 Comparative Analysis of the Mechanical Properties ofFeldspar Sandstone It was concluded from the above teststhat the dry-wet cycle could cause a certain degree of damageto the apparent properties and physical properties of thefeldspar sandstone It could be preliminarily predicted thatthe dry-wet cycle could degrade the mechanical properties offeldspar sandstone erefore the uniaxial compressivestrength elastic modulus and lateral deformation of the


feldspar sandstone after dry-wet cycles were mainly studiedas described in this section

331 Comparative Analysis of the Stress-Strain Curves ofFeldspar Sandstone To avoid the influence of differencesbetween individual feldspar sandstone samples on the testresults three parallel samples from each group were sub-jected to water-rock and dry-wet cycles with salt-rock in-teractions After uniaxial compression tests the test resultsof each group of sandstone were found to be roughly thesame erefore to avoid unnecessary repetitive efforts thestress-strain curves of the Group A samples numbered 0-15-1 10-1 15-3 20-1 and 25-2 and of the Group B samplesnumbered 0-1 5-1 10-2 15-3 20-1 and 25-1 were selectedfor analysis e results are shown in Figure 7

It can be seen from Figure 7(a) that the uniaxial loadingof the feldspar sandstone after the dry-wet cycles with water-rock interaction generally show a trend of first increasingand then decreasing and the curve has a notable compactionstage and destruction stage e feldspar sandstone stressincreased gradually with the increase in the strain and afterreaching the peak the stress dropped to zero almost rapidlyindicating that feldspar sandstone was very brittle ebrittle property of the feldspar sandstone still existed evenafter multiple dry-wet cycles e peak strength of thefeldspar sandstone was greatly affected by the dry-wet cyclesAs the number of dry-wet cycles increased the peak strengthdecreased gradually Additionally in terms of apparentphenomenon there was the sound of notable damage andthe ejection of a small number of rock pieces before the

5 10 15 20 250

10

20

30

40

Times of dry-wet cycles (time)

Group AGroup B

R (

)

Figure 6 Longitudinal wave velocity change rates of the feldsparsandstones after a dry-wet cycle

(a) (b) (c) (d) (e)

Figure 3 Apparent properties of the feldspar sandstones (group A) after a water-rock dry-wet cycle (a) 5 T (b) 10 T (c) 15 T (d) 20 T(e) 25 T

(a) (b) (c) (d) (e)

Figure 4 Apparent properties of the feldspar sandstones (group B) after a salt-rock dry-wet cycle (a) 5 T (b) 10 T (c) 15 T (d) 20 T (e)25 T

0 5 10 15 20 2540

45

50

55

60

65

70

Group AGroup B

w s (

)


Figure 5 Average saturated water absorption rate of the feldsparsandstones after a dry-wet cycle


critical destruction of the sample and the cracks at de-struction extended mainly in the vertical direction (longi-tudinal) is was mainly because water entered the interiorof the feldspar sandstone when the feldspar sandstone wassubjected to dry-wet cycles softening the internal structureof the feldspar sandstone and dissolving part of the mineralcomponents erefore as the number of dry-wet cyclesincreased the microcracks would coalesce when the feldsparsandstone was loaded eventually forming main cracks witha gradually increasing number [16]

It can be seen from Figure 7(b) that the stress-straincurves of the feldspar sandstone after the dry-wet cycles withsalt-rock interaction all experienced the initial stage com-paction stage softening stage and destruction stage estrength of the feldspar sandstone rapidly decreased afterreaching the peak strength indicating that although thefeldspar sandstone was subjected to multiple dry-wet cycleswith the salt solution the feldspar sandstone still showedremarkable brittle properties when loaded to destructionwhereas the brittle properties decreased with the increase inthe number of dry-wet cycles A comparison of the stress-strain curves with different erosion cycles showed that as thepeak stress was approached the stress was re-adjusted tovarious extents In the stress-strain curve the stress read-justmentmanifested as the curve dropped suddenly and thencontinues to rise at is to say when the rock was subjectedto loading the external part of the rock was damaged firstand part of the load was released instantly due to the localdestruction At the same time the load continued to becarried by the internal undamaged structure causing theinternal stress to increase rapidly due to the reduction of theload-carrying area A stress readjustment could be used tocharacterize the nonuniform load-carrying capacity ofmaterials e amount of stress readjustment of the Group Bfeldspar sandstone increased with the increase in the numberof dry-wet cycles with salt-rock interaction indicating thenonuniform structural damage to the Group B feldsparsandstone is result could also be verified by the apparentphenomenon After the dry-wet cycles the surface layer ofthe feldspar sandstone under loading was the first to be

damaged as manifested by the spalling of many rock piecesfrom the surface which was more pronounced with theincrease in the number of dry-wet cycles is result isconsistent with the phenomenon of flaky weathering at theGrottoes e stress-strain characteristics of the feldsparsandstone essentially reflected the damage caused by the dry-wet cycles with a salt solution e damage process occurredcontinuously from the outside to the inside resulting in thenonuniformity of the damage area of the feldspar sandstoneis provided a reference for the stability of the rock mass orpillar [17]

Figure 8 shows the curves of the uniaxial compressivestrength and the elastic modulus of the Group A and GroupB feldspar sandstones It can be seen that as the number ofdry-wet cycles increased from 0 to 25 for the Group Asamples the compressive strength decreased from2714MPa to 1397MPa with a reduction of 4853 and theelastic modulus decreased from 981MPa to 720MPa with areduction of 2661 For the Group B samples the com-pressive strength decreased from 3080MPa to 818MPawith a reduction of 7344 and the elastic modulus de-creased from 1532MPa to 423MPa with a reduction of7239 erefore the mechanical properties of the feldsparsandstone were reduced more by the dry-wet cycles with thesalt solution and the damage effect of the crystallizationstress on the feldspar sandstone was more remarkable

332 Comparative Analysis of the Lateral Strain of theFeldspar Sandstone An observation system using thedigital speckle correlation method (DSCM) was employedto observe and analyze the deformation and destructioncharacteristics of the feldspar sandstone after the dry-wetcycles of the Group A and B samples in order to obtain theevolution process of the lateral strain field Due to thelarge amount of variables and data the Group A and Bsandstone samples with the most notable damage(numbered 25-2 and 25-1) were selected for analysis eresults are shown in Figures 9 and 10 According to theliterature [18] the lateral strain evolution process could be

001 002 003 004 0050

5

10

15

20

25

30

0-15-110-1

15-320-125-2

Strain

Stre

ss (M

Pa)

(a)

0-15-110-2

15-320-125-1

001 002 003 004 0050

10

20

30

40

Strain

Stre

ss (M

Pa)

(b)

Figure 7 Stress-strain curves of the feldspar sandstones after a dry-wet cycle (a) Group A (b) Group B


roughly divided into four stages namely the uniformdistribution stage nucleation stage localization stage anddestruction stage On the stress-strain curve the repre-sentative points of the four stages in the evolution of thedeformation field were selected and the stress at eachrepresentative point was calculated as shown inFigures 9(a) and 10(a) Figures 9(b) and 10(b) show thedestruction patterns of the sample and Figures 9(c)ndash9(f )and 10(c)ndash10(f ) show the contours of the lateral shearstrain at each representative point e range of thehorizontal and vertical coordinates of the field of view inthe figure is 30mm times 80mm

e evolution process of the lateral deformation fieldactually reflected the crack activity within the feldsparsandstone [19] It can be seen from Figures 9 and 10 thatthe strain characteristics were remarkable at each stage ofthe evolution process of the lateral shear strain field euniform distribution stage was located in the initial stageof the stress-strain curve for which the shear strain wassmall and uniformly distributed As the stress-strain curveentered the linear elastic phase the stress level rose whichcompacted the sample and caused microcracks to appearAccordingly a spherical strain region appeared in theshear strain contour map that is the nucleation stageformed At the softening stage of the stress-strain curvebefore the peak the stress level of the feldspar sandstone ishigh macroscopic cracks began to appear and the lateralshear strain field changed from the original nucleus shapeto a band shape that is the strain localization formedwhich was the most important phenomenon before thedestruction of the feldspar sandstone After this stage thestress level of the feldspar sandstone sample was expectedto reach the peak and the overall structure was about to bedestroyed A comparison of the destruction pattern dia-gram and the strain contour map of the feldspar sandstonerevealed that the main macroscopic cracks occurred in thestrain localization area erefore the deformation anddestruction characteristics of the feldspar sandstone couldbe studied by observing the lateral strain field of thesample

34ComparativeAnalysis of theMicroscopicCharacteristics ofFeldspar Sandstone e above series of physical and me-chanical tests was mainly used to analyze the deteriorationof the feldspar sandstone after dry-wet cycles from amacroscopic point of view However the macroscopicphysical and mechanical behavior of the feldspar sandstonemainly resulted from the continuous change of its mi-crostructure In recent years the observation of the mi-croscopic properties of rock materials has graduallybecome an important and universal means of research Pastresearchers [20 21] used micromesoscopic observationequipment to study the destruction mechanism of modifiedmaterials such as cement mortar and mudstone and therelationship between their research results and the mac-roscopic destruction mechanism was widely recognizederefore it is important to study the micromesoscopicchanges of feldspar sandstone under dry-wet cycles inorder to reveal the deterioration mechanism of feldsparsandstone In this section the deterioration processes offeldspar sandstone after dry-wet cycles were comparativelyanalyzed from the micromesoscopic perspective using themeans such as XRD SEM and laser scanning confocalmicroscope (LSCM)

341 Comparative Analysis of the Mineral Composition ofFeldspar Sandstone Figure 11 shows the XRD patterns ofthe Group A and Group B feldspar sandstones after dry-wet cycles In the figure Y-0 represents the curve of thedry undisturbed feldspar sandstone A-25-2 is the curveof the Group A feldspar sandstone after 25 dry-wet cyclesand B-25-1 is the curve of the Group B feldspar sandstoneafter 25 dry-wet cycles where Q P K and I denotequartz sodium potassium feldspar kaolinite and illiterespectively e relative content of the minerals in thefeldspar sandstone was analyzed by the semiquantitativeanalysis software Xpert Highscore Plus as shown inTable 2

It can be seen from Figure 11 and Table 2 that quartz wasthe most abundant component in the feldspar sandstone and

5 10 15 20 250

5

10

15

20

25

30

35


Group AGroup B

Peak

stre

ngth

(MPa

)

(a)

Group AGroup B

0 5 10 15 20 25400

800

1200

1600


Elas

tic m

odul

us (M

Pa)

(b)

Figure 8 Mechanical strength of the feldspar sandstones after the dry-wet cycles (a) Peak strength (b) Elastic modulus


it had the highest diffraction intensity Compared with un-disturbed feldspar sandstone the Group A and Group Bfeldspar sandstones differed by a small amount in terms of thediffraction intensity and composition relative content indi-cating that the dry-wet cycles with water and salt solution hadlittle effect on quartz which was also the reason for thestability of the quartz In addition the diffraction intensityand the relative content of the K-feldspar and illite in Group Aand Group B were low and those of kaolinite were high iswas because of the hydrolysis of feldspar to form kaolinitee hydrolysis reaction of the water and feldspar was2KAlSi3O8 + 2H+

+ H2O 2K++ 4SiO2 + Al2 Si2O5( 1113857(OH)4

(3)

Compared with the attributes of the Group A feldsparsandstone the diffraction intensity and relative content ofthe feldspar in the Group B feldspar sandstone decreasedand those of the kaolinite in the Group B increasedis wasbecause Groups A and B both had aqueous solutions whileGroup B also contained sulfate solution erefore in ad-dition to the hydrolysis reaction there should have also beena reaction between the sulfate and the feldspar as follows

2Na AlSi3O8( 11138572 + 9H2O + H2SO4 Al2O32SiO2 middot 2H2O

+ Na2SO4 + 4H4SiO4

(4)

e reaction between the feldspar and the sulfate pro-duced kaolinite and at the same time released sodium ions toform more sulfate As a result sulfate contained in the waternot only damaged the structure of the feldspar sandstone butalso continuously damaged the feldspar sandstone due to therecycling of the sulfate ions which was consistent with thepattern of the macroscopic mechanical changes

342 Comparative Analysis of Feldspar Sandstone emicroscopic surface morphologies of the Group A andGroup B feldspar sandstones for dry-wet cycles are shown inFigures 12 and 13 It can be clearly seen from the apparentmorphology of the feldspar sandstone after no dry-wetcycles that the composition of the feldspar sandstone in-cluded quartz particles and minerals such as feldspar esurfaces of the quartz particles were relatively flat andsmooth acting as the skeleton while minerals such as

000 001 002 003

5

10

15

20

25

Point 4 075

Point 3 091

Point 2 065

Strain

Point 1 012Representative point Stress level of loading step

Stre

ss (M

Pa)

Stress-strain curve of 25-2Loading step

(a) (b)

0 10 20 30

80

60

40

20

0

ndash6

ndash4

ndash2

0

2

4

6times10ndash4

(c)

0 10 20 30

80

60

40

20

0

ndash002

ndash006

ndash004

0

002

004

(d)

0 10 20 30

80

60

40

20

0

ndash005

0

005

01

(e)

0 10 20 30

80

60

40

20

0ndash005

0

005

01

015

(f )

Figure 9 Evolution process of the lateral strain field of the feldspar sandstones (Group A) after the dry-wet cycles (a) e curve of therepresentative points (b) Destruction pattern (c) Point 1 (d) Point 2 (e) Point 3 (f ) Point 4


feldspar were relatively coarse acting as cementing materialfilled between particles along with the pores and fissures thatexisted between them acting as the linkage It can be seenfrom Figure 12 that the internal structure of the undisturbedfeldspar sandstone had a clear outline of the particles on thescan the particles and the cementing material were notablydivided and the particles were aligned closely and neatly Asthe number of dry-wet cycles increased the feldsparsandstone had a lowered surface compactness and a loosestructure and the mineral particles had rough surfaces with

Table 2 Relative content of the minerals in the feldspar sandstonesof Groups A and B after the dry-wet cycles

SamplesRelative content of minerals ()

Quartz Potassium sodium feldspar Kaolinite IlliteY-0 51 41 5 3A-25-2 50 36 12 2B-25-1 51 28 19 1

10 20 30 40 50 60 70 80

0

0

0

2000

2000

B-25-1

A-25-2

Y-0

2θ (deg)

KI

P Q

2000

Diff

ract

ion

inte

nsity

(CPS

)

Diff

ract

ion

inte

nsity

(CPS

)

lowast

lowast

lowast lowastlowast lowast

lowast

Figure 11 X-ray diffraction of the feldspar sandstones before andafter the dry-wet cycles

000 001 002 003 004 005

5

10

15

20

Point 4 072

Point 3 090Point 2 085

Representative point Stress level of loading step

Strain


Point 1 016

Stre

ss (M

Pa)

(a) (b)

0 10 20 30

80

60

40

20

0

0

1

ndash1

times10ndash4

(c)

0 10 20 30

80

60

40

20

0

ndash2

ndash4

ndash6

0

2

4

6

8times10ndash3

(d)

0 10 20 30

80

60

40

20

0

ndash001

ndash002

ndash003

ndash004

ndash005

0

(e)

0 10 20 30

80

60

40

20

0 ndash015

ndash01

ndash005

0

005

(f )

Figure 10 Evolution process of the lateral strain field of the feldspar sandstones (Group B) after the dry-wet cycles (a) e curve of therepresentative points (b) Destruction pattern (c) Point 1 (d) Point 2 (e) Point 3 (f ) Point 4


many small particlesis was largely related to the softeningand dissolution of the feldspar sandstone by water

It can be seen from Figure 13 that after 0 to 5 dry-wetcycles there was a small amount of near-spherical saltcrystals in the pores or fissures As the number of cyclesincreased the salt content in the pores gradually in-creased and it was enriched around the quartz particlesBased on the above analysis there were cementing ma-terials dominated by feldspar minerals around the quartzparticles e presence of the salt indicated that thecrystallization stress mainly affected the relatively weakcementing materials It was also found that as the numberof cycles increased crystallized salt first filled the tinypores and then the large pores e evaporation of waterwas the internal driving force of salt crystallization esmall volume of water in the tiny pores made the evap-oration relatively easy and it was easy to fill the relativelysmall space with salt crystals Salt crystals accumulatedcontinuously during the dry-wet cycles e saturated saltsolution first eroded the pores or fissures and even themicrocracks of feldspar sandstone As the water evapo-rated continuously the salt crystallized continuously onthe walls of the pores or the fissures After a certainnumber of times the salt filled the entirety of the pores orfissures and then compressive stress began to be gener-ated When the compressive stress was higher than thestrength of the relatively weak minerals (feldspar cement)microdestruction which may also be called microdamageoccurred inside the feldspar sandstone As the number oftimes of crystallization further increased the damage tothe feldspar sandstone gradually increased Such damageto the feldspar sandstone had a specific directionality iswas because the solution gradually entered from theoutside to the inside as the feldspar sandstone was im-mersed in solution so the damage to the feldspar sand-stone also needed to progress from the outside to theinside is result is consistent with that of [3] but it isdifferent from the earlier findings of [22 23]

343 Comparative Analysis of the Surface Roughness of theFeldspar Sandstone Roughness measurement is usually ap-plied to the friction and wear of metal materials while theroughness measurement of rock materials is only used for thepurpose of fissure characterization In this section the prin-ciple of roughness measurement is introduced to characterizethe degree of damage to the feldspar sandstonee cored andground feldspar sandstone samples initially had a flat andsmooth surface After different numbers of dry-wet cycles thesamples may have had different damages as also manifestedon their surfaces is has already been described in theanalysis of the apparent phenomenon (Section 31) eroughness of the outer surface of the feldspar sandstone afterthese different numbers of dry-wet cycles could be measuredto characterize the damage to the feldspar sandstone from adifferent perspectiveree areas were taken from each samplefor measurement and the final roughness was taken as theaverage of the data for the three areas

Belem et al [24] proposed four typical three-dimen-sional surface morphology parameters namely surfaceheight deviation Sa surface height distribution standarddeviation Sq surface skewness Ssk and surface kurtosis SkuAmong them Sa and Sq are generally used to express theheight of the surface morphology of a material Sku is used todescribe the steepness of the surface morphology of a ma-terial and Ssk is used to describe the asymmetry of thesurface height distribution In this study Sa was selected asthe parameter for roughness characterization It is calculatedas

Sa 1

MN1113944

Mminus1

k01113944

Nminus1

l1z xk yl( 1113857 minus u

11138681113868111386811138681113868111386811138681113868 (5)

where u (1MN)1113936Mminus1k0 1113936

Nminus1l1 z(xk yl) and M and N are

the length and width respectively of the three-dimensionalsurface image z(xk yl) is the height at the point (xk yl)

Table 3 shows the measured values of the height devi-ations Sa of the Group A and B feldspar sandstones after the

(a) (b) (c) (d) (e) (f )

Figure 12 Microstructure of the feldspar sandstones (Group A) after the dry-wet cycles (a) 0 T (b) 5 T (c) 10 T (d) 15 T (e) 20 T (f ) 25 T

(a) (b) (c) (d) (e) (f )

Figure 13 Microstructure of the feldspar sandstones (Group B) after the dry-wet cycles (a) 0 T (b) 5 T (c) 10 T (d) 15 T (e) 20 T (f ) 25 T


dry-wet cycles It can be seen that as the number of dry-wetcycles increased the surface deviation of the feldspar sand-stone generally showed an upward trend is indicates thatthe roughness of the outer surfaces of the Group A and GroupB feldspar sandstones gradually aggravated from 0 cycle to 25cycle the average value increased by 106 μm and 334 μmrespectively due to the impact of the dry-wet cycles on thefeldspar sandstone e above microscopic morphologyanalysis revealed that the quartz particles on the surface of thefeldspar sandstone had a hard texture and stable propertiesmaking it difficult to damage It was hence only possible thatthe relatively weak cementing materials of the feldspar weredamaged and they fell off eventually causing quartz particlesto be exposed on the surface and thus increasing the surfaceroughness is also confirmed the conclusion of the particlesfalling in the macroscopic apparent analysis e increase inthe surface roughness also indicated from another angle thatthe damage to the feldspar sandstone caused by the dry-wetcycles was increasingly aggravated A comparison of the dataof Group A and B found that the surface roughness of thefeldspar sandstone after salt crystallization was much higherthan that after dry-wet cycles consistent with the variationpattern of the macroscopic mechanical properties Addi-tionally the relatively large rate of increase in the surfaceheight deviation was attributed to the considerable effect ofsalt crystallization which caused the weak cementingmaterialto be destroyed rapidly is effect was much more re-markable than the mere effect of softening and dissolutioncaused by water e conclusion drawn from surfaceroughness analysis is essentially the same as the variationpattern of the macroscopic mechanical properties

4 Weathering Mechanism ofFeldspar Sandstone

41 Analysis of theWeatheringMechanism of theWater-RockInteraction At present the mechanistic analysis of water-rock interaction is conducted mainly from the single per-spective of macroscopic mechanical properties or micro-scopic observation whereas the analysis of themechanism ofwater-rock interaction from different scales is still rare

According to the analysis of the macroscopic physicaland mechanical properties the main physical and me-chanical parameters of the feldspar sandstones after multipledry-wet cycles were all weakened In particular the wavevelocity compressive strength and elastic modulus werereduced by 1620 4853 and 2661 respectively and the

saturated water absorption increased by 2802e variationof these measured macroscopic physical and mechanicalparameters represented the deterioration of the overallstructure of the feldspar sandstone after a specific number ofdry-wet cycles and in essence the change in the micromesoscopic structure such as the composition structure andpores or fissures of feldspar sandstone After the componentidentification and microscopic observation of the feldsparsandstone the primary internal structure of the feldsparsandstone that was not affected by the dry-wet cycles could berepresented as shown in Figure 14(a) e primary internalstructure of the feldspar sandstone mainly included two partsthe matrix and the skeleton e matrix included feldsparclay and the pore and fissure structure e skeleton wasmainly composed of quartz particles with a hard texture andstable properties e matrix and the skeleton mainly formeda stable feldspar sandstone structure by cementation ecomposition of the single quartz particle as the core sur-rounded by various components of thematrix was regarded asa simple unit of feldspar sandstone e unit contained all thebasic elements in the composition of feldspar sandstone asshown in Figure 14(c) During the dry-wet cycles water firstinvaded from the outside to the inside along the primarypores or fissures in the unit e primary pores became themain sites for the water effect Based on this secondary crackswere generated by the following three effects

(1) Since the sandstone samples in this study were madeof feldspar sandstone the K-Na feldspar in the unitchemically reacted with water to form kaolinite(formula (3)) In the process due to the differentphysical properties (composition and density) anddifferent spaces occupied by the new and old ma-terials a large number of microcracks that is sec-ondary cracks were generated

(2) e clay minerals in the unit had the characteristicsof water swelling e clay minerals included notonly kaolinite (which was secondary clay) formed bythe reaction between water and feldspar but also theprimary clay of feldspar sandstone When the clayminerals experienced water swelling a large numberof secondary cracks were produced

(3) e unit contained a large amount of soluble mineralssuch as feldspar or kaolinite ese minerals weredissolved in water in the form of ions and theevaporation of the water acted as an internal drivingforce to move the mineral ions out of the unit Studies

Table 3 Height deviations Sa of the feldspar sandstone surface in Groups A and B after the dry-wet cycles

Number of wet and dry cyclesMeasurement area

Surface height deviation of group A (μm) Surface height deviation of group B (μm)No 1 No 2 No 3 Average value No 1 No 2 No 3 Average value

0 437 521 552 503 484 552 499 5125 547 534 539 540 547 743 599 63010 557 584 548 563 636 615 668 64015 596 584 568 583 701 644 821 72220 584 583 619 595 747 1062 667 82525 580 621 626 609 936 753 878 856


[25 26] have shown that the solubility of feldspar isgreater than that of kaolinite erefore from athermodynamic perspective under certain condi-tions feldspar has a tendency to transform into ka-olinite eventually leading to enlarged primary poresand secondary cracks and hence providing the spatialconditions for corrosion and dissolution later on

With the above three actions a number of secondarycracks were generated in the unit As shown in Figure 14(d)these secondary cracks changed the structure of the unitBecause the feldspar sandstone sample was composed of alarge number of units numerous secondary cracks wereproduced in the feldspar sandstone after multiple dry-wetcycles Such secondary cracks can be viewed as a largenumber of damaged points in the macrostructure of thefeldspar sandstone substantially changing the overallstructure of feldspar sandstone as shown in Figure 14(b)e large number of secondary pores that were producedessentially changed the overall structure of the feldsparsandstone is resulted in a decrease in the wave velocityand an increase in the saturated water absorption for the

physical properties as well as a decrease in the compressivestrength for the mechanical properties of the feldsparsandstone thereby increasing the number of fine cracks atthe destruction of feldspar sandstone samples Due to thecorrosion and dissolution of the matrix by water the surfaceroughness of the feldspar sandstone gradually increasedeabove macroscopic and microscopic characteristics of thefeldspar sandstone subjected to dry-wet cycles were also amanifestation of the damage to the feldspar sandstone fromanother perspective

42 Analysis of the Weathering Mechanism of the Salt-RockInteraction According to the analysis of the results of themacroscopic physical and mechanical properties of theGroup B feldspar sandstone the physical and mechanicalparameters of the feldspar sandstone after multiple dry-wetcycles were also weakened In particular the wave velocitycompressive strength and elastic modulus were reduced by3327 7344 and 7239 respectively while the satu-rated water absorption was increased by 3698 ephysical and mechanical properties of the Group B feldsparsandstone after dry-wet cycles deteriorated more following

Quartz

Clay mineral

Feldspar

Microcrack

Original pore or crack

Damage point

(a)

(c) (d)

(b)

Figure 14 Microscopic process of a water-rock dry-wet cycle (a) Original structure of feldspar sandstone (b) Damage structure of feldsparsandstone (c) Original unit structure (d) Damage unit structures


salt-rock interactions than following water-rock interac-tions indicating the important influence of salt on thedamage to the sandstone e mechanism of the salt-rockinteraction included the following

(1) First there were three effects of water-rock inter-action Since the erosive solution was a salt solutionwith sulfate as the solute and water as the solvent themechanism of the salt-rock interaction first includedthe three effects of water and rock

(2) Second there was the reaction between the sulfateions and the feldspar sandstone components asshown in formula (4) e minerals such as feldsparand calcite in the composition of the feldsparsandstone reacted with the sulfate ions to produceclay materials such as kaolinite and gypsum whichwas similar to the effect of feldspar hydrolysis

(3) e mechanism of the salt-rock interaction was thatof the interaction between the salt solution and thefeldspar sandstone erefore in addition to themechanism of the water-rock interaction and theionic reaction salt crystallization was also importante site for salt crystallization that is the pores orcracks could be considered as a unit in the study asshown in Figure 15 When the feldspar sandstoneunderwent dry-wet cycles the saturated salt solutionentered the pores or cracks inside the feldsparsandstone As the water evaporated the salt grad-ually crystallized on the walls of the pores or crackscausing compressive stress on the rock structures onboth sides When the compressive stress exceededthe tensile strength of the cement of the feldsparsandstone secondary microcracks were produced asshown in Figure 15(a) As the number of dry-wetcycles increased the crystallization stress repeatedlyacted on the microcracks causing them to expandcontinuously to form secondary pores as shown inFigure 15(b) During the subsequent dry-wet cyclesthese secondary microcracks and the pores providedthe sites for the salt enrichment in return whichcaused the number of microcracks and pores tocontinuously increase thus forming a vicious circleas shown in Figure 15(c) With a sufficient source of

salt the crystallization caused stress damage to thestructure of the feldspar sandstone as the surface areaincreased continuously e structure of the feldsparsandstone changed under dry-wet cycles that isstructural damage was generated is was themechanism of the damage to the feldspar sandstone

Compared to the water-rock interaction the participa-tion of salt led to a relatively large number of secondarycracks and thus severe damage to the feldspar sandstoneduring the destruction process As reflected in the macro-scopic physical and mechanical properties the wave velocitydecreased the saturated water absorption increased and thecompressive strength decreased As reflected in the micromesoscopic characteristics a large number of microscopicpores were generated on the surface of the feldspar sand-stone the surface roughness increased rapidly and a largeamount of outside particles fell off Additionally the abovephenomena indicated a higher degree of damage than thatcorresponding to the dry-wet cycles with water

5 Conclusion

(1) At the macroscopic level the Group A and B feldsparsandstones had increased saturated water absorptionand decreased longitudinal wave velocities peakstrengths and elastic moduli as well as remarkabledeformation characteristics In addition the variationrate of Group B was higher than that of Group A

(2) At the micromesoscopic level the Group A and Bfeldspar sandstones had decreased relative content offeldspar increased relative content of kaoliniteenlarged microscopic pores more microcracks andlarger surface height deviations Additionally thevariation rate of Group B was higher than that ofGroup A

(3) e weathering mechanism of the feldspar sandstoneincluded water-rock interaction and salt-rock in-teraction e weathering mechanism of the water-rock interaction consisted of three effects namelythe hydrolysis of K-Na feldspar the water swelling ofthe clay minerals such as kaolinite and the disso-lution of soluble minerals e weathering


(a) (b) (c)

Secondary crack Secondary pore Crystalline stress

Figure 15 Microscopic process of the salt-rock dry-wet cycle (a) Pore unit (b) Crystallization that produced secondary pores or cracks(c) More pores or cracks produced


mechanism of the salt-rock interaction included inaddition to the above three effects salt crystallizationin the pores or fissures and the chemical reactionbetween the minerals (eg feldspar and calcite) andsulfate In particular the salt crystallization was themost remarkable for the deterioration of the feldsparsandstone

Data Availability

All data used in this article are available from the corre-sponding author by request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

is work was supported by the National Key RampD Plan ofChina (Grant no 2017YFC1503100) and the NationalNatural Science Foundation of China (Grant no 51474121)e authors thank LetPub (httpswwwletpubcom) for itslinguistic assistance during the preparation of thismanuscript

References

[1] R Z Liu B J Zhang H Zhang and M F Shi ldquoDeteriorationof Yungang grottoes diagnosis and researchrdquo Journal ofCultural Heritage vol 12 no 4 pp 494ndash499 2011

[2] X-S Wang L Wan J Huang W Cao F Xu and P DongldquoVariable temperature and moisture conditions in YungangGrottoes China and their impacts on ancient sculpturesrdquoEnvironmental Earth Sciences vol 72 no 8 pp 3079ndash30882014

[3] S J Yan Y Fang J H Liu and S E Tan ldquoDeteriorationexperiment with soluble salt on sandstone of Yunganggrottoes and its model creationrdquo Rock and Soil Mechanicsvol 34 pp 3410ndash3416 2013 in Chinese

[4] S J Yan J Q Chen Y Dou and P Sun ldquoCharacteristics ofYungang grottoes sandstone and weathering simulationtestsrdquo Geoscience vol 29 pp 442ndash447 2015 in Chinese

[5] Y Qin Y Wang L Li and J Huang ldquoExperimentalweathering of weak sandstone without direct water partici-pation by using sandstone from the Yungang grottoes inDatong Chinardquo Rock Mechanics and Rock Engineeringvol 49 no 11 pp 4473ndash4478 2016

[6] H Y Yao Z H Zhang C H Zhu Y C Shi and Y LildquoExperimental study of mechanical properties of sandstoneunder cyclic drying and wettingrdquo Rock and Soil Mechanicsvol 31 pp 3704ndash3714 2010 in Chinese

[7] M A Coombes and L A Naylor ldquoRock warming and dryingunder simulated intertidal conditions part II weathering andbiological influences on evaporative cooling and near-surfacemicro-climatic conditions as an example of biogeomorphicecosystem engineeringrdquo Earth Surface Processes and Land-forms vol 37 no 1 pp 100ndash118 2012

[8] M C Torres-Suarez A Alarcon-Guzman and R Berdugo-DeMoya ldquoEffects of loading-unloading and wetting-drying cy-cles on geomechanical behaviors of mudrocks in theColombian Andesrdquo Journal of Rock Mechanics and Geo-technical Engineering vol 6 no 3 pp 257ndash268 2014

[9] B Du H B Bai Z G Ma M Li and G M Wu ldquoExperi-mental study on the dynamic tensile properties of red-sandstone after cyclic wetting and dryingrdquo Chinese Journal ofRock Mechanics and Engineering vol 37 pp 1671ndash1679 2018in Chinese

[10] H F Deng J L Li K W Wang J Liu M Zhu and T LuldquoResearch on secondary porosity changing law of sandstoneunder saturation-air dry cyclesrdquo Rock and Soil Mechanicsvol 33 pp 483ndash488 2012 in Chinese

[11] Y Fu Z J Wang X R Liu et al ldquoMeso damage evolutioncharacteristics and macro degradation of sandstone underwetting-drying cyclesrdquo Chinese Journal of Geotechnical En-gineering vol 39 pp 1653ndash1661 2017 in Chinese

[12] A Ozbek ldquoInvestigation of the effects of wetting-drying andfreezing-thawing cycles on some physical and mechanicalproperties of selected ignimbritesrdquo Bulletin of EngineeringGeology and the Environment vol 73 no 2 pp 595ndash609 2014

[13] P D Sumner and M J Loubser ldquoExperimental sandstoneweathering using different wetting and drying moistureamplitudesrdquo Earth Surface Processes and Landforms vol 33no 6 pp 985ndash990 2008

[14] H M Zhang G D Ma and B Y Shu ldquoA discussion of thetreatment of water-seepage disease of the stone carvings in theYungang grotto near Datongrdquo Hydrogeology amp EngineeringGeology vol 31 pp 64ndash67 2004 in Chinese

[15] F Guo and G H Jiang ldquoDistribution of soluble salts andsulfur isotope in the Yungang Grottoes Datongrdquo Hydro-geology amp Engineering Geology vol 40 pp 126ndash130 2013 inChinese

[16] M Duda and J Renner ldquoe weakening effect of water on thebrittle failure strength of sandstonerdquo Geophysical JournalInternational vol 192 pp 1091ndash1108 2000

[17] X R Liu M H Jin D L Li and L Zhang ldquoStrength de-terioration of a shaly sandstone under dry-wet cycles a casestudy from the three gorges reservoir in Chinardquo Bulletin ofEngineering Geology and the Environment vol 76 pp 1ndash152017

[18] S P Ma and H Zhou ldquoSurface strain field evolution of rockspecimen during failure processrdquo Chinese Journal of RockMechanics and Engineering vol 27 pp 1668ndash1673 2008 inChinese

[19] S P Ma L G Wang and Y H Zhao ldquoExperimental study ondeformation field evolution during failure procedure of a rockborehole structurerdquo Rock and Soil Mechanics vol 27pp 1083ndash1086 2006 in Chinese

[20] I Farina F Fabbrocino F Colangelo L Feo andF Fraternali ldquoSurface roughness effects on the reinforcementof cement mortars through 3D printed metallic fibersrdquoComposites Part B Engineering vol 99 pp 305ndash311 2016

[21] A R Ismail M Z Jaafar W R W Sulaiman I Ismail andN Y Shiunn ldquoIdentification of sandstone core damage usingscanning electron microscopyrdquo in Proceedings of the Ad-vanced Materials Conference vol 28-29 pp 79ndash83 LangkawiMalaysia November 2016

[22] M Steiger ldquoCrystal growth in porous materials-II influenceof crystal size on the crystallization pressurerdquo Journal ofCrystal Growth vol 282 no 3-4 pp 470ndash481 2005

[23] P eoulakis and A Moropoulou ldquoMicrostructural andmechanical parameters determining the susceptibility ofporous building stones to salt decayrdquo Construction andBuilding Materials vol 11 no 1 pp 65ndash71 1997

[24] T Belem F Homand-Etienne and M Souley ldquoQuantitativeparameters for rock joint surface roughnessrdquo Rock Mechanicsand Rock Engineering vol 33 no 4 pp 217ndash242 2000


[25] Y Chen C J Wang X F Sun et al ldquoProgress on mineralsolubility and mechanism of dissolution secondary porosityforming in clastic reservoirrdquo Bulletin of Mineralogy Petrologyand Geochemistry vol 34 pp 830ndash836 2015 in Chinese

[26] X J Luo W D Yang R X Li et al ldquoEffects of pH on thesolubility of the feldspar and the development of secondaryporosityrdquo Bulletin of Mineralogy Petrology andGeochemistryvol 20 pp 103ndash107 2001 in Chinese


lowerefore the water (salt) and temperature are the mainfactors affecting the weathering of the Grottoes

To protect these stone cultural relics from weatheringthe Yungang Grottoes Research Institute among otherorganizations has also implemented a large scale of pro-tection work including protection measures such as seepageprevention dehumidification in the Grottoes and drainageAlthough these measures have had a protective effect theproblem of weathering has not been solved Yan et al andQin et al studied the weathering characteristics of theYungang Grottoes and conducted tests on the soluble saltweathering in the Grottoes e results show that the de-struction of the Yungang Grottoes sandstone resulted fromthe combination of physical and chemical weathering ewater salt solution and temperature were the main influ-encing factors and salt could aggravate the deterioration ofthe grotto structure [3ndash5] Yao et al investigated the me-chanical properties of sandstone after dry-wet cycles [6]eresults showed that the mechanical indexes of the rock afterdry-wet cycles decreased to varying extents Coombes andNaylor obtained the weathering mechanism of rock throughdry-wet cycle tests on limestone granite and concretematerials [7] Torres-Suarez et al examined the physical andmechanical properties of mudstone after dry-wet cycles [8]e results showed that the main destruction mechanism ofthe layered mudstone started with microscopic scale fissurecoalescence and it manifested as physical and chemicaldeterioration ere have been numerous studies on thephysical and mechanical properties of feldspar sandstoneand ordinary sandstone such as those above-mentioned[9ndash13] However there have been few studies on the damagemechanism of feldspar sandstone after dry-wet cycles fromthe perspective of chemical damage

erefore for this study feldspar sandstone of the samestratum and with similar lithology as that of feldsparsandstone where the Yungang Grottoes are scattered wasselected An experimental method was used that combinedlaboratory dry-wet cycle tests and macro-micromesoscopicobservation to obtain the macroscopic physical and me-chanical properties (eg saturated water absorption lon-gitudinal wave velocity strength elastic modulus anddeformation) as well as the variation patterns of the mi-crostructure and the mesoscopic roughness of feldsparsandstone after wet-wet cycles Based on this the mechanicalproperties and the weathering mechanisms of feldsparsandstone after dry-wet cycles were analyzed

2 Material and Methods

21 Preparation of the Materials

211 Preparation of the Feldspar Sandstone Given thehistorical value of the Yungang Grottoes the relevant de-partment in this scenic area disallowed the collection of alarge number of rock samples erefore feldspar sandstonein the same stratum as that of the Yungang Grottoes wasselected for the tests e mineral composition and theaverage relative content of this feldspar sandstone and thestatues of the Yungang Grottoes were compared and

analyzed by X-ray diffraction (XRD) e results are shownin Figure 1 and Table 1 In the figure Q is quartz P is K-Nafeldspar K is kaolinite and I is illite It can be seen that thefeldspar sandstone used in the experiment had similar li-thology to that of the sandstone of the Yungang Grottoes soit could represent the sandstone of the Yungang Grottoes Inthe laboratory the rock pieces of the feldspar sandstone wereprocessed using a JKZS-100 automatic coring machine and aYBDQ-4 rock cutter according to the specifications (SL264-2001 GBT50266-99) After the processes of core drillingcutting polishing grinding cleaning and drying a standardsample of feldspar sandstone with a size of φ50mmtimes 100mm was finally obtained as shown in Figure 2

212 Preparation of the Erosion Solution According to thefield investigation the weathered grotto faces within 1mfrom the ground are often moist and a large amount ofwhite salt appears in the dry season Extensive researchrevealed that the white salt was sulfate [14 15] erefore inthe tests the crystal salt of Na2SO4 (Glauberrsquos salt) was usedas the solute to prepare the saturated Na2SO4 solution as theerosion solution and distilled water was used as a controle standard samples were immersed in the preparederosion solution to carry out the dry-wet cycle tests withwater-rock interaction (Group A) and salt-rock interaction(Group B)

22 Multiscale Experimental Techniques

221 Dry-Wet Cycle Test e dry-wet cycle test was con-ducted in reference to the requirements of the free im-mersion method in the specification (GBT50266-99) estandard sample of feldspar sandstone was immersed in theerosion solution for 12 h e water level was first controlledat one-fourth of the height of the feldspar sandstone andthen the erosion solution was added after 2 h and 4 h to reachone-half and three-fourths of the height of the sample re-spectively After 6 h the sample was completely immersed inthe erosion solution until the end of the immersion durationNext the sample was taken out and dried in the oven for12 h with the drying temperature set to 50degC in consider-ation of the maximum temperature of around 60degC at thesurface of the Grottoes in summer en all of the sampleswere taken out and cooled to room temperature thuscompleting a dry-wet cycle of feldspar sandstone enumbers of cycles were set to six levels (0 5 10 15 20 and25 times T) After the dry-wet cycle test was completed at alevel the corresponding feldspar sandstone samples wereremoved to perform the subsequent tests

222 Experimental Study of the Physical Properties ofFeldspar Sandstone After the test at each level was com-pleted the mass and the saturated water absorption of thefeldspar sandstone were determined using an electronicbalance (accuracy 001 g) e longitudinal wave velocity ofthe feldspar sandstone was measured by an NM-4B-600nonmetal ultrasonic detector Before the measurement the












10 20 30 40 50 60 70 80

2500

0

2θ (deg)

2000

0

Diff

ract

ion

inte

nsity

(CPS

)

Diff

ract

ion

inte

nsity

(CPS

)


lowast

lowast lowastlowast

lowast

lowast

PQlowast

IK








ws mz minus md

md

times 100 (1)





R v0 minus vn

v0times 100 (2)








5 10 15 20 250

10

20

30

40


Group AGroup B

R (

)


(a) (b) (c) (d) (e)


(a) (b) (c) (d) (e)


0 5 10 15 20 2540

45

50

55

60

65

70

Group AGroup B

w s (

)









001 002 003 004 0050

5

10

15

20

25

30

0-15-110-1

15-320-125-2

Strain

Stre

ss (M

Pa)

(a)

0-15-110-2

15-320-125-1

001 002 003 004 0050

10

20

30

40

Strain

Stre

ss (M

Pa)

(b)








5 10 15 20 250

5

10

15

20

25

30

35


Group AGroup B

Peak

stre

ngth

(MPa

)

(a)

Group AGroup B

0 5 10 15 20 25400

800

1200

1600


Elas

tic m

odul

us (M

Pa)

(b)




+ H2O 2K++ 4SiO2 + Al2 Si2O5( 1113857(OH)4

(3)



+ Na2SO4 + 4H4SiO4

(4)



000 001 002 003

5

10

15

20

25

Point 4 075

Point 3 091

Point 2 065

Strain


Stre

ss (M

Pa)


(a) (b)

0 10 20 30

80

60

40

20

0

ndash6

ndash4

ndash2

0

2

4

6times10ndash4

(c)

0 10 20 30

80

60

40

20

0

ndash002

ndash006

ndash004

0

002

004

(d)

0 10 20 30

80

60

40

20

0

ndash005

0

005

01

(e)

0 10 20 30

80

60

40

20

0ndash005

0

005

01

015

(f )







10 20 30 40 50 60 70 80

0

0

0

2000

2000

B-25-1

A-25-2

Y-0

2θ (deg)

KI

P Q

2000

Diff

ract

ion

inte

nsity

(CPS

)

Diff

ract

ion

inte

nsity

(CPS

)

lowast

lowast


lowast


000 001 002 003 004 005

5

10

15

20

Point 4 072



Strain


Point 1 016

Stre

ss (M

Pa)

(a) (b)

0 10 20 30

80

60

40

20

0

0

1

ndash1

times10ndash4

(c)

0 10 20 30

80

60

40

20

0

ndash2

ndash4

ndash6

0

2

4

6

8times10ndash3

(d)

0 10 20 30

80

60

40

20

0

ndash001

ndash002

ndash003

ndash004

ndash005

0

(e)

0 10 20 30

80

60

40

20

0 ndash015

ndash01

ndash005

0

005

(f )







Sa 1

MN1113944

Mminus1

k01113944

Nminus1


11138681113868111386811138681113868111386811138681113868 (5)





(a) (b) (c) (d) (e) (f )


(a) (b) (c) (d) (e) (f )














0 437 521 552 503 484 552 499 5125 547 534 539 540 547 743 599 63010 557 584 548 563 636 615 668 64015 596 584 568 583 701 644 821 72220 584 583 619 595 747 1062 667 82525 580 621 626 609 936 753 878 856






Quartz

Clay mineral

Feldspar

Microcrack


Damage point

(a)

(c) (d)

(b)









5 Conclusion





(a) (b) (c)





Data Availability




Acknowledgments


References







































10 20 30 40 50 60 70 80

2500

0

2θ (deg)

2000

0

Diff

ract

ion

inte

nsity

(CPS

)

Diff

ract

ion

inte

nsity

(CPS

)


lowast

lowast lowastlowast

lowast

lowast

PQlowast

IK








ws mz minus md

md

times 100 (1)





R v0 minus vn

v0times 100 (2)








5 10 15 20 250

10

20

30

40


Group AGroup B

R (

)


(a) (b) (c) (d) (e)


(a) (b) (c) (d) (e)


0 5 10 15 20 2540

45

50

55

60

65

70

Group AGroup B

w s (

)









001 002 003 004 0050

5

10

15

20

25

30

0-15-110-1

15-320-125-2

Strain

Stre

ss (M

Pa)

(a)

0-15-110-2

15-320-125-1

001 002 003 004 0050

10

20

30

40

Strain

Stre

ss (M

Pa)

(b)








5 10 15 20 250

5

10

15

20

25

30

35


Group AGroup B

Peak

stre

ngth

(MPa

)

(a)

Group AGroup B

0 5 10 15 20 25400

800

1200

1600


Elas

tic m

odul

us (M

Pa)

(b)




+ H2O 2K++ 4SiO2 + Al2 Si2O5( 1113857(OH)4

(3)



+ Na2SO4 + 4H4SiO4

(4)



000 001 002 003

5

10

15

20

25

Point 4 075

Point 3 091

Point 2 065

Strain


Stre

ss (M

Pa)


(a) (b)

0 10 20 30

80

60

40

20

0

ndash6

ndash4

ndash2

0

2

4

6times10ndash4

(c)

0 10 20 30

80

60

40

20

0

ndash002

ndash006

ndash004

0

002

004

(d)

0 10 20 30

80

60

40

20

0

ndash005

0

005

01

(e)

0 10 20 30

80

60

40

20

0ndash005

0

005

01

015

(f )







10 20 30 40 50 60 70 80

0

0

0

2000

2000

B-25-1

A-25-2

Y-0

2θ (deg)

KI

P Q

2000

Diff

ract

ion

inte

nsity

(CPS

)

Diff

ract

ion

inte

nsity

(CPS

)

lowast

lowast


lowast


000 001 002 003 004 005

5

10

15

20

Point 4 072



Strain


Point 1 016

Stre

ss (M

Pa)

(a) (b)

0 10 20 30

80

60

40

20

0

0

1

ndash1

times10ndash4

(c)

0 10 20 30

80

60

40

20

0

ndash2

ndash4

ndash6

0

2

4

6

8times10ndash3

(d)

0 10 20 30

80

60

40

20

0

ndash001

ndash002

ndash003

ndash004

ndash005

0

(e)

0 10 20 30

80

60

40

20

0 ndash015

ndash01

ndash005

0

005

(f )







Sa 1

MN1113944

Mminus1

k01113944

Nminus1


11138681113868111386811138681113868111386811138681113868 (5)





(a) (b) (c) (d) (e) (f )


(a) (b) (c) (d) (e) (f )














0 437 521 552 503 484 552 499 5125 547 534 539 540 547 743 599 63010 557 584 548 563 636 615 668 64015 596 584 568 583 701 644 821 72220 584 583 619 595 747 1062 667 82525 580 621 626 609 936 753 878 856






Quartz

Clay mineral

Feldspar

Microcrack


Damage point

(a)

(c) (d)

(b)









5 Conclusion





(a) (b) (c)





Data Availability




Acknowledgments


References


































ws mz minus md

md

times 100 (1)





R v0 minus vn

v0times 100 (2)








5 10 15 20 250

10

20

30

40


Group AGroup B

R (

)


(a) (b) (c) (d) (e)


(a) (b) (c) (d) (e)


0 5 10 15 20 2540

45

50

55

60

65

70

Group AGroup B

w s (

)









001 002 003 004 0050

5

10

15

20

25

30

0-15-110-1

15-320-125-2

Strain

Stre

ss (M

Pa)

(a)

0-15-110-2

15-320-125-1

001 002 003 004 0050

10

20

30

40

Strain

Stre

ss (M

Pa)

(b)








5 10 15 20 250

5

10

15

20

25

30

35


Group AGroup B

Peak

stre

ngth

(MPa

)

(a)

Group AGroup B

0 5 10 15 20 25400

800

1200

1600


Elas

tic m

odul

us (M

Pa)

(b)




+ H2O 2K++ 4SiO2 + Al2 Si2O5( 1113857(OH)4

(3)



+ Na2SO4 + 4H4SiO4

(4)



000 001 002 003

5

10

15

20

25

Point 4 075

Point 3 091

Point 2 065

Strain


Stre

ss (M

Pa)


(a) (b)

0 10 20 30

80

60

40

20

0

ndash6

ndash4

ndash2

0

2

4

6times10ndash4

(c)

0 10 20 30

80

60

40

20

0

ndash002

ndash006

ndash004

0

002

004

(d)

0 10 20 30

80

60

40

20

0

ndash005

0

005

01

(e)

0 10 20 30

80

60

40

20

0ndash005

0

005

01

015

(f )







10 20 30 40 50 60 70 80

0

0

0

2000

2000

B-25-1

A-25-2

Y-0

2θ (deg)

KI

P Q

2000

Diff

ract

ion

inte

nsity

(CPS

)

Diff

ract

ion

inte

nsity

(CPS

)

lowast

lowast


lowast


000 001 002 003 004 005

5

10

15

20

Point 4 072



Strain


Point 1 016

Stre

ss (M

Pa)

(a) (b)

0 10 20 30

80

60

40

20

0

0

1

ndash1

times10ndash4

(c)

0 10 20 30

80

60

40

20

0

ndash2

ndash4

ndash6

0

2

4

6

8times10ndash3

(d)

0 10 20 30

80

60

40

20

0

ndash001

ndash002

ndash003

ndash004

ndash005

0

(e)

0 10 20 30

80

60

40

20

0 ndash015

ndash01

ndash005

0

005

(f )







Sa 1

MN1113944

Mminus1

k01113944

Nminus1


11138681113868111386811138681113868111386811138681113868 (5)





(a) (b) (c) (d) (e) (f )


(a) (b) (c) (d) (e) (f )














0 437 521 552 503 484 552 499 5125 547 534 539 540 547 743 599 63010 557 584 548 563 636 615 668 64015 596 584 568 583 701 644 821 72220 584 583 619 595 747 1062 667 82525 580 621 626 609 936 753 878 856






Quartz

Clay mineral

Feldspar

Microcrack


Damage point

(a)

(c) (d)

(b)









5 Conclusion





(a) (b) (c)





Data Availability




Acknowledgments


References
































5 10 15 20 250

10

20

30

40


Group AGroup B

R (

)


(a) (b) (c) (d) (e)


(a) (b) (c) (d) (e)


0 5 10 15 20 2540

45

50

55

60

65

70

Group AGroup B

w s (

)









001 002 003 004 0050

5

10

15

20

25

30

0-15-110-1

15-320-125-2

Strain

Stre

ss (M

Pa)

(a)

0-15-110-2

15-320-125-1

001 002 003 004 0050

10

20

30

40

Strain

Stre

ss (M

Pa)

(b)








5 10 15 20 250

5

10

15

20

25

30

35


Group AGroup B

Peak

stre

ngth

(MPa

)

(a)

Group AGroup B

0 5 10 15 20 25400

800

1200

1600


Elas

tic m

odul

us (M

Pa)

(b)




+ H2O 2K++ 4SiO2 + Al2 Si2O5( 1113857(OH)4

(3)



+ Na2SO4 + 4H4SiO4

(4)



000 001 002 003

5

10

15

20

25

Point 4 075

Point 3 091

Point 2 065

Strain


Stre

ss (M

Pa)


(a) (b)

0 10 20 30

80

60

40

20

0

ndash6

ndash4

ndash2

0

2

4

6times10ndash4

(c)

0 10 20 30

80

60

40

20

0

ndash002

ndash006

ndash004

0

002

004

(d)

0 10 20 30

80

60

40

20

0

ndash005

0

005

01

(e)

0 10 20 30

80

60

40

20

0ndash005

0

005

01

015

(f )







10 20 30 40 50 60 70 80

0

0

0

2000

2000

B-25-1

A-25-2

Y-0

2θ (deg)

KI

P Q

2000

Diff

ract

ion

inte

nsity

(CPS

)

Diff

ract

ion

inte

nsity

(CPS

)

lowast

lowast


lowast


000 001 002 003 004 005

5

10

15

20

Point 4 072



Strain


Point 1 016

Stre

ss (M

Pa)

(a) (b)

0 10 20 30

80

60

40

20

0

0

1

ndash1

times10ndash4

(c)

0 10 20 30

80

60

40

20

0

ndash2

ndash4

ndash6

0

2

4

6

8times10ndash3

(d)

0 10 20 30

80

60

40

20

0

ndash001

ndash002

ndash003

ndash004

ndash005

0

(e)

0 10 20 30

80

60

40

20

0 ndash015

ndash01

ndash005

0

005

(f )







Sa 1

MN1113944

Mminus1

k01113944

Nminus1


11138681113868111386811138681113868111386811138681113868 (5)





(a) (b) (c) (d) (e) (f )


(a) (b) (c) (d) (e) (f )














0 437 521 552 503 484 552 499 5125 547 534 539 540 547 743 599 63010 557 584 548 563 636 615 668 64015 596 584 568 583 701 644 821 72220 584 583 619 595 747 1062 667 82525 580 621 626 609 936 753 878 856






Quartz

Clay mineral

Feldspar

Microcrack


Damage point

(a)

(c) (d)

(b)









5 Conclusion





(a) (b) (c)





Data Availability




Acknowledgments


References


































001 002 003 004 0050

5

10

15

20

25

30

0-15-110-1

15-320-125-2

Strain

Stre

ss (M

Pa)

(a)

0-15-110-2

15-320-125-1

001 002 003 004 0050

10

20

30

40

Strain

Stre

ss (M

Pa)

(b)








5 10 15 20 250

5

10

15

20

25

30

35


Group AGroup B

Peak

stre

ngth

(MPa

)

(a)

Group AGroup B

0 5 10 15 20 25400

800

1200

1600


Elas

tic m

odul

us (M

Pa)

(b)




+ H2O 2K++ 4SiO2 + Al2 Si2O5( 1113857(OH)4

(3)



+ Na2SO4 + 4H4SiO4

(4)



000 001 002 003

5

10

15

20

25

Point 4 075

Point 3 091

Point 2 065

Strain


Stre

ss (M

Pa)


(a) (b)

0 10 20 30

80

60

40

20

0

ndash6

ndash4

ndash2

0

2

4

6times10ndash4

(c)

0 10 20 30

80

60

40

20

0

ndash002

ndash006

ndash004

0

002

004

(d)

0 10 20 30

80

60

40

20

0

ndash005

0

005

01

(e)

0 10 20 30

80

60

40

20

0ndash005

0

005

01

015

(f )







10 20 30 40 50 60 70 80

0

0

0

2000

2000

B-25-1

A-25-2

Y-0

2θ (deg)

KI

P Q

2000

Diff

ract

ion

inte

nsity

(CPS

)

Diff

ract

ion

inte

nsity

(CPS

)

lowast

lowast


lowast


000 001 002 003 004 005

5

10

15

20

Point 4 072



Strain


Point 1 016

Stre

ss (M

Pa)

(a) (b)

0 10 20 30

80

60

40

20

0

0

1

ndash1

times10ndash4

(c)

0 10 20 30

80

60

40

20

0

ndash2

ndash4

ndash6

0

2

4

6

8times10ndash3

(d)

0 10 20 30

80

60

40

20

0

ndash001

ndash002

ndash003

ndash004

ndash005

0

(e)

0 10 20 30

80

60

40

20

0 ndash015

ndash01

ndash005

0

005

(f )







Sa 1

MN1113944

Mminus1

k01113944

Nminus1


11138681113868111386811138681113868111386811138681113868 (5)





(a) (b) (c) (d) (e) (f )


(a) (b) (c) (d) (e) (f )














0 437 521 552 503 484 552 499 5125 547 534 539 540 547 743 599 63010 557 584 548 563 636 615 668 64015 596 584 568 583 701 644 821 72220 584 583 619 595 747 1062 667 82525 580 621 626 609 936 753 878 856






Quartz

Clay mineral

Feldspar

Microcrack


Damage point

(a)

(c) (d)

(b)









5 Conclusion





(a) (b) (c)





Data Availability




Acknowledgments


References


































5 10 15 20 250

5

10

15

20

25

30

35


Group AGroup B

Peak

stre

ngth

(MPa

)

(a)

Group AGroup B

0 5 10 15 20 25400

800

1200

1600


Elas

tic m

odul

us (M

Pa)

(b)




+ H2O 2K++ 4SiO2 + Al2 Si2O5( 1113857(OH)4

(3)



+ Na2SO4 + 4H4SiO4

(4)



000 001 002 003

5

10

15

20

25

Point 4 075

Point 3 091

Point 2 065

Strain


Stre

ss (M

Pa)


(a) (b)

0 10 20 30

80

60

40

20

0

ndash6

ndash4

ndash2

0

2

4

6times10ndash4

(c)

0 10 20 30

80

60

40

20

0

ndash002

ndash006

ndash004

0

002

004

(d)

0 10 20 30

80

60

40

20

0

ndash005

0

005

01

(e)

0 10 20 30

80

60

40

20

0ndash005

0

005

01

015

(f )







10 20 30 40 50 60 70 80

0

0

0

2000

2000

B-25-1

A-25-2

Y-0

2θ (deg)

KI

P Q

2000

Diff

ract

ion

inte

nsity

(CPS

)

Diff

ract

ion

inte

nsity

(CPS

)

lowast

lowast


lowast


000 001 002 003 004 005

5

10

15

20

Point 4 072



Strain


Point 1 016

Stre

ss (M

Pa)

(a) (b)

0 10 20 30

80

60

40

20

0

0

1

ndash1

times10ndash4

(c)

0 10 20 30

80

60

40

20

0

ndash2

ndash4

ndash6

0

2

4

6

8times10ndash3

(d)

0 10 20 30

80

60

40

20

0

ndash001

ndash002

ndash003

ndash004

ndash005

0

(e)

0 10 20 30

80

60

40

20

0 ndash015

ndash01

ndash005

0

005

(f )







Sa 1

MN1113944

Mminus1

k01113944

Nminus1


11138681113868111386811138681113868111386811138681113868 (5)





(a) (b) (c) (d) (e) (f )


(a) (b) (c) (d) (e) (f )














0 437 521 552 503 484 552 499 5125 547 534 539 540 547 743 599 63010 557 584 548 563 636 615 668 64015 596 584 568 583 701 644 821 72220 584 583 619 595 747 1062 667 82525 580 621 626 609 936 753 878 856






Quartz

Clay mineral

Feldspar

Microcrack


Damage point

(a)

(c) (d)

(b)









5 Conclusion





(a) (b) (c)





Data Availability




Acknowledgments


References






























+ H2O 2K++ 4SiO2 + Al2 Si2O5( 1113857(OH)4

(3)



+ Na2SO4 + 4H4SiO4

(4)



000 001 002 003

5

10

15

20

25

Point 4 075

Point 3 091

Point 2 065

Strain


Stre

ss (M

Pa)


(a) (b)

0 10 20 30

80

60

40

20

0

ndash6

ndash4

ndash2

0

2

4

6times10ndash4

(c)

0 10 20 30

80

60

40

20

0

ndash002

ndash006

ndash004

0

002

004

(d)

0 10 20 30

80

60

40

20

0

ndash005

0

005

01

(e)

0 10 20 30

80

60

40

20

0ndash005

0

005

01

015

(f )







10 20 30 40 50 60 70 80

0

0

0

2000

2000

B-25-1

A-25-2

Y-0

2θ (deg)

KI

P Q

2000

Diff

ract

ion

inte

nsity

(CPS

)

Diff

ract

ion

inte

nsity

(CPS

)

lowast

lowast


lowast


000 001 002 003 004 005

5

10

15

20

Point 4 072



Strain


Point 1 016

Stre

ss (M

Pa)

(a) (b)

0 10 20 30

80

60

40

20

0

0

1

ndash1

times10ndash4

(c)

0 10 20 30

80

60

40

20

0

ndash2

ndash4

ndash6

0

2

4

6

8times10ndash3

(d)

0 10 20 30

80

60

40

20

0

ndash001

ndash002

ndash003

ndash004

ndash005

0

(e)

0 10 20 30

80

60

40

20

0 ndash015

ndash01

ndash005

0

005

(f )







Sa 1

MN1113944

Mminus1

k01113944

Nminus1


11138681113868111386811138681113868111386811138681113868 (5)





(a) (b) (c) (d) (e) (f )


(a) (b) (c) (d) (e) (f )














0 437 521 552 503 484 552 499 5125 547 534 539 540 547 743 599 63010 557 584 548 563 636 615 668 64015 596 584 568 583 701 644 821 72220 584 583 619 595 747 1062 667 82525 580 621 626 609 936 753 878 856






Quartz

Clay mineral

Feldspar

Microcrack


Damage point

(a)

(c) (d)

(b)









5 Conclusion





(a) (b) (c)





Data Availability




Acknowledgments


References

































10 20 30 40 50 60 70 80

0

0

0

2000

2000

B-25-1

A-25-2

Y-0

2θ (deg)

KI

P Q

2000

Diff

ract

ion

inte

nsity

(CPS

)

Diff

ract

ion

inte

nsity

(CPS

)

lowast

lowast


lowast


000 001 002 003 004 005

5

10

15

20

Point 4 072



Strain


Point 1 016

Stre

ss (M

Pa)

(a) (b)

0 10 20 30

80

60

40

20

0

0

1

ndash1

times10ndash4

(c)

0 10 20 30

80

60

40

20

0

ndash2

ndash4

ndash6

0

2

4

6

8times10ndash3

(d)

0 10 20 30

80

60

40

20

0

ndash001

ndash002

ndash003

ndash004

ndash005

0

(e)

0 10 20 30

80

60

40

20

0 ndash015

ndash01

ndash005

0

005

(f )







Sa 1

MN1113944

Mminus1

k01113944

Nminus1


11138681113868111386811138681113868111386811138681113868 (5)





(a) (b) (c) (d) (e) (f )


(a) (b) (c) (d) (e) (f )














0 437 521 552 503 484 552 499 5125 547 534 539 540 547 743 599 63010 557 584 548 563 636 615 668 64015 596 584 568 583 701 644 821 72220 584 583 619 595 747 1062 667 82525 580 621 626 609 936 753 878 856






Quartz

Clay mineral

Feldspar

Microcrack


Damage point

(a)

(c) (d)

(b)









5 Conclusion





(a) (b) (c)





Data Availability




Acknowledgments


References

































Sa 1

MN1113944

Mminus1

k01113944

Nminus1


11138681113868111386811138681113868111386811138681113868 (5)





(a) (b) (c) (d) (e) (f )


(a) (b) (c) (d) (e) (f )














0 437 521 552 503 484 552 499 5125 547 534 539 540 547 743 599 63010 557 584 548 563 636 615 668 64015 596 584 568 583 701 644 821 72220 584 583 619 595 747 1062 667 82525 580 621 626 609 936 753 878 856






Quartz

Clay mineral

Feldspar

Microcrack


Damage point

(a)

(c) (d)

(b)









5 Conclusion





(a) (b) (c)





Data Availability




Acknowledgments


References








































0 437 521 552 503 484 552 499 5125 547 534 539 540 547 743 599 63010 557 584 548 563 636 615 668 64015 596 584 568 583 701 644 821 72220 584 583 619 595 747 1062 667 82525 580 621 626 609 936 753 878 856






Quartz

Clay mineral

Feldspar

Microcrack


Damage point

(a)

(c) (d)

(b)









5 Conclusion





(a) (b) (c)





Data Availability




Acknowledgments


References

































Quartz

Clay mineral

Feldspar

Microcrack


Damage point

(a)

(c) (d)

(b)









5 Conclusion





(a) (b) (c)





Data Availability




Acknowledgments


References



































5 Conclusion





(a) (b) (c)





Data Availability




Acknowledgments


References






























Data Availability




Acknowledgments


References





























MechanicalPropertiesofWeatheredFeldsparSandstoneafter...

Documents

Transcript of MechanicalPropertiesofWeatheredFeldsparSandstoneafter...