experimentalstudyoftheporestructuredeteriorationof...

Research ArticleExperimental Study of the Pore Structure Deterioration ofSandstones under Freeze-Thaw Cycles and Chemical Erosion

Jielin Li 123 Rennie B Kaunda2 Longyin Zhu13 Keping Zhou13 and Feng Gao13

1School of Resources and Safety Engineering Central South University Changsha Hunan 410083 China2Department of Mining Engineering Colorado School of Mines 1600 Illinois Street Golden Colorado 80401 USA3Research Center for Mining Engineering and Technology in Cold Regions Central South University Changsha 410083 China

Correspondence should be addressed to Jielin Li lijielin163com

Received 4 August 2018 Revised 23 October 2018 Accepted 16 December 2018 Published 16 January 2019

Academic Editor Yinshan Tang

Copyright copy 2019 Jielin Li et alis is an open access article distributed under the Creative Commons Attribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

e issue of rock deterioration in chemical environments has drawn much attention in recent years in the rock engineeringcommunity In this study a series of 30 freeze-thaw cycling tests are conducted on sandstone samples soaked in H2SO4 solution andin pure water prior to the application of nuclear magnetic resonance (NMR) on the rock specimens e porosity of the sandstonethe distribution of transverse relaxation time T2 and the NMR images are acquired after each freeze-thaw cycle e pore sizedistribution curves of the sandstone after freeze-thaw cycles four categories of pore scale and the features of freeze-thaw de-terioration for pores of different sizes in H2SO4 solution and pure water are established e result shows that with the influence ofthe acid environment and the freeze-thaw cycles the mass of the samples largely deteriorates As the freeze-thaw cycles increase theporosity of rocks increases approximately linearlye distribution of the NMR T2 develops gradually from 4 peaks to 5 or even to 6Magnetic resonance imaging (MRI) dynamically displays the process of the freeze-thaw deterioration of themicrostructure inside thesandstones under acid conditions e results also show pore expansion in rocks under the coupling effects of chemistry and thefreeze-thaw cycles which differ largely from the freeze-thaw deterioration of the rock specimens placed in pure water

1 Introduction

e issue of rock deterioration in chemical environmentshas drawn much attention in recent years in the rock en-gineering community due to hazards and risks posed toengineered structures Corrosion due to hydrochemicalsolutions can cause changes in mineralogical compositionand structure of rocks leading to the transformation of thephysical mechanical properties of rocks erefore thehydrochemically altered state of rock can pose a great threatto the long-term stability of rock engineering structures[1 2] e chemical elements in solution can drive theexpansion of cracks and the rate of the crack expansion Inaddition the stress strength factor and the stress strengthcoefficient of quartz materials are influenced by deionizedwater HCl NaOH and other acids and bases [3]

e chemical atmospheres may cause damage to all typesof stones especially calcite stones and the effect of acid

atmospheres is related with porosity [4] In the chemicalenvironment the mineral components in rocks tend to reactwith solutions via complex processes and mechanismsPrevious studies have been carried out to investigate thecharacteristics of chemical deterioration of rocks for in-stance Feucht and Logan [5] evaluated the effect of chemicalsolutions (NaCl CaCl2 and Na2SO4 solutions) on thefrictional properties of quartz-rich sandstones with triaxialcompression tests which were made with varying ionicstrengths and pH values Feng et al [6ndash8] conducted a goodnumber of laboratory experiments and theoretical analysessome advanced instruments were used to study the mi-crostructural damage of rocks in the chemical environmentsuch as CT SEM and X-ray analysis and the research ideasfor studying the fracture criteria of fractured rock consid-ering the effect of chemical solution were provided Otherscholars also conducted investigations on the rock damageconstitutive model under the effect of chemical corrosion

HindawiAdvances in Civil EngineeringVolume 2019 Article ID 9687843 12 pageshttpsdoiorg10115520199687843

[9ndash11] e results from these previous achievements haveprovided references for studies of the long-term stability ofrock engineering in chemical environments

As the research continues to advance the issues of rockdeterioration under the multifactor coupling conditions ofpressure chemical and other factors have drawn in-creasingly more attention such as the rock creep behaviourin a chemical environment [12] the damage of phys-icomechanical parameters of rocks under the couplingeffects of chemical environment and stress loading [13 14]and the mechanical properties of triaxial compression ofrocks immersed in different water chemical solutions [15]However besides the influence of the complex hydro-chemical environment on rock there is an essential need tostudy the damaging effect of the freeze-thaw cycles in coldregions on a rock mass [16] In mines located in cold re-gions for example the freeze-thaw disasters of the rockmass in mines can occur concurrently with the corrosion ofthe acid waste water acid rain or the deicing saline so-lution used at the mines whose influences have beenknown to interact in certain cases [17] Some research hasbeen performed on the deterioration of the rock mechanicsunder the decoupling influence of chemistry and the freeze-thaw Ning et al [18] conducted the splitting tests of theconcrete under the coupling effect of the acid corrosion andthe freeze-thaw cycles studied the features of the surfaceerosion and the mechanical properties of the concretes thatare of different pH values and being processed by differentnumbers of freeze-thaw cycles and analyzed the splittingprocess of the concrete corroded by acid and the freeze-thaw ey found that the acid erosion of concrete is in-versely proportional to the pH value and the erosionbegins on the surface of the concrete e coupling effectsof acid erosion and freeze-thaw cycles accelerate the de-terioration of mechanical properties of concrete In theweak acid environment freeze-thaw cycles play a leadingrole in concrete erosion As the pH value decreases theeffect of acid on concrete gradually increases Shi et al [19]studied the changes of different chemical diluents in theconcrete of Portland in the freeze-thaw environment andadopted SEM to study the mechanism of formation of poresand cracks in the test specimens and the results show thatNaCl the NaCl-based deicer and the K-acetate-baseddeicer were the most deleterious to the concrete Luet al [20] carried out the indoor simulation tests of con-cretes under the conditions of the dual corrosion of acid-base and freeze-thaw and he found that both strong acidand alkali are corrosive to concrete e corrosion of acidalkali and freeze-thaw cycle dominates at different timesaccelerating the deterioration of mechanical propertiesconcrete Gao et al [21] conducted a freeze-thaw cycleexperiment on rock samples which were soaked in fourdifferent solutions sulfuric acid solution sodium hy-droxide solution sodium chloride solution and pure waterand the microstructural changes of each group of rocksamples were tested by nuclear magnetic resonance (NMR)e results have shown that the influences of sodiumhydroxide and sodium chloride solutions are the mostsignificant and the influence of sulfuric acid solution is

relatively weak In the meantime NMR results show thechemical solutions have great effects on the microstructureof rocks

In the previous studies the research objectives aremainly aimed at the physical and mechanical properties ofbuildings in cold regions under chemical conditionserefore the reported previous studies tend to take con-crete as the research objective when studying the mechanicalproperties of the rocks under the influence of chemistry andfreeze-thaw Given that the focus is on macroscopic fracturefeatures very few of the studies have evaluated mechanismsrelated to the structural deterioration of pores therefore theresults are somewhat limited in terms of mechanisms andcharacteristics of the deterioration of the rock mass In thisstudy with the impact of acid waste water at mines as theengineering background rock is selected as the researchobject e study discusses freeze-thaw cycling tests ofsandstone in the acid environment the acquisition of themass of the rock specimens and observed changes such asthe exterior alteration It also analyzes and discusses thecharacteristics of the freeze-thaw deterioration of the mi-crostructure of the rocks in the acid environment withnuclear magnetic resonance technique

2 Materials and Methods

21 Materials e rock specimens consisted of fleshy redsandstone with a dense-and-fine fragment texture especimens were prepared from natural and fresh rockswhich had formed at a comparatively deeper level aniso-tropic and without any traces of cracks developed on thejoints According to the results of the X-ray diffraction testthe red sandstone is mainly composed of quartz albiteaerinite sanidine microcline laumontite and chabazitee bulk density of rock was 242 gcm3 e water ab-sorption test showed that the percent absorption of the rockspecimens was 165 the water saturation ratio was 174and the water saturation coefficient was 095 e rocks wereprepared as specimens of standard cylinders 50plusmn 1 mm indiameter by 30plusmn 1 mm tall according to ldquoe Codes of RockTests in Water Conservancy and Hydroelectrical Projects(SL 264-2001)rdquo standards

22 Experimental Setup and Test Procedures e rockspecimens were numbered C1ndashC9 and F1ndashF9 respectivelyto match with the H2SO4 solution group and the pure watergroup First prepare a H2SO4 solution with initial pH 15(the mass concentration of sulfuric acid is 15 gL) accordingto the lowest pH value in the mine waste water where thesampling site is located en the rock specimens wereseparately immersed in the H2SO4 solution and pure waterfor 48 hours to reach a state of natural saturation evolume of the sulfuric acid solution and pure water is basedon the thoroughly immersed specimens It ranges from 2 Lto 3 L Next the rock specimens were placed in a TDS-300freeze-thaw testingmachine for the freeze-thaw cycling testsAccording to the requirements of the freeze-thaw test theparameters of the freeze-thaw were the freezing temperature

2 Advances in Civil Engineering

was minus20degC the thawing temperature was 20degC and both thetime for freezing and the time for thawing were 4 hoursere were 30 freeze-thaw cycles to undergo and the rockspecimens were numbered 1ndash3 4ndash6 and 7ndash9 correspondingwith 0 10 20 and 30 freeze-thaw cycles respectively At theend of every 10 freeze-thaw cycles the rock specimens wereextracted to conduct the NMR tests using an AniMR-150MRI analyzing system (Suzhou Niumag Electronic Tech-nology Co Ltd) As shown in Figure 1 in the NMR porositytest the rock specimens that have completed the freeze-thawcycle test are taken out from pure water or H2SO4 solutionand the surface moisture (or solution) is wiped with a towelwrapped with a plastic wrap (to prevent evaporation ofwater) and then placed in the MRI analyzing system

e AniMR-150 MRI analysis system is mainly com-posed of the spectrometer system RF unit magnet cabinetindustrial personal computer and inversion software edevice is developed on the basis of a 1H relaxation responsee main magnetic field of the MRI system is03plusmn 005 Tesla the diameter of the probe coil is 150mm themain frequency of instrument is 128MHz the gain of thereceiver is greater than 40 dB and the maximum samplingbandwidth is greater than 300 kHz the RF power is 300Wand the maximum resolution of MRI is 100 μme numberof sampling peaks can reach 18000 the echo time is less than150ms and the sample relaxation time is measured from80 μs to 14 s [22]

In the NMR test the transverse relaxation time (T2) wasretrieved by using the NMR rock-core analyzing software(Version 110) [23] which could obtain the intensity ofnuclear magnetic signals and T2 spectra and composite themas the transverse relaxation time of the rock specimenDuring the test one specimen was placed at the center of theradio frequency (RF) coil for CPMG pulse sequence ex-periments e experimental parameters were as followsreceiver bandwidth SW 200 kHz frequency main valueSF 12MHz center frequency O1 53173099Hz samplingpoints TD 331208 waiting time Tw 3000ms number ofecho cycles NECH 6000 TE 0276ms coil waiting timeRFD 006ms analog gain RG1 20 db digital gainRG2 4 cumulative sampling NS 32

After the test the decay curve between echo signal andsampling time can be obtained by the AniMR-150 MRIanalysis system (Figure 2(a)) and the relationship betweenporosity increment and T2 relaxation time distribution(Figure 2(b)) can be derived from the decay curve by in-version methods e shaded area between the curve andhorizontal axis is termed as the spectra area and measuredporosity A final porosity of 36 can be obtained from theaccumulated porosity curve

3 Macroscopic Observation and Pore StructureAlteration Based on Quantification ofWater Imbibition

e appearance of the rock specimens soaked in H2SO4 andpure water after the freeze-thaw tests is as shown in Figures 3and 4 respectively A comparison of the appearances of thefrozen rock specimens shows that after 30 freeze-thaw

cycles the surface of the sandstone specimens which wereplaced in the acid environment was seriously eroded and theparticles on the surface peeled off in large quantities Incontrast the surface of the sandstone specimens placed inpure water did not show significant changes

In the following experiment after every round of freeze-thaw cycles (the number is predetermined) the rockspecimens were taken out and wiped dry and then a masstest was conducted erefore the change in the mass of therock specimens is also a useful indicator of deterioratione result of the mass of the rock specimens which changedwith the number of freeze-thaw cycles in the acid envi-ronment is shown in Figure 5 It is clear from Figure 5 thatafter 10 freeze-thaw cycles the average mass of the rockspecimens of the H2SO4 solution group and the pure watergroup increases by 020 and 016 respectively e ob-served changes in the average mass indicate that the 10freeze-thaw cycles had led to the expansion of minute cracksin the sandstones to various degrees and that water hadentered the pores which caused the increase of the mass ofrock

After 20 freeze-thaw cycles the mass of the specimensbegins to show a decrease at various degrees emass of thespecimens of the H2SO4 solution group and the pure watergroup shows a drop of 063 and 016 respectively Byobserving the appearance of the specimens one can find freeparticles in the solution erefore the 20 freeze-thaw cyclescause the surface of the specimens to undergo macroscopicfracture resulting in the peeling off of the particles from therock surface and the mass of those particles is apparentlylarger than that of the increase of the pore water In otherwords at the midstage of the freeze-thaw deterioration theacid environment will influence the freeze-thaw de-terioration of the rocks at a comparatively larger scale

After 30 freeze-thaw cycles the mass of the rock spec-imens in pure water almost remains nearly unchangedhowever the surface quality of the rock specimens placed inthe H2SO4 solution continues to worsen e implication isthat under the acid conditions the particles peeled off fromthe surface of the rock specimens at a higher rate and thenumber of free particles in the solution had increased sig-nificantly ere is a large number of solid sediments in thesolution leading to the deterioration of the overall qualityand integrity of the rock specimens

4 Pore Structure Alterations Characterized byNMR Response

41Porosity An assessment of porosity could directly reflectthe condition of deterioration within the rock specimense AniMR-150 MRI analyzing system was used to measurethe porosity of the sandstone specimens after every 10freeze-thaw cycles and the results are as shown in Table 1

Table 1 shows that with the addition of the freeze-thawcycles the porosity of the sandstones generally increases butthe scale of increase of the porosity of the sandstones inH2SO4 solution is relatively larger than that of the specimensplaced in pure water It is thus clear that for the samenumber of freeze-thaw cycles the minerals (such as quartz

Advances in Civil Engineering 3

albite and microcline) in the sandstones had reacted withH2SO4 solution chemically erefore the mineral elementsof the rocks changed and the links between particles wereweakened which led to the increase in porosityis result isin agreement with the changes in the mass and surfaceappearances of the specimens discussed in Section 3 whichshows that the interior and exterior deterioration of rock

occurred under the coupling effect of chemistry and thefreeze-thaw

e mean values of the porosity of every group of rockspecimens were analyzed and are shown in Table 1 It can beseen that under the same conditions of freeze-thaw cyclingH2SO4 solution apparently accelerated the deterioratingprocess within the rocks especially after 10 freeze-thaw

10000

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00 200 400 600 800

Echo time (ms)

Am

plitu

de o

f spi

n ec

ho

1000 1200 1400 1600 1800

(a)

020

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000001 01 1 10

Porosity = 36

Spectrum area

100 100000

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Acc

umul

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osity

()

Poro

sity

com

pone

nt (

)25

30

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40

T2 relaxation time (ms)

Porosity componentAccumulative porosity

(b)

Figure 2 Results of NMR analysis (a) echo signal decay curve (b) T2 relaxation time distribution curve

Slightly eroded

(a)

Having peeled off

(b)

Seriously eroded

(c)

Figure 3 Specimens macroscopic observation after different numbers of freeze-thaw cycles in H2SO4 solution (a) 10 cycles (b) 20 cycles(c) 30 cycles

NMR system

Magnetcabinet

Spectrometersystem

DisplayRF coil

Rock specimensH2SO4 solution

Pure water

Freeze-thaw device

Figure 1 Sequence showing experimental setup and test procedure requiring rock specimen preparation the TDS-300 freeze-thaw testingmachine and the AniMR-150 MRI analyzing system


cycles While the porosity of sandstones in pure waterchanged little the mass change is also small However theporosity of sandstones in H2SO4 solution increased linearlywith the increased number of the freeze-thaw cycles After 30freeze-thaw cycles the porosity increased by 395 in H2SO4solution and only by 212 in pure water Under the in-fluence of freeze-thaw cycles the pores inside the rock inpure water continue to develop and expand and the externalmoisture enters the newly created or expanded poresresulting in changes in mass and porosity In H2SO4 solu-tion freeze-thaw also leads to changes in pores of rock

samples e observed discrepancies in increased porosityindicate that H2SO4 solution had entered the newly pro-duced pores of rock and had undergone additional chemicalreactions incessantly with some of the activated minerals inthe rocks erefore the particles within the rocks corrodedcontinuously and the mineral elements of the rockschanged e solutes were drifted out of the rock in water toproduce sediments and then resulted in the decrease of massof the rock specimens (Figure 5) However the separation ofsolutes inside the rocks resulted in the formation of cavitieskarst voids and cracks of corrosion us the acid envi-ronment could produce a significant influence on the freeze-thaw deterioration of rock

42 T2 Spectral Distribution of NMR Previous studies[24 25] have shown that the T2 spectral distribution reflectsthe size and distribution of the pores of rock specimense size of pore is related to the position of the spectralpeak in particular the group of the small size of porescorresponds to smaller T2 values while the group of largesize of pores corresponds to larger T2 values Figure 6shows the distribution curves of NMR transverse relaxationtime T2 of the sandstone rock specimens after differentnumbers of freeze-thaw cycles in H2SO4 solution and inpure water It can be seen that there were mainly four T2spectral peaks for the sandstones With the increase of thenumber of freeze-thaw cycles and under the influence offreeze-thaw and the acid solution new pores have de-veloped within the rock and tiny pores have graduallyexpanded into large-sized pores And the number of peaksincreased from 4 to 5 or even to 6 It can be seen fromFigure 6(b) that after 30 freeze-thaw cycles the pores in therock expand and the large-sized pores increase under theaction of freeze-thaw cycles e water enters the newlycreated large-sized pores and caused the large pores toldquocollapserdquo causing the large-sized pores to be packed andtheir sizes to be changed us 30 freeze-thaw cyclesamples have shorter T2 values than after 20 cycles

Table 2 shows the peak areas of the NMR T2 spectra ofspecimens under different conditions It can be seen fromFigure 6 and Table 2 that the individual T2 spectral distri-bution of the sandstones in H2SO4 solution and in purewater differed largely After 30 freeze-thaw cycles the total

145

144

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141

1400 10 20

Number of freeze-thaw cycles (times)

Mas

s (g)

30

2

1

Figure 5 Curve of the changes of the mass of the rock specimensTwo different kinds of solution are labelled by ① H2SO4 solutionand ② pure water

Table 1 Result of the measurement of the porosity of the sand-stones (porosity ())

H2SO4 solution Pure water

SpecimensFreeze-thaw cycles


0 10 20 30 0 10 20 30C7 36 41 45 50 F7 35 40 39 42C8 40 46 50 54 F8 33 38 37 39C9 39 43 50 56 F9 32 36 36 38Average 38 43 48 53 Average 33 38 37 40

(a) (b) (c)

Figure 4 Specimens macroscopic observation after different numbers of freeze-thaw cycles in pure water (a) 10 cycles (b) 20 cycles (c) 30cycles


spectral area of the rock specimen C7 (in H2SO4 solution)increased by 356 and the number of peaks increased from4 to 6 In the meantime the total spectral area of the rockspecimen F7 (in pure water) increased by 21 and thenumber of peaks increased from 4 to 5

In addition the trend of each spectra peak is also dif-ferent e proportion of the 4th 5th and 6th spectra peaks inH2SO4 solution is gradually increasing that is the increaseof large-sized pores is obvious especially the 4th spectrapeak which increases by 28 times However in H2O so-lution it mainly shows that the proportion of the first spectrapeak has decreased and the proportion of the 3rd and 5thspectra peaks has increased Given that during the freezingand thawing processes the moisture within the poresfreezes and the bulk volume expands as a result [26 27]us the development and expansion of the pores areaccelerated to introduce chemical solution into the newpores e entry of chemical solution into the new poreswould be expected to corrode and lubricate the particleswithin the rock material erefore the cohesion betweenthe mineral particles decreased the pores grew larger andthe frictional force was reduced Under the repeated in-fluence of freezing and thawing the chemical solution in thepores would be expected to incessantly corrode the mineralsin the rock and to destroy the friction and the mineral

elements between the mineral particles Furthermore thepressure created by the volume expansion after the freezingof moisture would easily reach the extreme tensile strengthof the walls of the pores ese changes would lead to a rapidexpansion of the tiny pores and cause the larger pores tocollapse which leads to a macroscopic fracturing of thespecimens is chain of events ultimately leads to a mac-roscopic fracturing which also explains why the generalporosity of rocks increases seemingly linearly

Table 2 shows that under the coupling effects of freeze-thaw cycles and chemical conditions the changing trend ofdifferent size pores in rock which has been immersed in purewater and H2SO4 solution is different It also shows thatafter the different number of freeze-thaw cycles the pro-portion of the second spectrum peak in pure water is sig-nificantly higher than the proportion of the second spectrumpeak in H2SO4 erefore the porosity of the component ofT2 spectrum in pure water is higher than that in H2SO4 butthe total spectrum area is still large in H2SO4 solution

43 MRI Results Figure 7 displays the magnetic resonanceimaging (MRI) of the rock specimens after 0 10 20 and 30freeze-thaw cycles in the H2SO4 solution e maximumresolution of the MRI system used in the experiment was

000001 01

0 F-T cycles10 F-T cycles


1 10 100 1000 10000T2 (ms)

002

004

006

008

010

012

014

016

0181st spectra peak

2nd spectra peak

3rd spectra peak

4th spectra peak

5th spectra peak

Poro

sity

com

pone

nt (

)

(a)



001 01 1 10T2 (ms)

100 1000 10000

1st spectra peak

2nd spectra peak

3rd spectra peak

4th spectra peak

5th spectra peak

Poro

sity

com

pone

nt (

)

000

002

004

006

008

010

012

014

016

018

(b)

Figure 6 T2 distribution of sandstones after different numbers of freeze-thaw cycles (a) H2SO4 solution (b) pure water

Table 2 Statistics of the proportion of each peak area in the T2 curve

Solution SpecimenProportion of each peak area (vol)

Total peak area1st 2nd 3rd 4th 5th 6th

H2SO4

C7-0 4837 2827 1700 636 0 0 12467C7-10 5462 1999 2146 394 0 0 14417C7-20 4012 2809 2052 989 138 0 14378C7-30 4325 1811 1493 1807 484 080 16903

Pure water

F7-0 5176 3324 1089 410 0 0 11614F7-10 3250 4000 2246 504 0 0 13111F7-20 4287 2881 2094 582 156 0 12835F7-30 4151 2973 2044 636 195 0 14058


100 μm and the image was automatically generated by theNMR test system e illuminated areas in the image werethe places where the moisture was present and the darkareas represent the background color e brightness of theimage shows the quantity of water content ie the lighterthe image the greater the amount of moisture present in thatarea and the larger the pore size in that area At freeze-thawcycle at time 0 the light dots in the MRI are well-distributedwhich indicates that the interior of the sandstone specimenswas perfectly isotropic After 10 freeze-thaw cycles thenumber of light dots increases which indicates that thenumber of pores in the rocks had increased ere is a circleof light dots around the contour of the sandstones which hadbeen placed in H2SO4 solution which shows that with thedual effect of acid corrosion and the freezing and thawingsmall cracks on the outer layer of the rock specimens hadkept expanding while the rock specimens in pure water hadnot shown similar changes (Figure 8(b))

After 20 freeze-thaw cycles the number of light dotscontinue to increase in the MRI of the sandstones in H2SO4

solution covering almost the entire section e size of poresof the rock specimens continues to grow and the number oflarge-sized pores continues to grow also while the poreswithin the rock specimens in pure water did not displaysimilar changes After 30 freeze-thaw cycles the number andsize of the light dots in the MRI of the sandstones in H2SO4solution has clearly increased ere is a large quantity ofpores on the surface of the rock specimens and they aresurrounded by the pore water e NMR signals within therock specimens are very strong and the areas of light dotsare close to connecting with each other e observed trendshows that the acid solution had affected the interiorstructure of the sandstone which had led to the unusualdevelopment of the cracks within the rocks and the mac-roscopic fracture of the appearances of the rock specimens

In contrast as shown in Figure 8 the pores inside therock specimens in pure water do not display significantdevelopment and progression although the results still showthe process of the development of pores from the exterior tothe interior of the rock specimens under freeze-thaw effects

(a)

1

1

2 2

(b)

1

1

22

(c)

1

2

2

2

(d)

Figure 7 Images of sandstones of the H2SO4 solution group after different numbers of freeze-thaw cycles (a) 0 (b) 10 (c) 20 (d) 30 Twodifferent kinds of pore deformation are approximately labelled by① which indicates new pores are generated and② which indicates poresare deformed to larger size


After 30 freeze-thaw cycles there are some light dots nearlyin contact inside and outside the specimens however thedeterioration remains weak In addition close inspectionshows that there were relatively few macroscopic cracksformed in the surface appearance of the rock specimens Insummary the chemical solution had reacted with andcorroded the mineral structures in the acidic solution whichcaused the inner and outer shapes of rocks and the sizes ofparticles pores and cracks to transform e chemicaletching had largely influenced the development and ex-pansion of the cracks within the sandstone

5 Discussion

51e Effects of Freeze-aw on the Evolution of Rock Porese freezing and thawing cycles of the sandstone specimensin both acidic and nonacidic environments affected the sizenumber and distribution of pores within the entire rock

material as discussed in Section 4 Consequently freeze-thaw cycles in such environments have important impli-cations related to the permeability of the sandstones and tothe mechanical behaviour of the sandstone According to theNMR principle the NMR crosswise relaxation rate 1T2 isgiven as follows [28 29]

1T2

ρ2S

V1113874 1113875

porosity (1)

where S is the surface area of a pore (cm2) V is the porevolume (cm3) and ρ2 is the crosswise surface relaxationstrength (μmms)

If the pore radius is positively related to the throat radiusequation (1) becomes [30 31]

1T2

ρ2rc

Fs (2)

(a)

1

1

2

2

(b)

1

2

2

2

(c)

1

1

1

2

(d)

Figure 8 Images of sandstones of the pure water group after different numbers of freeze-thaw cycles (a) 0 (b) 10 (c) 20 (d) 30 Twodifferent kinds of pore deformation are approximately labelled by① which indicates new pores are generated and② which indicates poresare deformed to larger size


where rc is the pore radius and Fs is a geometrical factor (forthe spherical pores Fs 3 and for the columnar poresFs 2)

rc CT2 (3)

where C Fsρ2 and C is called the conversion coefficientIt can be concluded from equations (1)ndash(3) that the pore

radius is in direct proportion to T2 the smaller the T2 is thesmaller the represented pore becomes and the larger thepore the larger the T2 becomes

With the scaling and error analysis of the transverserelaxation time T2 and pore throat radius the best scalerange of the C value of the red sandstone is between 03 and05 μmms and the average value is 03125 μmms [32]erefore equation (4) can be achieved by simplifyingequation (3) as follows

rc 03125T2 (4)

According to equation (4) T2 spectra can be transformedinto the pore size distribution curve (Figure 9) ere hasbeen no agreed standard about the classification of the poresize of sandstone Based on the result of the classification ofthe pore size of sandstone acquired by some scholars [33ndash35] this paper divides the pore sizes into four categoriesmicropores (diameterlt 01 μm) minipores (diameters be-tween 01 and 1 μm) mesopores (diameters between 1 and50 μm) andmacropores (diameters ge50 μm) Figure 9 showsthe pore size distribution curve of rock specimens which aresoaked in H2SO4 solution and in pure water after 0 and 30freeze-thaw cycles respectively With the segmented sta-tistics of the pore size distribution curves the proportion ofthe distribution of different-sized pores soaked in two so-lutions after 0 10 20 and 30 freeze-thaw cycles are obtained(Table 3)

After 0 and 30 freeze-thaw cycles the numbers ofminipores and mesopores of sandstone in two solutions aredominant e rock specimen (rock specimen C7) inH2SO4 solution accounts for 744 and 743 respectivelyafter 0 and 30 freeze-thaw cycles and the rock specimen(rock specimen F7) in pure water accounts for 822 and752 respectively after 0 and 30 freeze-thaw cycles eresults show that there are relatively more minipores andmesopores and less micropores andmacropores in the initialsandstones With the growth of freeze-thaw cycles the poresdevelop and expand under the coupling effect of freeze-thawcycles and chemical reaction and the pores connect witheach other e pore sizes generally expand and the mi-cropores develop and the growth of the number of mar-copores is the most clear leading to the transformation ofthe pore structure of rock specimens

After 30 freeze-thaw cycles differences occur in thechanges of the pore structure of sandstone in the H2SO4solution and pure water Part of the minerals dissolve andare separated out and move out of the rocks in the H2SO4solution given that chemical reactions occur between theH2SO4 solution and the mineral granules within the rockspecimens erefore cavities are formed in the rockscausing the pore sizes to develop and expand and the

permeability of the rock is improved which facilitates themovement of the solution and intensifies the chemical re-action Consequently the number of mesopores grows by322 and the number of macropores grows from 0 to 08Conversely the numbers of micropores and miniporesdecline with the decrease ranges of minus27 and minus203respectively In contrast in the pure water where only theinfluencing factors of frost heave and water movement aresignificant the pores develop and expand continuouslywhich leads to the expansion of pore sizes and the creation ofnew micropores us micropores increase by 288 andmacropores increase from 02 to 20 the minipores andmesopores decline with decreasing ranges of minus108 andminus51 respectively

52 Pore Structure Deterioration under the Coupled Effect ofFreeze-aw and Chemical Solution e chemical compo-sitions of red sandstone are shown in Table 4

It can be seen in Table 4 that the red sandstone is mainlycomposed of SiO2 Al2O3 CaO MgO Na2O Fe2O3 andother minor chemical elements Among the constituentsSiO2 is the major element in the red sandstone Whenchemical solutions and rocks were put together during theexperiments a series of complex physical and chemical

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Poro

sity

com

pone

nt (

)Po

rosit

y co

mpo

nent

()

0 F-T cycles 30 F-T cycles

Pores expanded

New pores

New pores

Micropores(lt01μm)

Mesopores(1ndash50μm)

Macropores(ge50μm)

Minipores(01ndash1μm)

H2SO4

001 01 1 10T2 (ms)

100 1000 10000000

002

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New pores

New pores

Figure 9 Division of T2 spectra of sandstone specimens accordingto pore size in different solutions


reactions were bound to occur involving complex processesand mechanisms [36] Based on the ability of acid-dissolvingsandstone minerals the minerals could be divided into twoclasses [37] fast reacting minerals (with strong acid-dissolving ability) which includes aluminosilicate (authi-genic clay feldspar and calcite) and slow reacting minerals(clay splinter and quartz) During the acid-rock reaction theH2SO4 solution provides H+ and H2O

Under the condition of a strong acid SO42minus in the so-

lution slowly reacted or did not react with the major elementSiO2 which caused the difficult dissolution of quartz min-erals and thus the quartz minerals were prevented frommoving out of the rocks In the unlikely event that there werea few quartz minerals that were dissolved and generated freeSiO4

2minus the silicic acid still existed as a single molecule underthe strong acid condition where pH 1ndash3 and thus bio-polymers that were weak in water solubility would not beproduced erefore in the freeze-thaw process the massloss of rock specimens occurred slowly e reason for themass loss is that other chemical compositions (such as CaO)had dissolved and migrated out of the rocks explaining whythe mass loss of rock specimens was relatively little

e chemical formulae of chemical reactions betweenelements such as H+ and SO4

2minus in the H2SO4 solution purewater Al2O3 CaO and MgO are as follows

In pure water

CaO + H2O⟶ Ca(OH)2 (5)

Na2O + H2O⟶ 2Na(OH) (6)

K2O + H2O⟶ 2K(OH) (7)

P2O5 + H2O⟶ 2HPO3 (8)

In H2SO4

SiO2 + 2H2SO4⟶ Si SO4( 11138572 + 2H2O (9)

Al2O3 + 3H2SO4⟶ Al2 SO4( 11138573 + 3H2O (10)

CaO + H2SO4⟶ CaSO4 + H2O (11)

MgO + H2SO4⟶ MgSO4 + H2O (12)

Na2O + H2SO4⟶ Na2SO4 + H2O (13)

Fe2O3 + 3H2SO4⟶ Fe2 SO4( 11138573 + 3H2O (14)

K2O + H2SO4⟶ K2SO4 + H2O (15)

P2O5 + 3H2SO4⟶ 2H3PO4 + 3SO3 (16)

According to chemical formula (11) slightly solubleelement CaSO4 was produced after the chemical reactionbetween the rock specimens and the H2SO4 solution whichwould float on the surface of CaO to prevent the sulfuric acidfrom contacting CaO thus interfering in the chemical re-action is interference explains the observation that after30 freeze-thaw cycles the rock specimens in the H2SO4solution were not seriously damaged and only the rocksurface demonstrated corrosion and peeling off (Figure 3)erefore there were relatively few sediments that could beobserved during the experiment

In addition in the coupling environment of freeze-thaw andchemical effect the red sandstones treated in H2SO4 solutionwere clearly affected by the freeze-thaw effect When thetemperature was low the water or solution in the pores ex-panded due to freezing and produced pairs of frosting-heavingforces on the sidewalls of the mineral particles causing thedevelopment and expansion of cracks within the rocks andincrease in porosity [38 39] When the temperature rose thefrozen water and chemical solution melted and moved intonewly formed cracks and the acid solution and the mineralelementswithin the rocks reactedwith each other so that part ofthe minerals were dissolved and separated and migrated out ofthe rocks erefore cavities were formed in the rock speci-mens causing the pores to develop and expand continuouslye number of mesopores and macropores increased as dis-played in Table 3 which enhanced the rock damaging processWith the progressive increase of freeze-thaw cycles the cracks inthe rock fabric kept developing and expanding leading to thegradual increase of porosity In the meantime as the chemicalsolution from the outside entered the newly formed cracks andreacted with the mineral elements of the rocks the cohesiveforce between the mineral particles was weakened periodicallywhich further accelerated the rock damage leading to macro-scopic deterioration of the rock structures

6 Conclusions

In summary the coupling effects of acid solution and freeze-thaw had a significant influence on the microstructure of the

Table 3 Proportional variations of pore sizes in different solutions

Pore sizeProportion of pores in cores in H2SO4 solution () Proportion of pores in cores in pure water ()0 cycle 10 cycles 20 cycles 30 cycles 0 cycle 10 cycles 20 cycles 30 cycles

Micropores (lt01 μm) 255 243 157 248 177 209 211 228Minipores (01ndash1 μm) 458 434 474 365 489 416 471 436Mesopores (1ndash50 μm) 286 323 356 378 333 364 303 316Macropores (ge50 μm) 00 00 14 08 02 12 16 20

Table 4 Chemical composition of red sandstone ()

SiO2 Al2O3 CaO MgO Na2O Fe2O3 K2O TiO2 P2O5

525 114 58 38 32 23 18 05 01


red sandstone rock specimens e coupled effects aresupported by observations that rock specimens immersed inthe H2SO4 solution were damaged more adversely than rockspecimens immersed in pure water e differences in thepreconditioned states of the two categories of specimensprior to exposure to freeze-thaw cycles account for thedifferent types of pore structures observed with significantimplications for bulk permeability and macroscopic me-chanical properties e following conclusions can be made

(1) Compared with the sandstone specimens in purewater the freeze-thaw deterioration of the sandstonespecimens is more severe under acidic conditionse mass of the rock specimens decreases evidentlywith the increasing number of freeze-thaw cyclesand large particles peel off and fragments fall fromthe surface of the rock specimens

(2) e H2SO4 solution has a large effect on the changesin porosity of the sandstone specimens With theincreasing number of freeze-thaw cycles the trend ina linearly increasing porosity becomes clear giventhat the acid environment has accelerated the de-velopment and expansion of the cracks within thespecimens

(3) As the number of freeze-thaw cycles increases thepore structure of the rocks changes evidently underthe acidic conditions After 30 freeze-thaw cycles thetotal spectral area of the rock specimen C7 (inH2SO4 solution) increased by 356 and the numberof peaks increased from 4 to 6 In the meantime thetotal spectral area of the rock specimen F7 (in purewater) increased by 21 and the number of peaksincreased from 4 to 5 In addition the trend of eachspectra peak is also different

(4) e MRI of the freeze-thaw deterioration of thesandstones under the acidic environment shows thatthe freeze-thaw deterioration of the sandstones is agradual process which develops from the exterior tothe interior and is much more severe than observedfor the rock specimens in pure water erefore thechemical environment will produce significant ef-fects on the freeze-thaw deterioration of the rockspecimens

(5) Typically the pore sizes can be classified into fourcategories micropores minipores mesopores andmacropores After 30 freeze-thaw cycles differencesoccur in the changes of the pore structure ofsandstones in the H2SO4 solution and pure water inH2SO4 solution the numbers of mesopores andmacropores grow while the numbers of microporesand minipores decline In contrast in the pure watermicropores and macropores increase while theminipores and mesopores decline

(6) In the coupling environment of freeze-thaw andchemical effect cracks within the red sandstonedevelop and expand continuously with the influenceof the freeze-grow force which causes the porosity toincrease Furthermore as H2SO4 solution enters

periodically into new cracks and react with mineralelements part of the minerals are dissolved andseparated out which accelerates the rock damageprocess However given that the major compoundsSiO2 and H2SO4 in sandstone react slowly or do notreact at all the mass change of rock specimens isrelatively small Finally the generation of the slightlysoluble compound CaSO4 affects the chemical re-action and slows down the deterioration of the in-terior structure of the rock specimens

Data Availability

is study was supported by multiple datasets which areopenly available at locations cited in the reference section

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

is work was supported by the National Natural ScienceFoundation of China (nos 41502327 51474252 and51774323) National Major Scientific Instruments andEquipment Development Projects (2013YQ17046310) andOpen-End Fund for the Valuable and Precision Instrumentsof Central South University (CSUZC201801) e first au-thor would like to acknowledge the China ScholarshipCouncil for financial support to the visiting scholar(201706375077) at the Colorado School of Mines

References

[1] P Li J Liu G H Li J B Zhu and S G Liu ldquoExperimentalstudy for shear strength characteristics of sandstone underwater-rock interaction effectsrdquo Rock and Soil Mechanicsvol 32 no 2 pp 380ndash386 2011

[2] W X Ding and X T Feng ldquoDamage effect and fracturecriterion of rock withmulti-preexisting cracks under chemicalerosionrdquo Chinese Journal of Geotechnical Engineering vol 31no 6 pp 899ndash904 2009

[3] B K Atkinson and P G Meredith ldquoStress corrosion crackingof quartz a note on the influence of chemical environmentrdquoEctonophysics vol 77 no 1-2 pp 1ndash11 1981

[4] P Vazquez L Carrizo C omachot-Schneider S Gibeauxand F J Alonso ldquoInfluence of surface finish and compositionon the deterioration of building stones exposed to acid at-mospheresrdquo Construction and Building Materials vol 106pp 392ndash403 2016

[5] L J Feucht and J M Logan ldquoEffects of chemically activesolutions on shearing behavior of a sandstonerdquo Tectono-physics vol 175 no 1ndash3 pp 159ndash176 1990

[6] S L Chen X T Feng and H Zhou ldquoStudy on triaxial meso-failure mechanism and damage variables of sandstone underchemical erosionrdquo Rock and Soil Mechanics vol 25 no 9pp 1363ndash1367 2004

[7] W X Ding and X T Feng ldquoCT experimental research offractured rock failure process under chemical corrosion andpermeationrdquo Chinese Journal of Rock Mechanics and Engi-neering vol 27 no 9 pp 1865ndash1873 2008


[8] H Y Yao X T Feng Q Cui et al ldquoMeso-mechanical ex-perimental study of meso-fraeturing process of limestoneunder coupled chemical corrosion and water pressurerdquo Rockand Soil Mechanics vol 30 no 1 pp 59ndash78 2009

[9] K-B Min J Rutqvist and D Elsworth ldquoChemically andmechanically mediated influences on the transport and me-chanical characteristics of rock fracturesrdquo InternationalJournal of Rock Mechanics and Mining Sciences vol 46 no 1pp 80ndash89 2009

[10] Y S Liu W Liu and X Y Dong ldquoDynamic mechanicalproperties and constitutive model of rock under chemicalcorrosionrdquo Journal of Yangtze River Scientific Research In-stitute vol 32 no 5 pp 72ndash75 2015

[11] N Li Y Zhu B Su and S Gunter ldquoA chemical damagemodel of sandstone in acid solutionrdquo International Journal ofRock Mechanics and Mining Sciences vol 40 no 2pp 243ndash249 2003

[12] R H Brzesowsky S J T Hangx N Brantut and C J SpiersldquoCompaction creep of sands due to time-dependent grainfailure effects of chemical environment applied stress andgrain sizerdquo Journal of Geophysical Research Solid Earthvol 119 no 10 pp 7521ndash7541 2014

[13] S Miao M Cai Q Guo P Wang and M Liang ldquoDamageeffects andmechanisms in granite treated with acidic chemicalsolutionsrdquo International Journal of Rock Mechanics andMining Sciences vol 88 pp 77ndash86 2016

[14] H Zheng X-T Feng and P-Z Pan ldquoExperimental in-vestigation of sandstone properties under CO2ndashNaClsolution-rock interactionsrdquo International Journal of Green-house Gas Control vol 37 pp 451ndash470 2015

[15] T L Han Y S Chen J P Shi et al ldquoExperimental study ofmechanical characteristics of sandstone subjected to hydro-chemical erosionrdquo Chinese Journal of Rock Mechanics andEngineering vol 32 no 13 pp 146ndash159 2013

[16] J L Li Experiment study on deterioration mechanism of rockunder the conditions of freezing-thawing cycles in cold regionsbased on NMR technology PhD dissertation Central SouthUniversity Changsha China 2012

[17] W G Tian Experiment study on freezing-thawing damagemechanism of rock under the condition of Coupling of multiplefactors PhD dissertation Central South UniversityChangsha China 2013

[18] B K Ning S L Chen Q Zhang et al ldquoDouble corrosioneffects under acid and freezing and thawing erosion andfracture behavior of concreterdquo Journal of Shenyang Universityof Technology vol 27 no 5 pp 575ndash578 2005

[19] X Shi L Fay M M Peterson and Z Yang ldquoFreeze-thawdamage and chemical change of a portland cement concrete inthe presence of diluted deicersrdquo Materials and Structuresvol 43 no 7 pp 933ndash946 2009

[20] L H Lu S L Chen B K Ning et al ldquoTest study on concretemechanical effect under together work of chemistry and frostand thaw torrosionrdquo Highway vol 51 no 8 pp 154ndash1582006

[21] F Gao Q Wang H Deng J Zhang W Tian and B KeldquoCoupled effects of chemical environments and freeze-thawcycles on damage characteristics of red sandstonerdquo Bulletin ofEngineering Geology and the Environment vol 76 no 4pp 1481ndash1490 2016

[22] httpwwwniumagcomcategoryproducts[23] Suzhou Niumag Electronic Technology Co Ltd NMR Rock-

Core Analyzing Software Manual (Version 110) SuzhouNiumag Electronic Technology Co Ltd Suzhou China2013 in Chinese

[24] R L Kleinberg ldquoUtility of NMR T2 distributions connectionwith capillary pressure clay effect and determination of thesurface relaxivity parameter rho 2rdquo Magnetic ResonanceImaging vol 14 no 7-8 pp 761ndash767 1996

[25] X M Ge Y R Fan X J Zhu Y Chen and R Li ldquoDe-termination of nuclear magnetic resonance T2 cutoff valuebased on multifractal theorymdashan application in sandstonewith complex pore structurerdquo Geophysics vol 80 no 1pp 11ndash21 2015

[26] P J M Monteiro S J Bastacky and T L Hayes ldquoLow-temperature scanning electron microscope analysis of thePortland cement paste early hydrationrdquo Cement and ConcreteResearch vol 15 no 4 pp 687ndash693 1985

[27] M Hori and H Morihiro ldquoMicromechanical analysis ofdeterioration due to freezing and thawing in porous brittlematerialsrdquo International Journal of Engineering Sciencevol 36 no 4 pp 511ndash522 1998

[28] K R Brownstein and C E Tarr ldquoImportance of classicaldiffusion in NMR studies of water in biological cellsrdquo PhysicalReview A vol 19 no 6 pp 2446ndash2453 1979

[29] R L Kleinberg W E Kenyon and P P Mitra ldquoMechanismof NMR relaxation of fluids in rockrdquo Journal of MagneticResonance vol 108 no 2 pp 206ndash214 1994

[30] C H Lyu Z H Ning QWang andM Chen ldquoApplication ofNMR T2 to pore size distribution and movable fluid distri-bution in tight sandstonesrdquo Energy Fuels vol 32 no 2pp 1395ndash1405 2018

[31] H B Li J Y Zhu and H K Guo ldquoMethods for calculatingpore radius distribution in rock from NMR T2 spectrardquoChinese Journal of Magnetic Resonance vol 25 pp 273ndash2802008

[32] H Zhou F Gao X Zhou et al ldquoe translation research ofdifferent types sandstone of Yungang Grottoes in NMR T2-mercury capillary pressurerdquo Progress in Geophys vol 28no 5 pp 2759ndash2766 2013

[33] L Z Xiao Magnetic Resonance Imaging Well Logging andRock Magnetic Resonance and Its Applications Science PressBeijing China 1998

[34] W Z Shao J Y Xie X R Chi et al ldquoOn the relation ofporosity and permeability in low porosity and low perme-ability rockrdquo Well Logging Technology vol 37 no 2pp 149ndash153 2013

[35] J P Yan D N Wen Z Z Li et al ldquoe quantitative eval-uation method of low permeable sandstone pore structurebased on nuclear magnetic resonance (NMR) logging a casestudy of Es4 formation in the south slope of dongying sagrdquoChinese Journal of Geophysics vol 59 no 3 pp 313ndash3222016

[36] B Gou J C Guo and T Yu ldquoNew method for calculatingrock fracture pressure by acid damagerdquo Journal of CentralSouth University (Science and Technology) vol 46 no 1pp 275ndash281 2015

[37] M A Mahmoud H A Nasr-El-Din C A DeWolf et alldquoSandstone acidizing using a new class of chelating agentsrdquo inProceedings of the SPE International Symposium on OilfieldChemistry pp 1ndash17 Society of Petroleum Engineers eWoodlands TX USA April 2011

[38] I C McDowall ldquoParticle size reduction of clay minerals byfreezing and thawingrdquo New Zealand Journal of Geology andGeophysics vol 3 no 3 pp 337ndash343 1960

[39] T Ishikawa and S Miura ldquoInfluence of freeze-thaw action ondeformation-strength characteristics and particle crushabilityof volcanic coarse-grained soilsrdquo Soils and Foundationsvol 51 no 5 pp 785ndash799 2011


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Volume 2018

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

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wwwhindawicom Volume 2018

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Submit your manuscripts atwwwhindawicom

[9ndash11] e results from these previous achievements haveprovided references for studies of the long-term stability ofrock engineering in chemical environments

As the research continues to advance the issues of rockdeterioration under the multifactor coupling conditions ofpressure chemical and other factors have drawn in-creasingly more attention such as the rock creep behaviourin a chemical environment [12] the damage of phys-icomechanical parameters of rocks under the couplingeffects of chemical environment and stress loading [13 14]and the mechanical properties of triaxial compression ofrocks immersed in different water chemical solutions [15]However besides the influence of the complex hydro-chemical environment on rock there is an essential need tostudy the damaging effect of the freeze-thaw cycles in coldregions on a rock mass [16] In mines located in cold re-gions for example the freeze-thaw disasters of the rockmass in mines can occur concurrently with the corrosion ofthe acid waste water acid rain or the deicing saline so-lution used at the mines whose influences have beenknown to interact in certain cases [17] Some research hasbeen performed on the deterioration of the rock mechanicsunder the decoupling influence of chemistry and the freeze-thaw Ning et al [18] conducted the splitting tests of theconcrete under the coupling effect of the acid corrosion andthe freeze-thaw cycles studied the features of the surfaceerosion and the mechanical properties of the concretes thatare of different pH values and being processed by differentnumbers of freeze-thaw cycles and analyzed the splittingprocess of the concrete corroded by acid and the freeze-thaw ey found that the acid erosion of concrete is in-versely proportional to the pH value and the erosionbegins on the surface of the concrete e coupling effectsof acid erosion and freeze-thaw cycles accelerate the de-terioration of mechanical properties of concrete In theweak acid environment freeze-thaw cycles play a leadingrole in concrete erosion As the pH value decreases theeffect of acid on concrete gradually increases Shi et al [19]studied the changes of different chemical diluents in theconcrete of Portland in the freeze-thaw environment andadopted SEM to study the mechanism of formation of poresand cracks in the test specimens and the results show thatNaCl the NaCl-based deicer and the K-acetate-baseddeicer were the most deleterious to the concrete Luet al [20] carried out the indoor simulation tests of con-cretes under the conditions of the dual corrosion of acid-base and freeze-thaw and he found that both strong acidand alkali are corrosive to concrete e corrosion of acidalkali and freeze-thaw cycle dominates at different timesaccelerating the deterioration of mechanical propertiesconcrete Gao et al [21] conducted a freeze-thaw cycleexperiment on rock samples which were soaked in fourdifferent solutions sulfuric acid solution sodium hy-droxide solution sodium chloride solution and pure waterand the microstructural changes of each group of rocksamples were tested by nuclear magnetic resonance (NMR)e results have shown that the influences of sodiumhydroxide and sodium chloride solutions are the mostsignificant and the influence of sulfuric acid solution is

relatively weak In the meantime NMR results show thechemical solutions have great effects on the microstructureof rocks

In the previous studies the research objectives aremainly aimed at the physical and mechanical properties ofbuildings in cold regions under chemical conditionserefore the reported previous studies tend to take con-crete as the research objective when studying the mechanicalproperties of the rocks under the influence of chemistry andfreeze-thaw Given that the focus is on macroscopic fracturefeatures very few of the studies have evaluated mechanismsrelated to the structural deterioration of pores therefore theresults are somewhat limited in terms of mechanisms andcharacteristics of the deterioration of the rock mass In thisstudy with the impact of acid waste water at mines as theengineering background rock is selected as the researchobject e study discusses freeze-thaw cycling tests ofsandstone in the acid environment the acquisition of themass of the rock specimens and observed changes such asthe exterior alteration It also analyzes and discusses thecharacteristics of the freeze-thaw deterioration of the mi-crostructure of the rocks in the acid environment withnuclear magnetic resonance technique

2 Materials and Methods

21 Materials e rock specimens consisted of fleshy redsandstone with a dense-and-fine fragment texture especimens were prepared from natural and fresh rockswhich had formed at a comparatively deeper level aniso-tropic and without any traces of cracks developed on thejoints According to the results of the X-ray diffraction testthe red sandstone is mainly composed of quartz albiteaerinite sanidine microcline laumontite and chabazitee bulk density of rock was 242 gcm3 e water ab-sorption test showed that the percent absorption of the rockspecimens was 165 the water saturation ratio was 174and the water saturation coefficient was 095 e rocks wereprepared as specimens of standard cylinders 50plusmn 1 mm indiameter by 30plusmn 1 mm tall according to ldquoe Codes of RockTests in Water Conservancy and Hydroelectrical Projects(SL 264-2001)rdquo standards

22 Experimental Setup and Test Procedures e rockspecimens were numbered C1ndashC9 and F1ndashF9 respectivelyto match with the H2SO4 solution group and the pure watergroup First prepare a H2SO4 solution with initial pH 15(the mass concentration of sulfuric acid is 15 gL) accordingto the lowest pH value in the mine waste water where thesampling site is located en the rock specimens wereseparately immersed in the H2SO4 solution and pure waterfor 48 hours to reach a state of natural saturation evolume of the sulfuric acid solution and pure water is basedon the thoroughly immersed specimens It ranges from 2 Lto 3 L Next the rock specimens were placed in a TDS-300freeze-thaw testingmachine for the freeze-thaw cycling testsAccording to the requirements of the freeze-thaw test theparameters of the freeze-thaw were the freezing temperature



















10000

9000

8000

7000

6000

5000

4000

3000

2000

1000

00 200 400 600 800

Echo time (ms)

Am

plitu

de o

f spi

n ec

ho

1000 1200 1400 1600 1800

(a)

020

018

016

014

012

010

008

006

004

002

000001 01 1 10

Porosity = 36

Spectrum area

100 100000

05

10

15

20

Acc

umul

ativ

e por

osity

()

Poro

sity

com

pone

nt (

)25

30

35

40



(b)


Slightly eroded

(a)

Having peeled off

(b)

Seriously eroded

(c)


NMR system

Magnetcabinet

Spectrometersystem

DisplayRF coil


Pure water

Freeze-thaw device







145

144

143

142

141

1400 10 20


Mas

s (g)

30

2

1







(a) (b) (c)








000001 01



1 10 100 1000 10000T2 (ms)

002

004

006

008

010

012

014

016

0181st spectra peak

2nd spectra peak

3rd spectra peak

4th spectra peak

5th spectra peak

Poro

sity

com

pone

nt (

)

(a)



001 01 1 10T2 (ms)

100 1000 10000

1st spectra peak

2nd spectra peak

3rd spectra peak

4th spectra peak

5th spectra peak

Poro

sity

com

pone

nt (

)

000

002

004

006

008

010

012

014

016

018

(b)





H2SO4

C7-0 4837 2827 1700 636 0 0 12467C7-10 5462 1999 2146 394 0 0 14417C7-20 4012 2809 2052 989 138 0 14378C7-30 4325 1811 1493 1807 484 080 16903

Pure water

F7-0 5176 3324 1089 410 0 0 11614F7-10 3250 4000 2246 504 0 0 13111F7-20 4287 2881 2094 582 156 0 12835F7-30 4151 2973 2044 636 195 0 14058






(a)

1

1

2 2

(b)

1

1

22

(c)

1

2

2

2

(d)




5 Discussion



1T2

ρ2S

V1113874 1113875

porosity (1)



1T2

ρ2rc

Fs (2)

(a)

1

1

2

2

(b)

1

2

2

2

(c)

1

1

1

2

(d)




rc CT2 (3)




rc 03125T2 (4)







000

002

004

006

008

010

012

014

016

018

Poro

sity

com

pone

nt (

)Po

rosit

y co

mpo

nent

()


Pores expanded

New pores

New pores

Micropores(lt01μm)


Macropores(ge50μm)


H2SO4

001 01 1 10T2 (ms)

100 1000 10000000

002

004

006

008

010

012

014


New pores

New pores









In pure water


Na2O + H2O⟶ 2Na(OH) (6)

K2O + H2O⟶ 2K(OH) (7)

P2O5 + H2O⟶ 2HPO3 (8)

In H2SO4

SiO2 + 2H2SO4⟶ Si SO4( 11138572 + 2H2O (9)

Al2O3 + 3H2SO4⟶ Al2 SO4( 11138573 + 3H2O (10)



Na2O + H2SO4⟶ Na2SO4 + H2O (13)

Fe2O3 + 3H2SO4⟶ Fe2 SO4( 11138573 + 3H2O (14)

K2O + H2SO4⟶ K2SO4 + H2O (15)

P2O5 + 3H2SO4⟶ 2H3PO4 + 3SO3 (16)



6 Conclusions







525 114 58 38 32 23 18 05 01










Data Availability




Acknowledgments


References












































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia



















10000

9000

8000

7000

6000

5000

4000

3000

2000

1000

00 200 400 600 800

Echo time (ms)

Am

plitu

de o

f spi

n ec

ho

1000 1200 1400 1600 1800

(a)

020

018

016

014

012

010

008

006

004

002

000001 01 1 10

Porosity = 36

Spectrum area

100 100000

05

10

15

20

Acc

umul

ativ

e por

osity

()

Poro

sity

com

pone

nt (

)25

30

35

40



(b)


Slightly eroded

(a)

Having peeled off

(b)

Seriously eroded

(c)


NMR system

Magnetcabinet

Spectrometersystem

DisplayRF coil


Pure water

Freeze-thaw device







145

144

143

142

141

1400 10 20


Mas

s (g)

30

2

1







(a) (b) (c)








000001 01



1 10 100 1000 10000T2 (ms)

002

004

006

008

010

012

014

016

0181st spectra peak

2nd spectra peak

3rd spectra peak

4th spectra peak

5th spectra peak

Poro

sity

com

pone

nt (

)

(a)



001 01 1 10T2 (ms)

100 1000 10000

1st spectra peak

2nd spectra peak

3rd spectra peak

4th spectra peak

5th spectra peak

Poro

sity

com

pone

nt (

)

000

002

004

006

008

010

012

014

016

018

(b)





H2SO4

C7-0 4837 2827 1700 636 0 0 12467C7-10 5462 1999 2146 394 0 0 14417C7-20 4012 2809 2052 989 138 0 14378C7-30 4325 1811 1493 1807 484 080 16903

Pure water

F7-0 5176 3324 1089 410 0 0 11614F7-10 3250 4000 2246 504 0 0 13111F7-20 4287 2881 2094 582 156 0 12835F7-30 4151 2973 2044 636 195 0 14058






(a)

1

1

2 2

(b)

1

1

22

(c)

1

2

2

2

(d)




5 Discussion



1T2

ρ2S

V1113874 1113875

porosity (1)



1T2

ρ2rc

Fs (2)

(a)

1

1

2

2

(b)

1

2

2

2

(c)

1

1

1

2

(d)




rc CT2 (3)




rc 03125T2 (4)







000

002

004

006

008

010

012

014

016

018

Poro

sity

com

pone

nt (

)Po

rosit

y co

mpo

nent

()


Pores expanded

New pores

New pores

Micropores(lt01μm)


Macropores(ge50μm)


H2SO4

001 01 1 10T2 (ms)

100 1000 10000000

002

004

006

008

010

012

014


New pores

New pores









In pure water


Na2O + H2O⟶ 2Na(OH) (6)

K2O + H2O⟶ 2K(OH) (7)

P2O5 + H2O⟶ 2HPO3 (8)

In H2SO4

SiO2 + 2H2SO4⟶ Si SO4( 11138572 + 2H2O (9)

Al2O3 + 3H2SO4⟶ Al2 SO4( 11138573 + 3H2O (10)



Na2O + H2SO4⟶ Na2SO4 + H2O (13)

Fe2O3 + 3H2SO4⟶ Fe2 SO4( 11138573 + 3H2O (14)

K2O + H2SO4⟶ K2SO4 + H2O (15)

P2O5 + 3H2SO4⟶ 2H3PO4 + 3SO3 (16)



6 Conclusions







525 114 58 38 32 23 18 05 01










Data Availability




Acknowledgments


References












































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia






145

144

143

142

141

1400 10 20


Mas

s (g)

30

2

1







(a) (b) (c)








000001 01



1 10 100 1000 10000T2 (ms)

002

004

006

008

010

012

014

016

0181st spectra peak

2nd spectra peak

3rd spectra peak

4th spectra peak

5th spectra peak

Poro

sity

com

pone

nt (

)

(a)



001 01 1 10T2 (ms)

100 1000 10000

1st spectra peak

2nd spectra peak

3rd spectra peak

4th spectra peak

5th spectra peak

Poro

sity

com

pone

nt (

)

000

002

004

006

008

010

012

014

016

018

(b)





H2SO4

C7-0 4837 2827 1700 636 0 0 12467C7-10 5462 1999 2146 394 0 0 14417C7-20 4012 2809 2052 989 138 0 14378C7-30 4325 1811 1493 1807 484 080 16903

Pure water

F7-0 5176 3324 1089 410 0 0 11614F7-10 3250 4000 2246 504 0 0 13111F7-20 4287 2881 2094 582 156 0 12835F7-30 4151 2973 2044 636 195 0 14058






(a)

1

1

2 2

(b)

1

1

22

(c)

1

2

2

2

(d)




5 Discussion



1T2

ρ2S

V1113874 1113875

porosity (1)



1T2

ρ2rc

Fs (2)

(a)

1

1

2

2

(b)

1

2

2

2

(c)

1

1

1

2

(d)




rc CT2 (3)




rc 03125T2 (4)







000

002

004

006

008

010

012

014

016

018

Poro

sity

com

pone

nt (

)Po

rosit

y co

mpo

nent

()


Pores expanded

New pores

New pores

Micropores(lt01μm)


Macropores(ge50μm)


H2SO4

001 01 1 10T2 (ms)

100 1000 10000000

002

004

006

008

010

012

014


New pores

New pores









In pure water


Na2O + H2O⟶ 2Na(OH) (6)

K2O + H2O⟶ 2K(OH) (7)

P2O5 + H2O⟶ 2HPO3 (8)

In H2SO4

SiO2 + 2H2SO4⟶ Si SO4( 11138572 + 2H2O (9)

Al2O3 + 3H2SO4⟶ Al2 SO4( 11138573 + 3H2O (10)



Na2O + H2SO4⟶ Na2SO4 + H2O (13)

Fe2O3 + 3H2SO4⟶ Fe2 SO4( 11138573 + 3H2O (14)

K2O + H2SO4⟶ K2SO4 + H2O (15)

P2O5 + 3H2SO4⟶ 2H3PO4 + 3SO3 (16)



6 Conclusions







525 114 58 38 32 23 18 05 01










Data Availability




Acknowledgments


References












































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia







000001 01



1 10 100 1000 10000T2 (ms)

002

004

006

008

010

012

014

016

0181st spectra peak

2nd spectra peak

3rd spectra peak

4th spectra peak

5th spectra peak

Poro

sity

com

pone

nt (

)

(a)



001 01 1 10T2 (ms)

100 1000 10000

1st spectra peak

2nd spectra peak

3rd spectra peak

4th spectra peak

5th spectra peak

Poro

sity

com

pone

nt (

)

000

002

004

006

008

010

012

014

016

018

(b)





H2SO4

C7-0 4837 2827 1700 636 0 0 12467C7-10 5462 1999 2146 394 0 0 14417C7-20 4012 2809 2052 989 138 0 14378C7-30 4325 1811 1493 1807 484 080 16903

Pure water

F7-0 5176 3324 1089 410 0 0 11614F7-10 3250 4000 2246 504 0 0 13111F7-20 4287 2881 2094 582 156 0 12835F7-30 4151 2973 2044 636 195 0 14058






(a)

1

1

2 2

(b)

1

1

22

(c)

1

2

2

2

(d)




5 Discussion



1T2

ρ2S

V1113874 1113875

porosity (1)



1T2

ρ2rc

Fs (2)

(a)

1

1

2

2

(b)

1

2

2

2

(c)

1

1

1

2

(d)




rc CT2 (3)




rc 03125T2 (4)







000

002

004

006

008

010

012

014

016

018

Poro

sity

com

pone

nt (

)Po

rosit

y co

mpo

nent

()


Pores expanded

New pores

New pores

Micropores(lt01μm)


Macropores(ge50μm)


H2SO4

001 01 1 10T2 (ms)

100 1000 10000000

002

004

006

008

010

012

014


New pores

New pores









In pure water


Na2O + H2O⟶ 2Na(OH) (6)

K2O + H2O⟶ 2K(OH) (7)

P2O5 + H2O⟶ 2HPO3 (8)

In H2SO4

SiO2 + 2H2SO4⟶ Si SO4( 11138572 + 2H2O (9)

Al2O3 + 3H2SO4⟶ Al2 SO4( 11138573 + 3H2O (10)



Na2O + H2SO4⟶ Na2SO4 + H2O (13)

Fe2O3 + 3H2SO4⟶ Fe2 SO4( 11138573 + 3H2O (14)

K2O + H2SO4⟶ K2SO4 + H2O (15)

P2O5 + 3H2SO4⟶ 2H3PO4 + 3SO3 (16)



6 Conclusions







525 114 58 38 32 23 18 05 01










Data Availability




Acknowledgments


References












































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia






(a)

1

1

2 2

(b)

1

1

22

(c)

1

2

2

2

(d)




5 Discussion



1T2

ρ2S

V1113874 1113875

porosity (1)



1T2

ρ2rc

Fs (2)

(a)

1

1

2

2

(b)

1

2

2

2

(c)

1

1

1

2

(d)




rc CT2 (3)




rc 03125T2 (4)







000

002

004

006

008

010

012

014

016

018

Poro

sity

com

pone

nt (

)Po

rosit

y co

mpo

nent

()


Pores expanded

New pores

New pores

Micropores(lt01μm)


Macropores(ge50μm)


H2SO4

001 01 1 10T2 (ms)

100 1000 10000000

002

004

006

008

010

012

014


New pores

New pores









In pure water


Na2O + H2O⟶ 2Na(OH) (6)

K2O + H2O⟶ 2K(OH) (7)

P2O5 + H2O⟶ 2HPO3 (8)

In H2SO4

SiO2 + 2H2SO4⟶ Si SO4( 11138572 + 2H2O (9)

Al2O3 + 3H2SO4⟶ Al2 SO4( 11138573 + 3H2O (10)



Na2O + H2SO4⟶ Na2SO4 + H2O (13)

Fe2O3 + 3H2SO4⟶ Fe2 SO4( 11138573 + 3H2O (14)

K2O + H2SO4⟶ K2SO4 + H2O (15)

P2O5 + 3H2SO4⟶ 2H3PO4 + 3SO3 (16)



6 Conclusions







525 114 58 38 32 23 18 05 01










Data Availability




Acknowledgments


References












































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia



5 Discussion



1T2

ρ2S

V1113874 1113875

porosity (1)



1T2

ρ2rc

Fs (2)

(a)

1

1

2

2

(b)

1

2

2

2

(c)

1

1

1

2

(d)




rc CT2 (3)




rc 03125T2 (4)







000

002

004

006

008

010

012

014

016

018

Poro

sity

com

pone

nt (

)Po

rosit

y co

mpo

nent

()


Pores expanded

New pores

New pores

Micropores(lt01μm)


Macropores(ge50μm)


H2SO4

001 01 1 10T2 (ms)

100 1000 10000000

002

004

006

008

010

012

014


New pores

New pores









In pure water


Na2O + H2O⟶ 2Na(OH) (6)

K2O + H2O⟶ 2K(OH) (7)

P2O5 + H2O⟶ 2HPO3 (8)

In H2SO4

SiO2 + 2H2SO4⟶ Si SO4( 11138572 + 2H2O (9)

Al2O3 + 3H2SO4⟶ Al2 SO4( 11138573 + 3H2O (10)



Na2O + H2SO4⟶ Na2SO4 + H2O (13)

Fe2O3 + 3H2SO4⟶ Fe2 SO4( 11138573 + 3H2O (14)

K2O + H2SO4⟶ K2SO4 + H2O (15)

P2O5 + 3H2SO4⟶ 2H3PO4 + 3SO3 (16)



6 Conclusions







525 114 58 38 32 23 18 05 01










Data Availability




Acknowledgments


References












































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia



rc CT2 (3)




rc 03125T2 (4)







000

002

004

006

008

010

012

014

016

018

Poro

sity

com

pone

nt (

)Po

rosit

y co

mpo

nent

()


Pores expanded

New pores

New pores

Micropores(lt01μm)


Macropores(ge50μm)


H2SO4

001 01 1 10T2 (ms)

100 1000 10000000

002

004

006

008

010

012

014


New pores

New pores









In pure water


Na2O + H2O⟶ 2Na(OH) (6)

K2O + H2O⟶ 2K(OH) (7)

P2O5 + H2O⟶ 2HPO3 (8)

In H2SO4

SiO2 + 2H2SO4⟶ Si SO4( 11138572 + 2H2O (9)

Al2O3 + 3H2SO4⟶ Al2 SO4( 11138573 + 3H2O (10)



Na2O + H2SO4⟶ Na2SO4 + H2O (13)

Fe2O3 + 3H2SO4⟶ Fe2 SO4( 11138573 + 3H2O (14)

K2O + H2SO4⟶ K2SO4 + H2O (15)

P2O5 + 3H2SO4⟶ 2H3PO4 + 3SO3 (16)



6 Conclusions







525 114 58 38 32 23 18 05 01










Data Availability




Acknowledgments


References












































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia








In pure water


Na2O + H2O⟶ 2Na(OH) (6)

K2O + H2O⟶ 2K(OH) (7)

P2O5 + H2O⟶ 2HPO3 (8)

In H2SO4

SiO2 + 2H2SO4⟶ Si SO4( 11138572 + 2H2O (9)

Al2O3 + 3H2SO4⟶ Al2 SO4( 11138573 + 3H2O (10)



Na2O + H2SO4⟶ Na2SO4 + H2O (13)

Fe2O3 + 3H2SO4⟶ Fe2 SO4( 11138573 + 3H2O (14)

K2O + H2SO4⟶ K2SO4 + H2O (15)

P2O5 + 3H2SO4⟶ 2H3PO4 + 3SO3 (16)



6 Conclusions







525 114 58 38 32 23 18 05 01










Data Availability




Acknowledgments


References












































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia










Data Availability




Acknowledgments


References












































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia





































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia


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