experimental study on mechanical properties of fly ash stabilized with...

Research ArticleExperimental Study on Mechanical Properties of Fly AshStabilized with Cement

Shengquan Zhou1 Yongfei Zhang 1 Dawei Zhou1 Weijian Wang1 Dongwei Li2

and Zhaibang Ke3

1School of Civil Engineering and Architecture Anhui University of Science and Technology Huainan 232001 China2School of Civil and Architectural Engineering East China University of Technology Nanchang 330013 China3Anhui Key Laboratory of Green Building and Assembly Construction Hefei 230032 China

Correspondence should be addressed to Yongfei Zhang 1392324734qqcom

Received 25 December 2019 Revised 25 June 2020 Accepted 23 August 2020 Published 2 September 2020

Academic Editor Hui Yao

Copyright copy 2020 Shengquan Zhou et al -is is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

Cement-fly ash mixture has been commonly used for the foundation treatment projects in the fly ash stratum as it is effective inimproving foundation bearing capacity and reducing settlement of stratum In order to figure out the effect of dynamic and staticload on themechanical properties exhibited by the cement-fly ash and the reactionmechanism of cement-fly ash a combination ofthe unconfined compressive test impact test scanning electron microscopy (SEM) and X-ray diffraction (XRD) method wasadopted in this study to investigate the cement-fly ash test samples As demonstrated by the results the observed growth rate of0ndash60 days (d) is higher than that in the later stages and the typical stress-strain curve can be divided into six sections under theunconfined compressive test At the gas pressure of 02MPa the cement-fly ash samples exhibited obvious plastic properties inearly curing time (0ndash60 d) and brittle failure was observed in the final stage (90 d) It is obvious that the value of dynamiccompressive strength (DCS) is higher than that of unconfined compressive strength (UCS) -e analysis of XRD has revealed thatthe hydration products are primarily derived from the hydration reaction of cement in the early stage and the pozzolanic reactionin the late stage -e pores of cement-fly ash are found to be filled with the hydration products despite the presence of a mass ofpores in the interior

1 Introduction

-ermal power is regarded as one of the most significantmethods to generate electric energy However this pro-cess is frequently used to produce a large amount of fly ashin a solid waste which makes a safe and effective treat-ment [1ndash3] Part of the fly ash is utilized as an additive inother production activities to improve the performance ofconcrete Otherwise the fly ash could end up in landfills[4 5] Fly ash stratum is characterized by low bearingcapacity higher settlement and long settlement perioddue to the presence of fly ash [6 7] -ese properties couldpose a severe threat to the safety of buildings -e cement-fly ash shows advantages such as high efficiency conve-nience and low cost for which it has been widely used in

the weak stratum where high water content and highcompressibility are a commonplace [8ndash10]

To date plenty of studies have been performed to in-vestigate the mechanical properties of fly ash concrete byexploring the characteristics of adding fly ash into concreteMeanwhile the static characteristics of fly ash concrete havebeen analyzed in detail -e relevant results have clearlyindicated the changes to the mechanical properties such asunconfined compressive strength and microstructureGolewski [11] compared 20 and 30 fly ash content on theperformance of concrete which led to the discovery that thestrength of the test specimens increased with the fly ashcontent Meanwhile the fracture toughness was enhancedAs indicated by Xiao et al [12] the initial increase instrength of cement soil mixed with fly ash was lower

HindawiAdvances in Civil EngineeringVolume 2020 Article ID 6410246 11 pageshttpsdoiorg10115520206410246

compared to pure cement soil After 28 days the strength offly ash cement-soil increased at a faster pace due to poz-zolanic reaction Fan et al [13] conducted analysis of theeffect created by mortar with different replacement ratios offly ash-to-low-heat Portland cement which led to theconclusion that fly ash could be effective in reducing the totalheat and heat rate of hydration of Portland cement despitethe hydrate phase species remaining unchanged throughoutthe process Deschner et al [14] carried out a study on thehydration reaction of low-calcium fly ash and calcium sil-icate cement from the microscopic point with the assistanceof X-ray diffraction (XRD) obtaining the result that fly ashplayed role of fillers in the early hydration reaction systemand the content of Ca(OH)2 reduced at a slow pace in thesolution indicating that the pozzolanic reaction increasedthe late strength As the aforementioned studies on themechanical properties of test are primarily focused on the flyconcrete they could only provide the basic theories on thecement-fly ash system

However the focus of these studies is mainly placed onthe experimental results obtained under static load Bycontrast the research focusing on the characteristics ofimpact load remains quite limited With regard to engi-neering projects the cement-fly ash foundation is subject toboth static load and dynamic load for instance constructionvibrations vehicle-induced vibrations earthquake andother types of dynamic load [15ndash18] As for dynamic load ittends to have a significant impact on the performance ofmaterials and structures for which it is of great significanceto conduct a study on the mechanical properties possessedby cement-fly ash under dynamic load

At present the split Hopkinson pressure bar (SHPB)device has been extensively applied to assess the dynamicmechanical properties exhibited by the materials with astrain rate of 102 sminus1ndash104 sminus1 [19 20] Chen et al [21] adoptedthe method of SHPB to carry out a study on the dynamicmechanical properties of cement composites with differentfly ash contents which led to the discovery that the fly ashcement composites showed strain rate dependency andmaintained plastic flow during the impact processMohamed et al [22] conducted a SHPB test and appliedother methods to investigate the mechanical properties ofconcrete under high-volume fly ash with a strain rateranging from 3012 to 10142 sminus1 which led to the resultsindicating that the impact resistance of fly ash cementspecimens was more desirable compared to pure cementChien et al [23] assessed the influence of two differentmethods (static compression and SHPB experiments) on thecement-fly ash samples which led to the conclusion that thestrain rate had a more significant impact on the strength

Up to now a number of studies have been conducted onthe work of fly ash as an ameliorant to enhance the prop-erties of concrete However the number of investigationsabout fly ash stabilized by cement remains limited -ere-fore in this work the unconfined compressive strength testand the impact test were adopted to study the mechanicalproperties of cement-fly ash Meanwhile the variations inmicrostructure and material were obtained using XRD andSEM

2 Materials and Methods

21 Experimental Materials -e fly ash used in the exper-iment was collected from a construction site located inShangyao Huainan city China -e field was covered withfly ash that is the by-product of a power plant and fly ashwas widely distributed across the plant To remove soil thesurface clay layer was removed in the first place with thedepth of soil being 2-3 meters -e undisturbed soil wasmostly powdery of gray-brown color containing agglom-erates -e particle size composition of the fly ash is shownin Table 1 and the chemical composition index is presentedin Table 2 According to the table the fly ash refers to low-grade and low-calcium raw fly ash

-e Portland composite cement of the strength level of325 was adopted

22 Test Principle In accordance with the standard ofTechnical code for ground treatment of buildings (JGJ79-2012) the fly ash was first filtered using a 5mm sieve toremove impurities such as agglomeration and organicsbefore being placed at 105degC to obtain the dry fly ash

23 Preparation Samples of UCS Test In engineering thevalue of cement content was 12 in cement-fly ash forwhich the content of cement was set to 12 (mass ratio todry fly ash) during the production of samples -e relevantparameters of the unconfined compression test are listed inTable 3 -e dried fly ash water and cement with the mixproportion were thoroughly mixed in the blender to ensureuniformity -e 100mm cube samples were used (with therelease agent applied evenly in the mold) -e molds withmixture were placed into the concrete standard curing roomuntil the removal of the molds Subsequently the cement-flyash samples were placed in a Ca(OH)2 solution for curinguntil the curing time was reached

24 Preparation Samples of SHPB Test In order to preventthe potential size effect on the split Hopkinson pressure bar(SHPB) test [24 25] the mixtures of fly ash cement andwater were poured into a cylindrical mold with a height of25mm and a diameter of 50mm for the impact test to beconducted Table 4 shows the relevant parameters of theimpact test Both sample production and curing were per-formed to the same standard as the unconfined compressivetest

25 Experimental Apparatus

251 -e Test Machine of UCS -e UCS tests were per-formed on a WAW-1000 universal test machine at the StateKey Laboratory ofMining Response andDisaster Preventionand Control in Deep CoalMine Anhui University of Scienceand Technology As seen from Figure 1(a) the unconfinedcompression test apparatus was used to perform the test andFigure 1(b) illustrates the test sample used for unconfinedcompressive test

2 Advances in Civil Engineering

252 -e SHPB Test Device As shown in Figure 2 a smallamount of Vaseline was applied to the rounded surfaces forreducing friction [26] -e SHPB test device was employed toassist with this study obtained from the School of Civil En-gineering and Architecture of Anhui University of Science andTechnology -e length of the striker bar incident bar andtransmitted bar is 060m 240m and 120m respectively -edensity elastic modulus and longitudinal wave velocity of eachbar are 78 gcm3 210GPa and 5190ms -e value of gaspressure is set to 02MPa in this study

253 XRD and SEM Test In order to establish the reactionmechanism of materials in cement-fly ash the XRD andSEM devices sourced from the Analytical Testing Center ofAnhui University of Science and Technology were applied inthe study -e XRD patterns of pure fly ash and the cement-fly ash sample with different curing time were analyzed byusing MDI Jade software

3 Test Results and Analysis

When the cement-fly ash samples were subject to vibrationblack bubbles were observed on the surface of the cement-flyash samples In the meantime a large number of colorless

bubbles emerged from the periphery of mold and plenty offree water was precipitated on the surface After the curingtime had been reached (7 d 30 d 60 d 90 d 120 d) theintegrity of the test block reached a satisfactory level -esamples with flat surface and no obvious holes were selectedfor the UCS and DCS tests

31 Analysis of Unconfined Compressive Test Results

311 -e Relationship Curves of Stress-Strain under StaticLoad -e method of unconfined compressive test isadopted according to Technical code for ground treatmentof buildings (JGJ79-2012) -e six samples were collectedfrom each group for the unconfined compressive test withthe loading rate set to 3mmmin After removal of the errordata the average value was taken as the strength value of thetest samples As shown in Figure 3 it can be seen that thefailure patterns of UCS test samples vary under differentcuring times When the curing time is 30 d two main crackswere presented in the meantime transverse expansioncracks were obtained in the upper parts of sample Howeverwhen the curing time is upregulated to 120 d a small part offragments peeled from the sample and an approximatelylinear crack was run through the whole sample It is sug-gested that with an increase of curing time the failures beginto be changed from the plastic to the brittle deformation

-e stress-strain curves of 7 d 30 d 60 d 90 d and 120 dof cement-fly ash samples with the cement content of 12are shown in Figure 4 When the curing time ranges from 0to 30 d the test samples pass through the initial compactionsection and then the elastic phase and the yielding stage arepresented respectively When the curing time is extendedfrom 30 d to 120 d a little elastic phase and a platformsegment are observed between the initial compaction sectionand the elastic phase which suggests that the cement-fly ashsamples show a clear sign of plastic failure in the initial stageof curing time (7 d) and the brittle failure is manifested inthe later curing time -erefore the typical relationship ofstress-strain is determined by analyzing the relationshipbetween stress-strain and varying curing time with theresults presented in Figure 5

Figure 5 illustrates the typical stress-strain characteristiccurve of cement-fly ash which can be roughly split into 6different sections -e first one is the initial compaction stage(ondasha) when the particles are vertically displaced by force andthe pore volume is reduced-e second one is the initial elasticstage (a-b) when the curve is approximately straight -ecement-fly ash samples exhibit approximate elastic deforma-tion which is caused by the hydration products and the in-clusions of hydrated product Besides the particles of fly ashare compacted under the condition of load and the porevolume is further reduced -e third one is the platform stage(b-c) -is section lasts from the compaction section to theelastic stage -e hydration products the inclusion of fly ashand hydrated products and the unreacted materials contributeto the formation of a stress structure as facilitated by the effectof compaction Moreover the internal pores of the test sampleare gradually reduced to their minimum-e fourth one is the

Table 3 -e parameters of unconfined compressive test

Cementcontent ()

Curing time(d)

Moisturecontent ()

Samples of eachgroup

12 7 30 60 90and 120 3500 6

Table 4 -e parameters of dynamic impact test

Cementcontent ()

Curing time(d)

Moisturecontent ()


12 7 30 60and 90 3500 4

Table 1 Particle size composition of the fly ash

Particle size group (mm) Average ()5ndash20 21720ndash10 10610ndash05 21305ndash025 812025ndash01 779001gt 863

Table 2 Chemical composition of fly ash

Chemical composition Average ()SiO2 5849Al2O3 2919Fe2O3 465CaO 233K2O 132SO3 130Loss on ignition 05

Advances in Civil Engineering 3

(a) (b)

Figure 1 -e unconfined compressive strength test

Figure 2 -e SHPB test

(a) (b)

Figure 3 -e failure patterns of UCS test samples


elastic phase (c-d) when the stress is on the rise with strain andthe curve conforms approximately to elastic deformation -efifth one is the yield stage (d-e) As ε increases the growth rateof stress is reduced to zero gradually Meanwhile the value ofstress is maximum-e sixth and last one is the failure stage (e-f) as the strain continues to increase the stress graduallydeclines and the test sample breaks

312 -e Variation Laws of UCS As shown in Figure 6when the curing time is extended from 7d to 120d the UCSincreases gradually from 064MPa to 314MPa -e UCS ofcement-fly ash samples (7 d) is shown to be 064MPa and theUCS at the curing time of 30d is observed to surge by 11562to 138MPa At the curing time of 60d the UCS is seen on therise from 138MPa (30d) to 232MPa (60d) with the rate ofincrease reaching 6812 Nevertheless when the curing timereaches 90d the rate of increase for UCS plunges from 6832(60d) to merely 1853 (90d) while the value of UCS reaches275MPa When the curing time is extended to 120d thegrowth rate decreases on a continued basis to 1418withUCSreaching 314MPa which suggests that the value of UCS in-creases with curing time and the growth rate decreases from11562 to the minimum value of 1418-e variation law ofgrowth rate is that the value of early curing time (0ndash60d) ishigher than that in the later stage

32 Analysis of SHPB Test Results As shown in Figure 7 thetypical waveforms of the cement-fly ash samples are dis-covered including incident pulse transmitted pulse andreflected pulse and the waveforms are smooth (select the30 d sample waveforms)

As can be observed from Figure 8 under the condition ofcuring time the cement-fly ash samples display differentpatterns of failure depending on fragment size and thenumber of fragments At the gas pressure of 020MPa thefailure modes of cement-fly ash are basically powdery withvarying curing time However with the increase in curing

time the degree of broken fragments and amount ofpowdered materials decrease obviously In the meantimethe size of fragments and the number of broken fragmentsincrease remarkably indicating that the degree of sampleintegrity increases with the curing time

According to the two-wave method the stress and strainof the samples can be obtained respectively [27] -e

Cv = 1558Cv = 1306Cv = 930

Cv = 673

UCS

(MPa

)

Cv = 241400

05

10

15

20

25

30

35

40

45

20 40 60 80 100 1200Curing time (d)

Figure 6 Variation law of UCS

Volta

ge (V

)

Incident pulse

Transmitted pulse

Reflected pulse

ndash08

ndash06

ndash04

ndash02

00

02

04

06

02 04 06 08 1000Time (ms)

Figure 7 -e typical waveforms of the samples

Stre

ss (M

Pa)

7 (d)30 (d)60 (d)

90 (d)120 (d)

00

05

10

15

20

25

30

35

05 10 15 20 25 30 35 40 45 5000Strain ()

Figure 4 -e static stress-strain curves of cement-fly ash samples

a

Peak stress

f

Strain ()o

b

c

d

e

Stre

ss (M

Pa)

Figure 5 Typical stress-strain characteristic curve of cement-flyash


relevant analytical formula applied to the determination ofparameters is expressed as follows

εS(t) 2c0

LS

1113946t

0εr(t)dt

σS(t) SBE

SS

εt(t)

(1)

where εS(t) and σS(t) represent the strain and stress re-spectively c0 SB and E denote the longitudinal wave ve-locity cross-sectional area and elastic modulus of the barrespectively LS and SS indicate respectively the length andthe cross-sectional area of the cement-fly ash samples andεr(t) and εt(t) represent the reflected pulse and the trans-mitted pulse respectively

It can be observed from Figure 9(a) that under differentcuring times (7 30 60 and 90d) the stress-strain curves ofcement-fly ash show different characteristics of failure Forinstance when the curing time increases from 7 to 60d thecurves exhibit approximate elastic deformation firstly and thenenter platform stage After the stress peak value it decreasesrapidly indicating a plastic failure However when curing for90d the typical failure of brittle is shown in the stress-straincurve and the stress increases with growth of the strain untilreaching the peak value Finally it decreases gradually Ad-ditionally as seen from Figure 9(b) as the curing time variesDCS changes from the initial 104MPa to 513MPa It is 104199 385 and 513MPa respectively suggesting that thehydration products were generated constantly and the me-chanical performance of cement-fly ash was enhanced

-ere is a lot of information obtained from Figure 10(a)and the cement-fly ash shows variations of compressionstrength under static and impact load conditions At thesame curing time the value of DCS is higher than that ofUCS DIF is defined as the modulus of DCS to UCS and theformula of DIF is expressed as follows

DIF σd

σS

(2)

where σd and σS represent the stress of SHPB and unconfinedcompression tests respectively In Figure 10(b) the change ofthe DIF and curing time is observed When the curing timeincreases the DIF decreases first and then climbs back Underthe 7d initial curing the value of DIF is 164 but the DIF falls tothe lowest value at 143 after a curing time of 30d In com-parison the value of DIF increases with curing time and thevalues of DIF with curing time of 60d and 90d being 166 and187 respectively-e experimental data indicate that the load-bearing capacity of cement-fly ash shows different character-istics under the static and impact load conditions whichmeansthat the test samples are subjected to the impact test -esamples absorb more energy than that of static test indicatingthat more cracks are produced in the samples and the com-pression strength increases

33 Analysis of Microstructure

331 Analysis of XRD Phase -e XRD results of fly ash areshown in Figure 11 -e phases of fly ash are mullite phaseand quartz phase respectively as analyzed using the Jade

7d

60d

30d

90d

Figure 8 -e failure patterns of SHPB test samples


software Despite this even a small amount of Fe2O3 andCaO is not observed in the XRD spectrum

To facilitate the study on the variation laws of material twosamples under the curing time of 7 d (number A) and 120d(number B) were applied to conduct the test of XRD in cement-fly ash composition Figure 12 presents the XRD spectrum of Aand B and fly ash with the curve A suggesting that the gypsumhas been generated -at is to say the hydration of cement ismaintained In the meantime the CaCO3 phase has beenspotted in the spectrum Nevertheless in comparison with thefly ash the diffraction peak value of quartz shows a sharpdecline which implies the start to the pozzolanic reaction In

curve B the gypsum phase disappears which can explain whythe cement has hydrated completely while the diffraction peakof quartz continues a declining trend indicating that thepozzolanic reaction of fly ash is the major source of hydrationproducts in the later stage

332 Analysis Results of SEM -e cement-fly ash samplesof A (7 d) and B (120 d) were tested for the SEM and theresults are indicated in Figure 13

As shown in Figure 13 the amount of hydrationproducts increases with the curing time suggesting that the

Stre

ss (M

Pa)

DCS

UCS

00

05

10

15

20

25

30

35

40

45

50

55

9060307Curing time (d)

(a)

DIF

20 40 60 80 1000Curing time (d)

13

14

15

16

17

18

19

20

(b)

Figure 10 Relationship of strength between static and impact load test (a) -e relationship of DCS and UCS (b) -e curve of DIF withdifferent curing times

Stre

ss (M

Pa)

7 (d)30(d)

60(d)90(d)

00

05

10

15

20

25

30

35

40

45

50

55

05 10 15 20 25 3000Strain ()

(a)

Cv = 474

Cv = 488

Cv = 1005

DCS

(MPa

)

Cv = 1362

00

05

10

15

20

25

30

35

40

45

50

55

20 40 60 80 1000Curing time (d)

(b)

Figure 9 Test results of impact test (a) -e stress-strain curves of impact test (b) Variation law of DCS


interspace in the cement-fly ash is reduced gradually andthat the structure of cement-fly ash is made dense due to theeffect of cementation Under the curing time of 7 d the C-S-H gel gives rise to inclusions by encapsulating microbeadsand amorphous particles which are filled in the pores of thecement-fly ash despite a large number of pores present inthe interspace between the inclusions of each other -emeshy C-S-H gel can be observed after the curing time isextended from 7 d to 120 d Under alkaline environment thepozzolanic activity of fly ash is initiated the products of thefly ash hydrating are attracted to the surface of fly ashparticles and the interspace continues to diminish

From the XRD spectrums and the SEM image it can beknown that the cementation of cement-fly ash has twosources with one being the cement hydration in the earlystage and the other one being pozzolanic reaction in the

later stage -e hydration of ordinary Portland cement isprimarily 3CaOmiddotSiO2 of the cement clinker mineralsreacting with H2O and the reaction equation is expressedas follows

3CaO middot SiO2 + nH2O xCaO middot SiO2 middot yH2O +(3 minus x)Ca(OH)2

(3)

-e reaction equation is simplified as follows

C3S + nH C minus S minus H +(3 minus x)CH (4)

C3S is a gel and has a structure of foil and fiber grain witha low crystallization degree Besides this structure shows ahigher bearing capacity A part of CH is precipitated as a six-plate crystal and the rest dissolves into solution to facilitatethe pozzolanic reaction

Ca(CO)3 phaseQuartz phaseGypsum phase

Fly ash

A

B

Ca(CO)3

QuartzGypsum

Inte

nsity

(cou

nts)

10 20 30 40 50 60 7002θ (degree)

Figure 12 -e XRD spectrums of test samples

clubs spades

spades

clubs

clubsclubs

clubs

Mullite phase Quartz phase

clubs

spades

clubs

spades

Mullite phaseQuartz phase

Inte

nsity

(cou

nts)

0

2000

4000

6000

8000

10000

12000

14000

10 20 30 40 50 60 7002θ (degree)

Figure 11 -e XRD spectrum of fly ash


(a) (b)

(c) (d)

(e) (f )

(g) (h)

Figure 13 SEM observations of A and B (a) A1 (times500) (b) B1 (times500) (c) A2 (times2000) (d) B2 (times2000) (e) A3 (times4000) (f ) B3 (times4000) (g) A4(times6000) (h) B4 (times6000)


In alkaline environment the glass phase on the graysurface dissolves at a slow pace and the active objects ofSiO2 Al2O3 can be obtained-ese substances are capable ofreaction with water and CH to generate xCaOmiddotSiO2middotnH2Oand xCaOmiddotAl2O3middotnH2O and the reaction equations areshown as follows

SiO2 + xCa(OH)2 +(n minus 1)H2O xCaO middot SiO2 middot nH2O(5)

Al2O3 + xCa(OH)2 +(n minus 1)H2O xCaO middot Al2O3 middot nH2O(6)

4 Conclusions

In this study the static mechanical properties of cement-flyash with varying curing time were determined in the firstplace for comparison between static and dynamic load-en 7 d curing and 120 d curing were applied to the XRDand SEM Finally the mechanism of cement-fly ash wasexplained in detail -e conclusions drawn from the studyare as follows

(1) -e UCS experiences an increase as the curing time isextended and the growth rate of UCS in the initial stageof the curing time is higher than that in the later stageAfter the curing time of 30d the stress-strain curves ofstatic load can be split into six different sections includinginitial compaction stage initial elastic stage platformstage elastic phase yield stage and failure stage

(2) Under the curing time varying from 0 to 90 d thecurves of the cement-fly ash samples exhibit thecharacteristics of plastic failure in the impact testHowever brittle failure was clearly observed obvi-ously at the curing time of 90 d -e DIF valuedecreases first and then increases gradually with thelowest value of 143 obtained on 30 d

(3) As revealed by the microstructure and mineral com-position analysis a mass of pores was present in ce-ment-fly ash and the hydration of cement is the mainsource of hydrated products in the initial stageHowever the hydrated products are derived from thepozzolanic reaction of the fly ash in the later stage

-e mechanical properties of cement-fly ash have beenachieved under static and impact load However in the engi-neering project various curing agents will be added in the ce-ment-fly ash so that the characteristics of the cement-fly ashwithdifferent curing agents will be revealed in the future research

Data Availability

-e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

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

Acknowledgments

-is research was funded by the Major Universities NaturalScience Research Project in Anhui Province (KJ2016SD19)the National Natural Science Foundation of China(41977236 41672278 and 41271071) and the Natural Sci-ence Foundation of Jiangxi Province (2019ACBL20002)-eauthors sincerely thank the School of Civil Engineering andArchitecture National Engineering Laboratory for DeepShaft Construction Technology in Coal Mine in AnhuiUniversity of Science and Technology for providing theexperiment conditions

References

[1] Z X Yue and J N Chen ldquoFly ash the status of resource-oriented utilization in construction materialrdquo AdvancedMaterials Research vol 753ndash755 pp 628ndash631 2013

[2] S d Mao Z Li and Y Fang ldquoCurrent status of research onthe utilization of fly ashrdquo Concrete vol 7 pp 82ndash84 2011

[3] Z T Yao X S Ji P K Sarker et al ldquoA comprehensive reviewon the applications of coal fly ashrdquo Earth-science Reviewsvol 141 pp 105ndash121 2015

[4] M Ahmaruzzaman ldquoA review on the utilization of fly ashrdquoProgress in Energy and Combustion Science vol 36 no 3pp 327ndash363 2010

[5] Y S Luo J Li and A Chan ldquoStudy on the engineeringproperty of mixed-soil fly ashrdquo Advances in EnvironmentalGeotechnics vol 10 pp 721ndash727 2009

[6] H K Kim and H K Lee ldquoCoal bottom ash in field of civilengineering a review of advanced applications and envi-ronmental considerationsrdquoKSCE Journal of Civil Engineeringvol 19 no 6 pp 1802ndash1818 2015

[7] P S Toth H T Chan and C B Cragg ldquoCoal ash as structuralfill with special reference to Ontario experiencerdquo CanadianGeotechnical Journal vol 25 no 4 pp 694ndash704 1988

[8] J P Ming andW B Zhao ldquoTriaxial test and calculation aboutcollapsibility deformation of coal ashrdquo Rock and Soil Me-chanics vol 25 pp 32ndash38 2004

[9] Q Meng L Shao and Q Y Shi ldquoExperimental study on themechanical properties of fly ash cement soilrdquo Journal ofUniversity of Shanghai for Science and Technology vol 39pp 490ndash496 2017

[10] H Yanli ldquoBackfilling technology of substituting waste and flyash for coal underground in China coal mining areardquo En-vironmental Engineering amp Management Journal vol 10no 6 pp 769ndash775 2011

[11] G L Golewski ldquoEffect of curing time on the fracturetoughness of fly ash concrete compositesrdquo Composite Struc-tures vol 185 pp 105ndash112 2018

[12] H Xiao W Shen and F H Lee ldquoEngineering properties ofmarine clay admixed with Portland cement and blendedcement with siliceous fly ashrdquo Journal of Materials in CivilEngineering vol 29 no 10 Article ID 04017177 2017

[13] Z H Fan J J Zeng J B Xiong et al ldquoHydration charac-teristic of low heat Portland cement mixtures with fly ash orslagrdquo Port ampWaterway Engineering vol 599 pp 63ndash69 2019

[14] F Deschner F Winnefeld B Lothenbach et al ldquoHydration ofPortland cement with high replacement by siliceous fly ashrdquoCement and Concrete Research vol 42 no 10 pp 1389ndash14002012

[15] S Paya A N Mohammad U J Alengaram et al ldquoEngi-neering properties of lightweight aggregate concrete


containing limestone powder and high volume fly ashrdquoJournal of Cleaner Production vol 135 pp 148ndash157 2016

[16] C Gunasekara D Law and S Setunge ldquoDesign of ternaryblend high-volume fly ash concrete mixes using hydratedlimerdquo in Proceedings of the 6th International Conference onDurability of Concrete Structures vol 18 Leeds UK 2018

[17] Y Al-Salloum T S M Almusallam H I Abbas et al ldquoRatedependent behavior and modeling of concrete based on SHPBexperimentsrdquo Cement and Concrete Composites vol 55pp 34ndash44 2015

[18] Q Sun B Li S Tian et al ldquoCreep properties of geopolymercemented coal gangue-fly ash backfill under dynamic dis-turbancerdquo Construction and Building Material vol 191no 10 pp 644ndash654 2018

[19] J E Field S M Walley and W G Pround ldquoReview ofexperimental techniques for high rate deformation and shockstudiesrdquo International Journal of Impact Engineering vol 30no 7 pp 725ndash772 2004

[20] S Q Zhou D W Zhou Y F Zhang W-j Wang and D LildquoResearch on the dynamic mechanical properties and energydissipation of expansive soil stabilized by fly ash and limerdquoAdvances in Materials Science and Engineering vol 2019Article ID 5809657 13 pages 2019

[21] Z T Chen Y Z Yang and Y Tao ldquoImpact properties ofengineered cementitious composites with high volume fly ashusing SHPB testrdquo Journal of Wuhan University of Technology-Materials Science Edition vol 27 2012

[22] H M Mohamed A M Azrul H Roszilah et al ldquoDynamicproperties of high volume fly ash nanosilica (NVFANS)concrete subjected to combined effect of high strain rate andtemperaturerdquo Latin American Journal of Solids and Structuresvol 15 no 1 2018

[23] Y T Chien R Hamid and M Kasmuri ldquoDynamic stress-strain behaviour of steel fiber reinforced high-performanceconcrete with fly ashrdquo Advances in Civil Engineeringvol 2012 Article ID 907431 6 pages 2012

[24] J L Tao Y Z Chen and C J Tian ldquoAnalysis of the inertialeffect of the cylindrical specimen in SHPB systemrdquo ActaMechanica Solida Sinica vol 26 no 1 pp 107ndash110 2005

[25] Q Ping M J Wu P Yuan et al ldquoExperimental study ondynamic mechanical properties of high temperature sand-stone under impact loadsrdquo Chinese Journal of Rock Mechanicsand Engineering vol 38 pp 782ndash792 2019

[26] W Z Zhong A Rusine T Jankowiak et al ldquoInfluence ofinterfacial friction and specimen configuration in splitHopkinson pressure bar systemrdquo Tribology Internationalvol 90 pp 1ndash14 2015

[27] L Song and S S Hu ldquoTwo-wave and three-wave method inSHPB data processingrdquo Explosion and Shock Waves vol 25no 4 pp 368ndash373 2005


compared to pure cement soil After 28 days the strength offly ash cement-soil increased at a faster pace due to poz-zolanic reaction Fan et al [13] conducted analysis of theeffect created by mortar with different replacement ratios offly ash-to-low-heat Portland cement which led to theconclusion that fly ash could be effective in reducing the totalheat and heat rate of hydration of Portland cement despitethe hydrate phase species remaining unchanged throughoutthe process Deschner et al [14] carried out a study on thehydration reaction of low-calcium fly ash and calcium sil-icate cement from the microscopic point with the assistanceof X-ray diffraction (XRD) obtaining the result that fly ashplayed role of fillers in the early hydration reaction systemand the content of Ca(OH)2 reduced at a slow pace in thesolution indicating that the pozzolanic reaction increasedthe late strength As the aforementioned studies on themechanical properties of test are primarily focused on the flyconcrete they could only provide the basic theories on thecement-fly ash system

However the focus of these studies is mainly placed onthe experimental results obtained under static load Bycontrast the research focusing on the characteristics ofimpact load remains quite limited With regard to engi-neering projects the cement-fly ash foundation is subject toboth static load and dynamic load for instance constructionvibrations vehicle-induced vibrations earthquake andother types of dynamic load [15ndash18] As for dynamic load ittends to have a significant impact on the performance ofmaterials and structures for which it is of great significanceto conduct a study on the mechanical properties possessedby cement-fly ash under dynamic load

At present the split Hopkinson pressure bar (SHPB)device has been extensively applied to assess the dynamicmechanical properties exhibited by the materials with astrain rate of 102 sminus1ndash104 sminus1 [19 20] Chen et al [21] adoptedthe method of SHPB to carry out a study on the dynamicmechanical properties of cement composites with differentfly ash contents which led to the discovery that the fly ashcement composites showed strain rate dependency andmaintained plastic flow during the impact processMohamed et al [22] conducted a SHPB test and appliedother methods to investigate the mechanical properties ofconcrete under high-volume fly ash with a strain rateranging from 3012 to 10142 sminus1 which led to the resultsindicating that the impact resistance of fly ash cementspecimens was more desirable compared to pure cementChien et al [23] assessed the influence of two differentmethods (static compression and SHPB experiments) on thecement-fly ash samples which led to the conclusion that thestrain rate had a more significant impact on the strength

Up to now a number of studies have been conducted onthe work of fly ash as an ameliorant to enhance the prop-erties of concrete However the number of investigationsabout fly ash stabilized by cement remains limited -ere-fore in this work the unconfined compressive strength testand the impact test were adopted to study the mechanicalproperties of cement-fly ash Meanwhile the variations inmicrostructure and material were obtained using XRD andSEM

2 Materials and Methods

21 Experimental Materials -e fly ash used in the exper-iment was collected from a construction site located inShangyao Huainan city China -e field was covered withfly ash that is the by-product of a power plant and fly ashwas widely distributed across the plant To remove soil thesurface clay layer was removed in the first place with thedepth of soil being 2-3 meters -e undisturbed soil wasmostly powdery of gray-brown color containing agglom-erates -e particle size composition of the fly ash is shownin Table 1 and the chemical composition index is presentedin Table 2 According to the table the fly ash refers to low-grade and low-calcium raw fly ash

-e Portland composite cement of the strength level of325 was adopted

22 Test Principle In accordance with the standard ofTechnical code for ground treatment of buildings (JGJ79-2012) the fly ash was first filtered using a 5mm sieve toremove impurities such as agglomeration and organicsbefore being placed at 105degC to obtain the dry fly ash

23 Preparation Samples of UCS Test In engineering thevalue of cement content was 12 in cement-fly ash forwhich the content of cement was set to 12 (mass ratio todry fly ash) during the production of samples -e relevantparameters of the unconfined compression test are listed inTable 3 -e dried fly ash water and cement with the mixproportion were thoroughly mixed in the blender to ensureuniformity -e 100mm cube samples were used (with therelease agent applied evenly in the mold) -e molds withmixture were placed into the concrete standard curing roomuntil the removal of the molds Subsequently the cement-flyash samples were placed in a Ca(OH)2 solution for curinguntil the curing time was reached

24 Preparation Samples of SHPB Test In order to preventthe potential size effect on the split Hopkinson pressure bar(SHPB) test [24 25] the mixtures of fly ash cement andwater were poured into a cylindrical mold with a height of25mm and a diameter of 50mm for the impact test to beconducted Table 4 shows the relevant parameters of theimpact test Both sample production and curing were per-formed to the same standard as the unconfined compressivetest

25 Experimental Apparatus

251 -e Test Machine of UCS -e UCS tests were per-formed on a WAW-1000 universal test machine at the StateKey Laboratory ofMining Response andDisaster Preventionand Control in Deep CoalMine Anhui University of Scienceand Technology As seen from Figure 1(a) the unconfinedcompression test apparatus was used to perform the test andFigure 1(b) illustrates the test sample used for unconfinedcompressive test












Cementcontent ()

Curing time(d)

Moisturecontent ()


12 7 30 60 90and 120 3500 6


Cementcontent ()

Curing time(d)

Moisturecontent ()


12 7 30 60and 90 3500 4






(a) (b)



(a) (b)









Cv = 1558Cv = 1306Cv = 930

Cv = 673

UCS

(MPa

)

Cv = 241400

05

10

15

20

25

30

35

40

45

20 40 60 80 100 1200Curing time (d)


Volta

ge (V

)

Incident pulse

Transmitted pulse

Reflected pulse

ndash08

ndash06

ndash04

ndash02

00

02

04

06

02 04 06 08 1000Time (ms)


Stre

ss (M

Pa)

7 (d)30 (d)60 (d)

90 (d)120 (d)

00

05

10

15

20

25

30

35

05 10 15 20 25 30 35 40 45 5000Strain ()


a

Peak stress

f

Strain ()o

b

c

d

e

Stre

ss (M

Pa)




εS(t) 2c0

LS

1113946t

0εr(t)dt

σS(t) SBE

SS

εt(t)

(1)




DIF σd

σS

(2)




7d

60d

30d

90d








Stre

ss (M

Pa)

DCS

UCS

00

05

10

15

20

25

30

35

40

45

50

55


(a)

DIF

20 40 60 80 1000Curing time (d)

13

14

15

16

17

18

19

20

(b)


Stre

ss (M

Pa)

7 (d)30(d)

60(d)90(d)

00

05

10

15

20

25

30

35

40

45

50

55

05 10 15 20 25 3000Strain ()

(a)

Cv = 474

Cv = 488

Cv = 1005

DCS

(MPa

)

Cv = 1362

00

05

10

15

20

25

30

35

40

45

50

55

20 40 60 80 1000Curing time (d)

(b)







(3)





Fly ash

A

B

Ca(CO)3

QuartzGypsum

Inte

nsity

(cou

nts)

10 20 30 40 50 60 7002θ (degree)


clubs spades

spades

clubs

clubsclubs

clubs


clubs

spades

clubs

spades


Inte

nsity

(cou

nts)

0

2000

4000

6000

8000

10000

12000

14000

10 20 30 40 50 60 7002θ (degree)



(a) (b)

(c) (d)

(e) (f )

(g) (h)






4 Conclusions






Data Availability




Acknowledgments


References









































Cementcontent ()

Curing time(d)

Moisturecontent ()


12 7 30 60 90and 120 3500 6


Cementcontent ()

Curing time(d)

Moisturecontent ()


12 7 30 60and 90 3500 4






(a) (b)



(a) (b)









Cv = 1558Cv = 1306Cv = 930

Cv = 673

UCS

(MPa

)

Cv = 241400

05

10

15

20

25

30

35

40

45

20 40 60 80 100 1200Curing time (d)


Volta

ge (V

)

Incident pulse

Transmitted pulse

Reflected pulse

ndash08

ndash06

ndash04

ndash02

00

02

04

06

02 04 06 08 1000Time (ms)


Stre

ss (M

Pa)

7 (d)30 (d)60 (d)

90 (d)120 (d)

00

05

10

15

20

25

30

35

05 10 15 20 25 30 35 40 45 5000Strain ()


a

Peak stress

f

Strain ()o

b

c

d

e

Stre

ss (M

Pa)




εS(t) 2c0

LS

1113946t

0εr(t)dt

σS(t) SBE

SS

εt(t)

(1)




DIF σd

σS

(2)




7d

60d

30d

90d








Stre

ss (M

Pa)

DCS

UCS

00

05

10

15

20

25

30

35

40

45

50

55


(a)

DIF

20 40 60 80 1000Curing time (d)

13

14

15

16

17

18

19

20

(b)


Stre

ss (M

Pa)

7 (d)30(d)

60(d)90(d)

00

05

10

15

20

25

30

35

40

45

50

55

05 10 15 20 25 3000Strain ()

(a)

Cv = 474

Cv = 488

Cv = 1005

DCS

(MPa

)

Cv = 1362

00

05

10

15

20

25

30

35

40

45

50

55

20 40 60 80 1000Curing time (d)

(b)







(3)





Fly ash

A

B

Ca(CO)3

QuartzGypsum

Inte

nsity

(cou

nts)

10 20 30 40 50 60 7002θ (degree)


clubs spades

spades

clubs

clubsclubs

clubs


clubs

spades

clubs

spades


Inte

nsity

(cou

nts)

0

2000

4000

6000

8000

10000

12000

14000

10 20 30 40 50 60 7002θ (degree)



(a) (b)

(c) (d)

(e) (f )

(g) (h)






4 Conclusions






Data Availability




Acknowledgments


References































(a) (b)



(a) (b)









Cv = 1558Cv = 1306Cv = 930

Cv = 673

UCS

(MPa

)

Cv = 241400

05

10

15

20

25

30

35

40

45

20 40 60 80 100 1200Curing time (d)


Volta

ge (V

)

Incident pulse

Transmitted pulse

Reflected pulse

ndash08

ndash06

ndash04

ndash02

00

02

04

06

02 04 06 08 1000Time (ms)


Stre

ss (M

Pa)

7 (d)30 (d)60 (d)

90 (d)120 (d)

00

05

10

15

20

25

30

35

05 10 15 20 25 30 35 40 45 5000Strain ()


a

Peak stress

f

Strain ()o

b

c

d

e

Stre

ss (M

Pa)




εS(t) 2c0

LS

1113946t

0εr(t)dt

σS(t) SBE

SS

εt(t)

(1)




DIF σd

σS

(2)




7d

60d

30d

90d








Stre

ss (M

Pa)

DCS

UCS

00

05

10

15

20

25

30

35

40

45

50

55


(a)

DIF

20 40 60 80 1000Curing time (d)

13

14

15

16

17

18

19

20

(b)


Stre

ss (M

Pa)

7 (d)30(d)

60(d)90(d)

00

05

10

15

20

25

30

35

40

45

50

55

05 10 15 20 25 3000Strain ()

(a)

Cv = 474

Cv = 488

Cv = 1005

DCS

(MPa

)

Cv = 1362

00

05

10

15

20

25

30

35

40

45

50

55

20 40 60 80 1000Curing time (d)

(b)







(3)





Fly ash

A

B

Ca(CO)3

QuartzGypsum

Inte

nsity

(cou

nts)

10 20 30 40 50 60 7002θ (degree)


clubs spades

spades

clubs

clubsclubs

clubs


clubs

spades

clubs

spades


Inte

nsity

(cou

nts)

0

2000

4000

6000

8000

10000

12000

14000

10 20 30 40 50 60 7002θ (degree)



(a) (b)

(c) (d)

(e) (f )

(g) (h)






4 Conclusions






Data Availability




Acknowledgments


References





































Cv = 1558Cv = 1306Cv = 930

Cv = 673

UCS

(MPa

)

Cv = 241400

05

10

15

20

25

30

35

40

45

20 40 60 80 100 1200Curing time (d)


Volta

ge (V

)

Incident pulse

Transmitted pulse

Reflected pulse

ndash08

ndash06

ndash04

ndash02

00

02

04

06

02 04 06 08 1000Time (ms)


Stre

ss (M

Pa)

7 (d)30 (d)60 (d)

90 (d)120 (d)

00

05

10

15

20

25

30

35

05 10 15 20 25 30 35 40 45 5000Strain ()


a

Peak stress

f

Strain ()o

b

c

d

e

Stre

ss (M

Pa)




εS(t) 2c0

LS

1113946t

0εr(t)dt

σS(t) SBE

SS

εt(t)

(1)




DIF σd

σS

(2)




7d

60d

30d

90d








Stre

ss (M

Pa)

DCS

UCS

00

05

10

15

20

25

30

35

40

45

50

55


(a)

DIF

20 40 60 80 1000Curing time (d)

13

14

15

16

17

18

19

20

(b)


Stre

ss (M

Pa)

7 (d)30(d)

60(d)90(d)

00

05

10

15

20

25

30

35

40

45

50

55

05 10 15 20 25 3000Strain ()

(a)

Cv = 474

Cv = 488

Cv = 1005

DCS

(MPa

)

Cv = 1362

00

05

10

15

20

25

30

35

40

45

50

55

20 40 60 80 1000Curing time (d)

(b)







(3)





Fly ash

A

B

Ca(CO)3

QuartzGypsum

Inte

nsity

(cou

nts)

10 20 30 40 50 60 7002θ (degree)


clubs spades

spades

clubs

clubsclubs

clubs


clubs

spades

clubs

spades


Inte

nsity

(cou

nts)

0

2000

4000

6000

8000

10000

12000

14000

10 20 30 40 50 60 7002θ (degree)



(a) (b)

(c) (d)

(e) (f )

(g) (h)






4 Conclusions






Data Availability




Acknowledgments


References
































εS(t) 2c0

LS

1113946t

0εr(t)dt

σS(t) SBE

SS

εt(t)

(1)




DIF σd

σS

(2)




7d

60d

30d

90d








Stre

ss (M

Pa)

DCS

UCS

00

05

10

15

20

25

30

35

40

45

50

55


(a)

DIF

20 40 60 80 1000Curing time (d)

13

14

15

16

17

18

19

20

(b)


Stre

ss (M

Pa)

7 (d)30(d)

60(d)90(d)

00

05

10

15

20

25

30

35

40

45

50

55

05 10 15 20 25 3000Strain ()

(a)

Cv = 474

Cv = 488

Cv = 1005

DCS

(MPa

)

Cv = 1362

00

05

10

15

20

25

30

35

40

45

50

55

20 40 60 80 1000Curing time (d)

(b)







(3)





Fly ash

A

B

Ca(CO)3

QuartzGypsum

Inte

nsity

(cou

nts)

10 20 30 40 50 60 7002θ (degree)


clubs spades

spades

clubs

clubsclubs

clubs


clubs

spades

clubs

spades


Inte

nsity

(cou

nts)

0

2000

4000

6000

8000

10000

12000

14000

10 20 30 40 50 60 7002θ (degree)



(a) (b)

(c) (d)

(e) (f )

(g) (h)






4 Conclusions






Data Availability




Acknowledgments


References




































Stre

ss (M

Pa)

DCS

UCS

00

05

10

15

20

25

30

35

40

45

50

55


(a)

DIF

20 40 60 80 1000Curing time (d)

13

14

15

16

17

18

19

20

(b)


Stre

ss (M

Pa)

7 (d)30(d)

60(d)90(d)

00

05

10

15

20

25

30

35

40

45

50

55

05 10 15 20 25 3000Strain ()

(a)

Cv = 474

Cv = 488

Cv = 1005

DCS

(MPa

)

Cv = 1362

00

05

10

15

20

25

30

35

40

45

50

55

20 40 60 80 1000Curing time (d)

(b)







(3)





Fly ash

A

B

Ca(CO)3

QuartzGypsum

Inte

nsity

(cou

nts)

10 20 30 40 50 60 7002θ (degree)


clubs spades

spades

clubs

clubsclubs

clubs


clubs

spades

clubs

spades


Inte

nsity

(cou

nts)

0

2000

4000

6000

8000

10000

12000

14000

10 20 30 40 50 60 7002θ (degree)



(a) (b)

(c) (d)

(e) (f )

(g) (h)






4 Conclusions






Data Availability




Acknowledgments


References



































(3)





Fly ash

A

B

Ca(CO)3

QuartzGypsum

Inte

nsity

(cou

nts)

10 20 30 40 50 60 7002θ (degree)


clubs spades

spades

clubs

clubsclubs

clubs


clubs

spades

clubs

spades


Inte

nsity

(cou

nts)

0

2000

4000

6000

8000

10000

12000

14000

10 20 30 40 50 60 7002θ (degree)



(a) (b)

(c) (d)

(e) (f )

(g) (h)






4 Conclusions






Data Availability




Acknowledgments


References































(a) (b)

(c) (d)

(e) (f )

(g) (h)






4 Conclusions






Data Availability




Acknowledgments


References


































4 Conclusions






Data Availability




Acknowledgments


References































experimental study on mechanical properties of fly ash stabilized with...

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