shrinkage mechanism of laterite modified by lime and

Research ArticleShrinkage Mechanism of Laterite Modified byLime and Metakaolin

Yunzhi Tan 1 Yan Hu1 Rui Chen1 and Wenjing Sun2

1College of Civil Engineering and Architecture China ree Gorges University 8 University Road Yichang 443002 China2Department of Civil Engineering Shanghai University Shanghai 200433 China

Correspondence should be addressed to Yunzhi Tan yztanctgueducn

Received 22 February 2020 Accepted 24 June 2020 Published 24 July 2020

Academic Editor Junhui Zhang

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

In this study effects of metakaolin and lime on the microstructural characteristics unconfined compressive strength (UCS)shrinkage suction and shear resistance of laterite were investigated Soil samples treated with 5 wt of lime (LaL) or 4 wtmetakaolin and 5 wt of lime (LaLM) were prepared Samples with an optimal water content of 32 were compacted and curedfor 180 days followed by saturation and dehydration until the desirable water content of the samples was attainedampen the UCSshrinkage and suction and shear resistance of the samples at a normal stress of 200 kPa were determined In addition scanningelectron microscopy imaging as well as mercury intrusion porosimetry tests were performed to examine the microstructuralchanges Results indicate that the shrinkage of treated soil samples is significantly improved in comparison with that of theuntreated soil samples Lime effectively improves the UCS and shearing resistance of laterite Moreover metakaolin is composedof amorphous silicon and aluminium oxides and shared edge-face structures on the microscopic scale hence it can considerablycapture calcium ions from a lime solution generating cementitious hydrates in the interaggregates of laterite Results also revealedthat the combination of 5 wt of lime and 4 wt of metakaolin can improve the UCS and shearing resistance but the linearshrinkage is particularly restrained significantly decreasing by 4 times compared with that of the lime-treated soil sample and by 8times compared with that of the untreated soil sample ampe study results demonstrate that metakaolin and lime can be effectivelyused to improve laterite in lieu of the conventional lime treatment for mitigating geotechnical engineering disasters

1 Introduction

Laterite is the weathered product on parent rocks in hot andwet tropical climates It contains not only silicon and alu-minium oxides but also cementitious materials such as freeiron oxide hence it exhibits a red colour [1] It is widelydistributed in China (Hunan Yunnan and Guizhouprovinces as well as Guangxi Autonomous Region) andspans an area of 108 million square kilometres [2] Lateriteis present in problematic soil and it exhibits high watersensitivity It becomes mired when it absorbs a large amountof water and it shrinks and cracks when it loses waterMoreover under the long-term alternation of atmosphericrainfall and evaporation as well as other environmentalfactors laterite can lead to engineering accidents such asdecreased foundation bearing capacity slope cracking and

collapse [3 4] amperefore it is imperative to decrease orcontrol the water sensitivity of laterite

ampe water sensitivity of laterite is characterised by miringand water loss shrinkage [5] It is widely accepted that thelower the water content the greater the matrix suction andthe higher the strength of the unsaturated soil [6 7] ampusseveral researchers only focus on miring and believe that thepossibility of engineering accidents can be decreased as longas the migration or permeation of water in the soil is pre-vented However the shrinkage cracking behaviour of clay isextremely distinct [8 9] Some studies have reported thatwater loss shrinkage mainly causes a change in the porestructure of interaggregates rather than in that of intra-aggregates in compacted laterite [10] Although the loss ofwater increases thematrix suction it results in shrinkage andcracking leading to irreversible structural damage in

HindawiAdvances in Civil EngineeringVolume 2020 Article ID 6347597 9 pageshttpsdoiorg10115520206347597

compacted laterite ampus the increase in the matrix suctionand crack occurrence exerts opposite effects on the strengthof compacted laterite ampat is the cracking behaviour causedby the water loss shrinkage also should be consideredRecently researchers have reported that the shrinkage oflaterite can be hindered by the improvement of the initialcompactness water content or even adding some materialsuch as gravel [11ndash13] In addition the shrinkage of lateritecan be effectively ameliorated by the addition of lime [14]but whether lime-modified laterite can be applied in prac-tical engineering projects needs to be investigated further

Metakaolin exhibits high pozzolanic activity Whenkaolin is heated to 500degCndash700degC an amorphous material isproduced ampis material is 50ndash55 of SiO2 and 40ndash45 ofAl2O3 by weight and it is extremely reactive in an alkalinecalcium-rich solution In [15ndash17] it is reported that met-akaolin can efficiently absorb calcium hydroxide to con-sistently form a cementitious hydrate and kaolin absorbshydrated calcium ions which form a layer on the clayparticle surfaces and subsequently prevent the furtherdissolution of clay mineral platelets Metakaolin-contain-ing concretes exhibit behaviour similar to those of silica-fume-containing concretes that is the mechanical resis-tance is improved and the permeability and shrinkage ofconcrete are significantly reduced [18] However whethermetakaolin effectively impacts water sensitivity is notknown amperefore strength and shrinkage tests underdifferent moisture conditions on compacted specimens areconducted in this study Meanwhile the variation insuction was measured and microscopic tests were per-formed Finally the aforementioned formal tests revealedthe shrinkage mechanism of lime and metakaolin modifiedlaterite

2 Materials and Methods

21 Materials Laterite was obtained from Guilin GuangxiAutonomous Region (China) By X-ray fluorescence itschemical composition was determined to predominantlycomprise silicon aluminium oxide (74 wt) and iron oxide(19 wt) (Table 1) After the dried laterite was passedthrough a 05mm sieve its fundamental properties weremeasured according to the Chinese standard JTG E40-2007Table 2 summarizes the results As the liquid limit of lateriteexceeded 50 herein it was defined as a high liquid limitsoil Furthermore its optimum water content (302) andmaximum dry density (148 gcm3) were obtained by heavycompaction tests (Figure 1)

Lime was purchased from Suqian Jiangsu Province(China) and its chemical composition was predominantlyCaO (9834 wt) with a small amount of Al2O3 (057 wt)Its specific gravity was 232 and its initial water content was31 Metakaolin was purchased from Royal Dutch Shell plcand its chemical composition was predominantly Al2O3(462 wt) and SiO2 (495 wt) Its specific gravity was 263and its initial water content was 15 ampe particle distri-bution characteristics of laterite lime and metakaolin wereinvestigated using a Microtrac S3500 particle size analyser(Figure 2)

22 Sample Preparation To investigate the effects of met-akaolin and lime on the shrinkage of laterite six kinds ofspecimens were prepared (Table 3) Due to the differentspecific gravities of laterite lime andmetakaolin the specificgravity of mixed soil (Gm) was calculated as follows

Gm 1

1 minus Rl minus Rmk( 1113857Gla( 1113857 + RlGl( 1113857 + RmkGmk( 1113857 (1)

where Gmk Gl and Gla are the specific gravities of meta-kaolin lime and laterite respectively and Rmk andRl are themixing ratios (wt) of metakaolin and lime respectively

ampe relationship between the dry density (ρd) and initialvoid ratio (e0) was calculated as follows

ρd Gm

1 + e0 (2)

For comparison of test results all compacted sampleshave the same initial void ratio To be more specific theinitial dry density of the laterite specimens was 143 gcm3while those of the laterite-lime specimens and laterite-lime-metakaolin specimens were 1422 gcm3 and 1420 gcm3respectively

In this study the soil samples were dry mixed and thenwater was added to the mixture soils until the predictedwater content was attained to achieve sample moistureconditions Finally the mixtures of metakaolin andor lime-laterite with deionized water were compacted layer by layerin a sample compaction container until soil samples wereobtained with dimensions of 618mm (diameter)times 20mm(height) and 50mm (diameter)times 50mm (height) with aninitial water content of 32 Pure laterite samples wereprepared in the same manner as the control samples All testsamples exhibited the same initial void ratio to ensure thatdifferent samples exhibited the same initial pore volume

23 Experimental Procedures In this experiment aftercompaction all specimens were sealed and cured for 180days at 25degC which was followed by a saturation processampen each test was conducted as follows

(1) Shrinkage tests were conducted according to theChinese standard JTG E40-2007 [19]

(2) For the UCS tests and suction measurements somespecimens were placed in a chamber at a constanttemperature (55degC) and then their mass was esti-mated to determine the real-time water contentduring dehydration When the real-time watercontent approached the predetermined value thesamples were sealed and cured for 2 months in thechamber at 25degC to ensure homogeneity ampen10ndash20 g of each sample was used for suction mea-surement using a Decagon WP4C dewpointpotentiometer

Table 1 Major components of laterite

Composition Al2O3 SiO2 Fe2O3 TiO2 K2O OthersMass content () 406 333 191 24 21 25

2 Advances in Civil Engineering

(3) For direct shear tests some samples were dehydratedby the vapor equilibrium method (Table 4) Whenthe soil suction became constant (determined by thestabilization of the specimen mass) direct shear testswere conducted at a shear rate of 08mmmin undera vertical stress of 200 kPa

(4) For pore analysis tests after the specimens werefreeze-dried for 1 day a small block was used toobtain the pore size distribution with a Pore Master(PM 60GT) system

(5) For scanning electronmicroscopy (SEM) imaging todirectly determine the reaction mechanism in thetreated soil mixtures of compacted lime-kaolin andlime-metakaolin were used Each sample was

carefully cut into a size of 15mmtimes 15mmtimes 15mmto avoid disturbance and ensure porosity ampen thecut sample was placed into liquid nitrogen and thesample was dried by using a vacuum freeze-dryingdevice After drying the sample was used for SEManalysis

To further investigate the mechanism of metakaolin andlime modification of laterite X-ray diffraction (XRD) pat-terns thermogravimetric analysis (TGA) curves and infrared(IR) spectra were recorded to explain the manner in whichmetakaolin aids lime in restraining the shrinkage of laterite

3 Results and Discussion

31 X-Ray Diffraction (XRD) Results After the formation ofmetakaolin from kaolin by calcination at 500degCndash700degC XRDpatterns were recorded and the diffraction spectrum ofmetakaolin lacked clear diffraction peaks similar to those ofkaolin (Figure 3) Before calcination kaolin exhibited cleardiffraction peaks characteristic of kaolin but after calcina-tion these diffraction peaks disappeared indicating thatkaolin is transformed or disappeared during calcinationKonan et al [17] has reported the comparison of surfaceproperties between kaolin and metakaolin in concentratedlime solutions and also reported a similar result Kakali et al[20] has confirmed that kaolin is transformed to metakaolinduring calcination and becomes a high pozzolanic material

32 ermogravimetric Analysis (TGA) Results To under-stand the characteristics of metakaolin it is crucial to de-termine its composition and structure Kaolin comprisesfeldspar and mica particles with alumina-rich elements oracidic igneous rocks First it undergoes weathering anddisintegration and it is then deposited from Al(OH)3 andSi(OH)4 in solution Its chemical formula is Si2Al2O5(OH)4and its molecular structure is shown in Figure 4

Kaolin is transformed to metakaolin at high tempera-tures by dehumidification which is expressed as follows

Si2Al2O5(OH)4 ⟶500minus700degC Si2Al2O7 + 2H2O (3)

ampus four hydroxyl groups are transformed into twowater molecules and two oxygen anions remain in thematerial as shown in the following chemical reaction

4 OHminus( )⟶ 2H2O + O2minus (4)

In summary the hydrogen bond connected to the basicstructural unit disappears during dehumidification and thelaminated surface structure of kaolin is destroyed Figure 5shows the TGA curves of metakaolin and kaolin ampe experi-mental test conditions were as follows a TA thermogravimetricanalyser (SDT Q600) was utilized at a heating rate of 10degCminand a temperature range of 25degCndash1000degC under nitrogen

Table 2 Basic properties of laterite

Proportion Liquid limit () Plastic limit () Free swell () Optimum moisture content () Maximum dry density271 565 354 169 302 148 gcm3

12

13

14

15

Dry

den

sity

gcm

3

15 20 25 30 35 4010Water content ()

Wetting method

Drying method

Sr = 10

Sr = 09S

r = 08Sr = 07

Figure 1 Compaction curves of laterite

100

80

60

40

20

0

Pass

ing

()

10ndash1 100 101 102 103 104

Particle size (μm)

LateriteMetakaolinLime

Figure 2 Particle size distribution curves of testing materials

Advances in Civil Engineering 3

ampe results indicated that the weight of kaolin decreases by112 at 400degCndash750degCampeweight loss rate ofmetakaolin is lessthan 10 indicating that dehydroxylation was completedduring previous calcination In addition the weight loss ofkaolin at 400degCndash516degC is significantly greater than that at516degCndash750degC because the hydroxyl groups between the silicontetrahedron and the aluminoxy octahedron cannot escape fromthe kaolin as rapidly as those present on the surfaceampereforethe hydroxyl groups require a slow migration process

33 Infrared Spectroscopy (IR) Results After calcination thedistribution of the hydroxyl groups in kaolin also changedFigure 6 shows the IR spectra of metakaolin and kaolin

Table 4 Saturated salt solution and corresponding suction values (T 25degC)

Solution K2SO4 KCL NaCl KI NaBr K2CO3 MgCl2 CH3COOK LiClSuction (MPa) 376 2359 3892 5111 7568 11515 15294 20465 29914

Table 3 Testing plan

No Test name Sample category Initial state of sample

1 Shrinkage testLaLaLLaLM

e0 089ω 32

Ring knife sample(φ 618mmtimes 20mm)

2 Unconfined compression strength and suction test Same as above

e0 089ω 32

Cylinder sample(φ 50mmtimes 50mm)

3 Direct shear test Same as above

e0 089ω 32


4 Pore analysis test LaLLaLM

e0 089ω1 0 28

Side length of the cubeasymp15 cmNotice e0 is the porosity ratio after the sample was pressed ω is the original water content after the sample was pressed and ω1 is the water content of thesample during dehydration

K

K

K

KK

K KQKaolin

Metakaolin

10 20 30 40 50 60 70

Inte

nsity

(cou

nts)

K Kaolinite-1A (PDF14-0164)Q Quartz (PDF46-1045)

2θdeg (CuKα)

Figure 3 XRD pattern of kaolin and metakaolin

Silicatetrahedron

layer

Aluminoxyoctahedral

layer

O2ndash

Si4+

OHndash

A13+

Side

Surface

Figure 4 Basic structure unit of kaolin [21]

80

85

90

95

100

Wei

ght (

)

600400 10000 200 800Temperature (degC)

516degC

Δm =

11

5

KaolinMetakaolin

Figure 5 ampermogravimetric analysis curves of kaolin andmetakaolin


At a frequency range of 3200ndash4000 cmminus1 kaolinexhibited bands at 3680 and 3620 cmminus1 corresponding to theelongation vibrations of the hydroxyl group and the band at991 cmminus1 corresponds to the Si-O-Si elongation vibrationsampe band at 908 cmminus1 corresponds to the deformation vi-brations of the Al-O-H hydroxyl groups on the aluminafaces [17] (Figure 6) After calcination kaolin was trans-forms into metakaolin Four major changes are observed inthe IR spectrum (Figure 6(a)) (1)ampe peak corresponding tothe hydroxyl-bonded water disappear (2) the peak corre-sponding to Si-O-Si become broad and short (3) the peakcorresponding to Al-O-H nearly disappear (4) the peakcorresponding to Si-O-Al or Si-O-Mg observed at less than800 cmminus1 almost disappear As described above the com-bined water and structural water evaporated and the spatialarrangement of Si-O-Si Si-O-Al or Si-O-Mg in kaolinchange during calcination In addition notably the highreactivity of metakaolin has been reported to be also relatedto a change in the Al3+ coordination from octahedral inkaolin to tetrahedral in metakaolin (tetrahedral Al3+ istypically more reactive than octahedral Al3+ [22] ampereforethe high-temperature treatment leads to the increased ac-tivities of the silicon- and aluminium-containing groupsand these groups readily react with the calcium ions in thealkaline solution In fact a small amount of aggregate may beformed in metakaolin due to electrostatic interactions be-tween the edge and surface of the basic unit structure orincomplete dehydroxylation during which the structure istransforms from the original face-to-face ldquostackedrdquo structure

to an edge-to-surface ldquooverlappedrdquo shape (it can be seenclearly in SEM results (Figure 7))

Clearly metakaolin calcined from kaolin comprisessilica and alumina and kaolinite is the main mineral inlaterite ampe potential method for stabilizing laterite withmetakaolin and lime was found to be efficient and envi-ronmentally friendly

34 Shrinkage Strength andMicrotest Results Figure 8 showsthe shrinkage curves of the compacted specimens (La LaLand LaLM) All samples exhibit a shrinkage limit of 25 andthe linear shrinkage of LaL decreases from 195 to 091Notably the linear shrinkage of LaLM decreases by nearly afactor of 8 to 025 indicating that metakaolin can help limeto considerably hinder the shrinkage of laterite

Figure 9 shows the change in the suction of the com-pacted specimens (La LaL and LaLM) with the watercontent

Two series of samples were investigated saturated andunsaturated With the decrease in the water content suctiongradually increase especially at a water content of less than75 With the increase in suction the strength of theunsaturated soils increases However at a water content ofless than 25 the UCS of compacted laterite remained20MPa Notably at an extremely low water content theUCS decrease ampe saturated compacted laterite exhibits asimilar variation but its UCS is typically less than that ofcompacted laterite without dehydration at a water content ofless than 25 (Figure 10(a)) Kong et al [23] have proposedthat microcracks are formed in samples during dehydrationand the contribution of suction to the strength was opposedby the structural damage from the microcracks which ex-plains the phenomenon in Figure 10(a) (left) Nie et al [24]has hypothesises that saturation destroys the existingstructures or particle bonding in samples this process candecrease the strength of compacted laterite which wouldexplain the curve in Figure 10(a) (right)

Although the strengths of LaL and LaLM decreaseduring dehydration the values still exceed 20MPa underdifferent moisture conditions in contrast to that of lateriteIn contrast the strengths of LaL and LaLM increase ratherthan consistently decrease which is similar to that observedfor completely dried laterite samples (Figure 10(b)) ampisresult indicates that lime or metakaolin and lime can im-prove the strength of laterite during dehydration To furtherinvestigate the effect of dehydration on the compactedsamples direct shear strength was determined at the sametime Figure 11 shows the relationship between the directshear strength and water content

ampe direct shear strengths of LaL and LaLM are alwaysgreater than that of compacted laterite and the strength ofcompacted laterite initially increases and reaches a peak of05MPa at a water content of 25 which is near theshrinkage limit (Figure 8) this peak is followed by a de-creasing trend until a water content of 15 is attained ampeshear strength of compacted laterite reaches the peak at awater content of 275 during dehydration For treatedsoil the shear strength reaches the peak at a water content

100

80

60

40

20

100

80

60

40

20

0

Tran

smitt

ance

()

Tran

smitt

ance

()

4000 3200 2400 1600 800Wave number (cmndash1)

3680 36

20

(a)

(b)

Crest dissapeared

991

991

908

Figure 6 Infrared spectra of (a) metakaolin and (b) kaolin


of 25 followed by a decreasing trend In addition similartrends are observed in the UCS tests ampe UCS of untreatedsoil exhibits lower strength at all water contents after the

samples reach saturation and the treated soil maintains itsstrength even after saturation Yang [25] has reported thatseveral reticular cement substances are formed after the

(a) (b)

Figure 7 SEM images of (a) lime-kaolinite and (b) lime-metakaolin

25

Dehydration

5 10 15 20 25 30 350Water content ()

LaLaLLaLM

0

05

10

15

20

25

30

Line

shrin

kage

δsi

()

Figure 8 Shrinkage curves of treated and untreated laterite

30 25 20 15 10 5 0(35) 30 25 20 15 10 5 035Water content ()Water content ()

0

Dehydration aer saturationDehydration aer saturationnnnnnnnnnnnnnnnnn

LaLLaLM

L a

Direct dehydration Dehydration aer saturation

75 75

200

150

100

50

Suct

ion

(MPa

)

Figure 9 Suction as a function of water content


addition of lime to laterite these cements connect the soilparticles into a whole to resist the strength decrease duringdehydration Surprisingly the direct shear strength ofcompacted laterite tends to increase at a water content ofless than 15 which is related to the friction betweenlaterite aggregates due to dehydration under a verticalstress of 200 kPa

ampe ability of metakaolin to enhance the inhibitory effectof lime on the shrinkage of laterite can be attributed to itscomposition and structure Figure 7 shows the SEM mi-crographs of the structures of kaolin and metakaolin by theaddition of lime after curing for 28 days Metakaolin ischaracterised by an important structural disorder such asthe deformation of the silica network permitting the facilecapture of calcium ions in the hydrated lime solution due toits high pozzolanic activity A larger amount of cementitewas formed from the mixture of lime-metakaolin than thatfrom the mixture of lime-kaolin under the same curingconditions

Metakaolin exhibits a substantial ability to catch calciumions changing the calcium-ion concentration in the treatedsoil (Figure 12) ampe content of calcium ions in LaLM is lessthan that in LaL (Figure 12) ampis result can be extrapolatedto reveal that metakaolin efficiently adsorbs calcium ionsamperefore metakaolin and lime can rapidly generate a largeamount of cement between laterite clusters (particles) morethan lime-laterite increase the overall adhesion of lateriteparticles and improve the strength of laterite

ampe molecular structure of metakaolin plays an im-portant role in its ability to efficiently adsorb calcium ionsfrom solutions Konan et al [17] have reported that kaolinadsorbs calcium hydroxide not only at the edges of the clayparticles but also on the basal faces (Figure 4) As kaolincomprises a laminated structure the adsorbed hydrated


0

1

2

3

4

5

UCS

(MPa

)


20MPa

75

(a)

30 25 20 15 10 5 0 (35) 30 25 20 15 10 5 035Water content ()Water content ()

0

1

2

3

4

5

UCS

(MPa

)


20MPa75 75

LaLML aL

LaLML aL

(b)

Figure 10 UCS as a function of water content (a) Laterite (b) Treated laterite

15

0

02

04

06

08

τ (M

Pa)

30 25 20 15 10 5 035Water content ()

LaLaLLaLM

Figure 11 Peaks of direct shear strength vs moisture content


calcium ions form a layer on the clay particle surfacespreventing the further dissolution of the clay mineralplatelets [26] Metakaolin comprises several amorphoussilicon and aluminium oxides enabling the rapid formationof hydrated phases at the interfaces between metakaolin andlime solutions and rendering high structural strength be-tween the laterite aggregates ampe results can be attributed tothe special ldquooverlappingrdquo edge-surface structure

ampe comparison of the pore distributions of the twosamples (LaL and LaLM respectively) clearly reveals that ifonly lime is added to laterite pores between 10 μm and100 μm (Figure 13(a)) increase during dehydration How-ever with the addition of both lime and metakaolin tolaterite the pores barely change (Figure 13(b)) also indi-cating that metakaolin can enhance the structure of lime-stabilized soil hinder shrinkage and prevent microfissuredevelopment

4 Conclusions

In this study a series of tests were conducted on threesamples (La LaL and LaLM respectively) to determine theshrinkage UCS suction direct shear strength and pore sizedistribution In addition the shrinkage mechanism of lat-erite modified by lime and metakaolin was examined ampefollowing conclusions can be drawn

(1) After calcination not only the hydroxyl groupsdisappeared but also the spatial structures of Si-O-Siand Si-O-Al (Mg) in kaolin are changed

(2) Although the suction of compacted laterite increasesduring dehydration microcracks are observed duringthis period thereby impairing the strength of laterite Inaddition metakaolin is found to enhance the decreaseshrinkage of laterite and increase the strength overall

30 60 90 1200Curing time (d)

0

10

20

30

40

50

Calc

ium

conc

entr

atio

n (m

gL)

LaLaLLaLM

Figure 12 Calcium concentration as a function of curing time

08

06

04

02

0

Dist

ribut

ion

dens

ity (c

cμm

g)

Macropore increased

Pore size (μm)10ndash3 10ndash2 10ndash1 100 101 102 103

MC = 0MC = 26

(a)

08

06

04

02

0

Dist

ribut

ion

dens

ity (c

cμm

g)


MC = 0MC = 28

(b)

Figure 13 Pore size distributions of treated laterite (a) LaL (b) LaLM


(3) ampemicroscopic examination of metakaolin reveals asubstantial amount of amorphous silicon and alu-minium oxides and shares edge-surface contactstructures thereby enabling it to significantly cap-ture calcium ions in the lime solution and subse-quently generating cementitious hydrates in theinteraggregates of laterite

Data Availability

ampe authors declare that all the data presented in themanuscript were obtained from laboratory tests at Chinaampree Gorges University in Yichang Hubei China All thelaboratory testing data were presented in the figures andtables in the manuscript ampe data used in the study areavailable from the corresponding author upon request

Conflicts of Interest

ampe authors declare no conflicts of interest

Acknowledgments

ampis study was financially supported by the National NaturalScience Foundation of China (51579137 and 51979150) andYouth Innovation TeamProject of Hubei Province (T201803)

References

[1] M D Gidigasu Laterite Soil Engineering Pedogenesis andEngineering Principles Elsevier Scientific Publishing Com-pany New York NY USA 1976

[2] Y H Wang ldquoDefinition and demonstration of lateriterdquo inProceedings of the Second National Symposium on LateriteEngineering and Geology Guizhou Science And TechnologyPress Guizhou China pp 11ndash20 1991

[3] H S Yang H Wei Y L Yang J Y Li and X L YinldquoDeterioration reaction between alkali materials and lateritedamrdquo Chinese Journal of Geotechnical Engineering vol 34no 1 pp 189ndash192 2012

[4] K Mu L W Kong X W Zhang and S Yin ldquoExperimentalinvestigation on engineering behaviors of red clay under effectof wetting-drying cyclesrdquo Rock and Soil Mechanics vol 37no 8 pp 2247ndash2253 2016

[5] D LWang M T Luan and Q Yang ldquoExperimental study onunsaturated remoulded clay subjected to drying and wettingcycle pathsrdquo Chinese Journal of Rock Mechanics and Engi-neering vol 26 no 9 pp 1862ndash1867 2007

[6] X W Liu L J Chang and X R Hu ldquoExperimental researchof matric suction with water content and dry density ofunsaturated lateriterdquo Rock and Soil Mechanics vol 30 no 11pp 3302ndash3306 2009

[7] C N Shen X W Fang H W Wang S G Sun and J F GuoldquoResearch on effects of suction water content and dry densityon shear strength of remoulded unsaturated soilsrdquo Rock andSoil Mechanics vol 30 no 5 pp 1347ndash1351 2009

[8] P H Morris J Graham and D J Williams ldquoCracking indrying soilsrdquo Canadian Geotechnical Journal vol 29 no 2pp 263ndash277 1992

[9] C S Tang B Shi C Liu L P Zhao and B J WangldquoInfluencing factors of geometrical structure of surfaceshrinkage cracks in clayey soilsrdquo Engineering Geology vol 101no 3-4 pp 204ndash217 2008

[10] Y Z Tan B Yu X L Liu Z Wan and H X Wang ldquoPore sizeevolution of compacted laterite under desiccation shrinkageprocess effectsrdquo Rock and Soil Mechanics vol 36 no 2pp 369ndash375 2015

[11] S L Wen J L Ren Z Q Jiang and Z Q Li ldquoCase analysis ofred clay gravel pile composite foundationrdquo Chinese Journal ofGeotechnical Engineering vol 32 no 2 pp 302ndash305 2010

[12] J Peng J Zhang J Li Y Yao and A Zhang ldquoModelinghumidity and stress-dependent subgrade soils in flexiblepavementsrdquo Computers and Geotechnics vol 120 p 1034132020

[13] J Zhang L Ding F Li and J Peng ldquoRecycled aggregates fromconstruction and demolition wastes as alternative fillingmaterials for highway subgrades in Chinardquo Journal of CleanerProduction vol 255 Article ID 120223 2020

[14] F G Bell ldquoLime stabilization of clay minerals and soilsrdquoEngineering Geology vol 42 no 6 pp 223ndash237 1996

[15] C-S Poon L Lam S C Kou Y-L Wong and R WongldquoRate of pozzolanic reaction of metakaolin in high-perfor-mance cement pastesrdquo Cement and Concrete Research vol 31no 9 pp 1301ndash1306 2001

[16] A Shvarzman K Kovler G S Grader and G E Shter ldquoampeeffect of dehydroxylationamorphization degree on pozzola-nic activity of kaoliniterdquo Cement and Concrete Researchvol 33 no 3 pp 405ndash416 2003

[17] K L Konan C Peyratout A Smith J-P BonnetS Rossignol and S Oyetola ldquoComparison of surface prop-erties between kaolin and metakaolin in concentrated limesolutionsrdquo Journal of Colloid and Interface Science vol 339no 1 pp 103ndash109 2009

[18] J J Brooks and M A Megat Johari ldquoEffect of metakaolin oncreep and shrinkage of concreterdquo Cement and ConcreteComposites vol 23 no 6 pp 495ndash502 2001

[19] Ministry of Transport of the Peoplersquos Republic of China JTGE40-2007 Test Methods of Soils for Highway EngineeringMinistry of Transport of the Peoplersquos Republic of ChinaBeijing China 2007 in Chinese

[20] G Kakali T Perraki S Tsivilis and E Badogiannis ldquoampermaltreatment of kaolin the effect of mineralogy on the pozzolanicactivityrdquo Applied Clay Science vol 20 no 1-2 pp 73ndash802001

[21] H H Murray ldquoApplied clay mineralogy today and tomor-rowrdquo Clay Minerals vol 34 no 1 pp 39ndash49 1999

[22] C Panagiotopoulou E Kontori T Perraki and G KakalildquoDissolution of aluminosilicate minerals and by-products inalkaline mediardquo Journal of Materials Science vol 42 no 9pp 2967ndash2973 2007

[23] L W Kong Y W Zhao A G Guo and Y F Tuo ldquoAnalysisof engineering characters and mechanism of the dehumidi-fication process of undisturbed lateriterdquo in Proceedings of the9th Academic Conference of Soil Mechanics and GeotechnicalEngineering China Civil Engineering Society Tsinghua Uni-versity Press Beijing China pp 424ndash427 2003

[24] Q K Nie Y H Wang S Q Liang and Q X Zhang ldquoWater-sensitivity of compacted laterite clays in jingxi of Guangxiregionrdquo Rock and Soil Mechanics vol 31 no 4 pp 1134ndash1138 2010

[25] Z Q Yang and J Y Guo ldquoampe physio-mechanical propertiesand micro-mechanism in lime-soil systemrdquo Rock and SoilMechanics vol 12 no 3 pp 11ndash23 1991

[26] K L Konan C Peyratout J-P Bonnet et al ldquoSurfaceproperties of kaolin and illite suspensions in concentratedcalcium hydroxide mediumrdquo Journal of Colloid and InterfaceScience vol 307 no 1 pp 101ndash108 2007


compacted laterite ampus the increase in the matrix suctionand crack occurrence exerts opposite effects on the strengthof compacted laterite ampat is the cracking behaviour causedby the water loss shrinkage also should be consideredRecently researchers have reported that the shrinkage oflaterite can be hindered by the improvement of the initialcompactness water content or even adding some materialsuch as gravel [11ndash13] In addition the shrinkage of lateritecan be effectively ameliorated by the addition of lime [14]but whether lime-modified laterite can be applied in prac-tical engineering projects needs to be investigated further

Metakaolin exhibits high pozzolanic activity Whenkaolin is heated to 500degCndash700degC an amorphous material isproduced ampis material is 50ndash55 of SiO2 and 40ndash45 ofAl2O3 by weight and it is extremely reactive in an alkalinecalcium-rich solution In [15ndash17] it is reported that met-akaolin can efficiently absorb calcium hydroxide to con-sistently form a cementitious hydrate and kaolin absorbshydrated calcium ions which form a layer on the clayparticle surfaces and subsequently prevent the furtherdissolution of clay mineral platelets Metakaolin-contain-ing concretes exhibit behaviour similar to those of silica-fume-containing concretes that is the mechanical resis-tance is improved and the permeability and shrinkage ofconcrete are significantly reduced [18] However whethermetakaolin effectively impacts water sensitivity is notknown amperefore strength and shrinkage tests underdifferent moisture conditions on compacted specimens areconducted in this study Meanwhile the variation insuction was measured and microscopic tests were per-formed Finally the aforementioned formal tests revealedthe shrinkage mechanism of lime and metakaolin modifiedlaterite

2 Materials and Methods

21 Materials Laterite was obtained from Guilin GuangxiAutonomous Region (China) By X-ray fluorescence itschemical composition was determined to predominantlycomprise silicon aluminium oxide (74 wt) and iron oxide(19 wt) (Table 1) After the dried laterite was passedthrough a 05mm sieve its fundamental properties weremeasured according to the Chinese standard JTG E40-2007Table 2 summarizes the results As the liquid limit of lateriteexceeded 50 herein it was defined as a high liquid limitsoil Furthermore its optimum water content (302) andmaximum dry density (148 gcm3) were obtained by heavycompaction tests (Figure 1)

Lime was purchased from Suqian Jiangsu Province(China) and its chemical composition was predominantlyCaO (9834 wt) with a small amount of Al2O3 (057 wt)Its specific gravity was 232 and its initial water content was31 Metakaolin was purchased from Royal Dutch Shell plcand its chemical composition was predominantly Al2O3(462 wt) and SiO2 (495 wt) Its specific gravity was 263and its initial water content was 15 ampe particle distri-bution characteristics of laterite lime and metakaolin wereinvestigated using a Microtrac S3500 particle size analyser(Figure 2)

22 Sample Preparation To investigate the effects of met-akaolin and lime on the shrinkage of laterite six kinds ofspecimens were prepared (Table 3) Due to the differentspecific gravities of laterite lime andmetakaolin the specificgravity of mixed soil (Gm) was calculated as follows

Gm 1

1 minus Rl minus Rmk( 1113857Gla( 1113857 + RlGl( 1113857 + RmkGmk( 1113857 (1)

where Gmk Gl and Gla are the specific gravities of meta-kaolin lime and laterite respectively and Rmk andRl are themixing ratios (wt) of metakaolin and lime respectively

ampe relationship between the dry density (ρd) and initialvoid ratio (e0) was calculated as follows

ρd Gm

1 + e0 (2)

For comparison of test results all compacted sampleshave the same initial void ratio To be more specific theinitial dry density of the laterite specimens was 143 gcm3while those of the laterite-lime specimens and laterite-lime-metakaolin specimens were 1422 gcm3 and 1420 gcm3respectively

In this study the soil samples were dry mixed and thenwater was added to the mixture soils until the predictedwater content was attained to achieve sample moistureconditions Finally the mixtures of metakaolin andor lime-laterite with deionized water were compacted layer by layerin a sample compaction container until soil samples wereobtained with dimensions of 618mm (diameter)times 20mm(height) and 50mm (diameter)times 50mm (height) with aninitial water content of 32 Pure laterite samples wereprepared in the same manner as the control samples All testsamples exhibited the same initial void ratio to ensure thatdifferent samples exhibited the same initial pore volume

23 Experimental Procedures In this experiment aftercompaction all specimens were sealed and cured for 180days at 25degC which was followed by a saturation processampen each test was conducted as follows

(1) Shrinkage tests were conducted according to theChinese standard JTG E40-2007 [19]

(2) For the UCS tests and suction measurements somespecimens were placed in a chamber at a constanttemperature (55degC) and then their mass was esti-mated to determine the real-time water contentduring dehydration When the real-time watercontent approached the predetermined value thesamples were sealed and cured for 2 months in thechamber at 25degC to ensure homogeneity ampen10ndash20 g of each sample was used for suction mea-surement using a Decagon WP4C dewpointpotentiometer

Table 1 Major components of laterite

Composition Al2O3 SiO2 Fe2O3 TiO2 K2O OthersMass content () 406 333 191 24 21 25

















12

13

14

15

Dry

den

sity

gcm

3

15 20 25 30 35 4010Water content ()

Wetting method

Drying method

Sr = 10

Sr = 09S

r = 08Sr = 07


100

80

60

40

20

0

Pass

ing

()

10ndash1 100 101 102 103 104

Particle size (μm)











e0 089ω 32



e0 089ω 32



e0 089ω 32



e0 089ω1 0 28


K

K

K

KK

K KQKaolin

Metakaolin

10 20 30 40 50 60 70

Inte

nsity

(cou

nts)


2θdeg (CuKα)


Silicatetrahedron

layer

Aluminoxyoctahedral

layer

O2ndash

Si4+

OHndash

A13+

Side

Surface


80

85

90

95

100

Wei

ght (

)


516degC

Δm =

11

5

KaolinMetakaolin











100

80

60

40

20

100

80

60

40

20

0

Tran

smitt

ance

()

Tran

smitt

ance

()


3680 36

20

(a)

(b)

Crest dissapeared

991

991

908





(a) (b)


25

Dehydration

5 10 15 20 25 30 350Water content ()

LaLaLLaLM

0

05

10

15

20

25

30

Line

shrin

kage

δsi

()



0


LaLLaLM

L a


75 75

200

150

100

50

Suct

ion

(MPa

)








0

1

2

3

4

5

UCS

(MPa

)


20MPa

75

(a)


0

1

2

3

4

5

UCS

(MPa

)


20MPa75 75

LaLML aL

LaLML aL

(b)


15

0

02

04

06

08

τ (M

Pa)

30 25 20 15 10 5 035Water content ()

LaLaLLaLM





4 Conclusions




30 60 90 1200Curing time (d)

0

10

20

30

40

50

Calc

ium

conc

entr

atio

n (m

gL)

LaLaLLaLM


08

06

04

02

0

Dist

ribut

ion

dens

ity (c

cμm

g)

Macropore increased


MC = 0MC = 26

(a)

08

06

04

02

0

Dist

ribut

ion

dens

ity (c

cμm

g)


MC = 0MC = 28

(b)




Data Availability




Acknowledgments


References











































12

13

14

15

Dry

den

sity

gcm

3

15 20 25 30 35 4010Water content ()

Wetting method

Drying method

Sr = 10

Sr = 09S

r = 08Sr = 07


100

80

60

40

20

0

Pass

ing

()

10ndash1 100 101 102 103 104

Particle size (μm)











e0 089ω 32



e0 089ω 32



e0 089ω 32



e0 089ω1 0 28


K

K

K

KK

K KQKaolin

Metakaolin

10 20 30 40 50 60 70

Inte

nsity

(cou

nts)


2θdeg (CuKα)


Silicatetrahedron

layer

Aluminoxyoctahedral

layer

O2ndash

Si4+

OHndash

A13+

Side

Surface


80

85

90

95

100

Wei

ght (

)


516degC

Δm =

11

5

KaolinMetakaolin











100

80

60

40

20

100

80

60

40

20

0

Tran

smitt

ance

()

Tran

smitt

ance

()


3680 36

20

(a)

(b)

Crest dissapeared

991

991

908





(a) (b)


25

Dehydration

5 10 15 20 25 30 350Water content ()

LaLaLLaLM

0

05

10

15

20

25

30

Line

shrin

kage

δsi

()



0


LaLLaLM

L a


75 75

200

150

100

50

Suct

ion

(MPa

)








0

1

2

3

4

5

UCS

(MPa

)


20MPa

75

(a)


0

1

2

3

4

5

UCS

(MPa

)


20MPa75 75

LaLML aL

LaLML aL

(b)


15

0

02

04

06

08

τ (M

Pa)

30 25 20 15 10 5 035Water content ()

LaLaLLaLM





4 Conclusions




30 60 90 1200Curing time (d)

0

10

20

30

40

50

Calc

ium

conc

entr

atio

n (m

gL)

LaLaLLaLM


08

06

04

02

0

Dist

ribut

ion

dens

ity (c

cμm

g)

Macropore increased


MC = 0MC = 26

(a)

08

06

04

02

0

Dist

ribut

ion

dens

ity (c

cμm

g)


MC = 0MC = 28

(b)




Data Availability




Acknowledgments


References



































e0 089ω 32



e0 089ω 32



e0 089ω 32



e0 089ω1 0 28


K

K

K

KK

K KQKaolin

Metakaolin

10 20 30 40 50 60 70

Inte

nsity

(cou

nts)


2θdeg (CuKα)


Silicatetrahedron

layer

Aluminoxyoctahedral

layer

O2ndash

Si4+

OHndash

A13+

Side

Surface


80

85

90

95

100

Wei

ght (

)


516degC

Δm =

11

5

KaolinMetakaolin











100

80

60

40

20

100

80

60

40

20

0

Tran

smitt

ance

()

Tran

smitt

ance

()


3680 36

20

(a)

(b)

Crest dissapeared

991

991

908





(a) (b)


25

Dehydration

5 10 15 20 25 30 350Water content ()

LaLaLLaLM

0

05

10

15

20

25

30

Line

shrin

kage

δsi

()



0


LaLLaLM

L a


75 75

200

150

100

50

Suct

ion

(MPa

)








0

1

2

3

4

5

UCS

(MPa

)


20MPa

75

(a)


0

1

2

3

4

5

UCS

(MPa

)


20MPa75 75

LaLML aL

LaLML aL

(b)


15

0

02

04

06

08

τ (M

Pa)

30 25 20 15 10 5 035Water content ()

LaLaLLaLM





4 Conclusions




30 60 90 1200Curing time (d)

0

10

20

30

40

50

Calc

ium

conc

entr

atio

n (m

gL)

LaLaLLaLM


08

06

04

02

0

Dist

ribut

ion

dens

ity (c

cμm

g)

Macropore increased


MC = 0MC = 26

(a)

08

06

04

02

0

Dist

ribut

ion

dens

ity (c

cμm

g)


MC = 0MC = 28

(b)




Data Availability




Acknowledgments


References




































100

80

60

40

20

100

80

60

40

20

0

Tran

smitt

ance

()

Tran

smitt

ance

()


3680 36

20

(a)

(b)

Crest dissapeared

991

991

908





(a) (b)


25

Dehydration

5 10 15 20 25 30 350Water content ()

LaLaLLaLM

0

05

10

15

20

25

30

Line

shrin

kage

δsi

()



0


LaLLaLM

L a


75 75

200

150

100

50

Suct

ion

(MPa

)








0

1

2

3

4

5

UCS

(MPa

)


20MPa

75

(a)


0

1

2

3

4

5

UCS

(MPa

)


20MPa75 75

LaLML aL

LaLML aL

(b)


15

0

02

04

06

08

τ (M

Pa)

30 25 20 15 10 5 035Water content ()

LaLaLLaLM





4 Conclusions




30 60 90 1200Curing time (d)

0

10

20

30

40

50

Calc

ium

conc

entr

atio

n (m

gL)

LaLaLLaLM


08

06

04

02

0

Dist

ribut

ion

dens

ity (c

cμm

g)

Macropore increased


MC = 0MC = 26

(a)

08

06

04

02

0

Dist

ribut

ion

dens

ity (c

cμm

g)


MC = 0MC = 28

(b)




Data Availability




Acknowledgments


References






























(a) (b)


25

Dehydration

5 10 15 20 25 30 350Water content ()

LaLaLLaLM

0

05

10

15

20

25

30

Line

shrin

kage

δsi

()



0


LaLLaLM

L a


75 75

200

150

100

50

Suct

ion

(MPa

)








0

1

2

3

4

5

UCS

(MPa

)


20MPa

75

(a)


0

1

2

3

4

5

UCS

(MPa

)


20MPa75 75

LaLML aL

LaLML aL

(b)


15

0

02

04

06

08

τ (M

Pa)

30 25 20 15 10 5 035Water content ()

LaLaLLaLM





4 Conclusions




30 60 90 1200Curing time (d)

0

10

20

30

40

50

Calc

ium

conc

entr

atio

n (m

gL)

LaLaLLaLM


08

06

04

02

0

Dist

ribut

ion

dens

ity (c

cμm

g)

Macropore increased


MC = 0MC = 26

(a)

08

06

04

02

0

Dist

ribut

ion

dens

ity (c

cμm

g)


MC = 0MC = 28

(b)




Data Availability




Acknowledgments


References

































0

1

2

3

4

5

UCS

(MPa

)


20MPa

75

(a)


0

1

2

3

4

5

UCS

(MPa

)


20MPa75 75

LaLML aL

LaLML aL

(b)


15

0

02

04

06

08

τ (M

Pa)

30 25 20 15 10 5 035Water content ()

LaLaLLaLM





4 Conclusions




30 60 90 1200Curing time (d)

0

10

20

30

40

50

Calc

ium

conc

entr

atio

n (m

gL)

LaLaLLaLM


08

06

04

02

0

Dist

ribut

ion

dens

ity (c

cμm

g)

Macropore increased


MC = 0MC = 26

(a)

08

06

04

02

0

Dist

ribut

ion

dens

ity (c

cμm

g)


MC = 0MC = 28

(b)




Data Availability




Acknowledgments


References






























4 Conclusions




30 60 90 1200Curing time (d)

0

10

20

30

40

50

Calc

ium

conc

entr

atio

n (m

gL)

LaLaLLaLM


08

06

04

02

0

Dist

ribut

ion

dens

ity (c

cμm

g)

Macropore increased


MC = 0MC = 26

(a)

08

06

04

02

0

Dist

ribut

ion

dens

ity (c

cμm

g)


MC = 0MC = 28

(b)




Data Availability




Acknowledgments


References





























Data Availability




Acknowledgments


References




























shrinkage mechanism of laterite modified by lime and

Documents