laboratory electrical resistivity studies on cement...

Research ArticleLaboratory Electrical Resistivity Studies onCement Stabilized Soil

Nimi Ann Vincent,1 R. Shivashankar,1 K. N. Lokesh,1 and JinuMary Jacob2

1Civil Engineering Department, National Institute of Technology, Karnataka, Surathkal, India2Larsen and Toubro Constructions, Chennai, India

Correspondence should be addressed to Nimi Ann Vincent; [email protected]

Received 2 February 2017; Accepted 26 March 2017; Published 30 April 2017

Academic Editor: Fernando Monteiro Santos

Copyright © 2017 Nimi Ann Vincent et al. This 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 is properlycited.

Electrical resistivitymeasurement of freshly prepared uncured and cured soil-cementmaterials is done and the correlations betweenthe factors controlling the performance of soil-cement and electrical resistivity are discussed in this paper. Conventional qualitycontrol of soil-cement quite often involves wastage of a lot of material, if it does not meet the strength criteria. In this study, itis observed that, in soil-cement, resistivity follows a similar trend as unconfined compressive strength, with increase in cementcontent and time of curing. Quantitative relations developed for predicting 7-day strength of soil-cement mix, using resistivity ofthe soil-cement samples at freshly prepared state, after 1-hour curing help to decide whether the soil-cement mix meets the desiredstrength and performance criteria. This offers the option of the soil-cement mix to be upgraded (possibly with additional cement)in its fresh state itself, if it does not fulfil the performance criteria, rather than wasting the material after hardening.

1. Introduction

Soil electrical resistivity testing has been gaining importancein geotechnical and geoenvironmental fields due to its timeefficiency and cost. Soil electrical resistivity testing will becheaper and faster than conventional laboratory testing whendealing with a large number of soil samples. The electricalmeasurement method is one of the nondestructive methodswhich can be applied both in the laboratory and in thefield and considered as nondestructive geophysical methodin the case of the latter. Electrical resistivity of soils dependson many factors such as porosity, nature of ions present inthe pore fluid, mineral composition of the solids, density,degree of saturation, particle shape, orientation, and porestructure. The fundamental principle of the soil investigationwith electrical resistivity is that when a constant voltage isapplied to one of the two probes placed in the soil, thecurrent that flows between the probes is inversely relativeto the resistance of the soil. Electrical resistivity showsindeed strong variations that principally depend on soil watercontent variations.

Bery and Saad [1] performed laboratory electrical resistiv-ity tests for the engineering characterization of a clayey sand

soil. The empirical correlations between electrical parameter,liquid limit, plastic limit, plasticity index, moisture content,internal friction angle, and effective soil cohesion wereobtained. The results showed that internal friction angleis inversely proportional to the resistivity of samples andeffective cohesion is directly proportional to the resistivity.

Stabilization of soils with additives helps to increasestrength, reduce deformability, provide volume stability,reduce permeability, and reduce erodibility. Wei et al. [2]established a linear relationship between 28-day compressivestrength and resistivity of cement paste after 24 hours. Thecompressive strength of cement paste at 28 days could bepredicted easily using a quantitative relation developed withresistivity of cement paste at 24 hours. In this study, elec-trical resistivity measurements of freshly prepared uncuredand cured soil-cement materials are carried out and thecorrelation between the factors controlling the performanceof soil-cement and electrical resistivity are being studied.Simple regression equations are developed between electricalresistivity and strength parameters in an attempt to predictthe performance of soil-cement mixtures with respect tocompressive, tensile, and the shear strength parameters in

HindawiInternational Scholarly Research NoticesVolume 2017, Article ID 8970153, 15 pageshttps://doi.org/10.1155/2017/8970153

https://doi.org/10.1155/2017/8970153

2 International Scholarly Research Notices

the fresh state itself without having to wait for 7 days.Moreover, predicting the strength parameters at the freshlyprepared state could be advantageous and a necessity inmany cases. If the soil-cement material does not meet thestrength requirement as per the resistivity models developed,additional cement constituents could be added in the freshstate itself and used.This will prevent wasting of thematerialsafter hardening. The additional advantages of the techniqueare that it is quick and nondestructive.

2. Electrical Resistivity of Stabilized Soils

Liu et al. [3] conducted a study for investigating the factorscontrolling the electrical resistivity of soil-cement admix-tures.

2.1. Effect of Cement Content. With the increase in cementcontent, water content and void ratio of the soil-cementadmixture get decreased due to the hydration reaction andpozzolanic reaction. As a result, the path for the conductionof electrical current becomes more tortuous. Therefore, theelectrical resistivity of the soil-cement admixture increased.The higher the cement content, the higher the hydrationcompounds formed.

2.2. Effect of Degree of Saturation. Electrical resistivityincreased with the decrease in degree of saturation becauseless pore spaces were filled with pore water, as water getsutilized for hydration reaction and thus continuous waterbridging is not available for electrical conduction.

2.3. Effect of Water Content on Electrical Resistivity. Withdecrease in water content, the tortuosity of the conductionpath for the electrical current increases, resulting in increaseof electrical resistivity.

2.4. Effect of Curing Time on Electrical Resistivity. With theincrease in the curing time, the chemical reaction productssuch as calcium silicate hydrate (CSH) and calcium aluminatehydrate (CAH) formed bind finer soil particles togetherresulting in a denser soil structure. Hence electrical resistivityis increased.

Zhang et al. [4] worked on quantifying the effect ofcement content, porosity, and curing period on the electricalresistivity andUCS of cement treated soil.The general Archielaw, which includes the effect of water content and porosity,was modified to evaluate the effect of cement content andcuring periods on the electrical resistivity of cement stabilizedsoil. Archie [5] developed an empirical relationship thatrelates the electrical resistivity of saturated sand (𝜌) to theelectrical resistivity of its pore fluid (𝜌𝑤) and the porosity (𝑛)of the soil.

𝜌𝜌𝑤 = 𝑛

−𝑚, (1)

where 𝑚 is the material-dependent empirical exponent,which is a measure of pore tortuosity and the interconnec-tivity of the pore network.

0

20

40

60

80

100

120

Perc

enta

ge �

nes (

%)

0.01 0.1 1 100.001Particle size (mm)

AB

CD

Figure 1: Sieve analysis results of soil samples.

A new parameter, termed as (after curing porosity/cem-ent content-curing time) ratio, 𝑛𝑡/(𝑎𝑤𝑇), was proposed torelate the electrical resistivity values as

𝜌 = 𝐴( 𝑛𝑡𝑎𝑤𝑇)−𝐵

, (2)

where 𝐴 and 𝐵 are dimensionless constants.

3. Materials Used

Thesoils used in the present study are lithomargic soils, whichare products of laterization. These soils are locally called“Shedi soils” and are available in varied colours. These soilsare characterized by high silt content and low strengths [6].In order to vary the percentage of fines, in the different testsamples, controlled soil samples were prepared. River sandwas used for blending the Shedi soil. All these soil sampleswere used to study the geotechnical and electrical properties.The percentages of river sand used were 0, 10, 20, and 30%by weight of dry soil. The samples are designated as A, B, C,and D, respectively. For the experimental investigations, riversand passing IS 4.75mm sieve and retained on IS 75-micronsieve was considered.The sieve analysis curves of the samplesare shown in Figure 1.

4. Cement

43-grade Ordinary Portland Cement (OPC) was used in thestudy. The percentages of cement used were 2%, 4%, and 6%in each of the four soil samples, A, B, C, and D.These samplesare designated as A2, A4, A6, B2, B4, B6, C2, C4, C6, D2, D4,and D6, respectively.

5. Test Method

Electrical resistivity of all the controlled samples was done bymaking cylindrical samples of size 7.6 cm height and 3.8 cmdiameter. For each combination, in addition to the pointof maximum dry density and optimum moisture contentobtained from Standard Proctor and Modified Proctor tests,

International Scholarly Research Notices 3

a

b

c

d

e

Compaction curveA4

OMC: 26.3%

20 25 30 3515w (%)

1.35

1.37

1.39

1.41

1.43

1.45

1.47

1.49

MDD: 1.48 g/cc

a

b

c

d

e

Compaction curve

OMC: 28.3%

A2

25 30 3520w (%)

1.36

1.38

1.4

1.42

1.44

1.46

1.48

MDD: 1.46 g/cc

𝛾 d(g

/cc)

𝛾 d(g

/cc)

Figure 2: Light compaction curve for samples A2 and A4.

a

b

c

d

e

Compaction curveB2

OMC: 22.4%

1.35

1.4

1.45

1.5

1.55

1.6

15 20 25 30 3510w (%)

MDD: 1.56 g/cc

a

b

c

d

e

Compaction curve

OMC: 25.6%

A6

20 25 30 3515w (%)

1.375

1.4

1.425

1.45

1.475

MDD: 1.46 g/cc

𝛾 d(g

/cc)

𝛾 d(g

/cc)

Figure 3: Light compaction curve for samples A6 and B2.

two points each were selected on the dry side and wet sideof the compaction curve to study resistivity variation fordifferent compaction conditions (Figures 2–13). Figures 2–7show the compaction curve for light compaction (standardProctor compaction) and Figures 8–13 show compactioncurve for heavy compaction (modified Proctor compaction).

The resistivity measurements were taken for all the sevencuring days. Electrical resistivity was measured by usinga circuit consisting of a 30V DC power supply, two highprecisionmultimeters serving as ammeter and voltmeter, andelectrodes connecting to the sample as seen in Figure 14. Twocircular steel plates are placed touching the two ends of thesample which acts as current electrodes and two steel pins

at one-third length from both ends act as voltage electrodes.The stainless steel electrodes were arranged in Wenner 𝛼configuration.Wenner 𝛼 array is less affected by the electrodeposition error compared to dipole-dipole array [7].

Resistivity was measured in the freshly prepared state,after one-hour curing and after one to seven days of curing.The basic geotechnical properties of the soil stabilized withdifferent percentages of cement are given in Table 1.

6. Results and Discussions

Compaction and strength characteristics of the soil-cementsamples are shown in Table 1.


a

b

c

d

e

Compaction curveB6

OMC: 24%

1.4

1.45

1.5

1.55

20 25 3015w (%)

MDD: 1.54 g/cc

a

b

c

d

e

Compaction curveB4

OMC: 25.2%

15 20 25 3010w (%)

1.44

1.45

1.46

1.47

1.48

1.49

1.5

MDD: 1.495 g/cc

𝛾 d(g

/cc)

𝛾 d(g

/cc)

Figure 4: Light compaction curve for samples B4 and B6.

a

b

c

d

e

Compaction curveC4

OMC: 23.4%

1.49

1.5

1.51

1.52

1.53

1.54

1.55

1.56

1.57

15 20 25 3010w (%)

MDD: 1.56 g/cc

a

b

c

d

e

Compaction curveC2

OMC: 22.8%

1.44

1.46

1.48

1.5

1.52

1.54

1.56

1.58

MDD: 1.57 g/cc

15 20 25 3010w (%)

𝛾 d(g

/cc)

𝛾 d(g

/cc)

Figure 5: Light compaction curve for samples C2 and C4.

6.1. Variation of Electrical Resistivity with Time of Curing.From Figure 15, which shows variation of resistivity at OMCand corresponding maximum dry density with time ofcuring, it is seen that resistivity increases with curing period.The resistivity results show that, for all the soil-cementsamples, at freshly prepared state and after one hour ofcuring time, resistivities are high when compacted on dryside of optimum. With increase of moisture content and drydensity, resistivity decreases significantly. In the wet side,soil resistivity is low. The moulding water content whichwas available for electrical conduction at freshly preparedstate gets utilized for hydration of cement, which depletes

the free water film available for conduction, with time ofcuring.

6.2. Resistivity with Compaction Effort. The electrical re-sponse of soil when the soil samples are compacted withdifferent degree of compaction is also looked into. Lightand heavy mechanical compaction were performed on thesoil samples and the resistivity variation on these samples atdifferent compaction condition is being studied. In the bargraphs (Figures 16 and 17), “a” and “b” represent the dryside of optimum compaction points.The point “c” representsthe maximum compaction condition. The points “d” and “e”


a

b

c

d

e

Compaction curveD2

OMC: 20.6%

1.5

1.55

1.6

1.65

1.7

15 20 25 3010w (%)

MDD: 1.66 g/cc

a

b

c

d

e

Compaction curveC6

OMC: 23.2%

15 20 25 3010w (%)

1.44

1.46

1.48

1.5

1.52

1.54

1.56

1.58

MDD: 1.56 g/cc

𝛾 d(g

/cc)

𝛾 d(g

/cc)

Figure 6: Light compaction curve for samples C6 and D2.

a

b

c

d

e

Compaction curveD6

OMC: 20.4%

15 20 2510w (%)

1.59

1.6

1.61

1.62

1.63

1.64

1.65

1.66

MDD: 1.655 g/cc

a

b

c

d

e

Compaction curveD4

OMC: 18.8%

15 20 2510w (%)

1.58

1.59

1.6

1.61

1.62

1.63

1.64

1.65

1.66

1.67

1.68

MDD: 1.67 g/cc

𝛾 d(g

/cc)

𝛾 d(g

/cc)

Figure 7: Light compaction curve for samples D4 and D6.

represent the wet side of compaction points (as shown inFigures 2–13). It is seen from Figures 16 and 17 that resistivitydecreases with increase in water content and dry density onthe dry side but is dependent only on water content in the wetside of the compaction curve.

The solid particles of noncohesive soils are poor conduc-tive while electrical current flow occurs only in intergranularspaces filled with mineralized water. As a consequence, theelectrical conductivity of rocks and soils is clearly dependenton the amount of water in the medium, the conductivity ofwater, and how thewater is spread (porosity, the degree of sat-uration, cementation factor, and fracturing). From Figure 18,it is observed that the resistivities are comparatively lowerfor the samples compacted at heavy compaction conditions

than those compacted at light compaction conditions for allcuring periods. At heavy compaction conditions, soil attainsa denser state with higher degree of saturation and lesserair voids, which results in a lower apparent resistivity of thesoils. At freshly prepared state and after one hour of curing,the ions present in the saturated and continuous microporesslightly exhibit higher electrical conduction and hence alower resistivity in heavily compacted soil-cement samplescompared to lightly compacted samples.

After 7 days of curing, the soil-cement samples hardenand less water and ions will be available for conduction.The lightly compacted samples are more porous than heavilycompacted dense samples. After 7 days of curing, water inthese pores is utilized for hydration of cement and is replaced


a

b

c

d

e

Compaction curveA4

OMC: 21.9%1.49

1.51

1.53

1.55

1.57

1.59

1.61

1.63

1.65

15 20 25 3010w (%)

MDD: 1.64 g/cc

a

b

c

d

e

Compaction curveA2

OMC: 22.1%

1.5

1.52

1.54

1.56

1.58

1.6

1.62

1.64

1.66

15 20 25 3010w (%)

MDD: 1.64 g/cc

𝛾 d(g

/cc)

𝛾 d(g

/cc)

Figure 8: Heavy compaction curve for samples A2 and A4.

a

b

c

d

e

Compaction curveB2

OMC: 19%

15 20 2510w (%)

1.55

1.57

1.59

1.61

1.63

1.65

1.67

1.69

1.71

1.73

1.75

MDD: 1.73 g/cc

a

b

c

d

e

Compaction curveA6

OMC: 21.6%

15 20 25 3010w (%)

1.45

1.5

1.55

1.6

1.65

1.7

MDD: 1.645 g/cc

𝛾 d(g

/cc)

𝛾 d(g

/cc)

Figure 9: Heavy compaction curve for samples A6 and B2.

with air which offers infinite electrical resistance. Hence, aftera period of seven days of curing the lightly compacted soil-cement samples exhibit higher resistivity than the heavilycompacted ones.

6.3. Variation of Resistivity with Cement Content. It is ob-served that, in freshly prepared state, resistivity decreasesslightly with cement content for all the soil-cement samples(Figure 19). But on the other hand, resistivity is slightlyincreasing with cement content when measured after curing(Figure 20).

Cement reduces the plasticity and water-retention capac-ity of the soil and improves its strength. Immediately aftermixing, calcium (Ca) and hydroxyl (OH) ions go into

solution. Then after a few minutes a slow precipitation ofsemicrystalline calcium silicate hydrate (CSH) gel occurswhile theCa andOH ions concentrations continue to increaseslowly. Hence, initially the freshly prepared soil-cementsamples show some conductivity, which diminishes withtime. The Ca ion concentration reaches the saturation level,and the hydration reactions begin, with the crystallizationof solid calcium hydroxide and the deposition of CSH gelin voids. While the structure is progressing up, the porespaces decrease and the availability of ions and water willbe lesser, which results in a higher electrical resistivity. Thehydration compounds fill in pore spaces and intersect witheach other to form a denser structure. In the meantime,the free water space and porosity decrease and tortuosity


a

b

c

d

e

Compaction curveB6

OMC: 17.2%

1.64

1.66

1.68

1.7

1.72

1.74

1.76

1.78

10 15 20 255w (%)

MDD: 1.765 g/cc

a

b

c

d

e

Compaction curveB4

OMC: 19%

15 20 2510w (%)

1.6

1.62

1.64

1.66

1.68

1.7

1.72

1.74

MDD: 1.73 g/cc

𝛾 d(g

/cc)

𝛾 d(g

/cc)

Figure 10: Heavy compaction curve for samples B4 and B6.

a

b

c

d

e

Compaction curveC4

OMC: 16%

10 15 205w (%)

1.7

1.72

1.74

1.76

1.78

1.8

1.82

1.84

1.86

MDD: 1.84 g/cc

a

b

c

d

e

Compaction curveC2

OMC: 14.4%

10 15 205w (%)

1.69

1.71

1.73

1.75

1.77

1.79

1.81

1.83

1.85

MDD: 1.83 g/cc

𝛾 d(g

/cc)

𝛾 d(g

/cc)

Figure 11: Heavy compaction curve for samples C2 and C4.

ab

c

d

e

Compaction curveD2

OMC: 14.9%

1.65

1.7

1.75

1.8

1.85

1.9

10 15 205w (%)

ab

c

d

e

Compaction curveC6

OMC: 16.5%

12 14 16 18 20 2210w (%)

1.6

1.65

1.7

1.75

1.8

1.85

MDD: 1.82 g/cc MDD: 1.88 g/cc

𝛾 d(g

/cc)

𝛾 d(g

/cc)

Figure 12: Heavy compaction curve for samples C6 and D2.


a

b

c

d

e

Compaction curveD6

OMC: 16%

10 15 205w (%)

1.73

1.75

1.77

1.79

1.81

1.83

1.85

a

b

c

d

e

Compaction curveD4

OMC: 15.4%

10 15 205w (%)

1.651.671.691.711.731.751.771.791.811.831.85

MDD: 1.835 g/cc MDD: 1.835 g/cc

𝛾 d(g

/cc)

𝛾 d(g

/cc)

Figure 13: Heavy compaction curve for samples D4 and D6.

−

−

+

+−

+

A

V

Soil

Figure 14: Resistivity measurement.

increases. Consequently, electrical resistivity increases moresignificantly [4].

6.4. Resistivity with Porosity. Porosity of all the sample com-binations was found for all the curing days. Cement contenthas a great effect on electrical resistivity of soil-cement.The measured electrical resistivity of cement treated soilsincreases with the increase of cement content [4]. For a givencuring time, higher cement content yields higher amountof hydration products resulting in a denser structure. Withthis, free water space and porosity decrease and tortuosityincreases resulting in increase of electrical resistivity.

Figures 21–24 show the variation of electrical resistivitywith porosity for varying percentages of river sand. It canbe observed that, as cement content increases, porositydecreases. With curing time, for each percentage of cement,porosity decreases and the denser structure results in increaseof resistivity.

6.5. Scanning Electron Microscope (SEM) Analysis. FromSEM photos for sample A2 at different curing periods (asshown in Figures 25–32), it is observed that the pore spacesor the conductive path rapidly decreases with curing time.

The structure becomes more clustered with lesser voids withincrease of curing time. This is because of the formation ofhydration productswhich fills in the pore spaces anddevelopsthe bond strength and increases the resistivity with curingtime. Similarly for all the other samples A4, A6, B2, B4, B6,C2, C4, C6, D2, D4, andD6 also, themicro structure becomesmore dense and clustered with increase in curing time.

6.6. Resistivity with Unconfined Compressive Strength (UCS).Figures 33–35 show resistivity variation at different timessuch as in the freshly prepared state, after one hour ofcuring, and after seven days of curing with 7th day. Withthe increase in percentage of cement and river sand added,UCS is found to increase as particles become more clusteredand get bonded by the cementing action and the sandparticles which replace the finer particles of soil take upmore load. The difference in controlling parameters of theelectrical resistivity and the compressive strength such as ionconcentration in pore fluid and surface charges of the soilparticles, which are factors affecting ER but not UCS, wassuggested as the reason behind the nonlinear relationshipbetween electrical resistivity and unconfined compressivestrength of soil-cement by Zhang et al. [4].


Table1:Com

pactionandstreng

thcharacteris

ticso

fthe

soilcementsam

ples.

Parameter

Soil-cementsam

ples

A0

A2

A4

A6

B0B2

B4B6

C0C2

C4C6

D0

D2

D4

D6

𝛾 𝑑max,kN/m3(LC)

14.5

14.6

14.8

14.6

15.6

15.6

15.0

15.4

15.9

15.7

15.6

15.6

16.4

16.6

16.7

16.6

OMC(%

)(LC

)28.0

28.3

26.8

25.6

25.0

22.4

25.2

2423.2

22.8

23.4

23.2

21.0

20.6

18.8

20.4

𝛾 𝑑max,(kN

/m3)(HC)

14.9

16.4

16.4

16.5

15.9

17.3

17.3

17.7

16.4

18.3

18.4

18.2

17.5

18.8

18.4

18.4

OMC(%

)(HC)

27.0

22.1

21.9

21.6

22.0

19.0

19.0

17.2

21.0

14.4

1616.5

18.0

14.9

15.4

167-dayUCS

(kPa)(LC

)130.8

478.8

814.8

991.7

155.6

733

863.6

1691.8

162.2

769.3

1307.3

1703.5

289.2

1080.8

1507.5

2130.2

C(kPa)(LC

)23.5

290.0

340.0

480.0

21.0

265.0

280.0

390.0

19.0

190.0

245.0

320.0

18.5

140.0

180.0

260.0

Φ(degrees)(LC)

20.0

31.0

35.0

40.0

25.0

34.0

36.0

41.0

31.0

37.0

41.0

43.0

31.0

38.0

46.0

51.0

STS(kPa)(LC

)—

75.52

109.9

112.8

—64

.1104.2

107.0

3—

52.6

101.3

104.2

—55.5

98.4

101.3

Note.𝛾𝑑max:m

axdryd

ensity,OMC:

optim

ummoistu

recontent,LC

:lightcom

paction,HC:

heavyc

ompaction,UCS

:uncon

fined

compressiv

estre

ngth,C

:coh

esion,Φ:ang

leofinternalfrictio

n,andST

S:split

tensile

strength.


0

5

10

15

20

25

30

35

40Re

sistiv

ity (O

hm·m

)

1 hour 1 day 2 days 3 days 4 days 5 days 6 days 7 daysFreshTime of curing

A2A4A6

B2B4B6

C2C4C6

D2D4D6

Figure 15: Variation of resistivity at OMC and correspondingmaximum dry density with time of curing.

a to e as indicated in Figures 2–7

A4 A6 B2 B4 B6 C2 C4 C6 D2 D4 D6A2Soil samples

abc

de

0

1

2

3

4

5

6

7

8

9

Resis

tivity

(Ohm

·m)

Figure 16: Variation of resistivity at dry side and wet side points onthe standard Proctor compaction curve at day zero.

From Figure 33, an inverse relation is observed, betweenUCS (after 7 days’ curing) and resistivity (of freshly preparedsamples) when the cement content is varied. At freshlyprepared state, as the cement content increases electricalresistivity decreases due to high electrical conduction exhib-ited by the ions released due to chemical reactions by cementand water, which gradually slows down with time. At thesame time, electrical resistivity after 1-hour curing and 7days’ curing shows a direct relation with the unconfinedcompressive strength of soil-cement with increase in cementcontent (Figures 34 and 35).

Resistivity also follows the same trend as UCS withtime of curing and increase in cement content; the samples

a to e as indicated in Figures 8–13


abc

de

0123456789

Resis

tivity

(Ohm

·m)

Figure 17: Variation of resistivity at dry side and wet side points onthe modified Proctor compaction curve at day zero.

Light compactionHeavy compaction

0

1

2

3

4

5

6

7

8

9

10Re

sistiv

ity (O

hm·m

)


Figure 18: Variation of electrical resistivity at light (LC) and heavy(HC) day zero compaction conditions at OMC and maximum drydensity conditions.

with higher cement showed higher resistivity, since morehydration products formed fill the pore spaces and createa highly tortuous structure, bringing down the electricalconduction.

Multiple regression analysis carried out derived gener-alised equations which predicts the 7-day UCS of cementstabilized soil, by using the cement content (%) and theresistivity (Ohm⋅m) measured at freshly prepared state andalso after 1-hour curing period.The regression coefficients are0.9 and 0.95 for (3) and (4), respectively. The equations are asfollows.

UCS (kN/m2) = 197.3𝑥𝑐 (%) − 164.3𝑥𝜌0 (Ohm ⋅m)+ 1147.7,

(3)


4 62Cement (%)

AB

CD

0

1

2

3

4

5

6

7

8Re

sistiv

ity (O

hm·m

)

Figure 19: Resistivity (at freshly prepared state) versus cementcontent at LC (at max dry density and OMC).

4 62Cement (%)

AB

CD

25

27.5

30

32.5

35

37.5

40

42.5

45

47.5

Resis

tivity

(Ohm

·m)

Figure 20: Resistivity (after 7 days’ curing) versus cement contentat LC (at max dry density and OMC).

y = 43169x2 − 50949x + 15117

R2 = 0.787

y = 3E + 06x2 − 3E + 06x + 86892

R2 = 0.821

y = 4E + 06x2 − 4E + 06x + 90356

R2 = 0.895

At 2% cementAt 4% cementAt 6% cement

1 day

7 days

0.005.00

10.0015.0020.0025.0030.0035.0040.0045.0050.00

Resis

tivity

(Ohm

·m)

0.45 0.5 0.55 0.60.4Porosity

Figure 21: Variation of resistivity with porosity for sample A.

y = 1E + 07x2 − 1E + 07x + 3E + 06

R2 = 0.968

y = 1E + 07x2 − 1E + 07x + 3E + 06

R2 = 0.927

y = 2E + 07x2 − 1E + 07x + 3E + 06

R2 = 0.981


1 day

7 days

0.005.00

10.0015.0020.0025.0030.0035.0040.0045.0050.00

Resis

tivity

(Ohm

·m)

0.4 0.42 0.44 0.46 0.480.38Porosity

Figure 22: Variation of resistivity with porosity for sample B.

y = 2E + 07x2 − 1E + 07x + 3E + 06R2 = 0.981

y = 7E + 06x2 − 6E + 06x + 1E + 06R2 = 0.917

y = 1E + 07x2 − 8E + 06x + 1E + 06R2 = 0.936


1 day

7 days

0.005.00

10.0015.0020.0025.0030.0035.0040.0045.00

Resis

tivity

(Ohm

·m)

0.37 0.38 0.39 0.4 0.410.36Porosity

Figure 23: Variation of resistivity with porosity for sample C.

y = 3E + 19e−103.1x

R2 = 0.982

y = 3E + 06x2 − 2E + 06x + 42952

R2 = 0.969

y = 6E + 06x2 − 4E + 06x + 77852

R2 = 0.980


1 day

7 days

0.005.00

10.0015.0020.0025.0030.0035.0040.0045.00

Resis

tivity

(Ohm

·m)

0.34 0.35 0.36 0.37 0.380.33Porosity

Figure 24: Variation of resistivity with porosity for sample D.

where 𝑐 is the cement content and𝜌0 is the electrical resistivityat freshly prepared state.

UCS (kN/m2) = 269.3𝑥𝑐 (%) − 160.6𝑥𝜌1 (Ohm ⋅m)+ 1035894,

(4)


Figure 25: SEM image of soil-cement mix A2, at freshly preparedstate.

Figure 26: SEM image of soil-cement mix A2, after 1-day curing.

Figure 27: SEM image of soil-cement mix A2, after 2 days’ curing.







y = 24136e−0.00x

R2 = 0.689

y = 2E + 06e−1.421x

R2 = 0.9319

y = 12271e−0.01x

R2 = 0.970

y = 3578.e−0.00x

R2 = 0.919

6% c

6% c

4% c

6% c

4% c

6% c

2% c2% c

2% c

2% c

4% c4% c

0

500

1000

1500

2000

2500U

CS (k

N/m

2)

1 2 3 4 5 6 7 80Resistivity (Ohm·m)

AB

CD

Figure 33: 7-day UCS versus resistivity (at freshly prepared state).

y = 85.94e0.003x

R2 = 0.490

R2 = 0.7936

2% c

4% c

6% c

2% c

4% c

6% c

2% c4% c

6% c

2% c

4% c

6% c

0

500

1000

1500

2000

2500

UCS

(kN

/m2)

2 4 6 8 10 120Resistivity (Ohm·m)

AB

CD

y = 5888.3 ln(x) − 8522.6

R2 = 0.6057

y = 1461.7 ln(x) − 2305

R2 = 0.9346

y = 3058.6 ln(x) − 1981.2

Figure 34: 7-day UCS versus resistivity (after 1-hour curing).

y = 1533.8x − 60627R2 = 0.9052

y = 2067.4x − 80633R2 = 0.5971

y = 87.17x − 33883R2 = 0.872

y = 124.5e0.000x

R2 = 0.814

2% c4% c

6% c

2% c

4% c

6% c

2% c

4% c

6% c

2% c

4% c

6% c

0

500

1000

1500

2000

2500

UCS

(kN

/m2)


AB

CD

Figure 35: 7-day UCS versus resistivity (after 7 days’ curing).

where 𝑐 is the cement content and𝜌1 is the electrical resistivitymeasured after 1-hour curing.

6.7. Resistivity with Cohesion. Figures 36–38 show the vari-ation of cohesion with electrical resistivity measurements inthe freshly prepared state and after curing periods of one hourand seven days at different percentages of cement content forthe soil samples. Cohesion after seven days’ curing was foundby triaxial testing. With increase of cement content, more

y = 41518e−0.704x

R2 = 0.9853

y = 10696e−0.659x

R2 = 0.9022

y = 14395e−0.01x

R2 = 0.977

y = 265853e−3.621x

R2 = 0.9815

2% c

6% c

2% c

4% c

2% c

4% c

6% c

2% c4% c

6% c

6% c4% c

0

100

200

300

400

500

600

Coh

esio

n (k

Pa)


AB

CD

Figure 36: 7-day cohesion with resistivity (freshly prepared).

y = 65.125e0.209x

R2 = 0.9158

y = 85.94e0.003x

R2 = 0.490

y = 1.634x − 610.7

R2 = 0.910

2% c

4% c

6% c

2% c4% c

6% c

2% c

4% c

6% c

2% c

4% c6% c

0100200300400500600

Coh

esio

n (k

Pa)


AB

CD

R2 = 0.9694

y = 360.64 ln(x) − 225.73

Figure 37: 7-day cohesion with resistivity (after 1-hour curing).

y = 604.19x − 23812R2 = 0.9829

y = 1E − 12e0.008x

R2 = 0.603

y = 12.75x − 49521R2 = 0.964

y = 21.25e0.000x

R2 = 0.733

2% c

4% c

6% c

2% c

4% c

2% c4% c

6% c

2% c

4% c

6% c

0

100

200

300

400

500

600

Coh

esio

n (k

Pa)

30 35 40 4525Resistivity (Ohm·m)

AB

CD

Figure 38: 7-day cohesion with resistivity (after 7 days’ curing).

hydration products are formed and more binding results inincrease in the value of cohesion. But in the freshly preparedstate, more ion concentrations result in lesser values forresistivity as the cement content increases and hence showsan inverse relation with cohesion in this state. But a directrelation is seen after curing since pore water gets used up forhydration resulting in more air in the voids which increasesresistance.


y = 335.69e−0.335x

R2 = 0.9107

y = 201.33e−0.315x

R2 = 0.9784

y = 267.5e−0.00x

R2 = 0.994

y = 1446.7e−1.735x

R2 = 0.9798

2% c

6% c

2% c

6% c

2% c

4% c6% c

2% c

4% c

6% c

Ang

le o

f int

erna

l

4% c4% c

25

30

35

40

45

50

55fr

ictio

n (d

egre

es)


AB

CD

Figure 39: 7-day angle of internal friction with resistivity (freshlyprepared).

y = 15.982e0.096x

R2 = 0.7895

y = 20.324e0.0887x

R2 = 0.6063

R2 = 0.7049

y = 34.52 ln(x) − 154.1

R2 = 0.771

2% c

4% c

6% c

2% c4% c

6% c

2% c

4% c6% c

2% c

4% c

6% c

Ang

le o

f int

erna

l

2025303540455055

fric

tion

(deg

rees

)


AB

CD

y = 36.157 ln(x) − 19.737

Figure 40: 7-day angle of internal friction with resistivity (after 1-hour curing).

y = 27.831x − 1078.6

R2 = 0.9949

y = 1E − 06e0.4306x

R2 = 0.7608

y = 54.268x − 2076.9R2 = 0.7962

y = 13.78e0.000x

R2 = 0.931

2% c

4% c

6% c

2% c

4% c6% C

2% c4% c

6% c

2% c

4% c

6% c

Ang

le o

f int

erna

l

20

25

30

35

40

45

50

55

fric

tion

(deg

rees

)


AB

CD

Figure 41: 7-day angle of internal friction with resistivity (after 7days’ curing).

6.8. Resistivity with Angle of Internal Friction. The shearstrength parameter, angle of internal friction, was found bytriaxial testing on samples after a curing period of seven days.Figures 39–41 show the variation of electrical resistivity withangle of internal friction. As cement content increases, angleof friction is found to increase which results in an inverse

y = −40.31x + 371.15

R2 = 0.4998

y = −68.541x + 460.83

R2 = 0.7378

y = 652230e−2.005x

R2 = 0.882

y = −2.727x + 631.7

R2 = 0.818

2% c

4% c

6% c

2% c

4% c6% c

6% c

4% c

2% c

6% c4% c

2% c

020406080

100120140

Split

tens

ile st

reng

th (k

Pa)


AB

CD

Figure 42: 7-day split tensile strength with resistivity (freshlyprepared).

y = 10.095x + 16.569R2 = 0.3302

y = 8.9272e0.343x

R2 = 0.9996

R2 = 0.4274

R2 = 0.4515

2% c2% c

4% c 6% c 6% c

4% c

2% c

6% c

4% c

2% c

4% c6% c

020406080

100120

Split

tens

ile st

reng

th (k

Pa)


AB

CD

y = 103.42 ln(x) − 35.106

y = 267.08 ln(x) − 357.69

Figure 43: 7-day split tensile strength with resistivity (after 1-hourcuring).

y = 106.54x − 4164.7

R2 = 0.6903

y = 121.75x − 4721.2

R2 = 0.97

y = 4.212x − 16346

R2 = 0.533

y = 0.060x − 124.3

R2 = 0.998

2% c

4% c6% c

2% c

4% c

6% c

2% c

4% c 6% c

020406080

100120140

Split

tens

ile st

reng

th (k

Pa)


AB

CD

Figure 44: 7-day split tensile strength with resistivity (after 7 days’curing).

relationwith resistivity in the freshly prepared state and directrelation in all other curing periods when plotted for all thesoil-cement samples.

6.9. Resistivity with Split Tensile Strength. Split tensilestrength after seven days’ curing time and resistivity inthe freshly prepared state and after curing periods of onehour and seven days is correlated in Figures 42–44. Whencement content increases, the binding increases and hence


the samples with higher cement content can take up moreload when tested resulting in increase of split tensile strengthvalue. For all the soil samples, when the cement content isvaried, resistivity shows indirect relation with split tensilestrength for fresh samples and direct relation for curedsamples.

7. Conclusions

In this study, electrical resistivity measurement of freshlyprepared uncured and cured soil-cement materials is doneand the correlation between the factors controlling the per-formance of soil-cement and electrical resistivity are studied.By the time an unconfined compressive strength test canbe performed, to check the quality of the soil-cement, thematerial will be hardened in the field and if it does notmeet strength and performance criteria, the material willhave to be removed, collapsed, and remixed with additionalcement which is a very time and cost consuming task.At this phase, electrical measurements of soil-cement/limematerial save a great deal of expense and time by predictingthe strength properties without hardening of the material.Equations developed in this study, by multiple regressionanalysis, predict the unconfined compressive strength of thesoil-cement samples, at the freshly prepared state or after 1-hour curing. If the strength requirement is not met, it couldbe remixed with additional cement at the fresh state itself andreused.

Conflicts of Interest

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

References

[1] A. A. Bery and R. Saad, “Tropical clayey sand soil’s behaviouranalysis and its empirical correlations via geophysics electri-cal resistivity method and engineering soil characterizations,”International Journal of Geosciences, vol. 3, no. 1, pp. 111–116,2012.

[2] X. Wei, L. Xiao, and Z. Li, “Prediction of standard compressivestrength of cement by the electrical resistivity measurement,”Construction and Building Materials, vol. 31, pp. 341–346, 2012.

[3] S. Y. Liu, Y. J. Du, L. H. Han, and M. F. Gu, “Experimentalstudy on the electrical resistivity of soil-cement admixtures,”Environmental Geology, vol. 54, no. 6, pp. 1227–1233, 2008.

[4] D. Zhang, L. Chen, and S. Liu, “Key parameters controllingelectrical resistivity and strength of cement treated soils,”Journal of Central SouthUniversity, vol. 19, no. 10, pp. 2991–2998,2012.

[5] G. E. Archie, “The electrical resistivity log as an aid in determin-ing some reservoir characteristics,” Transactions of the AIME,American Institute of Mining, Metallurgical, and PetroleumEngineers, vol. 146, no. 1, pp. 54–62, 1942.

[6] V. George, R. Hegde, M. V. Vardhana, G. Santosh, andD. Gotamey, “Accelerated consolidation of coir reinforcedlithomargic laterite soil blends with vertical sand drains forpavements,” Electronic Journal of Geotechnical Engineering, vol.17, pp. 2115–2133, 2012.

[7] R. Clement and S. Moreau, “How should an electrical resistivitytomography laboratory test cell be designed? Numerical inves-tigation of error on electrical resistivity measurement,” Journalof Applied Geophysics, vol. 127, pp. 45–55, 2016.

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