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Arab J Sci Eng (2014) 39:6851–6862DOI 10.1007/s13369-014-1245-x
RESEARCH ARTICLE - CIVIL ENGINEERING
Improvement of Peat Using Portland Cementand Electrokinetic Injection Technique
Hossein Moayedi · Khairul Anuar Kassim ·Sina Kazemian · Mehdi Raftari · Mehdi Mokhberi
Received: 18 September 2012 / Accepted: 30 November 2013 / Published online: 2 July 2014© King Fahd University of Petroleum and Minerals 2014
Abstract Peat is often referred as problematic soil dueto its high compressibility, low shear strength, and highwater content. However, high surface electrical charge andhigh cationic exchange capacity of peat makes it a goodsource for transporting and/or exchange with cations. In thisstudy, a series of batch test is performed to find out theeffect of strength improvement of portland cement mixedwith the peat. Then, the feasibility of injecting cement elec-trokinetically into peaty soil environment has been assessed.The microstructure of the treated peat was also investigatedby scanning electron microscopy and energy-dispersiveX-ray spectrometer analysis. The results showed that theundrained shear strength, pH, and water content of treatedpeat are affected after electrokinetic treatment. Because ofthe electrokinetic process, the undrained shear strength wasimproved to maximum of 308 % and minimum of 30 % inthe normalized distance of 0.1 and 0.9 from anode, respec-tively. The pH was also increased to the maximum of 8 in thenormalized distance of 0.1 and 0.9 from the anode. However,the water content was reduced after 7 days of electrokineticprocessing.
H. Moayedi (B) · K. A. Kassim · M. RaftariDepartment of Geotechnics and Transportation,Faculty of Civil Engineering, UTM, Johor, Malaysiae-mail: [email protected]
H. Moayedi · M. MokhberiDepartment of Civil Engineering, Estahban Branch,Islamic Azad University, Estahban, Iran
S. KazemianDepartment of Civil Engineering, Payame Noor University,Tehran, Iran
M. RaftariDepartment of Civil Engineering, Khorramabad Branch,Islamic Azad University, Khorramabad, Iran
Keywords Peat · Soil improvement · Electrokinetic ·SEM · Cement
1 Introduction
Peats are composed of plant and animal remains that haveaccumulated, in varying stages of decomposition. Soilswith high organic content have exhibited inferior mechan-ical properties, for engineering purposes, to inorganic soils.These properties include high compressibility, low shearstrength, low permeability, and poor compatibility, which areattributed to a very high capacity of moisture retention by theorganic matter [1].
The two countries that have the largest areas of peat areRussia and Canada, at 150 and 170 million ha, respectively.In addition, peat covers a total area of 30 million ha in USA
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which, in turn, can be found in 42 states [2]. Table 1 providesthe information regarding the area of peat lands in some coun-tries of the world.
The Malaysian peats were selected for this research sincethe peat has been always identified as one of the major prob-lematic soil group in Malaysia. Peat covers approximately8 % of the land or 3 million hectares from the whole coun-try’s land area which is about 37 million ha [3]. Selangor(the state that samples were collected) is the fourth area ofthe peat land in Malaysia, constituting 3 % of the state andcovering about 0.194 million ha. In Malaysia, the depth ofthe peat ranges from less than a meter up to 25 m, dependingon the location [4]. Figure 1 shows the distribution of peatland in Malaysia.
Moreover, fibers present in it induce some anisotropy andinternal reinforcement [5]. Humification of the peats alsoalters the many mechanical properties of soil such as com-pressibility, strength, and hydraulic conductivity.
Table 1 Area of peat lands in some countries of the world [2]
Countries Area of peat land (km2)
Indonesia 170,000
Finland 100,000
Sweden 70,000
China 40,000
Norway 25,000
Malaysia 22,000
Germany 17,000
Brazil 16,000
Ireland 16,000
Uganda 16,000
Poland 15,000
Falklands 15,000
Chile 15,000
Zambia 15,000
Fig. 1 Distribution of peat land in Malaysia [4]
Thus, soil stabilization is necessary to improve the engi-neering characteristics of the peat in order to improve theparameters such as shear strength, compressibility, density,and hydraulic conductivity [6]. The important features ofground treatment includes as follows: improving the bear-ing capacity of the ground, reducing the potential for totaland differential settlement, reducing the time during whichthe settlement takes place, reducing potential for liquefac-tion in saturated fine sand or hydraulic fills, reducing thehydraulic conductivity of the ground, removing or excludingwater from the ground [7].
Electric current was first applied to ground improvementin the 1930s [8]. The electroosmosis is a method of reduc-ing the water content of the soil in situ and thereby increas-ing the shear strength. From this baseline technology, otherapplications were introduced including electroosmotic dewa-tering, ion injection [9,10], contaminant removal [11–13],electro-bioremediation [14,15], electrochemical remediation[16–18], and electrokinetic stabilization [10,19–21].
Electrokinetic remediation refers to the application of anelectrical current in order to promote the migration of chemi-cal contamination, in the form of dissolved ions, toward col-lection wells, from where it may be removed and treated.Electrokinetic stabilization refers to the technique of apply-ing an electrical current through a soil mass to promote themigration of chemicals from injection points, with the aim ofreacting beneficially with the soil to bring about an improve-ment in its properties [22].
The electrokinetic stabilization is an innovative groundimprovement method. When cations are used as stabilizingagents, ions migrate into soils through the processes of elec-tromigration and improve the soil strength [23]. This tech-nique is particularly well suited to soils of low permeabil-ity such as peat since the injection of the stabilizing agentsby hydraulic means is impracticable. In addition, the tech-nique treats soils without excavation which is an advantageover the traditional chemical stabilization [9]. This tech-nique is particularly suited to weak clayey soils that requirestrengthening and yet possess a low hydraulic conductiv-ity, thus preventing the economic introduction of chemicalgrout using conventional hydraulic means [10,19]. However,it can also be used to stabilize heavily over consolidated claysoils, which typically exhibit large volume increases whenwetted.
Electrokinetic method have been used to stabilize the finegrained soil such as clay. For both field stabilization and lab-oratory investigation, electrokinetic’s application has provedsuccessful [19,24–26]. However, this method is not widelyused yet. In this research, an attempt has been made to eval-uate the physical, chemical, and microstructural characteris-tics of stabilized peat by injecting cement grout using elec-trokinetic method.
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2 Material and Methods
The peat samples were collected from Kg. Jawa Klang, Selan-gor, Malaysia (Fig. 2). The site location was about 40 kmaway from laboratory. The containers for the disturbed soilwere capable of being sealed to prevent any loss or gain ofthe moisture. Precautions were taken to avoid any kind ofjolting during the transportation of the soil.
The physicochemical properties of the used peat in thisstudy are presented in Table 2. The peat samples were pre-
Fig. 2 Map showing location of Kampung Jawa, Klang, in the west ofKuala Lumpur
Table 2 Physicochemical properties of peat samples
Parameters Unit Standard Values #1 Values #2
Water content % BS 1377-2-3(1990)
161 164
Bulk density kN/m3 BS 1377-2-7(1990)
13.2 13.2
Specific gravity BS1377-2-8.4(1990)
1.33 1.34
Organic content % BS 1377-3-4(1990)
76 78
Fiber content % ASTM-1997-91
42 41
CEC meq 100 g−1 Gillmanet al. [29]
54 53
pH ASTM [30] 5.63 5.69
Zeta potential mV Pan [28] −17.2 −16.03
pared according to BS 1377-1 (1990) to evaluate the initialphysical and chemical properties of soil [27]. Various prop-erties such as organic content (BS 1377-3: 1990), liquid limit(BS 1377-2: 1990), water content (BS 1377-2-3: 1990), spe-cific gravity (BS 1377-2-8.4: 1990), pH (BS 1377-3-9:1990),ζ potential [28] are evaluated and mentioned in Table 2. Forgetting a good reproducibility and repeatability of the tests,three samples were selected with each sample to get mois-ture content and some other basic tests. Finally, the obtainedresults were averaged.
Cement includes various minerals. It is manufactured bycombining cement clinker (a sintered material of limestoneand clay) with 2–3 % gypsum. Cement has been widelyapplied to improve the soil characteristics. The strengthimprovement of the cement-stabilized soil is attributed tothe physicochemical reactions which take place, consistingthe hydration and hardening of the cement and the interac-tion between the substances in the soil and the products ofcement hydration [31].
2.1 Batch Test
Unconfined compressive strength (UCS) tests were con-ducted on the unstabilized peats and stabilized peat with dif-ferent cement ratio, as for the strength evaluation test. Thesampling and curing process for the unstabilized and stabi-lized samples was performed according to the EuroSoilStabdesign guideline [32]. The design guide: Soft soil stabiliza-tion, which was prepared as part of the EuroSoilStab [32]Project, describes the different methods of stabilizing softpeat, the design approaches that are normally adopted, thetests methods to determine the appropriate binder, and the siteequipment and installation procedure to be used. The speci-mens were then placed in a unique design sample box whichconsist of a plastic tray positioned in order to store specimensvertically. The tray was then filled with water up to 5.0 cmto simulate the in situ condition. After 10 and 30 days (cur-ing time) at room temperature, the specimens were extractedfrom the plastic tubes and the UCS tests performed. The sam-ples were 76 mm long and 38 mm in diameter. As stated, theeffectiveness of the treatment was evaluated by measuringthe shear strength by performing UCS test (BS 1377: Part 7:1990, Clause 7) after curing.
2.2 Large-Scale Electrokinetic Treatment
The electrokinetic test experiments are conducted in a cellcomprised of three compartments: an anode compartment, acentral electrokinetic box, and a cathode compartment. Thecell is made of Perspex glass which can be opened at thetop for each compartment. The central box is reserved forthe soil specimen with the dimension of 0.40 m long, 0.10 mwide, and 0.15 m high. The two outside compartments are
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reserved for the anode and the cathode chambers and con-tained the electrolyte solution. The anode and the cathodecompartments each contained three holes. The role of thetop hole is for measuring the electroosmotic flow, while thebottom holes are used to wash out the anode or the cath-ode compartment. The electroosmotic flow is determined bymeasuring the quantity of flow of solution collected in a grad-uated cylinder via a plastic tube connected to the top hole.The two walls separating the three compartments in the elec-trokinetic cell were perforated with a number of holes. Filterpaper is used in the inner edge for the middle compartmentthat is both ends of the soil specimen between the anodeand the cathode compartments. The filter paper inhibits themovement of soil particles from each side of the soil speci-men inside the cell (e.g., to reduce the colloidal transferringto the electrodes).
Two electrodes are placed in the anode and the cathode topass the DC current compartments. Two passive electrodesare inserted at the extreme edges of the soil specimen too.The electrodes were made of graphite which is inert. Inertelectrode can prevent the decomposition of the electrode andrelease the ions into the soils. Each graphite electrode wasmade to fit the inner dimensions of the anode and the cathodecompartments. Voltage of 60 V was used in the electrokinetictests. The setup of the EK injection is shown in Fig. 3.
The soil sample is placed inside the middle compartmentin the electrokinetic experiment cell. Soil samples were com-pacted directly in the central box thorough five equal layers.Every layer was compacted with the small hammer (1.2 kgweight) and 60 blows. The hammer dropped from 5 cm heightonly to keep the electrokinetic box in a safe position sincethe high compaction energy (i.e., higher height for hammer todrop) could damage the central electrokinetic cell. All com-pacted specimens were prepared with natural water contentof 161 % having the error bands of 5 %. The purpose of com-pact the soil is to homogenize the soil sample for every test.Then, the soil surface is leveled by removing the excess soil.
Fig. 3 Schematic view of large-scale electrokinetic equipment
Table 3 Electrokinetic tests codes
EK code Anolyte Catholyte
DW–DW Distilled water Distilled water
Ce–DW Cement (50 g/l) Distilled water
The box is sealed with silicone to prevent leakage. Next, dis-tilled water is poured into the outer compartment in order tosaturate the soil sample. However, the soil sample left to besaturated for the 24 h before every electrokinetic test whichmeans the peat water content raised up significantly and allthe voids were filled initially with water. All tests were con-ducted at constant electric current to control the boundarycondition under constant electrolysis rates. The electroki-netic test is started by providing a constant voltage drop of60 V across the soil sample throughout the test period of7 days. After the saturation is reached, the anode and cath-ode chambers were filled with anolyte and catholyte. Twodifferent tests are performed where the anolyte was different(Table 3).
The electrical potential is taken for six points at the dis-tance of 5, 11, 17, 23, 29, and 35 cm from anode whilethe current flowing in the circuit is taken too (Fig. 4). Foreach electrolyte, the value of pH, temperature, and efflu-ent is taken. All readings are taken every 24 h. No attemptsare made to control the current density or the pH of theelectrolytes.
The copper wires were placed in the soil, and the voltagewas measured using digital multimeter model GDM-8135.As mentioned, the soil compartment has a rectangular cross-section of 10 × 15 cm with 40 cm long. In order to acquirean ample view of the distribution of the electrokineticallyinjected cations into the soil at the end of the experiment,each treated soil specimen was subdivided into several equalsubdivisions. The soil specimen was, initially, cut horizon-tally into two halves where an upper segment and a lowersegment was produced. Each half was, then, subdivided intofive equal slices. After 7 days, the DC supply is disabled. Thesoil sample is left for 7 days of curing. After curing period, itwas subjected to vane shear test, water content test, and pHtest for top and bottom layer at the specific distance from theanode (i.e., 4, 12, 20, 28, 36 cm from the anode). The pointsthat the electrical voltage probes are installed is shown inFig. 4. Overflow at cathode and inflow at anode was measureddaily by volumetric cylinder. Both electrode compartmentsare similar and can hold up to 6.25 L effective volume ofelectrolyte. Ventilation ports were used at the compartmentsto allow gas bubbles (e.g., hydrogen and oxygen) to escapeand prevent pressure build up. One liter liquid reservoir wasconnected to the cathode to supply liquid and to measure pHwithout electrical interference.
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Fig. 4 Locations of vane shear, water content, and pH in both top and bottom layers
3 Results and Discussion
The UCS of treated peat with 2, 4, 6, 10, and 20 % of cementconcentrations (e.g., % of the wet peat) is showed in Fig. 5.The maximum UCS results for the treated peat with 2, 4, 6, 10,and 20 % were 16.3, 22.8, 30.1, 40.3, and 46.6 kPa, respec-tively (Fig. 5a). The UCS results of the treated peat increasedby increasing the percentages of cement additives. Since find-ing the optimum value for the UCS was not the objective ofthis research study, the cement addition stopped up to the20 % of the wet peat sample with respect to total mass beforetreatment. The water content of treated peat also showed inFig. 5b. It can be seen that increasing the cement concentra-tion caused a significant reduction in the water content (i.e.,low as 128 %). This is due to hydration process of cementwhere the peat water will be used during the curing time.
When cement mixed with water, it will form calcium sili-cate hydrate and calcium hydroxide (Ca(OH)2). Calcium sil-icate hydrate, generally referred to as CSH gel, forms on thesurfaces of the cement particles, and because it has a stronglycementing effect, it binds the soil together and increases itsstrength. Since the hydraulic reaction takes place consider-ably faster than the pozzolanic reaction, cement-stabilizedsoil normally attains higher strength than lime stabilized soil,particularly in the first few months [33]. Since some Ca(OH)2is formed during cement stabilization, pozzolanic reactionswill also take place, though to a lesser extent than in lime sta-bilization. Hence in cement stabilization, in addition to thecementation reaction, the same strength enhancing reactionproducts is formed as in lime stabilization in about one-fifthof the quantity [34].
In addition, it is difficult to stabilize the peats (as a soft soilthat requires strength improvement) due to its high organiccontents by using cement only. When the organic content ofthe soft soil is high, the organic matter impedes the hydrationof the cement [33]. The organic matter has a high retention
0
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2 4 6 10 20
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Cement concentration (% of the wet peat)
Fig. 5 a UCS, and b water content of the treated peat with cement (upto 20 % of the wet peat)
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il p
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Normalized distance from Anode
Natural pH DW-DW Ce-DW
(b)
Fig. 6 Results after the electrokinetic treatment. a Undrained shearstrength of treated soil, and b the soil’s pH
of liquids because of its special structural features whichwill cause the organic particles to be absorbed on the sur-face of cement and soil particles, which in turn impedes boththe formation of cement hydration products and the interac-tion between soil particles and the hydration products. As aresult, the process results in only a limited improvement ofthe cement soil strength [33]. Since the used peat samplesin this research were acidic (pH ∼ 5.6), this would slightlyinhibit cement reaction. The results from the previous stud-ies indicated that the soils with the very high organic contentproducing a pH lower than nine in the pore solution stronglyaffect the development of cementing products and almost nostrength gain can be noted; it means pH for cement reactinggenerally need to be around 12 [35].
3.1 Distribution of Shear Strength After ElectrokineticTreatment
The undrained shear strength for each test is shown in Fig. 6awhich is the average that taken from both of the top and
bottom layers. The electrokinetic stabilization, either elec-troosmosis or electromigration, increases the strength of soilsample compared to the strength obtained without electroki-netic test. However, the Ce–DW test shows a decreasingtrend in the undrained shear strength of anode toward thecathode (Fig. 6a). The increase in the shear strength couldbe due to the water reduction during the hydration processas well as chemical reactions that are taken after cationicinjection from cement decomposition. In Ce–DW system, thestrength is increased significantly near anode. When stabiliz-ing agents are used, the electromigration of ions (i.e., cationsthat released from anode as well as cement and/or anionsthat are released from cathode) moves into the soil wherethey react with the compound of the peat. The used ordinaryportland cement released Ca2+, Si4+, Al3+, and Fe3+ whenthey are dissolved. However, parts of the cement were settledat the bottom of the anode chamber. This makes it hard todetermine whether the movement of dissolved cations fromanode toward the cathode was the main reason for such shearstrength improvement or not.
In the DW–DW systems, the calcium (Ca2+) that is avail-able in the peat composition and hydroxide (OH−) ions thatare released from the cathode reacts in places near the cath-ode (Fig. 6a). OH− ions released by the cathode electrodeproduce the alkalinic (pH ∼ 9) conditions. Such condition isappropriate enough for dissolution of silica and alumina priorto the formation of calcium silicate hydrate (CSH) and cal-cium aluminate hydrate (CAH). These are the gels that crys-tallize to cause stabilization [36,37]. It is noteworthy that therate of dissolution increases greatly as pH = 10 is reached.The soil’s pH in the Ce–DW system is higher than DW–DWsystem along the central box. Besides, the soils near anodeand cathode showed a higher pH than other points (Fig. 6b).
As can be seen from the Fig. 7, the water content oftreated samples in both DW–DW system and Ce–DW system
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Wat
er C
on
ten
t (%
)
Normalized distance from Anode
Natural Wc DW-DW Ce-DW
Fig. 7 Water content of treated soils after electrokinetic processing
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Fig. 8 pH in electrolyte of eachEK test
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H o
f E
lect
roly
teTime (Hours)
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(Ce-DW) Cathode
(Ce-DW) Anode
is approximately higher than their natural condition. Theremight be a question why after the hydration process the watercontent is still as high its natural condition. The answer isrelated to the initial condition that we made where the peatsamples in the central electrokinetic box was fully saturated.After 7 days curing time, the samples once again hydratedand the water content is reduced to a much less values nearto their natural condition. This process can be seen in theCe–DW system.
3.2 pH Variations Throughout the Soil
Electrolysis occurred in both electrolytes. Oxidation at anodewill release ion hydrogen (H+), while reduction at cathodewill release ion hydroxide (OH−). Since the electric fieldis applied, the H+ will be attracted to the cathode, whereasOH− will be attracted to the anode. Thus, at near anode, thesoil would tend to be acidic and pH will be lower. Mean-while, the soil at near cathode will be alkaline and posseshigher pH. The pH in the electrolyte during the EK test isexpected to decrease in anolyte and increase in catholyte dueto electrolysis occurred. Figure 8 shows the pH variationsthroughout the soil sample for each tests. In anode, hydro-gen ion (H+) is produced, causing acidic conditions, whereasin cathode, hydroxide ion (OH−) is produced and tends tobe alkaline. In the three EK tests, they show the trend aspredicted where the pH is decreasing in anolyte, while thepH in catholyte is increasing as shown in Fig. 8. Thus, wecan conclude that electrolysis was happened during the EKtests.
3.3 The Electrical Potential Variation
The electrical potential profile can show the changes in ioniccompositions of the pore fluid [38]. If the electrical potentialprofiles plotted showing a decreasing trend which is fairly
linear, it means that the ionic composition in the pore wateris uniform throughout the soil sample [39]. When there isa sharp drop in the potential, it means that the precipitationis formed, resulting in a high resistivity zone. The electricalpotential across the electrokinetic box for various time treat-ments is shown in Fig. 9. It can be seen that in the DW–DWsystem, the electrical potential rapidly decreased in the firsttwo days that the electrokinetic test is started (Fig. 9a). How-ever, up to 4 days and in the Ce–DW system, the electricalpotential reduction was insignificant (Fig. 9b). Figure 10 alsoshows the variation of electrical voltage potential for differentelectrical probe during the electrokinetic test period. There isa large difference between both DW–DW and Ce–DW sys-tems. The electrical voltage potential (V/cm) is reduced in thefirst 72 h and tend to increase after that (Fig. 10b). However,in the DW–DW system, the potential was slowly reducedduring the test procedure (Fig. 10a).
It is well known that the potential energy of a system willbe increased as the positive charge ions (cations) in a mediatend to be closer together. This is the main reason why in theplaces in the vicinity of the anode there is a higher electri-cal potential energy than the cathode side. As can be seen inFig. 10, the electrical potential energy differences betweenthe anode and cathode side in the Ce–DW system is remark-ably higher than DW–DW system. This is also confirmingthe release of cations from the portland cement into the soil.Although, in the first 48 h after injecting the Ce–DW werestarted the electrical potential tend to increase, it is then con-tinuously decreased which shows the remained cations tendto move opposite from each other.
3.4 Variation of Soil Resistivity, Current Density, andEnergy Consumption in Electrokinetic Treatment
Soil resistivity is a factor to measure how much the soil resistswith respect to the flow of electricity. It is a critical parameter
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Fig. 9 Electrical potentialduring the treatment (v/cm). aDW–DW system, b Ce–DWsystem
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(b)
in design of systems that rely on passing electrical currentthrough the surface of the Earth. An understanding of thesoil resistivity and how it varies with depth in the soil is nec-essary to design the grounding system in an electrical sub-station or for lightning conductors. It is required for designof grounding (earthing) electrodes for high-voltage directcurrent transmission systems. In addition, the soil resistivityvalue is subject to great variation due to moisture, tempera-ture, and chemical content.
Soil resistivity is one of the driving parameters determin-ing the corrosiveness of soil. As stated by the British stan-dard BS-1377 (Part 3:1990, section 9.5), the peat soil duringthe DW–DW test is not considered as a corrosive soil sinceits resistivity is higher than 10,000 �cm; however, the peattreated with the cement is considered as moderately corro-sive to corrosive since its resistivity is between 1,000 and10,000� cm (Fig. 11).
Current density is a measure of the density of flow of a con-served charge [40]. Usually the charge is the electric charge,in which case the associated current density is the electriccurrent per unit area of cross-section, but the term current
density can also be applied to other conserved quantities. It isdefined as a vector whose magnitude is the current per cross-sectional area. Alshawabkeh and Bricka [41] stated that highcurrent levels generate more acid (e.g., more acid will workfor the electrokinetic process); however, it increases the totalionic concentration that helps the particles to flocculate moretogether [41]. The resulted current density from the Ce–DWsystem is much higher than DW–DW system (Fig. 12). It isin contrary with the results observed from the shear strengthimprovement of treated sample with cement (i.e., in batchtest and electrokinetic experiments) where the cemented soilshows much higher strength values.
Figure 13 shows the measured total energy consumptionfor both of the Ce–DW and DW–DW systems. Total energyconsumption that required for treating a unit volume of soildepends on many factors including stabilizer properties, soilcharacteristics, direct electrical applied, electrode config-uration, and spacing [42]. The energy consumption resultchanged during EK progress. It was very low for the DW–DW system and became much higher for Ce–DW system(Fig. 13).
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t (V
/cm
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Time (Hours)
2.5 cm 4.5 cm 6.5 cm
8.5 cm 12.5 cm
(b)
Fig. 10 Electrical potential gradient during the treatment (distancefrom the anode (v/cm)). a DW–DW system, b Ce–DW system
3.5 Microstructural Characteristics
For studying the microstructure of the treated soil, scan-ning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) tests were performed. EDX is ananalytical technique used for chemical characterization or theelemental analysis of a sample. The characterization capabil-ities of EDX are due in large part to the fundamental principlethat each element has a unique atomic structure allowing X-rays that are properties of an element’s atomic structure tobe identified uniquely from one another. It should be men-tioned that the EDX outputs were measured as the averageof three measurements of the same location, and microstruc-tural studies with equipment brand Hitachi Japan (ModelS3400N) were performed on each sample. The EDX outputof untreated peat is presented in Fig. 14. The EDX result ofnatural organic soil showed the presence of oxygen (46.0 %),carbon (29.0 %), calcium (3.0 %), alumina (2.5 %), and silica(5.0 %) accordingly.
100
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0 24 48 72 96 120 144 168
Res
isti
vity
, (Ω
-cm
)
Time (Hours)
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Fig. 11 Variation of soil resistivity during the course of EK experi-ments
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Fig. 12 Variation of current density with time
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Fig. 13 Variation of energy consumption with time
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Fig. 14 EDX of a unstabilized peat, and b stabilized peat with cementfrom anode side after electrokinetic treatment
It is important to investigate the role of inorganic mat-ter substitution of the peat and its roles on improving theundrained shear strength. The presence of alumina and sil-ica could probably due to the availability of the clay fractionand more specifically kaolinite. However, other clay miner-als (smectite, vermiculite, illite) also have alumina and sil-ica as their main substitutions. However, after X-ray diffrac-tion (XRD), kaolin [Al2Si2O5(OH4)] observed to play asthe main mineral. It can be concluded that the kaolinite is themain mineral of the clay fraction of the used peat.
Several samples from the highest resulted (i.e., nearanode) treated peat with electrokinetic technique wereselected in order to assess their microstructure changesby using SEM micrograph and EDX experiment. Addingcement to the soil will change the acidic environment to an
alkaline environment (e.g., a pH higher than 10). Although,the pH of the cement–water mixture in the anode chamberwas about 11.2, after mixing with such acidic soil, its pHreduces to about 10.2. As stated by Tremblay and Duchesne[35], producing a mixture with the pH lower than 9 in thepore solution strongly affects the development of cementingproducts and almost no strength gain can be noted. On theother hand, the maximum alumina and silica atoms dissolu-tion occurred in pH at 10 produced calcium silicate hydrate(CSH) and calcium aluminate hydrate (CAH) gel. That iswhy the significant improvement in the UCS result hap-pened in the pH between 9 and 11. In addition, reductionin the thickness of the electrical double layer and increasingin ionic concentration makes a better environment for the col-loidal particles such as humus or clay fractions to flocculate[17,43,44]. Similar to the batch test and due to the addi-tion of the cement to the baseline peat, a large proportionof the silicate, calcium, and aluminates added to the base-line peat and almost uniformly distrusted through the peatsamples (Fig. 15). Figure 15a shows the SEM micrographthat is taken from the treated peat near anode. In addition,the distribution of various important ions including alumina(Fig. 15b), silica (Fig. 15b), calcium (Fig. 15b) are depictedseparately.
4 Conclusions
The following conclusions are drawn based on this study:
• The results of the electrical potential for the Ce–DW sys-tem were higher than DW–DW system. Although, in theDW–DW system the electrical potential tends to decreasefrom the first day, in the Ce–DW system, the electricalpotentials were initially increased up to 48 h. The electri-cal potential was increased to the maximum of 56.2 V in0.2 normalized distance from the anode for the Ce–DWafter 48 h of test being started.
• The electrokinetic injection of cement additive throughthe peat environment changed the physical, chemical, andmicrostructural properties of peat. However, the cemen-tation effect was not consistent along the soil sample. Itwas more effective in the anode side (i.e., normalizeddistance of 0.1 from the anode) as the resulted undrainedshear strength was raised to 29 kPa. Comparing with theshear strength of the natural soil, the soil specimen fromthe Ce–DW system could increase the shear strength upto 308 %.
• Charged ions such as hydroxide and hydrogen aremigrated into the soil by the process of electromigration.The soil’s pH is changed due to such migration. Devel-oping the CSH and CAH gel, and the electrochemical
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Fig. 15 Spectral image taken from the treated peat near anode afterelectrokinetic treatment. a SEM micrograph, and distribution of b alu-mina, c silica, d calcium ions
properties of the peat colloids, is also affected when thepH along the electrokinetic cell is altered.
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