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Strength Measurement and Textural Characteristics of Tropical Residual Soil Stabilised With Liquid Polymer

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Strength measurement and textural characteristics of tropical residual soil stabilised with liquid polymer
  Strength measurement and textural characteristics of tropical residualsoil stabilised with liquid polymer Nima Latifi a, ⇑ , Ahmad Safuan A. Rashid b , Sumi Siddiqua c , Muhd. Zaimi Abd Majid a a Institute for Smart Infrastructure and Innovative Construction (ISIIC), Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia b Geotechnic & Transportation Department, Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia c School of Engineering, The University of British Columbia, Okanagan Campus, Kelowna, BC, Canada a r t i c l e i n f o  Article history: Received 23 November 2014Received in revised form 31 January 2016Accepted 10 May 2016Available online 10 May 2016 Keywords: Laterite soilLiquid polymerN 2 -BET surface areaTextureUCSPlasticity index a b s t r a c t The stabilisation of soils with additives is a chemical process that can be used to improve soils thatcontain weak engineering properties. The effects of non-traditional additives on thegeotechnical proper-ties of soils have been the focus of much investigation in recent years. It has been well established thatthe plasticity index and also the size, shape, and arrangement of soil particles will affect the treatmentprocess of natural soils with additives. In this study, a commercial liquid polymer (SS299) was used toimprove the strength of Malaysian residual soil. Unconfined compressive strength (UCS), field emissionscanning electron microscopy (FESEM), N 2 -BET surface area, and particle size analysis tests were usedto investigate the influence of SS299 and the plasticity index on the time-dependent compressivestrength and textural characteristics of tropical residual soil. The UCS results showed that the additionof6%(astheoptimumamount)oftheselectedadditiveincreasedthecompressivestrengthoflateritesoilnoticeably, after 7days of curing period. In addition, the increased compressive strength of the treatedsamples withthecuringtimewasevident. BasedontheFESEMresults, itwasfoundthat thestabilisationprocessmodified theporous networkof thelaterite soil. Furthermore, newwhite layers of reaction prod-ucts were formed on the surface of clay particles.   2016 Elsevier Ltd. All rights reserved. 1. Introduction Soil improvement is the process of improving the physical andengineering properties of soil to obtain some predeterminedvalues. It can be done in various ways such as mechanical, biolog-ical, physical, chemical and electrical [1–4]. Nowadays, usingchemical additives for soil stabilisation is becoming more popular.The aims of soil treatment using chemical stabilisers are toimprove stress–strain and strength properties, control of volumestability, hydraulic durability and conductivity [5–12].A stabiliser is a chemical compound that immediately or grad-ually enhances the soil’s engineering properties through a numberof mechanisms. There are two general groups that exist as soil sta-bilisers: traditional stabilisers and non-traditional additives [13].Traditional stabilisers include cement, lime, fly ash, and bitumi-nous materials; non-traditional additivesconsist of various combi-nations such as enzymes, liquid polymers, resins, acids, silicates,ions, and lignin derivatives [14–19]. It should be noted that theexact chemical compositions of non-traditional additives are notdiscloseddueto theproprietarynatureof commercial stabilisationadditives. In addition, it is well established that the majority of these products contain secondary additives such as catalysts, sur-factants and ultraviolet inhibitors. There is generally a dominantorprimarystabilisationmechanismsupportedbysecondarymech-anisms due to the insertion of complementary additives [20–22].Currently, non-calcium-based liquid soil additives are activelymarketed by a number of companies. Besides being cheaper totransport compared to traditional bulk stabiliser materials, theseproducts are a potentially attractive alternative for soil treatment.They are mostly sold as concentrated liquids, which are dilutedwith water at the site. Some are directly applied to the soil beforecompactionwhileothersarepressureinjectedintodeeperlayers.Itshould be stressed that the results of previous studies have indi-cated that non-traditional liquid additives can help to increase soilstrength with curing time [23–30].On the other hand, each type of chemical additive has differentmechanisms and influences on soil properties. For instance, therehave been noticeable important dissimilarities in the stabilisationmechanism of tropical soils from the moderate climates. Rockweathering in tropical areas is very rigorous and is characterisedby the speedy disintegration of feldspars and ferromagnesian, the   2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: (N. Latifi).Measurement 91 (2016) 46–54 Contents lists available at ScienceDirect Measurement journal homepage:  displacementof silicaandbases(Na 2 O,K 2 O,MgO),andtheabsorp-tion of iron and aluminium oxides [31]. This process is referred toaslaterisationandincludesleakageof SiO 2  anddepositionof Fe 2 O 3 and Al 2 O 3  [30]. Generally, laterite soils are highly weatheredreddish tropical soils that have concentrated oxides of iron andaluminium with kaolinite, the predominant clay mineral [18].Laterite soil can be found in six areas around the globe: Africa,India, Southeast Asia, Australia, Central America and South Amer-ica. However, there is an emphasis that due to the movements of climatic zones in the geological past, relevant regions of lateritecanbelocatedinplacesthatarenotwithinthetropics[32,33].Thissoil group usually exists at hillsides and offers brilliant borrowareas for wide adoption in many different construction operations.Optimum utilisation is determined by the quantity of issuesencountered in construction connected to their workability, fieldcompaction, and strength.Studies have demonstrated that laterite soil forms a large partof the soil in Malaysia, and it has been used in different areasand projects as natural soil [34,35]. This study investigates theinfluenceofanewnon-traditionaladditive(SS299)–acationicandalkalinepolymer, the plasticity index, andcuring time onthe com-pressive strength and textural properties of tropical residual soil.Laboratory tests that were performed included sieve analysis,Atterberg limits, standard compaction, and unconfined compres-sion strength (UCS) tests. Paired micro-characterisation was alsoused to study the structure and fabric of the soil-additive matrixusing field emission scanning electron microscopy (FESEM),Brunauer, Emmett and Teller (BET) surface area and particle sizeanalysis (PSA) tests. 2. Materials and methods  2.1. Materials Residual laterite soil was chosen for this research as it is notonlyabundantlyavailablebutalsousedinmanygeotechnicalengi-neering works in Malaysia. Laterite soil was obtained froma depthof 2–3m below the ground surface. The particle size distributionand engineering properties of natural laterite soil are shown inFig. 1 and Table 1, respectively. In addition, Table 2 presents the chemical characteristics of the used laterite soil in this study, asa result of the energy-dispersive X-ray spectrometry (EDAX) test.With reference to Table 2, the ratio of SiO 2  to Al 2 O 3  yields a valueof 0.81. The latter confirmed that the soil used in this study wasresidual laterite soil [36]. In addition, Fig. 2 illustrates the diffrac- togram resulted from the XRD analysis on the soil. The XRD resulthighlightedthat the mainminerals present in the soil were kaolin-ite(2 h  =12.5  , 20  , 35  , 38  , 46  , 55  ), quartz(2 h  =26  , 36.5  , 42.5  ,50  , 62  ), goethite (2 h  =21.5  , 37  , 41  , 53  ), and gibbsite (2 h  =18  ,19  , 27  , 39  ) [37]. Three different samples (referred to as soil A,soilB, andsoilC)withdifferentplasticityindexeswereusedinthisexperimental study. Soil A is the natural laterite soil, soil B is thesame soil with the addition of 20% bentonite by weight, and SoilC is the same soil with the addition of 30% bentonite by weight.According to their properties, the soils lie below the A-line in theplasticity chart, thus classifying them as silty soils with differentplasticity according to the Unified Soil Classification System(USCS). Additionally, the physicochemical properties of usedbentonite are given in Table 3.A cationic and alkaline polymer of a locally manufacturednon-traditional additive, known as SS299, had been selected forthis study. The additive had been prepared, sampled and sent tothe laboratory by the manufacturer GKS PRO CHEM (M) Sdn.Bhd., a local company in the Johor state of Malaysia. The exactchemical composition of this additive has not been released, sinceit is a commercially registered brand. Table 4 shows the importantphysicochemical properties of this selected additive.  2.2. Sample preparation The results of previous studies on laterite soils have revealedthat the plasticity and compaction properties of this soil werechanged significantly during the oven drying process [13].Consequently, the present study has used the air-drying method 01020304050607080901000.001 0.01 0.1 1 10    P  e  r  c  e  n   t  a  g  e   f   i  n  e  r   (   %   ) Particle size (mm) Fig. 1.  Particle size distribution of laterite soil.  Table 1 Characteristics of the natural laterite soil. Engineering and physical properties ValuespH (L/S=2.5) 5.35Specific gravity 2.69External surface area (m 2 g  1 ) 41.96Liquid limit, LL (%) 75Plastic limit, PL (%) 41Plasticity index, PI (%) 34BS classification MHMaximum dry density (mgm  3 ) 1.31Optimum moisture content (%) 34Unconfined compressive strength (kPa) 270  Table 2 Oxides and chemical composition of laterite soil. Chemical composition (oxides) Values (%)SiO 2  25.46Al 2 O 3  31.10Fe 2 O 3  35.53CO 2  7.91 N. Latifi et al./Measurement 91 (2016) 46–54  47  to prepare all the mix designs of the laterite soil. The air-dried soilwas broken into smaller particles and filtered through a 2mmsieve to confirm the uniformity of the specimens [18]. Deionisedwater was used in all features of the sample preparation, due tothe fact that it is generally recommended for chemical testingpractices. In order to prepare the various mix designs, a standardprotocol was used. The first step was conducted based on clause3.3.4.2ofBS1377:Part4:1990a.Thisstepincludedthedetermina-tion of the optimum moisture content (OMC) for natural soil andsoils mixed with different amounts of bentonite soil. For the sec-ondstep, therequiredamountsof polymer as apercentageof opti-mum water content were mixed and then added to the dry soils.The pure amounts of aqueous polymer were chosen as 3%, 6%, 9%and 12% by total weight of the amount of water needed to achievethe optimum water content. These amounts of polymer were thendiluted in water and mixed with the soil samples. To get ready ahomogeneous mix, irregular hand mixing with palette kniveswas done. Subsequently, target dry density and moisture contentwere reached by compressing the samples in a steel cylindricalmould fitted with a collar that accommodated all the mixtures.The required compaction was done by using a hydraulic jack withpersistent compaction based on clause 4.1.5 of BS 1924: Part 2:1990b. Finally, the cylindrical samples were extruded using a steelplunger, trimmed, cleaned of releasing oil, and placed in a plasticbottle, whichwas thenwrappedinseveral runsof clingfilm. Thesesamples were cured for 3, 7, 14, and 28days in a 27±2  C temper-ature controlled room [2].  2.3. Testing methods and devices The soil improvement index was determined by conducting aseries of UCS tests (BS 1924: Part 2: 1990) on multiple specimensat different time intervals. A rate of axial strength equal to 1% perminute was applied to the samples. The acquisition data unit(ADU) was used to automatically record the applied load and axialdeformation. The failure of each specimen was defined by its peakaxial stress. The failed specimens were dried and weighted at theconclusion of each test to calculate their moisture content. A min-imum number of three specimens were tested for each specificmixture by the UCS test to provide an index of soil improvement.It has been well established that the treatment done on soilusingchemicaladditiveshaseffectonthesoil’ssize,shape,andsoilparticle arrangement [4,6]. If the additives were added to improvethesoil’scondition,itsimprovementreliesonthequantity,quality,and formation pattern of the new particles around the soil parti-cles. In this study, a JSM-6701F JEOL field emission scanning elec-tron microscope (FESEM) was used to scrutinise the soil samples’fabric and bonding concerning clay materials prior to and aftertreatment. Through this technique, each sample was sputteredwith platinum for 120s at 30mA under high vacuum until theywere completely covered and ready to be used for the microscopicanalysis.Particle surface area is an essential feature in understandingboth the physical and chemical properties of the treated soil. Thisis because many chemical reactions in soils occur at the surface[29]. In this study, the Nitrogen-based Brunauer–Emmett–Teller(N 2 -BET) surface area method has been used to determine thechanges that occurred on the surface area and the micro pores of treatedsampleswiththeselectedadditive. Inthis process, thesur-face area was derived through the physical adsorption of nitrogengas by means of a micromeritics surface area analyser. It is alsomicroprocessor controlled and interacts with a XP-based PC whichallowsfor physisorption investigation. During this method, a smallamount of the cured sample was placed in the sample container.Nitrogen gas was pumped in after degassing for 1h at 130  C,and the outer area value was estimated through the adoption of the single point BET technique. Fig. 2.  XRD pattern of the laterite soil.  Table 3 Characteristics of bentonite soil. Engineering and chemical properties ValuespH (L/S=2.5) 9.12Specific gravity 2.64External surface area (m 2 g  1 ) 28.60Liquid limit, LL (%) 302Plastic limit, PL (%) 42Plasticity index, PI (%) 260BS classification CEMaximum dry density (mgm  3 ) 1.29Optimum moisture content (%) 38Unconfined compressive strength (kPa) 286SiO 2  (%) 64.50Al 2 O 3  (%) 20.72Fe 2 O 3  (%) 7.69MgO (%) 2.11Na 2 O (%) 3.18CO 2  (%) 1.80  Table 4 Important physicochemical properties of SS299. Physicochemical propertiespH (L/S=2.5) 11.5Phase LiquidPolymer type CationicSolvability in Water SolutionViscosity (cP) 260Density(g/cm 3 ) 1.3Colour Pink48  N. Latifi et al./Measurement 91 (2016) 46–54  Particlesizedistributionofsoilcanbeimportantinunderstand-ing its physical and chemical properties as it affects strength andload-bearing properties [6]. Particle size analyses were carriedout using the CILAS Particle Size Analyser. The CILAS 1180 ParticleSize Analyser, which utilises the laser diffraction technique with alaser light wavelength,  k  635nm, is able to measure particlesranging from 0.04 to 2500 l m. The size distributions of the testedspecimens were determined based on the Fraunhofer diffractiontheoryby usingthe softwareParticleExpert V5.12. Theentiretestswere carried out with approximately 0.2g of samples and othertest procedures were in accordance with BS ISO 13320:2009(Particle size analysis – Laser diffraction methods).  2.4. Testing programmes In order to simplify the presentation of the results, a specimendesignationschemewasemployed.Thefirstandsecondcharactersindicated the soil name and type of treatment, respectively. Theother characters included LC for laterite soil, GB for bentonite soil,UNT for untreated, T for treated, and D for days. For example, thenotation of LC(A)T3% represents the sample that is natural lateritesoil without mixed bentonite (LC(A)), with treated SS299 of 3% bytotal dry weight of the amount of soil (T3%). Table 5 shows a sum-mary of all the samples tested in this study. 3. Results and discussion This experimental study was conducted to investigate theeffects of the SS299 non-traditional additive, the plasticity index,and curing time on the unconfined compression strength andtextural changes of tropical residual soil. The properties of thetested soils in terms of particle size analysis, Atterberg limits,and compaction parameters are given in Table 6. The results of the UCS, FESEM, BET surface area, and particle size analysis (PSA)are discussed in the following sections.  3.1. Effect of polymer content, curing time and plasticity index on theUCS  The unconfinedcompressive strength (UCS) test was used as anindex test to investigate the effectiveness of the selected additiveon the compressive strength of natural laterite soil and soil mixedwith different percentages of bentonite soil. Fig. 3 shows theresults of the UCS tests of the laterite soil and the stabilised mix-tures of laterite soil with different amounts (3%, 6%, 9%, and 12%)of SS299 at different curing periods. Ostensibly, the SS299 treat-ment significantly enhanced the strength characteristics of thelaterite soil. Based on the results, it can be said that generally theadditionof SS299increased the UCSof the laterite soil at all curingperiods. However, the addition of 6% SS299 showed the largestincrement compared to the addition of 3% SS299. Besides that,the increase of UCS between 6% and 9% is smaller compared tothe increase of UCS between the addition of 3% and 6% of SS299.Generally, it seems that the changes in compressive strength for  Table 5 Summary of samples tested in this study. Type of soil % By weightof treatedSS299, TNotations Curingtime, D(days)Numberof testedsamplesNatural laterite soil-without bentonite, LC(A)Untreated(UNT)3%6%9%12%LC(A)UNTLC(A)T3%LC(A)T6%LC(A)T9%LC(A)T12%037142825Natural laterite soil-mixed with 20% byweight of bentonite,LC(B)Untreated(UNT)3%6%9%12%LC(B)UNTLC(B)T3%LC(B)T6%LC(B)T9%LC(B)T12%037142825Natural laterite soil-mixed with 30% byweight of bentonite,LC(C)Untreated(UNT)3%6%9%12%LC(C)UNTLC(C)T3%LC(C)T6%LC(C)T9%LC(C)T12%037142825Total 75  Table 6 Engineering properties of soil LC(A), soil LC(B), and soil LC(C). Property Soil LC(A) Soil LC(B) Soil LC(C)Specific gravity 2.69 2.64 2.61Mixed GB percentage (%) 0 20 30 Grain size Gravel (2–75mm), (%) 5 0 0Sand (0/075–2mm), (%) 35.3 29.3 24.5Silt (2–75 l m), (%) 26.5 31.2 33.4Clay (<2 l m), (%) 33.2 39.5 42.1  Atterberg limits Liquid limits, (%) 75 96 114Plastic limits, (%) 41 51 56Plasticity index, (%) 34 45 58 Compaction parameters Optimum Moisture Content, (%) 34 36.5 38.4Maximum dry unit weight, (g/cm 3 ) 1.31 1.21 1.17 200250300350400450500550 0 3 7 14 28    C   o   m   p   r   e   s   s   i   v   e   S   t   r   e   n   g   t    h    (    k   P   a    ) Curing Time (days) LC(A)UNT LC(A)T3% LC(A)T6% LC(A)T9% LC(A)T12% Fig. 3.  Strength gained for SS299 treated natural laterite soil-without bentonite, LC(A), with different additive content and curing time. N. Latifi et al./Measurement 91 (2016) 46–54  49
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