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Tropical Residual Soil Stabilization a Powder Form Material for Increasing Soil Strength

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Tropical Residual Soil Stabilization a Powder Form Material for Increasing Soil Strength
  Tropical residual soil stabilization: A powder form material forincreasing soil strength Nima Latifi a, ⇑ , Amin Eisazadeh b , Aminaton Marto c , Christopher L. Meehan d a Department of Civil and Environmental Engineering, Mississippi State University, Mississippi State, MS 39762, USA b School of Civil Engineering and Technology, Sirindhorn International Institute of Technology, Thammasat University, Khlong Nung, Khlong Luang District, Pathum Thani12120, Thailand c Malaysia-Japan International Institute of Technology, Universiti Teknologi Malaysia Kuala Lumpur, Jalan Sultan Yahya Petra, 54100 Kuala Lumpur, Malaysia d Department of Civil and Environmental Engineering, University of Delaware, 301 DuPont Hall, Newark, DE 19716, USA h i g h l i g h t s   Laterite soil stabilized using a calcium-based additive prepared from biomass silica.   Stabilized laterite exhibited significant strength gain, even with short curing times.   Strength gain attributed to formation of calcium aluminate hydrate cementing agents.   Selected stabilizer appears effective for field treatment of tropical laterite soil. a r t i c l e i n f o  Article history: Received 7 November 2016Received in revised form 10 April 2017Accepted 13 April 2017Available online 8 May 2017 Keywords: Laterite soilNon-traditional additiveUnconfined compression strength (UCS)X-ray diffractometry (XRD)Energy-dispersive X-ray spectrometry(EDAX)Field emission scanning electronmicroscopy (FESEM)Fourier transform infrared spectroscopy(FTIR) a b s t r a c t Stabilizationofproblematicsoilsforearthworkapplicationscanbeperformedusingavarietyofchemicaladditives, with lime, cement, or fly ash all being traditionally employed for this purpose. More recently,variousnewcalcium-basedadditives havebeenactivelymarketedbyanumberof companies forsoil sta-bilizationapplications. Thestabilizingmechanismsofthesecommerciallyavailableproductsarenotfullyunderstood, and their proprietary chemical composition makes it difficult to predict their effectiveness.The current study examines the effectiveness of SH-85, a new calcium-based powder additive which isprepared from biomass silica, for stabilization of a tropical residual laterite soil. At the macro-level,changesinsoil strengthduetoadditivestabilizationwereassessedusingaseriesofunconfinedcompres-sion strength (UCS) tests. The underlying mechanisms that contributed to the stabilization process wereexplored using spectroscopic and microscopic techniques, including X-ray diffractometry (XRD), energy-dispersive X-rayspectrometry (EDAX), fieldemissionscanning electron microscopy (FESEM), andFouriertransforminfrared spectroscopy (FTIR). The UCS test results indicated that the addition of SH-85 powderhadasignificantstabilizingeffectonthelateritesoil,withtheUCSvaluesincreasingfivefoldaftera7-daycuring period. At the micro-level, addition of SH-85 had a weathering effect on the clay minerals, chang-ingthe peakintensities of the observedminerals in theXRDspectrums as thestabilized soil was cured. Asignificant change in the soil fabric was also observed with curing time in the FESEM tests, with additivestabilization yielding a less porous and denser soil fabric, and changes in the surface appearance of trea-tedclay particles. This research study confirms the potential of SH-85 as an alternative to traditional sta-bilizers for construction involving tropical residual soils.   2017 Elsevier Ltd. All rights reserved. 1. Introduction For transportation earthwork applications in geotechnical engi-neering,theavailabilityofhighqualitysoilforconstructionisoftenlimitedinmanypartsoftheworld[1,2]. Moreoftenthannot, engi-neers are forced to find alternatives to the use of locally availablesoilsinordertomeetsoilstrength,compressibility,orpermeabilityrequirementsthatarestipulatedbyagivenproject.Formostappli-cations, engineers are generally left with two alternatives: (1)excavate and replace problematic soils with imported backfillmaterials, generally an expensive proposition with significantlogistical and sustainability problems, or (2) stabilize or otherwiseimprove locally available soils to achieve the required material   2017 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: (N. Latifi).Construction and Building Materials 147 (2017) 827–836 Contents lists available at ScienceDirect Construction and Building Materials journal homepage:  properties [3–7]. For the second approach, there are a variety of options available to chemically stabilize poor quality soils, usingeither traditional or non-traditional additives [8–15].In tropical regions, the weathering process for soil and rock istypicallymuchmorerapidthanwhatoccursinmoretemperatecli-mates, with speedy disintegration of feldspars and ferromagnesianraw materials, displacement of silica and bases (Na 2 O, K 2 O, MgO),and absorption of aluminum and iron oxides being common [16].This residual soil formation process, which includes leakage of sil-ica and decomposition of iron and aluminum oxides, is commonlyreferred to as  laterization  [17]. Tropical regions are ideal for forma-tion of laterite residual soils, as warm temperatures, significantquantities of rainfall, and the presence of deeper geologic depositsthat allow for subsurface drainage are common [18,19]. Conse-quently, substantial layers of lateritic residual soil are oftenformed, which typically have significant amounts of aluminum,iron, and kaolinite clays [16]. The existence of iron oxides makesthe color of laterite soils red (from light to bright red), with brownshades also being common [20,21]. The presence of significantquantities of fine-grained soil within most laterite deposits canbe attributed to the significant soil weathering that has occurred.The fine-grained nature of laterite soil deposits causes this typeof soil to be problematic from an engineering point of view, withnatural soils sometimes needing stabilization [22,23].Traditional chemical stabilizers such as cement, lime, fly ash,and bituminous materials are widely studied and their essentialstabilization mechanisms are generally well-understood [24–33].The list of non-traditional chemical additives is much broader,including enzymes, liquid polymers, resins, acids, silicates, ionsand lignin derivatives [34–39]. The chemical nature of these non-traditional additives is quite varied relative to traditional chemicalstabilizers,andthemannerinwhichtheyreactwithsoilduringthestabilization process is consequently also quite different for eachtype of stabilizer that is used [40–42]. Relative to traditional stabi-lizers, only limited information exists in the technical literatureabout the underlying stabilization mechanisms that occur whendifferent non-traditional additives are used to stabilize differenttypes of natural soils [43,44].In recent years, various types of non-traditional additives havebeen actively marketed by different companies for stabilizationof fine-grained soils [45,46]. Due to their proprietary chemicalcomposition, the stabilizing mechanism of these products is notfully understood and hence, it is difficult to predict their perfor-mance. Some previous studies have indicated that various non-traditional additives can be used to increase the strength proper-ties of certain natural soils [47–52]. Other studies have effectivelyused X-ray diffractometry (XRD), energy-dispersive X-ray spec-trometry (EDAX), field emission scanning electron microscopy(FESEM), and Fourier transform infrared spectroscopy (FTIR) teststo examine the mineralogical composition and micro-structure of soils [53–55]. These techniques have also been used to study themicro-structure of soils that have been stabilized using differenttypes of non-traditional additives [4,56–58].The objective of the current study is to assess the capabilitiesof SH-85, a commercially available calcium-based powder formaddi-tive prepared from biomass silica, for stabilization of a tropicalresidual laterite soil from Malaysia. To accomplish this task,changes in the macro- and micro-structural properties of a lateritesoil stabilized with SH-85 were explored over various curing peri-ods. A series of unconfined compression strength (UCS) tests wereperformed to examine the physical changes in soil strength thatwere induced by the additive stabilization process over time. Inparallel, changes in the soil micro-structure over time wereinvestigated using a series of spectroscopic and microscopictests, including XRD, EDAX, FESEM, and FTIR tests. The resultsfrom these tests are useful for understanding the effectiveness of tropical residual soil stabilization using SH-85, and for assessingthe underlying mechanisms through which the laterite soil wasstabilized. 2. Materials and experimental program  2.1. Materials For this study, soil testing was performed on a residual lateritesoilthatiscommonintropicalareas. Representativeblocksamplesof a reddish laterite clay rich in iron oxides were obtained from adepthof 2to3mbelowthegroundsurface, byperformingexcava-tionsinahillsidelocatedattheSkudaicampusofUniversitiTekno-logi Malaysia (UTM). The natural soil was air-dried underlaboratory conditions, after which pebbles and plant roots wereremoved. Grain size analyses of the resulting soil indicated that asignificant quantity of fine-grained particles are present, as showninFig. 1. Table1presentsthephysical properties of thissoil, which weredeterminedusingavarietyoftraditionalsoil characterizationtests.Additionalcharacterizationtestresultsforthissoil(includingmore details from compaction testing) are available in Marto et al.[8]. The color of this clayey soil is reddish due to the high amountof iron oxides that are present.The stabilizing additive that was utilized, which goes by thecommercial name SH-85, is a calcium-based powder additivewhich is prepared from biomass silica. The selected additive wassold by the Probase factory located in the Johor province of Malay-sia; the exact chemical composition of this stabilizer has not beenreleased by the manufacturer, since it is a commercially registeredbrand. Table 2 shows the general chemical properties of this addi-tive and the selected laterite soil, which were determined usingEDAX testing; the associated pH (L/S=2.5) for this additive is12.65. As shown in Table 2, the dominant compounds in SH-85are calcium oxide (68.21%), silica (9.25%), alumina (12.30%), andcarbon dioxide (10.24%). Grain Size (millimeters) 0.0010.010.1110    P  e  r  c  e  n   t   F   i  n  e  r   b  y   W  e   i  g   h   t 0102030405060708090100US Standard SievesHydrometer Silt or ClayF.Sand    2   0   0   1   4   0   1   0   0   6   0   4   0   3   0   2   0   1   6   1   0   8   6   4 M.SandC.S. Fig. 1.  Particle size distribution of the tested laterite soil.828  N. Latifi et al./Construction and Building Materials 147 (2017) 827–836    2.2. Sample preparation and testing program The results fromprevious studies on this laterite soil have indi-cated that its plasticity and compaction properties can be changedsignificantly by oven drying [8,22]. Consequently, the presentstudy has used air-drying for preparation of all of the associatedsoil/additive mixtures for testing. As a first step, in order to ensureuniformityof the soil prior to mixing, theair-driedsoil was brokenup into smaller particles using a mortar and pestle and sievedthrough a 2mmsieve [11]. De-ionizedwater was then mixed withthe air dried soil to achieve the desired moisture content. A seriesofstandardproctorcompactiontestswereconductedfollowingtheBritish Standardapproach(Clause 4.1.5of BS 1924: Part 2: 1990b),in order to determine the maximum dry density (MDD) and opti-mum moisture content (OMC) of the natural laterite soil [59].Inordertopreparehomogeneousmixturesforunconfinedcom-pressive strength (UCS) testing, hand mixing of air dried soil, de-ionized water and SH-85 was performed using palette knives.Additive-to-soil mix ratios of 3%, 6%, 9%, 12%, and 15% SH-85 bydry weight were prepared. UCS test specimens were created bycompressing a known mass of the resulting soil/additive mixtureina steel cylindrical mold of knownvolumeusing a hydraulicjack.This approachallowed for precise preparation of UCS specimens atthe OMC and at 90% of the MDD, as determined from the priorstandardproctorteststhatwereconducted[8].Theresultingcylin-drical specimens were extruded using a steel plunger, trimmed,and wrapped in several runs of cling film. These specimens werecuredfor3,7,14,28,and90daysinatemperaturecontrolledroom(27±2  C) prior to UCS testing. A minimum of three specimensweretestedforeachspecificmixture,inordertoassesstheaveragestrength gain of the soil that occurred after soil stabilization. UCSspecimens were loaded at an axial strain rate of 1% per minute,with an automated data acquisition unit being used to record theapplied load and axial deformation [60]. The ultimate strength of each UCS specimen was determined based on its peak axial stressfor tests conducted to a 15% strain level [39].A powder X-ray diffraction (XRD) technique was used to mea-sure the mineralogical changes in soil structure that occur withthe addition of the soil stabilizer, and to identify new crystallinecompounds that were formed during the stabilization process.XRD tests were performed on cured samples using a Bruker D8advanced diffractometer. Specimen scans were performed usingCuK a  radiation (k=1.54Å) at an angle scan (2 h ) between 6   and90  , with a 0.02   step size and dwelling time of 1s at each step.Acomparisonwas madebetweentheresultingdiffractionpatternsand the standard dataset of the Joint Committee for PowderDiffraction Standards [61].In order to capture high resolution images of soil fabric, a fieldemissionscanningelectronmicroscope(FESEM)thatwasequippedwithan energy-dispersive X-ray spectrometer (EDAX) was utilizedfor microstructural characterization of untreated and stabilizedsoil specimens. Each sample was sputtered with platinum for120sat 30mAunderhighvacuumuntil itwascompletelycoveredand ready to be used for the microscopic analysis. EDAX analysiswas used to characterize the major elemental changes that occuron the surface of treated particles as a result of the stabilizationprocess.Fouriertransforminfraredspectroscopy(FTIR)analysiswasuti-lized to study the changes in the molecular structure of treatedsamples. For each FTIR test, approximately 2mg of dried groundsoil was mixed with 200mg KBr. In order to measure the absorp-tion bands of the prepared KBr disc, it was exposed to an infraredspectra and scanned using a Perkin Elmer Spectrum 2000 instru-ment.Theadsorptionbandswereexaminedforcharacteristicwavenumbers ranging between 400 and 4000cm  1 .In the subsequent sections and associated figures in this manu-script, it is helpful to use abbreviations to describe the state of the  Table 1 Characteristics of the tested 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 * (kgm  3 ) 1.31Optimum moisture content * (%) 34Unconfined compressive strength (kPa) 226 * Determined using the Standard Proctor test.  Table 2 Chemical composition of the tested laterite soil and SH-85. Chemical composition (oxides) Values (%)Laterite SH-85SiO 2  25.46 9.25Al 2 O 3  31.10 12.30Fe 2 O 3  35.53 0CO 2  7.91 10.24CaO 0 68.21 Curing Time (Days) 37142890    C  o  m  p  r  e  s  s   i  v  e   S   t  r  e  n  g   t   h   (   k   P  a   ) 050010001500LUNTLT 3%LT 6%LT 9%LT 12%LT 15% Note: All bar charts are arranged with increasing additive concentrations being shown from left to right. Fig. 2.  Unconfined compressive strengths for untreated and SH-85 stabilized laterite soil, for different additive contents and curing times. N. Latifi et al./Construction and Building Materials 147 (2017) 827–836   829  specimen and curing period: the notation used for this purpose is LUNT   for untreated laterite clay,  LT   for treated laterite, and  D  fordays of curing. 3. Results and discussion  3.1. Unconfined compressive strength (UCS) test results The UCS test was used to investigate the effectiveness of theselectedadditiveforincreasingthecompressivestrengthoflateritesoil. Fig. 2 shows the results from UCS tests on untreated and SH-85stabilizedlateritesoil,atvariousstabilizermixratiosandcuringtime intervals. As shown, the compressive strength of the SH-85stabilized laterite was significantly larger than the compressivestrength measured for untreated specimens, for each of the curingtimeintervalsthat wasexamined.Ingeneral,thestabilizedlateritestrengths increased with increasing curing times, at a diminishingrate with each additional curing time increment (Fig. 2). Withrespect to the different additive levels that were examined, theadditionof9%SH-85showedasignificantjumpinstrengthrelativeto the change that was observed between 3% and 6% SH-85 addi-tive levels; moreover, additional stabilizer usage beyond 9% (i.e.,the 12% and 15% mixes) showed only marginal increases in com-pressive strength. Consequently, a 9% SH-85 additive level wasdetermined to be the optimum amount of stabilizer usage for thetested laterite soil.With respect to curing time, most of the observed gain instrength occurred in the first 7days. As an example, the 9% SH-85 treated samples with a 7-day curing time achieved a compres-sive strength of 1087kPa. This was approximately 5 times greaterthantheuntreatedsoilstrength(226kPa).Table3showscompres-sive strength values that have been measured by other researchersfor granitic residual soils from various places in the MalaysianPeninsula that have been mixed with different types of stabilizers.Comparedtotheotherstabilizersthatwereassessedinthesestud-ies, SH-85 yielded unconfined compressive strengths that weregenerally superior after 7days of curing. In particular, the perfor-  Table 3 Unconfined compressive strength of granitic residual soils sampled from variouslocations in the Malaysian Peninsula mixed with different types of stabilizers. Source Type of stabilizer Curing time(Day)Compressivestrength (kPa)Current Study SH-85 7 1087Rashid et al. [75] Cement 7 800Saeed et al. [76] Lime 7 325Eisazadeh et al. [18] Lime 240 633Geliga and Ismail [77] Fly Ash 7 260Basha et al. [28] Rice Husk Ash 7 150Basha et al. [28] Cement 7 320Chew et al. [33] Cement 7 600Chern [78] Lime 7 385 Two-Theta (Deg.) 102030405060708090    I  n   t  e  n  s   i   t  y   (   C  o  u  n   t  s   ) 200400600800    I  n   t  e  n  s   i   t  y   (   C  o  u  n   t  s   ) 200400600800    I  n   t  e  n  s   i   t  y   (   C  o  u  n   t  s   ) 200400600800    I  n   t  e  n  s   i   t  y   (   C  o  u  n   t  s   ) 200400600800 LT90DLT28DLT7DLUNT Calcium Aluminate Hydrate (CAH) KKKKGEK K = KaoliniteQ = QuartzGI = GibbsiteGE = Goethite GIGEQGIQGIGEQKQQ Fig. 3.  XRD intensity counts for untreated and SH-85 stabilized laterite soil at different curing times.830  N. Latifi et al./Construction and Building Materials 147 (2017) 827–836 
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