Compressive and Tensile Behavior of Polymer Treated Sulfate Contaminated CL Soil

Transcription

1 DOI /s ORIGINAL PAPER Comprssiv and Tnsil Bhavior of Polymr Tratd Sulfat Contaminatd CL Soil Ahmd S. Mohammd Cumaraswamy Vipulanandan Rcivd: 31 March 2013 / Accptd: 30 August 2013 Ó Springr Scinc+Businss Mdia Dordrcht 2013 Abstract In this study, th comprssiv and tnsil bhavior of polymr tratd sulfat contaminatd CL soil was invstigatd. Basd on th information in th litratur, a fild soil was contaminatd with up to 4 % (40,000 ppm) of calcium sulfat in this study. In addition to charactrizing th bhavior of sulfat contaminatd CL soil, th ffct of trating th soil with a polymr solution was invstigatd and th prformanc was compard to 6 % lim tratd soil. In trating th soil, acrylamid polymr solution (15 g of polymr dissolvd in 85 g of watr) contnt was varid up to 15 % (by dry soil wight). Addition of 4 % calcium sulfat to th soil dcrasd th comprssiv and tnsil strngths of th compactd soils by 22 and 33 % rspctivly with th formation of calcium silicat sulfat [trnsit Ca 5 (SiO 4 ) 2 SO 4 )], magnsium silicat sulfat (Mg 5 (SiO 4 ) 2 SO 4 ) and calcium-magnsium silicat (mrwinit Ca 3 Mg(SiO 4 ) 2 ). With th polymr tratmnt th strngth proprtis of sulfat contaminatd CL soil was substantially improvd. A. S. Mohammd Faculty in Civil Enginring, Univrsity of Sulaimani, Sulaimani, Iraq -mail: Asmohammd2@uh.du C. Vipulanandan (&) Dpartmnt of Civil and Environmntal Enginring, Cntr for Innovativ Grouting Matrials and Tchnology (CIGMAT) and Txas Hurrican Cntr for Innovativ Tchnology (THC-IT), Univrsity of Houston, Houston, TX 77204, USA -mail: cvipulanandan@uh.du Polymr tratd sulfat soils had highr comprssiv and tnsil strngths and nhancd comprssiv strss strain rlationships compard to th lim tratd soils. Also polymr tratd soils gaind strngth mor rapidly than lim tratd soil. With 10 % of polymr solution tratmnt, th maximum unconfind comprssiv and splitting tnsil strngths for 4 % of calcium sulfat soil wr 625 kpa (91 psi) and 131 kpa (19 psi) rspctivly in 1 day of curing. Similar improvmnt in th comprssiv modulus was obsrvd with polymr tratd sulfat contaminatd CL soil. Th variation of th compactd comprssiv strngth and tnsil strngth with calcium sulfat concntrations for th tratd soils wr quantifid and th paramtrs wr rlatd to calcium sulfat contnt in th soil and polymr contnt. Comprssiv strss strain rlationships of th sulfat soil, with and without lim and polymr tratmnt, hav bn quantifid using two nonlinar constitutiv modls. Th constitutiv modl paramtrs wr snsitiv to th calcium sulfat contnt and th typ of tratmnt. Kywords Calcium sulfat Polymr solution Lim Comprssiv strngth Splitting tnsil strngth Modls 1 Introduction Natural sulfat rich soils ar found in many parts of th world and ar considrd a challng in nginring

2 projcts not only on th soil bhavior but also th ngativ impact on th construction matrials (Huntr 1988; Mitchll and Drmatas 1992; Ptry and Littl 1992; Kota t al. 1996; Rollings t al. 1999; Puppala t al. 2002). Sulfat-inducd hav in stabilizd soils was first rportd by Shrwood (1962) and th problm rcivd national attntion only in th mid- 1980s whn Mitchll (1986) rportd a cas study basd on his xprinc in Las Vgas, Nvada. Thr ar diffrnt mthods usd for modifying th soils, which ar catgorizd undr soil tratmnt or stabilization mthods (Holtz t al. 2011). Soil stabilization is commonly don with cmnt, lim, fly ash, bitumn, bntonit, and chmical grouts (Crnica 1995; Vipulanandan and Ata 2000; Vipulanandan and Ozgurl 2009). Effcts of soil stabilization with cmnt, lim and polymr fibrs on th prformanc of various typs of soils hav bn documntd in th litratur by svral rsarchrs and fw of th findings in th past two dcads ar summarizd in Tabl 1. In ths cass both lim and cmnt hav bn usd in trating clays and sand by varying th stabilizr contnt up to 15 %, Also larg variation in th comprssiv strngths of tratd soils wr obsrvd. Arabani and Karami (2007) obsrvd that for clayy sand with low plasticity any incras in lim contnt byond 6 prcnt had a ngligibl ffct on th comprssiv strngth of tratd soil. Howvr, an incras in lim contnt up to 6 % rsultd in a noticabl incras in comprssiv strngth. Also 6 % lim contnt has bn slctd by othr rsarchrs such as Consoli t al. (2010) basd on th incras in ph to about 12.4 to sustain th ractions to stabiliz th soil. Many invstigations hav idntifid th failur mchanisms in high sulfat soils (Harris t al. 2005). Basd on th findings from som studis, four inorganic constitunts hav bn idntifid as ssntial for sulfat-inducd hav: watr, calcium, aluminum, and sulfat. Currnt tratmnt mthods of using lim or cmnt with sulfat soil sulfat is not ffctiv bcaus of ttringit formation as follows (Pillai t al. 2007): Th formation of ttringit in tratd soils (Eq. 1) and its xposur to moistur variations from sasonal changs rsult in diffrntial having, which in turn causs cracking of pavmnt structurs built on th tratd soils (Rajaskharan and Rao 2005; Pillai t al. 2007). If not addrssd immdiatly, this hav will furthr dtriorat th structurs to a condition whr thy nd immdiat and xtnsiv rhabilitation. Hnc altrnativ mthods hav to b dvlopd to bttr stabiliz th sulfat contaminatd soils. 1.1 Bhavior Modls Thr is vry limitd information in th litratur on th quantification of th ffcts of tratmnt and th bhavior of tratd soils. Consoli t al. (2010) quantifid th rlationship btwn unconfind comprssiv strngth (q u ) and splitting tnsil strngth (q t ) of artificially cmntd sand, as wll as th strngth ratio (q t /q u ) rlationship. Consoli t al. (2012) idntifid ky paramtrs for th control of strngth and stiffnss of cmntd soils by tsting two soils with diffrnt grading and quantifying th influnc of porosity/cmnt ratio on both initial shar modulus (G o ) and unconfind comprssiv strngth (q u ). It was shown that th porosity/cmnt ratio is an important paramtr to assss both th initial stiffnss and th unconfind comprssiv strngth of th soil cmnt mixturs studid. Th strss strain bhavior of strain softning matrials such as concrt, glass-fibr rinforcd polymr concrt, fin sands groutd with sodium silicat and cmnt mortar hav bn prdictd using th p q modl and b modls (Mbarkia and Vipulanandan 1992; Gonzala and Vipulanandan 2007; Bncardino t al. 2008; Vipulanandan and Paul 1990; Vipulanandan and Garas 2008). Usluogullari and Vipulanandan (2011) modld th strss strain bhavior of Portland cmnt stabilizd sand using th p q modl. Also th variation of comprssiv strngth, modulus, and CBR valus with curing tim for th cmntd sand wr rprsntd using hyprbolic rlationships. 6Ca 2+ +2Al (OH) - 4+4(OH) - +3(SO 4 ) H 2 O Ca 6 [Al (OH) 6 ] 2 (SO 4 ) 3 26H 2 O.. (1) [Additiv]+ [Clay] + [Contaminant] + [Watr] ð1þ

3 Tabl 1 Litratur rviw on soil stabilization with strngth modls Rfrnc Soil typ Tsts Sampl prparation Stabilizr typ Stabilizr (%) Curing tim (Days) Tmpratur, humidity USC (psi) Splitting tnsil (psi) Rmarks Das and Dass (1995) Silica sand, Poorly grad Splitting Tnsil, UCS Standard compaction tst Bll (1996) Clay soil UCS, CBR Standard compaction tst Puppala t al. (2006) Kumar t al. (2007) Consoli t al. (2010) Usluogullari and Vipulanandan (2011) Malkzadh and Bilsl (2012) Sulfat soil Stiffnss proprty, Shar Modulus CH Splitting Tnsil, UCS Non plastic sand Sand, Poorly grad Splitting Tnsil, UCS Standard compaction tst Standard compaction tst Standard compaction tst UCS and CBR 3 layrs static with a cylindrical tampr (25 mm diamtr 1 kg) 30 blows CH Splitting Tnsil, UCS Currnt study CL Splitting Tnsil, UCS Rmarks Diffrnt soil typs wr usd UCS is th popular tst to charactriz th strngth bhavior Standard compaction tst Standard compaction tst (3 layrs with 18 blows) Mainly standard compaction tst was usd Cmnt 4 and 8 14 Not spcifid Not availabl Lim 2, 4, 8 and 10 1, 3, 7, 14 and 21 Lim 4 0, 1, 2, 4, 8 h, and 1, 2, 3, 4, 5, 7 days Polystr Fibr 0.5, 1, 1.5 and 2 Portland cmnt (III) Portland cmnt Polypropyln Fibr 1, 2, 3, 5, 7, 9 and C Not availabl 23 ± 2 C, 95 % Not availabl Linar UCS- Cmnt contnt rlationship was obsrvd No rlationship was obsrvd Rlativly larg variation in strngth. No rlationship was obsrvd 7 and 28 Not spcifid Linar rlationship was obtaind btwn Split tnsil strngth and UCS with fibr contnt 6 23 ± 2 C, 95 % 1.5, 3 and 6 1, 3 and 7 Room condition 0, 0.5, 0.75 and 1 1 Room condition Nonlinar rlationship btwn UCS and tnsil strngth with porosity % was dvlopd Not spcifid Linar rlationship was obsrvd btwn CBR and UCS valus Linar rlationship was obtaind btwn Split Tnsil strngth and fibr contnt Lim 0, C, 100 % Hyprbolic rlationship was obsrvd btwn Tnsil Polymr solution Diffrnt typ of stabilizr wr usd 0, 5, 10 and 15 % Up to 15 % of stabilizr wr usd Curing tim was up to 28 days Mainly 25 C tmpratur was usd UCS varid from 10 to 511 psi Splitting tnsil varid from 4 to 80 psi and comprssiv strngth Comprssiv and tnsil strngth proprtis hav bn studid

4 Prdicting th prformanc of tratd soils is a major factor in slcting th most usful mthod for soil stabilization. Hnc thr is a nd to dvlop mthods to quantify th bhavior of stabilizd sulfat contaminatd soils. 2 Objctiv Th ovrall objctiv of this study was to invstigat and quantify th comprssiv strss strain rlationship and tnsil strngth of polymr tratd CL soil contaminatd with varying amounts of calcium sulfat. Th spcific objctivs ar as follows: 1. Compar th comprssiv and tnsil bhavior of polymr tratd sulfat contaminatd soil with lim tratd soil. 2. Quantify th strss strain rlationship of clay soil contaminatd with calcium sulfat up to 4 %, and tratd with polymr solution and lim. 3. Corrlat th comprssiv and tnsil strngth of polymr tratd sulfat contaminatd soil. Tabl 2 Tst mthods and physical proprtis of soil Proprty Tst mthod Valu Passing siv #200 (%) ASTM D Sand % ASTM D Silt % ASTM D Clay % ASTM D Spcific gravity ASTM D LL % ASTM D PI % ASTM D OMC % (standard compaction) ASTM D Max. dry dnsity (gm/cm 3 ) ASTM D Soil typ ASTM D 2487 CL comprssiv strngth tsts wr prformd according to ASTM Standards. Th tst rsults ar summarizd in Tabl 2. Th soil had 20 % clay and 35 % silt with a liquid limit of 23 % and plasticity indx of 9. Basd on th tst rsults and using th unifid soil classification systm (USCS) th soil was classifid as a CL soil (Tabls 3, 4). 3.2 Polymr 3 Matrials and Mthods A sris of laboratory tsts wr undrtakn to valuat th influnc of polymr solution on th tnsil and comprssiv strngth of sulfat contaminatd CL soil with up to 4 % of calcium sulfat (dry wight). Initially th comprssiv and tnsil bhavior of sulfat contaminatd CL soil with diffrnt prcntag of calcium sulfat up to 4 % was charactrizd. Also, th ffct of polymr solution tratmnt on th tnsion and comprssion strngth bhavior of sulfat contaminatd CL soil was valuatd and compard with th lim stabilizd soil. Th polymr solution contnt was varid up to 15 % by dry wight of soil. Th Brazilian tst or indirct tnsion tst was don to dtrmin th tnsil strngth of soils (Arabani and Karami 2007). 3.1 Soil Fild clay soil sampl was usd in prparing th sulfat soil. Attrbrg limits, grain siz distribution, hydromtr, standard compaction, spilt tnsion and unconfind Polymr solution was prpard by mixing 15 % of watr solubl acrylamid polymr with 0.5 % of catalyst, 0.5 % of activator and 84 % of watr. Hnc th polymr solution had 15 % polymr dissolvd in it. Th ph of th polymr solution was 10. Hnc, if 10 % of polymr solution contnt was usd to trat th soil (basd on dry wight of soil) actual amount of polymr usd was 1.5 %. 3.3 Lim In this study, hydratd lim was usd to trat th soil. Whn quicklim racts with watr it transforms into hydratd lim as follows: CaO þ H 2 O! CaðOHÞ 2 þhat: ð2þ Hydratd lim (Ca(OH) 2 ) racts with th clay particls and modifis th clay basd on its minralogy (Hassibi 1999). 3.4 Tst Mthods Soil was first drid in th ovn at a tmpratur of 60 C followd by pulvrizing and siving to slct

5 Tabl 3 Constitutiv modl paramtrs and th cofficints of variation Paramtr M N L K T F R 2 K T F R 2 K T F R 2 p q b Tabl 4 Strss strain modl paramtrs for sulfat soil tratd with polymr solution (P %) S % P % Lim (%) p q modl b modl p q R 2 b R th soil finr than # 4 sivs. Th pulvrizd soil was thn mixd with diffrnt prcntag of calcium sulfat and watr. Sulfat contaminatd soil sampls wr placd in moistur tight bags and curd for 7 days at room tmpratur bfor trating and tsting th soil. Th tsting program was invstigatd th strss strain rlationship and split tnsil tst rspons of polymr solution according with ASTM D 2166 and ASTM C 496 rspctivly. A total of 40 sampls wr usd in this study, twnty sampls for ach comprssion tst and split tnsil tst for sulfat contaminatd CL soil tratd with vary prcntags of polymr solution and 6 % of lim was usd XRD Charactrization X-ray diffraction (XRD) was usd to charactriz th soil and th raction products with 4 % calcium sulfat. Th XRD pattrns wr obtaind using th Simns D5000 powdr X-ray diffraction machin. Spcimns for XRD wr prpard from air-drid soils with and without contamination. Th soil sampl (&2 g) was placd in an acrylic sampl holdr which was about 3 mm dp. All sampls wr analyzd by using paralll bam optics with CuKa radiation at 40 kv and 30 ma. All sampls wr scannd for rflctions (2h) in th rang 0 to 70 at a stp siz of 0.02 and a 2 s count tim pr stp Standard Compaction Tst All th spcimns wr prpard by compacting with quivalnt nrgy to achiv th maximum dry dnsity at optimum moistur contnt as obtaind from th standard proctor compaction tst (ASTM D ) Unconfind Comprssion Tsts Th unconfind comprssion tsts wr conductd according to ASTM D Th unconfind comprssiv strngths wr dtrmind from th strss strain curvs. Th natural CL soil contaminatd with diffrnt prcntag of calcium sulfat up to 4 % and th sulfat soils wr modifid using diffrnt prcntag of polymr solution and 6 % lim wr all compactd at corrsponding optimum moistur contnt. Cylindrical stl molds, 3 in. diamtr and 6 in. hight wr usd to prpar th spcimns using th compaction nrgy in quation, Eq. (3). Th soil sampls wr thn xtrudd using a hydraulic jack. Th sulfat contaminatd soil spcimns (lim tratd and untratd) wr placd in moistur tight bags and placd in a 100 % humidity room for curing for 7 days at room tmpratur. Sulfat soil sampls tratd with

6 polymr solution wr curd for 1 day at room tmpratur bfor prforming th tsts. Th tst spcimns wr compactd in thr layrs with ightn blows pr layr. For th volum of th tst mold th spcific compaction nrgy (E) applid was dtrmind as follows: E ¼ No: blows pr layr No: of layrs ðwight of hammrþðdrop hightþš= Volum of Soil ¼ 18 blows 3 layrs 5:5 lb 1ft= 0: ft 3 ¼ 42:6 lb-ft=ft 3 : ð3þ This compaction nrgy was comparabl to that producd with th standard proctor quipmnt which provids about 12,370 ft-lb/ft 3 (ASTM D 698). During th comprssion tst th spcimns wr loadd to failur or until 10 % strain Split Tnsil Strngth Tsts For prforming th split tnsil tst, 75 mm (3 in) diamtr and 150 mm (6 in) hight cylindrical spcimns wr prpard at optimum moistur contnt in th sam mannr as in cas of unconfind comprssion tsts. Aftr curing, th curd spcimns wr placd horizontally btwn th two baring plats of th comprssion tsting machin adjustd for a machin displacmnt rat of 1.0 mm/min. Th split tnsil strngth (r t ) was obtaind using th following rlationship. r t ¼ 2P ð4þ PLD whr P = failur load; L = thicknss or lngth of spcimn; and D = diamtr of th spcimn. som of th changs obsrvd in th contaminatd soil bhavior could hav bn du to th changs in th soil minralogy. 4.1 Polymr Tratmnt Unconfind Comprssiv Strngth (UCS) Incras in calcium sulfat contnt rducd th unconfind comprssiv strngth of compactd soil. Th comprssiv strngth dcrasd from 22 psi (152 kpa) with no calcium sulfat to 17 psi (117 kpa) with 4 % calcium sulfat. Th chang in th strngth could b attributd to th changs in th soil minralogy du to th addition of 4 % calcium sulfat. Compactd comprssiv strngth of a fild CL soil (calcium sulfat concntration = 0 %) improvd from 22 psi (152 kpa) to 152 psi (1,048 kpa) using 10 % of polymr solution aftr 1 day of curing. Whil 4 % of sulfat contaminatd CL soil tratd with 10 % of polymr solution th comprssiv strngth incrasd by 433 % (Fig. 1) Comprssiv Modulus Th comprssiv modulus dcrasd by 13 % whn th calcium sulfat concntration incrasd from 0 to 4 % and could b attributd to th changs in th soil minralogy. Compactd comprssiv modulus of a fild CL soil with 0 % of calcium sulfat incrasd from 2.5 MPa (357 psi) to 39 MPa (5,577 psi) using 10 % of polymr solution aftr 1 day of curing. Whil 4 % of sulfat contaminatd CL soil tratd with 10 % 4 Rsults and Discussion Basd on th XRD analyss, th fild soil had thr paks corrsponding to calcium silicat (CaSiO 3 ), magnsium silicat (Mg 2 SiO 4 ) and Quartz (SiO 2 ). With th addition of 4 % calcium sulfat, thr sts of nw paks corrsponding to calcium silicat sulfat (trnsit (Ca 5 (SiO 4 ) 2 SO 4 ), magnsium silicat sulfat (Mg 5 (SiO 4 ) 2 SO 4 ) and calcium magnsium silicat (mrwinit Ca 3 Mg(SiO 4 ) 2 ) wr obsrvd. Hnc Fig. 1 Variation of comprssiv strngth of CL soil with calcium sulfat concntration

7 4.2 Lim Tratmnt Comprssiv Strngth Fig. 2 Variation of initial comprssiv modulus of CL soil with calcium sulfat concntration Th unconfind comprssiv strngth of sulfat contaminatd CL soil with diffrnt concntration of calcium sulfat up to 4 % varid from to 22 to 17 psi ( kpa, Fig. 1). Th comprssiv strngth of fild CL soil (calcium sulfat concntration = 0%) improvd from 22 to 42 psi (1 psi = 7 kpa) using 6 % of lim aftr 7 days of curing. Also th comprssiv strngth of 4 % calcium sulfat contaminatd CL soil tratd with 6 % lim was improvd by 29 % aftr 7 days of curing (Fig. 1). Th ffcts of polymr solution contnt and lim on th strss strain bhavior of calcium sulfat contaminatd CL soils ar shown in Fig Comprssiv Modulus Fig. 3 Variation of tnsil strngth of CL soil with calcium sulfat concntration of polymr solution th comprssiv modulus incrasd by 422 % (Fig. 2) Tnsil Strngth Th tnsil strngth of th soil sampls dcrasd by 33 % whn th calcium sulfat concntration was incrasd from 0 to 4 % and could b attributd to th changs in th soil minralogy. Also th tnsil strngth of th CL soil contaminatd with 4 % of calcium sulfat incrasd by 260 % whn th soil was modifid using 10 % of polymr solution (Fig. 3). Th ratio of tnsil strngth to comprssiv strngth for uncontaminatd and contaminatd soil with 4 % of calcium sulfat was 0.35 and 0.3 rspctivly. Whil ths ratios dcrasd to 0.15 and 0.21 rspctivly whn th soils tratd with 10 % polymr solution. Th comprssiv modulus dcrasd from 357 psi (1 psi = 7 kpa) to 312 psi whn th calcium sulfat concntration incrasd from 0 to 4 %. Th compactd comprssiv modulus of a fild CL soil with 0 % of calcium sulfat incrasd by 88 % using 6 % of lim aftr 7 days of curing. Whil 4 % of sulfat contaminatd CL soil tratd with 6 % of lim th comprssiv modulus dcrasd by 47 % compard to tratd uncontaminatd soil as shown in Fig Tnsil Strngth Basd on tst rsults, it appars that th tnsil strngth for sampls dcrasd by 33 % whn th calcium sulfat contnt changd from 0 to 4 %. Tnsil strngth incrasd by ovr 80 % whn th soil was tratd using 6 % of lim Fig. 3. Th ratio of tnsil strngth to comprssiv strngth for uncontaminatd and contaminatd soil with 4 % of calcium sulfat incrasd by 6 and 77 % whn th soil was tratd with 6 % lim. 5 Proprty Corrlations In ordr to bttr undrstand th ffcts of calcium sulfat contnt and polymr or lim contnt on th CL soil, it was important to quantify th proprty with th composition of th soil and typ of tratmnt.

8 Tabl 5 Comprssiv and tnsil strngth modl paramtrs for sulfat soil tratd with polymr solution (P %) Soil typ Tnsil strngth, r t Eq. (4) Comprssiv strngth, r c Eq. (9) r to A B R 2 r co H E R 2 Untratd % lim % P % P % P Tnsil Strngth 5.2 Comprssiv Strngth Th variation of tnsil strngth with calcium sulfat contnt was rprsntd using th proposd modl (Eq. 5) and th paramtrs and cofficint of dtrmination (R 2 ) ar summarizd in Tabl 5. r t r to ¼ Sð%Þ A þ BSð%Þ ð5þ A ¼ 0:015ðP%Þ 2 þ 0:23ðP%Þþ0:01 R 2 ¼ 0:88 ð6þ B ¼ 0:004ðP%Þ 2 0:075ðP%Þþ0:41 R 2 ¼ 0:87 ð7þ whr r t = tnsil strngth; r to = initial tnsil strngth (calcium sulfat concntration, S = 0 %), A, B = tnsil strngth hyprbolic constants. Th highst valu of tnsil strngth was with 10 % of th polymr solution contnt for all lvl of sulfat contnt (Fig. 4a). Rsults indicatd that comprssiv strngth could b rprsntd as a function of calcium sulfat concntration and prcntag of polymr solution as follows: r c ¼ f ðs; PÞ ð8þ whr r c = unconfind comprssiv strngth of soil (psi), f = function of calcium sulfat concntration and polymr solution contnt, S = calcium sulfat concntration (%), P = polymr solution (%). Th comprssiv strngth (r c ) variation with calcium sulfat concntration is shown in Fig. 1 and was rprsntd by th following rlationship. Sð%Þ r c r co ¼ ð9þ H þ ESð%Þ whr r c = comprssiv strngth of soil (psi), r co = initial comprssiv strngth of untratd and tratd soil without sulfat (calcium sulfat concntration, S = 0 %), H, E = comprssiv strngth hyprbolic constants. b a Fig. 4 Variation of strngth with polymr solution contnt. a Tnsil strngth and b comprssiv strngth

9 Variation of paramtr H and E valus with polymr solution contnt wr invstigatd. H ¼ 0:014ðP%Þ 2 þ 0:03ðP%Þ 0:03 R 2 ¼ 0:99 ð10þ E ¼ 0:002ðP%Þ 2 þ 0:04ðP%Þþ0:17 R 2 ¼ 0:93 : ð11þ Th variation of strngth with calcium sulfat contnt was rprsntd using th proposd modl (Eq. 9)andth paramtrs ar summarizd in Tabl 5. Th hyprbolic rlationships was usd to rprsnt chang in comprssiv strngth with calcium sulfat concntration for untratd sulfat soil and tratd using 6 % of lim and diffrnt prcntag of polymr solution as shown in Fig. 1. Th highst comprssiv strngth was obtaind with soils tratd with 10 % of th polymr solution contnt at all lvl of sulfat contnt as shown in Fig. 4b. 5.3 Comprssiv Modulus whr r = comprssiv strngth, r c, c = comprssiv strngth and corrsponding strain, p, q = matrial paramtrs. Paramtr q was dfind as th ratio of scant modulus at pak strss to initial tangnt modulus. Paramtr p was obtaind by minimizing th rror in th prdicatd strss strain rlationship. Effct of paramtrs p and q on th shap of th strss-strain rlationship ar shown in Fig. 5a. Hnc, paramtrs p and q in (Eq. 12) wr dtrmind basd on th strss strain bhavior of sulfat soil tratd with 10 % of polymr solution (by dry wight) and th valus and cofficint of dtrmination (R 2 ) ar summarizd in Tabl 4. In Fig. 6, th prdictd valus of comprssiv strngth for sulfat contaminatd CL soil tratd with diffrnt prcntag of polymr solution ar compard to th 6 % lim tratd soil. Th polymr tratd soils wr much strongr and stiffr than lim tratd soils. As summarizd in Tabl 4 th paramtrs p and q influnc by sulfat contnt and th mthod of Th initial modulus was almost constant whn th sulfat contnt for th fild soil incrasd from 0 to 4 %. Th highst initial modulus was obtaind whn th sulfat soil with 4 % calcium sulfat was tratd using 10 % of polymr solution contnt as shown in Fig. 2. Th highst comprssiv strngth was obtaind with soils tratd with 10 % of th polymr solution contnt at all lvl of sulfat contnt as shown in Fig Strss Strain Bhavior Modling Soils ar gnrally modld as linar lastic, linar lastic prfctly plastic or as strain hardning matrials. In this study th soil, with and without tratmnt, xhibitord strain softning bhavior as shown in Fig. 6. a p q Modl Basd on xprimntal rsults, modl proposd by Mbarkia and Vipulanandan (1992), was usd to prdict th strss strain bhavior of tratd sulfat contaminatd CL soil with diffrnt prcntag of polymr solution (Eq. 12). Th modl is dfind as follows: 0 1 B r ¼ c ðpþqþ=p Ar c ð12þ q þð1 p qþ c þ p c Fig. 5 Comprssiv strss strain rlationships. a p q modl and b b modl b

10 tratmnt. Hnc th following rlationships ar proposd to rlat th sulfat contnt and polymr contnt to th paramtrs p and q as follows: a p ¼ MpðS%Þ 2 þ NpðS%ÞþLp q ¼ MqðS%Þ 2 þ NqðS%ÞþLq ð13þ ð14þ whr Mp, Np, Lp, Mq, Nq and Lq = p q modl paramtrs. Variation of Mp, Np, Lp, Mq, Nq and Lq valus with polymr solution contnt (P %) ar rprsnt as follows: Mp; Np; Lp ¼ KðP%Þ 2 þ TðP%ÞþF Mq; Nq; Lq ¼ KðP%Þ 2 þ TðP%ÞþF ð15þ ð16þ whr paramtrs K, T, F and cofficint of dtrmination (R 2 ) ar summarizd in Tabl 3. b c Paramtr q Paramtr q rprsnts th nonlinar bhavior of th matrial up to pak strss. For calcium sulfat contaminatd CL soil th paramtr q was in th rang of 0.43 to 0.67 (Tabl 4). Trating th CL soil with 10 % polymr solution incrasd th q paramtr to b in th rang of 0.59 to 0.76 (Tabl 4) indicating that th matrial bhavior is mor linar with polymr tratmnt. For lim tratd soils, paramtr q varid from 0.43 to 0.75, covring a largr rang than 10 % polymr tratd soil. Paramtr p For untratd soils th paramtr p varid from 0.25 to 0.5. Soil tratd with 10 % polymr solution contnt th paramtr p varid from 0.13 to Hnc th dscnding part of th strain softning strss strain rlationship for th polymr tratd soils wr stpr compard to th untratd soils. For lim tratd soils th paramtr p rang was 024 to 0.52, similar to th untratd soils (Fig. 6) b Mthod Fig. 6 Comparison of modl prdictions and xprimntal strss strain rlationship for sulfat (S) contaminatd CL soil tratd with 6 % of lim and 10 % of polymr solution: a S = 0%,b S = 2%,c S = 3 % and d S = 4% d Ezldin and Balaguru (1992) proposd an analytical quation (Eq. 17) to gnrat th strss strain curv for normal strngth of stl fibr rinforcd concrt basd on th quation proposd by Carrira and Chu (1985) for uniaxial comprssion of plain concrt. This quation involvs a matrial paramtr b, which is th slop of th inflction point at th dscnding branch of th shar strss rlationship.

11 0 b B c C r b Ar c b 1 þ c 1 ð17þ whr r = comprssiv strngth, r c, c = comprssiv strngth and corrsponding strain, b = matrial paramtr. Effct of paramtr b on th strss-strain rlationships ar shown in Fig. 5b. Strss strain rlationship for sulfat soil modifid using polymr solution and lim and th modl prdication ar shown in Fig. 6. From Eq. (12), if (p? q = 1) thn th rlationship is as follows. Thn: 0 B r c 1 p q þ p c 1 C Ar c ð18þ if (p = 1/b) thn Eq. (18) is rprsntd as follows: b B r ¼ c C B c b Ar c b Ar c 1 1 b þ 1 b b 1 þ c c ð19þ Hnc b-mthod (Eq. 17) is a spcial cas of th p q modl (Eq. 12). Th rlation btwn paramtr b and th calcium sulfat concntration is as follows: b ¼ M b ðs%þ 2 þ N b ðs%þþl b ð20þ whr M b, N b, L b = b-modl paramtrs that dpnd on th polymr contnt. Basd on th tst rsults, th rlations of paramtr b with prcntag of polymr solution ar as follows: M b ; N b ; L b ¼ KðP%Þ 2 þ TðP%ÞþF ð21þ Th paramtrs K, T, F and cofficint of dtrmination (R 2 ) ar summarizd in Tabl 3. Paramtr b For untratd contaminatd soil paramtr b varid from 1.75 to 4. With 10 % of polymr solution tratmnt th paramtr b varid from 2.75 to 5 indicating fastr dscnding aftr th pak strss. For th lim tratd soil th paramtr b rang was 1.75 to 3.5, similar to untratd soil. 6 Corrlation btwn Comprssiv and Tnsil Strngths Polymr solution stabilizd sulfat soil sampls wr subjctd to indirct tnsil tst, also known as th Brazilian tst. Hnc in this study, comprssiv strngth (r c ) was rlatd to tnsil strngth (r t ). Basd on th tst rsults of th variation of tnsil strngth with th comprssiv strngth (Fig. 7) was rprsntd as th following non-linar hyprbolic rlationship. r r t ¼ c 0:04þ1:56r c R 2 ¼ 0:93 ð22þ r t 0:1r c For Concrt ð23þ Hnc th tnsil strngth of sulfat contaminatd CL soil, with and without tratmnt was highr than th 10 % of comprssiv strngth, which rlationship is gnrally usd for cmnt concrt (Eq. 23). 7 Conclusions σ c σ t = * σ c R 2 = 0.93 Fig. 7 Rlationship btwn tnsil strngth and comprssiv strngth of polymr tratd sulfat contaminatd soil In this study, th ffctivnss of polymr tratmnt of sulfat contaminatd soil was compard to lim tratd CL soil. XRD analyss showd that th major constitunts of th soil wr calcium silicat (CaSiO 3 ), magnsium silicat (Mg 2 SiO 4 ) and Quartz (SiO 2 ). Basd on th laboratory tsts and modling th comprssiv and tnsil bhavior of tratd sulfat contaminatd CL soil, th following conclusions ar advancd:

12 1. Th comprssiv strngth and tnsil strngth of CL soil dcrasd with incrasd sulfat contnt. With 4 % calcium sulfat contamination th comprssiv strngth and tnsil strngth of th soil dcrasd by 22 and 33 % rspctivly. With th addition of 4 % calcium sulfat, changs in soil minralogy was obsrvd and th nw constitunts wr calcium silicat sulfat (trnsit (Ca 5 (SiO 4 ) 2 SO 4 ), magnsium silicat sulfat (Mg 5 (SiO 4 ) 2 SO 4 ) and calcium magnsium silicat (mrwinit Ca 3 Mg(SiO 4 ) 2 ). Hnc som of th changs obsrvd in th contaminatd soil bhavior could hav bn du to th changs in th soil minralogy. 2. Polymr solution tratmnt substantially improvd th comprssiv and tnsil bhavior of th sulfat contaminatd CL soil. Hyprbolic rlationship was usd to prdict th changs in th comprssiv and tnsil strngths of th tratd contaminatd sulfat soils with diffrnt prcntags of polymr solution. 3. Polymr solution tratmnt showd much highr nhancmnt in th strngths and modulus of sulfat contaminatd soils compard to th lim tratmnt. Also th polymr solution tratmnt nhancd th sulfat contaminatd soil proprtis much mor rapidly compard to th lim tratd soils. Adding th low viscous polymr solution to th soil would hav coatd th soil particls and whn glld in plac would hav formd th polymr ntwork with soil mbddd in it rsulting in nhancd soil proprtis. 4. Nonlinar strss strain modls wr usd to prdicat th bhavior of polymr and lim tratd sulfat contaminatd soils. Th modl paramtrs wr snsitiv to th typ of tratmnt. Rfrncs Arabani M, Karami M (2007) Gomchanical proprtis of lim stabilizd clayy sands. Arabian J Sci Eng 32(1B):11 25 Bll G (1996) Lim stabilization of clay minrals and soils. Eng Gol 42: Bncardino F, Rizzuti L, Spada G, Swamy R (2008) Strss strain bhavior of stl fibr-rinforcd concrt in comprssion. J Matr Civ Eng 20(3): Carrira DJ, Chu KM (1985) Strss strain rlationship for plain concrt in comprssion. ACI J 82(6): Crnica PE (1995) Gotchnical nginring: soil mchanics. Wily, Nw York Consoli C, Cruz R, Floss M, Fstugat L (2010) Paramtrs controlling tnsil and comprssiv strngth of artificially cmntd sand. J Gotch Gonviron Eng ASCE 136(5): Consoli C, Fonsca V, Silva R, Cruz C, Fonini A (2012) Paramtrs controlling stiffnss and strngth of artificially cmntd soils. Gotchniqu 62(2): Das B, Dass RN (1995) Lightly cmntd sand in tnsion and comprssion. Golog Eng 13: Ezldin AS, Balaguru PN (1992) Normal- and high-strngth fibr rinforcd concrt undr comprssion. J Matr Civ Eng 4(4): Gonzala H, Vipulanandan C (2007) Bhavior of a sodium silicat groutd sand. GSP 168 grouting for ground improvmnt, pp 1 10 Harris P, Holdt J, Sbsta S, Scullion T (2005) Rcommndations for stabilization of high sulfat soils in Txas. TxDOT Rport No. FHWA/TX-06/ , pp 1 62 Hassibi M (1999) An ovrviw of lim slaking and factors that affct th procss. Papr prsntd at th 3rd intrnational Sorbalit symposium, Nw Orlans, Novmbr 3 5, vol 19, pp 1 19 Holtz RD, Kovacs WD, Shahan TC (2011) An introduction to gotchnical nginring. Prntic Hall, Nw York, p 733 Huntr D (1988) Lim-inducd hav in sulfat-baring clay soils. J Gotch Eng 114(2): Kota P, Hazltt D, Prri L (1996) Sulfat-baring soils: problms with calcium basd stabilizrs. Transportation rsarch rcord 1546, Transportation Rsarch Board, Washington, pp Kumar A, Walia B, Bajaj A (2007) Influnc of fly ash, lim, and polystr fibrs on compaction and strngth proprtis of xpansiv soil. Matr Civ Eng 19(3): Malkzadh M, Bilsl H (2012) Effct of polypropyln fibr on mchanical bhavior of xpansiv soils. EJGE 17:55 63 Mbarkia S, Vipulanandan C (1992) Comprssiv bhavior of glass-fibr-rinforcd polymr concrt. J Matr Civ Eng 4(1): Mitchll K (1986) Practical problms for surprising soil bhavior. Gotch Eng ASCE 112(3): Mitchll K, Drmatas D (1992) Clay soil hav causd by limsulfat ractions. innovations in uss for lim. ASTM STP 1135, Amrican Socity for Tsting and Matrials (ASTM), Philadlphia, pp Ptry M, Littl D (1992) Updat on sulfat-inducd havn tratd clays; problmatic sulfat lvls. Transportation Rsarch Rcord 1362, National Rsarch Council, Washington, pp Pillai A, Abraham B, Sridharan A (2007) Dtrmination of sulphat contnt in marin clays. Rs Appl (IJERA) 1(3): Puppala AJ, Viyanant C, Kruzic, Prrin L (2002) Evaluation of a modifid sulfat dtrmination mthod for cohsiv soils. Gotch Tst J 25(1):85 94 Puppala AJ, Kadam R, Madhyannapu RS, Hoyos LR (2006) Small-strain shar moduli of chmically stabilizd sulfatbaring cohsiv soils. J Gotch Gonviron Eng ASCE 132(3):

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