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Immobilization of Cr(VI) in bagasse ash blended cement pastes M.A. Tantawy , A.M. El-Roudi, A.A. Salem Chemistry Department, Faculty of Science, Minia University, Minia, Egypt article info Article history: Received 29 September 2011 Received in revised form 30 November 2011 Accepted 4 December 2011 Available online 29 December 2011 Keywords: Bagasse ash Blended cement Pozzolana Cement immobilization Solidification/stabilization Cr(VI) abstract The aim of the present work is to study the hydration characteristics and immobilization of Cr(VI) in bagasse ash blended cement pastes by setting time, compressive strength, bulk density, total porosity and immobilization efficiency measurements as well as XRD, FTIR and SEM techniques. It was investi- gated that hydration characteristics of bagasse ash blended cement pastes were enhanced especially at later ages of hydration. Immobilization of Cr(VI) in bagasse ash blended cement pastes reduces their set- ting time, accelerates hydration reactions due to precipitation of CaCrO 4 and affects the pore formation mechanism of hydrated cement pastes. The alkalinity of bagasse ash blended cement pastes were reduced due to pozzolanic action. Hence, the rate of precipitation of CaCrO 4 decreases with bagasse ash content. FTIR results indicate that C–S–H formed by the pozzolanic action of bagasse ash differs in its nature from that formed by hydration of OPC, encapsulates Cr(VI) ions and refines the microstructure of hydrated cement pastes as indicated from immobilization efficiency, XRD and SEM results. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Chromium is one of the heavy metals that has both beneficial and detrimental properties and is generated from many industrial processes such as electroplating, leather tanning, paints and pig- ments, textile, steel fabrication and production of chromium chem- icals. In the environment, chromium usually exists in its common oxidation states, trivalent chromium [Cr(III)] and hexavalent chro- mium [Cr(VI)]. The later is the most important one because of its toxicity, solubility, mobility characteristics, strong oxidizing and carcinogenic nature [1]. Cement-based immobilization treatment technology combines interrelated solidification/stabilization (S/S) processes that occur simultaneously to produce a material that will have reduced environmental impact when disposed or reused. The United States environmental protection agency US EPA has identi- fied S/S as the best demonstrated available technology for many of hazardous wastes [2]. Bagasse ash is the waste generated by the combustion of sugar cane bagasse. Apart from silica which is the major component, it contains other oxides as well as unburned carbon [3]. Up to 0.066 tons ash is generated per ton of sugar cane crushed [4]. Huge amounts of bagasse ash have been produced annually in developing countries. Limited amounts of bagasse ash has been used as soil amendment while the rest of bagasse ash is useless and being dis- posed to open landfills causing serious environmental impacts. However, bagasse ash can be utilized for production of building bricks [5] and as a cement replacement to improve the mechanical properties of cement mortar [6,7], normal concrete [8], self com- pacting concrete [9], conventional hollow concrete [10] and to im- prove the durability of concrete under aggressive environment [11]. The use of bagasse ash as a cement replacement for immobilization of heavy metals not only marks a novelty in the immobilization technology but also assists in alleviating disposal problem of ba- gasse ash heaps in developing countries. Many investigators have analyzed the effect of Cr(III) and (VI) on the different Portland cement phases [12,13] and its solidifica- tion in cementitious matrix [14,15]. Immobilization of chromium affects the pore formation mechanism causing a wide variety of pore diameters to appear indicating involvement of chromium in silicate formation in the C–S–H matrix [16]. Addition of Cr(VI) may retard hydration reactions as a result of the reduction in per- meability caused by precipitation of calcium chromate and coating on cement grain surfaces [17,18]. Addition of Cr(VI) increases the setting time of cement, inhibits cement hydration and reduces the compressive strength of the cement [19]. On contrast, addition of Cr(VI) may increase the setting time of cement and impair the strength development of blended cement [20]. Another possible mechanism was involved in immobilization of Cr(VI) in cement is the formation of modified Cr-ettringite 3CaOAl 2 O 3 3CaCrO 4 32H 2 O which may occur due to substitution of SO 2 4 in ettringite structure by CrO 2 4 [21,22]. However, this mechanism may require a high concentration of chromate ions in pore solution. The immobilization of Cr(VI) in cement can be re- lated to the formation of Ca–Cr aluminates compounds such as Ca 4 Al 6 O 12 CrO 4 and Ca 6 Al 4 Cr 2 O 5 [12,13]. At elevated pH (approxi- mately 12.8) the formation of calcium aluminosilicate hydrates is mainly responsible for Cr(VI) immobilization using quicklime and 0950-0618/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2011.12.016 Corresponding author. Mobile: +20 1002554075. E-mail address: [email protected] (M.A. Tantawy). Construction and Building Materials 30 (2012) 218–223 Contents lists available at SciVerse ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Immobilization of Cr(VI) in bagasse ash blended cement pastes

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Page 1: Immobilization of Cr(VI) in bagasse ash blended cement pastes

Construction and Building Materials 30 (2012) 218–223

Contents lists available at SciVerse ScienceDirect

Construction and Building Materials

journal homepage: www.elsevier .com/locate /conbui ldmat

Immobilization of Cr(VI) in bagasse ash blended cement pastes

M.A. Tantawy ⇑, A.M. El-Roudi, A.A. SalemChemistry Department, Faculty of Science, Minia University, Minia, Egypt

a r t i c l e i n f o a b s t r a c t

Article history:Received 29 September 2011Received in revised form 30 November 2011Accepted 4 December 2011Available online 29 December 2011

Keywords:Bagasse ashBlended cementPozzolanaCement immobilizationSolidification/stabilizationCr(VI)

0950-0618/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2011.12.016

⇑ Corresponding author. Mobile: +20 1002554075.E-mail address: [email protected] (M.A. T

The aim of the present work is to study the hydration characteristics and immobilization of Cr(VI) inbagasse ash blended cement pastes by setting time, compressive strength, bulk density, total porosityand immobilization efficiency measurements as well as XRD, FTIR and SEM techniques. It was investi-gated that hydration characteristics of bagasse ash blended cement pastes were enhanced especially atlater ages of hydration. Immobilization of Cr(VI) in bagasse ash blended cement pastes reduces their set-ting time, accelerates hydration reactions due to precipitation of CaCrO4 and affects the pore formationmechanism of hydrated cement pastes. The alkalinity of bagasse ash blended cement pastes werereduced due to pozzolanic action. Hence, the rate of precipitation of CaCrO4 decreases with bagasseash content. FTIR results indicate that C–S–H formed by the pozzolanic action of bagasse ash differs inits nature from that formed by hydration of OPC, encapsulates Cr(VI) ions and refines the microstructureof hydrated cement pastes as indicated from immobilization efficiency, XRD and SEM results.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Chromium is one of the heavy metals that has both beneficialand detrimental properties and is generated from many industrialprocesses such as electroplating, leather tanning, paints and pig-ments, textile, steel fabrication and production of chromium chem-icals. In the environment, chromium usually exists in its commonoxidation states, trivalent chromium [Cr(III)] and hexavalent chro-mium [Cr(VI)]. The later is the most important one because of itstoxicity, solubility, mobility characteristics, strong oxidizing andcarcinogenic nature [1]. Cement-based immobilization treatmenttechnology combines interrelated solidification/stabilization (S/S)processes that occur simultaneously to produce a material that willhave reduced environmental impact when disposed or reused. TheUnited States environmental protection agency US EPA has identi-fied S/S as the best demonstrated available technology for many ofhazardous wastes [2].

Bagasse ash is the waste generated by the combustion of sugarcane bagasse. Apart from silica which is the major component, itcontains other oxides as well as unburned carbon [3]. Up to0.066 tons ash is generated per ton of sugar cane crushed [4]. Hugeamounts of bagasse ash have been produced annually in developingcountries. Limited amounts of bagasse ash has been used as soilamendment while the rest of bagasse ash is useless and being dis-posed to open landfills causing serious environmental impacts.However, bagasse ash can be utilized for production of buildingbricks [5] and as a cement replacement to improve the mechanical

ll rights reserved.

antawy).

properties of cement mortar [6,7], normal concrete [8], self com-pacting concrete [9], conventional hollow concrete [10] and to im-prove the durability of concrete under aggressive environment [11].The use of bagasse ash as a cement replacement for immobilizationof heavy metals not only marks a novelty in the immobilizationtechnology but also assists in alleviating disposal problem of ba-gasse ash heaps in developing countries.

Many investigators have analyzed the effect of Cr(III) and (VI)on the different Portland cement phases [12,13] and its solidifica-tion in cementitious matrix [14,15]. Immobilization of chromiumaffects the pore formation mechanism causing a wide variety ofpore diameters to appear indicating involvement of chromium insilicate formation in the C–S–H matrix [16]. Addition of Cr(VI)may retard hydration reactions as a result of the reduction in per-meability caused by precipitation of calcium chromate and coatingon cement grain surfaces [17,18]. Addition of Cr(VI) increases thesetting time of cement, inhibits cement hydration and reducesthe compressive strength of the cement [19]. On contrast, additionof Cr(VI) may increase the setting time of cement and impair thestrength development of blended cement [20].

Another possible mechanism was involved in immobilization ofCr(VI) in cement is the formation of modified Cr-ettringite3CaO�Al2O3�3CaCrO4�32H2O which may occur due to substitutionof SO2�

4 in ettringite structure by CrO2�4 [21,22]. However, this

mechanism may require a high concentration of chromate ions inpore solution. The immobilization of Cr(VI) in cement can be re-lated to the formation of Ca–Cr aluminates compounds such asCa4Al6O12CrO4 and Ca6Al4Cr2O5 [12,13]. At elevated pH (approxi-mately 12.8) the formation of calcium aluminosilicate hydrates ismainly responsible for Cr(VI) immobilization using quicklime and

Page 2: Immobilization of Cr(VI) in bagasse ash blended cement pastes

M.A. Tantawy et al. / Construction and Building Materials 30 (2012) 218–223 219

fly ash through surface sorption, inclusion and physical entrap-ment [23] or through the formation of pozzolanic compounds suchas 3CaOAl2O30.5CaCrO40.5CaSO4�nH2O [24].

The mechanism by which Cr(VI) is bound to cementitious ma-trix influences the leaching mechanism [25]. The leachability ofCr(VI) from solidified cement mixtures depends on the initialCr(VI) concentration, leaching time [19] and leachant pH [26]. Car-bonation of cement mortars increases the leaching of chromiumions and addition of ground granulated blast furnace slag decreasesthe leaching of Cr(VI) from solidified fly ashes [26]. Cement immo-bilization of Cr(VI) was improved by blending cement with lime-stone [15] and marble dust [20]. The aim of the present work isto study the hydration characteristics and immobilization of Cr(VI)in bagasse ash blended cement pastes by XRD, FTIR and SEMtechniques.

2. Materials and experimental techniques

Raw materials used in the present work are: OPC [CEM I (No. 42.5)] from Beni-Suif Cement Co., Egypt and raw sugar cane bagasse ash was collected from the boi-ler of nearby sugar factory in Minia Governorate, Egypt. Raw bagasse ash was cal-cined in an electrical muffle furnace with a heating rate 10 �C/min at 700 �C for3 h, recharged from the muffle furnace, cooled to room temperature in desiccatorand ground to pass 90 lm sieve. 5% K2CrO4 solution (weight/volume) was prepared(13,000 ppm of Cr(VI)) in distilled water and used in cement immobilization ofCr(VI). Bagasse ash blended cement was prepared by partial replacement of OPCwith 10–25% bagasse ash and their mix composition is shown in Table 1.

The water of consistency, initial and final setting times were determined usingVicat apparatus according to ASTM designations [27,28]. In case of hydration char-acteristics, cement pastes were hydrated with their corresponding water of consis-tency. In case of immobilization of Cr(VI) in cement pastes, 60 ml of 5% K2CrO4

solution (completed by water to its appropriate water of consistency) was addedto 220 g of cement. Hence 1.36% wt/wt of K2CrO4 to dry cement (0.36% Cr(VI)) wereused. Freshly prepared cement pastes were molded in stainless steel molds(2 � 2 � 2 cm) at about 100% relative humidity, demolded after 24 h and curedfor 90 days in closed humidity chamber without mixing of hydrated cubes withwater to avoid leaching of chromium from hardened cement pastes.

Bulk density was determined using Archimedes principle [29]. The compressivestrength was measured using a manual compressive strength machine for a set ofthree cubes according to ASTM designation [30]. Free water content was deter-mined using domestic microwave oven (Olympic electric model KOR-131G,2450 MHz, 1000 W) [31]. The combined water content was determined usinghydration stopped specimen after being ignited in porcelain crucibles at 1000 �Cfor 1 h in a muffle furnace. The total porosity of the hardened cement paste was cal-culated from the values of bulk density, free and total water contents as describedelsewhere [32]. The Cr (VI) immobilization efficiency after 28 and 90 days of hydra-tion was determined according to US EPA toxicity characteristic leaching procedure(TCLP) [33]. Cr(VI) concentration of the leachate was determined spectrophotomet-rically by diphenylcarbazide method using Perkin–Elmer Lambda 35 UV/VIS spec-trometer [34].

X-ray fluorescence (XRF) and X-ray diffraction (XRD) analyses were carried outby Philips X-ray diffractometer PW 1370, Co. with Ni filtered CuKa radiation(1.5406 Å). The Fourier transform infrared (FTIR) analysis was measured by spec-

Table 1Mix composition in wt.% of bagasse ash blended cements.

Symbol OPC Bagasse ash

C 100 0B1 90 10B2 85 15B3 80 20B4 75 25

Table 2Chemical composition wt.% of OPC and bagasse ash calcined at 700 �C.

Material SiO2 Al2O3 Fe2O3 CaO MgO

OPC 20.88 6.08 3.18 63.00 1.50Bagasse ash 61.69 11.56 9.78 5.57 3.24

trometer Perkin Elmer FTIR system Spectrum X in the range 400–4000 cm�1 withspectral resolution of 1 cm�1. Scanning electron microscopy (SEM) was investigatedby Jeol-Dsm 5400 LG apparatus.

3. Results and discussion

3.1. Characterization of raw materials

Table 2 illustrates the chemical composition of the OPC and ba-gasse ash calcined at 700 �C for 3 h determined by XRF analysis. Ba-gasse ash contains high amount of SiO2 (61.69 wt.%) in addition tosmall amounts of CaO, Fe2O3, Al2O3, MgO, Na2O and K2O. The sumof SiO2, A12O3 and Fe2O3 equals to 83.03 wt.% which is in goodagreement with the requirements (>70 wt.%) stated in ASTM desig-nation for natural pozzolana [35]. According to Bouge’s calcula-tions, OPC is composed of 47.78 wt.% C3S, 23.83 wt.% b-C2S,10.73 wt.% C3A and 9.68 wt.% C4AF. Fig. 1 illustrates the XRD pat-terns of bagasse ash calcined at 700 �C for 3 h. Bagasse ash containsamorphous silica as indicated from the heap in the range 15–35 2hin addition to quartz, tridymite and christobalite. Fig. 2 shows theSEM micrograph of bagasse ash calcined at 700 for 3 h. Bagasse ashcontains high amount of silica aggregate which may appear as darkgrains (a) and residues which may appear as white small particles(b).

3.2. Hydration characteristics and immobilization of chromium (VI) inblended cement pastes

Fig. 3 illustrates the water of consistency, initial and final set-ting times of bagasse ash blended cement pastes hydrated withwater or 5% K2CrO4 solution. Water of consistency increases withbagasse ash content may be due to that bagasse ash markedly in-creases the amount of surface water which related to the specificsurface of the system [36]. Setting time elongates with bagasseash content may be due to increasing the amount of mixing water[37], decreasing OPC content [38] and formation of a layer of ba-gasse ash particles around anhydrous cement grains which delaysthe hydration of C3S. The thickness of this layer increases with ba-gasse ash content hence the rate of hydration of cement decreasesat early ages of hydration [39]. Setting time of OPC paste hydratedwith K2CrO4 solution is longer than that hydrated with water dueto that addition of Cr(VI) increases the setting time of cement[19,20]. Setting time of bagasse ash blended cement pastes hy-drated with K2CrO4 solution are shorter than those hydrated withwater due to that the incorporation of pozzolana may improve thehydration of cement in presence of Cr(VI). Addition of Cr(VI) mayaccelerate hydration reactions in presence of pozzolana due to pre-cipitation of calcium chromate and the increased demand for Ca2+

ions in the cement pore solution. As a result, unhydrated cementfraction satisfies the increased demand of Ca2+ ions and accelerateshydration of C3S [18].

Fig. 4 represents the bulk density and total porosity of bagasseash blended cement pastes hydrated with water or 5% K2CrO4 solu-tion for 90 days. The bulk density decreases while the total poros-ity increases with bagasse ash content due to increasing theamount of mixing water and decreasing clinker content. The bulkdensity decreases with bagasse ash content may be due to that ba-gasse ash have lower specific gravity than OPC. The bulk density of

SO3 Na2O K2O LOI P2O5 Total

1.60 0.22 0.24 2.35 0.15 99.200.04 1.06 0.49 1.41 4.05 98.89

Page 3: Immobilization of Cr(VI) in bagasse ash blended cement pastes

2 theta

Inte

nist

y, %

Q quartzCr christobalite T tridymite

Cr

T

Q

Q

Cr

15 20 25 30 35 40 45

Fig. 1. The XRD patterns of bagasse ash calcined at 700 �C for 3 h.

a

b

Fig. 2. SEM micrograph of bagasse ash calcined at 700 �C for 3 h.

27

29

31

33

35

C B1 B2 B3 B4

Mixes

Wat

er o

f con

sist

ency

,%.

50

150

250

350

450

550

Setti

ng ti

me,

min

.

Water of consistencyInitial Setting TimeFinal Setting TimeInitial Setting Time Cr VIFinal Setting Time Cr VI

Fig. 3. The water of consistency, initial and final setting times of bagasse ashblended cement pastes hydrated with water or 5% K2CrO4 solution.

1.88

1.92

1.96

2.00

2.04

2.08

2.12

2.16

2.20

2.24

1 10 100

Curing time, days

30

34

38

42

46

50

Tota

l por

osity

, %

1.88

1.92

1.96

2.00

2.04

2.08

2.12

2.16

2.20

2.24

1 10 100

Curing time, days

Bul

k de

nsity

, g/c

m3

Bul

k de

nsity

, g/c

m3

29

31

33

35

37

39

41

43

45

Tota

l por

osity

, %

C (BD) B1 (BD) B2 (BD) B3 (BD) B4 (BD)

C (TP) B1 (TP) B2 (TP) B3 (TP) B4 (TP)

(a)

(b)

Fig. 4. The bulk density and total porosity of bagasse ash blended cement pasteshydrated with water (a) or 5% K2CrO4 solution (b) for 90 days.

20

30

40

50

60

70

80

Com

pres

sive

str

engt

h, M

pa

C

B1

B2

B3

B4

20

30

40

50

60

70

80

1 10 100

Curing time, days

Com

pres

sive

str

engt

h, M

Pa

(a)

(b)

Fig. 5. The compressive strength of bagasse ash blended cement pastes hydratedwith water (a) or 5% K2CrO4 solution (b) for 90 days.

220 M.A. Tantawy et al. / Construction and Building Materials 30 (2012) 218–223

bagasse ash blended cement pastes hydrated with K2CrO4 solutionare lower than those hydrated with water because addition ofchromium affects the pore formation mechanism causing a widevariety of pore diameters [16].

Fig. 5 shows the compressive strength of bagasse ash blendedcement pastes hydrated with water or 5% K2CrO4 solution for90 days. The rate of strength development in blended cementpastes was enhanced at later ages of hydration. This may be dueto that the formation of a layer of bagasse ash particles aroundanhydrous cement grains at early ages of hydration which reducesthe rate of hydration. At later ages bagasse ash reacts with portlan-dite accumulated in the pore of hydrated cement pastes as a resultof hydration of clinker phases giving additional calcium silicate hy-drates. The compressive strength decreases with bagasse ash con-tent due to decreasing OPC content. The compressive strength ofbagasse ash blended cement pastes hydrated with K2CrO4 solution

Page 4: Immobilization of Cr(VI) in bagasse ash blended cement pastes

26 28 30 32 34 36 38 402 theta

Q quartz P Portlandite K K2CrO4

T C3S A C3A C CaCrO4

D C2S

C Cr VI

D

Q

P

B1 Cr VI

B4 Cr VI

K

C

P

T

A

C

B1

B4

Fig. 6. The XRD patterns of bagasse ash blended cement pastes hydrated withwater or 5% K2CrO4 solution for 90 days.

40080012001600200024002800320036004000

Cm-1

C Cr VI

B1 Cr VI

B4 Cr VI

C

B1

B4

Fig. 7. The FTIR patterns of bagasse ash blended cements hydrated with water or 5%K2CrO4 solution for 90 days.

M.A. Tantawy et al. / Construction and Building Materials 30 (2012) 218–223 221

are lower than those hydrated with water because addition ofchromium affects the pore formation mechanism and reduces thecompressive strength of the solidified cement especially at earlyages. The compressive strength decreases with bagasse ash contentdue to decreasing OPC content and retardation effect of calciumchromate layer coating bagasse ash particles.

Fig. 6 illustrates the XRD patterns of bagasse ash blended ce-ment pastes hydrated with water or 5% K2CrO4 solution for

C

C Cr VI

Fig. 8. SEM micrographs of C and B2 hydrate

90 days. The amount of unhydrated clinker phases (C2S, C3S) andportlandite decrease with bagasse ash content due to decreasingOPC content and that bagasse ash activates the hydration of cementat later ages of hydration. In case of bagasse ash blended cements hy-drated with K2CrO4 solution, the content of CaCrO4 decreases withbagasse ash content. Bagasse ash consumes part of portlandite byits pozzolanic activity, hence the alkalinity of hydrated cement pastscontaining bagasse ash decreases. As a result, the rate of precipita-tion of CaCrO4 decreases with bagasse ash content.

Fig. 7 illustrates the FTIR patterns of bagasse ash blended ce-ments hydrated with water or 5% K2CrO4 solution for 90 days. In caseof bagasse ash blended cements hydrated with water, the absorptionbands of CO2�

3 at 1429 cm�1 (asymmetric stretching vibration v3 ofCO2�

3 ) and 893 cm�1 (out-of-plane bending vibration v4 of CO2�3 ) in-

crease with bagasse ash content. Because the total porosity of hy-drated cement pastes increases with bagasse ash content, which inturn may increase the rate of carbonation of hydrated cement pastes.

B2

B2 Cr VI

d with water or 5% K2CrO4 for 28 days.

Page 5: Immobilization of Cr(VI) in bagasse ash blended cement pastes

75

80

85

90

C B1 B2 B3 B4

Mixes

Effe

cien

cy, %

28 days90 days

Fig. 9. The efficiency of Cr(VI) immobilization of bagasse ash blended cementpastes hydrated with 5% K2CrO4 solution for 28 and 90 days.

222 M.A. Tantawy et al. / Construction and Building Materials 30 (2012) 218–223

The absorption band of C–S–H at 978 cm�1 (stretching vibration v3

of SiO4�4 ) shifts to higher wavenumber values with increasing ba-

gasse ash content. This may be due to that C–S–H formed by the poz-zolanic action of bagasse ash differs in its nature from that formed byhydration of OPC. The absorption band of silica at 462 cm�1 (bendingvibration of O–Si–O) arises from the replacement of OPC with ba-gasse ash. The ettringite band at 1124 cm�1 disappeared may dueto that SO2�

4 ions were probably replaced by CO2�3 ions in case of ba-

gasse ash blended cement pastes. In case of bagasse ash blended ce-ments hydrated with K2CrO4 solution, the absorption bands of C–S–H at 978 and 1644 cm�1 decrease with bagasse ash content due todecreasing of OPC content and retardation effect of calcium chro-mate layer.

Fig. 8 shows the SEM micrographs of OPC and blended cementpaste containing 15% bagasse ash hydrated with water or 5%K2CrO4 solution for 28 days. Excess of portlandite prismatic aggre-gates fills some pores of OPC paste hydrated with water. Bagasseash reacts with portlandite forming additional C–S–H. In case ofOPC paste hydrated with K2CrO4, CaCrO4 was observed as a resultof the reaction between portlandite and K2CrO4. Bagasse ashblended cement paste hydrated with K2CrO4 shows refined micro-structure (i.e. have lower porosity) compared to that hydrated withwater. As illustrated from total porosity values in Fig. 4. This maybe due to that addition of Cr(VI) may accelerate hydration reac-tions in presence of bagasse ash [18].

Fig. 9 represents the efficiency of Cr(VI) immobilization of ba-gasse ash blended cement pastes hydrated with 5% K2CrO4 solutionfor 28 and 90 days. The efficiency of Cr(VI) immobilization was en-hanced with up to 15% bagasse ash content then decreased afterthat. This may be due to that formation of additional C–S–H as aresult of the pozzolanic activity of bagasse ash encapsulates Cr(VI)ions as detected in XRD results (i.e. decreasing the content ofK2CrO4 with bagasse ash content). The efficiency of Cr(VI) immobi-lization decreases with higher bagasse ash content due to increas-ing the amount of mixing water, decreasing OPC content andformation of a layer of bagasse ash particles around anhydrous ce-ment grains which delays the hydration of C3S.

4. Conclusions

The main conclusions of this investigation are:

1. Hydration characteristics of bagasse ash blended cement pastesincluding setting time, compressive strength and total porositywere enhanced especially at later ages of hydration.

2. Immobilization of Cr(VI) in bagasse ash blended cement pastesreduces their setting time, accelerates hydration reactions dueto precipitation of CaCrO4 and affects the pore formation mech-anism of hydrated cement pastes.

3. The alkalinity of bagasse ash blended cement pastes wasreduced due to pozzolanic action. Hence, the rate of precipita-tion of CaCrO4 decreases with bagasse ash content.

4. FTIR results indicate that C–S–H formed by the pozzolanicaction of bagasse ash differs in its nature from that formed byhydration of OPC.

5. XRD results indicate that C–S–H formed by the pozzolanicaction of bagasse ash encapsulates Cr(VI) ions.

6. SEM results indicate that bagasse ash blended cement pasteshydrated with K2CrO4 have refined microstructure comparedto those hydrated with water.

7. According to this investigation, it was recommended that theblended cement which contain 15–20% bagasse ash can be usedeffectively for immobilization of concentrated waste Cr(VI)solutions (�13,000 ppm Cr(VI)) after being mixed with thisblended cement in a water to cement ratio of about 30%.

References

[1] Katz SA, Salem H. The biological and environmental chemistry ofchromium. New York: VCH Publications; 1994.

[2] US EPA. Treatment technologies for site cleanup: annual status report, 11th ed.EPA-542-R-03-009; 2004.

[3] Umamaheswaran K, Batra VS. Physico-chemical characterization of Indianbiomass ashes. Fuel 2008;87:628.

[4] Iyer PVR, Rao TR, Grover PD. Biomass thermo-chemical characterization. 3rded. New Delhi: Indian Institute of Technology; 2002.

[5] Jawaid SMA, Raghatate S. Bagasse ash utilization in building industry. SolidWaste Tech Manage 2007;33(4):24.

[6] Suvimol S, Daungruedee C. Bagasse ash: effect of pozzolanic activity andapplication in cement use aspect. In: The 3rd ACF international conference-ACF/VCA; 2008. p. 165.

[7] Goyal A, Anwar AM. Properties of sugarcane bagasse ash and its potential ascement – pozzolana binder. In: 12th International colloquium on structuraland geotechnical engineering, Cairo, Egypt; 2007.

[8] Siripairod H, Polkert S, Sujjavanich S, Chaysuwan D. Development of concreteflooring tiles by wastes, bagasse ash and fly ash for replacing type I Portlandcement. In: The 3rd ACF international conference-ACF/VCA; 2008.

[9] Akram T, Memon SA, Obaid H. Production of low cost self compacting concreteusing bagasse ash. Constr Build Mater 2009;23:703.

[10] Banaag VFE, Cañada ALC, Meñes MO, Saldivar KQ, Lo DS. Bagasse as analternative aggregate in hollow CMU. Symposium on infrastructuredevelopment and the environment, seameo-innotech. Diliman, Quezon City,Philippines: University of the Philippines; 2006.

[11] Singh NB, Singh VD, Rai S. Hydration of bagasse ash-blended Portland cement.Cem Concr Res 2000;30:1485.

[12] Stephan D, Maleki H, Knofel D, Eber B, Hardlt R. Influence of Cr, Ni and Zn onthe properties of pure clinker phases. Part I. C3S. Cem Concr Res1999;29(4):545.

[13] Stephan D, Maleki H, Knofel D, Eber B, Hardlt R. Influence of Cr, Ni and Zn onthe properties of pure clinker phases. Part II. C3A and C4AF. Cem Concr Res1999;29(5):651.

[14] Park CK. Hydration and solidification of hazardous wastes containing heavymetals using modified cementitious materials. Cem Concr Res 2000;30(3):429.

[15] Trazza MA, Ferraiuelo MF. Hydration study of limestone blended cement in thepresence of hazardous wastes containing Cr(VI). Cem Concr Res 2003;33:1039.

[16] Goto S, Roy D. Diffusion of ions through hardened cement pastes. Cem ConcrRes 1981;11:757.

[17] Poon CS, Clark AI, Perry R. Permeability study of the cement basedsolidification process for the disposal of hazardous wastes. Cem Concr Res1986;16:161.

[18] Cannell BS, Eghmy TT, Krzow JE. Heavy metal stabilization in municipal solidwaste combustion bottom ash using soluble phosphate. Waste Manage2000;20:135.

[19] Wang S, Vipulanandan C. Solidification/stabilization of Cr(VI) with cementleachability and XRD analyses. Cem Concr Res 2000;30:385.

[20] Neeraj J, Mridul G. Effect of Cr(VI) on the hydration behavior of marble dustblended cement: solidification, leachability and XRD analyses. Constr BuildMater 2008;22:1851.

[21] Macias A, Kindness A, Glasser FP. Impact of carbon dioxide on theimmobilization potential of cemented wastes: chromium. Cem Concr Res1997;27:215.

[22] Bensted J, Varma SP. Ettringite and its derivatives. II. Chromate substitution.Silic Ind 1972;37:315.

[23] Dermatas D, Meng X. Utilization of fly ash for stabilization/solidification ofheavy metal containing soils. Eng Geol 2003;70(3–4):377.

[24] Dermatas D, Moon DH. Chromium leaching and immobilization in treatedsoils. Environ Eng Sci 2006;23(1):77.

Page 6: Immobilization of Cr(VI) in bagasse ash blended cement pastes

M.A. Tantawy et al. / Construction and Building Materials 30 (2012) 218–223 223

[25] Cheryl E, Amal HR, Beydoun D, Scott JA, Low G. Implications of the structure ofcementitious wastes containing Pb(II), Cd(II), As(V), and Cr(VI) on the leachingof metals. Cem Concr Res 2004;34:1093.

[26] Qijun YT, Nagataki S, Jinmei L, Saeki T, Hisada M. The leachability of heavymetals in hardened fly ash cement and cement-solidified fly ash. Cem ConcrRes 2005;35:1056.

[27] ASTM designation: C 187-98. Standard test method for normal consistency ofhydraulic cement. Annual Book of ASTM Standards, 04.01; 2002.

[28] ASTM designation: C 191-01a. Standard test method for time of setting ofhydraulic cement by Vicat needle. Annual Book of ASTM Standards, 04.01;2002.

[29] Gennaro R, Cappelletti P, Cerri G, Gennaro M, Dondi M, Langella A. Zeolitic tuffsas raw materials for lightweight aggregates. Appl Clay Sci 2004;25:71.

[30] ASTM designation: C109-80. Standard test methods for compressive strengthof hydraulic cements. Annual Book of ASTM Standards; 1983.

[31] Pavlik J, Tydlitat V, Cerny R, Klecka T, Bouska P, Rovnanikova P. Application of amicrowave impulse technique to the measurement of free water content inearly hydration stages of cement paste. Cem Concr Res 2003;33:93.

[32] Copeland LE, Hayes TC. Porosity of hardened Portland cement pastes. ACIMater 1956;27:633.

[33] US EPA. Method 1311: toxicity characteristic leaching procedure. In: EPA SW-846: test methods for evaluating solid waste, physical/chemical methods;1992.

[34] Gupta VK, Jain CK, Ali I, Sharma M, Sainia VK. Removal of cadmium and nickelfrom wastewater using bagasse fly ash-a sugar industry waste. Water Res2003;37:4038.

[35] ASTM designation: C 618-89. Standard specification for coal fly ash and raw orcalcined natural pozzolana for use as a mineral admixture in concrete. AnnualBook of ASTM standards; 1998.

[36] EI-Didamony H, Helmy IM, Amer AA, Heikal M. Utilization of Egyptian by-products in the preparation of blended cements. Zem Kalk Gips1995;48(9):502.

[37] Hwang CL, Shen DH. The effect of blast furnace slag and fly ash on thehydration of Portland cement. Cem Concr Res 1991;21:410.

[38] Khandaker M, Hossain A. Properties of volcanic pumice based cement andlightweight concrete. Cem Concr Res 2004;34:283.

[39] Yogendran V, Langan BW, Ward MA. Hydration of cement silica fume paste.Cem Concr Res 1991;21:691.