Construction and Building Materials 73 (2014) 391–398

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Construction and Building Materials

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Characterization and properties of elephant grass ashes assupplementary cementing material in pozzolan/Ca(OH)2 pastes

http://dx.doi.org/10.1016/j.conbuildmat.2014.09.0780950-0618/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author.

Erika Y. Nakanishi a, Moisés Frías b, Sagrario Martínez-Ramírez c, Sérgio F. Santos d, Michelle S. Rodrigues a,Olga Rodríguez b,⇑, Holmer Savastano Jr. a

a University of São Paulo, Faculty of Animal Science and Food Engineering, Av. Duque de Caxias Norte, 225, 13635-900 Pirassununga, SP, Brazilb Eduardo Torroja Institute (IETcc-CSIC), c/Serrano Galvache 4, 28033 Madrid, Spainc Matter Structure Institute (IEM-CSIC), c/Serrano 121, 28006 Madrid, Spaind São Paulo State University, Faculty of Engineering, Department of Materials and Technology, Guaratinguetá, SP, Brazil

h i g h l i g h t s

� Use of elephant grass ashes (EG) as pozzolan materials.� Chemical treatment with HCl decrease potassium and improve silica content in ashes.� Elephant grass ashes fixed significant amount of lime.� Main products of pozzolanic reaction were type II CSH gels.� This work confirms viability of recycling EG as supplementary cementing materials.

a r t i c l e i n f o

Article history:Received 16 June 2014Received in revised form 9 September 2014Accepted 24 September 2014

Keywords:Agro-industrial wasteElephant grassThermal activationPozzolanLime pastesAlternative binder

a b s t r a c t

This work presents the behavior of two elephant grass ashes, as pozzolans, elephant grass cameroon(EGC) and napier (EGN), calcined under controlled conditions (700 �C). The ashes were initially submittedto a chemical treatment with HCl in order to reduce the potassium content. Both ashes showed high poz-zolanic activity after 7 days of curing, with at least 85% of fixed lime. The thermogravimetric and micro-Raman analysis in elephant grass ashes/Ca(OH)2 pastes confirmed that the main hydrated phases duringthe pozzolanic reaction consisted of CSH gels, by the weight loss between 60 and 300 �C in TG analysisand the band at 680 cm�1 in Raman spectrums. Based on the achieved results, it is possible to concludethat elephant grass ashes can be used as supplementary cementing materials.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Studies have been developed in the last years about the usage ofpozzolans derived from combustion of agricultural solid waste asmineral addition in the manufacture of blended pastes, mortarsand concretes [1–6]. Mineral additions are added to reduce theamount of clinker in Portland cement what is important becauseapproximately 7% of global CO2 emissions come from the cementindustry [7]. Besides, during the process of biomass burning, someauthors nominate the CO2 produced as ‘‘neuter carbon’’. This defi-nition comes from the final carbon average in the atmospherebecause the carbon released in the burning process initially comes

from the photosynthesis process of the plant growth so, it does notbring up an increase of the carbon average in the atmosphere. Onthe other hand, when the fossil fuel kept under the ground is usedit releases an extra amount of carbon in the atmosphere causing anincrement on its concentration [7–9]. Moreover, the mineral addi-tion with higher content of amorphous SiO2 also provides improve-ment in the mechanical properties of the cement based material[10].

At present, the biomass waste ashes usually comes from sugarcane straw and bagasse, rice husk, paper sludge and forest residues[11]. However some power plants in Brazil are using up to 100% ofa vegetable plant called elephant grass [12] as biomass for the pro-duction of energy, which generates ashes that are deposed in land-fills with the consequent environmental, technical, economical andsocial issues.

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The Pennisetum purpureum Schum, known as elephant grass, isoriginal from the African continent and it was introduced in Brazilin the 1920s. However, only in Brazil is used as biomass with a pro-duction of 30 tns per hectare. The elephant grass is the perennialgrass of upright and caespitose growth which can reach 3–5 mhigh [13].

Being a species of fast growth and high vegetable biomass pro-duction, so physiologically similar to sugar cane, the elephant grasspresents high potential usage as an alternative source of energy [9].According to Stresov et al. [8] Brazil has the potential to produce1.2 Gt of charcoal and a 2 Gt-average of bio-oils per year from ele-phant grass. But its main use is as biomass source on the burningprocess for the energy production and one example of this is athermoelectric power plant (Sykué Bioenergia) located in the townof São Desidério, in the state of Bahia, Brazil which operates withelephant grass as one of the biomass plantations available. Thecontrolled calcination in laboratory conditions of elephant grassgenerated 4.52% of ashes as reported elsewhere [12].

In general this kind of ashes presents high silica content (>50%of SiO2), mostly reactive silica for its low crystalline and/or amor-phous nature which makes it suitable for use as active cementaddition.

Due to the absence of similar research works in this field, thepresent study reports the preliminary scientific aspects (chemicaland mineralogical characterization, pozzolanic properties, identifi-cation and evolution of hydrated phases, morphology) on the useof these new industrial wastes in ash/Ca(OH)2 pastes. These inputsare fundamental for the establishment of the scientific bases aspozzolans in the manufacture of future commercial eco-efficientcements. The obtained results with elephant grass ashes fromtwo different cultivars (cameroon and napier) were compared withsilica fume, a well-known pozzolan traditionally used in the civilconstruction industry.

2. Experimental

2.1. Materials

Both elephant grasses (P. purpureum cv. cameroon and napier) came from Pira-ssununga, in the state of São Paulo, once cut after 150 days of age, the whole plantwere triturated and submitted to a drying process at 60 �C for 72 h (Fig. 1a).

The commercial silica fume (SF) Elkem M920D was used as reference. The limeused for the production of the pastes with the pozzolans was an analytical gradecalcium hydroxide (95% minimum purity).

2.2. Methods and instrumental techniques

2.2.1. Calcining processOnce finished the previous treatment both grasses were submitted to a calcin-

ing process under controlled conditions in an electrical furnace with a 10 �C/minheating rate. Firstly treated at 400 �C for 20 min, with the purpose to produce amore homogeneous burning, followed by a burning process at 700 �C for 60 min

Fig. 1. Cameroon elephant grass triturated (

in order to obtain the final ashes: cameroon elephant grass ash (EGC) (Fig. 1b)and napier elephant grass ash (EGN), that have been used in the present study,the cooling of ashes was natural at room temperature. Later, the ashes were groundin a ball mill for 30 min.

2.2.2. Extraction treatmentFinally, the ashes were submitted to the potassium extraction treatment

(hydrochloric acid (HCl) solution (3% v/v) during 1 h at 90 �C [14] in order to reduceK content in ashes (values of up to 22% were found in the original ashes). Accordingto a previous work [15] high K content can promote a degradation process of thecement matrices by the alkali-aggregate reaction. With the methodology used, a68% for EGN and 61% for EGC of K reduction has been achieved.

2.2.3. Pozzolanic activity methodA non-standard accelerated chemical method was used to study the pozzolanic

activity of these materials [16]. This method consists in putting the pozzolan (1 g) incontact with the lime-saturated solution (75 ml) at 40 �C for 1, 7 and 28 days and atthe end of each period the CaO concentration in the solution was quantified. Thefixed lime was obtained by the difference between the concentrations in the satu-rated lime solution (17.68 mmol/l) and the CaO content in the solution in contactwith the sample.

2.2.4. Preparation of the calcium hydroxide pasteThe three samples (EGN, EGC and SF) and Ca(OH)2 were mixed in the proportion

of 1:1 by weight with the water:CH ratio equal to 1.0. The pastes were stored in thesaturated environment at 22 ± 2 �C during 0, 7, 28, 60 and 90 days of curing, andonce achieved the fixed reaction times, the hydrated samples were submerged inisopropyl alcohol and dried in an electric oven at 60 �C during 1 h (except for theSEM/EDX analysis, which a vacuum system for 24 h in order to interrupt the hydra-tion reaction.

2.2.5. Ashes and pastes characterizationThe chemical characterization was carried out by the X-ray fluorescence (XRF),

using the Advanced X-ray Axios spectrometer. The mineralogical composition wasdetermined by X-ray diffraction (XRD), using the X Pert Pro equipment, with X Cel-erator detector.

The particle size distributions and the respective equivalent diameter of theparticles were made in a model Sympatec Helos 12 KA laser Diffraction Spectrom-eter. This apparatus is equipped with a He/Ne 5 mW lamp. The test was conductedwith the feed system in isopropyl alcohol as nonreactive liquid [17].

The thermogravimetric and differential thermogravimetric analyses (TG/DTA)of pastes were carried out with TA Instruments SDT Q600. The temperature rangewas 25–1000 �C, heating rate 10 �C/min and nitrogen atmosphere.

Additional mineralogical characterization by micro-Raman was made with theRM 1000 Renishaw Raman microscopy equipped with a laser at 633 nm and a Leicamicroscopy, with 25 mW laser powder. Typical spectra from 100 to 4000 cm�1 wererecorded with a resolution of 4 cm�1. The time acquisition was 10 s and 5 scanswere recorded to improve the signal-to-noise ratio. Correct calibration of the instru-ment was observed by measuring the Stokes and anti-Stokes bands and checkingthe position of the Si band at ±520.6 cm�1. This technique is widely used to studythe Portland cement, clinker and hydration processes [18]. The pastes (with EGC,EGN and SF) were analyzed at 60 days of curing. The test was also carried out withthe ashes and SF before mixing with lime for the pastes production.

The morphology of the hydrated phases was determined with a scanning elec-tron microscopy (SEM) with the FEI INSPECT microscope equipped with an energydispersive X-ray analyzer (silicon/lithium detector and a DX4i analyzer, EDX). Thepowder samples were fixed to the metallic plate using a graphite ribbon tape in aBIO-RAD model SC 502, and coated with graphite to enhance electrons conductivity.

a) and cameroon elephant grass ash (b).

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The use of SEM/EDX gives additional information about the morphology, textureand chemical composition of the hydrated phases, and mainly information that can-not be obtained by means of XRD.

Fig. 2. XRD patterns of the treated cameroon (EGC) and napier (EGN) ashes andsilica fume (SF).

Fig. 3. Particle size distribution curves of the materials: (a) cumulative and (b)density.

3. Results and discussion

3.1. Characterization of the starting materials

The chemical composition by XRF is shown in Table 1. Thechemical composition requirement for a pozzolan is to present aminimum content of 50% by mass for the sum of the reactive oxi-des: SiO2, Al2O3 and Fe2O3 [19]. All tested samples in the presentwork achieved that minimum required value.

The main oxides present in the EGC are SiO2, CaO, P2O5, K2O andMgO; while the EGN ash shows a silicon rich nature (80% of SiO2),percentage closer to that of silica fume. It is important to note thechemical differences found between both elephant grass ashes,showing that the grass type (cameroon or napier) plays an impor-tant role in the composition of the ash and probably on theirbehavior in blended cement matrixes. Loss on ignition (LOI) ofEGC is approximately twice in comparison to EGN and SF. Asheswith high LOI require greater water consumption, and thus deter-mining the consequent change in the rheological properties of thematrices produced with these materials. Furthermore, the higherthe loss on ignition values, the lower the silica content in the ash[20].

The mineralogical composition obtained by XRD patterns(Fig. 2) evidences the presence of Cristobalite (21.9�, 28.5� and36.1� (2h)) and quartz (26.6� (2h)) as common crystalline com-pounds in both elephant grass ashes, followed by Sylvite traces(at 28.4 (2h)); while silicon (at 28.5�, 47.41� (2h)), Tridymite (at35.47� (2h)), Moissanite (at 35.47� (2h)) and Gupeite (at 45.14�(2h)) were identified in SF.

The raising in the baseline of XRD patterns between 15� and 40�(2h) in all cases indicates the presence of amorphous phases, beingmore intense such incidence in the EGC ash. This fact would berelated with the low crystallinity of reactive silica content that willhave a direct influence on the pozzolanic properties, as discussedin the results shown in Section 3.2.

The particle size distribution (fineness) of the pozzolan plays animportant role on both the hydration and pozzolanic reactions.Fig. 3 shows both the cumulative (Fig. 3a) and discrete (Fig. 3b)particle size distribution for the three starting raw materials usedin the present work. The cumulative particle size distributioncurves have different profiles for each analyzed material, indicatinga greater fineness for the silica fume (SF), followed by EGC andEGN. The granulometric parameters: D10, D50 and D90 are listedin Table 2.

According to these data, EGC presents finer particles than EGN,which improves the reactivity of the material in contact with cal-cium hydroxide [21].

3.2. Pozzolanic activity

The pozzolanic activity was evaluated by an accelerated chem-ical method during 28 days of reaction as described in Section2.2.3. The results of the fixed calcium hydroxide obtained for the

Table 1Chemical composition of treated EGC and EGN ashes, and SF.

SiO2 Al2O3 Fe2O3 SO3 MgOOxides (%)

EGC 49.4 0.47 0.83 0.47 4.22EGN 80.0 0.44 0.77 0.65 1.11SF 84.5 0.97 2.62 – 0.6

LOI = loss of ignition at 1000 �C.

mixture of lime with ashes or SF systems, are depicted in Fig. 4.All systems showed a high pozzolanic activity in terms of the fixed

P2O5 Cl K2O CaO LOI

9.91 0.46 8.6 10.40 14.60.56 0.95 7.05 1.85 6.310.14 – 1.04 2.93 7.53

Table 2Granulometric values for D10, D50 and D90 for the ashes and SF.

Sample D10 (lm) D50 (lm) D90 (lm)

EGC 4.65 25.49 64.03EGN 9.39 49.02 92.51SF 2.46 10.95 23.91

Legend: D10: particle size which lies below 10% of the material; D50 particle sizewhich lies below 50% of the material; D90: particle size which lies below 90% of thematerial.

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lime results. At the initial ages (1 day) in the lime solution the poz-zolanic activity was lower for the EGN ash (44% of fixed lime) thanfor the silica fume (74.8%) and EGC ash (90%). However, between 1and 7 days of reaction, a strong increase of the reaction rate wasobserved in the EGN-ash system, reaching a value of 85.5% of fixedlime, while the SF- and EGC-ash systems showed values close to93.5% and 96%, respectively. Subsequently the pozzolanic reactionprogresses slightly for the EGN-ash system, from 85.5% until 93.3%of fixed lime between 7 and 28 days. After 28 days, the pozzolanicreaction is practically non-existent in the SF-lime and EGC-limesystems. This pozzolanic behavior is similar to other agro-indus-trial waste ashes studied by Frías et al. [16]. They reported thevalue of 82% of fixed lime for the thermally activated bamboo leafashes at 1 day of reaction, reaching 90% at 3 days of age, and afterthat, the reactions virtually cease, with little change at 90 days(91.4%). However, Morales et al. [5] reported values about 90% offixed lime at 28 days of curing in a study of sugarcane wastes ashesactivated at 800 �C.

3.3. Identification and evolution of hydrated phases in pozzolan/Ca(OH)2 systems

3.3.1. TG/DTG resultsEach phase, including the hydrates, is characterized by its own

temperature range of decomposition and by a specific mass loss;for example, in the case of Portlandite, it is related to a loss ofwater. These temperature ranges are clearly defined by the edgesof the characteristic peak of the DTG curve. Thus, the thermal anal-ysis used in this study enables the thermogravimetric curve (TGA),and the derived thermogravimetric curve (DTG) can be analyzedsimultaneously on each sample. Thermogravimetry results(DTG) revealed weight losses when these EGC, EGN and SF

Fig. 4. Pozzolanic activity: fixed lime over time.

pozzolanic/Ca(OH)2 systems up to 60 days of reaction were sub-jected to a thermal process.

Fig. 5 shows DTG curves during the heating ramp up to 1000 �Cin relation to the material nature, showing two main weight lossesin all cases, that occurred in two ranges of temperature: between60 and 300 �C due to the dehydroxylation of hydrated phases pro-duced during the pozzolanic reaction and humidity loss, and from375 to 475 �C corresponding to the dehydroxylation of Portlandite.Table 3 shows the corresponding losses of pastes.

Fig. 5. DTG curves at different stages of curing: 0, 7, 28, 60 days, (a) EGC, (b) EGN,and (c) SF.

Table 4Lime consumption contents of pozzolan/lime pastes (%).

Sample Curing time (days)

7 28 60

EGC (%) 45.24 49.26 77.34EGN (%) 20.89 37.72 49.73SF (%) 13.53 79.47 76.65

Table 5Chemical analysis by EDX of the C–S–H gels at 60 days of reaction.

Oxides (%) EGCA EGNA SF

SiO2 26.76 ± 1.75 14.765 ± 0.70 39.89 ± 0.80CaO 52.41 ± 0.86 81.58 ± 1.85 54.29 ± 0.47MgO 7.95 ± 0.34 1.575 ± 0.21 1.24 ± 0.23K2O 9.91 ± 0.65 0.97 ± 0.18 1.92 ± 0.21P2O5 1.61 ± 0.47 0.26 ± 0.12 –Ca/Si ratio 1.96 5.53 1.36

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The first signal (60–300 �C) involves the contribution of severaloverlapping peaks: loss of adsorbed and structural water of bothinitial materials and the main hydrated phases formation duringthe pozzolanic reaction. Taking into account the silica rich natureand a total absence of alumina in the EGC, EGN and SF (Table 2),we assume that the band localised about of 90–92 �C would corre-spond to the dehydroxylation of C–S–H gels, being of higher inten-sity in the EGC and increasing its intensity with hydration time.This affirmation is supported by previous works related to otheragro-industrial (bamboo, sugarcane and rice husk) ashes and silicafume, which generated C–S–H gels as the main hydrated phasefrom pozzolanic reaction, with CaO/SiO2 ratios below 1 [22–25].From 0 to 60 days this loss of weight increases what indicatesthe increase on hydration reaction with higher reaction for EGC.

From the second signal (375–475 �C), the percentage of fixedlime during the pozzolanic reaction can be determined for allpozzolans mixed with Ca(OH)2 (1:1 ratio) (Table 4). The fixed limewas calculated with the loss of Portlandite in each period, accord-ing to Eq. (1) [26,27]:

Fixed limeð%Þ ¼ðCHÞ0 � ðCHÞpðCHÞ0

� 100 ð1Þ

where (CH)0 is the initial amount of Ca(OH)2 present in the blendedpaste and (CH)p is the amount of Ca(OH)2 of the same paste at cur-ing time ‘‘p’’.

It has been observed a higher consumption of Portlandite at7 days in EGC paste compared to both EGN and SF pastes, beingrespectively the percentage of 37.88%, 33.38% and 20.90% in agree-ment with higher C–S–H formation. Over time there has been agrowing consumption of Portlandite in the pastes. But at the endof 60 days, lime consumption for the EGC and SF is very close toeach other.

Other secondary bands are situated between 250 and 370 �Cthat due to the band form can be associated to a double effect toC–S–H gels, increasing with curing time [28], and probably to thepresence of graphite in the agro-industrial ashes (EGC and EGN).A second broad band localised between 550 and 650 �C is attrib-uted to the carbonate decomposition, formed by carbonation ofPortlandite, and to the temperature associated with the aQuartz ? b Quartz phase transition (580 �C). Finally, a third bandwas localised at 800–850 �C in EGC, which could be assigned tothe presence of some feldspar type [29] in form of traces.

3.3.2. SEM/EDXAmorphous C–S–H gels are the main hydration phases observed

by SEM/EDX in the three pozzolan/Ca(OH)2 paste systems focusedin the present work. The oxides analysis of C–S–H gels obtained bySEM/EDX for the EGC, EGN and SF pastes are listed in Table 5; datawere obtained as an average value of 10 analyses for each paste.Fig. 6a shows the general aspect of the EGC/lime paste at 60 days

Table 3Weight loss (%) for pozzolan/lime pastes.

0 7 28 60

100–300 �CEGC 23.89 36.72 22.46 46.93EGN 18.09 22.81 20.26 26.57SF 4.54 14.51 20.20 34.80

330–455 �CEGC 47.89 23.55 18.42 8.39EGN 64.14 47.44 33.45 26.85SF 72.03 48.72 6.48 7.84

of reaction. It was observed an irregular and porous morphologywith the presence of Portlandite (CH) and EGC ash (Fig. 6a), andaround these compounds the C–S–H gels have been identifiedspread throughout the paste. At 60 days of curing, the C–S–H gelsexhibit rounded shape of flaky aspect (Fig. 7a). The morphologyof hydration products in the EGN/lime pastes is similar to thatfound in EGC pastes (Fig. 6b), but silica-enriched particles, withpartially reacted (Si), were identified by EDX analysis, as well asC–S–H gels with spongy aspect (Fig. 7b). Finally, in the silicafume/lime system it was observed a more regular and uniformmorphology, unreacted silica particles, graphite and C–S–H phases(Figs. 6c and 7c).

The composition of a C–S–H phase is normally defined byits calcium/silicon ratio. According to the available informationC–S–H gels have a layer structure containing calcium silicatesheets in solid solution with Ca(OH)2 and H2O [30]. A number ofmodels for the nanostructure of C–S–H are summarized and com-pared in the literature [31,32] indicating that the C–S–H generallyhas an average Ca/Si ratio about 1.75 or within a range of valuesfrom 1.2 to 2.1, depending on the type of C–S–H phase. Accordingto the Taylor‘s classification, it would correspond to C–S–H gel typeII (Ca/Si > 1.5) [33], but if a paste contains pozzolans then the ratiois reduced, in some cases to less than 1.

A chemical analysis by SEM/EDX shows that the Ca/Si ratios ofthe C–S–H gels in ashes-lime systems are higher (1.96 for EGC/limeand 1.64 for EGN/lime respectively) than expected for blendedpastes (usually 1). Ca/Si ratio of both systems are similar to thatfound by other researchers in ternary cements (ratio of 1.85) elab-orated with lime, calcined paper sludge and fly ash [34].

3.3.3. Micro-Raman spectroscopyRaman spectroscopy can be used to identify both amorphous

and crystalline phases since Raman scattering is sensitive to thedegree of crystallinity in a sample. Typically a crystalline materialyields a spectrum with very sharp, intense Raman peaks, whilst anamorphous material will show broader less intense Raman peaks.

Micro-Raman spectroscopy has been used to analyse the pozzo-lanic reaction of the ashes (EGC and EGN) as well as the silica fumeafter 60 days. Fig. 8 shows the Raman spectra in the range2000–100 cm�1 pozzolanic/lime systems for initial samples(Fig. 8a) and after 60 days for the paste (Fig. 8b). No baseline cor-rection has been done.

All the samples have two broad resonances at 1600 and1323 cm�1corresponding to G (graphite peak) and D (disordered

Fig. 6. General aspect at 60 days of curing. Samples: (a) EGC/lime, (b) EGN/lime,and (c) SF/lime pastes.

Fig. 7. Morphological aspects by SEM of CSH gels at 60 days of curing. Samples: (a)EGC/lime, (b) EGN/lime and (c) SF/lime pastes.

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peak) bands respectively from carbon [35] in accordance withthe DTG results. For the silica fume there is also a sharp band ofmedium intensity with maximums at 518 cm�1 from SiO2 asCoesite.

From ashes samples (EGC and EGN) two more vibrations, ofmedium–low intensity, are observed in the spectra. The first oneis broad with maximum in the interval 1090–1050 cm�1 can beassigned to the symmetrical C–O stretching mode of carbonategroup m1 of CO3

2� [36]. The second band near to 953 cm�1 can beassociated to a complex hydrated sulfate, which can be presentin some ashes as minor component [12].

After 60 days of aging, the vibration observed at 357 cm�1

should be attributed at Ca–O from Portlandite. No correspondingsignal is present in SF spectrum in according with XRD and DTGresults. The small peak near 680 cm�1 is assigned to Si–O–Si bend-ing vibrations in C–S–H gel [37].

It is interesting to remark that EGC ash after 60 days of pozzola-nic reaction presents a sharp peak at 1070 cm�1 that can be due tothe presence of amorphous calcium carbonate and/or Hydrotalcitetype structures also in amorphous form since it has not beendetected by XRD. This phase is typically identified as a reactionproduct in thermally activated wastes containing carbonates [38] .

Fig. 8. Raman spectra of (a) initial samples and (b) after 60 days of pozzolanicreaction.

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4. Conclusion

Based on the scientific studies in the current work, the follow-ing conclusions can be drawn:

� Chemically, the two elephant grass ashes are formed by thesame oxides but with different contents. The main oxidesare silica (50–80%) and potassium (7.1–8.6%), followed bymagnesia (1.1–4.2%), phosphorus (0.6–10%) and calcium(1.8–10.4%) depending on the elephant grass cultivar (EGC-Cameroon or EGN-Napier).

� The ashes (EGC and EGN) are mineralogically formed byQuartz and Cristobalite as the main crystalline phases. Syl-vite was identified in EGN ash.

� The activated ashes obtained by calcination of the two ele-phant grass types showed high pozzolanic activity (in themethod of pozzolanic activity) during the first 7 days of reac-tion, 85.5% of fixed lime for EGN and 96% for EGC. The pozzo-lanic behavior of EGC is similar to the silica fume, in terms offixed lime values. At 60 days of reaction, the pozzolanicactivity of the three wastes was practically coincident.

� The reaction kinetics, based on the studies of identificationfrom different techniques (TG/DTG, XRD) confirmed thatthe main hydrated phases during the pozzolanic reaction inelephant grass ashes/Ca(OH)2 pastes consisted of C–S–H gels,similar to SF/Ca(OH)2 paste.

� The SEM/EDX analyses confirmed the presence of type II C–S–H gels as the unique hydrated phase produced duringthe pozzolanic reaction, with different morphologies mainlyin EGC pastes. EGC pastes present Ca/Si ratio of 1.96 and EGNpastes present the corresponding Ca/Si ratio of 1.64.

� Micro-Raman analysis identified both crystalline and amor-phous phases formed in the pozzolanic reaction. Carbonatevibrations from amorphous calcium carbonate and/orHydrotalcite have been indicated by Raman spectroscopyespecially in the case of cameroon ash/lime system after60 days of reaction.

The observations carried out in present work support the viabil-ity of recycling elephant grass ashes in order to obtaining futuresupplementary cementing materials as an alternative to tradition-ally used pozzolans (such as fly ash, natural pozzolans, silica fume)envisaging to environmental and social-economic benefits. Also,these results contribute for the achievement of activated elephantgrass blended binders for the partial substitution of ordinary Port-land cement.

Acknowledgments

The authors would like to thank the FAPESP (Grant n�. 2011/16842-5, 2010/16524-0 and 2009/17293-5) and to CSIC-FAPESPprogram (Grant n� 2013/50790-8) for their financial support. Theauthors are also grateful to the Framework Agreement of Collabo-ration between IETcc/CSIC (Spain) and FZEA/USP (Brazil) and toCNPq (Grant #306386/2013-5).

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