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Effect of Jute as Fiber Reinforcement Controlling the Hydration Characteristics of Cement Matrix Sumit Chakraborty, Sarada P. Kundu, Aparna Roy, Basudam Adhikari, and S. B. Majumder* Materials Science Centre, Indian Institute of Technology, Kharagpur 721302, West Bengal, India S Supporting Information *

ABSTRACT: The present investigation deals with the effect of jute as a natural fiber reinforcement on the setting and hydration behavior of cement. The addition of jute fiber in cement matrix increases the setting time and standard water consistency value. The hydration characteristics of fiber reinforced cement were investigated using a variety of analytical techniques including thermal, infrared spectroscopy, X-ray diffraction, and free lime estimation by titration. Through these analyses it was demonstrated that the hydration kinetics of cement is retarded with the increase in jute contents in cement matrix. A model has been proposed to explain the retarded hydration kinetics of jute fiber reinforced cement composites. The prolonged setting of these fiber reinforced cement composites would be beneficial for applications where the premixed cement aggregates are required to be transported from a distant place to the construction site.

1. INTRODUCTION Due to their economical, ecological, and environmentally efficient performances, natural fibers are nowadays found to be attractive reinforcing agents in cement matrix compared to steel and synthetic fibers. In the past few decades natural fibers have been widely used for construction purposes to overcome the inherent brittleness as well as to improve the strength and ductility of cement composite.1,2 Thus, Tonoli et al.3 reported that reinforcing cement matrix with eucalyptus pulp provides effective crack bridging to improve its mechanical properties. Jarabo et al.4 reported that hemp and corn pulps, extracted from agricultural waste, can be used as reinforcing agents for the production of fiber−cement composites. Sugar cane bagasse fiber5 is also used as a reinforcement for improving the strength of cement composite. The major advantage of fiber reinforcement is to impart additional energy absorbing capability by transferring a brittle material into a pseudoductile one. Additionally, jute fibers, dispersed in cement or concrete matrixes, serve as a crack arrestor to retard crack propagation leading to noncatastrophic failure of cement composites.6 In a recent study, we have demonstrated that chopped jute fibers are a potential reinforcing agent in cement matrix. We reported that, by reinforcing cement matrix with jute fiber, the compressive and flexural strengths of the resultant mortar can be increased to 9 and 16%, respectively, as compared to the mortar specimen without jute reinforcement. Additionally, the extensibility of these composites was also increased up to 31%. This implies that the brittleness of the fiber reinforced composites is reduced compared to that of composites without any fiber reinforcement. Although natural fibers improve the strength and ductility of cement composites, they alter the setting and hydration behavior of cement. The purpose of this study is to investigate the effect of jute on the setting and hydration behavior of cement. Cement in anhydrous state mostly consists of tricalcium silicate C3S (Ca3SiO5, alite), dicalcium silicate C2S (Ca2SiO4, © 2012 American Chemical Society

belite), tricalcium aluminate C3A (Ca3Al2O6), and tetracalcium aluminoferrite (Ca4AlnFe2−nO7, C4AF). It also contains small amounts of clinker sulfate (sulfates of sodium, potassium, and calcium) and gypsum. When water is added to cement, parts of the clinker sulfates and gypsum are readily dissolved to produce an alkaline sulfate rich solution. Soon after water addition the most reactive phase C3A reacts with water form an aluminate rich gel. Subsequently the gel reacts with the sulfate rich solution to form ettringite (Ca6Al2(SO4)3(OH)12·26H2O) with a small rodlike structure. The chemical reaction is represented as Ca3Al 2O6 + 3CaSO4 , 2H 2O + 26H 2O → Ca6Al 2(SO4 )3 (OH)12 ·26H 2O

(1)

After prolonged hydration ettringite is converted to a monosulfonate phase [AFm, Ca4Al2(OH)12·SO4·6H2O] and the chemical reaction is 2Ca3Al 2O6 + Ca6Al 2(SO4 )3 (OH)12 · 26H 2O + 4H 2O → 3Ca4Al 2(OH)12 ·SO4 ·6H 2O

(2)

C3S and C2S phases then take part in a hydration reaction to form calcium hydroxide (Ca(OH)2) and calcium silicate hydrate 3CaO·2SiO2·4H2O (C−S−H) gel. These phases are considered to be principal contributors to the strength of cement composite.7,8 The associated chemical reactions are 2Ca3SiO5 + 6H 2O → 3CaO· 2SiO2 ·4H 2O + 3Ca(OH)2 (3)

and Received: Revised: Accepted: Published: 1252

March 6, 2012 September 1, 2012 December 29, 2012 December 30, 2012 dx.doi.org/10.1021/ie300607r | Ind. Eng. Chem. Res. 2013, 52, 1252−1260

Industrial & Engineering Chemistry Research

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First the jute fibers were chopped into lengths of 5−6 mm followed by grinding them in a laboratory grinder for 15−20 min. The ground jute fibers were dried at 85 °C for 6 h for moisture removal and stored in a desiccator for further processing. Then 0.5, 1, 2, 3, and 4 g of ground jute fibers were weighted and immersed separately in distilled water for 24 h keeping the fiber:water ratio at ∼1:30 (weight:volume). The water absorption by jute fiber was estimated to be about 210%. The water saturated jute fibers were dispersed in cement water slurry (water:cement ratio ∼ 0.6). The control sample was made by mixing 100 g of cement in 60 mL of distilled water. In jute fiber modified slurries the cement and water ratios were kept identical; however, jute contents were systematically varied from 0.5 to 4.0 g. The control and fiber modified cement slurries were cast immediately in a glass Petri dish and allowed to set for 24 h in a desiccator. These samples were water cured for 28 days and ground with a mortar and pestle. The powder specimens, thus prepared, were washed with acetone and dried in a laboratory oven at 105 °C for 24 h. Washing with acetone was necessary to terminate the cement hydration reaction. The dried specimens were used for further characterization. The control sample was coded as “0CC”. The jute modified cement samples are coded as “XRJC”, where X denotes the respective weight percent of jute in cement slurry. 2.3. Characterization. The standard consistencies and setting times of control and fiber modified cement pastes were measured using Vicat apparatus in accordance with IS: 4031 part 4, 1988, and IS: 4031 part 5, 1988.17,18 Differential scanning calorimetry (DSC) of hydrated cement samples was performed with a DSC calorimeter (DSC200PC, NETZSCH, USA). The DSC measurements were performed in the temperature range between 30 and 600 °C maintaining a heating rate of 10 °C min−1 under dynamic N2 atmosphere. For effective comparison the weights of the samples were kept identical (∼10 mg) in all measurements. A thermogravimetric (TG) analyzer (TG209F1, NETZSCH, U.K.) was used for thermogravimetric analysis of the hydrated cement samples. The weights of the samples were kept identical (∼10 mg) for all TG measurements. The measurement was performed under dynamic air atmosphere in the temperature range between 30 and 1000 °C maintaining a heating a rate of 10 °C min−1. Fourier transform infrared spectra (FTIR) of 28 day water cured cement samples (without and with jute modification) were recorded using a FTIR spectrometer (Nexus 870, Thermo Nicolet Corp., USA). To record the FTIR spectra, a 1 mg powder sample was mixed with 100 mg of KBr to make circular pellets. The spectra were recorded in the range 4000−400 cm−1 with 2 cm−1 resolution and after 32 scans. X-ray diffraction (XRD) of hydrated cement samples was performed by using an X-ray diffractometer (ULTIMA III, RIGAKU Inc., Japan) using Cu Kα radiation and a Ni filter. The XRD scan was performed using a scan speed of 1 deg min−1 at 0.02 min steps. The powdered specimens were packed in the rectangular hole of a glass sample holder for all the X-ray diffraction measurements. To evaluate the extent of hydration of control and jute modified cement pastes, we have estimated the free lime (CaO) content in hydrated cement samples. These estimations are done in accordance with the modified Franke extraction method.19 For this purpose, 1 g of hydrated cement sample was refluxed with 40 mL of isopropyl alcohol and ethyl acetoacetate mixture (in 20:3 volume ratio) for 3 h. The refluxed solution

2Ca 2SiO4 + 4H 2O → 3CaO· 2SiO2 ·4H 2O + Ca(OH)2 (4)

All these hydration reactions are retarded when natural fibers and related additives are added to cement water slurry. The effect of some of these additives on the hydration behavior of cement is tabulated as in the Supporting Information. For example, as reported by Singh et al.,9 incorporation of bagasse ash in cement elongates the setting time by retarding hydration reaction. The natural fiber or natural substances mainly alter the cement hydration reaction equilibrium. Yasuda et al.10 reported that cement setting and the hydration reaction is retarded in the presence of wood. The main components of wood are cellulose, hemicelluloses, lignin, and some extractives which retard the cement hydration reaction.11 Cellulose, hemicelluloses, and lignin are in the family of polysaccharides, and these polysaccharides are composed of various types of sugars. These sugars act as setting and hydration retarding agents. Juengera and Jennings12 reported that the retardation effect of a sugar is due to its absorption on the surface of the hydrating cement particle and/or on the hydrated product. The layer of sugar based compounds forms a temporary barrier on the cement particle for further hydration. The mechanism of adsorption is through chelation, where the organic sugar compounds form a complex with the metal ions present in the cement. The retardation effect of sugar is also supported by the research findings of Thomas and Birchall.13,14 As reported by Bishop et al.,15 additives such as tartaric acid, lignosulfonate, etc. also retard cement setting and hydration. From review of the existing literature, it is apparent that effect of jute fiber on the hydration characteristics of cement has not yet been studied. The hydration kinetics of cement has mostly been studied using additives such as table sugar, sucrose, tartaric acid, etc. The hydration of cement is believed to be far more complex in natural fiber reinforced cement composites. The reasoning behind the retarded hydration kinetics in these fiber reinforced cement composites is quite scattered, and most of the instances are purely hand waving. Jute, being a natural fiber, contains organic components such as cellulose, hemicelluloses, lignin, etc. These organic compounds would affect the cement hydration. In view of this, we found it worthwhile to undertake systematic research to understand the underlying mechanism controlling the hydration behavior of jute fiber reinforced cement composites. Using thermal, infrared spectroscopy, and phase analyses of the hydration products, we have investigated the hydration behavior of unmodified jute fiber reinforced cement composites. Plausible mechanisms have been proposed to elucidate the interaction between the jute fiber and cement matrix. On the basis of the mechanism of such an interaction, the retardation of the hydration kinetics in jute fiber reinforced cement composites is explained.

2. EXPERIMENTAL SECTION 2.1. Materials. We have used portland pozzolana fly ash cement manufactured by Ambuja Cement Ltd. The cement is manufactured in accordance with IS: 1489, 1991,16 specifications. Tossa Indian jute (corhorus olitorius) of grade TD4, obtained from Gloster jute mill, Howrah, India, was used as reinforcing agent. 2.2. Sample Preparation. To study the effect of jute fiber on the hydration characteristics of cement, we prepared cement specimens following the procedures described bellow. 1253

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was cooled and filtered off using Whatman 41 filter paper. The filtrate was titrated against 0.1 N HCl using bromophenol blue as indicator. The free lime content was estimated using the following relation. percent of free lime = 0.2804

V W

affinity could not be completely eliminated. As compared to the control specimen, more water is required to make workable the jute modified cement mixture. As a result, the standard consistency was increased with the increase in jute contents in cement paste. The hydration characteristics of jute fiber modified cement specimens were characterized through the measurement of initial and final setting times. The initial setting time of cement occurs when the paste becomes stiff, whereas after final setting the cement becomes hard enough to sustain a specified load. Figure 1 also shows the variation of both initial and final setting times of fiber modified cements with jute contents. The initial and final setting times of the control cement were estimated to be 130 and 170 min, respectively. Both initial and final setting times are increased with the increase in jute contents. Thus the initial and final setting times were varied in the range 148−180 min (initial) and 191−246 min (final) respectively, when the jute contents in cement was varied in the range 0.5−4 wt %. Also as shown in Figure 1, the difference between the initial and final setting times is increased with the increase in jute contents in cement matrix. Reviewing Figure 1, it is apparent that, compared to the initial setting time, the final setting time is extended more with increase in jute loading in cement matrix. 3.2. Thermal Analysis. 3.2.1. DSC Analysis. To better understand the hydration behavior of jute modified cement, we have performed differential scanning calorimetry (DSC). The DSC plot of control cement paste, water cured for 28 days, is shown in Figure 2a. The DSC plots of the jute modified cement pastes are shown in the inset of Figure 2a. In the DSC plots, series of endothermic peaks are identified in the temperature range 60−510 °C. The endothermic peak at ∼97 °C is due to dehydration of calcium silicate hydrate (C−S−H).21,22 The next peak at ∼188 °C is due to the decomposition of monosulfate phase (C3A·CaSO4·12H2O), and the shoulder at ∼397 °C is thought to be due to the reaction product Fe2O3, produced from tetracalcium aluminoferrite (C4AF) during cement hydration. The characteristic endothermic peak at ∼485 °C is due to the decomposition of calcium hydroxide (Ca(OH)2). As shown in the inset of Figure 2a, the characteristic peak due to the decomposition of Ca(OH)2 is shifted to lower temperature with the increase in jute contents in cement matrix. Analyzing the endothermic DSC peak due to Ca(OH)2 decomposition, Midgley23 and Abdelrazig et al.24 have commented on the hydration kinetics of cement. It is reported

(5)

where V is the volume of 0.1 N HCl required for titration and W is the weight of the cement sample.

3. RESULTS 3.1. Standard Consistency and Setting Time. The standard consistency of cement is defined as the minimum

Figure 1. Variation of the standard consistency and setting times of cement with jute loading contents. The symbol ○ indicates standard consistency, △ indicates initial setting time, and ▽ indicates final setting time of the cement.

quantity of water required to make a workable mixture. The standard consistency was measured by Vicat apparatus following the procedure mentioned in Indian standards. The standard consistency of control cement was estimated to be ∼35%, but it was increased to 35.5% in 0.5% jute modified cement sample. As shown in Figure 1, we have found that the value of standard consistency increases with the increase in jute contents. Similar behavior has also been reported for bagasse ash modified cement.20 The increase of the standard consistency with the increase of fiber contents is due to the hygroscopic nature of natural fibers. In the present work, although the jute fibers were saturated with water, their water

Figure 2. (a) DSC plot of the control cement sample hydrated for 28 days. The inset shows the DSC plots of control and jute modified cement specimens. (b) Estimated variation of the enthalpy change due to Ca(OH)2 decomposition with jute contents (%) in cement matrix. 1254



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Figure 3. (a) TGA plot (dotted line) of the control cement specimen water cured for 28 days. The differential TG plot (solid line) of the control cement is also shown. (b) The estimated variation of mass loss (%) due to the decomposition of Ca(OH)2 with jute contents (%) in cement matrix.

Figure 4. (a) FTIR spectra of the control cement specimen water cured for 28 days. The vibration modes are indexed in the figure. (b) FTIR spectra of control and jute modified cement specimens water cured for 28 days. (c) Experimental (□) and fitted curve () of the FTIR spectra of the control cement specimen. The deconvoluted modes are indexed in the figure. (d) Variation of AO−H/AH−C ratio with jute contents (%) in cement matrix (see text).

that polymeric additives in cement reduce the decomposition temperature of Ca(OH)2.25 By estimating the area under the endothermic peak due to Ca(OH)2 decomposition, one can estimate the enthalpy change (ΔH) associated with the decomposition reaction. For control and jute fiber reinforced cement specimens, we have estimated the respective enthalpy changes of Ca(OH)2. The estimated enthalpy change is plotted as a function of jute loading in Figure 2b. As shown in Figure 2b, ΔH values are reduced exponentially with jute contents in cement matrix. Thus the ΔH of the control specimen, estimated to be ∼88.3 J/g, is significantly reduced to 72.1 J/g in 1% jute modified cement paste. The result is indicative of the fact that the amount of hydration product Ca(OH)2 is reduced

Table 1. Index of Vibration Modes of the FTIR Spectra of Control Cement Specimen peak position (cm−1) 3638 3400−3100 2928 1649 1477 and 1422 978

assignment O−H stretching of Ca(OH)2 symmetric and asymmetric stretching (ν1 and ν3) of O−H vibrator of water molecules asymmetric stretching of H−C bond present in organic compound ν2 deformation mode of molecular water H−O−H absorbed ν3 of CO32− ν3 stretching of Si−O bond of calcium silicate hydrate (C− S−H) which accounts for polymerization of SiO44− units present in C3S and C2S during hydration

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Figure 5. (a) XRD plot of the control cement specimen water cured for 28 days. The phases are indexed in the figure. (b) XRD plots of control and jute modified cement specimens water cured for 28 days. (c) Experimental (□) and fitted curve () of the X-ray diffractogram of the control cement specimen. The deconvoluted peaks are indexed in the figure. (d) Variation of Ap/Aa ratio with jute contents (%) in cement matrix (see text).

ettringite. The subsequent weight loss up to 400 °C is attributed to be due to the decomposition of various hydrated silicate and aluminate compounds. The characteristic weight losses at 444 °C and in the temperature range 590−675 °C are attributed to be due to the decomposition of Ca(OH)2 and carbonate phase, respectively.28 The mass losses due to the Ca(OH)2 decomposition for control and jute fiber modified cement specimens are plotted separately in Figure 3b. As shown in Figure 3b, the mass loss due to Ca(OH) 2 decomposition reduces exponentially with the increases in jute contents. This in turn indicates the amount of Ca(OH)2, formed during cement hydration, reduces with the increase in jute contents. These results are supportive of the fact that jute as a reinforcing agent retards the hydration kinetics of cement matrix.29,30 3.3. FTIR Spectroscopic Analysis. The hydration kinetics of cement and jute modified cement is characterized using Fourier transformed infrared spectroscopy. Figure 4a shows the FTIR spectrum of control cement sample hydrated for 28 days. The IR spectra of the control and jute modified cement specimens are plotted separately in Figure 4b. All the absorption bands are indexed, and the assigned modes along with their wavenumbers are tabulated in Table 1.31 As indicated in Table 1, the absorption mode at ∼3638 cm−1 is indexed to be due to O−H stretching of the portlandite (Ca(OH)2) phase.32−34 The mode at ∼2928 cm−1 is due to asymmetric stretching of the H−C bond from the organic moieties present in the cement sample. Considering the mode at ∼2928 cm−1 as an internal standard,35 the change in the intensity of the O−H stretching mode of portlandite phase (in both control and jute modified cement specimens) is estimated by fitting these

Figure 6. Variation of estimated free lime content (%) with jute contents (%) in cement matrix. The amount of HCl required to yield the end point in each case is also shown in the figure. The symbol ● indicates the volume of HCl (mL) required for the titration, and the symbol (■) indicates the estimated free lime content (%) of cement specimens.

with the increase in jute contents. In other words, jute as additive retards the hydration kinetics of cement. 3.2.2. Thermogravimetric Analysis. The effect of jute fiber in retarding the hydration kinetics of cement is further supported by thermogravimetric analyses. Figure 3a shows the TG plot of control cement. The corresponding differential plot is also shown in Figure 3a. Thermogravimetric analyses have been used as a characterization tool to study the hydration kinetics of cement.26,27 As shown in Figure 3a, the weight loss up to 200 °C is attributed to be due to either surface adsorbed water or loss of water from calcium silicate hydrate gel and 1256



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Figure 7. Schematic of the plausible interactions between the metal cation in cement slurry (viz., Ca2+) and (a) leached hemicelluloses, (b) lignin, and (c) cellulose in jute fibers.

modes using commercial software. The typical fitting and the deconvoluted modes for the control specimen are shown in Figure 4c. The ratio of the integrated area of the O−H stretching mode and the asymmetric H−C mode (AO−H/AH−C) is estimated from this fit. The estimated intensity ratio (AO−H/ AH−C) is plotted as a function of jute loading in Figure 4d. As indicated in Figure 4d, the intensity ratio is estimated to be ∼0.39 for control and this value gradually decreases with the increase of jute contents. This is indicative of the retardation effect of jute fiber on cement hydration kinetics.36 Probably the organic compounds present in the jute fiber retard the hydration of C3A, C3S, and C2S phases and thereby the amount of the hydration products (viz., Ca(OH)2, calcium silicate hydrate (C−S−H), etc.) are reduced. 3.4. Structural Analysis (X-ray Diffraction). X-ray diffraction analyses have been used as a characterization tool to investigate the effect of jute fiber on the hydration characteristics of cement. Figure 5a shows the X-ray diffractogram of control cement sample hydrated for 28 days. The X-ray diffraction patterns of the control and jute modified cement samples are shown separately in Figure 5b. It is known that the major constituents of portland pozzlana cement are alite (a) [tricalcium silicate, C3S (Ca3SiO5)], belite (b) [dicalcium silicate, C 2 S (Ca 2 SiO 4 )], tricalcium aluminate [C 3 A (Ca 3 Al 2 O 6 )], and tetracalcium aluminoferrite [C 4 AF (Ca4AlnFe2−nO7)].37,38 As compared to ordinary portland cement (OPC), the portland pozzolana cement contains a

substantial amount of quartz (q) and a minute quantity of gypsum (g) as well. The hydration of alite and belite phases produces Ca(OH)2 (p) (portlandite) and amorphous calcium− silica−hydrate (C−S−H). All the diffraction peaks corresponding to these phases in the water cured control cement specimen are indexed in Figure 5a. As noted in Figure 5a, the characteristic peak corresponding to portlandite phase (p) appears at 2θ ∼ 18°. The diffraction peak of the major reactant alite (a) is identified at 2θ ∼ 29.4°. Estimation of the ratio of the integrated areas of the portlandite (p) and alite (a) peaks could therefore be treated as the index of the degree of hydration.39 The XRD pattern of the cured cement specimen was fitted using commercial software (Peakfit 4.1, Jandel Scientific), and Figure 5c shows the fitted and deconvoluted XRD peaks in the 2θ range 15−40°. Similar fitting was also performed of the XRD patterns of jute modified cement samples (not shown). The estimated integrated peak area ratio of the peaks corresponding to the portlandite (p) and alite (a) phases (Ap/Aa) of the control sample and jute modified cement samples are plotted as a function of jute contents in Figure 5 d. As shown in Figure 5d, the estimated integrated peak area ratio of the control sample (∼0.169) is reduced to 0.134 in 1% jute modified cement sample and it decreases gradually with further increase in jute loading. This phenomenon confirms that jute retards the cement hydration reaction and this effect becomes more prominent with the increase in jute loading.40 1257



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Figure 8. Illustration of the hydration of control and jute fiber modified cement specimens. Schematic of the formation of an organic coating and surface activated jute layer around the anhydrous or partially hydrated cement grains. Such layers would retard the diffusion of water molecules required for cement hydration.

3.5. Estimation of Free Lime Content. The effect of jute in retarding the cement hydration reaction is also supported by the estimation of free lime content in the hydrated product. Free lime is liberated during the hydration of cement, and the amount of free lime is considered to be an indicator of the cement hydration reaction.41,42 Thus, as the content of free lime increases, the extent of the cement hydration reaction is greater. Figure 6 shows the variation of the estimated free lime with the jute contents in cement. The amount of HCl required to yield the end point is also shown in Figure 6. As shown in Figure 6, the free lime content is reduced exponentially with the increase in jute contents. In line with the inference drawn through the other characterization tools, free lime estimation also indicates that the cement hydration is retarded with the increase of jute contents in cement.

Adsorption of the retarders on the surface of the partially hydrated products could also inhibit the water diffusion, and as a result the hydration kinetics is slowed down.15,42 Additives such as sugar cane bagasse fibers and natural plant fiber extracts also retard the cement hydration; however, the underlying mechanism remains poorly understood.43,44 It is known that the jute fibers contain organic components such as cellulose, hemicelluloses, lignin, pectin, wax, etc. Water−cement slurry is highly alkaline, and in such an alkaline medium many of these organic components (viz., hemicelluloses, pectin, wax, etc.) of the jute fibers are easily leached out. As these organic components are leached out, the fiber surface becomes more reactive. The leached-out components as well as the surface modified jute fiber can interact with the metal cations of the cement slurry. Figure 7 shows schematically the plausible interactions between the metal cation in cement slurry (viz., Ca2+) with (Figure 7a) leached hemicelluloses, (Figure 7b) lignin, and (Figure 7c) cellulose in jute fibers. The interaction in turn reduces the metal ion concentration in cement slurry, and as a result the nucleation of hydrated products (viz., Ca(OH)2, C−S−H gel, etc.) get delayed15,45 and eventually the hydration kinetics are retarded. Another plausible mechanism of retarded hydration is illustrated schematically in Figure 8. Thus, for the case without any jute modification, the anhydrous cement reacts with added water to form hydrated cement products. The organic compounds leached out from the fiber surface may form insoluble sugar moieties in highly alkaline cement medium. As shown schematically in Figure 8, these insoluble organic compounds may form a protective layer on the partially hydrated cement grains. Alternatively, the surface

4. DISCUSSION As outlined in section 3, by characterizing the jute fiber modified hydrated cement specimens (using thermal, infrared spectroscopy, and phase analyses and free lime estimation) we have demonstrated that jute fiber as a reinforcing agent retards the setting and hydration kinetics of cement. In general, addition of different retarders such as sucrose, tartaric acid, lignosulfonate, etc. slow down the cement hydration in the following ways. Primarily, due to the addition of the retarders, calcium ions form either insoluble salts or chelated compounds and as a result the formation of calcium silicon based hydrated (C−S−H) gel is delayed.15 Alternatively, the nucleation and growth of hydrated products such as C−S−H or Ca(OH)2 could be inhibited due to the addition of these retarders.41 1258



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modified jute fibers also form a bond with hydrated cement product. Due to the formation of either a semipermeable organic layer or bonding with surface modified jute fibers, the water osmosis to the cement grain is slowed down resulting in retarded hydration of cement grains.46

(5) Onésippe, C.; Passe-Coutrin, N.; Toro, F.; Delvasto, S.; Bilba, K.; Arsène, M. A. Sugar cane bagasse fibers reinforced cement composites: Thermal considerations. Composites, Part A 2010, 41, 549. (6) Swamy, R. N.; Mangat, P. S. The Onset of Cracking and Ductility of Fiber Concrete. Cem. Concr. Res. 1975, 5, 37. (7) Mitchell, L. D.; Prica, M.; Birchall, J. D. Aspects of Portland cement hydration studied using atomic force microscopy. J. Mater. Sci. 1996, 31, 4207. (8) Zhang, L.; Catalan, L. J. J.; Larsen, A. C.; Kinrade, S. D. Effects of sucrose and sorbitol on cement-based stabilization/solidification of toxic metal waste. J. Hazard. Mater. 2008, 151, 490. (9) Singh, N. B.; Singh, V. D.; Rai, S. Hydration of bagasse ashblended portland cement. Cem. Concr. Res. 2000, 30, 1485. (10) Yasuda, S.; Ima, K.; Matsushita, Y. Manufacture of wood-cement boards VII: cement-hardening inhibitory compounds of hannoki (Japanese alder, Alnus japonica Steud.). J. Wood. Sci. 2002, 48, 242. (11) Nazerian, M.; Gozali, E.; Ghalehno, M. D. The Influence of Wood Extractives and Additives on the Hydration Kinetics of Cement Paste and Cement-Bonded Particleboard. J. Appl. Sci. 2011, 11 (12), 2186. (12) Juengera, M. C. G.; Jennings, H. M. New insights into the effects of sugar on the hydration and microstructure of cement pastes. Cem. Concr. Res. 2002, 32, 393. (13) Thomas, N. L.; Birchall, J. D. A Reply to a Discussion by S. Chatterji of “The Retarding Action of Sugars on Cement Hydration”. Cem. Concr. Res. 1984, 14, 761. (14) Thomas, N. L.; Birchall, J. D. The Retarding Action of Sugars on Cement Hydration. Cem. Concr. Res. 1983, 13, 830. (15) Bishop, M.; Barron, A. R. Cement Hydration Inhibition with Sucrose, Tartaric Acid, and Lignosulfonate: Analytical and Spectroscopic Study. Ind. Eng. Chem. Res. 2006, 45, 7042. (16) Portland-Pozzolana-Cement Specification, Part 1. Fly Ash Based; IS 1489; Bureau of Indian Standards: New Delhi, India, 1991, reaffirmed 2005. (17) Methods of Physical Tests for Hydraulic Cement, Part 4. Determination of Consistency of Standard Cement Paste; IS: 4031 (part 4); Bureau of Indian Standards: New Delhi, India, 1988, reaffirmed 2005. (18) Methods of Physical Tests for Hydraulic Cement, Part 5. Determination of Initial and Final Setting Times; IS: 4031 (part 5); Bureau of Indian Standards: New Delhi, India, 1988, reaffirmed 2005. (19) Presser, E. E.; Brunauer, S.; Kantro, D. L.; Weise, C. H. Determination of the Free Calcium Hydroxide Contents of Hydrated Portland Cements and Calcium Silicates. Anal. Chem. 1961, 33, 877. (20) Ganesan, K.; Rajagopal, K.; Thangavel, K. Evaluation of bagasse ash as supplementary cementitious material. Cem. Concr. Compos. 2007, 29, 515. (21) Sha, W.; Perira, G. B. Differential scanning calorimetry study of Ordinarry Portland Cement Paste Containing Metakaolin and Theoretical Approach of Metakaolin Activity. Cem. Concr. Compos. 2001, 23, 455. (22) Heikal, M.; Aiad, I. Influence of Delaying Addition Time of Superplasticizers on Chemical Process and Properties of Cement Pastes. Ceram.−Silikat. 2008, 52 (1), 8. (23) Midgley, H. G. The Determination of Calcium Hydroxide in Set Portland Cements. Cem. Concr. Res. 1979, 9, 77. (24) Abdelrazig, B. E. I.; Bonner, D. G.; Nowell, D. V.; Egan, P. J.; Dransfield, J. M. Estimation of the degree of hydration in modified ordinary portland cement pastes by differential scanning calorimetry. Thermochim. Acta 1989, 145, 203−217. (25) Afridi, M. U.; Ohama, Y.; Zafar, I. M.; Demura, K. Behaviour of Ca(OH)2 in polymer modified mortars. Int. J. Cem. Compos. Lightweight Concr. 1989, 11 (4), 235. (26) Monosi, S.; Moriconi, G.; Pauri, M.; Collepardi, M. Influence of Lignosulphonate, Glucose and Gluconate on the C3A Hydration. Cem. Concr. Res. 1983, 13, 568. (27) Collepardi, M.; Monosi, S.; Moriconi, G.; Pauri, M. Influence of Gluconate, Lignosulfonate or Glucose on the C3A Hydration in the

5. CONCLUSION In the present work we have systematically studied the effect of jute fiber on the setting and hydration behavior of portland pozzolana cement. Both initial and final setting times as well as the standard consistency of cement are found to be increased with the increase in jute contents (up to 4 wt % with respect to cement) in cement matrix. The difference between the initial and final setting times also increases systematically with the increase in jute contents. We have investigated the hydration characteristics of unmodified and jute fiber modified cement pastes using thermal analyses, infrared spectroscopy, structural characterization, and free lime estimation. Analyzing these experimental results, it was demonstrated that the hydration kinetics of cement is retarded with the increase in jute contents in cement matrixes. The prolonged setting of these fiber reinforced cement composites would be beneficial for applications where the premixed cement aggregates are required to be transported from a distant place to the construction site. Finally, a model has been proposed to explain the retarded hydration kinetics of jute fiber reinforced cement composites.

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ASSOCIATED CONTENT

S Supporting Information *

Effects of various additives on the setting and hydration behavior of cement are tabulated. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +91 3222 283986 or +91 (0) 9433611775. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The National Jute Board (formerly known as JMDC), Government of India, is gratefully acknowledged for financial support. S.P.K. gratefully acknowledges the financial support received from CSIR, Government of India, through a research fellowship.

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REFERENCES

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