Journal of Environmental Management 131 (2013) 228e238

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Use of coir pith particles in composites with Portland cement Gisela Azevedo Menezes Brasileiro a, b, *, Jhonatas Augusto Rocha Vieira a, Ledjane Silva Barreto a a

Programa de Pós-Graduação em Ciências e Engenharia de Materiais, Universidade Federal de Sergipe, Av. Marechal Rondon, S/N, 49100-000 São Cristóvão, Sergipe, Brazil b Instituto Federal de Educação, Ciência e Tecnologia de Sergipe, Av. Eng. Gentil Tavares da Motta, 1166, 49055-260 Aracaju, Sergipe, Brazil

a r t i c l e i n f o

a b s t r a c t

Article history: Received 21 March 2013 Received in revised form 6 August 2013 Accepted 18 September 2013 Available online 30 October 2013

Brazil is the fourth largest world’s producer of coconut (Cocos nucifera L.). Coconut crops generate several wastes, including, coir pith. Coir pith and short fibers are the byproducts of extracting the long fibers and account for approximately 70% of the mature coconut husk. The main use of coir pith is as an agricultural substrate. Due to its shape and small size (0.075e1.2 mm), this material can be considered as a particulate material. The aim of this study was to evaluate the use of coir pith as an aggregate in cementitious composites and to evaluate the effect of the presence of sand in the performance of these composites. Some composites were produced exclusively with coir pith particles and other composites with coir pith partially substituting the natural sand. The cementitious composites developed were tested for their physical and mechanical properties and characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy to evaluate the effect of coir pith particles addition in cement paste and sand-cement-mortar. The statistical significance of the results was evaluated by one-way analysis of variance (ANOVA) test followed by multiple comparisons of the means by Tukey’s test that showed that the composites with coir pith particles, with or without natural sand, had similar mechanical results, i.e., means were not statistically different at 5% significance level. There was a reduction in bulk density and an improved post-cracking behavior in the composites with coir pith particles compared to conventional mortar and to cement paste. These composites can be used for the production of lightweight, nonstructural building materials, according to the values of compressive strength (3.97e4.35 MPa) and low bulk density (0.99e1.26 g/cm3). Ó 2013 Elsevier Ltd. All rights reserved.

Keywords: Mortar Portland cement Coir pith particles Mechanical properties Physical properties

1. Introduction The construction industry consumes large amounts of natural resources, such as, sand, which is a non-renewable material. Several research projects are in development to evaluate the feasibility of replacing natural, fine aggregate by waste from different sources, such as waste from quarrying activities, construction and demolition waste, copper slag, and fly ash particles (Raman et al., 2011). Frigione (2010) studied the substitution of 5% fine aggregate (natural sand) by an equal weight of polyethylene terephthalate (PET) aggregates, which were obtained by grinding PET bottles to the size of 0.1e5 mm for use in the production of

* Corresponding author. Programa de Pós-Graduação em Ciências e Engenharia de Materiais, Universidade Federal de Sergipe, Av. Marechal Rondon, S/N, 49100000 São Cristóvão, Sergipe, Brazil. Tel.: þ55 79 21056875; fax: þ55 79 21056845. E-mail addresses: [email protected], [email protected] (G.A.M. Brasileiro). 0301-4797/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jenvman.2013.09.046

concrete. The results indicated that the concrete obtained had the same concrete workability and no segregation. There was no significant change in mechanical strength, but there was an increase in ductility. The lightweight PET aggregates represent an effective way to reduce the bulk density of cementitious composites. However, they have a high production cost and high shrinkage and water absorption (Frigione, 2010). Currently, the search for new materials necessitates the use of renewable resources to reduce environmental impact and production costs. The timber industry also generates wastes that have no economic value and that are discarded into nature or burned. An alternative use for the wastes from sawmills is in wood-cement panels in civil construction, whose low-cost and easy production have led to their acceptance in the world, presenting desirable properties from both wood and cement (Grandi, 1995; Stancato, 2000). Besides timber industry, the agro-industrial activities implemented in various regions of Brazil generate large amounts of waste that, in most cases, do not add any commercial value to the final

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product and also do not have an appropriate destination for their disposal: they are sent to dumps and landfills. These wastes can be converted into raw materials with potential use in the manufacture of elements targeted to civil construction. The reuse of agricultural wastes as raw material to replace mineral aggregates in cementitious matrixes provides an interesting alternative to the challenge of disposing these wastes (Almeida et al., 2002; Coatanlem et al., 2006). For example, Sales and Lima (2010) investigated the use of bagasse ash from sugarcane to replace 0%, 30% and 50% of the natural sand in concrete and concluded that it can be used as a partial substitute for the sand in concrete with mechanical design strength of up to 30 MPa. Coconut fiber is used in the production of composites (Asasutjarit et al., 2009; Khedari et al., 2001; Olorunnisola, 2009; Sen and Reddy, 2011), as it is versatile, renewable, and biodegradable and has the lowest thermal conductivity and bulk density compared with other fibers, such as sisal, jute and bamboo. The addition of coconut fibers reduces the thermal conductivity of composite materials and produces lightweight materials, for nonstructural walls and ceiling of housing. Brazil is the fourth largest producer of coconut (Cocos nucifera L.), with a production of 2.8 million metric tons. About 80% of the world’s coconut crop (Cocos nucifera L.) acreage is located in Asia, with India, the Philippines and Indonesia being the three largest, worldwide producers (Martins and Jesus Junior, 2011). In addition to the production of composites, the coconut husk can be used to produce long fibers that are used to fill car seats, carpets, mats, brooms, and for fuel for boilers (Fontenele, 2005). In processing coconut husk to obtain the long fibers, short fibers and coir pith are obtained as a byproduct, comprising approximately 70% by weight (Fontenele, 2005). The coir pith is mainly used as an agricultural substrate, but is also utilized in studies in search of new technological applications (Macedo et al., 2006). In this present study, coir pith particles were used because of their local availability and potential application based on coconut fiber characteristics. Their scope of applications was expanded to include materials for civil construction. Thus, adding value to the production chain of Cocos nucifera L. byproducts, coir pith is renewable and produces “green” composites that contribute to the reduction of construction material costs. The objective of this study was to evaluate the use of coir pith as an aggregate in cementitious composites and to evaluate the effect of the presence of sand in the performance of these composites. The cementitious composites developed were tested for their physical and mechanical properties and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive Xray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) to evaluate the effect of coir pith particles addition in the cement paste and sand-cement-mortar.

0e5% of carbonate material. The carbonate material used as addition must be at least 85% calcium carbonate (CaCO3). Portland cements with tricalcium aluminate (C3A) content equal to or less than 8% are considered sulfate resisting, whose properties are beneficial in conditions where there is a risk of damage to the composites from sulfate attack, in places such as soil, ground water, exposed to seacoast and sea water, water and sewage treatment plants. 2.1.2. Coir pith and natural sand The in natura coir pith sample (30.7% lignin, 35.6% cellulose and 33.7% hemicellulose) was obtained from Indufibras Indústria de Fibras Ltda. (Brazil). Fig. 1 represents a digital photograph of asreceived coir pith particles captured with an Olympus digital camera X-840. The as-received sample was allowed to air-dry for three weeks. Quartering technique was conducted on the sample according to ABNT NBR NM 27 (2001) standard that involves shoveling the bulk sample to form a cone, then the cone is turned over three times and flattened. The sample is then divided into four quarters and two of the diagonally opposite quarters discarded. The remaining quarters can be thoroughly mixed and further reduced by quartering. Quartering may be performed any number of times to obtain the required sample size. Therefore samples were separated for characterization of the in natura coir pith and for casting the test specimens. The natural sand was provided by a civil construction company from the state of Sergipe, Brazil. The sand was air-dried for one week. Quartering technique of the sample was performed according to ABNT NBR NM 27 (2001) standard. Samples were separated for characterization of the sand and casting the test specimens. According to ABNT NBR 7211 (1983), that shows the limits of particle size distribution of the aggregate, the fineness modulus (the sum of the cumulative percentages retained on specified sieves divided by 100) for sand was 1.32, and thus considered a very fine aggregate. The maximum nominal size (the smallest sieve in which at least 95%, by weight, of the sample passed) was 0.6 mm (ABNT NBR 7211, 1983). The natural sand was analyzed by X-ray diffraction (XRD) and identified only the presence of silicon oxide (quartz), SiO2, by comparison with the database of the Joint Committee on Powder Diffraction Standards e International Centre for Diffraction Data (JCPDS-ICDD, 791910). 2.2. Physical characterization methods of the materials The coir pith particles and natural sand were subjected to physical tests. All tests were performed in triplicate. For determining particle size distribution, three samples of dry coir pith of

2. Materials and methods 2.1. Materials The materials used in the study were Portland cement, coir pith particles and natural sand. 2.1.1. Portland cement Sulfate resisting Portland cement composed with pozzolan (CP IIZ-32 RS) is the only cement commercially sold in Sergipe by Votorantim Cimentos (Brazil) and was used for the production of the composites. According to ABNT NBR 11578 (1991) and ABNT NBR 5737 (1992), this Portland cement is composed of 76e94% of clinker þ calcium sulfate (gypsum), 6e14% of pozzolanic material and

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Fig. 1. Image of as-received coir pith particles.

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50 g each and three samples of dry sand of 300 g each were used. The particle size distribution was determined with mesh sieves of 4.8, 2.4, 1.2, 0.6, 0.3, 0.15 and 0.075 mm, in accordance with ABNT NBR NM 248 (2003). The weight of particles retained on each sieve was measured and compared to the total sample weight. Particle size distribution was then expressed as a percent retained by weight on each sieve size. Bulk density (the mass of the unit volume of bulk aggregate material) was determined according to ABNT NBR 7251 (1982), using an empty parallelepiped container, that was weighed and whose volume was calculated; then the empty container was filled with the sample in loose state and finally the weight of the container with aggregate was taken. Specific gravity was determined using a 50 ml pycnometer (DNER e ME e 093, 1994). The method involves the determination of the weight of the empty dry pycnometer (W1); fill the pycnometer with the sample and weigh it (W2); partially fill the pycnometer with water; remove the air in the sample using a vacuum pump for 15 min; add water to reach the volume marker of the pycnometer; next, weigh the pycnometer with the sample and water in it (W3); finally, empty the pycnometer and only add water to reach the volume marker of the pycnometer and then weight it (W4). The specific gravity (SG) is then calculated using Formula (1).

  SG g=cm3 ¼ ðW2  W1 Þ=½ðW4  W1 Þ  ðW3  W2 Þ

(1)

2.3. Production of the composites Four composites were produced: - Cement paste (CP): 100% cement with a water-cement ratio of 0.30, without the addition of vegetal or mineral aggregates; - Sand-cement mortar (SCM): 100% cement with 100% mineral aggregate, trace dry weight 1:1 (cement:sand), water-cement ratio of 0.40; - Coir pith-cement composite (CCC): 100% cement with 10% coir pith, trace dry weight 1:0.1 (cement:coir pith), water-cement ratio of 0.75; - Coir pith-sand-cement composite (CSCC): 100% cement with 90% mineral aggregate and 10% coir pith, i.e., partial substitution of 10% by weight sand by coir pith, trace dry weight 1:0.9:0.1 (cement:sand:coir pith), water-cement ratio of 0.85. The total mixing water was adjusted for each composite to obtain the same workability for casting and compaction of the specimens without pressing. The coir pith particles showed an elevated water absorption capacity at about 60%, 97%, 100%, 145% and 150% of their weight at 5, 30 min, 1, 2 and 24 h, respectively. Attempts to reduce the water-cement ratio making a mixture of cement with coir pith previously saturated were unsuccessful. The coir pith particles were dried in an oven at 65  5  C for 24 h, and the sand was dried at 105  5  C for 24 h. The mixture procedure was adapted from Olorunnisola (2009). Cement, sand and coir pith were dry-mixed in a laboratory cement mixer with a 5 dm3 capacity for 1 min at low speed. Deionized water was added and mixed for 1 min at low speed. Finally, the composites were mixed for 2 min at high speed. To produce the specimens, stainless steel molds were used, which were filled in two layers, with each layer compacted on a vibrating table for 5e15 s or until the surface begin to glow and then covered with a glass plate. The specimens were kept in the molds for 24 h at ambient laboratory temperature of 23  2  C. They were then demolded and cured, immersed in deionized water for 28 days. For compressive strength testing, three samples of 40  40  40 mm3 were cast and three samples of 20  20  80 mm3 were cast for flexural tests and physical tests.

2.4. Characterization of the composites 2.4.1. Mechanical characterization Mechanical tests were performed using an Instron Universal Testing Machine, model 3367. The compressive strength test utilized a 30 kN load cell, with a loading speed of 1.0 mm/min. The modulus of rupture was used to determine the flexural behavior of the composites. Flexural tests were conducted at three points using a 5 kN load cell, with a loading speed of 0.5 mm/min. A span of 50 mm was used. The modulus of elasticity was removed from the linear region of the graph by the slope of the load-displacement curve. The toughness was determined on the load versus deflection curve up to the point corresponding to 30% of the modulus of rupture (Tonoli et al., 2009). 2.4.2. Physical characterization To evaluate the composites, the physical properties of bulk density (BD), water absorption (WA) and apparent porosity (AP) were determined using the procedures from ABNT NBR 9778 (2005). The specimens were placed for 24 h in an oven at 100  5  C and dry weight (Wd) was obtained; then they were immersed in water for 24 h. After these 24 h, they were weighed in a hydrostatic balance and weight immersed in water was obtained (Wi). Saturated weight (Ws) was obtained after the specimen’ surface was dried with absorbent paper. The physical properties were then calculated using Formulas (2), (3) and (4).

  BD g=cm3 ¼ Wd=ðWs  WiÞ

(2)

WAð%Þ ¼ ðWs  WdÞ$100=Wd

(3)

APð%Þ ¼ ðWs  WdÞ$100=ðWs  WiÞ

(4)

2.4.3. Chemical and morphological characterization of the materials and composites 2.4.3.1. SEM and EDS analyses. The micrographs were obtained using a scanning electron microscope, model JSM 5700, coupled with an energy dispersive X-ray spectrometer. The samples were stuck to carbon tape and metallized with gold. 2.4.3.2. FTIR analyses. FTIR analyses were performed using a PerkineElmer FTIR system, Spectrum BX, in transmission mode in the range of 4000 cm1 to 450 cm1, resolution of 2 cm1 and 16 scans per measurement. 2.4.3.3. XRD analyses. XRD analyses were conducted using a SHIMADZU diffractometer, model XRD-6000, operating in scan mode, with Cu-Ka radiation (l ¼ 1.5418  A) and nickel filter with a voltage of 40 KV and 30 mA, scan rate 5 /min at 2Ө (5e80 ). The identification of mineral phases was obtained by comparison of X-ray diffractograms of the samples with the database of the JCPDS-ICDD.

2.5. Statistical analysis The results of mechanical and physical properties are expressed in the Figures as mean  standard deviation. The ShapiroeWilk test verified that the samples followed the normal distribution. Thus, the statistical significance of the results was evaluated by one-way analysis of variance (ANOVA), followed by multiple comparisons of the means by Tukey’s test, which obtained the 95% confidence intervals and the homogenous groups. It was assumed that the

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probability of incurring type I error (alpha error) was less than 5% for all analyses (p < 0.05), and the calculations were performed using IBM SPSS Statistics software, version 20. 3. Results and discussion The coir pith used in this work is defined as a fine aggregate as a function of the size distribution of its particles according to NBR 7211 (2009). The maximum nominal size was 2.4 mm (ABNT NBR 7211, 2009). According to the fineness modulus of 2.34, the coir pith particles fall in the optimal zone of fine aggregates used in mortars and concretes. Thus, because of its shape and small size (0.075e1.2 mm), it is considered as a particulate material. The particle size distribution of natural sand and coir pith is shown in Fig. 2. The morphology of as-received coir pith particles is illustrated by the micrograph in Fig. 3a, whose indicated region is magnified in Fig. 3b, with EDS analysis at Point 1. The coir pith particle has exfoliated structures, composed of overlapping sheets and plates (Macedo, 2005), some similar to a “sheet of crumpled paper.” This porous particle has the effect of improving the thermal and acoustic insulation properties of the composites (Aamr-Daya et al., 2008). In contrast to Olorunnisola (2009), who used a material called “coconut husk particles” resulting from the hammer-milling of coconut long fibers as an addition to cementitious matrices to produce lightweight composites, the coir pith used in this work is a byproduct generated in the physical process of separating the fibers of the coconut husk. Therefore, this corresponds mainly to the coating of the surface layers of the long coconut fibers, which are rich in hemicellulose and lignin, that provide rigidity to the celluloseehemicelluloseelignin network. Up until now, the use of coir pith in cementitious matrices has not been found in the literature. 3.1. Mechanical and physical properties of the composites Studies on vegetal aggregate-cement composites are growing in the literature. The composites with lignocellulosic materials and inorganic binders, such as Portland cement, contain 10e70% by weight vegetal material and conversely 90e30% inorganic binder (Cai and Ross, 2010). Stancato (2000) presented a lightweight mortar with fine vegetal aggregate substituting 100% of the natural sand: wood sawdust was used as this lightweight vegetal aggregate. The vegetal aggregate-cement composites produced with traces 1:0.4 or 1:0.6 (cement:vegetal aggregate) showed low bulk density, 0.73e0.97 g/cm3, and low thermal conductivity, 0.203e 0.265 W/mK, compared to conventional mortar. Compressive strength means ranged from 2.35 to 8.86 MPa, and tensile strength

Fig. 2. Particle size distribution of the natural sand and as-received coir pith, where LUL ¼ lower usable limit; LOL ¼ lower optimum limit; UOL ¼ upper optimum limit; UUL ¼ upper usable limit.

231

means ranged from 0.37 to 1.41 MPa. A similar study was conducted previously by Grandi (1995) to produce boards of cement mortar and sawdust. In general, studies on mechanical and physical properties of cementitious composites with vegetal particles do not evaluate fracture toughness behavior (Aamr-Daya et al., 2008; Almeida et al., 2002; Coatanlem et al., 2006; Okino et al., 2005; Olorunnisola, 2009), unlike studies of cementitious composites with vegetal fibers that highlight the functionality of the fibers in improving the toughness of the composites (Pehanich et al., 2004; Roma et al., 2008; Savastano Jr. et al., 2000). The results of the overall one-way ANOVA test for mechanical and physical properties of the composites showed that there were differences in the composites means (Table 1). The Tukey’s test results allowed comparing significant differences between means, creating homogenous groups. The results are presented in bar charts with errors bars that represent, respectively, mean and standard deviation. Means (bars) with the same letter (homogenous group) are not statistically different by the one-way analysis of variance test at 5% significance level. The results for the mechanical properties are shown in Fig. 4. As for compressive strength, when comparing the composite with replacement of 10% of the total amount of sand by 10% coir pith, the CSCC sample, to the cementitious composite exclusively with coir pith particles, the CCC sample, there was no statistically significant difference. However, there was a reduction in compressive strength (Fig. 4a) when compared to the CP and to the SCM. The statistically significant difference observed when comparing the group CCCCSCC to the group CP-SCM (p < 0.05) is expected, since the Portland cement is a ceramic material with high compressive strength and the natural sand is a hard, rigid aggregate, which cannot be directly compared to the composites with vegetal particles, which are soft and flexible, with less load carrying capacity. Similar behavior was observed for the modulus of rupture (Fig. 4a) and modulus of elasticity (Fig. 4b) of the two groups, CCC-CSCC and CPSCM, which were statistically different. As for fracture toughness behavior, Fig. 4b shows that the result for CP was also statistically different from the group CCC-CSCC. However, the SCM was not statistically different from CP, CCC or CSCC. The results indicate that the inclusion of sand and coir pith particles reduced toughness of the composites as a result of the reduction of the modulus of rupture, since toughness corresponds to the integration of the area below the load versus deflection curve. However, an increase in ductility for CCC and CSCC was observed (Fig. 5), unlike the brittle fracture of CP and SCM. The deflection was 0.82 mm for CCC and 0.54 mm for CSCC. The soft, flexible coir pith particles, different from hard, rigid sand particles, gave ductility to the composites. When exposed to load application, the coir pith particles were able to distend and absorb energy. The toughness results indicate that coir pith particles give greater ductility to the composites, preventing the brittle fracture that is characteristic of cementitious composites. Wolfe and Gjinolli (1997), studying wood particle-cement composites and cement composites reinforced with cellulosic fibers, found that particles of wood or cellulose fibers improve the fracture toughness by blocking the propagation of cracks, allowing the composite to receive a slightly greater load or to present a ductile fracture, with deflection until a strain limit is reached by the fiber or particle. The authors proposed that composites with wood particles showing stressestrain curves with ductile fracture are characterized as engineering materials for use with small structural loads, and besides this, can be used for architectural application in thermal and acoustic insulation. Considering the specific mechanical properties (mechanical property/bulk density) shown in Fig. 6, there were no effect of bulk

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Fig. 3. Scanning electron microscopy images of as-received coir pith particles: (a) magnification of 100; (b) magnification of 500, EDS analysis point are highlighted.

Table 1 Analysis of variance (Fcalc test) of the influence of the composite type on the mechanical and physical properties. Source of variation

CSa

MORb

Sum of squares

Sum of squares

Between groups Within groups Total h Fcalc

2862.78 3.45 2866.22 2213.93*

461.84 73.46 535.31 50.29*

MOEc

TEd

BDe

WAf

APg

Sum of squares

Sum of squares

Sum of squares

Sum of squares

Sum of squares

8002455.60 1454708.89 9457164.49 44.01*

229189.38 100414.29 329603.67 12.93*

2.42 0.00 2.42 2014.00*

1417.94 3.47 1421.41 1496.06*

381.151 4.00 385.15 349.67*

Note: * 5% significance level (p < 0.05). a CS ¼ compressive strength. b MOR ¼ modulus of rupture. c MOE ¼ modulus of elasticity. d TE ¼ toughness. e BD ¼ bulk density. f WA ¼ water absorption. g AP ¼ apparent porosity.

density for the specific modulus of rupture (Fig. 6a) and specific modulus of elasticity (Fig. 6b). However for specific toughness (Fig. 6b), the effect of bulk density was important. Different from the results for toughness (Fig. 4b), the composites with the exclusive addition of coir pith particles had superior results compared to composites with sand, with or without coir pith particles, though they were not statistically different. This result showed that toughness is actually an advantage of composites with exclusive addition of vegetal particles. For the specific compressive strength (Fig. 6a), the means of the four composites were statistically

different. The CCC sample had a result superior to the CSCC sample. This result was different from the results for compressive strength (Fig. 4a), which also showed the effect of the low bulk density of the CCC sample, suggesting that thicker parts can be produced with this lower density material. The specific gravity of the coir pith particles, sand and cement was, respectively, 1.34 g/cm3, 2.66 g/cm3 and 3.16 g/cm3. Bulk density of the coir pith particles, sand and cement was, respectively, 0.10 g/cm3, 1.62 g/cm3 and 1.40 g/cm3. Graphs of bulk density, water absorption and porosity of the composites are in Fig. 7. The

Fig. 4. Effect of the addition of coir pith particles on mechanical properties of the composites: a) compressive strength and modulus of rupture, b) modulus of elasticity and toughness. The same letters (a, b, a’, b’) indicate homogenous groups, i.e., the means of the composites are not statistically different by on-way ANOVA test at 5% significance level. Note: CP ¼ cement paste; SCM ¼ sand-cement mortar; CCC ¼ coir pith-cement composite; CSCC ¼ coir pith-sand-cement composite.

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Fig. 5. Effect of the addition of coir pith particles on ductility of the composites. Note: CP ¼ cement paste; SCM ¼ sand-cement mortar; CCC ¼ coir pith-cement composite; CSCC ¼ coir pith-sand-cement composite.

Fig. 6. Effect of the addition of coir pith particles on specific mechanical properties of the composites: a) specific compressive strength and specific modulus of rupture, b) specific modulus of elasticity and specific toughness. The same letters (a, b, c, d, a’, b’) indicate homogenous groups, i.e., the means of the composites are not statistically different by on-way ANOVA test at 5% significance level. Note: CP ¼ cement paste; SCM ¼ sand-cement mortar; CCC ¼ coir pith-cement composite; CSCC ¼ coir pith-sand-cement composite.

Fig. 7. Effect of the addition of coir pith particles on physical properties of the composites: a) bulk density, b) water absorption and apparent porosity. The same letters (a, b, c, d, a’, b’, c’, d’) indicate homogenous groups, i.e., the means of the composites are not statistically different by on-way ANOVA test at 5% significance level. Note: CP ¼ cement paste; SCM ¼ sand-cement mortar; CCC ¼ coir pith-cement composite; CSCC ¼ coir pith-sand-cement composite.

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Fig. 8. a) Scanning electron microscopy images of SCM, mortar with 100% cement and 100% sand, at 28 days, with magnification of 250; b) Mapping of the element calcium, Ca; c) Mapping of the element silicon, Si.

Table 2 Elemental chemical composition estimated for the composites (SEM-EDS). Figure

Composites

a

Fig.8(a)

SCM

Fig.10(b)

CCCb

a b

Points

1 2 3 1 2 3 4

Detection of chemical elements (% by weight) C

O

Na

Mg

Al

Si

S

K

Ca

Fe

9.35 1.86 1.91 25.35 10.43 28.61 11.53

13.48 20.33 19.30 49.63 46.39 49.82 50.32

0.10 0.03 0.08 0.12 0.18 0.01 0.26

0.03 0.13 0.03 0.13 0.06 0.15 1.51

0.07 0.16 0.34 0.54 1.77 0.47 1.95

71.26 1.16 1.08 0.79 11.20 0.53 9.92

0.58 0.00 0.03 0.19 0.58 0.15 0.57

0.38 0.44 0.71 0.19 0.50 0.19 0.37

4.74 72.57 75.05 21.86 28.30 20.05 22.60

0.00 3.31 1.47 1.22 0.60 0.00 0.98

SCM ¼ sand-cement mortar. CCC ¼ coir pith-cement composite.

porosity characteristics of the coir pith particles contributed to the increased porosity and water absorption of the CCC and CSCC samples, besides reducing their bulk densities. The mechanical results showed that, in the composites with addition of coir pith particles, the presence of natural sand does not cause significant changes, except for the ductility that is greater in composites without sand, the CCC. The effect of the addition of sand only improved the physical properties of the composites with coir pith particles. The values for the compressive strength of materials with coir pith particles are comparable to those of typical lightweight construction materials and mortars, which have values around 3.5e 4.5 MPa (Aamr-Daya et al., 2008; Coatanlem et al., 2006). It is expected that the values for coir pith composites are not comparable

Fig. 9. Fractured surface of the coir pith-cement composite (CCC).

to those for CP and SCM, but show that coir pith can play the role of fine aggregate in lightweight composites, even giving the material ductility due to chemical interaction in the particle-matrix interface. 3.2. Fracture analysis of the composites SEM analyses were performed with measurements of EDS to observe the fracture behavior of the study’s composites (Figs. 8, 10 and 11). Fig. 8a shows a microscopy of the SCM sample and the EDS analysis points. Point 1 is located on a sand particle. Fig. 8(b,c), mapping the elements calcium and silicon, respectively, shows the surrounding rich in calcium and the rich region in silicon, suggesting that it is a sand particle, indicating the difference in density between the particle and cementitious matrix. Points 2 and 3 are located in cement paste adhered to the particle and in its surrounding. Table 2 shows the chemical composition of the composites, by weight of the element, at the points indicated in the microscopy. The fracture surface of the CCC (Fig. 9), digital photograph captured with an Olympus digital camera X-840, shows that the coir pith particles were well distributed and well dispersed in the cementitious matrix, with no observed points of accumulation or absence of particles. The CCC microscopies and the EDS analyses points are shown in Fig.10(a,b). The Fig. 10a image shows the fine, exfoliated structures of the coir pith particles surrounded by cement paste. Fig. 10b presents an enlargement that better shows that the cement paste penetrates the voids existing in the structure of the coir pith particles, promoting particle-matrix adhesion. Points 1 and 3 are located in the coir pith particles, and Points 2 and 4 in the cement paste. The contents of carbon (C) in Points 1 and 3 are higher than

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235

Fig. 10. Scanning electron microscopy images of the coir pith-cement composite (CCC) at 28 days, with magnification of 200 and 500: CCC (a,b). EDS analysis points are highlighted.

those of Points 2 and 4, due to the chemical composition of the coir pith particles (Table 2). According to compositional analysis estimated by EDS of the coir pith particle at Point 1 in Fig. 3b, the element calcium was 0.25% by weight. If compared to the values in Table 2 for the concentrations of the element calcium at the points defined on the surface of the coir pith particle in the composites, particularly in the CCC sample, there was a significant increase in the relative concentration of this element. Lignocellulosic materials have the ability to fix calcium on their surface e a behavior observed by Sedan et al. (2008). The calcium ions are highly mobile in the cement hydration solution; thus, there is an accumulation of hydration products, Ca(OH)2 and CSH, in the lignocellulosic material-cement interface. These products lead to the formation of a physical anchorage between the vegetal particles and the paste, due to the porosity of the vegetal materials, in addition to hydrogen bonds (Wei et al., 2004), unlike sand particles that have almost impermeable surfaces. Due to the exposed surface of the sand particle (Fig. 8a), it was observed that the fracture in the SCM occurred in the sand-matrix interface or transition zone, this region usually being more porous,

Fig. 11. Scanning electron microscopy image of coir pith-sand-cement composite (CSCC) at 28 days, with magnification of 200.

less densified, and consequently, with less strength. A different behavior was observed in the composites with coir pith particles (Fig. 10). The rupture of coir pith particles was observed in these composites. It is suggested that the fracture model for coir pith particles does not match the model for rigid particles, but is a model for flexible

Fig. 12. a) FTIR spectrum of the coir pith particles, b) FTIR spectra of the CP, SCM, CCC and CSCC. Note: CP ¼ cement paste; SCM ¼ sand-cement mortar; CCC ¼ coir pithcement composite; CSCC ¼ coir pith-sand-cement composite.

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particles similar to the model for vegetal fibers. The morphology of crumpled sheets or porous plates of coir pith particles provides greater surface contact with the cementitious matrix, since the particle surface resembles the surface of a sheet enveloping the cementitious matrix and being enveloped by it. Thus, the cementitious matrix penetrates the voids and covers the surface of the crumpled sheet, giving better particle-matrix adhesion. There is clearly total integration between the coir pith particles and the cementitious matrix. In the process of fracture, there is a transfer of stresses in the lignocellulosic material-cement matrix on the surface of the sheet, mainly from existing hydrogen bonds responsible for adhesion. Thus, it is proposed that the stresses of adhesion do not exceed the strength of the particle, causing a deflecting of the particle with the morphology of crumpled sheets or plates. In this process, there is absorption of energy that leads the composites to a ductile rupture. The breaking of hydrogen bonds in the interface

Table 3 Vibrational wavenumbers in the infrared region of the in natura coir pith. Wavenumbers (cm1)

Assignments/components and molecules

3338

Stretching vibrations (n) generated by hydroxyl groups (OH) present in the structure of cellulose, hemicellulose and lignin (Saw et al., 2011); CeH stretching of methyl and methylene groups of cellulose, hemicellulose and lignin (Krishnan and Haridas, 2008; Rosa et al., 2010; Saw et al., 2011); Stretching vibrations n(C]O) of acetyl groups in hemicellulose (Sgriccia et al., 2008) and carbonyl stretching of lignin (Saw et al., 2011); Stretching vibrations n(C]C) of aromatics in the phenyl ring of the lignin (Krishnan and Haridas, 2008; Rosa et al., 2010); C]O bonds of hemicellulose (Sgriccia et al., 2008); C]O stretching of lignin and carbonyl group of the hemicelluloses (Mothé and de Miranda, 2009; Mwaikambo and Ansell, 2002); Stretching vibrations n(C]C) of the aromatic phenyl ring of the lignin (Macedo, 2005; Krishnan and Haridas, 2008); Stretching vibrations n(C]C) and symmetric deformation of CH2 in aromatic groups of lignin, hemicellulose (Troedec et al., 2008) and cellulose (Mothé and de Miranda, 2009; Rosa et al., 2010); CeO stretching vibrations of methoxy groups (OeCH3) of the lignin phenol (Krishnan and Haridas, 2008; Yang et al., 2007); OeH bending of acids in hemicellulose and lignin (Krishnan and Haridas, 2008; Rosa et al., 2010; Yang et al., 2007); CeH deformation of cellulose, hemicellulose and lignin (Rosa et al., 2010); Stretching vibrations d(eCH3) of methyl and methylene groups (Macedo, 2005); OeH deformation in phenolic group of cellulose (Krishnan and Haridas, 2008); CeH deformation of hemicellulose (Mwaikambo and Ansell, 2002); Stretching vibrations n(CeO) of esters, ethers or phenols groups (Macedo, 2005); CeO stretching vibrations of the acetyl group of lignin (Sgriccia et al., 2008) and hemicellulose (Rosa et al., 2010); CeOeC stretching in cellulose chain (Mothé and de Miranda, 2009; Yang et al., 2007); Asymmetric stretching of CeOeC in cellulose, hemicellulose (Troedec et al., 2008) and lignin (Rosa et al., 2010); OeH bending and CeO stretching in secondary alcohol (Krishnan and Haridas, 2008); Stretching and deformation vibrations of CeO in primary alcohol, ethanol (Yang et al., 2007).

2920

1730

1606

1514

1446

1369

1260 1242

1150

1097 1049, 1034

results in greater toughness of the composite due to the consumption of energy until a strain limit is reached by the particle and completely fracturing the material. This model explains the increased ductility (Fig. 5) observed in these composites. The Fig. 11 microscopy shows a fracture surface from the CSCC sample. It is possible to see the two types of fracture. In the center, a particle of sand can be seen embedded in the cementitious matrix with the surface partially exposed after the fracture of the specimen in the sand-matrix interface; and to the right, a coir pith particle can be seen embedded in the cementitious matrix, with the surface ruptured, a fracture mode similar to that observed for the CCC sample (Fig.10b). The FTIR analyses results of the coir pith particles and composites are shown in Fig. 12 and the assignments are in Tables 3 and 4, respectively. In the CCC and the CSCC, the presence of two discrete peaks stand out, a peak at 1710 cm1 and another peak at 1224 cm1,

Table 4 FTIR characterization of hardened cement paste. Band assignments

Wavenumbers (cm1)

Interpretations of assignments, components and molecules

Cement paste

n OH

3644

(n1 þ n3) H2O

3440

n CeH

2334

n2 H20

1634

n3 CO2 3

1432

n3 SO2 4

1108

n3 SiO2 4

1108

n3 SiO4 4

976

n2 CO2 3

874

n4 CO2 3

712

n4 SiO2 4

667

Stretching vibrations (n) generated by O eH bonds in calcium hydroxide (García Lodeiro et al., 2009); Broad and very weak band due to symmetric and asymmetric stretching vibration of water (OeH) bound in hydration products (Yilmaz and Olgun, 2008); Organic matter e stretching vibrations generated by CeH of cellulose, hemicellulose and lignin (Stepkowskaa et al., 2004); Bands due to symmetric deformation vibrations (n2) of adsorbed water molecules (OeH) (Stepkowskaa et al., 2004); Asymmetric stretching vibration (n3) C eO attributed to CO2 3 group in calcium carbonate (García Lodeiro et al., 2009); SeO (n3) stretching bands of SO2 4 group in gypsum and ettringite (C6ASH32) (Hidalgo et al., 2007; Stepkowskaa et al., 2004; Yilmaz and Olgun, 2008); Asymmetric stretching vibration (n3) of SieO in silicates (Stepkowskaa et al., 2004); Asymmetric stretching (n3) due to SieO vibrations of tetrahedron SiO4 4 in silicate phase presented as dicalcium silicate and tricalcium silicate in anhydrous cement and as calcium silicate hydrate, CeSeH (Stepkowskaa et al., 2004); Symmetric bending (n2) of CeO in CO2 3 group as calcium carbonate vibrations (García Lodeiro et al., 2009; Hidalgo et al., 2007; Yilmaz and Olgun, 2008); Asymmetric bending (n4) of CeO, CO3 group, as calcium carbonate vibrations (Hidalgo et al., 2007); SieOeSi bending vibrations (d) due to Si eO of SiO2 4 tetrahedron in silicate phase presented as dicalcium silicate and tricalcium silicate in anhydrous cement and as calcium silicate hydrate, CeSeH (García Lodeiro et al., 2009; Hidalgo et al., 2007).

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referring to the vegetal material, hemicellulose and lignin. The absence of Ca(OH)2 peaks around 3644 cm1 was associated with inhibition or retardation of the hydration reaction of Portland cement because of the presence of extractives, such as pectins, simple carbohydrates, terpenes, alkaloids, saponins, phenols, natural gums, resins and greases, among others, soluble in water or organic solvents (Jorge et al., 2004; Silva et al., 2009). Coir pith particles were analyzed by XRD, showing predominantly the amorphous phase in their structure, attributed to cellulose, hemicellulose and lignin, with halo at around 2q ¼ 22 , typical of lignocellulosic materials (Fig. 13a). The peaks are due to quartz or silicate commonly found in natural fibers (Macedo et al., 2008). Quartz, silicon oxide (SiO2) that appears in the XRD diffractograms of SCM and CSCC samples is due to the presence of sand in these composites (Fig. 13b). The diffractograms (Fig. 13b) of the CCC and CSCC samples showed that if there was inhibition of the

237

hydration reaction, it was small, because there was consumption of the cement constituents and formation of hydration products. The retardation of the hydration reaction leads to a less densified matrix, with less formation of calcium silicate hydrate (CeSeH) and calcium hydroxide, which also contributes to the reduction of mechanical strength in the composites with coir pith particles. However, the mechanical results in this work for CCC and CSCC compressive strength, respectively, were 4.35  0.02 MPa and 3.97  0.18 MPa; and modulus of rupture of 2.28  0.37 MPa and 2.24  0.29 MPa, results superior to those obtained by Olorunnisola (2009), who observed a compressive strength of 2.6e3.9 MPa and a modulus of rupture of 1.3e1.8 MPa. Unpublished studies show that the compatibility of coir pith particles with Portland cement can be improved by chemical treatments for removal of compounds inhibiting the hydration reaction, which increases the mechanical properties of the composites. Ongoing studies are evaluating the durability of coir pithcement composites. 4. Conclusions  Coir pith particles can be classified as a fine aggregate, according to particle size distribution.  Cementitious composites exclusively with coir pith had mechanical properties similar to or greater than the composites with the partial substitution of sand by coir pith.  The composites with addition of coir pith particles were ductile, supporting loads for a longer time before rupture without total disintegration. Coir pith particles had the ability to absorb energy during fracture, acting as toughening agents.  Due to the low bulk density, cementitious composites exclusively with coir pith may be used in applications requiring lightweight materials. Coupled with the reduction in bulk density, there was increased porosity, which favors the use as a material for thermal and acoustic insulation.  The compressive strength values of the composites with coir pith are within the range allowed for lightweight construction materials.  The compressive strength results specifically showed the effect of the low bulk density of the CCC sample, suggesting that thicker parts can be produced with this lower density material.  The reduction of the mechanical properties corroborated by FTIR results also showed a retardation of the hydration reaction due to less calcium hydroxide formation, influenced by the presence of extractives and hemicellulose.  Due to the greater water absorption of the coir pith-cement composites, they can be suggested for use in lightweight, interior materials, such as nonstructural masonry boards or blocks. Acknowledgments The authors would like to thank CNPq, CAPES and FAPITEC-SE for their financial support. References

Fig. 13. a) X-ray diffractograms of the coir pith particles, b) X-ray diffractograms of the composites at 28 days, where: 1 ¼ tricalcium silicate, C3S, (JCPDS-ICDD, 420551); 2 ¼ dicalcium silicate, C2S, (JCPDS-ICDD, 360642); 3 ¼ calcite or calcium carbonate, CaCO3, (JCPDS-ICDD, 240027); 4 ¼ ettringite (JCPDS-ICDD, 371476); 5 ¼ calcium hydroxide, Ca(OH)2, (JCPDS-ICDD, 040733); 6 ¼ calcium silicate hydrate, CeSeH, (JCPDSICDD, 451479), Q ¼ quartz (JCPDS-ICDD,791910). Note: CP ¼ cement paste; SCM ¼ sand-cement mortar; CCC ¼ coir pith-cement composite; CSCC ¼ coir pithsand-cement composite.

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Use of coir pith particles in composites with Portland cement.

Brazil is the fourth largest world's producer of coconut (Cocos nucifera L.). Coconut crops generate several wastes, including, coir pith. Coir pith a...
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