Construction and Building Materials 72 (2014) 65–71

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Construction and Building Materials

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Potential of bamboo organosolv pulp as a reinforcing elementin fiber–cement materials

http://dx.doi.org/10.1016/j.conbuildmat.2014.09.0050950-0618/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Tel.: +55 19 3565 4176.E-mail address: vivicostcor@yahoo.com.br (V.C. Correia).

Viviane da Costa Correia a,⇑, Sergio Francisco Santos b, Gonzalo Mármol a,Antonio Aprigio da Silva Curvelo c, Holmer Savastano Jr. a

a University of São Paulo, Faculty of Animal Science and Food Engineering, Department of Biosystems Engineering, Duque de Caxias Norte Street, 225, 13630-000 Pirassununga,SP, Brazilb State University of São Paulo, Faculty of Engineering, Department of Materials and Technology, Ariberto Pereira da Cunha, 333, 12516-410 Guaratinguetá, SP, Brazilc University of São Paulo, Institute of Chemistry of São Carlos, Trabalhador são-carlense Avenue, 400, 13560-970 São Carlos, SP, Brazil

h i g h l i g h t s

� Organosolv pulping eliminates the need to recovery of reagents and sulfur emissions.� Bamboo is a promising fiber to be used for pulping and as reinforcement.� Cellulose pulp is a good micro-reinforcement in cement composites at early ages.� Its possible to apply 8% of bamboo organosolv pulp in non-conventional fibercement.

a r t i c l e i n f o

Article history:Received 27 May 2014Received in revised form 2 September 2014Accepted 3 September 2014

Keywords:Organosolv pulpBambooReinforcementCementitious compositesDurability

a b s t r a c t

The potential application of bamboo organosolv pulp as a reinforcement agent in cementitious matriceswas evaluated in the present experimental work. Composites with contents of bamboo pulp of 6%, 8%,10% and 12% were tested. The composites containing 8% pulp were subjected to accelerated aging via50, 100 and 200 aging cycles. The properties of the composites were modified after the aging cycles whileconsidering the porosity refining due to matrix densification, which consequently improved themechanical properties. The results indicated that the composites reinforced with bamboo organosolvpulp showed promising behavior, which was preserved in the Portland cement environment after aging.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Fiber–cement composites have been mainly reinforced with cellu-lose pulps. The use of cellulose fibers in composites is importantbecause of the retention of Portland cement particles in the Hatschekprocess and some reinforcement effects in the early ages. Pinus pulphas replaced asbestos fiber as a reinforcement agent in commercialPortland cement products in conjunction with polyvinyl alcohol(PVA) fibers for air-cured (non-autoclaved) products [1,2]. A consider-able research effort has been made to apply fast growing agriculturalcrops and crop residues as cheaper alternatives for the fiber supply,especially in countries with limited forest resources [3].

Softwood (mainly Pinus radiata) and hardwood (eucalyptus)fibers have been extensively applied as the sole reinforcing

element in commercial autoclaved and air-cured Portland cementproducts [1,2]. Pulped cellulose fibers, require less energy in theirpreparation that most common synthetic reinforcing fibers, suchas polyvinyl alcohol (PVA) and polypropylene (PP), and can be con-sidered green products [4].

Bamboo is a promising fiber to be used as a raw material forpulping and reinforcement, considering its fast growth, its statusas a major non-wood forest product and wood substitute, itsworldwide abundance and relatively low cost compared to othervegetable resources. It can be used in construction materials, suchas Portland cement-based composites [1,5]. The use of renewableresources, such as vegetable fibers, by the civil constructionindustry can contribute to the development of more sustainablebuilding materials [6]. Although bamboo has also been used invarious forms in the construction industry, the informationconcerning the use of bamboo pulp fiber in the scientific literatureis limited [1].

66 V.C. Correia et al. / Construction and Building Materials 72 (2014) 65–71

The growing industrial and environmental importance of bam-boo requires the development of more comprehensive statistics onbamboo resources, utilization and trade. Approximately 75 generaand 1250 species of bamboo are found in different countriesaround the world. Guadua angustifolia Kunth is also applied as abuilding material, and it is a common plant in Asia and LatinAmerica, especially in Colombia, Peru and Ecuador [7,8]. Bamboo iscurrently applied in many different fields, including the aeronautical,chemical, civil, electrical, hydraulic, nautical and mechanical engi-neering fields [8]. A study on bamboo developed by the FAO (Foodand Agriculture Organization of the United Nations) and INBAR(International Network for Bamboo and Rattan) that aimed toprovide the first comprehensive assessment of the world’s bambooresources indicated that 16 countries in Asia reported a total of 24million ha of bamboo resources. Five African countries reported 2.8million ha. Ten Latin American countries are estimated have over10 million ha of bamboo resources [9].

Bamboo is an optimized biocomposite that naturally exploitsthe concept of functionally graded materials [10,11]. Between20% and 30% of the cross-sectional area of bamboo culm consistsof longitudinal reinforcing elements (denominated as fibers here)that are distributed non-uniformly through the wall thickness,the concentration being most dense near the exterior. The orienta-tion of these fibers makes bamboo an orthotropic material withhigh longitudinal strength and low transversal (to fibers) strength[12,13]. Such materials possess continuously graded propertiesand are characterized by spatially varying microstructures createdby non-uniform distributions of the constituent phases. In thesematerials, the role of reinforcement and matrix (base) materialcontinuously interchanges [14]. The smooth variation of propertiesmay offer advantages, such as a reduction of stress concentrationand increased bonding strength [15].

Organosolv pulping is based on organic reagents and providesan interesting alternative for the achievement of reinforcing cellu-lose fibers. The most used pulping chemical processes are alkalineprocesses, such as the Kraft process, and acidic processes, such asthe sulfite process [16]. Organosolv pulping has economic andenvironmental advantages because the use of organic solvents(ethanol, for instance) enables the operation of smaller and morecompact plants, eliminates the need for the recovery of inorganicreagents and eliminates sulfur emissions [17,18].

Cellulose pulp presents a satisfactory mechanical performanceas a micro-reinforcement at early ages in composites, whose majordisadvantage is low durability due to the chemical degradation thatresults from the aggressive effect of the high alkalinity of thecementitious matrix [19,20]. The cementitious matrix can be mod-ified with the addition of pozzolanic material to minimize alkalineattack. The literature generally agrees that pozzolanic the reactionbetween metakaolin and calcium hydroxide helps to refine the bin-der capillary porosity, which directly improves the mechanical per-formance mainly at early ages as well as the durability [20–22].

Table 1X-ray fluorescence chemical analysis of the particulate raw material (% by mass).

Oxide composition Ordinary Portland cement CP V-ARI Metakaolin

SiO2 19.40 52.10Al2O3 4.11 40.30Fe2O3 2.30 2.44MnO – <0.10MgO 3.13 0.30CaO 63.50 <0.10Na2O 0.24 <0.10K2O 1.09 0.79TiO2 – 1.45P2O5 – <0.10SO3 2.97 –BaO – –

This work presents the preparation and chemical/morphologicalcharacterization of bamboo organosolv pulp. The work alsoanalyzes the mechanical and physical behavior of cementitiouscomposites reinforced with different levels, from 6% to 12% bymass, of non-conventional bamboo organosolv pulp fibers andmetakaolin as partial substitute of ordinary Portland cement.Moreover, this work aimed to assess the effects of accelerated agingconditions on the performance of the bamboo pulp and the fiber–matrix interface in a cementitious matrix using soak and dry cycles.

2. Material and methods

2.1. Preparation and characterization of bamboo organosolv pulp

The bamboo pulp was prepared at the laboratory scale with an organosolvpulping process according to the prior work developed by Joaquim et al. [23]. Thepulping processing was carried out in a 7-L stainless steel reactor. The bamboofibers were immersed in an ethanol/water solution (1:1) at a fibers/solvent ratioof 1:10 (w/v). The work pressure was 2068 kPa at 190 �C for 2 h. The averagedistributions of the length and width of the fibers were analyzed with a Pulptec™MFA-500 Morphology Fiber and Shive Analyser—MorFiTrac according to themethodology adopted by Tonoli et al. [2].

According to Correia et al. [24], the chemical components, such as lignin, holo-cellulose, a-cellulose and hemicellulose, were determined following Refs. [25–28],respectively.

2.2. Raw materials

Ordinary Portland cement (OPC) type CP V-ARI correspondent to ASTM-C150[29] Type I was selected because of its finer particle size and higher reactivity atearly ages. The oxide compositions of OPC and metakaolin are listed in Table 1.The specific surface area and specific density of metakaolin were 26.5 m2/g and2.6 g/cm3 and those of OPC were 0.98 m2/g and 3.10 g/m3, respectively.

2.3. Composites production

The inorganic matrix was composed of ordinary Portland cement, Cauê brandand type CP V-ARI, provided by InterCement from São Leopoldo – MG, Brazil, andmetakaolin 40 HP, provided by Metacaulim do Brasil, as pozzolanic material forthe partial replacement (25% by mass) of cement. The contents of bamboo organo-solv pulp for reinforcement were 6%, 8%, 10% and 12% by mass in relation to thetotal dry mass content, which corresponded to approximately 11%, 14%, 17% and20% by volume, respectively. A similar range of fiber content was adopted by otherresearch groups [1,30] and is frequently applied in the industrial scale production offiber–cement materials that use cellulose pulp as the sole reinforcing element. Thisrange of fiber contents is also linked to the production method used (a crude repro-duction of the Hatschek industrial method), which allows the inclusion of a signif-icant amount of fiber in the inorganic matrix.

The composites were produced in thin plates, measuring 200 mm � 200 mm �5 mm. A slurry vacuum dewatering method, followed by a pressing technique asadopted by Savastano Jr. et al. [31], was used to cast the plates. The samples werecured in saturated air conditions (i.e., sealed in plastic bags) at 25 �C for 2 days, andthe samples were then subjected to thermal curing inside a chamber at 45 �C and90% RH for 5 days [32].

2.4. Mechanical and physical tests

The eight specimens by formulation were subjected to non-destructive physicaltests to determine the water absorption (WA), bulk density (BD) and apparent voidvolume (AVV) according to ASTM C-948-81 [33]. Mechanical tests were performedin wet conditions using a universal testing machine Emic DL-30000 equipped with a1-kN load cell. A four-point bending configuration was employed to evaluate themodulus of rupture (MOR), limit of proportionality (LOP), modulus of elasticity(MOE) and specific energy (SE) of the eight specimens by formulation. The calcula-tions for MOR, LOP, MOE are explained elsewhere [3,34].

The SE was defined as the work carried out during the bending test and dividedby the specimen cross-sectional area. The work was calculated by integrating thearea below the load–deflection curve to the point corresponding to a reduction inthe load carrying capacity to 90% of the maximum. A displacement rate of1.5 mm/min was adopted in the bending test, and the deflection was recorded witha deflectometer positioned in the middle span, in the downside of the specimen.Pads were wet-cut into four specimens with a thickness of 5 mm, width of40 mm and length of 160 mm using a water-cooled diamond saw.

The load versus deflection curve was obtained for the point corresponding to areduction in the load carrying capacity to 5% of the maximum load. The specificdeflection was calculated by dividing the deflection by the length of the greaterspan (135 mm).

V.C. Correia et al. / Construction and Building Materials 72 (2014) 65–71 67

2.5. Accelerated aging

The optimum level for the initial age (8 days) were prepared based on theresults of the composites containing 6%, 8%, 10% and 12% of organosolv bamboopulp to study the durability via accelerated aging cycles.

The accelerated aging test aims to simulate natural weathering using soakingand drying cycles. The specimens were successively immersed in water at20 ± 5 �C for 170 min and heated to 60 ± 5 �C for 170 min in a ventilated oven afteran interval of 10 min. The samples were then stored at room temperature for10 min prior to the next cycle, as recommended by the EN 494 Standard [34,35].

The samples were submitted to 50, 100, and 200 accelerated aging cycles. Thespecimens were subsequently subjected to the same physical and mechanical testsas previously described.

Fig. 1. Length range (a) and width (b) of bamboo organosolv pulp fibers.

2.6. Microstructural characterization of the composites

Mercury Intrusion Porosimetry (MIP) measurements were used to determinethe pore size distribution using a Micromeritics Poresizer 9320 to compare the porestructure of the composites reinforced with 6%, 8%, 10% and 12% of bamboo organo-solv pulp. The method was applied according to Almeida et al. [34], with a pressureup to 200 MPa, stabilization time in the low and high pressure settings of 10 s, anassumed surface tension of 0.485 N/m and a contact angle of 130�, which was usedin the Washburn equation to convert the applied pressure to the pore diameter.Even though this technique loses its accuracy for ‘‘ink-bottle’’ pores and fracturescan be possibly induced in samples under high intrusion pressure [36], the MIPmeasurement is the preferred method for pore structure evaluation due to its largerange of pore size measurements and easy operation.

The durability of the bamboo organosolv pulp in the fiber–cement resultingfrom the mechanical tests 8 days and after accelerating aging were analyzed onthe polished surfaces by scanning electron microscopy (SEM). The composites usedin microscopy were impregnated with a mixture of epoxy resin and catalyst at aratio of 1:0.13, respectively, and allowed to stand for 24 h. The embedded sampleswere then sanded with 600-grit sandpaper using alcohol as lubricant and a force of10 N for 4 min, followed by sanding with the same sandpaper at 15 N for 4 min.After being sanded, the samples were subjected to an ultrasonic bath in isopropylalcohol for 8 min. After the treatment in the ultrasonic bath, the samples were pol-ished using diamond suspensions lubricants, with progressively smaller averageparticle sizes of 6, 3 and 1l for 4 min with a force of 15 N for each polishing step.

Polished samples were carbon coated before being analyzed with a tabletopmicroscope and energy-dispersive X-ray spectroscopy (EDS), model TM3000, Hit-achi Oxford Instruments Analytical.

3. Results and discussion

3.1. Characteristics of bamboo organosolv pulp

The chemical characteristics and fiber dimensions of theorganosolv pulp fibers are summarized in Table 2.

ACI 544. 1R-2 [37] of the American Concrete Institute recom-mends the use of cellulosic pulp fibers with lower amounts ofresidual lignin and hemicelluloses, which are less alkali-resistantthan cellulose. The chemical composition of bamboo organosolvpulp shows low amount of lignin, extractives and hemicelluloseand a high cellulose content (Table 2). The lignin content can onlybe further decreased with more severe pulping and/or usingbleaching stages. The utilization of pulps with such residual lignincontents is an important improvement if fiber damage is absent.

Fig. 1a and b shows the distribution of the weighted length andwidth of the organosolv bamboo pulp. The distributions show thathigher a percentage of fibers have a length and width in the range0.6–1.3 mm and 12–23 lm, respectively. The high dispersion of thelength and width of the fibers is a feature of vegetable fibers. Thisdispersion can cause heterogeneity in the reinforcement ability offibers; however, it may also further aid the packing of fibers withinthe composite.

Table 2Chemical and morphological characteristics of bamboo organosolv pulp.

Lignin (%) Extractives (%) a-Cellulose (%) Hemicellulose (%) Av

14.4 1.5 76.0 8.8 0.

The aspect ratio is an important factor to guarantee fiberefficiency as reinforcement in Portland cement-based compositematerials. The bamboo organosolv pulp presented the sameaverage length as unbleached eucalyptus pulp, which was approx-imately 0.8 mm as reported by Almeida et al. [34] and Tonoli et al.[2]. However, the aspect ratio of bamboo organosolv pulp isapproximately 51, similar to that exhibited by unbleachedeucalyptus pulp. Savastano Jr. et al. [38] found an aspect ratio of61 and 53 of the eucalyptus and pines pulp, respectively, whichmight be associated with an improved reinforcing capacity in thecementitious matrix.

According to Coutts and Warden [39], a higher aspect ratio gen-erally improves the flexural strength and fracture toughness andconsequently increases the dissipation of frictional energy, as sug-gested by Coutts [40] and Savastano Jr. et al. [41] for pulp fiber-reinforced brittle matrices. The use of cellulose fibers in Portlandcement composites is also important because of the filteringproperties and retention of Portland cement particles inindustrial processes in addition to a reinforcement effect in theearly ages.

3.2. Mechanical and physical behavior of the composites

Fig. 2 shows the typical stress versus strain curves of the com-posites reinforced with 6%, 8%, 10% and 12% bamboo organosolvpulp after thermal curing for eight days. The curves represent themechanical behavior of specimens for each bamboo pulp content.The tenacity (the area under the curves) is significantly greaterfor composites produced with 10% and 12% of fiber, showing strain

erage length (mm) Average width (lm) Aspect ratio (length/width)

8 19.8 40.4

Fig. 2. Typical stress � strain curves of the composites containing 6%, 8%, 10% and12% bamboo organosolv pulp during flexure tests after 8 days of thermal curing.

Fig. 3. (a) Accumulative and (b) discrete pore size distribution for compositescontaining 6%, 8%, 10% and 12% bamboo organosolv pulp.

Fig. 4. Typical stress � strain curves during flexure tests of the compositesreinforced with 8% bamboo organosolv pulp after 50, 100 and 200 soak and drycycles.

68 V.C. Correia et al. / Construction and Building Materials 72 (2014) 65–71

hardening behavior and a continuous increase in the stress afterthe first cracking point (LOP). This behavior demonstrates thatthe organosolv bamboo pulp fiber plays a remarkable role as areinforcement and toughness agent and thus in the mechanicalbehavior of the composites in the initial age.

Table 3 shows the average values of the physical properties –the water absorption (WA), apparent void volume (AVV) and bulkdensity (BD) – and the mechanical properties obtained from theflexural test, such as the modulus of rupture (MOR), limit of pro-portionality (LOP), ratio MOR/LOP, modulus of elasticity (MOE)and specific energy, of the composites reinforced with 6%, 8%,10% and 12% bamboo organosolv pulp after thermal curing foreight days.

The water absorption and apparent void volume of the compos-ites reinforced with 6% and 8% of bamboo organosolv pulp werelower than those of the other composites. The high porosity isdue to the high fiber contents at 10% and 12%; the utilized cellulosepulps are hydrophilic, and the production process of the compos-ites promotes the formation of interconnected capillary pores viaa suction drainage process. Nevertheless, the obtained results forall samples are considered acceptable according to the BrazilianStandard NBR 5640 [42], which establishes 37% as the maximumlimit of water absorption for fiber–cement products.

The increase in the water absorption and apparent void volumewith the fiber content, which was accompanied by the expecteddecrease in the bulk density, can also be related to a transitionzone in the fiber–matrix, which becomes increasingly representa-tive in the volume of the composite, as it increases the fiber con-tent in the composite. These transition zones are formed bywater surrounding the fibers that becomes a porous area oncethe hydration process is completed.

The mechanical results of the composites reinforced with 6%,8%, 10% and 12% of bamboo organosolv pulp in Fig. 2 and Table 3show that the composites containing 6% and 8% pulp exhibitedthe best properties before cracking and specific deformation asso-ciated with maximum stress compared to composites reinforcedwith 10% and 12% of pulp. This finding is demonstrated by the

Table 3Physical and mechanical properties of composites reinforced with 6%, 8%, 10% and 12% ba

Fiber content (%) WA (%) AVV (%) BD (g cm�3) MOR (MPa)

6 25.4 ± 1.3 38.7 ± 0.9 1.53 ± 0.03 6.4 ± 0.98 26.5 ± 0.3 39.0 ± 0.2 1.47 ± 0.03 7.5 ± 0.1

10 30.3 ± 1.6 42.1 ± 2.6 1.39 ± 0.02 6.8 ± 1.412 30.9 ± 2.7 39.6 ± 2.3 1.30 ± 0.02 5.8 ± 1.5

higher average values of the limit of proportionality (LOP)modulus of elasticity (MOE) and modulus of rupture (MOR) ofthe composites containing 6% and 8% pulp. Bamboo pulp fiber

mboo organosolv pulp after thermal curing.

LOP (MPa) MOR/LOP MOE (GPa) Specific energy (kJ m�2)

3.8 ± 1.5 1.4 ± 0.24 10.6 ± 0.5 0.8 ± 0.15.4 ± 0.6 1.4 ± 0.16 9.6 ± 0.8 1.2 ± 0.13.2 ± 1.2 2.0 ± 0.02 6.2 ± 1.3 1.9 ± 0.32.3 ± 1.0 2.3 ± 0.04 4.5 ± 0.6 2.1 ± 1.0

Table 4The physical and mechanical properties of composites reinforced with 8% bamboo organosolv pulp after 50, 100 and 200 soak and dry cycles.

Age/Number of aging cycles WA (%) AVV (%) BD (g cm�3) MOR (MPa) LOP (MPa) MOR/LOP MOE (GPa) Specific energy (kJ m�2)

8 days 26.5 ± 0.3 39.0 ± 0.2 1.47 ± 0.02 7.5 ± 0.1 5.4 ± 0.6 1.4 ± 0.2 9.6 ± 0.8 1.2 ± 0.150 cycles 23.6 ± 2.7 33.7 ± 3.1 1.43 ± 0.04 8.1 ± 0.4 7.0 ± 0.6 1.2 ± 0.1 10.9 ± 1.4 0.6 ± 0.1100 cycles 21.1 ± 1.4 30.9 ± 1.3 1.46 ± 0.04 8.2 ± 0.8 7.1 ± 0.9 1.2 ± 0.1 10.6 ± 1.0 0.5 ± 0.1200 cycles 19.0 ± 1.5 28.4 ± 1.5 1.49 ± 0.04 8.3 ± 0.7 7.2 ± 1.0 1.2 ± 0.1 11.2 ± 2.1 0.6 ± 0.2

500 µµm

a

200 µm

b

Fig. 5. SEM micrographs in the back-scattered mode (BSED) of the fiber–cementcontaining 8% w/w of bamboo organosolv pulp after exposure to 200 soak and drycycles.

V.C. Correia et al. / Construction and Building Materials 72 (2014) 65–71 69

contents of 6% and 8% are sufficient to assure reinforcement afterinitial crack propagation (LOP), as indicated by the MOR/LOP ratio.

The mechanical performance of the matrix of composites rein-forced with 10% and 12% pulp was lower due to the excessiveporosity added by the fiber, while the toughness in post-crackingconditions was higher. The optimal level of reinforcement mustbe selected based on the application of the composite, i.e. theapplication dictates whether a material requires higher mechanicalstrength or higher impact resistance.

The accumulative and discrete pore size distributions of thefiber–cement containing 6%, 8%, 10% and 12% bamboo organosolvpulp measured by MIP are shown in Fig. 3. The results show thatthe pore volumes of composites containing 10% and 12% pulp arehigher than those of composites containing 6% and 8% pulp, specif-ically the gel structure and small capillary pores. The high inci-dence of capillary pores is often connected to the dimensionalvariation, cracking and reduced durability of cement-based prod-ucts [43–45]. The capillary pores form as a result of the concentra-tion of the particle and fiber, the distribution of the particle andfiber, the curing process, and the drying process, among other fac-tors at early ages of the composite [46]. According to Coutts and Ni[1], the packing of fibers in the matrix becomes less efficient whenthe fiber content is increased, which increases the void volume andwater absorption while concomitantly decreasing the density.

Although the composites containing 10% and 12% bambooorganosolv pulp showed higher post-cracking toughness, whichis a necessary condition for fibers used as reinforcement of cemen-titious material, 8% bamboo pulp content composites were selectedto be assessed in order to catalogue their performance according toNBR 15498 [47] and ASTM C 1186 [48] standards, which detail theflexural strength as the only mechanical parameter considered forproduct classification.

3.3. Mechanical and physical performance of the composite afteraccelerated aging test

Fig. 4 shows the typical stress � strain curves of the compositessubjected to 50, 100 and 200 accelerated aging cycles compared tothe stress � strain curve of the early age composite. The specificenergy of the composite clearly decreased after the acceleratedaging cycles and the LOP markedly increased as a consequence ofthe matrix densification, while the strength of the compositeslightly increased (Table 4).

Table 4 shows the physical and mechanical properties of thecomposites reinforced with 8% bamboo organosolv pulp after beingsubjected to 50, 100 and 200 soak and dry cycles.

The decrease in the water absorption and apparent void volumeof the composite and the increase in the bulk density are primarilyrelated to the number of aging cycles. These results are attributedto the filling of the voids in the matrix with hydration products,carbonation and modification of the fiber–matrix interface. As pre-viously stated, accelerated aging increases the modulus of rupture,limit of proportionality and modulus of elasticity values, whichindicates an improvement in the mechanical behavior of thematrix by its densification. However, the average value of the spe-cific energy decreases dramatically after 50 soak and dry cycles.Thus, these results might be attributed to the modification of theadhesion between the fibers and matrix. This modification in the

transition zone between fibers and matrix indicates the re-precipi-tation of Portland cement hydration products around the fibers,which primarily consists of a gel structure and small capillary pores.

However, the formation of Portland cement hydration productsaround fibers results in a densification of the fiber–matrixinterface, which decreases the pullout process after acceleratedaging. Thus, the pullout process directly interferes with the specificenergy, as shown in Table 4.

Mohr et al. [19] showed that the values of the mechanical prop-erties are not linearly correlated with an increase in the number ofaccelerate aging cycles. Most of the loss in the mechanical strengthand specific energy of the composite take place during the initialaging cycles. In fact, the values of the specific energy of thecomposites are similar after 100 and 200 cycles of soak and drytesting (Table 4).

Jamshidi et al. [49] have suggested that the ductility and tough-ness should also be considered to assess the durability perfor-mance of fiber–cement sheets. According to these researchers,the evaluation of the durability performance of fiber–cementsheets by comparing the modulus of rupture (MOR) defined bystandards is not sufficient to assess the mechanical behavior ofthese cement-based composites after durability tests.

Fig. 5a and b suggests that the higher percentage of metakaolinreplacements in Portland cement improved the degradation

Fig. 6. SEM micrographs and EDS maps in the back-scattered mode (BSED) of the fiber–cement with 8% w/w of bamboo organosolv pulp, after exposure to 200 soak and drycycles.

70 V.C. Correia et al. / Construction and Building Materials 72 (2014) 65–71

resistance of the bamboo organosolv pulp via pozzolanic mecha-nisms. These mechanisms included a reduction in the amount ofcalcium hydroxide, an increase in the ionic absorption from thepore solution with the formation of supplementary C–S–H, andsubsequent reductions in ettringite and portlandite re-precipita-tion [20].

Fig. 6 shows the probable C-S-H products around several bam-boo organosolv pulp fibers after 200 soak and dry cycles, whichwere also verified via the chemical elemental mapping of polishedsamples. The metakaolin is most likely related to the stabilizationof the alkali content in the matrix. Thus, ettringite and calciumhydroxide re-precipitation are proposed to be minimized or pre-vented, which improved the composite durability [20,50].

4. Conclusions

The results demonstrate the potential of bamboo organosolvpulp as an alternative to wood fibers in Portland cement-basedcomposites. Studies carried out in the present paper demonstratedthat the bamboo organosolv pulp contained low amounts of lignin,extractives and hemicelluloses as well as a high cellulose content,which indicates an important result to mitigate durability prob-lems. Although the content of lignin in bamboo organosolv pulpwas not as low as in bleached pulps, which are more expensivethan unbleached pulps, the amount of residual lignin of the bam-boo organosolv pulp has not diminished the physical–mechanicalperformance of the composites.

The aspect ratio of the bamboo organosolv pulp is similar tothat of the eucalyptus pulp and can play an important role onthe reinforcement of Portland cement-based composites. The fol-lowing principal conclusions are deduced from the conductedstudies.

Composites containing 8% bamboo pulp meet the BrazilianStandard NBR 15498 and ASTM C 1186, which are both standardsfor non-asbestos fiber cement flat sheets. These standards require aminimum modulus of rupture of 7.0 MPa for composites that fall in

category 3. These composite materials have a wider range of appli-cations, which require higher strength than materials in categories1 and 2.

The increase in the modulus of rupture, limit of proportionality,and modulus of elasticity of the aged composites indicates animprovement in the mechanical performance of the matrix as aresult of the re-precipitation of the Portland cement hydrationproducts into and around the fibers and the consequent filling ofpores in the interface between the fiber and matrix. Increasingthe soaking and drying cycles can also reduce the specific energy(toughness) because the energy consumed during fiber fracture isminimal compared to that developed during the pullout process.

The physical–mechanical behavior of composites reinforcedwith 8% bamboo organosolv pulp by mass demonstrates that thisnon-conventional non-wood fiber can be applied in combinationwith inorganic matrices based on Portland cement with a partialsubstitution of metakaolin.

Acknowledgments

The authors were supported by grants offered by CAPES, Brazil,through the Pro-Engineering Project (Grant no 103/2008), CNPq(Grant no 305792/2009-1) and Fapesp (Grant no 2011/01128-5,2009/17293-5 and 2010/16524-0). The authors also thank Dr.Pescatori Fernando Henrique Silva and Fibria for the technicalcontribution.

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