Plant-based natural fibre reinforced cement composites

Cement and Concrete Composites 68 (2016) 96e108

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Plant-based natural fibre reinforced cement composites: A review Obinna Onuaguluchi*, Nemkumar Banthia Department of Civil Engineering, University of British Columbia, 6250 Applied Science Lane, Vancouver, BC V6T 1Z4, Canada

a r t i c l e i n f o

a b s t r a c t

Article history: Received 24 December 2014 Received in revised form 17 July 2015 Accepted 16 February 2016 Available online 19 February 2016

The quest for sustainability in construction material usage has made the use of more renewable resources in the construction industry a necessity. Plant-based natural fibres are low cost renewable materials which can be found in abundant supply in many countries. This paper presents a summary of research progress on plant-based natural fibre reinforced cement-based composites. Fibre types, fibre characteristics and their effects on the properties of cement-based materials are reviewed. Factors affecting the fresh and hardened properties of cement-based composites reinforced with plant-based natural fibre are discussed. Measures to enhance the durability properties of cement-based composites containing plant-based natural fibres are appraised. Significant part of the paper is then focused on future trends such as the use of plant-based natural fibres as internal curing agents and durability enhancement materials in cement-based composites. Finally, applications and recommendations for future work are presented. © 2016 Published by Elsevier Ltd.

Keywords: Natural fibres Sustainability Cement composites Strength Durability Nano-reinforcement

1. Introduction Sustainability was defined by the World Commission on Environment and Development (WCED) as meeting the needs of the present without compromising the ability of future generations to meet their own needs [1]. One major problem facing mankind is the increasing world population and the associated pressure on the built environment. Demands for built infrastructure have caused significant waste generation, energy and material consumption by the construction industry. According to Melchert [2], the building construction industry is not only a major consumer of energy, raw materials and land; it also contributes immensely to environmental pollution, especially greenhouse gas (GHGs) emission. To improve sustainability in construction materials usage, the construction industry must embrace the reuse of industrial by-products and renewable materials in construction. Presently, because of their proven performance, the use of synthetic fibres in cement composites is becoming increasingly popular. Cement research literature is replete with studies showing that the ductility, tensile strength, toughness, fatigue strength, impact resistance and absorbed energy of cement-based materials could be enhanced significantly through the addition of steel and polymeric fibres [3e6].

* Corresponding author. E-mail address: [email protected] (O. Onuaguluchi). http://dx.doi.org/10.1016/j.cemconcomp.2016.02.014 0958-9465/© 2016 Published by Elsevier Ltd.

There are three types of natural fibres available for concrete reinforcement: animal-based, mineral-derived and plant-based. Animal fibres, comprising specific proteins, include silk, wool, and hair fibre. Mineral-derived fibres include asbestos, wollastonite and palygorskite. Finally, plant-based fibres include cotton, hemp, jute, flax, ramie, sisal, bagasse, specialty fibres processed from wood and etc. Significant enhancement in the properties of cementitious materials is also possible by reinforcing them with plant-based fibres described above. Opportunely, such fibres are obtained from renewable sources and are readily available at relatively low cost compared to man-made fibres. The benefits from large scale utilization of plant-based natural fibres as raw materials for cementbased composites are immense in terms of environmental, energy and resource conservation. Several investigations on plant-based natural fibre reinforced cement composites have been undertaken by researchers in the past three decades. This paper will present the current state-of-theart knowledge on the use of short and pulp fibres from plant sources as reinforcement for cement paste and mortar. Emphasis will be on fibre characterization, fresh and hardened properties of composites. The mechanical and durability performance of plantbased natural fibre reinforced cement composites will be discussed. Information on recent developments, future trends and applications for cement-based materials reinforced with plantbased natural fibres will also be presented.

O. Onuaguluchi, N. Banthia / Cement and Concrete Composites 68 (2016) 96e108

2. Types of plant-based natural fibres 2.1. Bast fibre Bast fibres are usually extracted from the outer bark of plant stems. Some examples of bast fibres are jute (Corchorus olitorius/ Corchorus capsularis), flax (Linum usitatissimum), abaca (Musa textilis), and kenaf (Hibiscus cannabinus). Retting is the process through which these bast fibres are extracted, and is accomplished through biological or chemical degradation of cut plant stems. Long fibre bundles with high tensile strength is the typical characteristics of bast fibres, hence they are traditionally used in making yarn, textile, rope, sack, etc. 2.2. Leaf fibre Leaf fibres are coarse and hard fibres obtained from leaf tissues by hand scraping after beating/retting process or mechanical extraction. Owing to the relatively high strength, leaf fibres are typically used for the production of ropes, fabrics, carpets and mats. Some examples of leaf fibres are sisal (Agave sisalana), caroa (Neoglaziovia variegate), henequen (Agave fourcroydes) and pineapple (Ananas comosus).

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bond enhancement and alkali resistance features. Furthermore, quality controlled manufacturing of these type of fibres ensure that the huge variability in dimensional and mechanical properties associated with unprocessed plant-based fibres is significantly reduced. 3. Fibre extraction processes After the retting process, single fibres from plant-based strand fibres are mostly obtained by manual mechanical separation or the use of a decorticator. On the other hand, pulping procedure is used to reduce strand fibres or wood chips to individual fibres. In mechanical pulping, fibre strands or wood chips are ground in three different ways; without steaming, with steaming (thermo-mechanical pulping) and chemical/steam pre-treatment (chemithermo-mechanical pulping). Conversely, in chemical pulping, heat and chemicals (kraft and sulfite process) are utilized in removing lignin from strands and wood chips thereby individualizing bundled fibres. Although chemical pulping yields lower quantities of pulp, the produced fibres are longer, stronger and brighter. Depending on application, further postpulping processing of fibres such as bleaching and mechanical beating are also performed. 4. Hygric, chemical and mechanical structure

2.3. Seed fibre Coir fibre is a typical example of seed fibre, and it is extracted from the coconut husk. These lightweight and strong fibres are mainly used in the production of ropes, mats, sacks, brush, geotextile and etc. Another set of seed fibres are also extracted from the pod or boll of some plant seeds. Examples are cotton, kapok (Ceiba pentandra), and milkweed floss which are widely used in textile, water safety equipment, insulation, upholstery and mattress products as a result of their softness and buoyancy. 2.4. Stalk fibre These are fibres from plant stalks, and are typically extracted from plants such as sugarcane, corn, eggplant, sunflower, wood and the straw of various grain crops such as barley, wheat, rice and etc. Pulp from some of these fibres has been utilized in paper and paperboard products. 2.5. Grass and other fibre crop residue Widely available tall grasses such as ryegrass (Lolium perenne), elephant grass (Pennisetum purpureum), switchgrass (Panicum virgatum) and bamboo (Bambusa vulgaris) are important sources of fibres. Furthermore, The Food and Agriculture Organization of the United Nations (FAO) estimated a 55% increase in world crop cultivation over the period from 1997/99 to 2030 [7]. Hence, fibrous crop residues such as pulse seed coat, peanut shell, hazelnut husk, corn husk, millet stover, and etc. can potentially be used as fibre reinforcements in cement-based composites. 2.6. Wood and specialty fibres Wood fibres are sourced from a wide variety of trees. Hence, they are in abundant supply across the world. Wood fibres are broadly divided into two groups, softwood and hardwood. The major difference between these two groups is that while softwood fibres are generally longer than hardwood fibres, the number of fibres in a given gram of pulp is significantly higher for hardwood pulp. On the other hand, specialty cellulose fibres are industrially processed plant-based natural fibres with unique attributes such as

Micrographs of some non-woody fibre bundles [8] are shown in Fig. 1. From the longitudinal view of these fibres, the surface of coir fibre did not only contain significant number of small indentations, it appears to be rougher compared to the surfaces of the other fibres. Cross-sections through these fibres also indicate that while the cell walls of the abaca fibre were thicker than those of coir and sisal fibres, the lumen diameter of all the fibres varied from 3 to 15 mm. Hence, given the open lumen of these fibres and the existence of pores on the cell walls, plant-based fibres could absorb significant quantity of water. Symington et al. [9] reported moisture absorption variation of 70%e164% in several plant-based fibres they investigated. Their findings indicated that coir and abaca fibres recorded the lowest and highest moisture content, respectively. The poor water absorption of coir fibre was attributed to the existence of air entrapping indentations on its surface as shown in Fig. 1a. In a related study, Ramadevi et al. [10] observed 135%e200% increase in the moisture content of untreated abaca fibre immersed in different types of water solution. Plant-based natural fibres consist of cellulose, hemicellulose, lignin, extractives and ash. The concentrations of these components depend on factors such as fibre type, growth condition, dimension, age, location on plant, extraction and processing method. Table 1 shows the variations in chemical composition of some selected fibres [11e13]. These natural fibres are also very hydrophilic, and this is traceable to the presence of hemicelluloses and the hydroxyl group in the cell walls. Alvarez et al. [14] were of the opinion that the high content of hydroxyl group in cellulose increases moisture absorption properties of plant-based fibres. Hence, the cumulative effect of open lumen, cell wall pores and the presence of hydroxyl group makes plant-based fibres susceptible to moisture sorption induced dimension instability. Faruk et al. [15] suggested that the moisture content of plant-based fibres has a tremendous effect on their mechanical properties and performance in composites. Previous studies have shown that the chemical composition of plant-based fibres has a great influence on its mechanical properties. This is because cellulose, hemicellulose and lignin are mainly responsible for the bond behavior and degradation of natural fibres in composites. According to Li et al. [16], the strength and stiffness of natural fibres depends on the cellulose content and the orientation of microfibrils in the cell wall. The chemical composition and

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Fig. 1. SEM images of selected non-woody fibre bundles [8]. Table 1 Chemical composition of plant-based natural fibres. Grouping

Fibre

Cellulose

Hemicellulose

Lignin

Extractives

Ash

Reference

Bast

Jute Hibiscus Banana trunk Banana Sorghum Bagasse Bagasse Wheat Rice Barley Sisal Sisal Banana Pineapple Corn stover Coir Coir Coir Coconut tissue Eucalyptus

33.4 28.0 31.48 60e65 27.0 32e48 41.7 33e38 28e36 31e45 38.2 73.11 25.65 70e82 38e40 36e43 33.2 21.46 31.05 41.57

22.7 25.0 14.98 6e8 25.0 19e24 28 26e32 23e28 27e38 26.0 13.33 17.04 18.0 28.0 0.15e0.25 31.1 12.36 19.22 32.56

28.0 22.7 15.07 5e10 11.0 23e32 21.8 17e19 12e14 14e19 26 11.0 24.84 5e12 7e21 41e45 20.5 46.48 29.7 25.4

e e 4.46 e e

e e 8.65 4.7 e 1.5e5 3.5 6.8 14e20 2e7 e 0.33 7.02 0.7e0.9 3.6e7 2.7e10.2 e 1.05 8.39 0.22

[11] [11] [12] [13] [13] [13] [12] [13] [13] [13] [11] [12] [12] [13] [13] [13] [11] [12] [12] [12]

Stalk

Straw

Leaf

Seed

Wood

mechanical properties of natural fibre is also influenced by fibre extraction methods. While chemical or chemithermo-mechanical pulping reduces the amount of lignin and other chemical

4 e e e e 1.33 9.84 e e e e 8.77 1.74 8.2

components in fibres, chemically produced pulps are stronger than those produced mechanically. Further refinement of pulp fibres by mechanical beaten not only softens fibres, it also increases the


surface area of fibres. Mechanical properties of some plant-based fibres are also highlighted in Table 2 [15]. Despite the low modulus of elasticity and high variability of the strength values shown, the tensile strengths of these fibres are reasonably high. Hence, given the low density and cost of these fibres, they have potential for use as reinforcement materials in cement composites. 5. Fibre-cement composite properties and performance 5.1. Fresh properties 5.1.1. Consistency Mansur and Aziz [17] observed decrease in the workability of cement paste and mortar as the length and content of jute fibre increased. Compared to the reference mixture without fibre, Savastano et al. [18] observed reduced workability of cement composites reinforced with eucalyptus pulp, coir or eucalyptus pulp combined with sisal fibres. These reported decreases in workability are as a result of moisture absorption by hydrophilic natural fibres. The key factors which influence the degree of workability loss in natural fibre reinforced cement mixtures are fibre aspect ratio and volume fraction in mixtures. The reduced workability of mixtures could be remedied by fibre pre-treatment to reduce the water absorbing chemical components of fibres. Natural fibres could also be pre-wetted before inclusion in mixtures. Alternatively, fairly workable natural fibre reinforced cement mixtures could be produced by considering the water absorption property of fibres in mixture design. 5.1.2. Setting time Some studies have shown that plant-based natural fibres have a negative effect on the hydration of cement composites. Bilba et al. [19] observed delayed setting time and reduced heat of hydration in sugarcane bagasse fibre reinforced cement composites. They attributed this occurrence to water soluble sugars formed as a result of the alkaline hydrolysis of lignin and partial solubilization of hemicellulose contained in these fibres. Likewise, Sudin and Swamy [20] suspected that the delayed setting time they recorded in bamboo flakes reinforced Portland cement matrix was caused by high quantities of sugars in the fibre. The dissolution of these soluble sugars produces calcium compounds in the cement matrix. These compounds lower cement hydration temperature and delay the formation of hydration products. Similar delay in the setting time of cement composites containing hemp fibres was also observed by Sedan et al. [21], and this was attributed to the presence of pectins contained in these fibres, which acted as a calcium silicate hydrate (CSH) growth inhibitor. In a more recent study, Fan et al. [22] suggested that the reduced cement hydration in

99

woodecement composites they investigated was caused by carbohydrates and hemicelluloses contained in the wood. Vaickelionis and Vaickelioniene [23] were of the opinion that delay in hydration depends on the concentration of soluble sugars in mixtures, and could be mitigated through the addition of pozzolan. The negative effect of plant-based natural fibres on cement hydration could also be reduced through the use of pre-treated fibres containing low amounts of lignin in cement composites. Furthermore, increased curing temperature, the addition of chemical accelerators and supplementary materials with high surface area such as finely ground limestone powder to mixtures could also help in enhancing early age hydration. 5.1.3. Plastic shrinkage Plastic shrinkage cracking occurs as a result of restrained volume contraction associated with the evaporation of water from the exposed surface of fresh cement based mixtures. Several studies have shown that the incorporation of different types of plant-based fibres can ameliorate the tensile stresses generated in plastic n and Tole do Filho [24], low cement mixtures. According to Sanjua volume sisal and coconut fibres were effective in controlling cracking in mortars and also seem to delay slightly the initiation of reınforcement corrosion in samples. In a related study, Toledo Filho and Sanjuan [25] observed that low volume sisal fibre was very effective in reducing free plastic shrinkage and crack development in cement mortars. Similarly, Toledo Filho et al. [26] investigated the effect of low volume fraction of short sisal and coconut fibres on the shrinkage of fresh and hardened mortar matrices. Their findings indicated that both fibres reduced free plastic shrinkage and delayed initial cracking for restrained plastic shrinkage. This improved plastic shrinkage resistance was probably as a result of higher elastic modulus of fibres compared to the cement matrix at early age and crack abridgement induced by these fibres [25,26]. Boghossian and Wegner [27] showed that low volume fraction of short flax fibres were also effective in reducing restrained plastic shrinkage cracks in cement mortar. Figs. 2 and 3, adapted from Ref. [27] show that maximum crack width and crack area reduced as flax fibre content of mixtures increased. At a fibre length of 10 mm and volume fraction of 0.3%, about 99.5% reduction in maximum crack width and 99.9% reduction in total crack area relative to the reference mixture were recorded. The increased plastic shrinkage resistance of specimens may have been as a result of enhanced fibre-matrix bond induced by hydrophilic flax fibres [27]. Reduced rate of settlement of particles and decreased bleeding induced by fibres could also contribute to the increased plastic shrinkage resistance observed in these aforementioned studies. Compared to the reference mixture, Soleimani et al. [28] observed that the number of cracks and crack width in mortar mixtures containing 0.25e0.75% estabragh (Asclepias procerais) fibre reduced

Table 2 Mechanical properties of selected fibres [15]. Grouping

Fibre source

Tensile strength (MPa)

Young Modulus (GPa)

Elongation at break (%)

Density (g/cm3)

Bast

Abaca Flax Jute Hemp Kenaf Ramie Bamboo Sisal Curaua Pineapple Coir Oil palm

400 345e1035 393e773 690 930 560 140e230 511e635 500e1150 400e627 175 248

12 27.6 26.5 70 53 24.5 11e17 9.4e22 11.8 1.44 4e6 3.2

3e10 2.7e3.2 1.5e1.8 1.6 1.6 2.5 e 2e2.5 3.7e4.3 14.5 30 25

1.5 1.5 1.3 1.48 e 1.5 0.6e1.1 1.5 1.4 0.8e1.6 1.2 0.7e1.55

Leaf

Seed/fruit

100


Maximum crack width (mm)

2.5 2 1.5 1 0.5 0 0% 0.05% 0.1% 0.3% 0.05% 0.1% 0.3% 0.05% 0.1% 0.3% 10 mm

19 mm

38 mm

Flax fibre length and volume Fig. 2. Maximum crack width of plastic shrinkage specimens [27].

280

Total crack area (mm2)

240 200 160 120 80 40 0 0% 0.05% 0.1% 0.3% 0.05% 0.1% 0.3% 0.05% 0.1% 0.3% 10 mm

19 mm

38 mm

Flax fibre length and volume Fig. 3. Total crack area of plastic shrinkage specimens [27].

by 67% and 90%, respectively. These reductions in plastic shrinkage were attributed to crack abridgement by the fibres. 5.2. Hardened properties of cement composites 5.2.1. Drying shrinkage In hardened cement-based mixtures, free and restrained drying shrinkage problems do occur regularly. Some studies have shown that the addition of plant-based natural fibres to cement mortar could not curtail these problems. Results from studies by Toledo Filho et al. [26] showed that the drying shrinkage of cement mortars increased with 2e3% by volume addition of short sisal and coconut fibres. They further reported that drying shrinkage was higher in composites containing sisal fibre due to the high water absorption and less smooth surface of sisal fibre compared to coconut fibre. Silva et al. [29] equally observed high drying shrinkage in their study of sisal fibre reinforced cement matrix. They attributed this occurrence to the increased porosity of samples induced by these fibres. Hence, it seems that the drying shrinkage behavior of plant-based natural fibre reinforced cement mortar mixtures depend on fibre characteristics, fibre volume fraction and the consequent effect on matrix pore structure. 5.2.2. Mechanical strength Generally, the addition of synthetic fibres to cement composites enhances toughness, ductility and impact resistance properties [3e6]. Similar results have also been reported for some cement composites containing plant-based natural fibres. Excerpts from

the impact resistance test results reported by Ramakrishna and Sundararajan [30] are shown in Fig. 4. The results show that the impact resistance of plant-based fibre reinforced mortar slabs was 3e18 times higher than those of the unreinforced slabs. The impact resistance of all the slabs increased as the volume fraction and length of the reinforcing fibres increased. However, the highest impact resistance was recorded in coir fibre reinforced slabs. The good performance of coir fibre may be attributed to its high elongation at break (Table 2) compared to the other fibres. According to Munawar et al. [31], coconut fibre is the toughest natural fibre, and their strain capacity is about 4e6 times greater than those of other natural fibres. The high ductility of coir fibres is very beneficial in reducing the brittleness associated with cement based composites. An overview [32e36] of the 28d mechanical properties of air cured cement composites reinforced with different pulp fibres are shown in Table 3. From Table 3, the mechanical strength of strand sisal fibre reinforced cement paste was lower than those of the composites containing sisal pulp fibres. The higher strength of the sisal pulp reinforced composite is as a result of the reduced stiffness and increased specific surface area of the pulp fibres which enhanced fibre-matrix interaction. Further refinement of pulp fibres by beating, and increased aspect ratio of fibres equally influence fibre-matrix interaction. The high aspect ratio of abaca fibres, increased fibre softening and high specific surface area engendered by refinement contributed to the very high mechanical strength of the abaca fibre reinforced cement composite. Table 3 also shows that flexural strength and toughness exhibit different trends. While toughness increased as fibre volume increased in composites, the optimum fibre content for flexural strength is 8e10%. Moisture content has a significant effect on the mechanical strength of plant-based natural fibre reinforced cement composites. Table 4 shows the percentage change in flexural strength and toughness of composites due to water absorption. While water saturation of specimens caused 18e51% reduction in flexural strength, the toughness of composites increased significantly. According to [37], water absorption destroys the hydrogen bonds between fibres or between fibres and matrix. Consequently, the flexural strength of composites containing softened fibres with weakened fibre-cement matrix bond became reduced. Moreover, due to the weakened bond interface, the failure mode of the fibres is predominantly by pull-out. On the other hand, improvement in toughness is due to increased frictional stress and pull-out force induced by swollen fibres [38]. A related study [39] equally showed that moisture content of specimens influence the mechanical strength and failure mechanism of cement composites. They reported that oven-dried pulp fibre reinforced mortar specimen recorded higher flexural strength and lower toughness compared to air or wet cured specimens. From the foregoing, it is apparent that for effective performance of composites, moisture absorption by plant-based natural fibres should be controlled. 5.2.3. The effect of fibre degradation on the durability properties of cement composites Durability is a very important consideration in the design of cement-based materials since it has a significant impact on the long-term resistance of composites to deleterious substances. Studies have shown that plant-based natural fibre reinforced cement composites are susceptible to deterioration in cement matrices due to absorbed water and alkaline pore solution weakening of these fibres. Deterioration of composites is also expedited by weathering. One major reason for the deterioration of plantbased natural fibre in cement composites is the dissolution of lignin and hemicellulose linking individual fibre cells by alkaline pore solution [40]. Degradation is further exacerbated by alkaline hydrolysis induced de-polymerization of fibres, whereby linked


Ref

Sisal

Coir

Jute

101

Hibiscus cannabinus

Final impact energy (Joules)

300 250 200 150 100 50 0 0%

2.0% 1.5% 1.0% 0.5% 2.0% 1.5% 1.0% 0.5% 2.0% 1.5% 1.0% 0.5% 20 mm

30 mm

40 mm

Fibre length and content by weight of cement in mixtures Fig. 4. Impact energy absorbed by mortar slab specimens [30].

Table 3 28d mechanical strength of cement composites reinforced with different vegetable fibres. Cement matrix

Fibre type

Fibre volume

Fibre aspect ratio

Flexural strength

Paste

e Refined softwood kraft pulp

0 4 8 12 4 8 12 4 8 12 4 8 12 4 2 4 6 8 10 12 14 2 4 6 8 10 0.5 1 1.5 2 4 6 8 10 12

e 53

11.8 19.2 23.5 25.0 16.5 21.5 20.3 15.5 19.5 20.1 15.6 21.4 22.2 14.4 10.9 12.1 16.2 17.4 18.6 19.2 21.8 17.5 21.8 26.3 27.3 24.7 9.2 9.9 11.3 12.7 15.9 16.7 18.3 15.0 10.3

Unrefined waste sisal kraft pulp

Unrefined Banana kraft pulp

Unrefined Eucalyptus kraft pulp

Sisal strand Refined bamboo kraft pulp

Refined abaca kraft pulp

Mortar

Unrefined Sisal kraft pulp

glucose molecules are disrupted and molecular chain length shortened [40,41]. The rate of degradation depends on the crystallinity and fibrillar morphology of the cellulose contained in these fibres [42]. Hence, degradation rate is slower the higher the crystallinity of cellulose. Ramakrishna and Sundararajan [11] observed reductions in

122

127

61

89 e

400

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

3.7 1.9 0.8 2.1 0.6 1.6 1.4 1.3 1.4 2.5 0.8 0.9 1.3 1.0 1.5 1.3 1.0 0.9 1.2 1.5 1.7 2.0 2.1 1.6 3.2 3.9 0.7 0.8 0.8 1.2 1.2 1.0 1.3 1.7 1.6

Flexural toughness 0.04 0.64 1.32 1.93 0.39 0.92 1.41 0.21 0.53 1.01 0.29 0.82 1.50 0.58 0.07 0.15 0.23 0.32 0.45 0.54 0.70 0.47 0.93 1.76 2.08 2.19 0.25 0.45 0.62 0.84 1.64 2.05 2.49 2.47 3.07

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.01 0.09 0.11 0.42 0.06 0.13 0.20 0.03 0.08 0.15 0.04 0.11 0.18 0.17 0.01 0.02 0.02 0.03 0.07 0.05 0.06 0.10 0.24 0.48 0.33 0.78 0.02 0.03 0.07 0.08 0.17 0.29 0.47 0.46 0.58

Reference [32]

[33] [34]

[35]

[36]

lignin, hemi-cellulose and cellulose content of coir, sisal, jute and hibiscus fibres exposed to water, saturated lime and sodium hydroxide (NaOH) solutions. Further use of these corroded fibres in cement mortar caused a reduction in sample mechanical strengths. do Filho et al. [40] investigated the strength loss of sisal and Tole coconut fibres immersed in alkaline solutions, as well as the

102


Table 4 The effect of 48 h water saturation on mechanical strength. Cement matrix

Fibre type

Fibre volume

Flexural strength

Flexural toughness

Reference

Paste

Refined abaca

Flax e 510 CSF

32.6 29.4 40.7 45.8 51.0 26.4 17.6 22.4 22.4 26.1 22.4 27.7 27.6 25.2 35.1 23.5 31.0 23.4 31.7 38.7 44.7

þ100.0 þ223.7 þ156.8 þ130.3 þ87.7 þ26.3 þ108.8 þ95.8 þ107.1 þ80.7 þ30 þ62.2 þ101.2 þ84.8 þ44.4 þ11.1 þ5.7 þ87.3 þ81.3 þ70.3 þ68.3

[35]

Mortar

2 4 6 8 10 2 4 6 8 10 2 4 6 8 12 2 4 6 8 10 12

Flax e 555 CSF

Flax e 555 CSF

durability of cement mortars containing these fibres on exposure to weathering conditions. They observed that the immersed fibres completely lost their flexibility while the mortar composites suffered significant loss of toughness. Mohr et al. [43] reported significant reduction in the mechanical strength of kraft pulp fibre reinforced cement paste specimens after exposure to 25 wet/dry cycles. Studies by Roma Jr. et al. [25,44] on the mechanical properties of cement-based roofing tiles reinforced with sisal and eucalyptus fibres, indicated that on exposure to weathering, the toughness of these fibre reinforced cement composites decreased substantially. From these aforementioned studies, it is clear that poor resistance of plant-based natural fibres to alkaline pore solution and weathering limits its successful utilization as reinforcement in cement-based composites. Hence, various approaches have been explored in order to mitigate the degradation of these fibres in cement-based materials. 6. Enhancement of the properties of plant-based fibre reinforced cement composites 6.1. Use of supplementary cementitious materials (SCMs) By reducing the soluble alkali content of cement and the depletion of portlandite through pozzzolanic reaction, partial substitution of cement with SCMs reduces the alkalinity of do Filho et al. [45] cement-based mixtures. Studies by Tole revealed that early carbonation and reduced alkalinity through partial replacement of cement by undensified silica fume was very effective in preventing the deterioration of plant-based natural fibres in cement composites. Mohr et al. [46] reported that binary and ternary blends of slag, metakaolin and silica fume were effective in reducing the degradation of pulp fibre reinforced cement composites exposed to wet-dry cycles. In a do Filho et al. [47] suggested that the loss of another study, Tole toughness and the long-term embrittlement of sisal fiberecement based laminates could be eliminated through the use of calcium hydroxide free cement matrix. Similarly, Silva et al. [29] reported that sisal fibre-cement composites modified with metakaolin and calcined waste crushed clay brick showed an ultimate bending strength, approximately 4 times higher and toughness 42 times higher than those of the control specimens. John et al. [48] reported that despite some lignin decomposition

[38]

observed in coir fibres, extracted from 12 years old low alkaline ground granulated blast furnace slag cement composite, these extracted fibres appeared undamaged. Thus, these cited studies have shown that the durability of plant-based natural fibre reinforced cement composites could be enhanced through the addition of SCMs to mixtures. 6.2. Fibre pre-treatment and its impact on composite properties Dimensional instability of plant-based natural fibres which is traceable to the propensity of these fibres to readily absorb and loss water under varying humidity conditions has a significant influence on fibre-cement matrix bond behavior. Consequently, various processes such as silane treatment, acetylation, acrylation, alkali treatment, pulping, hornification etc. has been explored by researchers as a means of reducing dimensional instability of plantbased fibres. Pre-treatment of fibres with alkalis can remove natural and artificial impurities and break down fibre bundle into smaller fibres, thereby increasing the effective surface area. It also produces a rough surface topography which can offer higher resistance to the pull-out of the fibre from the matrix [47]. Bledzki and Gassan [49] reported improvements in the fibreematrix adhesion of acetylized and silane surface treated natural fibres; they attributed this to the reduced moisture absorption property of the fibres. Li et al. [50] observed improved fibre-cement paste bond and toughness in alkalized coir fibre reinforced cement mortar. Sedan et al. [21], observed that alkali treatment not only improves the fibre strength, it also enhances the fibreematrix adhesion in a positive way. Other modification approaches were also explored by do Filho et al. [45] indicated that the researchers. Findings by Tole immersion of sisal and coconut fibres in a silica fume slurry before their addition to cement mortar was very effective in reducing the embrittlement of the composite. Bleaching removes residual lignin and extractives from fibre cell wall thereby improving the whiteness/brightness of pulp fibres. Although, depolymerization reaction during the bleaching process softens fibres, thereby reducing its tensile strength [51,52]; the bleaching process equally has a significant effect on the permeability and bond behavior of fibres in cement composites. Coutts [53] was of the opinion that fibre-cement bond is largely influenced by the hydroxyl group present on the surface of fibres and the refining/bleaching induced softness of fibres which promotes


intimate interaction with cement paste. Similarly, improved fibrecement matrix bond Mohr et al. [54] and increased bonding index of bleached fibres Tonoli et al. [52] were ascribed to fibre surface modification induced by the bleaching process. Hence, with enhanced fibre-cement paste interface, the peak mechanical strengths of composites are expected to increase. However, there are some drawbacks associated with the use of bleached fibres in cement composites. Enhanced fibre-cement paste bond reduces pull-out fibre failure mechanism or transforms it to fracture failure mode thereby lowering the ductility of cement composites. Compared to unbleached fibre reinforced cement composites, reduced fiber pull-out length Mohr et al. [43] and decreased ductility of bleached pulp fibre reinforced cement composites Tonoli et al. [52] have been reported. Furthermore, bleached fibres are also susceptible to accelerated mineralization due to increased permeation of calcium hydroxide through the cell wall. Research findings by Refs. [43,52] showed that degradation was slower in composites containing unbleached fibres. The reduced mineralization of unbleached fibres in these aforementioned studies was attributed to the protective layer of lignin and other extractives which impeded the ingress of cement ions. Fibre pre-treatment can also be done mechanically by beating. According to [53], mechanical refinement not only increases the fineness of vegetable fibre, it also softens these fibres. Hence, by making these fibres finer and less stiff, mechanical refining promotes fibre-cement matrix interaction. Savastano Jr. et al. [55] confirmed that low-temperature thermo-mechanical and chemical-thermo-mechanical pulped fibre reinforced cements had good adhesion between the phases. Their results equally showed that the highly porous interfacial areas usually associated with strand fibre reinforced materials were absent. In a related study, Tonoli et al. [56] submitted that moderate refinement and pulp beating of sisal fibre, improved fibre-paste adhesion and matrix densification thereby enhancing the modulus of rupture, limit of proportionality and modulus of elasticity of cement composites. Hornification, whereby fibres are alternately dried and rewetted to irreversibly decrease its water retention value has also been shown to enhance fibre-cement bond [57] and fibre durability in cement matrix [58,59]. Recent study by Ferreira et al. [57] showed that compared to 25 mm long untreated fibres, the adhesion stress and frictional stress of hornified fibres of the same length, in a cement mortar matrix increased by 40% and 50%, respectively. Claramunt et al. [58] reported that the hornification of kraft pulp and cotton linter fibres reduced the water retention capacity thereby improving the dimensional stability of these fibres in cement mortar composites. In a related study, Claramunt et al. [59] confirmed that these hornified fibres improved the mechanical strength and resistance of cement mortar composites to accelerated aging induced by alternate wetting and drying cycles. Similarly, heat treatment (pyrolysis) of fibres at 200 C has also been reported to improve the adhesion of vegetable fibres to ne et al. [60], oxygen free pycement matrix. According to Arse rolysis dehydrates the chemical components of plant-based fibre, increases its surface roughness thereby enhancing fibre-matrix adhesion. Table 5 shows that with the exception of acid treatment, alkaline and pyrolysis pre-treatment of fibre could enhance the flexural strength of composites [21,60,61]. However, the level of improvement is influenced by fibre type and matrix composition. For composites exposed to different accelerated aging conditions, Fig. 5a and b adapted from Ref. [62] shows that compared to untreated agave lecheguilla fibre reinforced composites, paraffin fibre pre-treatment reduced the flexural strength loss of samples considerably. Moreover, except for samples exposed to sulfate environment, the performance of composites were further

103

enhanced due to the addition of fly ash to the mixtures. 6.3. Specialized composite processing Accelerated carbonation curing of cement based materials is generating attention because of its carbon dioxide (CO2) sequestration potential and its positive impact on the durability properties of cement composites. Reports by Refs. [63,64] showed that CO2 uptake during accelerated curing enhances early strength gain, improves the resistance of cement composites to sulfate attack, water absorption and chloride ion penetration. Thus, given that accelerated carbonation curing not only reduce the alkalinity of a cement-based material, but also improves its durability. Some studies have investigated the effect of accelerated carbonation curing on cement composites reinforced with plant-based fibres. Research findings show that decreasing matrix alkalinity and the precipitation of dense calcium carbonate through accelerated carbonation improves the mechanical and durability properties of plant-based fibre reinforced cement composites [65e67]. Carbon capture from increased cultivation of fibre plants and the use of accelerated carbonation in curing plant-based fibre reinforced cement composites presents enormous environmental benefit. Moreover, these aforementioned fibre durability improvement techniques could be combined to yield much better performances. The performance of accelerated carbonation cured (ACC) and non-carbonation cured (NCC) eucalyptus pulp reinforced cement composite is shown in Fig. 6. Results show that accelerated carbonation curing increased the 28d flexural strength of samples substantially and prevents strength loss under different aging conditions. This curing method not only reduced the alkalinity of cement matrices, the precipitation of dense carbonate products reduced the pore volume of composites [67]. Hence, approximately 110e131% increase in strength relative to the un-aged NCC samples was observed. Thus, given the ongoing world concern about GHGs emission, and research efforts at CO2 gas sequestration; accelerated carbonation curing of small-sized plant-based natural fibre reinforced cement composites presents an enormous potential that should be explored. 7. Recent developments and future trends 7.1. Cellulose fabric reinforcement Reinforcing of cement composites with fibre fabrics is an emerging technique that is promising. With fibre fabric reinforcement, fibre content of composites could be increased without the workability and fibre dispersion difficulties usually experienced in discrete plant-based fibre reinforced composites. While many studies have investigated the performance of synthetic fibre fabric reinforced cement composites [68e72], only few studies have reported the mechanical performance of cellulose fabric reinforced cement composites [73e75]. Similarly, Silva et al. [74] reported that the modulus of elasticity and tensile strength of a five-layer sisal fabric reinforced cement composite containing 10% by volume of fibres were 34 GPa and 12 MPa, respectively. Hakamy et al. [75] reported that the addition of a two-layer hemp fabric containing about 2.5 wt% fibres to plain cement paste increased the flexural strength from 5.18 to 6.87 MPa and the fracture toughness from 0.356 to 0.656 MPa m1/2. Presently, the main drawbacks to the use of cellulose fabrics as reinforcements for cement composites is the dearth of information on production techniques, failure mechanism, the effect of fabric geometry/fibre alignment on mechanical properties. Hence, more studies are required in order to optimize the performance of cellulose fabric reinforced cement composites.

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Table 5 The effect of fibre pre-treatment on the flexural strength of cement composites. Composite

w/c ratio

Fibre treatment

Fibre content (%)

Length (mm)

Flexural strength (%)

Reference

Hemp/cement paste

0.5

0.62

Bagasse/cement paste

0.42

Banana trunk/cement paste

0.42

16 vol. e e 10 vol. e 2 wt e e 1-5 wt 2 wt e e 1-5 wt

1e10 e e 1e10 e 10 e e e 10 e e e

þ39.0 þ94.0 þ49.0 þ250.0 þ500.0 þ100.0 3.2 þ112.9 þ138.7 þ3.2 25.8 25.8 þ22.6

[21]

Hemp/lime paste

None NaOH AlCl3 None NaOH None H2SO4 Ca(OH)2 Pyrolysis None H2SO4 Ca(OH)2 Pyrolysis

a

Untreated

Paraffin treated

Non-carbonated curing

Paraffin treated+FA

[60]

[60]

Accelerated carbonated curing

25

30 25

20

Flexural strength (MPa)

Loss of strength (%)

[61]

20 15 10 5

15

10

5

0 Wet/dry

Humid/Temp

150 d Humid

150 d NaCl

150 d Na2SO4

0 28d/ un-aged

200 wet/dry cycle

Exposure condition

b

Untreated

Paraffin treated

400 wet/dry cycle

1 yr weathering

Aging condition Fig. 6. Flexural strength of eucalyptus fibre reinforced cement paste composite exposed to aging conditions [67].

Paraffin treated+FA

40

Loss of strength (%)

35

fibre dispersion and the effect of fibre properties on the fresh and hardened performance of cement composites internally cured with saturated cellulose fibres is also required.

30 25 20 15

7.3. Durability enhancement

10 5 0 Wet/dry

Humid/Temp

150 d Humid

150 d NaCl

150 d Na2SO4

Exposure condition Fig. 5. a) Flexural strength loss of 0.65 w/c ratio agave lecheguilla reinforced mortar exposed to accelerated aging [62]. b)Flexural strength loss of 0.35 w/c ratio agave lecheguilla reinforced mortar exposed to accelerated aging [62].

7.2. Fiber as an internal curing agent Internal curing is another emerging technology for the design of high performance cement composites with reduced internal cracking potential. Several studies [76e82] have investigated the internal curing mechanism of superabsorbent polymers (SAP) and pre-wetted fine light-weight aggregate [LWA] in cement-based materials. Research findings indicate that SAPs and LWA effectively reduce autogenous cracking in cement composites. Though, these few studies [83e86], have also shown that saturated cellulose fibres can potentially serve as internal curing agents in cement paste and mortar. More research on the effect of fibre type, fibre hornification, fibre content, fibre moisture sorption and desorption mechanism are required. Detailed information on mixture design,

To achieve sustainable infrastructures, innovative and cost effective methods of reducing degradation processes such as curling, corrosion, water and chloride permeability which impair the functionality and serviceability of cement composites are required. In comparison to plain unreinforced slab, recent study by Banthia et al. [87] reported reduced curling and cracking in concrete slabs incorporating 0.3% volume fraction of specialty cellulose fibre. Hence, compared to other approaches of reducing the curling of flatworks such as the use of thicker end sections, the addition synthetic fibres and continuous top reinforcements in slabs, the use of low volume fraction of cellulose fibres could be more economical. Banthia et al. [88] used cryoporometry (CP) and Mercury intrusion porosimetry (MIP) to investigate the effects of 0.1% and 0.3% volume fraction of cellulose fibres on cement paste pore volume and size distribution. While MIP results in Fig. 7 [88] indicated decreasing volume of 60e80 nm sized pores as the fibre volume fraction of cement paste increased, CP results showed increased volume of 5e6 nm sized pores as the cellulose fibre content of mixtures increased. Thus, by refining and redistributing large pores to very fine pores, the latter results indicate that cellulose fibres could potentially reduce the ingress of deleterious substances into cement composites.


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D apparent

D effective

Fig. 7. Pore size distribution in plain and cellulose fibre reinforced cement paste [88].

Chloride diffusion coefficient (10-7 cm2 /s)

1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 0

0.1

0.2

0.3

0.4

0.5

Fibre volume fraction (%) Fig. 9. Apparent and effective chloride diffusion coefficients of plain and specialty cellulose fibre reinforced concrete [90].

55

Time to corrosion onset (weeks)

Reduced water permeability of stressed and unstressed concrete specimens as the cellulose fibre content of mixtures increased was reported by Banthia and Bhargava [89]. Fig. 8 adapted from Ref. [89] showed that at a 0.5fu (ultimate compressive strength) stress on specimens, maximum decrease in water permeability induced by pore compression and crack suppression was observed in specimens containing 0.5% volume fraction of fibres; a reduction of approximately 55% in comparison to the plain reference specimens exposed to the same stress level. Similarly, in a related study on the effect of low volume fraction of cellulose fibres on chloride diffusion and reinforcement corrosion in concrete, Fig. 9 extracted from Sappakittipakorn and Banthia [90] indicates that while the total chloride content of specimens increased as fibre content of mixtures became higher, reverse trend was observed for free chloride content. The reduction of free chlorides in the fibre reinforced specimens and the delayed corrosion initiation time shown in Fig. 10 for specimens subjected to 15 kN loading suggest the existence of a chloride binding mechanism. These aforementioned studies highlight the potentials of cellulose fibres as a key raw material for the enhancement of the long-term performance of cement composites.

44

33

22

11

0 0

0.1

0.2

0.3

0.4

0.5

Fibre volume fraction (%) Fig. 10. Corrosion initiation time of plain and specialty cellulose fibre reinforced concrete [90].

7.4. Cellulose nano-reinforcement Nano-manufacturing of a vast range of high performance materials and composites is presently generating enormous interest across many industries. Cellulose nanofibres (CNFs) and cellulose nanocrystals (CNCs) are high strength and high surface area particles which can be isolated from cellulose fibres by mechanical

The effect of stress on water permeability (S)

0% Fibre

0.1% Fibre

0.3% Fibre

0.5% Fibre

1.4 1.2 1 0.8 0.6 0.4 0.2 0 0

0.1

0.2

0.3

0.4

0.5

0.6

Stress level (fu) Fig. 8. Relative water permeability of stressed plain and specialty cellulose fibre reinforced concrete [89].

fibrillation and acid hydrolyses, respectively. Although both CNFs and CNCs are nano-sized, their chemical composition and dimensions are different. While amorphous cellulose containing CNFs form interlinked network of fibres, with each fibre measuring between 2 and 5 mm in length, the more crystalline and shorter CNCs typically measures a few hundred nanometers in length. Many studies have investigated the possibility of extracting CNF and CNC from various wood and plant sources [91e99]. These studies have shown that nanofibres and nanocrystals could be extracted successfully from wood, rice straw, wheat straw, bagasse, banana, pineapple leaf, cotton and etc. Although research studies on the use of cellulose nanofibres as reinforcements in cement composites are limited, the few available studies suggest potential, if nanofibres could be dispersed homogenously in cement matrices. Claramunt et al. [100] observed that mortar mixtures containing nanofibrillated fibre recorded higher flexural strength, higher flexural modulus and reduced fracture energy compared to mixtures reinforced with conventional sisal fibre. In comparison to sisal microfibre reinforced mortar, Ardanuy et al. [101] reported 36% and 71% increase in flexural strength and flexural modulus, respectively in mortar mixtures reinforced with sisal nanofibres. They also observed that the nanofibre composites were brittle, with fracture energy decreasing by about 53%. The higher strength of the nanocomposites was as a result of increased fibre-matrix bond engendered by the high specific surface area of the nanofibres.

106


Conversely, the reduced fracture energy of the nanocomposites was ascribed to ineffective crack abridgement by the nanofibres; and this could be remedied by micro and nanofibre hybridization in composites [100,101]. Despite the delayed hydration of mixtures, Onuaguluchi et al. [102] reported increased cumulative heat of hydration and 106% improvement in flexural strength relative to the unreinforced reference mixture for cement paste containing 0.1% cellulose nanofibre by mass of cement. Thus far, research study on CNC reinforced cement composites is limited in the literature. Future studies should investigate the effects of CNF and CNC on cement hydration, pore solution viscosity, mechanical and durability properties. Moreover, comparative studies on CNF and CNC reinforced composites would help ensure that appropriate nanocellulose material is selected for cement-based composites. 8. Applications for plant-based fibre reinforced cement composites Conventional cement composites aside, there are other potential uses for plant-based natural fibre reinforced materials in the construction industry. Soil and embankment stabilization using synthetic fibre geotextiles is widespread, and has been reported to be very effective Bergado et al. [103]. However, for situations whereby the need for ground improvement is short-term and sustainability in construction is a consideration, biodegradable fibres and fabrics could be used. For long-term soil stabilization, a combination of chemically pre-treated plant-based natural fibres and cementation may also be ideal. Sarsby [104] was of the opinion that for transient separation of sub-soil and sub-base in road construction, erosion control and embankment support, well designed plant-based natural fibres such as coir, sisal and flax may record performance superior to those of synthetic geotextiles. In a related study, substantial improvement in the ductility of flax fibre reinforced soil-cement composite was reported by Ref. [105]. They further suggested that spray-on pre-coating of these fibres may enhance the observed mechanical properties. Presently, affordable housing and energy conservation are among the topical issues in building construction. Some studies have shown that the incorporation of plant-based natural fibres in building construction materials is not only feasible, they can also reduce material handling costs and heat transfer in buildings. According to Aggarwal [106], the mechanical and durability performance of cement bonded bagasse composites met the requirements of ISO: 8335-1987 and BS: 5669: Part 4: 1989 standards. Hence, they could be used as internal and external components in building construction. A study by Binici et al. [107] revealed that while fibre reinforced mud bricks were lighter than the conventional mud brick, the compressive strength of these fibre reinforced bricks were higher. In a further study, Binici et al. [108] reported that straw fibre increase the thermal insulation capacity of mud bricks thereby conserving energy in buildings. Research findings by Khedari et al. [109] showed that compared to unreinforced samples; coir fibre reinforced soil-cement blocks were lighter in weight, with reduced thermal conductivity. Similarly, Goodhew and Griffiths [110] reported that the thermal conductivities of un-fired clay bricks reinforced with paper, straw or wool were below the United Kingdom Building Regulations limit. New applications such as thin cement bonded cellulose macro fibre and fabric boards could be used as sound and thermal insulation materials in buildings. Increased energy efficiency of buildings will reduce energy demands, heating costs and the environmental impacts associated with energy production. In addition to being utilized as internal curing agent and durability enhancer in cement composites, saturated cellulose pulp fibres could also be used in surface curing of concrete infrastructures.

These studies [111,112] have shown that lane closures associated with traditional methods of curing shotcrete repairs on bridge soffits could be avoided through the use of wet-sprayed cellulose pulp fibres. Furthermore, reduced water vapor permeability and oxygen diffusion in nano-biocomposites reinforced with well dispersed CNC has been reported [113]. Thus, viscous and crystalline CNC could also be utilized in the manufacture of high performance cement nano-composites with increased tortuosity and significantly reduced permeability to water and deleterious ions. 9. Concluding remarks Research on plant-based natural fibre reinforced cement composites has continued to evolve as a result of the increasing demand for sustainability in raw materials usage, as well as the low cost, low density, strength and local availability of these fibres. However, as highlighted in this review article, in the past moisture absorption capacity of plant-based fibres which influence the mechanical and durability properties of reinforced cement composites negatively has remained a factor mitigating their use. There are however scenarios such as hot-weather concreting where water absorption capacity of plant-based fibers can be seen as a bonus. Inability of some of these fibers to resist a high pH cementitious environment also remains a concern and has discouraged their use. Further studies are required in order to evaluate the effects of fibre pre-treatment methods and alternative curing methods on the long-term performance of composites. Detailed research studies on the effect of plant-based fibres on crack abridgement, cement matrix pore structure, water and chloride permeability are also required. A new approach of utilizing the water retention capacity of plant-based fibres to produce high performance cement composites through the internal curing technology should also be explored. References [1] World Commission on Environment and Development (WCED), Our common future: the brundtland report on environment and development, Oxford University Press, Oxford, 1987. [2] L. Melchert, The Dutch sustainable building policy: a model for developing countries? Build. Environ. 42 (2007) 893e901. [3] N. Banthia, A. Moncef, K. Chokri, J. Sheng, Micro-fiber reinforced cement composites. I. Uniaxial tensile response, Can. J. Civ. Eng. 21 (6) (1994) 999e1011. [4] N. Banthia, J. Sheng, Fracture toughness of micro-fiber reinforced cement composites, Cem. Concr. Comp. 18 (4) (1996) 251e269. [5] Y. Wang, V.C. Li, S. Backer, Tensile properties of synthetic fiber reinforced mortar, Cem. Concr. Compos. 12 (1) (1990) 29e40. [6] L.R. Betterman, C. Ouyang, S.P. Shah, Fiber-matrix interaction in microfiberreinforced mortar, Adv. Cem. Based Mater. 2 (1995) 53e61. [7] The Food and Agriculture Organization of the United Nations (FAO), World Agriculture: towards 2015/2030. An FAO Perspective, in: J. Bruinsma (Ed.), Earthscan Publications Ltd, London, 2003. Retrieved on 5th March, 2013, from: p://ftp.fao.org/docrep/fao/005/y4252E/y4252e.pdf. [8] A. Kicinska-Jakubowska, E. Bogacz, M. Zimniewska, Review of natural fibers. Part Idvegetable Fibers, J. Nat. Fibers 9 (2012) 150e167. [9] M.C. Symington, W.M. Banks, O.P. West, R.A. Pethrick, Tensile testing of cellulose based natural fibers for structural composite, J. Compos. Mater. 43 (2009) 1083e1108. [10] P. Ramadevi, D. Sampathkumar, C.V. Srinivasa, B. Bennehalli, BioResources 7 (3) (2012) 3515e3524. [11] G. Ramakrishna, T. Sundararajan, Studies on the durability of natural fibres and the effect of corroded fibres on the strength of mortar, Cem. Concr. Compos. 27 (2005) 575e582. ne, H. Savastano Jr., S.M. Allameh, K. Ghavami, W. Soboyejo, [12] M.-A. Arse Cementitious composites reinforced with vegetable fibers, in: Proceedings of the First Inter-American Conference on Non-conventional Materials and Technologies in the Eco-construction and Infrastructure, Joao-Pessoa, Brazil, November 2003, pp. 13e16. [13] N. Reddy, Y. Yang, Biofibers from agricultural byproducts for industrial applications, Trends Biotechnol. 23 (1) (2005) 22e27. [14] V.A. Alvarez, R.A. Ruscekaite, A. Vazquez, Mechanical Properties water absorption behavior of composites made from a biodegradable matrix and alkaline-treated sisal fibers, J. Compos. Mater. 37 (17) (2003) 1575e1588.

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