Download pdf - Flax fiber reinforced concrete a natura1 fiber … fiber reinforced concrete-a natura1 fiber biocomposite for sustainable building materials J. E. Femandez Building Technology Progrum,

Flax fiber reinforced concrete-a natura1 fiberbiocomposite for sustainable building materials

J. E. FemandezBuilding Technology Progrum, Dept. of Architecture, Massachusetts Institute of Technology, USA.

Abstract

developing regions.for a class of concrete biocomposites for use in a variety of building types inespecially steel. For architectural applications, the results indicategood potentialoffers strategies that may lead to substantial savings in construction materials,strength of structural members composed of the flax fiber reinforced concretelength of 3cm for flax fiber in concrete. As a result, an increase in the shearcomposite. A theoretical analysisconfiied the empirical results of an optimumpotential to substantially increase the flexural toughness of the concretedecrease with others, results from the optimized formulation indicated thestrength was shown to increase with the inclusion of particular fiber lengths andincreased strength and toughness of the natural fiber-reinforced concrete.Whilemechanical laboratory testing yielded positive conclusions regarding thetoughness and crack management from the various samples. Results fromin concrete was sought in obtaining the highest possible ultimate strength,cured concrete. Specifically, an optimal ratio mix and fiber length of flax fiberswithin a concrete matrix is intended to augment the energy absorption of theindustrial capacity to process them. Generally, the inclusion of natural fibersregions with access to significant sources of cellulose fibers and small-scaleuse of natural fiber reinforced concretes (NFRCs) for buildings in developingconcrete (FFRC). The mechanical results are intended as a demonstrationof theThis paper presents the laboratory results o f an optimized flax fiber reinforcedpotential for architectural applications has not been adequately investigated.and inexpensive source of mechanically useful cellulose, the full extent of thepolymeric, earthen or otherwise. While natural fibers offer a widely availableand volume filler within the matrix of a composite material; cementitious,important use of the mechanical properties of natural fibers is tensile reinforcingarchitectural applications in structural and non-structural assemblies. OneFibers of many types, including some natural fibers, have been used widely for

© 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved.Web: www.witpress.com Email [email protected] from: High Performance Structures and Composites , CA Brebbia and WP de Wilde (Editors).ISBN 1-85312-904-6

194 High P e r j o m m ~ c eStmctur.es and Composites

1 Introduction

components [1][2][3][4][5].addressing the use of biomass as a source of raw materials for buildingThe work presented in this paper serves to augment the substantial literature

stock to house growingurban populations.face substantial challengesin providing the necessary infrastructureand buildingquantities, the raw biomaterial. In addition, developing regions also continue toin this field are also those that have the capability to produce, in large enoughand productivity. It stands to reason that the regions of the world most interestedAfrica, have led t i s work during periods of greatest sustained research interestuniversities. Researchers in India and Latin America, and to a lesser extentdeveloping regions of the world, primarily in collaboration with Europeanwide-ranging work has occurred at research centers and universities inbeen an ongoing project for many decades [3]. Much of the most promising and

The use of biologically derived materials in components for buildings has

technologiesin a particular area, given a particular culture.valuable resource for evaluating what may be considered appropriatesubstantial experience with the materials at hand. This experience is often aespecially those derived of agricultural practices, brings with it the lessons ofembedded knowledge base of indigenous peoples. The use of natural materials,techniques of technology transfer for development that t i e advantage of the

Furthermore, recent research [6] has indicated the value of investigating

Fibers 1I I

I l I ~ lNatural Man-madeI

I I IAnimal MineralVegetable

Figure 1: Fiber classification

mix.which the fiber reinforcing serves to increase the overall toughness of the finalpolymeric composites. These composites are generally low-strength materials infibers produced by plants for tensile reinforcing in earthen, cementitious andfrom many different angles, the primary path of research has been the use ofWhile the potential of biomass in building components has been investigated

paper and fabric coatings,not to mention ethanol as a petroleum fuel substitute.biomass such as starch-derivedplastics, biopolymers for secondary oil-recovery,[7]. Specialty products have been formulated from materials derived of plantmillion tons of waste biomass is generated each year in the United States aloneenergy production has been well documented. It has been estimated that 280

In addition, the availability of biomass for use in large scale industrial and


High P e r f i m m n c e Stmctures und Composites 195

I Renewable Resources l

materialsCompositeand filmsBiopolymersadhesivesIndustrialdetergentsSoaps andvarnishesPaints anddyesPigments andand inksSoybeanoils LiquidSolid

MethanolBagasseEthanolLigninFuel OilCoke

Gas I%wsMethane IHydrogen 1

Figure 2: Current bio-based products

chemicalsAgriculturalsurfactantsIndustrialacidsAcetic and fattySpecialty chemicalsPhenols and fiu-fwalOxy-fuel additivesActivated carbon

2 Mechanical properties of flax fiber reinforced concretem0

crack inhibitor in a cementitious composite.natural fibers in terms o f tensile strength, a property critical to the behavior of afibers because of their lesser tensile strengths. Note that flax rates highest amongalso clear that natural fibers may not be used as a simple substitute for syntheticproperties for use as structural reinforcement in an archtectural composite. It ismodulus that a number of natural fibers possess reasonably good mechanicalglass, aramide and carbon fibers. It is clear from the results for Young'sTable 1 [l] lists various properties for a number of natural fibers as well as


196 High Performance Structures and Composites

Table 1: Various properties of selected natural and synthetic fibers

7.0-8.0(MP4 (GP4

C”/.) strength ModulusFiber Density Elongation Tensile Young’s

(&m3)

Cotton 1.5-1.6 287-597 5.5-12.6

kraftSoft wood 1.5(cord)Viscose 11.4Coir 1.2 30.0Sisal 1.5RamieHempF l a x l.5 2.7-3.2Jute 1.3 1.5-1.8

1.6

2.0-2.53.6-3.8

593175511-635400-938690345-1035393-773

1000

27.626.5

11.04.0-6.09.4-22.061.4-128

40.0

(standard)Carbon 1.4(normal)Aramide 1.4S-glass 2.5E-glass 2.5

3.3-3.7 3000-3150 63.0-67.02.82.5

1.4-1.8

2000-3500 70.04570 86.0

4000 230.0-240.0

the economic costs associated.various positive attributes to the task of tensile reinforcing that stand to temperoverall importance of the fiber as a tensile reinforcing agent. Natural fibers bringthat of e-glass. However, this fact alone should not affect consideration of theflax fiber rates among the more expensive of the natural fibers, often exceedinghandling indicate good possibilities for their use in composites. In terms of cost,

These mechanical properties, along with relatively low cost and ease of

biocomposite material technologies.processes. Natural fibers from plant material are the primary source for newprimary material or secondary by-product of well-established agricultural

1.Natural fibers are found globally and often commonly harvested as either a

and maturation of the plant is restricted to the soil in which it is planted.biodegradable. In addition, the environmental impact during seeding, growing

2. Natural fibers, as the product of natural processes, are renewable [l] and often

in the atmosphere [ 1][7].fixed thereby contributing a net zero sum gain to the overall amount of carbondecomposition is returned to the environment from which it was originally

3. Natural fibers fix and retain carbon. The CO2 released during combustion or

This widespread familiarity in cultivation, harvesting, processing andand social history within developing and predominantly agricultural regions.

4.Natural fibers are a group of materials with a long economic, technological


and vernacular expertise [61.technologies utilizing natural fibers can build upon this existing knowledgevarious products for thousands of years. Any development of contemporaryviable sustainable production processes. Certain fibers have been in use formanipulationof natural fibers is an important component in the formulationof

High Pe$omance S t rwtwes and Composites 197

recycling [7].biodegradable and may therefore re-enter the organic material cycle throughprocessing required - relative to synthetic fibers. In addition, natural fibers are

5. Natural fibers embody low levels of energy due to the low levels of

7.Natural fibers possess generallyhigh strength to weight ratios.carbon.This lower abrasiveness aids in the various processing steps [ 5 ] .

6.Natural fibers are much less abrasive than synthetic fibers such as glass and

1.Natural fibers are strongly hydrophilic. This property is primarily due to thespecificcharacteristicsof flax fibers.productive characteristics, should also be listed here before we introduce the

The most important negative characteristics, or more precisely counter-

and fiber.the fibers [8] as well as the integrity of the interfacial bond between matrixbefore, during and after casting and curing, may affect both the durability ofa problem in both polymer and cementitious matrices. Water absorptionbonding of hydrogen to the hydroxyl groups of the cellulose molecule. This is

application in building components.materials) with variations in a wide range of properties important to theircomplex mixture of cellulose, hem-cellulose and lignin (among otherspecies and even among fiber bundles of the same species. Natural fibers are a

2.Mechanical and physical properties of natural fibers vary widely between

natural fibers.water soluble substances. Table 2 lists the component mean values of several

Natural fibers consist of cellulose, hem-cellulose, lignin, pectin, waxes andof the pH level of any matrix material [8][9][lo][1l].to attack in an alkaline environment. Careful consideration needs to be taken

3.The cellulose molecule, the structural backbone of all plant fibers, is sensitive

Table 2: Component contentof selected natural fibers

Cotton Jute Flax Ramie Sisal82.7 64.4 64.1 68.6 65.8

WaXWater solubleLigninPectincelluloseHem-Cellulose

5.7 12.0 l&7

5.7 0.2 X.811.8 2.0

1.0 1.1 3.90.6 0.5 15

13.1 12.0

0.31.29.90.8

0.35.50.61.9

level of polymerization determines the supramolecular structure of the fiber. In(Table 3) is an important aspect of the morphology of cellulose in the fiber. Thecondensation polymer of anhydroglucose units. The degree of polymerization

Cellulose can perform the structural functionof the plant because it is a linear


propertiesof the fiber itself [ l].addition, this supramolecular structure detemnes most mechanical and physical198 High Performance Structwes and C'omposites

Table 3: Degree of polymerization (P,)

Ramiem l xCottonF i b e r

6500"J7oooP"

2.1 Concrete and flax fiber

integrity in structural members.an important way to offer low-cost alternative methods for achieving flexuralflexure. The substitution, or partial substitution,of steel in reinforced concrete isof certain members, it is a dangerous practice when applied to members inoverall mass of the final cast. While this may be suffkient for uniaxial loadingSubstandard contracting practiceshave reduced the use of steel by increasing theloading from earthquakes is critical to the safe occupation of the buildings.ultimately formed on site - especially in areas where the resistance to dynamicThis is a major concern with regard to the quality of concrete delivered andits high expense contributes substantially to the overall cost of the composite.steel used within reinforced concrete is relatively small in weight and volume,the composite is often a relatively expensive component. While the amount ofavailability of low-skilled, inexpensive labor. However, the reinforcing steel ofcommon being the relative low-cost of the constituent materials as well as theparticularly prevalent in developing regions for a number of reasons; the mostenvelope of a variety of buildings of all types and scales. Reinforced concrete ispredominate material for the superstructure and, to a lesser extent, the exteriorthroughout the world. This relatively simple composite serves as thedeveloping world today. It is a primary structural material, along with steel,

Reinforced concrete dominates the construction industry in much of the

The crop then spread to the Middle East, Europeand eventually tothe Americas.detemned to have been an important crop throughout Mesopotamia and Egypt.important and useful of flax varieties, found its way around the Near East and islinseed oil, linen fiber for fabrics and food grain. Linum usitatissimum, the mostwas one of the earliest sources of a variety of important products, includingenergy and attention was devoted to the cultivation of the flax plant. This cropsettlements in the Near East. It is clear that, from a very early date, substantialnumber of archeological sites dating back to the time of the earliest agriculturalEvidence of the use of flax for food as well as textiles has been recovered from a

Flax has been used for a variety of products for roughly 10,000 years [121.

of approximately 100 micrometers in diameter. Each fiber bundle containsthis study ranged between 10 and 17 cm. Flax fiber is composed of fiber bundlesand separated mechanically using a variety of techniques. Fibers acquired forAmerica and China. The useful fiber is produced within the stem of the plant

Flax is a temperatebast plant currently cultivated in Europe, North and South


fiber from the stem.though compressive rollers - has been the method of choice [131 for removingwalls. Historically, retting - a process of rotting the stems and running themor less cylindrical in section with a very fine lumen and relatively thick cellbetween 20 and 50 fibrils of 20 micrometers in diameter each. The fibril is more

High Perjomance Str~rctwes and Composites 199

materials and other applications.and coir, as holding great promise for use in composites for construction

Several researchers [l][121 have identified flax, along with hemp, kenaf, jute

Figure 3: Flax fiber Figure 4: SEM image of flax fibril

FFRC, the following tests were conducted:general mechanical properties and eventually the structural capacity of theIn order to establish a set of data that would be most useful in detemning the

1) tensile splitting test: 10 x 20cm cylinder2) uniaxial compression test: 10 x 20cm cylinder3) 3-point bending test: 100x 100 x 35Omm beam

are as follows:were 1, 3, 5, 7.5 andlocms. The mixing proportions and actual materials usedof the various materials was held constant while the length of the fibers testedoverall mechanical properties of the material. For all tests the mixing proportiontests were considered to be the minimum number required to establish the

Some details regarding the choice and use of the tests are given below. These


200 High Perfomance Str.uctwes and Composites

Table 4: FFRC mixture ratio

Material M i x Proportion(%) DescriptiodManufacturer, origin

1. Flax fiber 5% (by volume) Natural, unprocessedflax fiber bundles(Flax)

2. Sand

3. Type 3 cementU N I M I N , Industrial Quartz

0.295 7030 sand

0.188 Tap waterDragon CompanyPortlandCement

0.369 7,14 and 28 day cureC )

(S)

4. Water

e r (ADVA)6. Superplasticiz

(SF)5. Silica fume

W )

Grace Company0.009 AJNA Flow

Grace Company0.138 Force 10,000

the following:particles and t ie natural fiber [ l@. The most successful mixing procedure wasproperties, the silica was used to provide a denser filling between all hydrationcellulose fiber reinforced cement composites [8][9][ lo][1l]. In addition to thesepozzolans as substantially contributing to reduced moisture sensitivity ofminimizes this issue. Silica fume was used based on studies that have identifiedachieving homogeneous distribution in the concrete mix. The superplasticizersurface the bundles tend to clump together posing some problems withconcrete mix [5].Because of their substantial water absorption and roughaggregates would hinder the random and uniform distribution of fibers in theelements would have on the flax fiber bundles and individual fibrils. Theseaggregate was used because of the damaging effect these relatively largeuse any treatments and incur the associated costs in production. Also, noincremental increase in tensile strength [ 14][15][16][171, the study chose not toincrease their longevity in the concrete matrix as well as contribute to an

While there is substantial evidence that various treatments of the fibers may

a) Dry mixing (S+C+SF): 5 minb) Adding water (60%) (S+C+SF+W+ADVA):3minc) Adding Flax (40%) (S+C+SF+W+ADVA+Flax): 12mnd) Adding water (40%) (S+C+SF+W+ADVA+Flax):3mine) Adding flax (60%) (S+C+SF+W+ADVA+Flax): 12mnf) Total mixing (S+C+SF+W+ADVA+Flax):3mn

1) ultimate strength, and2) toughness.

The tests listed above were most illuminatingin terms of two separate values:

highest load carried by the specimen, whether in compression, bending or tensileseparately. The ultimate strength is the easier value to define as i t is simply thestress the importance o f evaluating the contribution of the fiber and matrixabsorption of the material was possible. Also, Hannant and Piggott [19][20]

By characterizing these two values a useful understanding of the energy


establishing a value for toughness has been in debate for several years.definition is not in dispute, the method of obtaining a valid set of data fort ie definition given under ASTM C 1018, 3. Terminology, 3.1.5. While thisload-displacement curve as obtained by experimental measurement. This is alsoenergy absorption capacity of the material as determined by the area under the[21][22][23][24][25]. As described by Barr [21] toughness can be defined as theof guidelines for the measuring and quantification of toughnessRecently a good deal of work has been accomplished toward the establishmentway, is an increasingly important property for fiber-reinforced composites.splitting. The value of toughness, while empirically derived in a more complex

H i g h Perfbrnzance Structures m d Composites 201

LOAD(N)

,,-l4OOCGil A

150C€Cl

200000

250000

300000

35oocu7day cureCompression test

FC-BFC-A

1B

DISPLACEMENT(mm)

45CWO -V

4OKoJ-

35KOO-3cKQo-

15CCO3-

0 . , . , . , . , . , . , . , . , 1

0 1 2 3 4 5 6 7 8

Figures 5A & B: Graphical results of load testing


greater displacement and therefore having a significantly larger toughness value.yield load, resisting a significant fraction of the yield load through a much1Ocm fiber inclusion specimen demonstrates a dramatically better response to itscatastrophic (that is, the drop off from the yield load is steep). However, thethese samples, the failure mechanisms for all of these specimens was relativelysamples (FC-A, FC-B). Even though there is an increase in the ultimate load forand 5cm (l-A, l-B, 5-A) flax fibers in comparison with the unreinforceddisplacement-load curve indicates that there is little benefit in tie inclusion of 1In Figure 5A one can see that the toughness, as measured by tie area under the202 High Perfornmnce Stmctwes and C'onzposites

specimen.measuring tie crack mouth opening displacement (CMOD) directly from thedirectly from the test specimen. We also obtained values for deflection fromload frame, it was decided to measure deflection, with respect to its neutral axis,net deflection of the loaded specimen from measurements obtained through theactual behavior of the fiber bundles. In addition, due to the overestimation of thenotched beam loaded in 3-point bending is particularly useful for assessing thematrix. For the incorporation of natural fibers within a cement matrix theevaluation of the toughness due to the incorporation of fibers within a brittlestrength of the material [26]. The notched beam test is commonly used for the

At failure, the maximum bending stress is considered to be the flexural

Figure 6: 3-point bending framework

further discussion on the advantages of a CMOD measurement scenario and themeasurementof the net central displacement as stipulated in ASTM C 1018. Formechanism. As in [21] we also determined the toughness through alarger than deflection therefore making it more sensitive to the failurethe displacement across the crack opening, and the increase in CMOD is muchspecimen; CMOD is easier to measure than deflection, it is a direct measure ofUsing the CMOD has certain advantages over a measure of the deflection of the


P11.overall advantages of evaluating toughness using notched specimens see Barr

High Perjor-nzmce Structures and C'onzposites 203

was the experimentally derived optimal length.flax fiber in concrete.From these tests it was detemned that a length of 3cmwas carried out to detemne a clearer conclusion regarding the optimal length of

After reviewing the results of these and other tests, a further series of loading

3 Scanning electron microscope analysis

cementitious matrix at the FS.character of the distribution and morphology of the fiber bundles within thethe FS. Three general conclusions were reached by studying the microscopicmethod [27]for analyzing the character of bonding between fiber and matrix atmicroscope. The SEM methods used an unpolished specimen as the primarybond at the fracture surface (FS) were investigated using a scanning electronThe distribution and characterization of the fiber bundles and the interfacial

crystals as describedby Savastano[28]interior. The high porosity of the natural fibers induces the formation of theseimages of the formation of large crystals of portlandite in the transition zonesurface showed surfaces covered with cement paste. There is evidence from thecement paste. In addition, many fibers that were left exposed at the fracturebundles. No areas between individual fibers or fiber bundles were found void ofhad infiltrated into these spaces and had fully surrounded both fibers and fiberbundles and fibrils. However, it was found without exception, that cement pastethere was a concern that cement pastemay not penetrate into the spaces betweenSecond, as a result of the relative ease of separation into fibrils during casting,substantially contribute to the overall strengthof the fiber reinforcement [20].fibrils. This dissipation can be multiplied by the number of bundles and mayexistence of fiber bundles aids in the dissipation of imperfections in individualimportant to note that fiber bundles were found intact in the matrix because thefound evenly distributed within the matrix, as far as could be examined. It isno clear preponderance of one condition over another and both situations wereseparated into individual fibrils in the hydrated and cured concrete. There was

First, it is clear that the fiber bundles were found to be both intact and

toughness through tensile reinforcementat crack formationand propagation.of fibers, in a variety of failure modes, are contributing to the augmentation ofseem to have occurred in failed specimens, indicating that a substantial numberof the composite. Fiber rupture, debonding, friction, slippage and pull-out allclear that a variety of failure modes are contributing to the fracture mechanism

Third, from this initial examination of at least 36 tested specimens, it seems

untreated flaxfibers.evidence for good interfacial bond between the concrete matrix and theadditional SEM analysis. Yet these preliminary results do indicate that there is

These conclusions are only preliminary and need to be substantiated by

SEM images A, B, C, E, and F all show good interaction between hydratedIn Figures 7A through F, various interfacial bond conditions may be seen.


establishing a working mechanical interfacial bond.However, the images show that the cement and flax fibers are clearlyto establish the amount of clumping that is occurring in the cured specimens.fibers in the matrix. A more detailed examination of failed samples is necessaryin which imperfect distribution of fibers has resulted in some minor clumping ofadhered to the fiber surfaces. Image D shows an area along the fracture surfaceand F. It is also clear in images B and E, that calcium-silicate-hydrates arecement paste on their surfaces even after pull-out from the matrix, see Images Efibers are all seen to be closely bonded to the matrix as well as retaining areas ofshows a fiber bundle separated as it emerges from the matrix. In addition, thethe random distribution of fibers is clearly visible in images C and F. Image Aconcrete and the surface of the flax fibers, bundles and fibrils alike. In addition,204 High Petfbrnzance Structures urd ('omposites

Figures 7A, B, C, D, E, F: SEM images of fracture surface (FS)


High Perjormance Structwes and Composites 2054 Conclusions

3. a positive inclusion morphology of the fibers in concreteis possible with2. flax fiber in concrete is optimized at a lengthof around 3cm,1. flax fiber contributes well to both the strength and toughness of concrete,analysis indicate that:good potential for architectural applications. Results of tie testing and SEMfor NFRCs are promsing. The results of testing flax fiber in concrete indicatesload testing of flax fiber reinforced concrete. From previous research, the resultsThis paper presents the result of the formulation,mixing procedure, casting and

4. flax fibers contribute to the augmentationof the mechanical properties of

mechanisms,the concretecomposite througha complex ranger of fibedmatrixfailure

the proper mixing protocol,

buildings of short to moderate spans.of overall strength and toughness for a viable structural material for

5. flax fiber reinforced concreteapproaches to within reasonable expectations

specific steps needed to be taken during themixing and casting process.simply required a certain experience that, once acquired, determined that certainis a major ingredient. In this study it was found that the handling of the fibersdistributed volumes of fiber within the matrix of the composite for which waternatural fibers are highly hydrophilic and this leads to difficulty including well-grades leads to the fibers fomng unmanageable clumps when handling. Alsomolds and forms. The rough surface of the fibers and their varying lengths anddiffkult to handle as part of any wet process such as the casting of concrete intonatural fibers. One of the most important is that natural fibers are relatively

However, flax fibers demonstrate the usual negative characteristics of most

5 References

Third World.Routledge, London, 1990.[6] Adams, W.M., Green Development, Environment and Sustainability in theand Son Ltd., London, 1988.[ 5 ] Swamy, R.N., ed., Natural Fiber Reinforced Cement and Concrete, BlackieLondon: Chapman and Hall, 1990.Proceedings of the Second International Symposium sponsored by RILEM,[4] Sobral, H.S., ed. Vegetable Plants and their Fibres as Building Materials,FNSpon, 1992.Fourth International Symposium held by RILEM, ed. R.N. Swamy, London, E L%

[3] Coutts, R.S.P., “From Forest to Factory to Fabrication,” Proceedings oftheand Stability59 (1998) 251-261.renewable resources- from components to finished parts,” Polymer Degradation[2] Hermann, A.S., Riedel, U., “Construction materials based upon biologicallyfibers,” Progress in Polymer Science, 24 (1999)221-274.[l] Bledzlu, A.K., Gassan, J., “Composites reinforced with cellulose based


by alkali treatment of fibres. Composites Science and Technology, 59 (1999)[141 Gassan, J., Possibilities for improving properties of jute/epoxy compositesConcrete, ed. R.N. Swamy, Blackieand Son Ltd., London, 1988.reinforcement in cement composites,” Natural Fiber Reinforced Cement and[13] Fordos, Z., “Chapter 5 - Natural or modified cellulose fibres ascommunication.[12] Llyod, E., Seber, D., “Bast Fiber Applications for Composites”, privateF W Spon, 1992.Fourth International Symposium held by RILEM, ed. R.N. Swamy, London, E 8~sensitivity of cellulose fiber reinforced cement composites,” Proceedings of the[111 Soroushian, P., Marikunte, S., “Long-term durability and moistureComposites2 1(1999) 189-196.cellulose fiber reinforced cement composites,” Cement and Concrete[lo] Macvicar, R., Matuana, L.M., Balatinecz, J.J., “Aging mechanisms inCement and Concrete Composites 22 (2000) 127-143.of alkali-sensitive sisal and coconut fibres in cement mortar composites,”[9] Toledo Filho, R.D., Scrivener,K., England, G.L., Ghavam, K., “DurabilitySon Ltd., London, 1988.Natural Fiber Reinforced Cement and Concrete, ed. R.N. Swamy, Blackie and[ti] Gram, Hans-Erik, “Chapter 4 - Durability of natural fibres in concrete,”Washington, DC, 2000.Priorities for Research and Commercialization. National Academy Press,on Life Sciences, National Research Council, Biobased Industrial Products,[7] Committee on Biobased Industrial Products, Board on Biology, Commission206 High Perjormance Strwtures and Composites

Measurement- the Need to Think Again. Cement and Concrete Composites, 18[21] Barr, B., Gettu, R., Al-Oraim, S.K.A., Bryan, L.S., ToughnessOxford, England 1980,pgs 131-32.[20] Piggott, M.R., Load Bearing Fibre Composites, Pergamon Press Ltd.,Ltd., Wiley Interscience Publication,New York, 1978.[19] Hannant, D.J., Fibre Cements and Fibre Concretes, John Wiley & Sons,pastes,” Cement&L Concrete Composites22 (2000) 97-113.[181Richardson, I.G., “The nature of the hydration products in hardened cement1735.novolac comsposites. Composites Science and Technology, 60 (2000) 1729-anhydride on swelling and mechanical properties of plant-fiber-reinforced[17] Mishra, S., Naik, J.B., Patil, Y.P., The compatibilising effect of maleicComposites: Part B, 30 (1999) 321-331.Chemical modification of henequen fibers with an organosilane coupling agent.[161Valadez-Gonzalez, A., Cervantes-Uc,J.M., Olayo, R., Herrera-Franco,P.J.,fiber reinforced composites. Composites: Part B, 30 (1999) 309-320.Effect of fiber surface treatment on the fiber-matrix bond strength of natural[151Valadez-Gonzalez, A., Cervantes-Uc, J.M., Olayo,R., Herrera-Franco,P.J.,1303-1309.

(1996) 281-297.


cement paste composites,” Cement and Concrete Composites21 (1999) 49-57.[28] SavastanoJr., H., Agopyan, V., ‘Transitionzone studies of vegetable fibre-concrete,” CementAi Concrete Composites17 (1995) 311-318.[27] Marusin,S.L., “Sample Preparation- Key to SEM studies of failed1988.[26] Mallick,P.K., Fiber-Reinforced Concretes.Marcel Dekker, Inc. New York,56.composites. RZLEM Drafr Recommendations, Mater. 8 z Struct., 17(1984)441-[25] RILEM 49TFX. Testing methods for fibre reinforced cement-basedJ. , 85(6) (November-December1988)583-93.[24] ACI, Measurements of properties of fiber reinforced concrete, ACZ Mater.Testing and Materials, Philadelphia, PA, 1998.with Third-Point Loading), Committee on Standards, American Society forToughness and First-Crack Strength of Fiber-Reinforced Concrete (Using Beam[23] ASTM C 1018-97, Vol. 4.02, Standard Test Method for Flexural254.Fiber Reinforced Concretes,” Cement and Concrete Composites 17 (1995) 239-[22] Gopalaratnam, V S , “ On the Characterization of Flexural Toughness in

High Performance Structures u n d Composi tes 207
